The Library of Work and Play: Mechanics, Indoors and Out
by Fred T. Hodgson · English · Gutenberg #45083 · 505,999 chars · public domain (US)
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Title: The Library of Work and Play: Mechanics, Indoors and Out
Author: Fred T. Hodgson
Release date: March 8, 2014 [eBook #45083]
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Language: English
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*** START OF THE PROJECT GUTENBERG EBOOK THE LIBRARY OF WORK AND PLAY: MECHANICS, INDOORS AND OUT ***
THE CHILDREN'S LIBRARY OF WORK AND PLAY
CARPENTRY AND WOODWORK
By Edwin W. Foster
ELECTRICITY AND ITS EVERYDAY USES
By John F. Woodhull, Ph.D.
GARDENING AND FARMING
By Ellen Eddy Shaw
HOME DECORATION
By Charles Franklin Warner, Sc.D.
HOUSEKEEPING
By Elizabeth Hale Gilman
MECHANICS, INDOORS AND OUT
By Fred T. Hodgson
NEEDLECRAFT
By Effie Archer Archer
OUTDOOR SPORTS, AND GAMES
By Claude H. Miller, Ph.B.
OUTDOOR WORK
By Mary Rogers Miller
WORKING IN METALS
By Charles Conrad Sleffel
[Illustration: Photograph by Underwood & Underwood
A MOTOR BOAT MODEL
"In the making of little models of this kind, you will encounter many
things that will tax your skill and ingenuity, as amateur workmen."
]
_The Library of Work and Play_
MECHANICS, INDOORS
AND OUT
BY FRED T. HODGSON
[Illustration: Cover Page]
Garden City New York
DOUBLEDAY, PAGE & COMPANY
1911
ALL RIGHTS RESERVED, INCLUDING THAT OF TRANSLATION
INTO FOREIGN LANGUAGES, INCLUDING THE SCANDINAVIAN
COPYRIGHT, 1911, BY DOUBLEDAY, PAGE & COMPANY
ACKNOWLEDGMENT
The publishers wish to acknowledge their indebtedness to the Horace Mann
School for their courtesy in permitting certain of the photographs to be
taken for this volume.
CONTENTS
PART I
CHAPTER PAGE
I. A Pathway of Cement 3
Purchasing property, River Passaic--Removing rocks and other
obstacles--Preparing for cement sidewalk--Digging trench and
purchasing materials--Making, laying, and properly placing
concrete--The lever and roller and application--Moving heavy bodies
with lever and roller--Finishing the cement sidewalk--How to make
good concrete walks.
II. Building of a Boat House 36
Qualities of the inclined plane--Dismantling an old barn and
out-houses--Blocks and tackle, ropes and pulleys--Strength and care
of ropes--Building a boat-house, using old materials--Strength
of timber floors--Method of construction--Holding power of
nails--Doors and windows for boat-house--The use of rollers in
moving heavy weights--Sliding ways for boat--How heavy stones were
raised to tops of Egyptian Pyramids.
III. Bridge and Boat Work 65
Dimensions of the launch--Arrival of The _Mocking-Bird_--An
interesting boat talk--A sail on the river--Building a small
foot-bridge--The same completed--Some rules for sailing a
launch--Fitting up boat-house and dock--Preparing block for
keel--The winch and its construction--The wheel and axle as a
mechanical power--The fusee, and what it means--Some problems
solved.
IV. Making a Gasolene Launch 84
Arrival of boat material--Laying keel and keelson--Setting up the
boat and giving her shape--Laying engine bed--Installing engine and
propeller--Nailing on planking--Table of offsets--Gasolene engine
and carburetor--Dimensions of engine and propeller--Gas engines,
generally--Danger of using gasolene--The proper use of yacht flags
for signalling.
V. A Talk About Engines 110
Water around the cylinder--The carburetor and spark coil--Running
the engine in boat-house--Varnishing the boat--A steamboat on the
river--A story of the first steam engine--How the steam acted in
the case--The slide valve, piston and steam chest--Internal and
external engine heaters--Horse-power and how calculated--Foot
pounds, dry steam and condensation--Expansion of gases,
turbines--Gilding the name--Constructing picnic tables and
seats--Height of tables, chairs and benches.
VI. Propeller and Other Screws 136
The launch of the _Caroline_--Trial of the new boat--Description
of the screw as a power--The wheel and worm and endless
screw--Formula for counting power of wheel and worm screws of
various kinds--Archimedian screw and water lifter--Some data of
power of "wheel and worm"--The screw propeller, with data--How to
calculate force of propeller screws--Finding pitch and other lines
for propeller--The screw auger or boring tool--Adhesion of ordinary
wood screws--How to loosen and withdraw rusty screws.
VII. Aeroplanes 158
Seats for riverside--Model aeroplane for the "Fourth"--Dimension
on construction of planes--Why a monoplane rises from the
earth--The gyroscope as a balancer--The biplane and its
construction--Aeroplanes generally--The French aeroplane
"Demoiselle"--How to make a model aeroplane--Illustrations and
details of model aeroplane--Some general remarks.
VIII. Kites, Sundials, Patents 185
The theory of kite-flying--The highest kite ascent--The flat
plane kite--The kite a small aeroplane--A box kite of common
type--Cellular kites of various kinds--Pairs and bevies of
kites--Bird flight and motion--War kites of various kinds--Wind
gauges and wind force--Patents and how to secure them--A simple
sundial--How to make an oval flower bed.
IX. Tides 212
The "why" of the tides explained--Globular form of the earth
proved--Day and night--Phases of the moon--Attraction of the sun
and moon--Newton's theory of the tides--Height of tides--A simple
hygrometer--The Australian boomerang--Theory of the pump.
X. Wall Making and Plumbing 237
Protecting the river bank--Concrete retaining walls--Big dams
in the West--Galveston sea wall--The great dam across the
Nile--Proposed irrigation works in Babylon--Some properties
of light and sound--Hints on amateur plumbing--The peppermint
test--Barometers of various kinds--Thermometers, and their
uses--Something about steel springs--How to make a cross-bow--The
gyroscope and its uses.
PART II
I. Some Practical Advice 271
The inventor, ancient and modern--Barriers to mechanical progress
in the past--Laws of gravitation--How to adjust sewing machines.
II. Mechanical Movements 306
Coffee mills--Pulleys--Pumps--Pistons--Levers--Steam engine and
water wheel governors, etc.
III. The Weather and Indoor Work 349
How to make a rain gauge--Hail--Snow--Designing, making
and inflating paper balloons--Magnetized watches--A boy's
wheelbarrow--Vacuum cleaners.
IV. Motors and Typewriters 387
Motors, gasolene and steam--Automobile frames--The modern
typewriter--Directions for securing copyrights.
ILLUSTRATIONS
A Motor-Boat Model _Frontispiece_
FACING PAGE
Boat-House and Workshop 42
The Creek 70
Making a Motor Launch 88
Finishing the Motor Launch 112
The Monoplane Model Complete 160
Making an Aeroplane Model 180
Making Kites 190
A Sundial Made of Concrete 208
PART I
I
A PATHWAY OF CEMENT
"I do wish papa would buy the land from Mr. Breigel. The weather will
soon be fine enough to play out of doors!"
So said Jessie Gregg, a rosy-cheeked girl of twelve, to her eldest
brother, Fred, one evening in March, as they stood in the porchway of
their home, situated near the bank of the Passaic River, a few miles from
the city in which Mr. Gregg had his business offices.
"Why, Jessie," said Fred, "papa told me this morning, at breakfast, he
expected to close the deal, that is, get the deed of the property, this
afternoon. I am just as anxious as you are to have the matter settled,
for if he gets the land, I will have a lot of work to do, and I want to
commence it right away. The land must be ours, for papa is later than
usual this evening. Oh! there's the train just coming in; he will be here
in a few minutes, and then we'll know."
"Oh, Fred! he and George are coming now. I see them at the turn of the
road. I'll run to meet them." Away she scampered, and almost upset her
father by jumping into his arms, as she was quite a plump, husky girl and
evidently a pet, for her father kissed her fervently as she slid from his
arms to the ground. Then the three trudged homeward.
"Jessie," said George, a younger brother, "I have a secret for you if you
won't tell Fred, until papa has told him."
"What is it?"
"Papa has bought the land, and has got it in his pocket."
"Oh! I am so glad," said Jessie, "but how can he have it in his pocket."
"George means that I have there the papers, deeds, conveyances, and
receipts, giving me the sole ownership of the land, and all that is on
it, including the trees, old barn, and other structures; so, girlie, you
can get down to the river now without having to climb a fence."
Fred met his father on his arrival at the house, but was too well behaved
to ask him about the land, though he was as anxious to know as he could
be. His father saw the boy's anxiety and after tea asked him to go with
him into his den, a little room nicely fixed up some time previous,
containing many articles of wood, brass, and plaster of Paris, Fred and
George had made during the past winter. Jessie, also, had contributed many
little things toward the decoration of "the lion's den," as she called
the room into which her father retired to have his evening smoke, to take
a friend, or to do a little private business.
When seated, Mr. Gregg called Fred to his desk, and talked over some home
affairs before he said: "Now, my boy, since I have secured the property
behind us, as you children desired, I shall expect you and George to help
by your labour, and by the knowledge you obtained at the training school,
in making the improvements on the land and the water front we have talked
of so often. I am sure, with my advice and assistance, you will be able
to do most of the work, or at least to superintend it in such a way that
the labour and expenditure will not be wasted. You know, Fred, I am not
a rich man, so cannot afford to waste money on experiments."
"Indeed, father," said Fred, "I will do all I can. You may count on my
giving my best attention to whatever work and improvements you entrust me
with."
"That is well said, my boy, and what I expected from you. We will begin
operations by putting down a cement pathway from the walk now leading to
the house from the street, and continue it to the river, where you must
build a small boat house and workshop, as I intend either to purchase a
small gasoline launch for our own use, or have you build one, if you feel
equal to that."
"Oh! father, you are so good," said Fred. "There is nothing I'd like
better than to do this work, and particularly to build a boat. I'm sure
I can do that with your help and advice. As to putting down the pathway,
that I can do very well, after my good training in cement works."
"All right, my son. We'll see in the morning what old material we have
on the two places which can be used. There must be quite a quantity of
lumber, timber, bricks, hard mortar, and plaster in and about the old barn
and the smaller buildings."
The next morning George evidently had something on his mind, and seemed
to be on the point of explosion. Mrs. Gregg noticed this and said to
him, "Why are you so restless this morning? Why don't you finish your
breakfast?"
"Oh! mother," he exclaimed, "I am too glad. I am so full of the good
things Fred told me last night and this morning I haven't any room for
breakfast."
"What did Fred say to you?" asked the mother.
"Oh! he told me he was going to build a cement walk right from the door
here to the river, and do lots of other things; and best of all, mother,
he is going to build a boat, a real boat, that will be driven by a
gasoline engine, just like Walter Scott's. That will be glorious! I can
take you and Jessie up the river to Belville to see aunty, whenever you
want to go."
"Very well, George; we will see about that after the boat is ready to take
on passengers."
Breakfast over, the whole family walked out to see the newly acquired
property. They had all seen and walked over the grounds often, but never
before with that feeling of pride in ownership which possession creates.
As there could be no objection to the removal of the line fence between
the newly acquired property and the homestead, Fred got a handsaw, and cut
down a part of it, making an opening some nine or ten feet wide, so that
all could pass into the new place without climbing or stumbling.
The old barn was the first thing examined, and it was found to be in a
state of good preservation, and quite large. It had been built--perhaps in
Colonial times--of heavy timber, oak, chestnut, and pine, and it contained
enough timber and lumber to build two or three small cottages. There
was a big pile of broken bricks and mortar lying against one side of the
barn; and another large pile of bowlders, or field stones, near the fence.
"These," Fred said, "will be fine to build a little landing place or pier
for the boat. The broken bricks and hard mortar will make grand stuff for
the foundation of the cement pathway."
There were also two or three small buildings on the place. One had been
used for a poultry house, another for a tool house, and a third seemed
to have been a sort of cattle shed. Mr. Gregg suggested their removal, of
which all approved.
There were quite a number of good-sized trees on the grounds, and these
rendered it a little difficult to set out a straight line to the river
for the cement walk, without cutting down several, which could not be
considered. There was one direction, however, that would admit of a walk,
about four feet wide, but there were some big rocks or bowlders in the
way, that would have to be removed before a straight path could be made.
Still it was decided to put it there.
"The rocks," said the father, "can be removed by blasting, by lifting
them out of their beds and rolling them aside, or moving them down to the
river, where they will form a good protection against both current and
ice."
"I think they can be moved," said Fred, "if I can get levers and rollers;
and they will make fine breakwater stones."
Jessie found two suitable trees, upon which Fred promised to put up a
strong rope swing, as soon as the place could be cleaned up and made tidy.
"Now, Fred," said the father, "this cement walk should be commenced at
once, so that it will be dry and hard before you go on with other work. I
will employ a labouring man to help you, one who will do the heavy work,
as I do not want you to over-exert yourself. You have a number of tools
now in the shed, and, when I come home from the office this evening, we
will make out a list of the other tools and materials you will require to
finish the intended work. In the meantime you and George can be making
a number of wooden stakes, about eighteen inches long and two inches
square. Point them sharply at one end so that they may be driven into
the ground their whole length. You will require thirty or forty of these.
After getting them, take a clothes line, old halyard, or any rope or heavy
string your mother can find for you, and stretch it from the house down to
the river, at the point we decided upon. Drive in a stake near the river,
tie one end of the rope to it, pull tightly, and stretch the rope from the
river to the house. It will then show you where one edge of the walk is
to be. After that is done, get another rope or string and, starting from
the house end of the walk, measure off four feet for the proposed width.
Drive in a stake at that point, and tie one end of the second rope to it;
then go toward the river with the other end, making the rope extend the
whole length of the path and drive in another stake which must be four
feet from the first rope. To this stake tie the end of the rope and make
it tight. Be sure to have the two ropes exactly four feet apart at each
end, as well as along the whole length. You will find it to your advantage
to get a straight strip of wood, say, one or two inches thick both ways,
and cut it exactly four feet long. It can then be used as a measuring
stick or gauge, for the distance between the ropes, which is to be the
width of the walk, and by using it you will have a parallel and uniform
path from start to finish."
Mr. Gregg had passed an examination in the Massachusetts School of
Technology, and had won a position as civil engineer in New York which
later he abandoned for the profession of law; hence his knowledge of
practical mechanics and engineering.
After Jessie and George had gone to school, Fred started on his new
undertaking with enthusiasm. He found quite a number of pieces of wood,
out of which he made over forty stakes, and pointed them nicely with the
large hatchet he always kept sharp and in good order. By tying several
pieces together, it did not take him long to find cord enough to set out
the whole walk. An old halyard that had been taken from the flag pole
and replaced by a new one answered the purpose admirably. Driving a stake
into the ground, near the house, he tied one end of his cord to that, and
stretched it down to the river bank to the point chosen for the end of
the walk, where another stake was driven in and the cord tied to it. The
long stretch between the two stakes would not allow the cord to be tight
enough to make a straight line between the two points, but Fred left it
as it was, to be adjusted when his father came. With his rod he measured
off four feet from the first stake, across the intended path, and drove
in another stake to which he attached another cord. Then going down to
the river he measured off the width of the walk from the long cord, and
drove in another stake. He was now ready to have his father examine the
work he had done, and to make suggestions or changes if such were deemed
necessary.
Jessie and George arrived home from school, having run most of the way,
"to help Fred make the walk," and were quite disappointed to be told there
was nothing they could do until the work was further advanced.
"We might, perhaps, commence taking down the old buildings," said Fred,
"and pile the lumber where it will be snug and dry."
"All right," said George; so the three of them went over to the poultry
house and Fred began by taking out the two or three small windows, and
removing the doors by unscrewing the hinges. George's desire to pull,
tear, and smash the old material was held in check by Fred, who advised
him to be careful, and not break or destroy anything that could be used.
After the doors had been taken off and laid nicely away--"to be used on
the boat house"--and the windows and frames placed in a dry spot, Fred
began to remove the old siding, or clapboards. He found this a rather
difficult job, as they were nailed on with old-fashioned wrought-iron
nails which could not readily be drawn, and, in trying to get the boards
loose, the ends kept breaking and splitting; so he stopped, went inside
the building, and took off the lining there; this also was a little
difficult to do, but, as the boards were an inch thick, he did not split
many of them.
He then sawed off the boards alongside the studs, on the corners, and
at the doorways to relieve the siding at the ends, and give him a good
chance to wedge off the boards wherever they were nailed. With the help of
George, he succeeded in getting most of them loose without serious damage.
Of course, he had to begin tearing the boards off at the top of the wall,
as they lapped over each other like the scales of a fish.
Mr. Gregg arrived, went over the ground, and was well pleased with the
results of Fred's day's work. He assisted in straightening the long
cords, and made a number of suggestions for the boys to follow. He had
a strong-looking man with him, who he told Fred was to help him. He was
an Italian, named Nicolo, called "Nick" for short, a kindly fellow, who
could speak English fairly, for he had been employed in Newark, as a handy
labouring man for years. He, Fred, and George soon became good companions,
and even Jessie, though a little shy at first, soon became quite friendly
toward him. When it was explained what was wanted of him, he was quite
satisfied, and agreed to begin work in the morning.
Next day Fred and George were at work before their father was out,
and soon Nick arrived, bringing a spade, a crowbar, and a pick. He was
immediately set to work by Fred, digging a shallow trench for the pathway,
a little over four feet wide and about eight inches deep. The stretched
cord and the four-foot rod were the guides.
[Illustration: Fig. 1. Section of sidewalk]
There were a number of rocks to be removed from the trench, one of them
near the river bank weighing over a ton. These were left to be removed
later. Their father, on coming out, was glad to see them all at work; he
showed Fred and Nick how to prepare the edges of the trench by putting
planks along them, as shown in Fig. 1. The boards, about twelve inches
wide, and from twelve to sixteen feet long, had been taken from the old
barn.
After breakfast Fred worked along with his man, and got the trench well
cleaned out, except for a few of the larger rocks. The smaller bowlders
were wheeled down to the river and rolled over the bank to the water's
edge. Near one side of the walk grew a large tree, whose main root ran
under the proposed path. Mr. Gregg had noticed this in the morning and had
told Fred to see that the root was cut off close to the line on both sides
and pulled out altogether. "If it isn't cut off, it will grow larger, lift
up the cement flags, and perhaps break them." Fred saw the force of this,
so had the root cut off and taken out. The operation would not kill the
tree, though it might do it some injury.
Now came the process of taking out the big stones, and a lever, ten or
twelve feet long, was brought from the barn, in the shape of a red cedar
pole, five or six inches in diameter at the larger end. Nick took an axe
and chopped the big end a little flat on two sides, so that it could be
shoved under the stone. A flat plank was next laid behind the stone on
the ground, on which a fulcrum was to be placed, in order to get what
is termed by workmen a "purchase." On the side of the stone next to the
river, three planks taken from the floor of the barn were laid down flat
at the bottom of the trench. Three other planks were laid on the top of
the first layer, thus making a bed in the trench, two planks in thickness,
on which the big stone was to be rolled. A fulcrum, consisting of an old
fence post, was laid upon the plank, and forced up as close to the stone
as possible. Everything was now ready for lifting the bowlder out of the
bed, where it had lain perhaps for thousands of years.
As had been arranged, the work at this stage was suspended, and other
work gone on with, until Mr. Gregg made his appearance. Upon his arrival
all hands went to the stone, Jessie included. Having approved what had
been done, the father suggested that rollers be placed between the two
thicknesses of plank to increase the ease of moving the stone to the river
when it was started. Fred and Nick went to the barn, and among a big pile
of old planks, boards, and timber found eight or ten old fence posts, six
or eight inches in diameter, and long enough to make two rollers, each
three feet long, when cut in two. These were quickly stripped of bark by
George and Jessie, while Nick and Fred, with axe and hatchet, soon had a
number of them round enough to serve as rollers. The father then directed
that the ends nearest the river, of the top layer of planks, be raised
up, and one of the rollers placed between the two layers of plank near the
stone, while the ends of planks nearest the stone should be left resting
on the bottom ones. Another roller was placed nearer the river end of the
planks, and all was made, as shown at Fig. 2--where fulcrum, lever, stone,
planks, and rollers may be seen.
[Illustration: Fig. 2. Raising rock with lever]
All was now ready; the lever was adjusted in place under the stone and
on the fulcrum. Mr. Gregg, Nick, and the children were gathered about the
lever, each one pushing down, and the stone began to move, as the top end
of the lever came down, much to the delight of Jessie and George, who kept
shouting, "There she goes! Up she goes!" Finally the great stone turned
over on the plank, and was moved to near the centre. Now came the labour
of getting the monster down to the bank. This was made easier by raising
the ends of the upper planks under the stone and inserting another roller,
five or six feet from the end. The planks holding the stone were now
resting on rollers, as seen in Fig. 3, and it was found easy to move, but
in order to get it to the bank of the river the "runway," or lower planks,
had to be laid down that distance; this would take too many planks, so it
was decided to lay only a second length on the ground, and then when the
load had travelled to this length, the plank behind the stone should be
carried forward and laid down again. This was continued until the load
was slid into the water. Mr. Gregg called the children and told them to
push against the stone, and they all were filled with wonder to see this
great stone move along so easily on the rollers.
[Illustration: Fig. 3. Moving rock on rollers]
Fred and Nick got more rollers to put between the planks as the stone was
pushed forward, for, of course, these were continually coming out at the
rear end of the loaded planks. The rollers had also to be watched and kept
square across the plank or they would slide, making it hard to move the
load.
When the river bank was reached, Fred and Nick made a rough slide of
old timber down to its side from the trench. Getting the lever properly
adjusted under the planks and stone, the latter was turned over on the
slide, when it plunged into the river with a great splash, causing the
water to fly and sprinkle each one of the workers, much to the delight of
George, who thought it fine fun to see his father, Fred, and Nick get a
wetting.
It was decided that the stone as it lay in the water should form the
end of the pier for the boat, as it was nicely situated and the proper
distance out, being about a foot out of the water at high tide. The other
stones were easily removed from the trench by Fred and his man, and were
either rolled or wheeled down to the river, where Nick built them as well
as he could on both sides of the big rock, leaving a hollow space between
the walls, to be filled in afterward with small stones, mortar, and broken
bricks, for the making of a good, strong boat pier.
Mr. Gregg then took out his note-book and pencil, and figured out the
quantity of cement, sand, and gravel required to complete the cement work.
He found there was good sand, clean and sharp, on one corner of the new
lot. A big pile of gravel and broken stones out on the street had been
left over from the building of a two-story concrete house nearby, so he
concluded to buy it, if not too dear.
Measuring the trench, he found it to be 300 feet long, by 4 feet wide,
making a surface of 1,200 feet to be laid with cement, concrete, and
gravel, or broken stones. He calculated that every 100 superficial feet
of the concrete walk would require about a barrel and a third of Portland
cement; and that the top dressing of cement and sand, or fine crushed
stone, required another third of a barrel; which totaled up to 20 barrels,
all told. The concrete to be used was to be proportioned as follows: One
part of cement, two parts of good, clean sand, and five parts of gravel,
or broken stones, which should be small enough to pass through a ring
having a diameter of not more than two inches. This mass should be well
mixed, dry, on a wooden floor or movable platform, and then wetted just
enough to have stones, sand, and cement, well moistened. All should be
again mixed before being placed in the trench, and it should not be thrown
in place, but shovelled in gently.
Mr. Gregg ordered the cement by telephone, to be delivered at once, either
in barrels or bags; and he got into communication with the owner of the
gravel, and bought the whole pile. He then engaged a team of horses,
wagon, and driver, to commence work the next day. By this time Nick had
gone home, and the children came rushing into the house, anxious to tell
their mother all the work they had done that day.
The keen appetites of the younger folks gave positive proof of their
having earned their supper, by actual work, and, when the meal was over,
the father invited Jessie and the boys into his little room. George was
asked to take with him his portable blackboard, some chalk, and a ruler,
and all marched into their father's den.
"Now," said Mr. Gregg, "I have often told you I would explain to you
some things about the mechanical powers, and this seems to be the most
appropriate time to begin, as you have fresh in your minds the application
of the lever as we used it to-day in raising and moving the big rock. I
am glad to see that Fred grasped the idea so readily, for that encourages
me to let him use his own judgment while doing this job.
"The lever is known to accomplished mechanics, as 'the first mechanical
power', and Archimedes said of it, if he only had one long and strong
enough, together with a suitable fulcrum, he could, alone, lift the earth
from its place.
"This Archimedes was a celebrated Greek philosopher and mathematician, who
lived from about 287 to 212 B. C. The discovery of the law of specific
gravity, which I will some day tell you about, is attributed to him. I
think George can tell you something about this great man, as I saw him and
Jessie the other day reading Plutarch's 'Lives,' in which he is mentioned.
[Illustration: Fig. 4. Principle of lever and fulcrum]
"A lever may be formed of any strong, stiff material, wood, iron, steel,
or similar stuff, and it may be of any length, or dimensions, according
to the purpose for which it is to be used. In theory, it is supposed to
have no weight, and is simply figured as a straight line having neither
breadth nor thickness. In practice, however, a lever may be a handspike,
a pry, a crowbar, a fire poker, a windlass bar, or any other appliance
or instrument that can be used for prying. While we may not know the
proper name of the little steel tool the dentist employs when preparing
one's teeth to receive the filling, by cleaning out the cavities, we are
safe in calling it a small lever. When your mother stirs the fire in the
grate, she makes a lever of the poker, and bars of the fireplace become
fulcrums. The fulcrum is the fixed point on which the lever rests when
in use. The force applied is called the power and the object to be acted
upon is called the weight. The spaces from the power and the weight,
respectively, to the fulcrum, are called the arms of the lever. There
are three different ways of using the lever, according to the relative
positions of power, weight, and fulcrum. This rough sketch I am drawing
on the blackboard (Fig. 4) shows the lever being used to raise one end of
a heavy stone. Suppose W is a big rock, C will be the fulcrum, B the end
of the lever under the stone, and O the power. The weight thrown on the
lever by the man at O, raises the stone so that it can be blocked up, the
lever and fulcrum arranged for another lift, and the process repeated.
This can be continued until the stone is raised to the height required,
or until it is turned over. This method applies to the raising of any sort
of weight, engine, boiler, heater, etc.
"In this sketch the distance from B to C shows the short arm of the lever,
and the distance from C to O shows the length of the long arm.
"A lever, used in this way, is called a lever of the first kind, because
of its simplicity and easy adaptation to many purposes. I saw George
digging in the garden the other day, making a flower bed for his mother.
The spade he used formed an excellent lever. He forced it into the ground
to its full depth, pried the handle toward him, and broke loose the soil,
after which he turned over the earth in the bed. Now, in this case, the
top of the blade or foot-plate of the spade, rested on the hard ground,
which was the fulcrum; the soil dug up was the weight, and George's
hand at the top of the spade handle, furnished the power. I am sure you
all understand the working of a lever of this kind, but I will give you
another illustration.
[Illustration: Fig. 5. Lever as a mechanical power]
[Illustration: Fig. 6. Double lever as scales]
"Here's another sketch (Fig. 5), in which A,B,C, together show the lever,
also the power A, the fulcrum B, and the weight C. If I should place the
fulcrum B so that it would be in the middle between the ends A C, there
would be what is termed an equilibrium between the weight and the power,
and if they are equal there will be a perfect balance maintained. It is
on this principle that scales for druggists are made, the lever being
suspended in the centre of its length, as I show in the sketch (Fig. 6).
These scales are very nicely adjusted, and the chains and receivers are
made as nearly alike in weight as possible. The arms of the lever being
of equal length from the centre, or pivot, permit the lever to stand in a
perfectly horizontal position, unless disturbed by having a weight placed
in either one or other of the receivers. In this case, the pivoted point
P is the fulcrum, and the two points O and X may be taken as the power
and the weight. If one pound is placed in the receiver at O, it will
tip the scale down, and that will become the weight, while any commodity
placed in the receiver at X, until the lever is again brought level, or
horizontal, may be called the power. As another illustration I'll tell you
of something that took place the other day. In the vacant lot are several
piles of bricks, stones, and planks. George, seeing this, took one of the
planks and threw it across several others, making a 'Teeter Tauter,' or,
as some children call it, a 'Seesaw.' He balanced the plank nicely, and
then invited Jessie and her cousin to sit on it, one at each end. The two
girls were about the same weight, and George held the plank until both
were seated. It remained level and balanced, until George got on the top
of it, and stood on the centre of its length, placing his feet so that one
was on one side of the centre, or fulcrum, and the other on the other. By
causing his weight to rest on his right foot, the right end of the plank
would dip downward; then by throwing his weight on his left foot, the
movement of the plank would be reversed, and the motion continued until
George ceased to exert any extra pressure on either of his feet. What do
you call the boy or girl who stands on the plank?"
"Sometimes," said Jessie "we call him a 'candlestick' and sometimes 'the
balancer'."
"This teeter tauter and the explanation of the druggist scales," said
the father, "show you that many of our conveniences are due to the lever
in one way or another. These are but a few of the thousands of instances
I could name. Take a nut-cracker, for instance. There we have a sort of
double lever, the joint being the fulcrum, the nut the weight, and the two
handles the combined power or lever. By pressing the handles or levers,
we crack the nut or overcome the weight, by crushing it. We owe many of
our amusements to the lever in one form or another. Even our pianos would
be impossible were it not for the combination of levers in the adjustment
of the keys. Machinery and all kinds of moving instruments, including
watches, clocks, and other fine mechanism, could not be perfected without
the lever. The common every-day wheelbarrow is a good illustration of
the use of the lever combined with the wheel. George fills up his barrow
with stones or other materials that weigh two or three times the amount
he could lift easily. Yet he gets away with the load, apparently with
very little trouble. The handles form the lever or power, the wheel the
fulcrum, and the stones the weight. George raises the handles, and throws
the greater part of the weight on the fulcrum, which is the wheel, and
this latter, acting as a roller, is easily moved around its own axle, thus
enabling George to move his threefold load with ease.
"This example shows you how, by a simple combination of mechanical
devices, labour may be reduced. The roller is related to the wheel and
axle class--another of the mechanical powers.
"In your bicycles you have a fine illustration of the application of the
roller principle, in the ball-bearings. The little round balls, over which
the axle of the wheel runs, are simply rollers rounded in every direction,
and placed there to destroy friction, which they do almost entirely.
"Another excellent illustration of the use of the roller is seen in the
hanging of the grindstone we have in our back shed. The axle passing
through the stone rests on two pairs of wheels or rollers, one pair at
each side of the stone. If you turn the stone on its axis, you will notice
the wheels turn also, and the effort required to turn the stone is hardly
noticeable. If the grindstone were well balanced and true, and the little
wheels the same, so that they could be run without friction on their
bearings, the stone, by giving it one good turn with the hand, would keep
revolving a very long time. So you see how much we are indebted to the
mechanical powers for our present state of civilization."
Next morning being Saturday, George was up early, put on a pair of
overalls his mother had bought, and, when breakfast was over, all but the
mother went out to the new property. They found Nick helping a teamster
to unload gravel, also a load of cement, which was placed in a dry and
convenient place, for once damp or wet in the least it becomes of little
use, unless worked up immediately. George was full of glee. He got his
wheelbarrow and wanted to commence work without delay. The father took
Fred and Nick to the trench and explained what was to be done and the way
to do it. "The trench is now eight inches deep," he said, "and you must
wheel gravel, broken bricks, hard mortar, or cinders into it so that there
will be about five inches of it in the trench from one end to the other.
Put all the larger stones at the bottom, but before throwing in any, tamp
or pound the ground at the bottom of the trench until it is solid and
hard, making a good bottom for the stones to rest on, and ensuring the
walk from settling or sinking in spots. Where the big root and rocks are
taken out, the holes must be filled up level, and tamped solid. Rake off
the largest of the gravel, and let George wheel as much of it as he can,
and dump it in the trench, while Nick or you wheel in the balance. Finish
the top of the gravel off with smaller sized stones, and after you have
filled in about five inches, throw water on the whole with the garden hose
until quite wet, and then pound the gravel down until it is compact and
firm. This bed forms a good foundation for the concrete which must be laid
on it about four inches thick, and well tamped.
"After you have raked off the larger gravel, take a wire sieve, with
meshes not larger than four to the inch, and sift the finer gravel out,
to save for the top finish. Before filling in the concrete, strips of wood
having straight edges on top must be nailed to the stakes on both sides of
the walk, as I showed you on the blackboard in Fig. 1, marked A A. These
strips must be placed at proper grade in their length, and level across
from one to the other. A straight edge made of wood, and long enough to
reach over the walk, and the strips as well, must be provided, and it may
be notched out as I show at X, in Fig. 1. This straight edge is to be used
in levelling off the top or finishing coat, by keeping both ends on the
strips A A, and moving it along lengthwise of the walk. If the top of the
walk is to be below the edges of the strips, you may notch the ends, as
shown, to suit whatever depth may be required."
Fred told his father he thoroughly understood the process as far as
explained, and the latter then left. By this time Nick and George--and, we
might add, Jessie--had wheeled into the trench quite a lot of gravel, but
for the want of a proper "tamper" they had to stop. So Fred cut two pieces
off a fence post, each about a foot long, and with an auger or boring
tool, made a hole in the centre of the end of each, about eight inches
deep, into which he inserted a round wooden handle, about three feet long.
These made excellent "tampers," not too heavy for George to use. Jessie,
persuaded Fred to make her "just a little one," but he told her not to use
it much or her hands would get sore and too stiff to practise her music.
The strips for the stakes were prepared, nailed on, and properly adjusted,
and then it was time to commence the real work. Nick had nailed some
boards on three pieces of scantling about six feet long, which made a
good mixing table for the concrete. This was carried up near the top end
of the walk, and placed where it would be handy. A pailful of cement was
put on the board, next two pailfuls of nice clean sand, and then five
pails of gravel that had no stones in it larger than would pass through
a ring having a clear diameter of two inches. All this gravel, sand, and
cement being in one heap on the board, Fred and Nick worked at it steadily
for more than ten minutes, mixing it up until the sand and cement were
thoroughly and evenly blended with the gravel. Fred then sprinkled the
mixture with clean water from the hose, while Nick kept shovelling it over
and over until the whole was damp, but not so much so that the cement and
sand were washed from the gravel. The whole mass looked like a pile of
dirty stones that had just been under a light shower.
"This," said Fred to Nick, "is a very important process, for if we make
the stuff too wet, it will starve the concrete by washing away the cement,
and if we leave it too dry the work will be rotten and crumble away."
Fred might also have added that the proper proportioning of the materials
was as essential as the proper mixing, and in this case, where we
are making it one of cement, two of sand, and five of gravel--all by
measurement--we must adhere closely to the rule or the walk will be uneven
in texture and colour.
The concrete being properly mixed, Fred and Nick began to shovel it into
the trench, spread it to about four inches in thickness, and tamped it
down until the top mass looked sloppy and muddy. While in this condition,
a new lot of cement mixture was made, consisting of one part of cement
and two parts of sand and the fine of the gravel that had been sifted.
All were mixed thoroughly while dry, and afterward wet to the consistency
of thick mortar. This was spread over the concrete to about one inch in
thickness and levelled down by the notched straight edge until the proper
thickness and level were obtained. The surface was then ready to smooth,
or "float," as the workman calls it, which always gives to the top of
the work a nice, even, level appearance, and makes it solid and firm. The
"floating" is done with a tool made of wood, as shown in Fig. 7, and may
be finished off with a plasterer's steel float, merely to give the surface
a better finish.
[Illustration: Fig. 7. Floats and trowels]
The floating operation is laborious, for it must be done at once, while
the operator is on his knees. Fred and Nick, however, worked away at it
until they made a good job of the portion that they were putting down. All
of the walk they could finish at one time was about sixteen or eighteen
feet, so that the whole job required a number of days to complete.
The first instalment being done, so far as the floating was concerned,
it was now in order to make joints in the walk across the face, firstly
for the purpose of marking it off into flag sizes, four feet square;
secondly to prevent expansion. If there were no joints made in the walk,
it would "lift" up, crack, break, and ultimately be destroyed. Fred, who
knew that the walk would contract in cold and expand in warm weather,
explained this peculiarity to George and Nick, and having a "jointer"
along with the floats which the father had sent, he, with Nick's help, ran
some joints, at four-foot intervals, across the walk, while Nick pushed
his spade through the joints to the ground, actually cutting cement and
concrete into sections of four feet each. This would allow for expansion
or contraction, and even admit the raising of some of the sections above
the others, without cracks or breaks occurring.
The first instalment of the walk being made, it was left to George to
wheel damp sand and scatter it over the face of the walk about an inch
thick, to keep the sun and rain from injuring it.
Then he received instructions to wet the surface every morning for a week.
At the end of two or three days the cement was hard, or "set" enough to
bear walking on, and in a week it was cleaned off for use. One peculiarity
about concrete or cement work is, that it improves and gets stronger with
age.
The walk was complete in due time, in sections of about sixteen feet
long, and proved quite satisfactory. Mr. Gregg was pleased with it, and
he explained to Fred, George, and Jessie that it might have been made
more ornamental, as there were many tools for rounding off the edges,
indenting the surface, to make it less slippery, or for laying the flags
off in panels; but in this case all were pleased with the way the boys
had finished it.
II
BUILDING OF A BOAT HOUSE
The cement walk being finished to the satisfaction of all concerned, and
the admiration of the neighbours, Fred turned his thoughts to the building
of a boat house and workshop. It was decided to make it 16 feet wide and
22 feet long, as these dimensions would suit the timbers in the old barn,
and be ample for stowing away the boat and allowing space for a work
bench.
Lines for a foundation were set out, and stakes driven in the ground
at the corners, alongside the cement walk and pier. A trench about two
feet deep was dug on the two sides and ends; and in this were laid large
rocks and stones, in a single course all round. Nick, who was quite handy
at this kind of work, built up a wall of smaller stones laid in cement
mortar. This mortar was composed of one part of cement to five of sand,
and made quite thin and easy to spread. When the wall was high enough,
about level with the highest part of the ground, it was levelled off by
using smaller stones and plenty of cement mortar. The level was obtained
by laying a straight plank flat on the top of the cement finishing, and
then applying an ordinary spirit-level. Any errors in the level of the
wall showed at once, and were made right by adding more mortar, or by
taking some off the top of the wall.
[Illustration: Fig. 8. Framing studding]
Timbers from the old barn were next pressed into service, chestnut wood
that had served as girths and beams. Two pieces were cut, 22 feet long,
and two of 16 feet. The ends were then halved, as shown in Fig. 8--the
simplest method of framing a corner--and the timbers were spiked and so
squared as to make right angles at the corners.
Fred then took the old window and door frames, and measured off on the
foundation timbers the outside distance where each one was to be placed.
He put the double doors in the end of his boat house, next to the river
front. The other door and windows were set in the best places to provide
an entrance opening on the cement walk, light above the work bench, and
views over the river and grounds. Fred decided to build his house ten feet
high; so a quantity of studding, 2 × 4 inches in section, was taken out
from the walls of the barn, and cut exactly ten feet long. These were to
form the side walls between the corners, doors, and windows. Heavier studs
were found in the barn, and Fred wisely used them next to the windows and
doors.
[Illustration: Fig. 9. Side of boat house frame]
These heavy studs were set up in the places marked on the timber sills,
also at the four corners, and were toe-nailed at the bottom to hold them
in place. They were then made vertical or plumb, by aid of a spirit-level,
and the corners were braced temporarily to hold them in that position. The
picture (Fig. 9) shows how the side of the building next to the cement
work looked when the studding was all in place. The dark ends shown are
the joists on which the floor is laid. The lower joists were made from
timbers taken from the barn floor, 2 × 8 inches wide and long enough
to reach across the building. The joists on top were 2 × 6 inches, by
16 feet long. These latter floor beams were set about 15 inches apart,
ready to receive the flooring plank, which was nailed solid to them. You
will notice that cross pieces of studding are nailed between the studs
at the window openings. These form the tops and bottoms of the window
frames. The spaces above and below are also filled in with short pieces of
studding, to nail the clapboards to, as shown. The ends of the building
were finished as shown in Fig. 10, a small window being left in each to
admit light and air, also lumber, poles, or other stuff that could be put
into the loft through these openings. Inside the building a trapdoor was
to be left, so that Fred or George could get up to take in or hand out
the stuff.
[Illustration: Fig. 10. End of boat house frame]
The end (Fig. 10) shows how Fred and Nick, with George's help, built
that portion, the collar beam, O O, and the rafter being seen, while the
details in Fig. 8 give larger sketches of the manner of doing the work.
The stone-work, as built by Nick, for foundation walls, is shown in both
Figs. 9 and 10.
All the clapboards having been taken off the barn and old sheds, the
better portions were selected for covering the outside of the new frame,
and a lot of old boards were used for lining the inside of the walls and
nailing on to the rafters. The next thing was to lay on the shingles.
These had been provided some days before by Mr. Gregg, who had figured out
the number required. He found the roof would measure 24 feet in length,
including the projections over the ends of gables, and that the length of
the rafters was 17 feet each, including the overhanging eaves or cornice.
This made the whole stretch of length on both sides of the roof 34 feet.
Multiplied by 24 feet, the length of the roof, this was 816 feet. To
cover an area of 816 feet about 8,000 shingles would be required, as 100
surface feet require nearly 1,000 shingles, laid 4 inches to the weather,
according to the usual custom. Mr. Gregg explained to Fred what is meant
by the term "weathering," applied to shingles, clapboards, slates, or
anything similar. The "weathering" part of a shingle is that portion of it
exposed to the weather, when in place on the roof. It makes no difference
how wide or how narrow a shingle may be, it is that portion showing from
the lower end of one shingle to the lower end of the next one above it,
that is the "weathering." This is generally four inches wide and it runs
from end to end of the roof. Another thing Mr. Gregg explained--the term,
"a square of shingling." "In this case, as in flooring, clapboarding or
similar work, a square is an area 10 × 10 feet; or 100 superficial feet.
In nailing down shingles," went on Mr. Gregg, "the nails should be driven
so that the next course or layer will cover up the nail heads, thus
protecting them from rain and damp, and preventing them from rusting. When
laying the shingles, after the first courses are on, which should be laid
double at the eaves, a string or chalk line must be stretched from one
end of the roof to the other, four inches up from the ends of the first
courses. This string or chalk line may first be rubbed over with chalk or
soft charcoal, and when drawn tight from each end, it may be 'struck' or
'snapped' by raising it up in the middle and letting it strike the roof
suddenly so that a mark will be left on the shingles from end to end. This
will be the guide for the thick ends of the shingles to be laid against
when nailing on the next course, and the process must be continued until
the ridge, or top of the roof, is reached. When you paint your boat house,
don't forget the roof, for a good coat of paint on the shingles will
lengthen the life of the roof fully five years."
Fred, to whom these instructions were more particularly given, told his
father he understood the whole matter, and he was directed to go on with
the work. In the meantime the father ordered the shingle-nails required;
five pounds for each thousand shingles, or forty pounds altogether.
The building being small, the whole work was soon completed, windows put
in, doors hung, and floors laid; and Mr. Gregg was greatly pleased with
the manner in which Fred had managed the job.
[Illustration: Photograph by Frank H. Taylor
BOAT HOUSE AND WORKSHOP
"A Good Coat of Paint on the Shingles Will Lengthen the Life of the Roof
Fully Five Years."
]
The next thing was to take down the heavy timbers of the barn, still
standing. Fred saw at once that they were too heavy to be removed without
mechanical aid or more human help, so he brought from his father's stable
a rope and set of pulley-blocks like the ones shown in Fig. 11. Nick,
who had seen some service at sea, hooked the block into a loop formed by
a short piece of rope tied over a limb projecting from one of the trees.
The question of lifting the timber now was an easy one, as another short
rope was tied to the heavy post W, in this case the weight P being the
power. Each of the blocks shown contains pulleys which make the relation
of the weight to the power as one to four. The weight being sustained by
six cords, each bears a sixth and a weight of six pounds will be kept in
equilibrium by a power of one pound. The blocks used in a system of this
character are called single if there is one pulley in each, double if
there are two, treble if there are three, and quadruple if there are four.
Fred, George, Nick, and Jessie who liked to help whenever she could,
counted for four times their number when they all pulled together on the
rope P. It was astonishing to the youngsters how easily the heavy timbers
were taken down and piled in a nice heap.
Two timbers, each about twenty-five feet long, were chosen and marked, to
be used for slides or ways, on which the proposed boat could be hauled in
and out of the boat house. It was quite a distance from the timber to the
river end of the boat house, and, the former being heavy, Fred decided
to make an inclined plane of planks--of which there was an abundance--so
that the timbers could be slid or rolled down to the river. It took but
a few minutes to lay the planks, and as the incline was gentle, rollers
were used and the timbers went down as easily as the big rock had done.
This pleased the younger children very much.
"When papa comes home," said Jessie, "I'm going to get him to tell me
about the 'inclined plane' as well as the ropes and pulleys."
The two timbers were rolled into the river and floated to the boat house,
where one end of each was raised to the floor level at the doorway and
made fast; the other end sank to the bottom, where Nick dug down and made
a bed for it to rest in. These beds were made deep enough to bury the
ends, and large stones were then thrown in to keep them from moving, but
these were not allowed to reach within 18 inches of the surface of the
water, which was then at its lowest mark. The timbers were kept about
three feet apart, ample space to admit of any ordinary launch or row boat
being taken into the boat house.
"Oh, Fred," said Jessie, "do you think those two sticks will be strong
enough to hold the boat while you are pulling it up?" "Why, yes; strong
enough to hold a dozen boats no larger than the one we intend having made.
I don't know how much weight these timbers will support, nor how heavy our
boat will be with the engine in it, but I'm sure the timbers are strong
enough."
Jessie's question, however, caused Fred to think over the matter, and
he set to work to find out how to tell the strength of timber beams. He
discovered that to be able to determine the strength of beams and wooden
pillars under all sorts of conditions required considerable training in
mechanics and mathematics, but that the case before him was comparatively
easy. A general rule for finding the safe carrying capacity of wooden
beams of any dimensions, for uniformly distributed loads, is to multiply
the area of section in square inches, by the depth in inches, and divide
their product by the length of the beam in feet. If the beam is of
hemlock, this result is to be multiplied by seventy, ninety for spruce
and white pine, one hundred and twenty for oak, and one hundred and forty
for yellow pine. The product will be the number of pounds each beam will
support. For short-span beams, the load may be increased considerably.
Fred, who had some knowledge on the subject, acquired at the training
school, determined to pursue his studies in this direction.
In talking over the matter of nails with his father, their holding power
was mentioned, and Mr. Gregg told Fred of a test that had been made some
time ago by the U. S. Ordnance Department, where cut and wire nails had
been tested respectively, showing a decided superiority for the former,
both in spruce, pine, and hemlock. Thus in spruce stock nine series of
tests were made, comprising nine sizes of common nails, longest 6 inches,
shortest 1-3/8 inches; the cut nails showed an average superiority of
47.51 per cent.; in the same wood six series of tests, comprising six
sizes of light common nails, the longest 6 inches and the shortest 1-1/8
inches, showed an average superiority for cut nails of 47.40 per cent.;
in 15 series of tests, comprising 15 sizes of finishing nails, longest
4 inches and shortest 1-1/8 inches, a superiority of 72.22 per cent.
average was exhibited by the cut nails; in another six series of tests,
comprising six sizes of box nails, longest 4 inches and shortest 1-1/4
inches, the cut nails showed an average superiority of 50.88 per cent.;
in four series of tests, comprising four sizes of floor nails, longest
4 inches and shortest 2, an average superiority of 80.03 per cent. was
shown by the cut nails. In the 40 series of tests, comprising 40 sizes of
nails, longest 6 inches and shortest 1-1/8 inches the cut nails showed an
average superiority of 60.50.
Speaking of the ropes used in blocks, while taking down the old barn
timbers, Mr. Gregg suggested that it would not be a bad idea if the boys
were taught a few general items concerning hempen ropes; so he asked them
to memorize the following: A rope 1/4 inch in diameter will carry 450
pounds, and 50 feet of it will weigh one pound. If 5/8 inch in diameter,
it will carry 3,000 pounds and 7 feet will weigh one pound. When a rope is
3/4 inch in diameter, it will carry 3,900 pounds, and 6 feet will weigh
1 pound. A rope one inch in diameter, the same as we have in our blocks,
will carry 7,000 pounds, and 3 feet 6 inches will weigh one pound. "It is
not likely that sizes greater than these will ever be used by you. If they
are, you can obtain a fair knowledge of their strength by finding their
areas, and comparing them with the areas of the ropes given, taking the
rope having one inch in diameter, as a constant example."
Wire ropes are much stronger than hempen ones, whether made of steel,
brass, or bronze. The care and preservation of ropes is deserving
of consideration, particularly in localities where the atmosphere is
destructive to hemp fibre. Such ropes should be dipped when dry into a
bath containing 20 grains of sulphate of copper per gallon of water, and
kept soaking in this solution some four days, before they are dried. The
ropes will thus have absorbed a certain quantity of sulphate of copper,
which will preserve them for some time, both from the attacks of animal
parasites and from rot. The copper salt may be fixed in the fibres by a
coating of tar or by soapy water. In order to do this the rope is passed
through a hot bath of boiled tar, drawn through a ring to press back the
excess of tar, and suspended afterwards on a staging to dry and harden.
The figures given are intended for new manila ropes, and do not hold good
for ropes made of inferior hemp. It is always safer never to load a rope
to more than 60 per cent. of its capacity, and not even this much when it
is old and weathered.
Jessie reminded her father of his promise to give them some information
regarding the power of blocks and tackle and the qualities of the inclined
plane. Accordingly, Fred, George, and Jessie joined their father in his
den after supper, and George placed his blackboard in a convenient place
with chalk, rule, and other requisites.
When all were seated, the father said: "Some time ago I tried to explain
to you the uses of the lever in quite a number of different situations;
to-night I'm going to show you how the various ropes and pulley blocks
are made to do service for mankind. These devices are used very generally,
especially in building operations, where heavy beams, girders, or blocks
of stone have to be raised. On board ship, it is the favourite mechanical
power by which rigging is raised, cords and ropes tightened, and goods
lifted from or lowered into the hold.
[Illustration: Fig. 11. Blocks and tackle]
"The pulley, the main feature of the third mechanical power, may be
explained almost on the same principle as the lever, as you will see upon
examining the sketch (Fig. 11) I now make on the blackboard.
"The pulleys seen in the blocks around which the rope runs may be
considered so many levers whose arms are equal, and whose centres are
fulcrums.
"In describing this power, it will perhaps be better to begin with the
first and simplest form of the combination. The pulley, weight, and rope
I show now (Fig. 12) is the simplest form of making use of this power. It
is called a snatch-block and often employed for drawing water from wells,
or for hoisting light weights. It is very handy, but we do not get any
additional power from it, though we get a change of direction and quick
movement. From its portable form, its low cost, and the handiness with
which it can be applied, this arrangement is one of the most useful of
our mechanical contrivances.
[Illustration: Fig. 12. Theory of block and tackle]
"When pulleys are adjusted, as I show you in this sketch (Fig. 13), the
block which carries the weight is called a movable pulley, and the whole,
as shown, a system of pulleys.
[Illustration: Fig. 13. Double block and tackle]
"In this illustration, suppose the weight is 20 pounds. It is supported
by two cords, A and B; that is, the two sections of the cord support 10
pounds each. Now, the cord being continuous, the power must be 10 pounds.
"We leave out of consideration the weight of pulley and the friction of
the various parts.
"We have seen that the weight is sustained by two cords; if, therefore,
it has been raised two feet, each cord must be shortened two feet. To do
this, the power P must run down four feet. To get the full value of this
machine the cords must be parallel.
"If we increase the number of movable pulleys, as sketched at Fig. 14, to
three, the relation of P to W will be as 1 to 8 and the distance through
which P will travel will be eight times that through which W is raised.
[Illustration: Fig. 14. Multiple blocks and tackle]
"If we apply this principle to the sketch (Fig. 11), which illustrates
the blocks you used to-day in lifting the large timbers, and which is
the usual form of pulley employed to lift heavy weights, you will notice
that there is a four-sheave block at the top, and a three-sheave block
at the bottom, with the end of the rope fixed from the top block. The
three-sheave block is movable. A power of 10 pounds will, with this form
of pulley, balance a weight of 60 pounds.
"Suppose a block of stone weighing 8,000 lbs. is to be raised to the top
of a wall and we use a system of pulleys where each of the two blocks has
four pulleys; we shall find that it will require a power of 1,000 pounds
to raise it.
"Now, as to the inclined plane: this is called the fourth mechanical
power, and it is not in any way related to the lever, but is a distinct
principle. Some writers on the subject reduce the number of mechanical
powers to two, namely, the lever and the inclined plane. The advantages
gained by this are many for just so much as the length of the plane
exceeds its perpendicular height is an advantage gained. Suppose A B C
(Fig. 15), I make in the sketch, is a plane standing on the table. If
length A B is three times greater than the perpendicular height C B then
a cylinder at R P may be supported upon the plane A B by a power equal to
a third of its own weight. That is, a block of that weight would prevent
the roller or cylinder from going farther. From this we gather that one
third of the force required to lift any given weight in a perpendicular
direction will be quite sufficient to raise it the same height on the
plane; allowance, of course, must be made for overcoming the friction,
but then, you see, you will have three times the space to pass over, so
that what you gain in power, you will lose in time. We see the use of the
inclined plane every day we pass a building under construction, where the
workmen wheel bricks, mortar, and other materials from the street to the
floors above, using long planks for the plane or tramway. Merchants, too,
often make use of an inclined plane when rolling heavy boxes and packages
from the street to the floors of their warehouses.
[Illustration: Fig. 15]
"An excellent, practical illustration was given you to-day when Nick and
Fred built the ways on which the proposed boat is to be slid into the new
house. It would require five or six strong persons to lift the boat bodily
into the new house; but I expect two or three will easily slide it up into
the building on the ways; and by arranging a winch--another mechanical
contrivance--at one end of the boat house, Fred, or George, for that
matter, will be able to haul the boat up. The winch for this purpose will
be a very simple affair, merely a ready adaptation of the wheel and axle,
as I will show you later. Now, however, we are talking about inclined
planes, and to illustrate its early application to the building arts, it
is only necessary to tell a few things we know regarding the moving and
raising of the great stones used in building the Pyramids. For centuries
it was a mystery how the heavy stones in these structures had been placed
in their present positions. Recent investigations have led many scientific
men to believe the stones were taken up inclined planes, on rollers, and
then put in place by the workmen, who moved them to the different sides of
the building on strong timber platforms, where rollers, or rolling trucks,
carried the load. According to one authority, there are the remains of the
approach to an inclined plane near the Great Pyramid, which, if continued
at the angle, as now seen, would rise to the apex. According to this
writer, the foot of the plane was more than a mile from the building,
fifty or sixty feet wide, and had been one huge embankment, formed of
earth, sand, and the clippings and waste of stone made by the workmen.
This, of course, would be an expensive and a tedious method, but in those
days time and labour went for little. Every time a course of stones was
laid and completed, the plane was raised another step, to the height of
the next tier of stones. The same angle of incline was probably maintained
during the whole period of erection, and this angle, you may rest assured,
was made as low and easy as possible; for the Egyptian engineers were not
slow in adapting the easiest and quickest methods available.
"This method of conveying the heavy stones to their places in the Pyramids
was simple and effective, with no engineering difficulties that could
not be readily overcome. Moreover, it was really the very best method
considering the narrow limits of their appliances.
"You may ask, 'How were these big stones carried to the foot of the
inclined plane?' The quarries, in some cases, were five hundred miles
distant, and most of the stones had to be brought across the Nile to the
works. We know from the monuments, and from the papyrii that have come
down to us from remote periods, that many of the stones were brought down
the river on large rafts or floats, and on barge-like vessels; and we
also know that many of the larger ones were hauled or dragged down from
the quarries at Assowan to Memphis, alongside the river, a distance of
580 miles. This is particularly true of the obelisks, for all along an
old travelled road evidences have lately been found that these stones had
been taken that way, and that resting places for the labourers had been
provided at stations about twelve miles apart, along the whole distance.
It has been estimated that a gang of men--say forty--well provided with
rollers, timbers, ropes, and necessary tools, could easily roll an obelisk
like that in Central Park, New York, twelve miles in twelve hours; and
doubtless this was the system employed in conveying those immense stones
that great distance.
"A large number of obelisks were erected near Memphis, though there are
none there now, for the Greek and Roman engineers, at the command of the
rulers, took a number down and carried them to the city of Alexandria;
but we have less knowledge of how these later engineers transferred the
stones to the newer city, than we have of the methods of the older. The
beautiful column known as Pompey's Pillar was once an obelisk, and was
transformed into a pillar, by either Greek or Roman artisans, it is not
clear which. The work of putting those huge stones in place was not easy,
as Commander Gorringe discovered when he stood the New York obelisk in
the place it now occupies.
"But let us get back to our inclined plane.
"I have shown you how a weight or roller acts on the incline, but I did
not explain it clearly, nor in a scientific way, as I do not want to
puzzle or confuse you with terms and problems you cannot understand. I
will, however, give you another illustration or two on the subject, in
which another factor plays a part, namely--gravitation. Let us suppose
you have two golf balls laid on a table that is perfectly horizontal or
level in every direction; they will remain at rest wherever placed, but
if we elevate the table so that the raised end is half the length of the
top higher than the lower end, the balls will require a force half their
weight to sustain them in any position on the table. But suppose they are
on a plane perpendicular to the table top, the balls would descend with
their whole weight, for the plane would not contribute in any respect to
support them; consequently they would require a power equal to their whole
weight to hold them back. It is by the velocity with which a body falls
that we can estimate the force acted upon it, for the effect is estimated
by the cause. Suppose an inclined plane is thirty-two feet long, and its
perpendicular height sixteen feet, what time should a ball take to roll
down the plane, and also to fall from the top to the ground by the force
of gravity alone? We know that by the force of attraction or gravitation,
a body will be one second in falling sixteen feet perpendicularly, and as
our plane in length is double its height at the upper end, it will require
two seconds for the ball to roll down from top to bottom. Suppose a plane
sixty-four feet in perpendicular height, and three times sixty-four feet,
or one hundred and ninety-two feet long; the time it will require a ball
to fall to the earth by the attraction of gravitation will be two seconds.
The first it falls sixteen feet, and the next forty-eight feet will be
travelled in the same time, for the velocity of falling bodies increases
as they descend. It has been found by accurate experiments that a body
descending from a considerable height by the force of gravitation, falls
sixteen feet in the first second, three times sixteen feet in the next;
five times sixteen feet in the third; seven times sixteen feet in the
fourth second of time; and so on, continually increasing according to the
odd numbers, 1, 3, 5, 7, 9, 11, etc. Usually, the increase of velocity is
somewhat greater than this, as it varies a trifle in different latitudes.
In the example before us we find that the plane is three times as long
as it is high on a perpendicular line; so that it will take the ball to
roll down that distance (192 ft.) three times as many seconds as it took
to descend freely by the force of gravity, that is to say, six seconds.
"The principle of the inclined plane is made use of in the manufacture of
tools of many kinds, as in the bevelled sides of hatchets, axes, chisels
and other similar tools, the examples of which are in a great measure
related to this power, though many of them partake largely of the wedge,
of which we shall now have something to say.
[Illustration: Fig. 16. Action of the wedge]
"The wedge may be a block of wood, iron, or other material, tapered to a
thin edge, forming a sort of double inclined plane, =A P B=, (Fig. 16)
where their bases are joined, making =A B= the whole thickness of the
wedge at the top. In splitting wood as is shown in the illustration, =R R=
being the wood, the wedge must be driven in with a large hammer or heavy
mallet which impels it down and forces the fibres of the wood to separate
and open up. The wedge is of great importance in a vast variety of cases
where the other mechanical powers are of no avail, and this arises from
the momentum of the blow given it; which is greater beyond comparison
than the application of any dead weight or pressure employed by the other
mechanical powers. Hence, it is used in splitting wood, rocks, and many
other things. Even the largest ships may be raised somewhat by driving
wedges below them. Often, in launching a vessel, wedges are used to start
it on its way. And they are also used for raising beams or floors of
houses where they have given way by reason of having too much weight laid
upon them. In quarrying large stones, it is customary to wedge or break
off the rock by first drilling a number of holes on the line of cleavage.
Wooden wedges are then driven tightly into these and left there until
they get wet, when they expand and split off the rock as required. This
method of quarrying large stones was well known to the old Egyptians, and
employed by them in quarrying their famous obelisks.
"Owing to the fact that the power applied to force a wedge is not
continuous, but a series of impulses, the theory of the wedge is less
exact than that of the other mechanical powers. Considering the power and
the resistance on each side, however, as three forces in equilibrium, it
may be demonstrated that the
Resistance (R) equals P × Length of equal side/Back of wedge
Then the mechanical advantage will be--
R/P equals Length of equal side/Back of wedge
So that by diminishing the size of the back and increasing the length of
the side--that is, diminishing the angle of penetration--the mechanical
power of the wedge is increased. While I did not intend to inflict you
with arithmetical or algebraical formulæ, I have been compelled to give
you that simple example which I know you can all work out, as it is
concise, and the same would be long and tedious if rendered in text."
Next morning, as Fred and his father were out on the new place early,
looking over the boat house, the slide for the boat, and some other
matters, Mr. Gregg suggested that a winch be placed at the upper end of
the house, to haul the boat out of the water. He also suggested that Fred
prepare for work on the boat at once, and provide himself with all the
tools and materials necessary. He promised to call on a friend of his
in the city, who is a noted boat builder, and ask him the best method to
adopt in building the craft.
"Perhaps," said the father, "it might be a good plan to buy a full set
of shapes or patterns from some one of the professional boat builders
who advertise such. They are sold at a very low rate--being made of
paper--and many firms sell all the material that is required to build
a boat complete; with the sweeps, ribs, and curved stuff cut out to the
required shape and numbered all ready to set up.
"What we want, Fred," continued the father, "is a boat sixteen or
eighteen feet long, just the size of the one belonging to your friend,
Walter Scott; that is plenty large enough for all our purposes. His
boat can stand as a kind of a model for you to work after in case you do
not thoroughly understand the patterns you are to get, or the manner of
arrangement. The gasolene motor we'll order from some manufacturer, with
whom we'll arrange to install it, with a suitable propeller and necessary
attachments."
Fred was quite satisfied with all his father had said and started to
get ready. Jessie began to question him about several things she did not
fully understand in her father's talk the night previous. Fred explained
matters, made them quite clear to her, and then asked her to get her
memorandum book and write down the following, which he said, she would
often find useful: "There are six mechanical powers, two of which father
has not told us about, but will no doubt do so, before long. These are
called, the Lever, Pulley, Wheel and Axle, Inclined Plane, Wedge, and
Screw. The Screw and the Wheel and Axle, you have yet to hear about. Now,
study carefully the following rules:
"_The Lever._--Rule: The power required is to the weight as the distance
of the weight from the fulcrum is to the distance of the power from the
fulcrum.
"_The Pulley._--A fixed pulley gives no increase of power. With a single
movable pulley the power required will equal half the weight, and will
move through twice the distance. Increasing the number of pulleys,
diminishes the power required. Rule: The power is equal to the weight,
divided by the number of folds of rope passing between the pulleys.
"_The Wheel and Axle._--Rule: The power is to the weight as the radius of
the axle is to the length of the crank or radius of the wheel.
"_The Inclined Plane._--Rule: The power is to the weight as the height of
the plane is to the length.
"_Wedge._--Rule: Half the thickness of the head of the wedge is to the
length of one of its sides as the power which acts against its head is to
the effect produced on its side.
"_The Screw._--Rule: As the distance between the threads is to the
circumference of the circle described by the power, so is the power
required to the weight."
Fred told George also to copy the foregoing in his memorandum book, so
that he would be able to work out any problems for himself.
III
BRIDGE AND BOAT WORK
The next day Fred and his father talked over the proposed boat, the result
being that Walter Scott was asked over the telephone if he would come down
in his launch to the Gregg property in the evening, as Mr. Gregg and Fred
would like to see the craft, hear all about it, and find out if it had
any defects that might be avoided in the building of another one. Walter
said he'd be glad to sail down, and would take his sister to see Jessie.
In the meantime some addresses of boat builders were handed to Fred, with
instructions to write and ask for catalogues, prices of materials, and
the other information usually sent out to prospective customers. Fred
immediately wrote to a number of firms, including several who manufactured
motors and other requisites for small launches.
A little after the city clock struck four, Jessie, who was home from
school, saw _The Mocking-Bird_ sailing down the river at good speed, with
Walter, his sister Grace, and their mother on board. Fred went down to the
water's edge, and helped Walter haul the boat to the unfinished landing
place, where Mrs. Scott and Grace were safely landed.
Fred and Walter soon became deep in "boat talk," and kept it up until
the arrival of Mr. Gregg, who began to make inquiries regarding the
speed, capacity, and safety of _The Mocking-Bird_. All his questions were
intelligently and favourably answered by Walter, a bright and earnest
little fellow. He was some months the senior of Fred, but was not so
strong or robust looking.
"She's just 18 feet long over all," said he, "with a 5-foot beam, a draft
aft of about 18 inches, and a forward draft of 1 foot. She is fitted with
a 6-horse-power gasolene engine, and her speed is from 8 to 9 miles an
hour."
An illustration of her, as she appeared when partly built, is shown in
Fig. 17, where a plan and a section of her length may be seen. The manner
of her construction is also shown, also the lines of ribs, portion of
inside lining, position of motor, rudder, and propeller.
[Illustration: Fig. 17. Plan and section of _The Mocking-Bird_]
Mr. Gregg also ascertained from Walter that his father had sent to a firm
who made a business of preparing the complete wood-work for many kinds of
boats on the "knockdown" system, selling the whole material ready to set
up without the aid of an expert. Printed instructions came along with
each boat, so that the buyer would have but little difficulty in setting
up the wood-work and making it ready for use. An expert workman had been
engaged by Walter's father to install the engine, line up the propeller
shaft, and connect the wheel and shaft to the engine. On the arrival of
the materials--within a week after the order was sent--Walter had gone to
work; and inside of fourteen days, _The Mocking-Bird_ took to the water.
So fully and so satisfactorily did Walter explain to Mr. Gregg all that
he asked about, that Fred was able at once to order the material for a
similar launch, to be sent on immediately. In order to hurry matters, a
cheque was inclosed with the order, and Fred, Walter, and George walked
over to the postoffice with the letter, so that it went by the night mail.
On returning, it was suggested that the boys, Grace, and Jessie go for a
sail on the river, and all were soon at the landing. Walter adjusted his
engine and made all ready as George and the girls got on board, while
Fred cast off the rope which held the boat to the dock, then stepped
after them. The engine was started, Fred took the tiller, and they were
soon afloat, sailing with the tide in their favour at a rapid speed,
and returning to the landing place inside of an hour, well pleased with
their little outing. Fred showed Walter his new boat-house and workshop,
explained to him how Nick and he, with the help of George and the advice
of his father, had completed the work and the building. He also pointed
out other work he was going to do as soon as his boat was finished.
Though not yet dark, it was getting rather late, and Walter's mother
advised that they start for home as soon as he was ready. So wishing Fred
every success in the building of his boat, Mrs. Scott, her daughter, and
Walter left for home.
"Well, Fred," said Mr. Gregg, when his family were all seated in the
living room, "you are now in for quite a job, one that will test your
working qualities; but I am sure you will come out with flying colours.
You will meet difficulties, but you must overcome them, and when the boat
is finished, painted, and ready to name, you can have some of your friends
up for the launching. Mother will have a special tea for you all, and
we'll christen the new craft. Meantime we must think over the matter of
a name, and decide upon one we shall all like."
Next morning, Fred and his father went down to the river's edge to examine
the little ravine that had been cut out by the spring and fall freshets.
It was a small affair, only about six feet deep and ten or twelve feet
wide. At present, the opposite side was reached by crossing a couple of
planks, safe enough while the land had been in a measure unoccupied. To
leave it so now would be a different matter, as Jessie or her mother,
attempting to cross, might easily fall over; so it was decided to have a
foot-bridge built over the creek, which was nearly dry the greater part
of the year. There was plenty of material on the ground for the purpose,
and Fred was asked by his father to get Nick to help, so that the bridge
might be ready as soon as possible.
Fred felt he was getting to be quite an important person when his father
trusted him with work which must necessarily entail considerable expense,
but he accepted the responsibility with pleasure, and promised to commence
at once, so as to have it finished by the time the material for the boat
arrived. So, when Nick arrived, operations began immediately.
[Illustration: The Creek]
Taking a tape line, Fred sent the Italian to the other end of it, and they
picked out a favourable location to measure across, making it over 11 feet
at the narrowest spot from one edge to the other. Allowance was then made
for bearings five feet on either side of the span, so that timbers 21 feet
long would be required to cross the chasm. This width would require three
string-pieces, or chords, to run across, one on each side, and one in the
centre. These, covered with three-inch plank from end to end, would make
a good, solid deck sufficient for all purposes. The planks were cut off
seven feet long, to have the deck of the bridge, over all, exactly seven
feet wide.
Among the timbers taken from the old barn were nine pieces, measuring 22
feet in length, 8 × 10 inches in section, so Fred decided to make use of
three of these just as they were, without cutting, and to place them on
their edges to get the most strength out of them. He then had six posts
cut off the old cedar fence posts, about two feet long, which were sunk
into the ground their whole length, as shown in Fig. 18, three on each
side of the creek, and the tops made level, so that a flat timber or plank
would rest on them, touching each one. This plank was made nine feet long,
so as to project over the posts about a foot at each end. This was, of
course, the same at each end of the bridge. After the flat timbers had
been laid on the ends of the posts and fastened with spikes, there were
laid the three long timbers spanning the gully. The spaces between were
equally divided, and then covered with three-inch planks taken from the
floor of the old barn. The boards were cut off to the proper length and
fastened down on the three timbers with spikes five inches long, the
planks not laid close together, but kept about three-eighths of an inch
apart, in order to let the water run off after a rain, as well as to allow
air to circulate underneath and between the joints to prevent the planks
from decay.
[Illustration: Fig. 18. Frame of foot-bridge]
In order to make the bridge safe, it was necessary to build a rail on each
side. Two pieces of timber about 20 feet long and 6 × 6 inches square were
used for the rails, while posts and braces were made of timber of about
the same dimensions. The bottoms of the posts were halved, so that they
could be spiked or nailed to the long outside string-pieces, as shown in
the illustration. Tenons were made on the top of these posts, and these
fitted into mortises made in the top rails, and all were then put together
and fastened with wooden pins.
Nick dug away the surplus earth from the approaches to the bridge, and
made an easy grade to its deck. This completed the work all but the
painting, which was left to be done some other day.
Mr. Gregg inspected the bridge, pronounced it all right, and congratulated
Fred on his workmanship, at the same time saying a good word to Nick and
George, both of whom had helped very much to make the effort a success.
In the evening Mr. Gregg told Fred and George that a friend of his had
given him a copy of the rules to be observed when running a launch, so he
asked the boys to get their note-books, and take these down as he read
them out. Even Jessie, too, he thought, ought to be acquainted with the
rules, as she might be called upon some time to make use of them, so three
pencils were soon at work, as the father read out the following:
"1. When at the wheel, remember as a first consideration, that you
cannot entertain the boat's occupants as well as steer.
"2. Keep your course, and know what that course is.
"3. Regulate your speed to the company you are in. Marine motors
are, as a rule, very flexible.
"4. Do not cut corners.
"5. When approaching a landing, learn to judge exactly the distance
your boat will travel after your propeller has stopped, so as to
run alongside without using your reverse gear. This requires some
practice, but is amply rewarded by time saved, in the long run,
and decrease of wear and tear on engine, gear, and propeller. Any
one can get to a landing in time by alternately running full speed
ahead and then astern.
"6. When aboard your boat, and facing the bow your right hand is
starboard, your left, port. Keep to the right. Should you be
overtaking any one, it is your duty to pass clear on their left.
The above applies only to narrow waters.
"7. When going up or down stream, should you wish to cross over to
the other side and return, and another boat is overtaking you on
your left, don't attempt to cross its bow; slow down until it has
passed.
"8. Keep clear of non-engined crafts. You have greater freedom
of action than they; it costs you nothing, and their occupants
appreciate your courtesy.
"9. Do not tow canoes or skiffs alongside. If towed at all, they
should be right aft with as short a towline as possible.
"10. Finally; remember the rules of the road--
"'Green to green or red to red
Perfect safety--go ahead
If to starboard red appear
'Tis your duty to keep clear.
When upon your port is seen
A steamer's starboard light of green,
There's not so much for you to do
As green to port keeps clear of you.'"
The children all promised to memorize these rules.
As the stuff for the boat was not expected for some days, Fred and Nick
kept at work about the new boat house, and building up the landing dock.
The former fitted up a work bench, and put his little shop in readiness
for actual use. Fred also hunted for a nice stick of timber among the old
barn ruins, on which to set up the boat. A good piece found, he cut it
to a length of 20 feet, and then he and Nick got it into the boat house,
where Fred planed it off a little with a rough jack plane, keeping a sharp
lookout for nails, sand, or gravel. Nothing destroys the cutting edges of
tools more than nails, bits of iron, glass, sand, or small pebbles, which
sometimes escape the vigilance of the workman. Especially is this true of
saws, which Fred knew quite well since he had once run a good sharp saw
against a nail, while cutting a piece of timber in two. This taught him a
lesson he never forgot, and whenever he had to cut up old material, he was
always careful to examine it all round, and to scrape or brush off all the
dirt and sand from the parts through which the saw teeth had to travel.
In planing, or "dressing" the stick of timber, the same precautions were
taken, and the surface of the wood was made as clean and free from dirt
and sand as it possibly could be. Notwithstanding all this, Fred found
it almost impossible to keep the cutting iron of his jack plane sharp
enough to take off shavings. He had to sharpen it every few minutes. This
is nearly always the case when working up wood which has previously been
used. However, he managed to "dress" his stick very nicely, and after
finishing it, laid it down along the middle of the floor of the shop,
putting blocks of wood under it here and there to raise it up from the
floor five or six inches. It was then made level on top and fastened down
so that it would not move or get out of line. This was about all they
could do on the boat until the materials arrived. Nick had managed to fill
in the space between the two walls of the little pier with heavy bowlders,
and had strengthened the whole with coarse rubble-stone work in such a
manner that there was little danger of injury from floating ice or flood
tides; and he had covered the whole over with small stones, gravel, and
a good thick layer of cement concrete, which made it correspond with the
cement walk.
The question of a winch was then taken up with Mr. Gregg and it was
decided to construct a simple affair at the end of the boat-house opposite
the large doors, where the boat would have to enter.
[Illustration: Fig. 19. Winch and crank]
Mr. Gregg suggested, in order to make the end of the building strong
enough, that two upright posts be set up, well braced by being fastened
to both floor and ceiling, and that the winch be attached to them in a
way that would be easy to work, as shown in Fig. 19, room enough being
left between the posts and the wall for the crank to turn without the
hand of the operator striking the boards. The cylinder around which the
rope should wind ought to be about six inches in diameter, and the crank
or handle on the end, not less than fifteen or sixteen inches long. The
longer the crank, the less force it would require to haul in the boat. If
desired, a crank could be fitted to the other end of the cylinder so that
two persons could work at one time, pulling in the weight.
In the evening Mr. Gregg asked the boys and Jessie to visit his room, and
he would try to explain the principle and advantages of the wheel and
axle, as the winch they were to make was in a measure related to that
principle. Mr. Gregg began by saying: "The wheel and axle is merely a
modification of the lever and consists of a couple of cylinders turning on
a common axis, the larger cylinder is usually called the wheel, the lesser
one the axle. This arrangement, which I draw on the blackboard herewith,
forms a kind of lever of the first or second class. Considered as a lever,
the fulcrum is at the common axis, while the arms of the lever are the
radii of the wheel and of the axle.
"The fulcrum is at C, the centre. The arm of the weight is W W, and the
arm of the power is A C. In Fig. 20 the arm of the power is the spoke of
the wheel, while the arm of the weight is the radius of the axle. Fig.
19 shows the ordinary winch, often used in well-digging for hauling up
dirt and rock, and also for raising planks, shingles, rafters, and other
light stuff, to the roofs and upper floors of buildings. Often it is made
more powerful by adding spur or geared wheels to the end of the shaft,
consisting of a pinion and a larger spurred wheel. The crank or handle
is attached to the pinion, and the power is increased according to the
difference in diameters of the spur wheels. The machine is then called a
'crab' and it is often used for lifting safes and other heavy weights to
elevated situations. In Fig. 20 the length of the crank (in a straight
line) is the arm of the power.
[Illustration: Fig. 20. Wheel and axle]
"The mechanical advantage of the wheel and axle equals the ratio between
the diameter of the wheel and of the axle.
[Illustration: Fig. 21. Capstan and hand bars]
"It is not necessary that an entire wheel be present. In the case of the
windlass and the capstan (Fig. 21), the power may be applied to a single
arm or to a number of arms placed in the holes shown. The cable or rope
on the barrel of the capstan is hauled in by turning the capstan on its
axis, with handspikes or bars. The capstan is prevented from turning back
by a pawl attached to its lower part, working in a circular ratchet on
the base.
[Illustration: Fig. 22. Compensating fusee]
"As an illustration of the lever action, and of work put into and got
out of a machine, there is no better illustration than the ingenious
contrivance termed the fusee (Fig. 22). In good watches and clocks, where
the elastic force of a coiled spring is used to drive the works, the
fusee compensates the gradually diminishing pull of the uncoiling spring.
The driving of the works at a constant rate is the object for which a
watch or clock is designed. This usually entails a constant resistance
to be overcome, but since one of the most compact and convenient forms of
mechanism into which mechanical force can be stored is that of the coiled
spring, and since the very nature of the spring is such that its force
decreases as it uncoils, we must employ some compensating device between
this variable driving force and the constant resistance. The fusee does
this in a most accurate and complete manner. As the fusee to the right is
to compensate for the loss of force of the spring as it uncoils itself,
the chain is on the small diameter of the fusee when the watch is wound
up, as the spring has then the greatest force.
"In the differential, or Chinese windlass (Fig. 23), different parts of
the cylinder have different diameters, the rope winding upon the larger
and unwinding from the smaller. By one revolution the load is lifted a
distance equal to the difference between the circumference of the two
parts.
[Illustration: Fig. 23. Chinese winch and pulley]
"There are many other contrivances and appliances of the wheel and axle
for performing various services, but I think the examples I have shown you
will be sufficient to enable you to make use of the device to perform any
duty you may be called upon to attempt in ordinary life, but, should you
enter professional life as civil, mechanical, naval, or mining engineer
or architect, you will be obliged to pursue the study of these subjects
further.
"Before closing I may add a few problems for you to solve at your leisure
by the application of the rules I have given you when describing the other
mechanical powers.
"The pilot wheel of a boat is 3 feet in diameter; the axle is 6 inches;
the resistance of the rudder is 240 pounds. What power applied to the
wheel will move the rudder? Here the difference between the axle and wheel
is 18 inches.
"Four men are hoisting an anchor of 3,000 pounds' weight; the barrel
of the capstan is 8 inches in diameter; the circle described by the
handspikes is 7 feet 6 inches in diameter. How great a pressure must each
of the men exert?
"With a capstan four men are raising a 1000-pound anchor; the barrel of
the capstan is a foot in diameter; the handspikes used are 5 feet long;
friction equals 10 per cent. of the weight. How much force must each man
exert to raise the anchor?
"The circumference of a wheel is 8 feet; that of its axle is 16 inches;
the weight, including friction, is 85 pounds. How great a power will be
required to raise it?
"A power of 70 pounds on a wheel whose diameter is 10 feet balances 300
pounds on the axle. Give the diameter of the axle.
"An axle 10 inches in diameter fitted with a winch 18 inches long is used
to draw water from a well. How great a power will it require to raise a
cubic foot of water, which weighs 62-1/2 pounds?"
The first mail in the morning brought word that the whole of the partly
prepared stuff for the boat had been shipped by "fast freight," and that
it would reach its destination in the course of a few days. The paper
patterns, directions, and all necessary instructions for building would
be mailed at once.
IV
MAKING A GASOLENE LAUNCH
Two or three days after Mr. Gregg had talked over the principles of the
wheel and axle, with the children, Fred received notice that a consignment
of wood-work was at the station awaiting his orders. Mr. Gregg made
immediate arrangements with the railway people, and by the time he got
home from his office, the stuff was being unloaded by the boys, who
carried it piece by piece into the workshop, each section being laid
by itself in the order in which it was to be put in place in the boat.
Printed instructions were in the equipment for laying the keel, setting up
the frames, and even for taking the stuff out of the packages and putting
it in heaps, so that it could be readily picked out when wanted for use.
Each rib was numbered, and marked or stamped "right" or "left," and all
the pieces were cut off to the right length and to the right bevel or
angle to suit the positions they were to occupy, as specified in the
printed instructions. This made the setting up an easy matter, requiring
only care, patience, and a fair knowledge of the use of wood-working
tools. That Fred possessed these qualities, was partly due to the training
he had received in the technical school, and partly to his natural
aptitude for picking up methods, ideas, and new applications.
Fred, George, and Mr. Gregg himself, were much interested in the selection
of the various materials, and when the plank that was to form the keel
had been unpacked, George was anxious that it should be laid down on the
bed that had been prepared for its reception. He was quite disappointed
when he found it considerably shorter than he had expected the boat to
be. It was explained to him, however, that the overhanging of the stern,
and therefore shortening of the forefoot, or stem, necessitated the keel
being shorter than the boat would be when measured over all on top. The
keel was found to be a fine piece of tough oak, nicely dressed, made the
proper shape at each end, bored and gained to receive the stern post, the
stern ribs, and side stanchions. Everything was marked, and each timber
was sized so that it would fit in place snugly without using a tool on
it, except a hammer or mallet.
At tea time George felt it difficult to keep reasonably quiet, he was so
enthusiastic about the boat--much to the amusement of his father, who knew
exactly how the boy felt.
[Illustration: Fig. 24. Stem of launch]
After tea, all walked to the boat house, and the father assisted Fred to
set up the keel, which was in two pieces, halved together midway and well
fastened with screws. The joint was painted with a heavy coat of white
lead and linseed oil paint, before being put together and screwed up. The
keel is the lowest timber in a boat or ship, and it runs nearly the length
of the craft. Sometimes there is a keelson placed on the top of the keel,
and the ribs of the boat, or stanchions, are made fast to that timber, as
shown in the illustration, (Fig. 24,) in which the gains for the ribs or
moulds are made. This portion of the boat was put together temporarily, so
Fred had no difficulty in assembling the various pieces. The stem, keel,
keelson, and deadwood were all made of oak, and looked strong. The keel
and keelson were properly laid and adjusted, and after some explanations
by Mr. Gregg the manner of setting up the ribs was thoroughly understood.
Fred decided to telephone Walter Scott to come down next day, as it was
Saturday, and help him to set up the skeleton.
As the weather was getting warm, the whole family spent the evening on
the veranda and George introduced the question of naming the boat. He
suggested _Red Bird_, but this did not seem to take well, and several
others were proposed but none seemed to suit everybody. Jessie sat quietly
on the steps till asked by Fred what her choice would be.
"I would like it called after mamma, _Caroline_."
"That's a good idea, Jessie," said her father, "and if the boys or your
mother don't object, I think we'll settle on _Caroline_."
Early next morning the boys were out watching for _The Mocking-Bird_,
which very soon made its appearance. Fred and Walter tied the boat up
to the new dock and went into the boat house, where the latter began to
examine the boat stuff, and to explain the manner of setting it up and
fastening it in place.
Nick, who was on hand to help, did the heavy work, and helped to put up
the stanchions. Walter seemed quite familiar with the work, and he and
Fred soon had the boat so well in hand that it seemed to grow under their
fingers. The ribs were easily selected, as they were tied together in
pairs and numbered. They were then set in their places according to their
numbers and were fastened to the keelson with the strong copper nails.
All the nails required for the boat were of copper, because that metal is
less likely to corrode than iron or steel.
It was found necessary to brace the ribs in order to keep them in line.
Thin pieces of lath were tacked on the tops to hold the ribs the proper
distance apart, and longer and stronger strips of wood were used for
bracing the boat sideways. These were nailed to the joints in the ceiling
or high up on the walls of the boat house.
[Illustration: Copyright, 1911, by Underwood & Underwood, N. Y.
MAKING A MOTOR LAUNCH
"All the Nails Required for the Boat Were of Copper, Because That
Metal is Less Likely to Corrode Than Iron or Steel"
]
[Illustration: Fig. 25. Section of launch--abeam]
At noon the boys had the skeleton of the boat well advanced, and to one
standing in front of the bow, it presented an appearance like the sketch
shown at Fig. 25.
[Illustration: Fig. 26. Methods of sheathing]
The launch might be called "carvel ribbon built," or nearly so, and it
would have a displacement of 14 or 15 hundred-weight when fairly loaded.
This weight would bring her down to the third W. L., as shown in the end
sketch. To load her to the fourth W. L., would give her a load far beyond
these figures. The sections had to be closely spaced, and the ribbons or
slats let into the temporary section moulds before the outside boarding
could be put on, the edges of the boarding being clinch fastened, as shown
in the ribbon carvel, Fig. 26. Other styles of sheathing boats, as shown,
are often used, but the _Caroline_ was "ribbon carvel."
It is usual to lay off the sheer profile on a suitable floor, and line
in the rebate line, scarf of stem, deadwoods, fork timbers, etc., making
thin moulds of each member to be lined off, sawn, and bolted together.
The section moulds, from which the boat derives its shape, are also laid
off, and the planking, 3/8-in. thick, deducted when making them.
The stem, of crooked oak, was 2-1/4 in. thick by about 3 in., shaped as
shown in Fig. 24. The fore deadwood was 2-1/2 in. thick, moulded about
3 in., and through-bolted to the stem and keel with 3/8-in. copper
bolts; and the stern-post, 3-1/2 in. thick, was wrought to shape, as
shown. The centre line of the shaft, as shown, is subject to alteration,
since different makes of motors have different sizes of propellers and
flywheels. The fork timbers were let into the stern-post, and carried the
transom, wrought out of a flitch of elm 3-1/2 in. thick. The planking,
of 3/8-in. cedar, was closely jointed and varnished, and secured to the
ribbons. The timbers were of rock elm, 7/8 in. by 1/2 in., steamed and
bent or sawn to shape, and through-fastened at the top and bottom edges
of the planking. These were spaced on 7-1/2-in. centres, with two clinch
nails into the ribbons between them. Three or four solid floorings should
be worked into the motor space; fitting of the motor bed thwartships gives
great support to the boat.
The thwarts were of oak, 8 in. wide and 1 in. thick, with the side seats,
7/8 in. thick, supported by turned legs of oak. The decks at each end
should be of 1/2-in. oak or cherry reeded into 3 in. widths, and filled
with marine glue. The covering board, 2-1/2 in. wide, with a nosing worked
on the edges, and 1/2 in. thick, was carried by a clamp or binding stake,
2-1/2 in. by 5/8 in., through-fastened at every timber. The knees were of
oak, 1 in. thick, about 10 in. on the foot by about 3 in. at the head,
and through-fastened. A breast hook 2 in. thick should be fitted. The
floor boards may be of 3/4-in. spruce, elm, or ash grating, as preferred.
The centre of the motor was at No. 6 section, as indicated, the gasolene
being stored in a strong tank under the forward deck, just high enough
to feed by gravitation. After being cleaned off and sandpapered, a coat
of good shellac varnish, may be followed, if desired, by three coats of
best yacht varnish. The spacing of the sections was: No. 1, from face to
stem, 1 foot 2 in.; No. 2, from No. 1, is 1 ft. 2 in., the other sections
to No. 11 each 1 ft. 6 in.; No. 12 was 1 ft. 1 in. from No. 11 (see Fig.
25). The water-lines were 5 in. apart, and the buttock-lines, A and B, 1
ft. and 1 ft. 9 in. respectively from the middle line.
The boys followed these directions, and with the help of the following
table, managed to get the boat ready to varnish and finish up. The
following table, which refers more particularly to the section shown
in Fig. 25, shows the sheer lines, counting from L W L (low water
line). While all the work and calculations regarding the plan had been
already done, Mr. Gregg, who had watched the work's progress for a
week, thought they should know the principles on which the craft was
being built, and therefore advised them to examine the illustration and
table, so that they would have some knowledge of the science required
to build a boat intelligently. Fred and George did this, and were
helped along by Walter, who seemed to have mastered the subject pretty
thoroughly.
TABLE OF OFFSETS
===============+=========+=========+=========+=========+=========
| |
| _Stem_ | _Section Numbers_
---------------+---------+---------+---------+---------+---------
| | 1 | 2 | 3 | 4
---------------+---------+---------+---------+---------+---------
|_ft. in._|_ft. in._|_ft. in._|_ft. in._|_ft. in._
| | | | |
Sheer heights | | | | |
above L.W.L. | 1 7 | 1 6 | 1 5 | 1 4-1/8| 1 3-1/4
| | | | |
L.W.L. to | | | | |
rebate line | | 7 | 8-3/4| 9 | 9-1/4
| | | | |
Half-breadths | | | | |
at gunwale | | 8-1/4| 1 3-1/8| 1 9-1/2| 2 1-1/8
| | | | |
Half-breadths | | | | |
at 4 W.L. | | 6-7/8| 1 1-1/2| 1 8 | 2 0-1/2
| | | | |
Half-breadths | | | | |
at 3 W.L. | | 5-7/8| 11-5/8| 1 6-3/8| 1 11
| | | | |
Half-breadths | | | | |
at L.W.L. | | 4-3/8| 9-3/8| 1 3-5/8| 1 8-3/4
| | | | |
Half-breadths | | | | |
at 1 W.L. | | 2-1/2| 5-3/4| 10-1/2| 1 3
| | | | |
Buttock A | | | | |
from L.W.L. | | | 5-1/2| 4-1/8| 6-3/8
| | | | |
Buttock B | | | | |
from L.W.L. | | | | | 3/8
---------------+---------+---------+---------+---------+---------
===============+=========+=========+=========+=========+=========
|
| _Section Numbers_
---------------+---------+---------+---------+---------+---------
| 5 | 6 | 7 | 8 | 9
---------------+---------+---------+---------+---------+---------
|_ft. in._|_ft. in._|_ft. in._|_ft. in._|_ft. in._
| | | | |
Sheer heights | | | | |
above L.W.L. | 1 2-3/4| 1 2-1/4| 1 2-1/8| 1 2-1/8| 1 2-1/2
| | | | |
L.W.L. to | | | | |
rebate line | 9-1/2| 9-7/8| 10 | 10-1/2| 10-3/4
| | | | |
Half-breadths | | | | |
at gunwale | 2 3-1/2| 2 4-1/2| 2 4-3/8| 2 3-5/8| 2 2-1/8
| | | | |
Half-breadths | | | | |
at 4 W.L. | 2 2-7/8| 2 4 | 2 3-7/8| 2 3-1/4| 2 1-3/4
| | | | |
Half-breadths | | | | |
at 3 W.L. | 2 2 | 2 3-1/4| 2 3-1/4| 2 2-1/2| 2 0-3/4
| | | | |
Half-breadths | | | | |
at L.W.L. | 2 0 | 2 1-1/2| 2 1-1/2| 2 0-5/8| 1 9-1/2
| | | | |
Half-breadths | | | | |
at 1 W.L. | 1 6-3/4| 1 8-1/2| 1 8-1/2| 1 6-1/2| 1 0-7/8
| | | | |
Buttock A | | | | |
from L.W.L. | 7-5/8| 8 | 8 | 7-1/2| 5-1/4
| | | | |
Buttock B | | | | |
from L.W.L. | 3-3/8| 4-3/4| 4-3/4| 3-1/2| 3/8
---------------+---------+---------+---------+---------+---------
===============+=========+=========+=========+=========
| | _End of_
| _Section Numbers_ |_Transome_
---------------+---------+---------+---------+---------
| 10 | 11 | 2 |
---------------+---------+---------+---------+---------
|_ft. in._|_ft. in._|_ft. in._|_ft. in._
| | | |
Sheer heights | | | |
above L.W.L. | 1 3 | 1 3-5/8| 1 4-1/4| 1 6
| | | |
L.W.L. to | | | |
rebate line | 11 | | |
| | | |
Half-breadths | | | |
at gunwale | 2 0 | 1 9-1/2| 1 6-3/4|
| | | |
Half-breadths | | | |
at 4 W.L. | 1 11-3/8| 1 7-1/4| |
| | | |
Half-breadths | | | |
at 3 W.L. | 1 9-1/4| 8-1/2| |
| | | |
Half-breadths | | | |
at L.W.L. | 1 2-1/8| | |
| | | |
Half-breadths | | | |
at 1 W.L. | 5-3/4| | |
| | | |
Buttock A | | | |
from L.W.L. | 1 | 6 | 11-3/4|
| | | |
Buttock B | | | |
from L.W.L. | | | |
---------------+---------+---------+---------+---------
It was necessary, before installing the motor, that a foundation should
be laid for it, so varnishing and the final finish were left over until
the engine and propeller should be put in and tried.
[Illustration: Fig. 27. Starboard side of motor]
[Illustration: Fig. 28. Port side of motor]
The engine was brought to the boat house from Newark, and the expert,
engaged by Mr. Gregg some time previous, came along with it, bringing
such tools as he might want. He examined the bed for the engine, and saw
that all was properly fastened and in good condition to place the engine
and the propeller shaft. Mr. Watts (the machinist) laid off a line for
the propeller shaft and with a long auger bored a hole from the engine
bed through to the stern-post, large enough to permit the shaft of the
propeller to revolve in it easily. A bearing, or "box," was adjusted to
the stern-post in which the shaft ran, and the "box" was made water-tight
to prevent any inflow. The propeller was made of bronze, had been nicely
fitted to the shaft before it came, and had a set screw in its hub to hold
it firmly on the shaft. The diameter of the propeller wheel measured 15
inches and it had two blades. The shaft and wheel being properly adjusted,
the next thing was to place the engine, which weighed about 200 lbs. The
blocks and tackle used in taking down the old barn were rigged up to the
ceiling by cutting a hole through the floor, laying a short timber across
the joists, hitching a rope around the timber, and letting a loop hang
down through the hole made in the floor. The hook of the upper block was
attached to the loop, a sling was fastened to the engine, the whole was
hoisted by Nick with the greatest ease, and the machine dropped on its
bed. As it did not lie quite level, it was raised again and held suspended
until the bed was trued up, when it was permanently lowered into place
and fastened down. Two views of the engine are shown in Figs. 27 and 28.
[Illustration: Fig. 29. Carburetor]
In "shop talk," the engine may be described as follows--Bore of cylinder
4-1/2 in. Stroke 4-1/2 in. Crank shaft 1-3/8 in. Revolutions per minute
from 60 to 750. Propeller shaft one inch. About 15 or 16 horse-power.
A float-feed carburetor, Fig. 29, was installed at the same time. This
carburetor is an excellent one. It insures a regular supply of gasolene
and air, in proper proportion, and prevents trouble when the motor is in
use. The float guarantees an even level of gasolene in the float chamber
at all times. The proper balance of the cork float closes the supply of
gasolene automatically when it reaches the proper level. This prevents
waste of fuel, every drop being thoroughly vaporized and mixed with the
proper amount of air. The spraying nozzle is higher than the gasolene
in the float chamber, and prevents the gasolene from getting into the
engine, unless it is running. The throttle valve on the carburetor gives
the operator the power to change instantly the speed, without changing
the timer, and affords him absolute control of the engine.
When all the machinery was in place, and the propeller attached, Mr. Watts
told the boys that he would finish up the work of installing the next day,
and would then run the engine "dry" for an hour or two, to get everything
working nicely before declaring the _Caroline_ ready for sea.
It was just two weeks from the day the stuff arrived when the engine was
finally installed.
"That's pretty quick work," declared Walter, "and if the boat were
varnished, we could have her in the water in a couple of days."
In the evening, as all the Greggs were seated on the veranda, Fred tried
to explain to his father the installation of the engine, but he failed to
make himself quite clear.
Mr. Gregg said to him: "You seem to have grasped the theory of the matter,
but I see you don't understand some important points, so I think a few
suggestions may be of use to you. I will not confine myself to marine
motors altogether, as gasolene engines are used for many purposes, more
and more every day. With regard to installing an engine in a boat, the
first question is the bed, as you have seen in your own case, where your
foundation is made good and solid.
"Small engines may be supported upon a single cross piece at each end of
the bed, but this method should be employed only for the smallest sizes.
"The heaviest, and in most cases the hardest, pipe to fit up is the
exhaust. It runs from the exhaust nozzle on the engine to the muffler and
thence outboard.
"The muffler is commonly placed in the stern with the outlet directly
outboard. It may, however, be in any convenient position, like under the
seats in the standing room, and the piping led outboard. In any case, the
piping for the exhaust should be as direct and as free from sharp bends
as possible.
"When the motor is near the middle of the boat, a good practice is to
lead the exhaust pipe out through the bottom, and along it to a point near
the stern, where it again enters the boat and connects with the muffler.
The outlet from the muffler then leads directly outboard as before. This
method, especially on a large cabin boat, avoids much loss of space and
the disagreeable heat of the exhaust pipe. The surrounding water quickly
cools the exhaust, reduces the pressure and makes the exhaust almost
noiseless.
"The particular function of the muffler is to afford a comparatively large
space into which the exhaust may pass and expand, greatly reducing the
pressure. The gas, under the reduced pressure, then passes out with little
disturbance. The muffler need be of no particular shape, as long as the
volume is sufficient. It is usually made of cast iron in the smaller sizes
and of sheet iron in the larger. In many cases a long piece of rather
large pipe will answer the same purpose.
"The muffler may be dispensed with and much space saved by carrying the
exhaust directly through the bottom of the boat and exhausting under
water. Although this is a very convenient and many times satisfactory way,
great care must be used or poor results will be obtained. When the exhaust
leads directly out, a certain amount of pressure is used in displacing
the water. This pressure is, of course, supplied by the piston and is a
'back pressure,' retarding the piston and decreasing its power.
"A small expansion chamber or muffler should be provided between the
engine and the outlet, in order to break up the violent pulsations and
make the flow fairly constant. Some form of shield should be fitted over
the outer end of the exhaust pipe to guide the stream of the exhaust aft
and prevent the water being forced into it by the movement of the boat.
Several forms of these are on the market in the shape of brass castings
which bolt on to the outside of the hull and have a thread on the inside
to take the exhaust pipe.
"When the under water exhaust is fitted, a pet cock should be put in the
exhaust pipe near the engine. This is opened when the engine is stopped,
thus preventing the water from being drawn up into the cylinders by the
vacuum caused by the cooling of the gases in the pipe and cylinders.
"The under water exhaust is a very neat and simple method, when correctly
installed, as all noise and heat from the exhaust pipe are avoided. The
exhaust may be considerably cooled and the noise reduced by dispersion.
"With regard to stationary engines, used for domestic or other purposes,
any old place is considered good enough to put them in. Now, this is one
of the biggest and most expensive mistakes one can make, for as soon as
some small screw gets loose in the far corner, the engine, salesman and
manufacturer are unjustly blamed, simply because the present owner has not
left enough room to make the small adjustments necessary in every engine
and piece of machinery. Therefore, it pays always to install the engine in
a light, dry place, easy of access and with sufficient space all round to
enable all parts to be reached and to give plenty of room for turning the
fly wheels in starting. Whenever possible, place the engine on the ground
floor. On an upper floor, the necessary provision should be made to avoid
vibration; if installed in the basement, place it in the best light.
"Without a good foundation, an engine may be expected to give more or
less trouble from vibration, since it is subjected to forces, suddenly and
repeatedly exerted, which produce violent reactions. Care should be taken
to excavate down to good soil and to line the bottom with a substantial
thickness of concrete in order to form a single mass of artificial stone.
The foundations may then be built up of either concrete, brick, or stone.
Anchor plates should be extended to the bottom of the masonry and fastened
so as to prevent turning while the nuts are being screwed up. Place gas
pipes or tubes with an inside diameter twice the diameter of the bolts
around them, while the foundation is being built; this allows the bolts
to be adjusted, and any variations between the tubes may be filled with
thin cement after the engine is set.
"The top of the foundation should be finished perfectly flat and level
with a dressing of cement, and after this is thoroughly dry the engine
may be placed in position. When bolting down the engine, it is better
to draw each bolt down a little at a time until all are tight and thus
avoid straining the engine crank. After the nuts are drawn tight, if the
crank turns unreasonably hard without loosening the main bearing caps,
it may indicate an uneven foundation, which is a strain in the engine bed
casting.
"When setting up large engines, for farm or other purposes, especial care
must be taken to avoid straining the bed castings. Foundations hung from
an upper floor, or built upon it, should be placed as close to the wall
as possible. For the smaller sizes of engines it is a good plan to lay
wooden beams on top of the foundations and then to place the engine on
top of them so that when the frame is bolted down it beds itself into the
timber. The timber cap often saves an annoying vibration when it can be
overcome in no other way.
"All the connections should be as short and as free from turns as
possible, and no mistake can be made by having plenty of unions, so as to
disconnect with ease. The gasolene tank should be set as near the engine
as is convenient, with the top of the tank, preferably, not more than
a foot or two below the base of the engine. In cases where the gasolene
tank must be set from forty to fifty feet away, it is necessary to place a
check valve in the suction pipe near the tank. Both suction and overflow
pipes must have a gradual rise all the way from the tank to the pump and
should be as straight as possible to avoid the air traps, which prevent
a steady flow of gasolene. It is most essential to clean thoroughly all
pipes and fittings before they are put together, by hammering lightly to
loosen any scale and washing out with gasolene, as solid matter of this
nature may be responsible for some of the simple, but hard-to-get-at
troubles common to gasolene engines.
"Shellac is best for joints in gasolene piping, but when this cannot be
obtained common laundry soap will answer the purpose just about as well.
Remember, also, that gasolene is a rubber solvent, and should never be
applied to joints where rubber is used. In some cases it will be found
advisable to use gravity feed instead of a pump, except in the case of the
tank, which must be so arranged that its lowest point is slightly above
the generator valve.
"The exhaust pipe must be of full size, free from turns and short as
possible, since the shorter it is the more economically the engine will
run. It will be found advisable to place the muffler and exhaust piping
away from combustible material, and never to turn the exhaust into any
chimney or flue.
"There are two general methods of supplying the water, the first being
that of the cooling tank commonly used with small engines. For convenience
in piping, the tank should be slightly elevated, and both pipes, having as
few bends as possible, should slope from the tank to the engine, a valve
being placed in the bottom pipe near the tank. By using a circulating
pump, fitted to the engine or shaft, water may be used from an underground
cistern or tank.
"The other method is to use a continuous cooling stream from water-works
or other source. When city water is used, it is a good plan to have a
break and funnel inserted in the drain pipe so that the current of water
flowing through the cylinder jacket may be seen. For making joints in
water pipes, either thick lead or graphite may be used with almost equal
success. It may be well to place particular emphasis on the fact that
it will pay to get into the habit of always shutting off the water at
the tank and draining the cylinder every time the engine is stopped--not
necessary in summer, but absolutely essential in winter--as a fair
percentage of gasolene users know to their cost.
"The greatest care must be employed in using and handling gasolene, as it
is dangerous and highly explosive. It has been known to explode when 20
or 30 feet from light, the vapours having reached the fire in the way of a
gas, igniting and firing the liquid. And, now, right here, let me impress
on you this warning; never handle gasolene near a fire or light under any
circumstances, and be very careful with it under all conditions.
"Fortunately, there are few accidents resulting from gasolene, when we
consider the large amount used since it has become almost a universal
fuel for engines, and it is also used largely for domestic heating and
lighting.
"It is a product of petroleum, of which in its crude form about 76 per
cent. is turned into kerosene, 11 per cent. into gasolene, 3 per cent.
into lubricating oils, and the balance into vaselines, paraffine, coke
and so forth.
"Different petroleums produce different proportions of the various
products, some of them being considerably richer in gasolene than 11 per
cent.
"Gasolene is usually designated according to its specific gravity by an
arbitrary measure, known as Baume's hydrometer scale. This designation
is in degrees, the most common gasolene ranging between 65 degrees and
85 degrees, and the average being 70 degrees, the usual density used in
engines.
"You will find it somewhat difficult at first to start up your engine when
you wish to, so I will give you a few hints to show how this difficulty
may often be overcome.
"There is always a reason why a gas engine refuses to obey the behest of
its driver.
"In the first place, see that the compression is right and the admission
valve so tight that it will admit only enough of the mixture (gasolene
and air) to make a charge that will take fire from the sparker and move
the piston forward. Next see that the sparker is clean, that it will make
a bright spark at white heat when the contact is broken, and at the right
time. 'In time' means to go if everything else is right, and 'out of time'
means not to go even when everything else is right.
"The valve of the engine must be kept well ground down with emery and oil
so as to preclude the possibility of a leak, as one would very seriously
weaken the power of the engine even after it had started. The spark must
be made when the connecting rod of the engine is on the 'up stroke,' with
the crank shaft about three inches below the horizontal line of the centre
of the index, and herein lies the whole secret of the greatest efficiency
from the least amount of gasolene. As there is an interval of time after
the spark is made until it ignites the charge, it is very evident that the
movement of the machinery continues and the moment of ignition should take
place when the compression is greatest. This will be when the piston is
on its farthest 'in stroke,' _i. e._, in perfect line with the centre of
the cylinder. But if the charge be ignited at this point the engine will
not develop the greatest power, as the interval spoken of will elapse and
the piston will have started on its 'out stroke', thereby not getting its
full force of the expansive gases liberated by combustion of the air and
gasolene.
"So you will readily see that you must allow for the interval spoken of,
if you would get full returns for the energy used in propelling the motor.
I have tried to make this plain, and I hope my efforts will help you out
with your engine, either in starting or developing the power at which it
is rated."
It was not yet late, so the boys took down from the book shelf a code of
yacht flag signals, and found the following:
"There are no hard and fast rules regarding shapes and colours of yacht
bunting, but the following are generally accepted by the prominent clubs
in the United States and in foreign countries.
1. The "pennant" (a triangular shaped flag) is used for the club burgee.
2. The "shallow tail" is adopted for the private signal.
3. The rectangular flag is chiefly used for a flag officer's signal.
4. The shape, consequently, at once denotes whether a flag is that of a
club, a flag officer, or a member.
5. The majority of flag officers' signals are coloured: Blue for
commodore, red for vice-commodore, and white for rear-commodore.
6. The international code of signals enables yachts to communicate with
each other, and is also used for dressing ship.
The ensign should be flown from the peak of the main-sail on a sailing
yacht, when under way, and from a stern flag pole when moored.
On a yawl, it should be hoisted at the mizzen truck.
On a steamer, launch, or dinghy, it should be flown from a stern flag
pole, when under way or at anchor.
_Club Burgee._--The burgee should measure in length about one-half inch
for each foot of height of truck from the water; width to be two-thirds
of the length. Private signals may be smaller.
The burgee should be flown from the mast-head or truck of a cutter,
sloop, or cat-rigged yacht, the main truck of a yawl, the fore truck of
a schooner and steamer, and from the bow pole of a launch or dinghy.
Flag officers' and private signals should be flown from the truck of a
cutter, sloop, or cat-rigged yacht, the main truck of a schooner, yawl,
or steamer, and from the bow pole of a launch or dinghy.
The following flags are not considered as colours:
_Night Pennant_ (_blue_).--Is hoisted at the main truck from sundown to
8 A. M.; also occasionally used as a tell-tale when racing or sailing.
_Owner's Absent Flag_ (_blue rectangular_).--Is flown from the main
starboard spreader when yacht is at anchor only. It denotes owner is not
on board, but should never be flown when under way.
_Owner's Meal Flag_ (_white rectangular_).--Is flown from the main
starboard spreader, and denotes the owner is at meals--boarding a yacht
when this flag is flying is considered bad form.
_Crew Meal Flag_ (_red triangular_).--Is flown from the foreport spreader
on schooners and main-port spreader on single-masted yachts. This denotes
that the crew is at meals.
_The Ensign._--Displayed on a vessel indicates distress and want of
assistance.
_Flag "B,"_ of the International Code of Signals, is used for a protest
flag, and is conspicuously displayed in the rigging of a yacht protesting
during a race.
A yacht, on withdrawing from any race, should at once lower its racing
colours, and allow yachts still competing the right of way.
This code was studied by the boys until both of them thoroughly understood
its full meaning, and George became so enthusiastic over it that he
exclaimed: "Fred, I am going to be an admiral of the navy!"
V
A TALK ABOUT ENGINES
Mr. Watts was early at the Gregg residence next day, and busied himself
preparing the engine to start up. A big tub was taken to the boat house
filled with water by a hose attached to the suction pipe, and dropped
into the water. This was a mystery to George, who inquired about the use
of the water and the other attachments. It was explained to him, that
outside the cylinder there was a hollow space, called the "water jacket,"
extending over the top of the cylinder, and this had to be kept full of
cold water by continual circulation. It was pumped in by the engine and
forced out by the same means, a simple contrivance being arranged for the
purpose. This circulation of water is necessary to keep the inside of the
cylinder cool, otherwise the walls would soon become red hot, on account
of the rapid explosions of gas and air employed in the cylinder to keep
the piston moving to and fro.
George seemed to grasp the idea thoroughly. Mr. Watts also explained
the use of the carburetor, the spark coil, the battery, and the method
of contact to produce a spark at the proper moment. After some screwing
of bolts, adjusting the piston, and trying the valves, the tank in the
carburetor was supplied with gasolene and Mr. Watts tried the engine for
a few revolutions, as gently as it could be done. It was a little stiff
at first, some of the connections fitting too tight, and the piston,
being new and harsh, did not work smoothly. By the judicious use of
good lubricating oil and a few turns of some of the nuts on the bolts,
a little more freedom was given to the machine and the starting was easy
and smooth. George and Jessie were delighted with the rapid movement of
the machine, the buzz of the propeller, and particularly interested in
the movement of the water in the tub.
Mr. Watts allowed the engine to run quite a little while, and arranged the
exhaust so as to beat regularly and to "pop! pop!" as little as possible.
He then called Fred into the boat and taught him how to run the machine,
arrange the contact breaker, and regulate the feeding of fuel. The engine
was stopped to cool and to be examined again by Mr. Watts, who pronounced
it all right. Mr. Gregg, who had arrived just before the engine was
stopped, examined all its parts and watched it work for a minute or so.
Fred arranged his pots and brushes, and he and George went to work
varnishing, so that before sunset the _Caroline_ looked quite smart and
trim. The boys were very careful in applying the varnish to put it on
light and thin so as not to let the coats lap over one another as they
went along. They finished each "streak" from end to end, before starting
on the next, and following this method they obtained a nice, even surface.
The varnish did not look "blotchy" or patched, as it would have done had
the ends of the varnish lapped. To avoid "lapping" is one of the most
essential operations in varnishing, when a nice piece of work is desired.
[Illustration: Copyright, 1911, by Underwood & Underwood, N. Y.
FINISHING THE MOTOR LAUNCH
"To Avoid 'Lapping' is One of the Most Essential Operations in
Varnishing"
]
It was decided to give the little craft two more coats of shellac varnish
before launching her, and the following spring to give her a good coat of
marine varnish. Mr. Gregg thought that in another week, say the following
Wednesday, the _Caroline_ might be launched with safety, as the varnish
would get dry and hard, and the inside paint would also be hard enough.
Jessie and the boys were given permission to invite a few friends each to
the boat launching, and were promised suitable refreshments to be served
on the new grounds, if the weather was favourable. Fred asked his father
if he could not build up some temporary picnic tables and seats for the
occasion, as there was plenty of material still left unused from the old
barn stuff. Permission was granted, and after counting up the number that
would probably be present, it was found that three tables, each about
fifteen feet long, with necessary seats, would give ample room for the
accommodation of the proposed guests, with a good allowance for overflow.
Just then the whistle of a small steam tug, that often plied on the river,
gave warning of her approach; and all went down to the river edge to watch
her pass and to see what effect her "wash" would have on the new pier and
the boat house "skid" or slides. She came up stream rapidly against the
tide--which was on the ebb--and there was a considerable "wash" from her
wheel, but it struck the bank, the pier, and the "skids" without doing
the least harm or giving any evidence that trouble would result from any
reasonable wash. The little steamer's exhaust, as she passed, made quite
a noise and Jessie was somewhat puzzled at this, as the exhaust from the
gas engine of the _Caroline_ only made a plaintive puff in comparison.
Her father promised to explain the reason after tea.
Returning to the boat house, George suggested that the name of the boat
be painted on both sides of the bow, in large letters, but Mr. Gregg and
Fred, thought it better to have "Caroline" placed on the second streaks
of sheathing, in gold, the letters to be not more than two inches over
all. This was agreed upon, and a young artist, who was a near neighbour,
was suggested as the person to do the work.
[Illustration: Fig. 30. Hero's steam engine]
After tea, Jessie and the boys followed their father into the den, where
Mr. Gregg gave the children a brief history of the steam engine, as far
back as known, commencing with the Colipyle, the invention of Hero of
Alexandria about 130 B.C. An illustration of this is shown in Fig. 30. It
was simply a pot or boiler, partly filled with water, the lid or cover
being fastened down tightly. On the top of this was attached a hollow
bent tube having a tap fitted to it, which supported and communicated
with a hollow metal ball hung on another tube or bearing on the other
side in such a manner that the ball could revolve easily. Attached to
this hollow ball or sphere were four other hollow tubes, so fastened as
to project from the surface two or three inches, and these were bent at
their outer end, as shown in the illustration. These tubes were of course
attached and bent in a direction at right angles to the axis of rotation.
The tap leading to the hollow ball, when turned open, allowed the steam
from the boiler to rush into the ball and fill it up. If it was closed
entirely, the ball would remain still, but the steam exerting an equal
pressure on all points of the inner surface, and finding the openings,
escaped through with a rush and noise as it condensed in the air, which
it pressed against, causing the ball to revolve in an opposite direction
to the outflow of steam. This Hero engine or Colipyle, was doubtless the
beginning of steam motors, but during the 2,000 or more years since Hero's
toy engine was invented, great strides have been made toward bringing the
steam engine to its present efficiency.
"But I do not intend," said Mr. Gregg, "to give a history of the growth
and development of the machine, at this time. There are numerous works on
the subject, obtainable in any fairly-equipped library."
[Illustration: Fig. 31. Steam cylinder and piston]
Steam, as everybody knows, is generated by heat being applied to a closed
metal kettle or boiler containing water. This boiler must be strong and
properly arranged so as to admit more water--which is usually injected
with a force pump--and it must have an outlet for the release of the steam
to the cylinder of the engine. Generally, there is a small dome on the top
of the boiler, called the "steam dome," and to this the steam outflow pipe
is attached. The actual use of this dome is to hold a volume of steam that
will remain unmixed with water, as it is placed considerably above water
level. On the top of the dome there is an automatic arrangement called
a "safety valve," so that when there is too much pressure of steam in
the boiler, it will open and allow the over-pressure to escape, and thus
prevent the boiler from exploding or being over strained. This valve is
controlled by a simple device, somewhat similar to a steelyard. A movable
weight is arranged to slide on a long arm which is loosely fixed to the
valve flange by a bolt and nut, and extends some distance past the seat
of the valve. The arm or lever has an iron pin attached to it directly
over the valve seat, which holds down the valve and keeps the steam from
escaping. The movable weight on the arm is adjusted so as to regulate
the pressure on the valve. When there is too great a pressure, the valve
forces up the lever, and at the same time opens a passage for the extra
pressure of steam to escape. There are several other contrivances for
relieving the boiler of over stress, but the one described, or rather the
principle on which it is built, is most in use on this country. There are
many kinds of boilers, or steam generators, but the best, and very likely
the strongest, are those employed on our first-class railway locomotives.
These are frequently under a pressure of 200 or more pounds to the
square inch, which seems an enormous load for a hollow shell to carry,
yet, so near perfection are they, we rarely hear of a locomotive boiler
explosion. As there are many kinds of boilers, so also are there many
kinds of steam engines, but all of these latter, with very few exceptions,
have a cylinder and piston for converting the force of the steam into
useful and effective motion. The manner of using this force and keeping
it under proper control is somewhat complex and difficult to describe
briefly, without elaborate diagrams, but Mr. Gregg explained, in his own
way, how the great force was converted into motion. On the blackboard he
drew a rough diagram of a cylinder and valve or steam-chest, with piston
and slide-valve, about as shown in Fig. 31, which gives a longitudinal
section of the whole arrangement. Here we see near each end, the opening
of a double conduit aa, made in the thickness of the side; these are the
openings by which the steam comes alternately to work on one end, then on
the other, of the piston. These are called the steam-ports. These two open
outward on a well-polished surface, and between the two a third opening,
E, is seen, which serves to let the steam escape when it has done its
work, and is called for that reason the exhaust port. C is the pipe by
which the steam gains access to the open air or to the condenser, where
it parts with its elastic force.
Here is shown by what contrivance the distribution is effected,
consisting, as it does, of two partial operations; the admission of the
steam and its escape, which must be repeated twice to obtain a complete
phase of the to-and-fro movement of the slide-valve. There are various
methods employed according to different engines--but the first described
is the one represented by the illustration.
In the valve chest, BB, is seen a prismatic box, open on one side, called
the slide-valve, and this is applied by its open face to the well-polished
plane on which, as mentioned before, the three ports open. The space BB,
is called the valve or steam chest. The steam coming from the boiler by
the pipe C spreads out freely in it, but the inside of the slide-valve, on
the contrary, is always closed to the entering steam, though constantly in
communication with the escape pipe and also with first one then the other
of the entrances to the cylinder. Lastly, the movement of the slide-valve
is produced by the engine itself, aided by a rod and an eccentric fixed
to the shaft of the fly-wheel.
[Illustration: Fig. 32. Steam valves--different positions]
By following the successive and alternating motions of the slide-valve,
as represented in Fig. 32, we can easily comprehend the different phases
of the distribution of the steam.
This is the machinery for the distribution of steam generally. There
are other engines, such as rotary and oscillating, that are supplied by
other contrivances, but most of these have fallen, or are fast falling
into disuse, as they are not so satisfactory as the ordinary slide-valve.
It will be seen upon examination of the sketch, shown in Fig. 32, how
the steam enters and leaves the cylinder and the position of the piston
under the various positions of the valves. The arrows show the direction
of the slide, also the direction of the piston and its position when the
slide covers the ports X, or leaves them open, or partly so. The ports
for egress or ingress are shown at X, the slide-valve at V, and the
cylinder at C. When the piston is near one end of the cylinder, the steam
is admitted and forces the piston in the opposite direction, while the
valve is so arranged that when the piston starts in that other direction,
it begins to open the port at the other end of the cylinder through which
the exhausted steam escapes. This makes the noise Jessie asked her father
about. There are some engines so devised that the exhaust is made to
assist in driving another engine.
Of course, there are many kinds of steam engines, but all are run on the
same principle, or nearly so. As you know, steam is generated in boilers
by fire being applied to the outside and the water made hot enough to
raise steam. A steam engine is said to be externally heated, while gas,
oil, and other similar engines are internally heated, because instead of
the steam driving the piston, the gas, oil, or other explosive matter
is admitted into the clearance or space between the piston and the
end of the cylinder, where it is exploded by an electric spark from a
battery provided for the purpose, and this is called the "ignition." The
explosion causes the gas and air in the cylinder to expand, bringing a
great pressure on the piston, forcing it to move toward the other end of
the cylinder, and making the whole machine move. One great advantage of
employing a gas engine is that no boiler is required, a very important
matter, as boilers take up a great deal of space. The coal or wood
necessary to keep up steam also takes space that could be used for other
purposes, all of which make the use of steam objectionable when it is
possible to employ suitable gas engines. Besides, the make-up of a steam
engine is of such a character that it is very expensive, while the first
cost of gas engines is much lower.
All gas, oil, or other explosive engines are internal heaters, because
the heat is generated in the cylinder at each explosion, and this is one
of the main features that distinguishes the gas from the steam engine.
Of course, there are many attachments and connections to steam and gas
engines that would take too long to describe, and in a great measure be
unnecessary. A few items may prove both useful and profitable and it is
well to know firstly: How to estimate the horse-power of an engine.
When steam engines were first introduced they were largely used to take
the place of the horses previously employed for raising water from mines.
Naturally people inquired, when buying an engine, what amount of work it
would perform as compared with horses. The earliest engine builders found
themselves very much at a loss to answer this question so they had to
ascertain how much a horse could do.
The most powerful draught horses and the best of any then known were the
London brewers' horses. These, it was ascertained, were able to travel at
the rate of two and a half miles per hour and work eight hours per day.
The duty, in this case, was hoisting a load of 150 pounds out of a mine
shaft by means of a cable. When a horse moves two and a half miles per
hour, he travels 220 feet in a minute, and, of course, at the speed named,
the 150-pound load would be raised vertically that distance. That is equal
to 300 pounds lifted 110 feet per minute, or, 3,000 pounds lifted 11 feet
or 33,000 pounds lifted one foot high in one minute. That is the standard
of horse-power, as we all know. It is much more, however, than the average
horse can do, and therefore the builders were confident that the engines
would take the place of fully as many horses as the horse-power would
indicate that they should.
Of course, 33,000 pounds lifted 1 foot per minute is much more convenient
for calculation than 150 pounds lifted 220 feet, and therefore the former
rate has been adopted. The amount of work, or number of "foot-pounds,"
is the same in either case. A foot-pound represents the amount of
power required to lift one pound one foot high. To find the number of
horse-power in any engine, we multiply the area of the piston by the
average pressure per square inch upon it; multiply this result by the
distance which the piston travels per minute in feet and the result is
the number of foot-pounds per minute which the engine can raise. Divide
by 33,000 and the result will be the number of horse-power. The number
of feet per minute travelled by the piston is twice the number of strokes
per minute multiplied by the length of the stroke. This gives the amount
of horse-power sufficiently accurate for all practical purposes.
It necessarily takes time to do work, but the amount of work done has
nothing whatever to do with the time taken to do it.
If a man, weighing 150 pounds, walks up the 900 steps leading to the
highest attainable level in the Washington Monument, 500 feet high, he
does work against gravity equal to 75,000 foot-pounds, irrespective of the
time taken in the ascent. Then the work done in a given time, divided by
the time, is called the power of activity.
Power is the time rate of doing work. In the English gravitational system,
the unit of power is the horse-power (H.P.); it is the rate of doing work
equal to 33,000 foot-pounds a minute, or 550 foot-pounds a second.
In the centimetre-gramme-second (C.G.S.) system (in which the unit is 1
gramme moving at the rate of 1 cm. a second), the unit of power is the
watt. It equals work done at the rate of one joule (10,000,000 ergs) a
second.
One horse-power is equivalent to 746 watts.
A kilowatt (K.W.) is 1,000 watts.
It is therefore nearly 1-1/3 horse-power.
To convert kilowatts into horse-power add one-third; to convert
horse-power into kilowatts, subtract one-fourth.
For example, 60 K.W. equals 80 H.P. and 100 H.P. equals 75 K.W.
The expression foot-pound is in general use among English-speaking
engineers, and as explained it is the unit of work done by a force of one
pound working through a distance of one foot. It is not a fixed standard
of measurement, since the weight of a pound is not the same in all heights
above sea level, and on this ground it is open to objection. It is the
nearest constant, however, we have yet discovered, hence its general
adoption.
"Dry steam" is the steam in which no condensation is visible, and it
may generally be obtained at a 10-pound pressure per inch, but no exact
dividing line of pressure can be defined between dry steam and wet. If
care is taken in covering pipes and cylinders, to prevent condensation, a
pressure of 10 pounds should make steam as dry as gas, and if the steam
pipe is carried through a good, hot fire at some point, the fire will
superheat the steam and render it more dry. Wet steam, of course, is steam
that can be seen, through having been more or less condensed by contact
with air or cold. There can be no steam without heat, but steam does not
require as much heat as is generally supposed. Suppose we take one pound
of water at 32 degrees Fahrenheit and apply a fixed and known quantity of
heat until it boils; we will assume that it takes 20 minutes, and we have
supplied the water 180 heat units, which, added to the 32 contained in the
water at the start, makes 212 degrees Fahrenheit or heat units, and is the
sensible heat of steam at atmospheric pressure. Now let us continue the
same quantity of heat per minute until all the water has evaporated into
steam, and we will then find that it has taken five and one-third times as
long, or 107 minutes to do this work. Consequently we have used five and
one-third times 180 or 960 heat units; or, to be exact, 966 heat units.
Now the temperature of the steam is the same as the water from which it
has evaporated, or 212 degrees Fahrenheit, and this 966 heat units is the
latent heat of steam at atmospheric pressure. All steam has a sensible
heat corresponding with the temperature of the water it has evaporated
from. If you boil water under a pressure of five atmospheres, or 75 pounds
pressure, the sensible heat is 306 degrees Fahrenheit, the boiling point
at that pressure, but the latent heat has decreased by the same number of
heat units that the boiling point increased, so the total is the same in
all cases. In the first instance we have 212 degrees minus 32, plus 966,
or 1,146; and in the second 306 degrees minus 32, plus 872 or 1,146 heat
units. This may be considered a fair description of latent heat.
The most useful quality of steam yet discovered is its power of expansion.
It follows what is known as Marriott's Law of Expanding Gases, which means
one-half the pressure double the volume. So if we let steam into an engine
cylinder, at 80 pounds' pressure, and cut it off at one-fourth stroke, it
is at 80 pounds up to the point of cut-off. At one-half stroke, because it
has doubled its volume, it is reduced to one-half pressure, or 40 pounds;
while at three-fourths stroke the volume has trebled and the pressure
has dropped to nearly 27 pounds, and this is why it is economical to run
engines that use steam expansively. Steam at 27 pounds' pressure is very
much cooler than steam at 80 pounds, and this difference in temperature
has been converted into mechanical work by our steam (heat) engine.
There are many other peculiarities about steam and steam engines that a
young boy should know, and the information can readily be obtained from
books in any good library.
The steam turbine, of which so much has been heard lately, is not
constructed like an ordinary steam engine with cylinder, slide-valve and
other attachments; but more like the Hero engine, with this difference
that the steam jet or jets act on a wheel having vanes or blades, the
expansion producing a velocity which rotates the wheel containing the
vanes. A modern turbine, of the Parsons type, such as are employed on the
great Atlantic steamers, is a tremendously high speed engine. It does not
derive its power from the static force of steam expanding behind a piston,
as in a reciprocating engine. In this case the expanding steam produces
kinetic energy of the steam particles, which receive a high velocity by
virtue of the expansion, and, acting upon the vanes of a wheel, force it
around at a high speed of rotation in the same manner as a stream of water
rotates a water-wheel. The expansion produces velocity in a jet of steam,
and this is the main difference between the ordinary engine and the modern
steam turbine.
Among gas and internal explosion engines there exist some differences,
both in construction and in the manner of supplying fuel. The
gas-producing engine may be considered the better class, though it has
not as yet gained the popularity of the gasolene one. The gas by which
this style of engine is operated is produced by a special process, namely,
by passing air and steam through a fire of hot coals. After generation
the gas passes over a flash-boiler and a portion of its great heat is
withdrawn, thus permitting it to enter a scrubber--a cylinder filled with
coke and sawdust--while fairly cool. In passing over the flash-boiler
the great heat raises all the steam necessary for the production of gas
required in the operation of the engine and plant. In passing through
the scrubber the gas is not only cooled, but is freed from particles
of suspended matter, the coke removing the heavier particles, and the
sawdust, the tar, or any other volatile matter that may be left.
One of the most important requirements in a gas-producer is that it shall
be adapted to the work it has to do. Its construction should be compact
and simple, so as to permit the easy removal of worn out parts. The
feeding device should be such as to secure a uniform distribution of fuel.
The blast should be so introduced as to burn out all the carbon in the
ash zone, and yet not produce localized combustion along the walls. The
construction should permit the easy removal of ashes, and render the
machine safe, while the entire process of gasification should be clean.
The radiation loss should be low, and the producer must be made efficient
to insure satisfaction.
It should be borne in mind that because of the presence of carbon
monoxide, producer gas will always be more or less poisonous. The carbon
monoxide has a specific toxic effect on the human system, and when inhaled
enters into direct combination with the blood, and brings about very
dangerous effects.
As water is always required for cooling purposes when running a gasolene
engine, it is well to know about how much will be required. One authority
says: "The quantity of water required at the ordinary temperature of 60
degrees F. inlet and 150 degrees outlet, to keep the cylinder of gas
engines cool is 4.5 to 5 gallons per indicated horse-power-hour. The
jacket pipe should be from 1 to 2 inches diameter for engines up to 20
horse-power, while for larger engines the sizes are generally 2 to 3
inches for the inlet and 2.5 to 3.5 inches for the outlet. Tanks for
circulating the water are generally made with a capacity for furnishing 20
to 30 gallons per indicated horse-power. This rule may be taken as about
correct, but, if anything, it is rather an over-estimation of quantity
necessary."
All the foregoing was made as clear as possible to the listeners by Mr.
Gregg before the children went to bed.
Next morning Fred called up his artist friend, and got him to come down
to gild the name "Caroline" on the boat before the next coat of varnish
should be applied. The artist made an outline of the name while George
and Jessie stood by and watched the process with considerable interest.
They saw him measure off each letter, outline it with a pencil lightly,
and then paint inside the lines with a substance known as "gold size,"
obtained from any store dealing in painters' supplies. While the size was
still sticky the artist applied "gold leaf," which he had brought in a
little book along with him. Jessie was surprised to see him cut the gold
with a thin pallette knife, having a blunt but smooth edge. She watched
him pick up the small pieces of gold with a camel's hair brush, which he
rubbed in his own hair now and again whenever it would not pick up the
gold. The metal was applied bit by bit over and beyond the lines of the
letters, and a light puff of breath forced it down to the size. When one
side of the boat was finished, so far as laying on the coat of gold was
concerned, Jessie was very much disappointed, as the name seemed merely
a smudge. She could not make out the letters, but the artist told her to
wait until to-morrow and he would show her how well they could be seen.
Next day with a flat camel's hair brush he dusted away the surplus gold,
and the letters showed up in good style, much to the gratification of
Jessie and George. This part of the work being done, the boys took down
their varnish pots, and gave the little craft another coat, to make her
quite spruce and gay.
Fred, and Nick, who was still in the employ of Mr. Gregg, laid off a space
on the ground for tables and seats to accommodate the young folks who
were coming to the launch on the following Wednesday. Nick found a number
of old cedar posts, and with a saw cut off 18 pieces about two feet long
and as many more twice that length. The first were intended to place the
seats on; the second lot were to sustain the tables. The spots for the
tables were chosen, measured off, and small stakes driven into the ground
to show where the posts were to be placed. Five posts were intended for
each table--two at each end, two feet apart, and nine feet apart in the
length of the table. The single post was placed in the centre of the table
both ways. When the stakes were all in place, Nick made holes deep enough
to take in the posts so that their tops measured just two feet and two
inches above the level of the ground. The tables were to be two feet and
six inches high when finished, as that is the regulation height. It was
attained, in this case, as follows--First by the height of the posts from
the ground, two feet two inches; then by a plank two inches thick laid
across the two posts, making the height two feet four inches, and the
table top, two inches thick, laid on these cross planks, which brought it
up to the required height. A piece of plank the same thickness was nailed
on the centre post across, so that it would support the table top. Planks
that had been used in the loft of the old barn did service for the table
tops, bearing pieces, and the bench seats. The last were constructed
in the same manner as the tables, the short posts being let into the
ground--three under each seat--and fourteen inches above ground so that
when the plank seat was nailed on top of them, the seats were just sixteen
inches, the regulation height of stools, benches, and chairs, though it
is sometimes varied to suit conditions. The benches were placed about
four inches out from the edge of the table and were found to be "just the
thing."
When Nick had planted the first post for the tables and got it the right
height, he took that one for his guide and by the aid of a long parallel
straight edge which he laid on the guide post and the one he was setting,
and also a spirit-level on the straight edge, he managed to get all the
posts alike in height and this made the tops of the three tables nice
and level. It was quite an achievement to have three large tables and six
long seats placed in "picnic style" at so small a cost and with so little
effort.
In order to have the tables and seats neat and clean, George turned on the
garden hose and gave them a good wash off, and when they were dry again
the place was as inviting as a country hotel dining-room. When Mrs. Gregg,
Jessie, and Grace Scott had the tables set and garnished for the launch,
the lay out was charming, none the less so because it was a little rustic.
Another coat of varnish, the third, was given the boat the day before she
was to be launched, and Fred had a strong rope attached to the winch, with
a heavy iron hook fastened to the end of it. A stout iron ring was bolted
to the stern of the boat and made secure. Mr. Gregg had purchased a number
of small flags and "burgees" and had one made with the name "Caroline"
in large letters wrought on it, ready to be unfurled when the launch was
made, and Walter Scott, his mother and sister Grace, and others had been
invited to attend.
A number of temporary swings were fixed up by Nick and Fred to the trees,
some for the large folks, others for the smaller ones, and everything was
at last ready for the great event, which was to take place the next day
at two o'clock.
VI
PROPELLER AND OTHER SCREWS
Wednesday morning was light and sunny and the boys were up and dressed
somewhat earlier than usual, so, while waiting for breakfast, they took
a stroll down to the river, where they found their father looking over
the grounds and examining tables, benches, swings, and particularly the
foot-bridge; for, as he told Fred, "it was very likely all the guests
might be on the bridge at one time and the combined weight would be rather
trying if it had not been securely put together." He satisfied himself,
however, that the bridge was strong enough to support three times the
weight it would be called upon to sustain. Everything else seemed to be
sufficiently strong, to apprehend little danger, no matter how much the
children romped.
Nick had the grounds nicely raked off; the decayed branches and shrubs
he moved, and made everything about the place as clean and as neat as
possible. Flags and other decorations were hung or placed about the
grounds, on the trees and buildings, but particularly about the tables
and the boat house. Newspapers were spread over the tables, linen covers
above them, and the whole surroundings took on a most festive appearance.
It was just 11 o'clock when _The Mocking-Bird_ arrived and tied up to
the new dock. On board were Mrs. Scott, Grace, and the maid, who came to
help, besides several of the invited guests whom Walter had brought down
with him. All were welcomed by Fred, Jessie, and George and then the women
visitors went to the house to assist Mrs. Gregg.
Mr. Gregg came home from his office earlier than usual and took a half
holiday in honour of the occasion. The guests, in little groups, arrived
on time, and before the clock struck two Nick had everything prepared for
the launch. He and Fred and George had the _Caroline_ nicely placed on
the skid, ready to "let go" the winch, and a flag pole was fixed up on the
bow of the boat. To this the flag with the name on it was lightly tied, in
such a manner that when a string was pulled it would unfurl, and show the
name. The string looping up the flag was left long enough to enable Mr.
Gregg, standing on the dock, to hold the end in his hand, and by pulling
it to loosen the flag as soon as the boat touched the water.
Everything being ready, Walter Scott invited as many of the young people
to get into the _Mocking-Bird_ as could crowd on board with comfort,
and each was provided with a whistle or a horn, as he ran his boat half
way across the river. The children on shore were also given horns and
whistles, and all were told to blow as loud as they pleased when the boat
touched the water. Mr. Gregg, having Mrs. Gregg and Mrs. Scott standing
beside him, gave the word, "Ready!" Nick and Fred answered, "Aye, aye,
sir!" and the master of ceremonies called out in a loud voice: "Let her
go!"
Nick freed the winch, Fred and George gave a little push, and the
_Caroline_ slid down the skids, into the water, without the least hitch.
The horns and whistles made a great din, and when the flag was let free to
open up and show the name "Caroline" there was another blast of noise by
horns and whistles, mingled with voices of the younger people, who cried
out with all their might, "Hurrah for the _Caroline_!"
The launch being over, and everything having gone all right, the young
people were called to lunch. They all sat at the tables which were nicely
garnished and well supplied, and there was plenty of small talk, and much
laughter and jollity. After lunch, Fred, Walter and George boarded the
_Caroline_, supplied her with gasolene, and tried to run her. They found
a little difficulty in starting, but after the engine was warmed up a
little, she went off beautifully, and answered her tiller in fine style.
The boys ran her up and down the river for a while, then tied her to the
dock, and Walter and Fred invited all the girls to "Come and have a sail."
The boys were promised one when the two boats returned, which they did
in the course of half an hour. The swings were put in use, dancing and
romping began, and the afternoon was passed in fun and frolic.
In the evening, Mr. Gregg, Jessie, and the boys took a trip, and Mr.
Gregg was well pleased with the boat's performance, particularly with
the working of the screw. In mentioning this, he awakened the curiosity
of George, who reminded his father that he had not yet explained to them
about the screw as a mechanical power.
[Illustration: Fig. 33. Theory of screw]
That evening George was told to bring his blackboard and equipment
into the den, and the father at once began explaining the mechanical
qualities of the screw. He told of its great usefulness in the industrial
arts. As one of the mechanical powers, it may be considered an inclined
plane, wrapped spirally round a solid cylinder. The advantage gained by
it depends on the slowness of its forward or backward progress, that
is, on the number of turns or threads, as they are called, in a given
distance. It is always used in combination with a lever of some sort. When
employed as a lifting machine it has great power, and is used to produce
compression or to raise or move heavy weights. If a screw is formed on
the inside surface of a hollow cylinder, it is called a nut, and used
to overcome a resistance; either the screw or the nut may be fixed and
the other movable. The acting force is generally applied at the end of
a lever or wrench or rim of a wheel. Fig. 33 represents a screw and nut
operated by a lever or length of radius _r_; _p_ is the pitch of the screw
or height of the inclined plane for one revolution of the screw. W is
the resistance at the nut and P is the force at the end of the lever _r_.
Remembering that, while the resistance W is raised the distance _p_ the
force P revolves around a complete circle and moves a distance 2[pi][nu].
Let us now apply the condition [sum] work = 0 and we have
P2[pi][nu] - Wp = 0 or -- = P2[pi][nu]/p (6).
[Illustration: Fig. 34. Worm wheel and screw]
The worm gear (Fig. 34) is a special case of screw and nut, where the
latter is replaced by a toothed wheel called a worm wheel. The teeth work
in with the thread of the screw or worm, and thus, as the worm revolves,
the worm wheel revolves about its axis. P is the force acting on the worm
at a radius _r_. _r´_ is the pitch radius of the teeth in the worm wheel
and _r´´_ is the radius of the drum on which W acts. Let K, corresponding
to W in equation W P (6), be the force at the pitch circle and worm
threads due to the force P; then
K = P2W/p (7).
Now apply [sum]m = 0 to the worm wheel and we have
Kr´´ = Wr´´ or K = wr´´ (8).
Substituting the value of K in (7) in equation (8) we have
P2[pi][nu] = Wr´´ or P2[pi][nu] = Wr´´p (9).
Now it is evident that the distance _p´_ moved by W while K moves
through the distance _p_ is to _p_ as _r´´_ is to _r´_ or
_p´_ :_p_ :: _r´´_ : _r´_ or _p´_ = _pr´´_/_r´_ (10).
Substituting this value of _pr´´_/_r´_ in equation (9) we have
P2[pi][nu] = Wp´ or the condition [sum] work = 0, since 2[pi][nu] is the
distance moved by (P) while W moves the distance _p´_.
No provision for friction has been made in any of the examples given,
so that allowance must be made for this propensity whenever any of the
foregoing rules are applied to practice. The amount of allowance required
will vary and must be made to suit conditions.
An endless screw is sometimes used as a component part of graduating
machines, counting machines, etc. It is also employed in conjunction with
a wheel and axle to raise heavy weights. The distance between the threads
of the screw is called the pitch or step. These threads are sometimes
square, sometimes acutely pointed or edged, sometimes rounded off on the
edges. Power is often applied by means of a lever or other contrivance
attached to the end of the screw, or by a long handled wrench (a monkey
wrench for instance), which, when turned, moves forward in the direction
of its axis, overcoming resistance. In the case of the screw-jack, it may
be used to raise a heavy weight. The relation between the force applied
and the resistance to be overcome is important to note, for every time the
screw performs one revolution it moves forward through a distance equal
to the space between one thread and the next.
[Illustration: Fig. 35. Archimedian screw]
The Archimedian screw we have read and heard so much about is simply a
hollow pipe wound around a cylinder. It was often used in olden times for
raising water, but is now only occasionally applied. The lower end of the
spiral pipe is, of course, left open and immersed in water, as shown in
the illustration (Fig. 35), a device for raising water, the supply stream
being the motive power. The oblique shaft of the wheel has extending
through it a spiral passage, the lower end of which is immersed in water;
and the stream, acting upon the wheel at its lower end, produces its
revolution, by which the water is conveyed upward continuously through
the spiral passage and discharged at the top. An arrangement like this
could easily be constructed at the edge of most rivers to raise water to
irrigate the grounds, if so desired, and the little flutter wheel at the
bottom of the inclined shaft would be powerful enough to lift all the
water required. Fred thought that would be a great scheme, and determined
to try his hand at it one of these days, but he was told that a wheel
of that kind could only work at intervals, as the river's flow was often
running in opposite directions owing to the inflow of the tidal water.
[Illustration: Fig. 36. Spiral conveyor]
These Archimedian water raisers are often fitted with a crank handle on
top, and a man, standing on a platform, turns the crank and thus lifts up
all the water the machine will carry. The Archimedian screw is used for
many other purposes than raising water. With wide, thin wings, similar to
the construction shown at Fig. 36, and enclosed in a case or jacket, it
is employed by millers to convey grain and other mill requirements, and
it is also good for moving coal, ore, gravel, and like material, but when
used for these coarser purposes the propelling blades are made of steel,
riveted or bolted to a strong iron shaft. The case or jacket containing
the revolving blades, if horizontal, need not be covered on top, as the
blades will propel the material without jamming or clogging, if the jacket
is smooth inside, and fits fairly close to the blades.
This style of a screw may be used as a sort of turbine water wheel, if
cased in a cylindrical penstock or tube, and a body of water allowed to
fall into the upper end of the tube. The force of the water will give a
rotary motion to the blades and shaft, and, the latter having a geared
wheel or pulley attached to its top, motion is imparted to other shafts
and wheels.
[Illustration: Fig. 37. Theory of screw and gear]
Another application of the screw is shown at Fig. 37, where one is
arranged on a shaft or axle to give a rotary motion. This device is called
a "worm and wheel," and is frequently used in the make-up of machine
engines and mathematical instruments. The illustration shows how the power
or force of a screw may be conceived. For instance, suppose the wheel C
has a screw on its axis working in the teeth of the wheel D, having 48
teeth. It is plain that for every time the wheel C and screw are turned
round by the handle or crank A, the wheel D will be turned once round.
Then, as the circumference of a circle, described by the crank A, is equal
to the circumference of a groove round the wheel D, the velocity of the
crank will be 48 times as great as the velocity of any given point in
the groove. Consequently, if a line C goes round the groove, and has a
weight of 48 pounds hung to it, a power equal to one pound at the handle
will balance and support the weight. To prove this by experiment, let
the circumference on the grooves of the wheels C and D be equal to one
another; and then if a weight H, of one pound, is suspended by a line
going round the groove of the wheel C, it will balance a weight of 48
pounds hanging by the line G; and a small addition to the weight H will
cause it to descend, and to raise the other weight.
If a line C, instead of going round the groove of the wheel D, goes
round its axle I, the power of the machine will be as much increased as
the circumference of the groove exceeds the circumference of the axle,
supposing which to be six times 8, then one pound at H will balance 288
pounds, hung to the line on the axle; thus showing the advantage of this
machine as being 288 to 1. A man who can lift by his natural strength
alone, 100 pounds, by making use of this combination, will be able to
raise 28,800 pounds alone, and if a system of pulleys were applied to the
cord H, the power would be further increased to an amazing degree.
When a screw and wheel are attached, as shown, the screw is sometimes
called a "worm" and sometimes an "endless screw."
The propeller wheel (Fig. 38) is a screw having a large helical dimension.
The example shown has four blades, each of which, when rotated, may be
said to make one quarter of a revolution and when at work in the water
has the same effect as the working of a nut, producing motion in direction
of the axis and so propelling the boat or vessel. The action of the wheel
pressing backward against the water tends to push the craft forward.
[Illustration: Fig. 38. Complete screw propeller]
This figure shows a propeller with four blades, but two and three bladed
ones, particularly for small craft, are mostly used. The _Caroline_
carries a two bladed screw and her performances will be entirely
satisfactory. The blades, of course, are exactly in line with each other
on the shaft, and equally balanced, or of equal weight. A three-bladed
propeller should have its extreme points in a horizontal plane, so that
they will form an equilateral triangle.
The principal features of a propeller may be described as: diameter,
pitch, area, speed of revolution, and slip. The diameter is that of the
circle described by the tips of the blades. The pitch, considering the
propeller to be a portion of a screw, is the amount which it advances in
one turn, supposing it to travel in a solid medium. The blade area is the
actual area of all the blades.
The speed of the revolution is customarily reckoned in turns per minute.
The slip is the difference between the amount which the propeller actually
advances per turn and the amount which it would advance if turning in
a solid medium. For example, if the pitch of a screw is 30 in. it would
advance 30 in. at each turn if there were no slip. Suppose that it only
advances 20 in. per turn, then the slip is 10 in. per turn, or as usually
figured, 33-1/3 per cent. As a further example, suppose a propeller of 30
in. pitch, turning 300 turns per minute, drives a boat at the rate of 6
miles per hour. The advance of the propeller in feet per minute is 30/12
× 300 = 750 while the advance of the boat is 6 × 5,280/60 = 528 ft. per
minute. The slip is then 750 - 528 = 222, or as a percentage, 222/750
= 29.6 per cent. It might seem at first sight, that a perfect screw
propeller should have no slip; but this is a practical and theoretical
impossibility.
The most important dimension, from the standpoint of the absorption
of power, is the blade area. A certain blade area may be obtained by
a relatively wide blade on a small diameter, or by a narrow blade on a
relatively large diameter. In the former case the area of the blades bears
a greater proportion to the area of the circle through the tips than in
the latter case. There are certain limits for this proportion of blade
to disc area for well-designed wheels, beyond which it is not well to go.
These are as follows:
For two blades .20 to .25.
For three blades .30 to .40.
For four blades .35 to .45.
This means that for a 24 in. diameter propeller, whose disc area is 452
sq. in. the blade area should not, for ordinary use, be made greater than
these proportions, as the blades then become so wide as to interfere
one with another. Of course where a propeller, for shallow draft, must
be unusually small in diameter, the proportion of blade area can be
increased, but with some loss in economy. Strictly speaking, for a well
balanced propeller, the blade area fixes the amount of power which the
propeller can deliver, while the pitch, combined with the turns per
minute, governs the speed. As a matter of fact, for the average propeller
the two are closely related, each having a certain influence upon the
other. To illustrate, a propeller may have a small blade area and so great
a pitch that the blades act somewhat like fans and simply churn the water,
offering great resistance and absorbing the power of the engine, but doing
little effective work toward driving the boat.
To get the measurements for a wheel required to perform a given service,
say a three-bladed propeller for a small boat or tug of 20 nominal or 75
indicated horse-power:-- assume that the size determined on is 4 ft. 6
in. in diameter and 7 ft. 6 in. pitch, the diameter of loss may be assumed
to be 8 in. swelled to be 11 in. in the middle, and 11 in. long. The tug
would be, say, 60 ft. long, 12 ft. beam, and 7 ft. deep. First delineate
the path of the point and root of one blade through half a revolution as
in Fig. 39. This should be drawn to a scale of not less than 1-1/2 in. to
1 ft. by the ordinary method of projecting a screw thread. The semicircle
shows the half plan with twelve equal divisions, and the half elevation
is divided into the same number of equal parts. The helix or thread is
then obtained by drawing the curves through the intersections of similar
divisions. Then _a b_ will be the helix for point of the blade, and _c d_
the helix for the root of the blade. These will be found to be practically
straight lines which might have been obtained in a simpler manner if
intended for a working drawing only; but it is useful to have demonstrated
the proper nature of the full curve.
[Illustration: Fig. 39. Diagram screw lines]
The practical way of setting off the blade follows: First for dimensions:
as 20-in. (pitch) is to 11 in. (length of boss and therefore virtual
length of propeller), so is 169.6 in. (circumference due to outer
diameter) to the length of circumference occupied by the blade, 169.6 ×
11/9 = 20.73, say 20-3/4 in. In Fig. 40 describe a circle equal to the
diameter of the propeller, and on each side of the centre line step off
20-3/4 in. to half the scale, making the whole length of arc to scale
20-3/4 in. Draw vertical lines from the ends of the arc, and from the
arc on the centre line set up a height of 11 in. and draw horizontal
lines. Join _a b_, and this will be the angle of the end of the blade.
On the elevation of the propeller circle describe a small circle equal
in diameter to the faces of the boss; draw radial lines from the ends of
the arc first found, and from the intersection with the boss circle draw
vertical lines to cut the horizontal lines of the plan of boss. Join _c
d_, and this will be the angle of the blade at the root.
[Illustration: Fig. 40. Part of screw blade]
Now describe an arc at every three inches from the circumference within
the radical lines; or for large propellers every 6 in. Draw vertical lines
from the intersections of the arcs with the radical lines to meet _a c_
and _b d_, as shown, and joining the points thus found, the diagonal lines
will represent the plan or angle of the blade to each 3 in. difference of
radius--in other words, its real width at the different points, supposing
it to be a plain geometrical portion of a screw thread. As a matter of
fact, the blades are always more complex than this, the edge being curved
to enter the water more easily, to avoid vibration, and also to lessen
the risk of fracture in the event of striking any object in the water.
Sometimes the blades are curved in the opposite direction, as if the
points were being left behind while the blade is advancing.
[Illustration: Fig. 41. Plan of screw blade]
The next step is to draw a flattened elevation or development of one
of the blades, in order to give the actual curves of its outline, and
afterward its thickness at various points. Draw a horizontal line from
_c_ and _f_ (Fig. 41), and through this a centre line. This will give the
length of the blade from the boss, and the centre line of the propeller
shaft may be added below. Then take the lengths _a b_ and _c d_ from Fig.
40, and set them off on Fig. 43, as shown, joining all four points. This
figure would be the true outline of the blade if there were no curves. The
actual outline is found by drawing the curves according to the dimensions.
[Illustration: Fig. 42. Propeller lines complete]
Lay out the propeller, as shown in Fig. 42, which will give the elevation
of the blades, all being alike.
To find the area of a propeller blade, mark it off in parallel lines,
say 3 in. apart, and note the width at the centre of each portion. Add
the widths together, and divide by the number of widths. This will give
the mean width, which must then be multiplied by the length of blade to
obtain the area. If the measurements are all in inches, the result should
be divided by 144 to give the area in square feet, and then be multiplied
by the number of blades to give the total area.
[Illustration: Fig. 43. Angle of propeller blade]
To measure the pitch of a propeller, lay it down on a level surface, hold
a straight edge level across centre of blade with a square up from the
lower edge, as in Fig. 43. Measure the distance B and H and the radius
R from the centre to the part where the measurement is taken; then
B : 2wR :: H to pitch, P or P = 2wRH/B. The measurements may be made in
more than one place and the average taken, as the blades are
sometimes twisted slightly.
Scaling only from the drawing,
P = 2wRH/B
2 × 3.1416 × 1.6 × 1/1.27 = 7.74,
say 7 ft. 9 in. pitch, whereas the intended pitch was 7 ft. 6 in.
A good illustration of the use of the screw may be seen in the carpenter's
auger, used for making or boring holes in wood. These tools are provided
with a small tapered screw on their points, and this is followed by
cutting edges and a larger spiral. The larger spiral is for the purpose
of drawing up the chips or shavings. Another tool is made having two
blades attached to the bottom of an iron bar formed like the blades of a
propeller, which is sometimes employed for boring or digging post holes
in clayey or soft soil. The machine is turned by a cross handle on top,
and is frequently drawn up to bring out the soil until the hole is deep
enough. The ordinary wood screw is one of the most useful of contrivances
for fastening wood together, and for attaching to surfaces, hardware,
ornaments, or other materials. The adhesive strength of nails is already
shown, and the adhesive strength of wood screws, according to Bevan, is
set down as follows:
WOOD SCREWS
The following are the thicknesses or diameters corresponding to
the list numbers. Other thicknesses can be interpolated, each size
varying in succession 1/64 in.--
============+====+====+====+====+====+====+====+====+====+====+====
No. | 00 | 0 | 1 | 5 | 10 | 14 | 18 | 22 | 27 | 32 | 40
------------+----+----+----+----+----+----+----+----+----+----+----
Thicknesses | | | | | | | | | | |
in parts | | | | | | | | | | |
of inches |1/32|3/64|1/16| 1/8|3/16| 1/4|5/16| 3/8|7/16| 1/2| 5/8
------------+----+----+----+----+----+----+----+----+----+----+----
An ordinary 2-in. wood screw, driven through a 1/2-in. board into hard
wood, was found to be 790 lbs., and a force of about 395 lbs. was required
to extract it from soft wood.
When screws are hard to drive or screw in place, a long screw-driver
should be used, as screw-drivers with long handles seem to have a much
greater leverage than short handled ones in driving screws home. Screws,
however, are often split at the head, if care is not taken when using a
long driver.
If a screw is rusted, hard to move or withdraw, it can be loosened by
applying a hot iron to the head and making it hot. The heat expands the
screw and, of course, makes the hole larger, and when the screw cools it
contracts a trifle so that it may be withdrawn quite easily.
VII
AEROPLANES
George and Fred were so much interested in the _Caroline_ that they
neglected to do some work Mr. Gregg had suggested, but a hint or two
from him reminded them that sailing the new boat every day would get so
monotonous it would cease to be a pleasure. Fred, therefore, set to work
to put the new property in apple-pie order, by cleaning up the grounds,
burning the rubbish, and tidying the place generally. Nick, not being
needed longer, was allowed to go, with the promise that whenever a man
was required about the place, he would be chosen. His departure left all
the work to Fred and George, both of whom gladly accepted the duty.
The first thing was to set up three or four long benches on the river
bank. These were built exactly in the same manner as the seats alongside
the tables. Three short posts were let into the ground for each seat, and
a good, sound plank spiked solid to their tops. One of the seats was made
four or five inches lower than those at the tables, so as to accommodate
the smaller children. The two boys did the work well, though they found
it a little hard to dig the holes in the ground and saw off the posts.
George's hands became a little blistered and sore, but his mother soon
cured them, though she warned him against working too hard or too long at
a kind of labour to which he was not accustomed.
After tea was over, it being a fine, warm, spring evening, the whole
family went down to the river's edge to sit on the new seats and enjoy
the view. Noticing the current of the river, Jessie questioned her
father about its going one way sometimes, and then turning in the other
direction. Her father explained that it was the movement of the tide that
made the water flow against the stream at times, and that when there was
no tide, the current took its natural course. This explanation did not
seem to satisfy Jessie, and she asked why there were any tides. So Mr.
Gregg promised to explain all that was known about tides to her in the
near future. "I wish you would," said George, "and tell us about kites,
balloons, and flying machines."
"Oh, yes," said the father, "I'll try to do that to-morrow night."
"I'm glad, father," said Fred, "as I want to try and make a model for
George before the Fourth if I can, so he can have one to fly across the
river that day, instead of fooling with fire-crackers and other dangerous
fireworks."
"That's a good idea, Fred," said the father. "A model aeroplane, decorated
with silk flags would give a great deal more real pleasure than firing off
all the fire crackers in the state. It would be quite easy, now you have
a boat, for one of you to be on this side of the river, the other on the
opposite side, and to keep a number of little machines going to and fro
across the water."
George seemed delighted at the prospect. Walter Scott had also been
stricken with the aeroplane fever, and was busy making models, though, as
yet, he had not finished any. Both Fred and George were anxious to hear
all their father had to say concerning these machines, as they knew he
would be thorough, and make it all plain. Mr. Gregg told the boys that to
explain fully the theory and practice of building an aeroplane of any kind
would take some time, but he would willingly give it for their benefit,
and would discuss the subject of aeronautics at length so as to give them
some pointers about the design and practical making of flying machines.
[Illustration: Copyright, 1911, by Underwood & Underwood, N. Y.
THE MONOPLANE MODEL COMPLETE
"A Model Aeroplane, Decorated with Silk Flags Would Give a Great
Deal More Pleasure Than Firing off All the Fire Crackers in the
State"
]
On the following evening, Jessie did not forget to remind her father of
his promise to tell them all about "air-ships and things," as she put it.
"All right, my dear," said Mr. Gregg, "I'll take you all into the 'lion's
den' shortly after tea. But tell me, why is it you are so anxious to know
all about 'air-ships and things'?"
"Oh! that's all right, papa; Fred is going to build a great big ship, as
soon as he knows how, and he has promised to take me up to the clouds in
it for a ride."
"Well, my dear, it will take some time to tell you all about these things
but I will make an attempt. For ages man has wanted to fly, and the Greeks
tell us of a mythical personage named Icarius, and another named Dædalus,
who flew to the sun. There have been many attempts to fly, both with
and without mechanical aid, but history gives us nothing definite on the
subject until about the year 1785, when two Frenchmen, named Montgolfiers,
built a balloon sixty feet high and forty-three feet in diameter, and
filled it with heated air. Attached to the bottom was a light cage made
of wicker-work, into which were placed a lamb, a duck, and a rooster. The
balloon was cut from its moorings and rose to a height of over 1,400 feet
so that these animals were the first that ever went up in a machine made
by hands.
"The Montgolfiers attained considerable notoriety, and out of their
experiments grew the present dirigible Zeppelin, which measures 446
feet in length, over 42 feet in diameter, and is capable of carrying
eight able-bodied men a distance of over 900 miles. This great machine
is charged with gas, and driven by four three-bladed propellers, which
are run by two gas engines of 110 horse-power. This is simply a monster
balloon, suspended in the air by 529 to 700 cubic feet of hydrogen, or
coal gas, which is much lighter than ordinary air.
"It may be said there are four distinct kinds of flying machines, each
unlike the other in construction and in principle. The first is the
old-fashioned balloon which has an envelope or covering of some air-tight
fabric, and is inflated with a light gas. To it is attached a framework of
some kind called a Nacelle, that carries the aviator, the steering gear,
and the necessary engines to operate the propeller or propellers.
"The second kind of flier is the aeroplane, which, as its name indicates,
is supplied with 'air planes,' that give it the power of rising and
falling at the will of the operator when the machine is in motion. These
planes play a very important part in the successful operation of the
machine, as I will explain later. The first type of machine is classed as
a 'lighter-than-air' machine or a balloon, while the planes of all kinds
are classed as 'heavier-than-air' machines. Among other types of 'fliers,'
there is the helicoptere, which is raised by screws or propellers on
vertical shafts. These revolve rapidly, and drive
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