Mars and Its Canals
by Percival Lowell · English · Gutenberg #47015 · 546,497 chars · public domain (US)
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Title: Mars and Its Canals
Author: Percival Lowell
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Transcriber's Notes
When italics were used in the original book, the corresponding text has
been surrounded by _underscores_. The oe ligature has been replaced by
the letters oe. The Greek letter lambda has been represented as
[lambda]. Some presumed printer's errors have been corrected. These
have been listed in a second transcriber's note at the end of the text.
MARS AND ITS CANALS
------------------------------------------------------------------------
[Illustration: _Mars’ Hill_]
------------------------------------------------------------------------
MARS
AND ITS CANALS
BY
PERCIVAL LOWELL
DIRECTOR OF THE OBSERVATORY AT FLAGSTAFF, ARIZONA; NON-RESIDENT
PROFESSOR OF ASTRONOMY AT THE MASSACHUSETTS INSTITUTE OF
TECHNOLOGY; FELLOW OF THE AMERICAN ACADEMY OF ARTS AND
SCIENCES; MEMBRE DE LA SOCIÉTÉ ASTRONOMIQUE DE FRANCE;
MEMBER OF THE ASTRONOMICAL AND ASTROPHYSICAL SOCIETY
OF AMERICA; MITGLIED DER ASTRONOMISCHEN GESELLSCHAFT;
MEMBRE DE LA SOCIÉTÉ BELGE D’ASTRONOMIE; HONORARY
MEMBER OF THE SOCIEDAD ASTRONOMICA DE MEXICO;
JANSSEN MEDALIST OF THE SOCIÉTÉ ASTRONOMIQUE
DE FRANCE, 1904, FOR RESEARCHES ON MARS;
ETC., ETC.
_ILLUSTRATED_
New York
THE MACMILLAN COMPANY
LONDON: MACMILLAN & CO., LTD.
1906
_All rights reserved_
COPYRIGHT, 1906,
BY THE MACMILLAN COMPANY.
-------
Set up and electrotyped. Published December, 1906.
Norwood Press
J. S. Cushing & Co.—Berwick & Smith Co.
Norwood, Mass., U.S.A.
------------------------------------------------------------------------
To
G. V. SCHIAPARELLI
THE COLUMBUS OF A NEW PLANETARY WORLD
THIS INVESTIGATION UPON IT
IS APPRECIATIVELY
INSCRIBED
PREFACE
Eleven years have elapsed since the writer’s first work on Mars was
published in which were recorded the facts gleaned in his research up
to that time and in which was set forth a theory of their explanation.
Continued work in the interval has confirmed the conclusions there
stated; sometimes in quite unexpected ways. Five times during that
period Mars has approached the earth within suitable scanning distance
and been subjected to careful and prolonged scrutiny. Familiarity with
the subject, improved telescopic means, and long-continued training
have all combined to increased efficiency in the procuring of data and
to results which have been proportionate. A mass of new material has
thus been collected,—some of it along old lines, some of it in lines
that are themselves new,—and both have led to the same outcome. In
addition to thus pushing inquiry into advanced portions of the subject,
study has been spent in investigation of the reality of the phenomena
upon which so much is based, and in testing every theory which has been
suggested to account for them. From diplopia to optical interference,
each of these has been examined and found incompatible with the
observations. The phenomena are all they have been stated to be, and
more. Each step forward in observation has confirmed the genuineness of
those that went before.
To set forth science in a popular, that is, in a generally
understandable, form is as obligatory as to present it in a more
technical manner. If men are to benefit by it, it must be expressed to
their comprehension. To do this should be feasible for him who is
master of his subject and is both the best test of, and the best
training to, that post. Especially vital is it that the exposition
should be done at first hand; for to describe what a man has himself
discovered comes as near as possible to making a reader the
co-discoverer of it. Not only are thus escaped the mistaken glosses of
second-hand knowledge, but an aroma of actuality, which cannot be
filtered through another mind without sensible evaporation, clings to
the account of the pioneer. Nor is it so hard to make any well-grasped
matter comprehensible to a man of good general intelligence as is
commonly supposed. The whole object of science is to synthesize, and so
simplify; and did we but know the uttermost of a subject we could make
it singularly clear. Meanwhile technical phraseology, useful as
shorthand to the cult, becomes meaningless jargon to the uninitiate and
is paraded most by the least profound. But worse still for their employ
symbols tend to fictitious understanding. Formulæ are the anæsthetics
of thought, not its stimulants; and to make any one think is far better
worth while than cramming him with ill-considered, and therefore
indigestible, learning.
Even to the technical student, a popular book, if well done, may yield
most valuable results. For nothing in any branch of science is so
little known as its articulation,—how the skeleton of it is put
together, and what may be the mode of attachment of its muscles.
CONTENTS
PAGE
PREFACE vii
PART I
NATURAL FEATURES
CHAPTER
I. ON EXPLORATION 3
II. A DEPARTURE-POINT 12
III. A BIRD’S-EYE VIEW OF PAST MARTIAN DISCOVERY 20
IV. THE POLAR CAPS 32
V. BEHAVIOR OF THE POLAR CAPS 41
VI. MARTIAN POLAR EXPEDITIONS 54
VII. WHITE SPOTS 73
VIII. CLIMATE AND WEATHER 82
IX. MOUNTAINS AND CLOUD 96
X. THE BLUE-GREEN AREAS 108
XI. VEGETATION 119
XII. TERRAQUEOUSNESS AND TERRESTRIALITY 128
XIII. THE REDDISH-OCHRE TRACTS 148
XIV. SUMMARY 159
PART II
NON-NATURAL FEATURES
XV. THE CANALS 173
XVI. THEIR SYSTEM 184
XVII. GEMINATION OF THE CANALS 192
I. THE DIPLOPIC THEORY 196
II. THE INTERFERENCE THEORY 201
III. THE ILLUSION THEORY 202
XVIII. THE DOUBLE CANALS 204
XIX. CANALS IN THE DARK REGIONS 243
XX. OASES 249
XXI. CARETS ON THE BORDERS OF THE GREAT DIAPHRAGM 265
XXII. THE CANALS PHOTOGRAPHED 271
PART III
THE CANALS IN ACTION
XXIII. CANALS: KINEMATIC 281
XXIV. CANAL DEVELOPMENT INDIVIDUALLY INSTANCED 304
XXV. HIBERNATION OF THE CANALS 313
XXVI. ARCTIC CANALS AND POLAR RIFTS 325
XXVII. OASES: KINEMATIC 330
PART IV
EXPLANATION
XXVIII. CONSTITUTION OF THE CANALS AND OASES 337
XXIX. LIFE 348
XXX. EVIDENCE 360
XXXI. THE HUSBANDING OF WATER 366
XXXII. CONCLUSION 376
INDEX 385
LIST OF ILLUSTRATIONS
PLATES
MARS’ HILL _Frontispiece_
PAGE
THE HERMITAGE 8
THE SAN FRANCISCO PEAKS 18
MARTIAN MAPS BY:
I. BEER AND MAEDLER. 1840 26
II. KAISER. 1864 26
III. FLAMMARION (RÉSUMÉ). 1876 27
IV. GREEN. 1877 27
V. SCHIAPARELLI. 1877 28
VI. SCHIAPARELLI. 1879 28
VII. SCHIAPARELLI. 1881 29
VIII. SCHIAPARELLI. 1884 29
IX. LOWELL. 1894 30
X. LOWELL. 1896 30
XI. LOWELL. 1901 31
XII. LOWELL. 1905 31
SOUTH POLAR CAP. 1905 42
NORTH POLAR CAP. 1905 44
MARE ERYTHRAEUM, MARTIAN DATE, DECEMBER 30 120
MARE ERYTHRAEUM, MARTIAN DATE, JANUARY 16 122
MARE ERYTHRAEUM, MARTIAN DATE, FEBRUARY 1 124
MARE ERYTHRAEUM, MARTIAN DATE, FEBRUARY 21 126
MARS, ON MERCATOR’S PROJECTION 384
CUTS APPEARING IN TEXT
SOUTH POLAR CAP IN WINTER 56
HELLAS IN WINTER 59
WHITE SOUTH OF NECTAR AND SOLIS LACUS 59
NORTHERN CAP HOODED WITH VAPOR 64
NORTHERN CAP UNMASKED 65
DEPOSITION OF FROST 70
FIRST NORTHERN SNOW 72
WHITE IN ELYSIUM 75
WHITE IN THE PONS HECTORIS 78
PROJECTION ON TERMINATOR 101
LINES IN DARK AREA 117
MAP OF NORTH AMERICA AT THE CLOSE OF ARCHÆAN TIME 132
NORTH AMERICA AT OPENING OF UPPER SILURIAN PERIOD 134
MAP OF NORTH AMERICA AFTER THE APPALACHIAN REVOLUTION 135
NORTH AMERICA IN THE CRETACEOUS PERIOD 136
NORTH AMERICA, SHOWING THE PARTS UNDER WATER IN THE
TERTIARY ERA 137
EARTH’S DESERT AREAS, WESTERN HEMISPHERE 156
EARTH’S DESERT AREAS, EASTERN HEMISPHERE 157
SHOWING THE EUMENIDES-ORCUS 183
MARTIAN DOUBLES 206
MARTIAN DOUBLES 207
MOUTHS OF EUPHRATES AND PHISON. JUNE, 1903 219
PECULIAR DEVELOPMENT OF THE GANGES 228
DJIHOUN, THE NARROWEST DOUBLE 229
THE SABAEUS SINUS, EMBOUCHURE FOR THE DOUBLE HIDDEKEL
AND GIHON 232
THE PROPONTIS, 1905 247
FONS IMMORTALIS, JUNE 19 254
UTOPIA REGIO. 1903 256
ASCRAEUS LUCUS AND GIGAS. MARCH 2, 1903 258
PECULIAR ASSOCIATION OF THE LUCI ISMENII WITH DOUBLE
CANALS 260
LUCUS ISMENIUS. MARCH, 1903 262
SHOWING SEASONAL CHANGE. I 285
SHOWING SEASONAL CHANGE. II 285
MEAN CANAL CARTOUCHES 298
SHOWING DEVELOPMENT OF THE BRONTES:
I. FEBRUARY 25 306
II. MARCH 30 307
III. APRIL 3 307
IV. MAY 4 308
V. MAY 7 308
VI. JULY 18 309
CARTOUCHES OF THE BRONTES 311
AMENTHES ALONE IN FEBRUARY 319
AMENTHES FEEBLER AND STILL ALONE IN MARCH 319
APPEARANCE OF THOTH WITH TRITON AND CURVED NEPENTHES.
AMENTHES VANISHED, APRIL 20 320
ADVENT OF THE LUCUS MOERIS. MAY 29 321
AMENTHES WITH THOTH-NEPENTHES. JULY 322
CARTOUCHES OF AMENTHES, THOTH, AND THEIR COMBINATION 323
PHENOLOGY CURVES—EARTH 342
PHENOLOGY CURVES—MARS 343
PART I
NATURAL FEATURES
MARS AND ITS CANALS
CHAPTER I
ON EXPLORATION
From time immemorial travel and discovery have called with strange
insistence to him who, wondering on the world, felt adventure in his
veins. The leaving familiar sights and faces to push forth into the
unknown has with magnetic force drawn the bold to great endeavor and
fired the thought of those who stayed at home. Spur to enterprise since
man first was, this spirit has urged him over the habitable globe.
Linked in part to mere matter of support it led the more daring of the
Aryans to quit the shade of their beech trees, reposeful as that
umbrage may have been, and wander into Central Asia, so to perplex
philologists into believing them to have originated there; it lured
Columbus across the waste of waters and caused his son to have carved
upon his tomb that ringing couplet of which the simple grandeur still
stirs the blood:—
Á CASTILLA Y Á LEON
NUEVO MONDO DIÓ COLON;
(To Castile and Leon beyond the wave
Another world Columbus gave;)
it drove the early voyagers into the heart of the vast wilderness,
there to endure all hardship so that they might come where their kind
had never stood before; and now it points man to the pole.
Something of the selfsame spirit finds a farther field today outside
the confines of our traversable earth. Science which has caused the
world to shrink and dwindle has been no less busy bringing near what in
the past seemed inaccessibly remote. Beyond our earth man’s penetration
has found it possible to pierce, and in its widening circle of research
has latterly been made aware of another world of strange enticement
across the depths of space. Planetary distances, not mundane ones, are
here concerned, and the globe to be explored, though akin to, is yet
very different from, our own. This other world is the planet Mars.
Sundered from us by the ocean of ether, a fellow-member of our own
community of matter there makes its circuit of the sun upon whose face
features show which stamp it as cognate to that on which we live. In
spite of the millions of miles of intervening matterless void, upon it
markings can be made out that distantly resemble our earth’s topography
and grow increasingly suggestive as vision shapes them better; and yet
among the seemingly familiar reveal aspects which are completely
strange. But more than this: over the face of it sweep changes that
show it to be not a dead but a living world, like ours in this, and
luring curiosity by details unknown here to further exploration of its
unfamiliar ground.
To observe Mars is to embark upon this enterprise; not in body but in
mind. Though parted by a gulf more impassable than any sea, the
telescope lets us traverse what otherwise had been barred and lands us
at last above the shores we went forth to seek. Real the journey is,
though incorporeal in kind. Since the seeing strange sights is the
essence of all far wanderings, it is as truly travel so the eye arrive
as if the body kept it company. Indeed, sight is our only far viatic
sense. Touch and taste both hang on contact, smell stands indebted to
the near and even hearing waits on ponderable matter where sound soon
dissipates away; only sight soars untrammeled of the grosser adjunct of
the flesh to penetrate what were otherwise unfathomable space.
What the voyager thus finds himself envisaging shares by that very fact
in the expansion of the sense that brought him there. No longer tied by
means of transport to seas his sails may compass or lands his feet may
tread, the traveler reaches a goal removed in kind from his own
habitat. He proves to have adventured, not into unknown parts of a
known world, but into one new to him in its entirety. In extent alone
he surveys what dwarfs the explorer’s conquests on Earth. But size is
the least of the surprises there in store for him. What confronts his
gaze finds commonly no counterpart on Earth. His previous knowledge
stands him in scant stead. For he faces what is so removed from every
day experience that analogy no longer offers itself with safety as a
guide. He must build up new conceptions from fresh data and slowly
proceed to deduce the meaning they may contain. Science alone can help
him to interpretation of what he finds, and above all must he wean
himself from human prejudice and earthbound limitation. For he deals
here with ultramundane things. With just enough of cosmogony in common
to make decipherment not despairable this world is yet so different
from the one he personally knows as to whet curiosity at every turn. He
is permitted to perceive what piques inquiry and by patient adding of
point to point promises at last a rational result.
Like mundane exploration, it is arduous too; _ad astra per aspera_ is
here literally true. For it is a journey not devoid of hardship and
discomfort by the way. Its starting-point preludes as much. To get
conditions proper for his work the explorer must forego the haunts of
men and even those terrestrial spots found by them most habitable.
Astronomy now demands bodily abstraction of its devotee. Its deities
are gods that veil themselves amid man-crowded marts and impose
withdrawal and seclusion for the prosecution of their cult as much as
any worshiped for other reason in more primeval times. To see into the
beyond requires purity; in the medium now as formerly in the man. As
little air as may be and that only of the best is obligatory to his
enterprise, and the securing it makes him perforce a hermit from his
kind. He must abandon cities and forego plains. Only in places raised
above and aloof from men can he profitably pursue his search, places
where nature never meant him to dwell and admonishes him of the fact by
sundry hints of a more or less distressing character. To stand a mile
and a half nearer the stars is not to stand immune.
Thus it comes about that today besides its temples erected in cities,
monasteries in the wilds are being dedicated to astronomy as in the
past to faith; monasteries made to commune with its spirit, as temples
are to communicate the letter of its law. Pioneers in such profession,
those already in existence are but the precursors of many yet to come
as science shall more and more recognize their need. Advance in
knowledge demands what they alone can give. Primitive, too, they must
be as befits the still austere sincerity of a cult, in which the
simplest structures are found to be the best.
Still the very wildness of the life their devotee is forced to lead has
in it a certain fittingness for his post in its primeval detachment
from the too earthbound, in concept as in circumstance. Withdrawn from
contact with his kind, he is by that much raised above human prejudice
and limitation. To sally forth into the untrod wilderness in the cold
and dark of a winter’s small hours of the morning, with the snow feet
deep upon the ground and the frosty stars for mute companionship, is
almost to forget one’s self a man for the solemn awe of one’s
surroundings. Fitting portal to communion with another world, it is
through such avenue one enters on his quest where the common and
familiar no longer jostle the unknown and the strange. Nor is the
stillness of the stars invaded when some long unearthly howl, like the
wail of a lost soul, breaks the slumber of the mesa forest, marking the
prowling presence of a stray coyote. Gone as it came, it dies in the
distance on the air that gave it birth; and the gloom of the pines
swallows up one’s vain peering after something palpable, their tops
alone decipherable in dark silhouette against the sky. From amid
surroundings that for their height and their intenancy fringe the
absolute silence of space the observer must set forth who purposes to
cross it to another planetary world.
[Illustration: _The Hermitage_]
But the isolation of his journey is not always so forbidding. His
coming back is no less girt with grandeur of a different though equally
detached a kind. Even before the stars begin to dim in warning to him
to return, a faint suffusion as of half-suspected light creeps into the
border of the eastern sky. Against it, along the far pine-clad horizon,
mesa after mesa in shaggy lines of sentineling earth, stands forth dark
marshaled in the gloom, informed with prescience of what is soon to
come. Imperceptibly the pallor grows, blanching the face of night and
one by one extinguishing the stars. Slowly then it takes on color,
tingeing ever so faintly to a flush that swells and deepens as the
minutes pass. One had said the sky lay dreaming of the sun in pale
imagery at first that gathers force and feeling till the dreamer turns
thus rosy red in slumbering supposition of reality. Then the blush dies
out. The crimson fades to pink, the pink to ashes. The stars have
disappeared and yet it is not day. It is the supreme moment of the
dawn, the hush with which the Earth awaits its full awakening. For now
again the color gathers in the east, not with the impalpable suffusion
it had before but nearer and more vivid. No longer reflectively remote,
rays imminent of the sun strike the upper air, the most adventurously
refrangible turning the underside of a few stray clouds into flame-hued
bars of glowing metal. They burn thus in the silent east first red,
then orange, and then gold, each spectral tint in prismatic revelation
coming to join the next till in a sudden blinding burst of splendor the
solar disk tops the horizon’s rim.
Not less impressive is the journey when the afternoon watch has
replaced the morning vigil by the drawing of the planet nearer to the
sun. Lost in the brilliance of the dazzling sky, the planet lies hid
from the senses’ search. The quest were hopeless did not the mind guide
the telescope to its goal. To theory alone is it visible still, and so
to its predicted place the observer sets his circles, and punctual to
the prophecy the planet swings into the field of view. One must be
dulled by long routine to such mastery of mind not to have the act
itself clothe with a sense of charmed withdrawal the object of his
quest.
So much and more there are of traveler’s glimpses by the way,
compensation that offsets the frequent discomfort, and even balking of
his purpose by inopportune cloud. For the best of places is not
perfect, and a storm will sometimes rob him of a region he wished to
see. He must learn to wait upon his opportunities and then no less to
wait for mankind’s acceptance of his results; for in common with most
explorers he will encounter on his return that final penalty of
penetration, the certainty at first of being disbelieved.
In such respect he will be even worse off than were the other world
discoverers of the fifteenth and sixteenth centuries. For they at least
could offer material proof of things that they had seen. Dumb Indians
and gold spoke more convincingly than the lips of the great navigators.
To astronomy, too, that other world was due. Without a knowledge of the
earth’s shape and size got from Francisco of Pisa, Columbus had never
adventured himself upon the deep. But more than this, an astronomer it
was, in the person of Americus Vespucius, who first discovered the new
world, by recognizing it as such; Columbus never dreaming he had
lighted upon a world that was new. Nor does it impair one jot or tittle
of his glory that he knew it not. Nothing can deprive him of the
imperishable fame of launching forth into the void in hope of a beyond,
though he found not what he sought but something stranger still.
So, curiously, has it been with the trans-etherian. To Schiaparelli the
republic of science owes a new and vast domain. His genius first
detected those strange new markings on the Martian disk which have
proved the portal to all that has since been seen, and his courage in
the face of universal condemnation led to exploration of them. He made
there voyage after voyage, much as Columbus did on Earth, with even
less of recognition from home. As with Columbus, too, the full import
of his great discovery lay hid even to him and only by discoveries
since is gradually resulting in recognition of another sentient world.
CHAPTER II
A DEPARTURE-POINT
As the character of the travel is distinctive, so the outcome of the
voyage is unique. If he choose his departure-point aright, the observer
will be vouchsafed an experience without parallel on Earth. To select
this setting-out station is the first step in the journey upon which
everything depends. For it is essential to visual arrival that a
departure-point be taken where definition is at its best. Now, so far
as our present knowledge goes, the conditions most conducive to good
seeing turn out to lie in one or other of the two great desert belts
that girdle the globe. Many of us are unaware of the existence of such
belts and yet they are among the most striking features of physical
geography. Could we get off our globe and view it from without we
should mark two sash-like bands of country, to the poleward side of
either tropic, where the surface itself lay patently exposed. Unclothed
of verdure themselves they would stand forth doubly clear by contrast.
For elsewhere cloud would hide to a greater or less extent the actual
configuration of the Earth’s topography to an observer scanning it from
space.
One of these sash-like belts of desert runs through southern
California, Arizona, New Mexico, the Sahara, Arabia Petræa and the
Desert of Gobi; the other traverses Peru, the South African veldt, and
Western Australia. They are desert because in them rain is rare; and
even clouds seldom form. In a twofold way they conduce to astronomic
ends. Absence of rain makes primarily for clear skies and secondarily
for steady air; and the one of these conditions is no less vital to
sight than the other. Water vapor is a great upsetter of atmospheric
equilibrium and commotion in the air the spoiler of definition. Thus
from the cloudlessness of their skies man finds in them most chance of
uninterrupted communion with the stars, while by suitably choosing his
spot he here obtains as well that prime desideratum for planetary work,
as near a heavenly equanimity in the air currents over his head as is
practically possible.
From the fact that these regions are desert they are less frequented of
man, and the observer is thus perforce isolated by the nature of the
case, the regions best adapted to mankind being the least suited to
astronomic observations. In addition to what nature has thus done in
the matter, humanity has further differentiated the two classes of
sights by processes of its own contriving. Not only is civilized man
actively engaged in defacing such part of the Earth’s surface as he
comes in contact with, he is equally busy blotting out his sky. In the
latter uncommendable pursuit he has in the last quarter of a century
made surprising progress. With a success only too undesirable his
habitat has gradually become canopied by a welkin of his own
fashioning, which has rendered it largely unfit for the more delicate
kinds of astronomic work. Smoke from multiplying factories by rising
into the air and forming the nucleus about which cloud collects has
joined with electric lighting to help put out the stars. These
concomitants of advancing civilization have succeeded above the dreams
of the most earth-centred in shutting off sight of the beyond so that
today few city-bred children have any conception of the glories of the
heavens which made of the Chaldean shepherds astronomers in spite of
themselves.
The old world and the new are alike affected by such obliteration. Long
ago London took the lead with fogs proverbial wholly due to smoke, fine
particles of solid matter in suspension making these points of
condensation about which water vapor gathers to form cloud. With the
increase of smoke-emitting chimneys over the world other centres of
population have followed suit till today Europe and eastern North
America vie with each other as to which sky shall be the most
obliterate. Even when the obscuration is not patent to the layman it is
evident to the meteorologist or astronomer. By a certain dimming of the
blue, smoke or dust reveals its presence high up aloft as telltalely as
if the thing itself were visible. Some time since the writer had
occasion to traverse Germany in summer from Göttingen to Cologne and in
so doing was impressed by a cloudiness of the sky he felt sure had not
existed when he knew it as a boy. For the change was too startling and
extensive to be wholly laid to the score of the brighter remembrances
of youth. On reaching Cologne he mentioned his suspicion to Klein, only
to find his own inference corroborated; observations made twenty years
ago being impracticable today. Two years later in Milan Celoria told
the same story, the study of Mars having ceased to be possible there
for like cause. Factory smoke and electric lights had combined to veil
the planet at about the time Schiaparelli gave up his observations
because of failing sight. With a certain poetic fitness the sky had
itself been blotted just at the time the master’s eye had dimmed.
America is not behind in this race for sky extinction. In the
neighborhood of its great cities and spreading into the country round
about the heavens have ceased to be favorable to research. Not till we
pass beyond the Missouri do the stars shine out as they shone before
the white man came.
Few astronomers even fully appreciate how much this means, so used does
man get to slowly changing conditions. It amounts, indeed, between
Washington and Arizona to a whole magnitude in the stars which may be
seen. At the Naval Observatory of the former sixty-four stars were
mapped in a region where with a slightly smaller glass one hundred and
seventy-two were charted at Flagstaff.
Besides their immediate use as observing stations these desert belts
possess mediate interest on their own account in a branch of the very
study their cloudlessness helps to promote, the branch here considered,
the study of the planet Mars. They help explain what they permit to be
visible. For in the physical history of the Earth’s development they
are among the latest phenomena and mark the beginning of that stage of
world evolution into which Mars is already well advanced. They are
symptomatic of the passing of a terraqueous globe into a purely
terrestrial one. Desertism, the state into which every planetary body
must eventually come and for which, therefore, it becomes necessary to
coin a word, has there made its first appearance upon the Earth.
Standing as it does for the approach of age in planetary existence, it
may be likened to the first gray hairs in man. Or better still it
corresponds to early autumnal frost in the passage of the seasons. For
the beginning to age in a planet means not decrepitude in its
inhabitants but the very maturing of this its fruit. Evolution of mind
in its denizens continues long after desolation in their habitat has
set in. Indeed, advance in brain-power seriously develops only when
material conditions cease to be bodily propitious and the loss of
corporeal facilities renders its acquisition necessary to life.
The resemblance, distant but distinctive, of the climatic conditions
necessary on earth for the best scanning of Mars with those which prove
to be actually existent on that other world has a bearing on the
subject worth considerable attention. It helps directly to an
understanding and interpretation of the Martian state of things. Though
partial only, the features and traits of our arid zones are
sufficiently like what prevails on Mars to make them in some sort
exponent of physical conditions and action there. Much that is hard of
appreciation in a low, humid land shows itself an everyday possibility
in a high and dry one. The terrible necessity of water to all forms of
life, animal or vegetal, so that in the simple thought of the
aborigines rain is the only god worth great propitiation upon the due
observance of which everything depends, brings to one a deeper
realization of what is really vital and what but accessory at best. One
begins to conceive what must be the controlling principle of a world
where water is only with difficulty to be had, and rain unknown.
But in addition to the fundamental importance of water, the relative
irrelevancy of some other conditions usually deemed indispensable to
organic existence there find illustration too. On the high plateau of
northern Arizona and on the still higher volcanic cones that rise from
them as a base into now disintegrating peaks, the thin cold air proves
no bar to life. To the fauna there air is a very secondary
consideration to water, and because the latter is scarce in the
lowlands and more abundant higher up, animals ascend after it, making
their home at unusual elevations with no discomfort to themselves. Deer
range to heights where the barometric pressure is but three fifths that
of their generic habitat. Bear do the like, the brown bear of northern
American sea-level being here met with two miles above it. Nor is
either animal a depauperate form. Man himself contrives to live in
comfort and propagate his kind where at first he finds it hard to
breathe. Nor are these valiant exceptions; as Merriam has ably shown in
his account of the San Francisco peak region for the Smithsonian
Institution—a most interesting report, by the way—the other animals
are equally adaptive to the zones of more northern latitudes on the
American continent, zones paralleled in their flora and fauna by the
zones of altitude up this peak. All which shows that paucity of air is
nothing like the barrier to life we ordinarily suppose and is not for
an instant to be compared with dearth of water. If in a comparatively
short time an animal or plant accustomed to thirty inches of barometric
pressure can contrive to subsist sensibly unchanged at eighteen, it
would be rash to set limits to what time may not do. And this the more
for another instructive fact discovered in this region by Merriam: that
the existence of a species was determined not by the mean temperature
of its habitat but by the maximum temperature during the time of
procreation. A short warm season in summer alone decides whether the
species shall survive and flourish; that it has afterward to hibernate
for six months at a time does not in the least negative the result.
[Illustration: _The San Francisco Peaks_]
That the point of departure should thus prove of twofold importance,
speeding the observer on his journey and furnishing him with a _vade
mecum_ on arrival, is as curious as opportune. Without such
furtherance, to the bodily eye on the one hand and the mind’s eye on
the other, the voyage were less conclusive in advent and less
satisfactory in attent.
CHAPTER III
A BIRD’S-EYE VIEW OF PAST MARTIAN DISCOVERY
With Mars discovery has from the start waited on apparent disk. To this
end every optical advance has contributed from the time of Galileo’s
opera-glass to the present day. For apparent distance stands determined
by the size of the eye. But although it is the telescopic eye that has
increased, not the distance that has diminished, the effect has been
kin to being carried nearer the planet and so to a scanning of its disk
with constantly increasing particularity. Mankind has to all intents
and purposes been journeying Marsward through the years. Any historic
account of the planet, therefore, becomes a chronicle of seeming bodily
approach.
Perhaps no vivider way of making this evident and at the same time no
better preface to the present work could be devised than by putting
before the eye in orderly succession the maps made of Mars by the
leading areographers of their day, since the planet first began to be
charted sixty-five years ago. The procedure is as much as possible like
standing at the telescope and seeing the phenomena steadily disclose.
Seen thus in order the facts speak for themselves. They show that from
first to last no doubt concerning what was seen existed in the minds of
those competent to judge by systematic study of the planet at first
hand, and furthermore, from their mutual corroboration, that this
confidence was well placed. For, far from there being any conflict of
authorities in the case, those entitled to an opinion in the matter
prove singularly at one.
Beginning with Maedler in 1840 the gallery of such portraitures of the
planet comprises those by Kaiser, Green and Schiaparelli, continued
since Schiaparelli’s time by the earlier ones of the present writer. To
this list has been added one by Flammarion, which though not solely
from his own work gives so just a representation of what was known at
the date, 1876, as to merit inclusion. The remarkable drawings of Dawes
and the excellent ones of Lockyer in 1862-1864 were never combined into
maps by the observers, and though the former’s were so synthesized by
Proctor in 1867, the result was conformed to what Proctor thought ought
to be and so is not really a transcript of the drawings themselves.
Each of the maps presented marked in its day the point areography had
reached; and each tells its own story better than any amount of text.
They are all made upon Mercator’s projection and omit in consequence
the circumpolar regions. The later ones give, too, only so much of the
surface as was shown at the opposition they record, for Mars, being
tipped now one way, now another, regards the earth differently
according to its orbital position. In comparing them, therefore, the
equator must be taken for medial line. Mercator’s projection has been
the customary one for portraying Mars except for such oppositions as
chiefly disclose the arctic pole. And this, too, with a certain poetic
fitness. For it comes by right of priority to delineation of a new
world; seeing that Mercator was the first to represent in a map the
mundane new world in its entirety, by the rather important addition of
North America to the southern continent already known, and to give the
whole the title America with ‘Ame’ at the top of the map and ‘rica’ at
the bottom.
In looking at the maps it is to be remembered that they are what we
should call upside down, south standing at the top and north at the
bottom. Inverted they show because this is the way the telescopic
observer always sees the planet. The disk would seem unnatural to
astronomers were it duly righted. Just the same do men in the southern
hemisphere look at our own Earth topsy-turvy according to our view, the
Sun being to the north of them and the cold to the south. Certain
landmarks distinguishable in all the maps may serve for specific
introduction. The V-shaped marking on the equator pointing to the north
is the Syrtis Major, the first marking ever made out upon the planet
and drawn by the great Huyghens in 1659. The isolated oval patch in
latitude 26° south is the Solis Lacus, the pupil of the eye of Mars;
while the forked bay on the equator, discovered by Dawes, is the
Sabaeus Sinus, the dividing tongue of which, the Fastigium Aryn, has
been taken for the origin of longitudes on Mars.
Twelve maps go to make the series. They are as follows:—
MAKER DATE
I. Map of Beer and Maedler 1840
II. Map of Kaiser 1864
III. Map of Flammarion (Résumé) 1876
IV. Map of Green 1877
V. Map of Schiaparelli 1877
VI. Map of Schiaparelli 1879
VII. Map of Schiaparelli 1881
VIII. Map of Schiaparelli 1884
IX. Map of Lowell 1894
X. Map of Lowell 1896
XI. Map of Lowell 1901
XII. Map of Lowell 1905
If these maps be carefully compared they will be found quite remarkably
confirmatory each of its predecessor. To no one will their
inter-resemblance seem more salient than to draughtsmen themselves. For
none know better how surprisingly, even when two men have the same
thing under their very noses to copy, their two versions will differ.
Judgment of position and of relative size is one cause of variation;
focusing of the attention on different details another. What slight
discrepancies affect the maps are traceable to these two human
imperfections. Maps IV and V make a case in point: it was to his
new-found canals that Schiaparelli gave heed to the neglect of a due
toning of his map; while Green, less keen-eyed but more artistic,
missed the delicate canaliform detail to make a speaking portraiture of
the whole.
Amid the remarkable continuity of progression here shown, in which each
map will be seen to be at once a review and an advance, we may,
nevertheless, distinguish three stages in the perception of the
phenomena. Thus we may mark:—
I. A period of recognition of larger markings
only; 1840-1877
II. A period of detection of canals intersecting
the bright regions or lands; 1877-1892
III. A period of detection of canals traversing
the ‘seas’ and of oases scattered over
the surface; 1892-1905
Each period is here represented by four charts; and each expresses the
result of a more minute and intimate acquaintance with the disk than
was possible to the one that went before. To realize, however, how
accurate each was according to his lights it is only necessary to have
the seeing grow steadily better some evening as one observes. He will
find himself recapitulating in his own person the course taken by
discovery for all those who went before, and in the lapse of an hour
live through the observational experience of sixty years; in much the
same way that the embryological growth of an individual repeats the
development historically of the race.
Two verses of Ovid, which the poet puts into the mouth of Pythagoras,
outline with something like prophetic utterance the special discoveries
which mark the three periods apart. Ovid makes Pythagoras say of the
then world:—
Vidi ego, quod fuerat quondam solidissima tellus
Esse fretum; vidi factas ex aequore terras;
—OVID, _Metamorphoses_ XV, 262.
(Where once was solid ground I’ve seen a strait;
Lands I’ve seen made from out the sea.)
True as the verses are of Earth, the poet could not have penned them
otherwise had he meant to record the course of astronomic detection on
Mars. For they sound like a presentiment of the facts. A surface
thought at first to be part land, part water; the land next seen to be
seamed with straits; and lastly the sea made out to be land. Such is
the history of the subject, and words could not have summed it more
succinctly. “Vidi ego, quod fuerat quondam solidissima tellus esse
fretum” rings like Schiaparelli’s own announcement of the discovery of
the ‘canals.’ Indeed, I venture to believe he would have made it had he
chanced to recall the verse. So “vidi factas ex aequore terras” tells
what has since been learned of the character of the seas.
Of the three periods the first was that of the main or fundamental
markings only. It came in with Beer and Maedler, the inaugurators of
areography. That they planned and executed their survey with but a
four-inch glass shows that there is always room for genius at the top
of any profession and that instruments are not for everything in its
instrumentality. Up to their day the reality of the planet’s features
had been questioned by some people in spite of having been certainly
seen and drawn by Huyghens and others. Beer and Maedler’s labors proved
them permanent facts beyond the possibility of dispute.
The second period was the period of the discovery of the now famous
canals,—a new era in the study of Mars opened by Schiaparelli in 1877
(Map V). Unsuspicious of what he was to stumble on, he seized the then
favorable opposition to make, as he put it, a geodetic survey of the
planet’s surface. He hoped this undertaking feasible to the accuracy of
micrometric measurement. His hopes did not belie him. He found that it
was possible to measure his positions with sufficient exactness to make
a skeleton map on which to embody the markings in detail—and thus to
give his map vertebrate support. But in the course of his work he
became aware of hitherto unrecognized ligaments connecting the seas
with one another. Instead of displaying a broad unity of face the
bright areas appeared to be but groundwork for streaks. The streaks
traversed them in all directions, tesselating the continents into a
tilework of islands. Such mosaic was not only new, but the fashion of
the thing was of a new order or kind. Straits, however, Schiaparelli
considered them and gave them the name _canali_, or channels. How
unfamiliar and seemingly impossible the new detail was is best
evidenced by the prompt and unanimous disbelief with which it was met.
[Illustration: Map I. Beer and Maedler, 1840.]
[Illustration: Map II. Kaiser, 1864.
(From Flammarion’s _Mars_.)]
[Illustration: Map III. Résumé by Flammarion, 1876.
(From Flammarion’s _Mars_.)]
[Illustration: Map IV. Green, 1877.
(From Flammarion’s _Mars_.)]
Unmoved by the universal scepticism which rewarded what was to prove an
epoch-making discovery, Schiaparelli went on, in the judgment of his
critics, from bad to worse—for in 1879 (Map VI) he took up again his
scrutiny of the planet to the detecting of yet more particularity. He
re-observed most of his old canals and discovered half as many more;
and as his map shows he perceived an increased regularity in his lines.
In 1881-1882 (Map VII) he attacked the planet again and with results
yet further out of the common. His lines were still there with more
beside. If they had looked strange before, they now appeared positively
unnatural. Not content with a regularity which seemed to the sceptics
to preclude their being facts, he must needs see them now in duplicate.
To the eyes of disbelief this was the crowning stroke of factitiousness.
In consequence no end of adverse criticism was heaped upon his
observations by those who could not see. But curiously enough,—what
did not attract attention,—the blindness of the critics was as much
mental as bodily. For they failed to perceive that the very
unnaturalness which seemed to them to discredit his observations really
proved their genuineness. His discoveries were so amazing that any
change in strangeness simply went to confirm the universal scepticism
and clouded logic. Yet properly viewed, a pregnant deduction stands
forth quite clearly on a study of the maps.
[Illustration: Map V. Schiaparelli, 1877.
(From Schiaparelli’s _Memoria_.)]
[Illustration: Map VI. Schiaparelli, 1879.
(From Schiaparelli’s _Memoria_.)]
[Illustration: Map VII. Schiaparelli, 1881.
(From Schiaparelli’s _Memoria_.)]
[Illustration: Map VIII. Schiaparelli, 1884.
(From Schiaparelli’s _Memoria_.)]
On comparing maps V, VI and VII an eye duly directed is struck by a
difference in the aspect of the lines. In his first map the ‘canals’
are depicted simply as narrow winding streaks, hardly even roughly
regular and by no means such departures from the plausible as to lie
without the communicatory pale. Indeed, to a modern reader prepared
beforehand for geometric construction they will probably appear no
‘canals’ at all. Certainly the price of acceptance was not a large one
to pay. But like that of the Sibylline Books it increased with putting
off. What he offered the public in 1879 was much more dearly to be
bought. The lines were straighter, narrower, and in every way less
natural than they had seemed two years before. In 1881-1882 they
progressed still more in unaccountability. They had now become regular
rule and compass lines, as straight, as even, and as precise as any
draughtsman could wish and quite what astronomic faith did not desire.
Having thus donned the character, they nevermore put it off.
Now, this curious evolution in depiction points, rightly viewed, to an
absence of design. It shows that Schiaparelli started with no
preconceived idea on the subject. On the contrary, it is clear that he
shared to begin with the prevailing hesitancy to accept anything out of
the ordinary. Nor did he overcome his reluctance except as by degrees
he was compelled. For the canals did not change their characteristics
from one opposition to another; the eye it was that learned to
distinguish what it saw, and the brain made better report as it grew
familiar with the messages sent it. In other words, it is patent from
these successive maps that the geometrical character of the ‘canals’
was forced upon Schiaparelli by the things themselves, instead of
being, as his critics took for granted, foisted on them by him. We have
since seen the regularity of the canals so undeniably that we are not
now in need of such inferential support to help us to the truth; but
too late, as it is, to be of controversial moment the deduction is none
the less of some corroboratory force.
With the third period enters what has been done since Schiaparelli’s
time. For that master was obliged, from failing sight, to close his
work with the opposition of 1890. In 1892 W. H. Pickering at Arequipa
was the chief observer of the planet and made two important
discoveries: one was the detection of small round spots scattered over
the surface of the planet and connected with the canal system; the
other the perception of what seemed to him more or less irregular lines
traversing the Mare Erythraeum. Both were notable detections. The first
set of phenomena he called lakes, the second river-systems, sometimes
schematically ‘canals,’ but without committing himself to canaliform
characteristics as his drawings make clear. The same phenomena were
seen at that opposition at the Lick, by Schaeberle, Barnard and others,
and called streaks. These discoveries took from the _maria_ their
supposed character of seas—a most important event in knowledge of Mars.
[Illustration: Map IX. Lowell, 1894.]
[Illustration: Map X. Lowell, 1896.]
[Illustration: Map XI. Lowell, 1901.]
[Illustration: Map XII. Lowell, 1905.]
The next advance was the detection at Flagstaff in 1894 of their
canaliform characteristics by my then assistant Mr. Douglass, who in
place of the irregular streaks and river-systems of his predecessors
found the seas to be crossed by lines as regular and as regularly
connected as the canals in the light regions. To him they appeared
broad and ill defined, but so habitually did to him the canals in the
light areas, while for directness and uniformity the one set showed as
geometrically perfect as the other. All the dark _maria_ of the
southern hemisphere he found to be laced with them and that they formed
a network over the dark regions, counterparting that over the light.
Still more significant was the fact that their points of departure
coincided with the points of arrival of the bright-region canals, so
that the two connected to form in its entirety a single system. After
the publication of his results (Lowell Observatory Annals, Volume I,
1895) Schiaparelli identified some of those in the Syrtis with what he
had himself seen there in 1888 (_Memoria_, VI, 1899), though his own
had not been sufficiently well seen of him to impress him as canals.
Of other additions to our knowledge since made by the writer the
present book treats; as also of the theory they originally suggested to
him and which his later observations have only gone to confirm.
CHAPTER IV
THE POLAR CAPS
Almost as soon as magnification gives Mars a disk that disk shows
markings, white spots crowning a globe spread with blue-green patches
on an orange ground. The smallest telescope is capable of this far-off
revelation; while with increased power the picture grows steadily more
articulate and full. With a two and a quarter inch glass the writer saw
them thirty-five years ago.
After the assurance that markings exist the next thing to arrest
attention is that these markings move. The patches of color first made
out by the observer are shortly found by him to have shifted in place
upon the planet. And this not through mistake on his part but through
method in the phenomena; for all do it alike. In orderly rotation the
features make their appearance upon the body’s righthand limb (in the
telescopic image), travel across the central meridian of the disk and
vanish over its lefthand border. One follows another, each rising,
culminating and setting in its turn under the observer’s gaze. A
constantly progressing panorama passes majestically before his sight,
new objects replacing the old with a march so steady and withal so
swift that a few minutes will suffice to mark unmistakably the fact of
such procession. But for all this ceaseless turning under his gaze,
after a certain lapse of time it is evident that the same features are
being shown him over again. With such recognition of recurrence comes
the first advance toward acquaintance with the Martian world. For that
in all their journeying their configuration alters not, proves them
permanent in place, part and parcel of the solid surface of that other
globe. This surface, then, lies exposed to view and by its turning
shows itself subject, like our earth, to the vicissitudes of day and
night.
In such self-exposure Mars differs from all the four great planets,
Jupiter, Saturn, Uranus and Neptune. Features, indeed, are apparent on
the first two of these globes and dimly on the other two as well, but
they lack the stability of the Martian markings. They are forever
exchanging place. In the case of Jupiter what we see is undoubtedly a
cloud-envelop through which occasional glimpses may possibly be caught
of a chaotic nucleus below. With Saturn it is the same; and the
evidence is that the like is true of Uranus and Neptune. What goes on
under their great cloud canopies we can only surmise. With Mars,
however, we are not left to imagination in the matter but so far as our
means permit can actually observe what there takes place. Except for
distance, which, through science, year by year grows less, it is as if
we hovered above the planet in a balloon, with its various features
spread out to our gaze below.
Attention shows these areographic features to be on hand with punctual
precision for their traverse of the disk once every twenty-four hours
and thirty-seven minutes. For over two hundred years this has been the
case, their untiring revolutions having been watched so well that we
know the time they take to the nicety of a couple of hundredths of a
second. We thus become possessed of a knowledge of the length of the
Martian day and it is not a little interesting to find that it very
closely counterparts in duration our own, being only one thirty-fifth
the longer of the two. We also find from the course the markings pursue
the axis about which they turn; and just as the period of the rotation
tells us the length of the Martian day so the tilt of the axis, taken
in connection with the form of the orbit, determines the character of
the Martian seasons. Here again we confront a curious resemblance in
the circumstances of the two planets, for the tilt of the equator to
the plane of the orbit is with Mars almost precisely what it is for the
Earth. The more carefully the two are measured the closer the
similitude becomes. Sir William Herschel made the Martian 28°,
Schiaparelli reduced this to 25°, and later determination by the writer
puts it nearer 24°. The latter is the one now adopted in the British
Nautical Almanac for observers of the planet. This is a very close
parallelism indeed; so that in general character the Martian seasons
are nearly the counterpart of ours. In length, however, they differ;
first because the year of Mars is almost double the length of the
terrestrial one and secondly because from the greater ellipticity of
Mars’ orbit the seasons are more unequal than is the case with us, some
being run through with great haste, others being lingered on a
disproportionate time. It is usual on the Earth to consider spring as
the period from the vernal equinox, about March 21, to the summer
solstice, about June 20; summer as lasting thence to the autumnal
equinox; autumn from this latter date, about September 20, to the
winter solstice on December 21; and winter from that point on to the
next spring equinox again. On this division our seasons in the northern
hemisphere last respectively: spring, 91 days; summer, 92 days; autumn,
92 days; and winter, 90 days. On Mars these become, reckoned in our
days: spring, 199 days; summer 183 days; autumn, 147 days; and winter,
158 days. If we had counted them in Martian days they would have
totaled about one thirty-fifth less in number each.
In its days and seasons, then, Mars is wonderfully like the Earth;
except for the length of the year we should hardly know the difference
in reckoning of time could we some morning wake up there instead of
here. Only in one really unimportant respect should we feel strange; in
months we should find ourselves turned topsy-turvy. But lunations have
nothing to do with climate nor with the alternation between night and
day; and in these two important respects we should certainly feel at
home.
Though the axis could be determined by the daily march of any marking
and thus the planet’s tropic, temperate and polar regions marked out,
the process is made easier by the presence of white patches covering
the planet’s poles and known, in consequence, as the polar caps. It is
from measures of the patches that the position of the Martian poles has
actually been determined. These polar caps are exactly analogous in
general position to those which bonnet our own Earth. They reproduce
the appearance of the ice and snow of our arctic and antarctic regions
seen from space, in a very remarkable manner. In truth they are things
of note in more ways than one and would claim precedence on many
counts. Priority of recognition, however, alone entitles them to
premier consideration. Among the very first of the disk’s detail to be
made out by man, they justly demand description first.
With peculiar propriety the polar caps have thus the _pas_. Not only do
they stand first in order of visibility, but they prove to occupy a
like position logically when it comes to an explanation of the planet’s
present physical state. It is not matter of hazard that the most
evident of all the planet’s markings should also be the most
fundamental, the fountainhead from which everything else flows. It is
of the essence of the planet’s condition and furnishes the key to its
comprehension. The steps leading to this conclusion are as interesting
as they are cogent. They start at the polar caps’ visibility. For their
size first riveted man’s attention and then attention to them disclosed
that most vital of the characteristics of the planet’s surface: change.
Just as almost all of the features we note are permanent in place,
showing that they belong to the surface, so are they all impermanent in
character. Change is the only absolutely unchanging thing except
position about the features the planet presents to view. It was in the
aspect of the polar caps that this important fact first came to light.
Not only did they thus initially instance a general law, they have
turned out to make it; for by themselves changing they largely cause
change in all the rest. But for a long time they alone exemplified its
workings. To Sir William Herschel we owe the first study of their
change in aspect. This eminent observer noted that their varying size
was subject to a regular rhythmic wax and wane timed to the course of
the seasons of the planet’s year. The caps increased in the winter of
their hemisphere and decreased in its summer and being situate in
opposite hemispheres they did this alternately with pendulum-like
precision. His observations were soon abundantly confirmed, for the
phenomena take place upon a vast scale and are thus easy of
recognition. At their maximum spread the caps cover more than one
hundred times as much ground as when they have shrunk to their minimum.
In the depth of winter they stretch over much more than the polar zone,
coming down to 60° and even 50° of latitude north or south as the case
may be, thence melting till by midsummer they span only five or six
degrees across.
In this they bear close analogue to the behavior of our own. Ours would
show not otherwise were they viewed from the impersonal standpoint of
space. Very little telescopic aid suffices to disclose the Martian
polar phenomena in this their more salient characteristics and convince
an observer of their likeness to those of the earth. Any one may note
what is there going on by successive observations of the planet with a
three-inch glass. Nor is the change by any means slow. A few days at
the proper Martian season, or at most a couple of weeks, produces
conspicuous and conclusive alterations in the size of these nightcaps
of the planet’s winter sleep. Resembling our own so well they were
early surmised to be of like constitution and composed, therefore, of
ice and snow. Plausible on its face, this view of them was generally
adopted and common sense has held to it ever since. It has encountered,
of course, opposition, partly from very proper conservatism, but
chiefly from that earth-centred philosophy which has doubted most
advances since Galileo’s time, and carbonic acid has been put forward
by this school of sceptics to take its place. We shall critically
examine both objections; the latter first, because a certain physical
fact enables us to dispose of it at once. In casual appearance there is
not much to choose between the rival candidates of common sense and
uncommon subtlety, water and frozen carbonic acid gas, both being
suitably white and both going and coming with the temperature. But,
upon closer study, in one point of behavior the two substances act
quite unlike, and had half the ingenuity been expended in testing the
theory as in broaching it this fact had come to light to the suggestors
as it did upon examination to the writer and had served as a touchstone
in the case. At pressures of anything like one atmosphere or less
carbonic acid passes at once from the solid to the gaseous state.
Water, on the other hand, lingers in the intermediate stage of a
liquid. Now, as the Martian cap melts it shows surrounded by a deep
blue band which accompanies it in its retreat, shrinking to keep pace
with the shrinkage in the cap. This is clearly the product of the
disintegration since it waits so studiously upon it. The substance
composing the cap, then, does not pass instantaneously or anything like
it from the solid to the gaseous condition.
This badge of blue ribbon about the melting cap, therefore,
conclusively shows that carbonic acid is not what we see and leaves us
with the only alternative we know of: water.
CHAPTER V
BEHAVIOR OF THE POLAR CAPS
Assured by physical properties that our visual appearances are quite
capable of being what they seem we pass to the phenomena of the cap
itself. Like as are the polar caps of the two planets at first regard,
upon further study very notable differences soon disclose themselves
between the earthly and the Martian ones; and these serve to give us
our initial hint of a different state of things over there from that
with which we are conversant on Earth.
To begin with, the limits between which they fluctuate are out of all
proportion greater on Mars. It is not so much in their maxima that the
ice-sheets of the two planets vary. Our own polar caps are much larger
than we think; indeed, we live in them a good fraction of the time. Our
winter snows are in truth nothing but part and parcel of the polar cap
at that season. Now, in the northern hemisphere snow covers the ground
at sea-level more or less continuously down to 50° of latitude. It
stretches thus far even on the western flanks of the continents, while
in the middle of them and on their eastern sides it extends ten degrees
farther yet during the depth of winter. So that we have a polar cap
which is then ninety degrees across. In our southern hemisphere it is
much the same six months later, in the corresponding winter of its year.
On Mars at their winter maxima the polar caps extend over a similar
stretch of latitude. They do so, however, unequally. The southern one
is considerably the larger. In 1903, 136 days after the winter
solstice, in the Martian calendar February 27, it came down in
longitude 225° to 44° of latitude and may be taken to have then
measured ninety-three degrees across; in 1905, 121 days after the same
solstice, it stretched in longitude 235° to latitude 42°, and 158 days
later, in longitude 221° to latitude 41°; values which, supposing it to
have been round, imply for it a diameter on these occasions of
ninety-six and ninety-seven degrees. It was then February 20 and March
10 respectively of the Martian year. These determinations of its size
at the two oppositions agree sufficiently well considering the great
tilt away from us of the south pole at the time and the horizonward
foreshortening of the edge of the snow. It seems from a consensus of
the measures to have been some five degrees wider in 1903 than in 1905,
which may mean a colder winter preceding the former date. The cap was
still apparently without a dark contour in both years, showing that it
had not yet begun to melt.
[Illustration: South Polar Cap.
(Lowell Observatory, 1905.)]
Less has been learnt of the northern cap. In 1896-1897 when it was
similarly presented skirting the other rim of the disk, a gap occurred
in the observations corresponding to the time by Martian months between
February 24 and March 22. On the former date the cap came down only to
latitude 55° in longitude 352°; on the subsequent one and for several
days after the latitude of the southern limit of the snow was such as
to imply a breadth to it of about eighty degrees. The cap was now
bordered by a dark line, proving that melting had already set in. It
cannot, however, at its maximum have covered much more country than
this, in view of its lesser extent on February 24.
Fair as our knowledge now is of the dimensions of the Martian polar
caps at their maxima, we have much more accurate information with
regard to their minima, and this, too, was obtained much earlier. That
we should first have known their smallest rather than their greatest
extent with accuracy may appear surprising, exactly the opposite being
our knowledge of our own. It is not, however, so surprising as it
appears, inasmuch as it is an inevitable consequence of the planet’s
aspect with regard to the sun. When the tilt of the axis inclines one
hemisphere toward the sun, that hemisphere’s polar cap must melt and
dwindle, while at the same time it is the one best seen, the other
being turned away from the sun and therefore largely from us as well;
so that even such part of the latter as is illumined lies low down
toward the horizon of the disk where a slight change of angle means a
great difference in size.
It has thus come about that both the south and the north polar caps
have been repeatedly well seen and measured at their minimum; and the
measures for different Martian years agree well with one another. For
the northern cap six degrees in diameter is about the least value to
which it shrinks. The south one becomes even smaller, being usually not
more than five degrees across, while in 1894 it actually vanished, a
thing unprecedented. Its absence was detected by Douglass at Flagstaff
and shortly after the announcement of its disappearance the fact was
corroborated by Barnard at the Lick. The position the cap would have
occupied was at the time better placed for observation in America than
in Europe, inasmuch as the cap is eccentrically situated with regard to
the geographic pole and its centre was then well on the side of the
disk presented to us while in Europe it was turned away. This, together
with the fact that it undoubtedly came and went more than once about
this time, accounts for its disappearance not having been recognized
there, haze left by it having apparently been mistaken for the cap
itself.
[Illustration: North Polar Cap.
(Lowell Observatory, 1905.)]
On Earth the minima are much larger. In the northern hemisphere the
line of perpetual snow or pack-ice in longitude 50° east runs about on
the 80° parallel, including within it the southern end of Franz Joseph
Land. Opposite this, in longitude 120° west, above the North American
continent, it reaches down lower still to 75°. So that the cap is then
from twenty to thirty degrees in diameter. In the southern hemisphere
it is even larger. In longitude 170° west the land was found by Ross to
be under perpetual snow in latitude 72°. Cook had reached in longitude
107° east an impassable barrier of ice in latitude 70° 23′. The season
was then midsummer, January 30. So that we are perhaps justified in
considering 71° south as about the average limit of perpetual snow or
paleocrystic ice. This would make the southern cap at its minimum
thirty-eight degrees across. Pack-ice with open spots extends still
farther north. The Pagoda in 1845 was stopped by impenetrable pack-ice
in south latitude 68° and the Challenger in 1874 encountered the pack
in latitude 65° on the 19th of February, which corresponds about to our
19th of August, the time at which the sea should be most open. The
limit of perpetual snow is thus lower in the southern than in the
northern hemisphere. Here again, then, the two minima differ, but in
the reverse way from what they do on Mars.
From this we perceive that the variations in size of the caps are much
more striking on Mars than on the Earth and that these are due chiefly
to the difference in the minima, the maxima not varying greatly.
To explain these interesting diversities of behavior in the several
polar caps we shall have to go back a little in general physics in
order to get a proper take off. It is a curious concomitant of the law
of gravity that the amount of heat received by a planet in passing from
any point of its path to a point diametrically opposite is always the
same no matter what be the eccentricity of the orbit. Thus, a planet
has as many calories falling upon it in travelling from its vernal
equinox to its autumnal as from the autumnal to the vernal again,
although the time taken in the one journey be very different from that
of the other. This is due to the fact that the angle swept over by the
radius vector, that is, the imaginary bond between it and the sun, is
at all points proportional to the amount of heat received; just as it
is of the gravity undergone, the two forces radiating into space as the
inverse square of the distance. Thus the heat received by a point or a
hemisphere, through any orbital angle, is independent of the
eccentricity of the orbit.
But it is not independent of the axial tilt. For the force of the sun’s
rays is modified by their obliquity. The amount of heat received at any
point in consequence of the tilt turns upon the position of the point,
and for any hemisphere taken as a whole it depends upon the degree to
which the pole is tilted to the source of heat. In consequence of being
more squarely presented to its beams, the hemisphere which is directed
toward the sun and therefore is passing through its summer season gets
far more insolation than that which is at the same time in the depth of
its winter. For a tilt of twenty-four degrees, the present received
value for the axis of Mars, the two hemispheres so circumstanced get
amounts of heat respectively in the proportion of sixty-three to
thirty-seven.
But, though the summer and winter insolation thus differ, they are the
same for each hemisphere in turn. Consequently the mere amount of heat
received cannot be the cause of any differences detected between the
respective maxima and minima of the two polar caps. If heat were a
substance which could be stored up instead of being a mode of motion,
the effect produced would be in accordance with the quantity applied
and the two caps would behave alike. As it is the total amount has very
little to say in the matter.
Not the amount of heat but the manner in which this heat is made at
home is responsible for the difference we observe. Now, though the
total amount is the same in passing from the vernal to the autumnal
equinox as from the autumnal to the vernal, the time during which it is
received in either case varies from one hemisphere to the other. It is
summer in the former while it is winter in the latter and the
difference in the length of the two seasons due to the eccentricity of
the orbit makes a vast difference in the result. Winter affects the
maxima, summer the minima, attained. Of these opposite variations
presented to us by the two caps, the maxima, the one most difficult to
detect, is the easiest to explain, for the difference in the maxima
seems to be due to the surpassing length of the antarctic night.
Owing to the eccentricity of the orbital ellipse pursued by Mars and to
the present position of the planet’s solstices, the southern hemisphere
is farther away from the sun during its winter and is so for a longer
time. The seasons are in length, for the northern hemisphere: spring,
199 days; summer, 183 days; autumn, 147 days; and winter, 158 days;
while for the southern hemisphere they are: spring, 147 days; summer,
158 days; autumn, 199 days; and winter, 183 days. The arctic polar
night is thus 305 of our days long; the antarctic, 382. Thus for 77
more days than happens to its fellow the southern pole never sees the
sun. Now, since the total sunlight from equinox to equinox is the same
in both hemispheres, its distribution by days must be different. In the
southern hemisphere the same amount is crowded into a smaller compass
in the proportion of 305 to 382; that being that hemisphere’s relative
ratio of days. But since during winter the cap increases, there is a
daily excess of accumulation over dissipation of snow and each
twenty-four hours must on the average add its tithe to the sum total.
Since the northern days are the warmer each adds less than do the
southern ones; and furthermore there are fewer of them. On both these
scores the amount of the deposition about the northern pole should be
less than about the southern one. Consequently, the snow-sheet there
should be the less extensive and show a relatively smaller maximum,
which explains what we see.
With the minima the action is otherwise. Inasmuch as the greater heat
received during the daylight hours by the southern hemisphere is
exactly offset by the shortness of its season, it would seem at first
as if there could be no difference in the total effect upon the two
ice-caps.
But further consideration discloses a couple of factors which might,
and possibly do, come in to qualify the action and account for the
observed effect. One is that though the total amount of heat received
is the same, the manner of its distribution differs in the two
hemispheres. In the northern one the time from vernal to autumnal
equinox is 382 days against 305 in the southern. Consequently, the
average daily heat is then five fourths more intense in the southern
hemisphere. Indeed, it is even greater than this and nearer four
thirds, because the melting occurs chiefly in the spring and in the
first two months of summer when the contrast in length of season
between the two hemispheres is at its greatest. Now, a few hotter days
might well work more result than many colder ones. And this would be
particularly true of Mars where the mean temperature is probably none
too much above the freezing-point to start with. Ice consumes so much
caloric in the process of turning into any other state, laying it by in
the form of latent heat before it can turn into water and then so much
more before this water can be converted into steam that a good deal has
to be expended on it before getting any perceptible result. Once
obtained, however, the heat is retained with like tenacity. So that the
process works to double effect! If sufficient heat be received the ice
is first melted, then evaporated and finally formed into a layer of
humid air, the humidity of which keeps it warm. Dry air is unretentive
of heat, moist air the opposite. And for the melting of the ice-cap to
proceed most effectively the temperature that laps it about must be as
high as possible and kept so as continuously as may be. If between days
it be allowed to fall too low at night much caloric must needs be
wasted in simply raising the ice again to the melting-point. This a
blanket of warm air tends to prevent, and this again is brought about
by a few hot days rather than by many colder ones. It is not all the
heat received that becomes effective but the surplus heat above a
certain point. The gain in continuity of action thus brought about is
somewhat like that exhibited between the running of an express and an
accommodation train. To reach its destination in a given time the
former requires far less power because it does not have to get up speed
again after each arrest. Thus the whole effect in melting the snow
would be greater upon that hemisphere whose summer happens to be the
more intense.
The greater swing in size of the cap most exposed to the effects of the
eccentricity is, then, the necessary result of circumstances when the
precipitation is not too great to be nearly carried off by the
subsequent dissipation. This is the state of things on Mars and the
second of the factors above referred to. On the Earth as we have seen
the polar caps are somewhat larger at their maximum and very much so at
their minimum. Now, this is just what should happen were the
precipitation increased. Suppose, for example, that the amount of
precipitation were to increase while the amount of summer melting
remained the same, and this would be the case if the vapor in the air
augmented for one cause or another, and the result of each fresh
deposit was locked up in snow. After a certain point the cap would grow
in depth rather than in extension; the winter deposit would be thicker
but the summer evaporation would remain the same. Now, if this
occurred, it is evident that the minimum size of the cap would increase
relatively much faster than the maximum, and furthermore, that the
relative increase of the minimum in the two caps would be greatest for
that which had seasons of extremes. The result we see in the case of
the Earth. In the arctic cap, where in consequence of the eccentricity
of the orbit the winter is shorter, the maximum is less than in the
antarctic and this extra amount of precipitation cannot be wholly done
away with in its intenser summer, so that the minimum too is greater
there.
We reach, then, this interesting conclusion. We find that eccentricity
of orbit by itself not only causes no universal glaciation in the
hemisphere which we should incidentally suppose likely to show it, but
actually produces the opposite result, in more than offsetting by
summer proximity what winter distance brings about. To cause extensive
glaciation we must have, in addition to favorable eccentricity, a large
precipitation. With these two factors combined we get an ice age, but
not otherwise. The result has an important bearing on geologic glacial
periods and their explanation.
Once formed, an ice-sheet cools everything about it and chills the
climate of its hemisphere. It is a perpetual storehouse of cold. Mars
has no such general glaciation in either hemisphere, and the absence of
it, which is due to lesser precipitation, together with the clearness
of its skies, accounts for the warmth which the surface exhibits and
which has been found so hard hitherto to interpret. Could our earth but
get rid of its oceans, we too might have temperate regions stretching
to the poles.
CHAPTER VI
MARTIAN POLAR EXPEDITIONS
Polar expeditions exert an extreme attraction on certain minds, perhaps
because they combine the maximum of hardship with the minimum of
headway. Inconclusiveness certainly enables them to be constantly
renewed, without loss either of purpose or prestige. The fact that the
pole has never been trod by man constitutes the lodestone to such
undertakings; and that it continues to defy him only whets his endeavor
the more. Except for the demonstration of the polar drift-current
conceived of and then verified by Nansen, very little has been added by
them to our knowledge of the globe. Nor is there specific reason to
suppose that what they might add would be particularly vital. Nothing
out of the way is suspected of the pole beyond the simple fact of being
so positioned. Yet for their patent inconclusion they continue to be
sent in sublime superiority to failure.
Martian polar expeditions, as undertaken by the astronomer, are the
antipodes of these pleasingly perilous excursions in three important
regards, which if less appealing to the gallery commend themselves to
the philosopher. They involve comparatively little hardship; they have
accomplished what they set out to do; and the knowledge they have
gleaned has proved fundamental to an understanding of the present
physical condition of the planet.
The antithesis in pole-pursuing between the two planets manifests
itself at the threshold of the inquiry, in the relative feasibility
with which the phenomena on Mars may be scanned. For, curiously enough,
instead of being the pole and its surrounding paleocrystic ice which
remains hidden on Mars, it is rather the extreme extent of its
extension and the lowest latitudinal deposit of frost which lies
shrouded in mystery. The difficulty there is not to see the pole but to
see in winter the regions from which our own expeditions set out. And
this because the poles are well displayed to us at times which are
neither few nor very far between; while favorable occasions for marking
the edge of the caps when at their greatest have neither proved so
numerous nor so favorable. The tilt of the planet’s axis when
conveniently placed for human observation has been the cause of the one
drawback; the planet’s meteorological condition in those latitudes at
that season the reason for the other.
What knowledge we have of the size of the caps in degrees upon the
surface of the planet at this their extreme equatorward extension has
been given in the last chapter. Their aspect at the time together with
what that aspect betokens was not there touched upon. With it,
therefore, and the peculiarities it presents to view we shall begin our
account of the caps’ annual history.
[Illustration: South Polar Cap in winter.]
When first the hemisphere, the pole of which has for half a Martian
year been turned away from the sun, begins to emerge from its long
hibernation, the snow-cap which covers it down even to temperate
regions presents an undelimited expanse of white, the edges of which
merge indistinguishably into the groundwork color of the regions round
about. Of a dull opaque hue along its border, its contour is not sharp
but fades off in a fleecy fringe without hard and fast line of
demarcation. Such notably was the aspect of the north temperate zone in
1896 when, tilted as it then was away from us into a mere northern
horizon of the planet’s limb, it showed prior to the definite
recognition of the north polar cap in August of that year, and such too
was the look of the disk’s southern edge both before and after the
first certain detection of the southern cap in 1903 and 1905. Each was
then in the depth of winter. For in Martian chronology the season
corresponded in each at the time to what we know in our northern
hemisphere as the latter part of February and the early part of March
and the appearance of the planet’s surface in both was not unlike what
we know at the same season in latitude 45°. Indeed, there is reason to
suppose bad weather there then and the extreme fringe, from the pale
tint it exhibited, to have been cloud rather than snow.
It is quite in keeping with what we know on earth or can conceive of
elsewhere that such aspect should characterize the cap at or near the
attainment of its greatest development. Whether it were not yet quite
arrived at this turning-point of its career or had but slightly passed
it a vagueness of outline would in either event proclaim the fact. For
were the frost still depositing, the cap’s edge would show indefinite;
and on the other hand had it just begun to melt, evaporation would give
it an undefined edge before the melting water had gathered in
sufficient quantities to be itself noticeable.
Its behavior subsequent to recognition bore out the inference from its
aspect when it first appeared. While for many days prior to its coming
unmistakably into view it was impossible to say whether what was seen
of the southern cap in 1903 and 1905 was cloud or snow; so even after
it had definitely disclosed itself it continued to play at odds with
the observer. Showing sharp at the edges one day it would appear but
hazily defined the next, thus clearly demonstrating itself to be at the
then unstable acme of its spread. Such a state of things we are only
too familiar with in our own March weather when after days of sunshine
that have melted off the winter’s white and fringed it with rivulets
and awakening grass, a snow-storm falling upon it powders the ground
again that was beginning to be bare and at one stroke extends the
domain of the snow while mystifying the actual limits it may be said to
occupy. The same condition of things, then, is not unknown on Mars, and
to fix the precise date of so wavering a phenomenon is not so much
matter of difficult observation as of physical impossibility.
[Illustration: Hellas in winter.]
Nor is the southern cap, at this the height of its winter expansion,
confined strictly to its own proper limits. Faint extensions, now so
connected with its main body as to form part and parcel of it, now so
detached and dull of tint as to make the observer doubtful of the exact
relationship, are generally to be seen attendant on it. Hellas in
winter is much given to such questionable garb, and has in consequence
been mistaken by more than one observer for the cap itself, appearing
as it does well upon the southern limb and being often the only region
to show white. Indeed, frost-bound as it then is, to consider it the
polar cap, though possibly geographically incorrect, may
climatologically be sustainable. Its northern extremity extends down to
latitude 30°, a pretty low latitude for frost. Still such equatorward
extension is not without corroborating parallel. In 1903, at what was
in Martian dates April 26, the whole of the region south of the Solis
Lacus and the Nectar showed white, with a whiteness which may as well
have been hoarfrost as cloud. Now, the Nectar runs east and west in
latitude 28°. So that in this instance, too, it is possible that arctic
conditions knocked at the very doors of the tropics. Encroachment of
the sort is equivalent to snow in Cairo and permanent snow at that; not
an occasional snow flurry, but something to linger on the ground and
stay visible sixty millions of miles away.
[Illustration: White south of Nectar and Solis Lacus.]
Knowledge of either cap in this the midwinter of its year has been a
matter of the most recent oppositions of the planet. Up to within the
last few years our acquaintance with either cap was chiefly confined to
the months,—one might almost say the weeks,—immediately surrounding
the summer solstice of its respective hemisphere. The behavior of the
caps during the rest of their career was largely unknown to us, from
the very disadvantageous positions they occupied at the times the
planet was nearest to the earth. Beginning with 1894, however, our
knowledge of both has been much extended, by a proportionate extension
of the period covered by the observations. It used to be thought
impracticable to observe the planet far on either side of opposition;
now it is observed from as much as four months before that event to the
same period after it. The result is a systematic series of observations
which in many ways has given unexpected insight into Martian
conditions. One of the benefits secured has been the lengthening of the
period of study of the cap’s career, a pushing of inquiry farther back
into its spring history and a longer lingering with it in its autumnal
rebuilding. Yet up to the very last opposition a gap in its chronology
still remained between February 25 and April 1. The opposition of 1905
has bridged this hiatus and brought us down to the latter date, at
which the melting of the cap begins in earnest.
From this point, April 1 on, we have abundant evidence of the cap’s
behavior. Its career now for some time is one long chronicle of
contraction. Like Balzac’s _Peau de Chagrin_ it simply shrinks, giving
out of its virtue in the process. The cap proceeds to dwindle almost
under the observer’s eye till, from an enormous white counterpane
spread over all the polar and a large part of the temperate zone, its
area contracts to but the veriest nightcap of what it was before. From
seventy degrees across it becomes sixty, then fifty, then forty, till
by the middle of the Martian May it has become not more than thirty
degrees in diameter. During this time, from the moment the melting
began in good earnest, the retreating white is girdled by a dark band,
of a blue tint, which keeps pace with the edge of the cap, shrinking as
it shrinks, and diminishing in width as the volume of the melting
decreases.
After the melting has been for some time under way and the cap has
become permanently bordered by its dark blue band a peculiar phenomenon
makes its appearance in the cap itself. This is its fission into one or
more parts. The process begins by the appearance of dark rifts which,
starting in from the cap’s exterior, penetrate into its heart until at
last they cleave it in two. Rifts have been seen by several observers
and in both caps; and what is most suggestive they always appear in the
same places, year after year. Sometimes oppositions elapse between
their several detections for they are not the least difficult of
detail; but when they are caught, they prove to lie just where they did
before.
The permanency in place of the rifts, a characteristic true of them
all, shows them to be of local habit. Thus the rift of 1884 and 1897
reappeared again to another observer in the same position in 1901. They
are, therefore, features of, or directly dependent on, the surface of
the planet. But it will not do from this fact to infer that they are
expressive of depressions there. The evidence is conclusive that great
irregularities of surface do not exist on Mars. As we shall see when we
come to consider the orology of the planet it is certain that
elevations there of over two or three thousand feet in altitude are
absent. Differences of temperature, able to explain a melting of the
ice in one locality coincidentally with its retention in an adjacent
one, must in consequence be unknown. And this much more conclusively
than at first appears, for the reason that the smaller the planet’s
mass the less rapidly does its blanket of air thin out in ascent above
the surface. This is in consequence of the greater pull the larger body
exerts and the greater density it imparts to a compressible gas like
our atmosphere. Gravity acts like any force producing pressure and by
it the envelope of air is squeezed into a smaller compass. But as this
is done throughout the atmospheric layer it means a more rapid
rarefaction as one leaves the body. The action is such that the height
necessary to reach an analogic density varies inversely as the gravity
of the mass. In consequence of this, to compass a relative thermometric
fall for which a moderate difference of elevation would suffice on
Earth, an immoderate one must be made on Mars. For gravity there being
but three eighths what it is here, eight thirds the rise must be made
to attain a proportionate lowering of temperature. This fact renders
the above argument against elevation and depression being the cause of
the phenomenon three times as cogent as it otherwise would be.
With so gradual a gradient in barometric pressure there and so low a
set of contour lines, altitude must be a negligible factor in Martian
surface meteorologic phenomena. Both density and temperature can be but
little affected by such cause, and we must search elsewhere for
explanation of what surface peculiarities we detect.
Meanwhile the rifts themselves, from being lines which penetrate the
cap from its periphery in toward its centre, end by traversing it in
its entirety and separating portions which, becoming outlying
subsidiary patches, themselves proceed to dwindle and eventually
disappear. The rifts usually take their rise from such broader parts of
the cap-encircling blue belt as make beads upon that cordon and are
clearly spots where the product of the melting of the cap is either
specially collected, or produces its most visible effect.
So far the description might apply with substantial accuracy to either
cap. Yet the conduct of the two is in some ways diverse and begins to
accentuate itself from this point on.
[Illustration: Northern Cap hooded with vapor.]
From the time that the north polar cap reaches a diameter of about
twenty-five degrees, a singular change steals over it. From having been
up to then of a well-defined outline it now proceeds to grow hazy and
indistinct all along its edge. This change in its character at the same
period of its career has been quite noticeable at each of the three
last oppositions, so that small doubt remains that the metamorphosis is
a regularly recurrent one in the history of the cap. Coincident with
the obliteration of its contour, its dimensions seemingly enlarge. It
is as if a hood had been drawn over the cap of a dull white different
from the dazzling brilliance of the cap itself and covering more
ground. Such is probably what occurs; with vapor for veil. The
excessive melting of the cap produces an extensive evaporation which
then in part condenses to be deposited afresh, in part remains as a
covering, shutting off from our view the outlines of the cap itself. It
would seem that at this time the cap melts faster than the air can
carry it off. A sort of steaming appears to be going on, taking place
_in situ_. For it clearly is not wafted away. The time of its coming
too is significant. For the season is May 15, the height of time for a
spring haze to set in. Then later it dissipates with the same quiet
indefiniteness with which it gathered.
[Illustration: Northern Cap unmasked.]
It is some time in Martian June before the spring haze clears away, and
when it does go, only a tiny polar cap stands revealed beneath it, from
six to eight degrees across, or from a tenth to a fifteenth of what it
was when it passed into its curious spring chrysalis. The date of
emergence varies. In 1903 it occurred early, the haze not being marked
after June 3, though recurring again at intervals for a day or so. In
1905 it was later; perceptibly thin after June 21 it did not certainly
clear away till June 9 and came back again on July 16 and possibly on
the 25th.
These vicissitudes of aspect give us glimpses into a sweet
unreasonableness in Martian weather which makes it seem more akin to
our own. And this on two counts, diurnal and annual. From day to day
atmospheric conditions shift for purely local cause; while,
furthermore, successive Martian years are not alike. In some the season
is early; in others late. So that Mars is no more exempt than are we
from the wantonness of weather.
Clearly disclosed thus reduced to its smallest possible terms it
remains for some months of our days, for six weeks of its own. During
that period it continues practically unchanged, neither increasing nor
decreasing significantly in size, nor altering notably in aspect.
Measures of the drawings of it then make it from five to eight degrees
across and it is possible that it really fluctuates between narrow
limits, though its clear-cut outline at all times renders the variation
difficult to explain. We are not so near it as we could wish; for on
these occasions even at their best it is over two hundred times as
distant as the moon and the greatest magnification possible still
leaves it a hundred thousand miles away.
To the south polar cap a somewhat similar history attaches, but with a
difference. In its case no such regularly recurrent spring haze has yet
been noted. The melting of this cap would seem to be of a more orderly
nature than its fellow and not to outdo what can conveniently be
carried off.
That an excess of evaporation should not take place is the more
peculiar from the fact that at its maximum it is the larger of the two
and therefore has the greater quantity of matter to get rid of. Its
summer, also, is shorter than the arctic one, so that it has the less
time to dispose of its accumulations. The only other respect in which
it seems to be differently circumstanced from its antipodes is in the
character of its surroundings. About it are large blue-green areas
which with intermissions stretch down in places to within less than ten
degrees of the equator; whereas the other pole is continuously
encircled for long distances by practically uninterrupted ochre. The
character of the environment seems thus the only thing that can account
for the difference in behavior and this proves the more plausible when
we come to consider what those two classes of regions respectively
represent.
In other ways as well the southern cap is the more self-contained. The
rifts, indeed, break it up into separate portions and these in part
remain as outlying detachments of the main body, as was notably the
case in 1877 and in 1894, but they hardly have the permanency and
importance of those similarly formed about the arctic pole. Nothing
antarctic for instance compares with the subsidiary patch of the north
polar regions lying in longitude 206°, which both in Schiaparelli’s
time, and during the late oppositions as well was almost as fixed a
feature of the arctic zone as the cap proper. Not quite so constant,
however, and not so solid-looking a landmark is this patch for all its
extent, which nearly equals the area of the more legitimate portion. It
bears on its face a more pallid complexion as if it were thinner, and
this is borne out by the fact that it occasionally disappears, an event
which so far at least has never befallen the northern cap itself.
Less constant the southern one is to its own minimum than the northern.
In some seasons, in most in fact, it reaches like the other a more or
less definite limit of diminution which it does not pass. But this is
not always the case. In 1894 it disappeared entirely at the height of
its midsummer. The season was probably unusually hot then in the
southern hemisphere of Mars.
In position the caps have something to say about physiographic
conditions. Both caps at their minima are then irregular and the centre
of the south one is markedly eccentric to the areographic pole. It lies
some six degrees north along the thirtieth meridian. The northern one
is also probably eccentric, but much less so, with a divergence not
much exceeding a degree and of doubtful orientation. Not only are both
caps not upon their respective poles but they are not opposite each
other, the one lying in longitude 30°, the other in 290°. This speaks,
of course, for local action. In some wise this must depend on the
configuration of the surface, yet so far as markings go there is
nothing to show what the dependence is.
The eccentring of the caps is paralleled by the like state of things on
earth. The pole of cold does not coincide in either hemisphere with the
geographic pole. On the earth its position is largely determined by the
distribution of the land-masses. Continents are not such equalizers of
heat as oceans because of their conductivity on the one hand and their
immobility on the other. In winter they part with their heat more
quickly and convection currents cannot supply the loss. This accounting
for thermal pole eccentricity is inapplicable to Mars because of the
absence there of bodies of water. And it is significant that the degree
the earthly poles of cold are out much exceeds what is the case on
Mars. Possibly areas of vegetation there replace to some effect areas
of water. It is certainly in favor of this view that the arctic regions
there are more desert than the antarctic and that the north pole of
cold occupies more squarely the geographic pole.
Not till 1903 did the actual starting again of either cap chance to be
seen. Nor was this, indeed, a matter of hazard but of persistent
inquiry by observation prolonged after the planet had got so far away
that its scanning had hitherto been discontinued. Such search beyond
the customary limits of observation was essential to success, because
of the relation of the axial tilt to the position of the planet in its
orbit. At an opposition well placed for nearness, the tilt is such as
largely to hide the pole and to present the polar regions too obliquely
to view for effective scanning. This is true both of the arctic and the
antarctic regions in turn. For the Martian axis being inclined somewhat
as our own is to the plane of the planet’s orbit, we at times see well
and at times but poorly the arctic or antarctic zones.
The cap, the starting to form of which was thus caught, was the arctic
one; the date 128 days after the northern summer solstice, or
thereabouts, for as is perhaps natural the advent of the phenomenon
partook of the wavelike advance of such things familiar on earth, an
advance succeeded by a recession and then followed by another advance.
So much is proof of local weather there as here. Hoar-frost was
successively deposited and then melted off.
[Illustration: Deposition of frost.]
What is significant, the deposition of the frost took place
simultaneously over large areas. The very first patch of it, in about
longitude 320°, extended at one stroke down to latitude 55°. For it
actually crossed the Pierius somewhat to the south. A second patch
stretched to the east of the cap. Two wings these made to the kernel of
cap itself. Through the wings could be marked the line of the canal:
the Pierius upon the one side, the Enipeus upon the other. Such
visibility of the canals through the white stretches proved the white
not to be due to cloud suspended between us and them, but a surface
deposit which found no lodgment upon the canals themselves. The same
avoidance of dark markings was evidenced by the showing of the dark rim
round the cap’s kernel. Now, if the deposit were indeed hoarfrost, this
failure to find permanent foothold on the dark markings is what we
should expect to witness. For whether they were vegetation or water,
equally in either case the frost would melt from them first. Probably
they were both vegetal, though some doubt might exist about the latter,
the band around the kernel. It was then August 20 in that hemisphere.
Such deposition over great stretches of country is perhaps not so
surprising as it appears at first sight when seen from without in its
totality. After all, something not unlike it occurs in our snow-storms
when hundreds of square miles are whitened at once. Furthermore, with
an atmosphere as thin as Mars seems to possess the temperature must be
perilously near the freezing-point in the arctic and subarctic regions
at the close of summer.
Steadily, with intermissions, the white sheet increased until even the
dark border to the cap became obliterate, the kernel showing at first
through the veil like the ghost of what it had been, and then ceasing
to be visible at all, its delimitations being buried under deeper and
deeper depositions of frost.
[Illustration: First northern snow.]
The perennial portion of the cap was thus merged in the new-fallen
snow. This marked the on-coming of the arctic winter in full force and
happened even before the polar sun had wholly set. For the pole did not
enter into the shadow till two of our months later, the autumnal
equinox occurring 183 days after the summer solstice or 55 days after
the first fall of frost. Then the pole passed into its star-strewn
arctic night, a polar night of twice the duration of our own and the
circumpolar regions entered upon their long hibernation of ten of our
months.
CHAPTER VII
WHITE SPOTS
In addition to the polar caps proper and to the subsidiary polar
patches that often in late summer flank them round about, other white
spots may from time to time be seen upon the disk. In appearance these
differ in no respect, so far as observed, from the arctic subsidiary
snow-fields. Of the same pure argent, they sparkle on occasion in like
manner with the sheen of ice. Equally with the polar caps they remain
permanent in place during the period of their visibility and are
themselves long-lived. Though by no means perpetual their duration is
reckoned by weeks and even months, and they recur with more or less
persistency at successive Martian years. That, when seen, they show in
particular positions apparently unaffected by diurnal change precludes
their being clouds, and this fact taken in connection with the
character of their habitat is the puzzling point about them. For they
affect chiefly the north tropic belt. They, or at least their nuclei,
are small, about two or three degrees in diameter, and are not
particularly easy of detection as a rule, though certain larger ones
are at times conspicuous. Chromatic, rather than formal, definition is
necessary to their bringing out, as is witnessed by the superb colors
the disk presents at the times when they are best seen. It is then that
Mars puts on the look of a fire-opal.
The first such spot to be noticed was one which Schiaparelli detected
in 1879, at the second opposition in which he studied the planet. He
called it the Nix Olympica, showing that he recognized in it a
cousinship to the polar snows. Yet it lay in latitude 20° north,
longitude[1] 131°, in the midst of the ochre stretches of that part of
the disk. It was a small roundish white speck of not more than two
thirds the diameter of the polar cap. Reseen by him in 1881, it failed
to appear at subsequent oppositions and was not caught again until
1888. Then once more it vanished, not to be detected anew till many
years after at Flagstaff, coming out rather surprisingly in 1903. It
showed, however, in the same place as before; so that its position but
not its existence is permanent.
A similar but smaller patch was apparent to Schiaparelli at the same
opposition of 1879. This one which he styled the Nix Atlantica lay
between the Thoth and the Syrtis Major. It was about half the size of
the Nix Olympica and has never since been seen, though it should have
been had it continued to be what it then was.
[Illustration: White in Elysium.]
On the other hand, phenomena of the sort undetected of Schiaparelli
have been remarked at Flagstaff. On May 18, 1901, I was suddenly struck
by the singular whiteness of the southeast corner of Elysium where that
region bordered the Trivium. Elysium has a way of being bright but not
with such startling intensity as this spot presented nor in so
restricted an area as was here the case. The spot was so much whiter
than anything I had ever previously seen outside the polar caps that it
arrested my attention at once. And this the more that I had observed
this same part of the planet the day before and perceived nothing out
of the ordinary. Once detected, however, the spot continued visible.
The next day it was there with equal conspicuousness, and now thrust an
arm across the Cerberus, entirely obliterating the canal for the space
of several degrees. In this salience it remained day after day till the
region passed from sight, to reappear with it six weeks later when the
region again rounded into view. The hour of the Martian day seemed to
make no difference in its visibility. It was seen from early morning
till Martian afternoon, as late as the phase permitted. Clearly there
was nothing diurnal about its revealing, and it lasted for at least
three months and a half, until the planet got so far away that
observations were discontinued.
It was to all appearances and intents snow. But now comes the singular
fact about it. It lay within ten degrees of the equator and showed from
the end of June to the latter part of August. To our ideas there could
be no more inopportune place or time for such an exhibition. For it
cannot have been due to a snow-capped peak, as we know for certain that
there are no mountains in this, or in any other, part of the planet.
Besides, it had not appeared in previous Martian years; which it
infallibly would have done had it been a peak. Indeed, it baffles
explanation beyond any Martian phenomenon known to me. It seems
directly to contradict every other detail presented by the disk.
The phenomenon is thus unique in kind; it is not, however, unique as a
specimen of its kind. The eastern coast of Aeria where that region
borders the Syrtis Major is prone to a brilliance of the same sort. It
is a narrow belt of country that shows thus, nothing but the coastline
itself, but this for a considerable distance stretching several hundred
miles in length. It has stood out saliently bright now at every
opposition which I have observed, beginning with 1894. Sometimes it has
been described in the notes as bright simply, sometimes as white, and
once, in 1901, as glistening at one point like ice. Yet when upon the
terminator it has never stood forth as a mountain range should have
done to declare its character.
It has been evident regardless apparently of the Martian season. In
1894 it was bright from October 25 to January 16 (Martian chronology);
in 1896, from December 22 to January 7; in 1901, from July 13 to the
15th; in 1903, at about the same date and so in 1905. It was whitest
during the latter oppositions, showing that the effect is most marked
in its midsummer. All of the above instances of extra-polar white have
been located within the tropics. Examples of the same thing, however,
occur in the north temperate zone. Tempe, a region just to the west of
the Mare Acidalium, is exceedingly given to showing a small white spot
close upon the Mare’s border in latitude 50° north. This spot, too, on
occasion glitters as it were with ice. It is also at times very small.
So that whereas much of Tempe is by nature bright but a small kernel of
it is dazzling.
The list might be easily extended from the record book. Thus on March 1
and 2, 1903, the disk showed speckled with minute white spots, one in
Arcadia in latitude 41° north, one in Tharsis near the equator, a third
just north of the Phoenix Lucus in 10° south, and a fourth, the Nix
Olympica, and on April 11, a glittering pin-point starred like a
diamond the centre of the Pons Hectoris. On both these occasions the
Martian season was summer; July 9 for the latter, June 21 for the
former date.
[Illustration: White in the Pons Hectoris.]
As one approaches the north pole spots of like character become more
numerous. Especially are such visible north of the Mare Acidalium in
the arctic region thereabout, from 63° to 75° north.
From so widespread a set of instances the only explanation which seems
to fit the phenomena is that the mean temperature of Mars is low, not
very much above freezing, and that whatever causes a local fall in the
temperature results in hoar-frost. Such an explanation accords well
with the distance of the planet from the sun and the thinness of its
atmosphere. At the same time it shows that the mean temperature over
the greater part of the planet the greater part of the time is above
the freezing-point and that consequently it is no bar to vegetation of
a suitable sort.
That the hoar-frost should be found even at the equator may perhaps be
due to the very thinness of the air-covering of Mars, which would tend
to make the actual insolation more of a factor than it is with us, and
by the great length of the Martian seasons. In midsummer the greatest
insolation occurs in the arctic and temperate, not in the tropic
regions; on the other hand, an atmosphere tends to accumulate heat for
the tropics. With us the latter factor is prepotent; it would be less
effective on Mars. Then again the double duration of summer would tend
to emphasize insolation as the important factor in the matter. But it
is possible that greater deposition plays a part in the matter. On
earth the rainfall is greatest near the equator and something of the
sort may be true of the zones of moisture on Mars. That the most
striking spots are found to the west of large dark areas may in this
connection have a meaning inasmuch as, such regions being
vegetation-covered, the air over them is probably more moisture-laden.
One point about the position of the spots is of moment: they have all
been found in the northern hemisphere or within ten degrees of it in
the southern equatorial region. This seems at first a question of
hemispheres; but when we consider that the light areas of the surface
are chiefly in the boreal hemisphere and in the south tropic belt, we
perceive that it may be rather the character of the surface there than
the particular hemisphere in the abstract that is decisive in the
matter. Nevertheless, the austral hemisphere is the hemisphere of
extremes, possessing a shorter, hotter summer and a longer, colder
winter than its antipodes. This would not favor sporadic small
depositions of frost in summer so much as would a climate of a more
mean temperature.
From the relative lack of atmospheric covering over the planet we
should expect the nights to prove decidedly cool, while the days were
fairly warm. Of this we have perhaps evidence in a singular aspect
shown by the Mare Acidalium in June, 1903. The account of it in the
Annals reads thus: “On May 22 an interesting and curious phenomenon
presented itself. On that day, so soon as the Mare Acidalium had well
rounded the terminator on to the disk, at λ352°, the whole of its
central part showed white, the edges of the marking alone remaining as
a shell to this brilliant core. So striking was the effect that beside
appearing in the drawing it found echo in the notes. The next day no
mention is made of it, and a drawing made under λ20° shows the Mare as
usual and the bright spot in Tempe in its customary place. Neither was
anything of the sort noticed on the 24th and 25th. But on the 26th, the
day of the projection (upon the terminator), the effect of the 23d
reappeared, the longitude of the centre being 332°. Fortunately on that
day a further drawing was secured which enabled its subsequent behavior
to be followed. Made three hours later than the other, the longitude of
the centre being 13°, this drawing shows the Mare well on the disk, its
whole area as dark as usual and with Tempe bright to the right of it
toward the terminator. The terminator in question was the sunrise one,
and we are offered two suppositions in explanation of the phenomenon:
either the white was due to a morning deposition of hoar-frost which
dissipated as the sun got up, or obliquity rendered some superficial
deposit visible which more vertical vision hid. That the former
inference is the more probable seems hinted at by the simultaneous
appearance from the 19th to the 26th of other areas of white between
the Mare and the pole. May 26 was 88 days after the northern summer
solstice, and corresponded to July 31 on the earth.” Annals, Volume
III, §564.
In this connection mention may pertinently be made of Schiaparelli’s
repeated observation of regions that whiten with obliquity, a
proclivity to which he particularly noticed Hellas and certain
‘islands’ in the Mare Erythraeum to be prone. Here as with the Mare
Acidalium we certainly seem to be envisaging cases of matutinal frost
melted by midday under the sun’s rays.
-----
Footnote 1:
Martian longitudes are now reckoned from the Fastigium Aryn, the
mythologic cupola of the world, a spot easy of recognition because
making the tongue in the jaws of the Sabaeus Sinus. It further
commends itself because of lying within a degree of the equator. The
longitudes are reckoned thence westward all the way round, or to 360°.
CHAPTER VIII
CLIMATE AND WEATHER
In gazing at the successive phases presented by the polar caps as their
annual history unrolls itself to view, beginning with vast white cloaks
that in winter hide so effectively the planet’s shoulders, to little
round knobs that in summer sit like guardsmen’s caps more or less askew
upon the poles, the bodily eye sees only the glisten of far-off snow.
The mind’s eye, however, perceives something more: the conviction they
carry of the presence of an atmosphere surrounding the planet. Elusive
as water vapor is to sight for its transparency and to spectroscopic
determination for its earthly omnipresence, recognition of its
existence elsewhere by deduction raises such reasoning at once to a
more conspicuous plane than it might otherwise assume. Especially is
this true where the deduction is itself conclusive, as is here the
case. For it depends on phenomena not its own, but which are in their
turn dependent on it. We are not even beholden to any knowledge of the
substance composing the caps for the fundamental inference that an
atmosphere surrounds them. Whatever that substance were, the fact that
the caps dissipate and reform shows us with absolute certainty that
they pass into the gaseous state, to be later solidified afresh. This
gas constitutes of itself an atmosphere; while another phenomenon, to
wit, their blue girdles as they melt, affirming their substance to be
snow and ice, enables us to precise the fact that this gas is water
vapor.
From such premise given us by the polar caps we are able to infer much
more by the help of the kinetic theory of gases. But the speed of
parting by a planet with its gases is conditioned by the mean speed of
each gas. Water vapor will, therefore, go before nitrogen, oxygen or
carbonic acid gas. If, then, we find it present over the surface of a
planet we are assured of the possibility that the other three may be
there too, and from the similarity of matter in space strong reason to
suspect that they actually are.
Corroborative evidence of the accuracy of the deduction as to the
presence of a Martian air is shown in several other ways; in the
existence of clouds to begin with. Rare as they are, these certainly
float at times over parts of the planet, although it is doubtful
whether they can then be seen. Fortunately for assurance we have other
ways of ascertaining their presence than that of obscuration. Nor is it
of account to the argument that they should be few and far between, as
they unquestionably are. One single instance of such mediumistic
support is enough to support the theory of a medium; and that instance
has been more than once observed.
Direct evidence of atmosphere is further forthcoming in the limb-light.
This phenomenon might be described as a brilliant obscuration. It is a
circlet of illumination that swamps the features as they near the full
edge of the disk, the limb of the planet as it is called. Obliteration
of the sort is evident, more or less markedly, at all times, and is not
due to foreshortening, as the broadest areas are affected. The fading
out of the detail at the limb suggests nothing so much as a veil drawn
between us and it, lighter in tint than what it covers. Such a veil can
be none other than air or the haze and cloud that air supports. From
its effect, impartial in place and partial in character, cloud is
inadmissible as a cause and we are left with air charged with dust or
vapor in explanation. Obscuration due to it should prove most dense at
the limb, since there the eye has to penetrate a greater depth of it;
just as on the earth our own air gives azure dimness to the distance in
deepened tinting as the mountains lie remote.
Another bit of evidence lies in the apparent detection of a twilight
arc. In 1894 measures made of the polar and equatorial diameters of the
planet showed certain systematic residuals left after all known
corrections had been applied. The only thing which would account for
them was the supposition that a twilight arc had been unconsciously
seen and as unconsciously measured. In delicate quantities of the sort
too great reliance cannot be put, but if the residuals be not referable
to other cause they give us not only further evidence of an atmosphere,
but at the same time our only hint of that atmosphere’s extent. From
them it would seem that the air must be rare, not more than about four
inches of barometric pressure, as we reckon it, and probably less; a
thin, high air more rarefied than prevails upon our highest mountain
tops.
Corroborative of this is the aspect of the planet. From the general
look of the disk a scant covering of air is inferable. For one of the
striking things about the planet’s features is their patent exposure to
our sight. Except in the winter time of its hemisphere or in the spring
after the greatest melting of the polar cap, nothing seems to stand in
our way of an uninterrupted view of the surface, whether in the arctic,
temperate, or tropic zones. From the openness of its expression,
however, too much case should not be made as we really know but little
of how an atmosphere-enshrouded planet would look. We find no
difficulty in seeing objects a hundred miles away across the surface of
the earth and yet the thickness of the air strata in such horizontal
traversing is many fold what it is when we look directly up. It is also
out of all proportion laden with dust and smoke. In the purer regions
of the earth, a clear air imposes but little bar to sight, and conjures
up far things startlingly distinct.
Nevertheless, every evidence points to a thin air upon Mars: _a priori_
reasoning, indirect deduction and direct sight. Now, from a thinness of
atmosphere it would follow, other things equal, that the climate was
cold. About this there has been much question, but less of answering
reply. From the distance of the planet from the sun it is certain less
heat is received by it than falls upon the earth in something like the
ratio of one to two. But that the amount effective is as the amount
received is far from sure. The available heat is much affected by the
manner of its reception. A blanket of air acts like the glass of a
conservatory, letting the light rays in, but hindering the heat rays
out. The light rays falling on the ground or the air are transformed
into heat rays that, finding the return journey less easy, are
consequently trapped. All substances are thus calorifiers, but water
vapor is many times more potent than ordinary air to heat-ensnaring. A
humid air has a hothouse tang to it most perceptible. Now, what the
relative percentage of water vapor in the Martian atmosphere may be we
do not know.
The thinness of the Martian air has caused it to be likened to that
upon our highest mountain peaks which are in large part covered with
perpetual snow. But the comparison is not well founded. A peak differs
materially from a plateau in the countenance it gives to the heat
falling upon it. On a plateau each warmed acre of ground helps the
retention of heat by its neighbor; while in addition to being destitute
of side support the higher winds generated about an isolated peak blow
its own caloric away. Still less does any analogy hold between the two
when the plateau is a world-wide one.
From these considerations it is evident glosses are possible upon the
bald idea of a much lower temperature prevailing on the Martian surface
than on the earth’s. Doubtless the theoretic cold has been greatly
overdone. Reversely, recent observations tend to lower the apparent
temperature disclosed by the features of the disk, and between the
rising of the theoretic and the falling of the observed we are left
with a very reasonable compromise and reconcilement as the result.
The various look and behavior of the surface of Mars point to a mean
temperature colder than that of the earth, but above the freezing-point
of water; for regions, at least, outside of the polar caps and during
all but the winter months. Except at certain special spots, and
possibly even there, frost is unknown at all times within the tropics
and except in winter in temperate latitudes. These anomalous
localities, mentioned in the preceding chapter, may be said to be the
exceptions that prove the rule of general non-glaciation. For if they
be snow, they stand witness to its absence elsewhere upon the disk, and
if they are not, they testify the more emphatically to the same effect.
As between different parts of the surface, the tilt of the Martian axis
and the greater length of the Martian seasons, the one the same as, the
other the double of, our own, tend to an accentuation of the heat in
the temperate and arctic or antarctic zones. The greatest insolation on
earth is not, as we might suppose, at the equator, but at the parallels
of 43.°5 north and south; even the poles themselves receiving a quarter
as much heat again on midsummer day as ever falls to the lot of the
line. This broad physical fact is equally true of Mars, while in the
matter of consecutive exposure Mars in summer outdoes the earth. For
the longer the seasons, the more nearly does the effective heat
approach the received amount. Thus both on the score of heat received
and of heat husbanded these zones must be relatively warm. And this
shows itself in the look of the surface. In summer it is clearly warmer
within the polar regions than is the case on earth, to judge by the
effect. In winter the cold is doubtless proportionately severe.
For the diurnal range of temperature we have less data. There is
evidence pointing to chilly nights, but it is meagre, and we are left
to fall back on the cold of our deserts at night for analogic condition
of the state of things over the Martian desert levels after the sun
goes down.
If we are uncertain of the precise character of the Martian climate, we
know on the other hand a good deal about the Martian weather. A
pleasing absence of it over much of the planet distinguishes Martian
conditions from our own. That we can scan the surface as we do without
practical interruption day in and day out proves the weather over it to
be permanently fair. In fact a clear sky, except in winter, and in many
places even then, is not only the rule, but the rule almost without
exceptions. In the early days of Martian study cases of obscuration
were recorded from time to time by observers, in which portions of the
disk were changed or hidden as if clouds were veiling them from view.
More modern observations fail to support this deduction, partly by
absence of instances, partly by other explanation of the facts.
Certainly the recorded instances are very rare. Indeed, occasions of
the sort must to any Martians be events, since only one possible
example has presented itself to me during the course of my
observations, extending more or less over eleven years. Even in this
case there was no obliteration, though a certain whiteness overspread
an area near the equator temporarily. Position seemed to point to its
identity with a cloud which made its appearance about that time upon
the terminator, and lasted for some thirty-six hours. The cloud,
however, showed evidence of being, not the kind with which we are
familiar, but a dust-storm, in keeping, indeed, with the desert region
(Chryse) in which it originated.
With the exception of sporadic disturbance of the sort the whole
surface of the planet outside the immediate vicinity of the polar caps
seems free from cloud or mist and to lie perpetually unveiled to space.
In the neighborhood of the caps, however, and especially round about
their edge, a very distinct pearly appearance is presented during the
months at which the cap is at its maximum, or in other words, in the
depth of its winter. Of a dull white hue and indefinite contour the
phenomenon suggests cloud. Where it lies spread no markings are
visible; an absence explicable by obscuration due an interposed medium,
but equally well by seasonal non-existence of the markings themselves,
which from the general behavior of these markings we know to be to some
extent certainly the fact. Of the regions where the effect is
noticeable, Hellas is the most striking. So conspicuously white during
the winter of the southern hemisphere as to have been often mistaken
for the polar cap, its ghost shows thus almost regularly every Martian
year. What is as suggestive as it is striking, the blanching is
confined to the solid circle constituting Hellas and does not extend
into the dark regions by which it is circumscribed. Hellas is as
self-contained when thus powdered as when, in its normal ochre or
abnormal red, it stretches like a broad buckler across the body of the
disk. That the land there lies at a higher level than its surroundings
is pretty certain, but that the difference can amount to enough to
explain its silveriness as ice is improbable. In latitude Hellas is
distinctly temperate, lying between the parallels of 55° and 30°; but
on Mars this is no warrant of a like climate. Again, though close on
the south to what constitutes the polar cap, it does not strictly form
part of that cap, but occupies both in position and in kind a something
intermediary between the frost-bound regions of periodic snow and the
warmer ones of perpetual sunshine. It seems to be afflicted with the
winter weather of the north of Europe, and to owe its pearly look at
such times to the same cloud canopy that then distressingly covers
those inclement lands.
Similar in behavior to it is the long chain of so-called islands that,
beginning southwest of Thaumasia, runs thence westward even to the
eastern edge of Hellas. These belt the planet in a west-northwesterly
direction by a strip of territory from ten to fifteen degrees wide, the
medial line of which begins at 55° south and ends in about 40°. They
are parted from the main bright areas by blue-green ‘seas’ of about the
same width as themselves, the Mare Sirenum, the Mare Cimmerium and Mare
Tyrrhenum. These ‘seas’ the white that covers the ‘islands’ never
crosses; though the continent, as we may call it for convenience,
descends at the east to 30° south. Since the ‘seas’ are not seas, the
cause which might bound the snow, were they such, cannot be the cause
here. Nevertheless, they have an effect of some sort on the isothermal
lines as is shown not only by latitudinal comparison with the state of
things in Hellas, but with that in Thaumasia as well. For 30° south is
also the limit apparently of the white on Thaumasia, where ochre desert
stretches ten degrees farther south still; the region in its southern
part being white-mantled, in its northern part not. Here again, then,
the ochre areas make exception to what affects the blue-green ones.
Clearly the blue-green regions temper the action of what gives them
wintry cloak. But why they should do this is not easy to explain on any
supposition terrestrial or marine. Bodies of water tend to foster the
formation of clouds; so, less markedly, do areas of vegetation. Neither
the old ideas, then, nor the new lend themselves in explanation. It may
be that while we here seem to be envisaging cloud we are in reality
looking at hoar-frost. On the other hand, light cloud would show less,
superposed over a dark background, than over an ochre one; and this,
the simplest of all explanations, may be the true one. It is facts like
these that intrigue us in the study of the Martian surface by revealing
conditions which render offhand analogy with the earth unsafe. Indeed,
we are more sure of some things which appear too strange to be true
than of others so simple on their face as to enlist belief. Among the
most difficult and perplexing are meteorological problems like the
above. Here we can only say provisionally that while cloud best answers
to the appearance, frost best fits the cause. For vegetation might melt
frost, yet not dissipate cloud. By raising our conception of the mean
temperature the facts can, however, be reconciled and this is probably
the solution of the difficulty after all.
As we saw in the annual history of the polar caps a dimness somewhat
different affects the northern cap in May and June. After the melting
of the cap is well under way a haziness sets in along its edge which
befuddles its outline and effectually hides what is going on within it.
When at last the screen clears away the cap is found to be reduced to
its least dimensions. Such obstructing sheet looks to be more of the
nature of mist caused by the excessive melting of the cap.
Unfortunately, there are here no patches of blue-green to test a
possible partiality in its behavior over such tracts; nor has similar
action ever yet been remarked in the case of the cap of the southern
hemisphere.
Regular recurrence at the appropriate season of the planet’s year,
together with extensive action at the time, takes this springtide mist
to some extent out of the domain of weather into that of climate. For
it prevails all round the cap and repeats itself in place as each fresh
spring comes on. At least it has done so for the past three oppositions
at which it has been possible to observe well the arctic zones. It is
thus both general in its application and fixed in its behavior.
Nevertheless, it betrays something of the fickleness which
characterizes that more inconstant thing: weather. For it comes and
goes, one thinks for good, only to find it there again some days later.
Not less captious is the meteorologic action shown in the making of the
new polar cap. When the northern one starts to form, vast areas of
frost are deposited in a single night. These, however, are not
permanent. The ground thus covered is during the next few days again
partially laid bare. Then a new fall occurs, hiding the surface a
little more completely than before, and the lost domain is more than
regained. By such wavelike advance and recession the tide of frost
creeps over and submerges the arctic regions as the late summer passes
into the autumn. In this alternate coming and going with succeeding
days, we have an unsteadfastness of action most fittingly paralleled by
our own weather. It would seem that local causes there as here are
superposed upon the orderly progress of the seasons and though at the
on-coming of the autumn the cold is steadily gathering strength,
nevertheless warm days occur now and then to stay its hand, only to be
succeeded in their turn by frosts more biting than before. Even on Mars
nothing in the way of weather is absolutely predicable but
impredicability.
CHAPTER IX
MOUNTAINS AND CLOUD
In all ways but one our scrutiny of the planet is confined to such view
as we might get of it from the car of a balloon poised above it in
space; from which disadvantage-point we should see the surface only as
a map spread out below us, a matter of but two dimensions. The
exception consists in the observation of what are called projections;
irregularities visible when the disk is gibbous upon that edge of the
planet where the light fades off. Striking phenomena in themselves they
are of particular value for what may be deduced from them. For by them
we are afforded our only opportunity of gaining knowledge of the
surface other than in plan and thus of determining between peak,
plateau, or plain that to a bird’s-eye view alike lie flattened out to
one dead level.
It might at first be thought that our best chance of noting any
elevations or depressions of the Martian surface lay in catching that
surface in profile, by scanning the bright edge of it which stands
sharp-cut against the sky and is called the limb. For this is
practically what we do on earth when we mark a mountain against the
horizon and measure its height by triangulation. Unfortunately the
method fails in the case of Mars because of the great distance we are
away. Unless the planet were distinctly more generously equipped than
the earth in the matter of mountains, nothing could be hoped from so
forthright an envisaging. So relatively insignificant to the size of
its globe is the relief of the earth’s surface that an orange skin
would seem grossly rough by comparison. The same proves true for Mars.
With the greatest magnification we can produce, the Martian limb still
appears perfectly smooth.
Luckily, while direct vision is thus impossible, oblique illumination
enables us to get an insight into the character of the surface we had
otherwise been denied. When mountains or valleys chance to lie upon the
boundary of light and darkness, the rim of the disk known as the
terminator in contradistinction to the limb where the surface itself
comes to an end, they make their presence evident through an indirect
species of magnification, the elongate effect of oblique lighting. With
a practical instance of it every one is familiar who has walked by
night along a road imperfectly starred at intervals by electric lights.
Startled between posts by what seemed deep holes and high furrows he
has involuntarily imitated a spavined horse for fear of stubbing his
toes, only to encounter when his foot fell a surface on contact
surprisingly smooth. The slant illumination by lengthening the shadows
had painfully deceived him into exaggerated inference of irregularity.
What proves disturbing to a wayfarer misguided by arc lights is made to
do the eye service when it comes to planetary interpretation. On the
boundary of light and shade, those parts of the surface where it is
sunrise or sunset upon the planet, the sun’s rays fall so athwartwise
as to throw enormous shadows from quite small elevations to an eye so
placed as to view the surface with anything approaching
perpendicularity. A mountain mass there will thus proclaim itself by
protracted profile upon the plain in hundredfold magnification.
Similarly a peak there will advertise its height by catching the coming
or holding the lingering light at many times the distance of its own
elevation away from the night side of the planet. Here, if anywhere,
then, could mountains be expected to disclose themselves, and here,
when existent, they have as a matter of fact been found.
Our own moon offers us the first and easiest example of such
vicariously visible relief. When the moon is near the quarter, and for
three or four days on either side of that, a keen eye can usually
detect one or more knobs, like warts, projecting from its terminator,
easily distinguished from the limb both by reason of being less bright
and of being bounded by a semi-ellipse instead of a semicircle. If a
telescope or even an opera-glass be substituted for the eye, it is
possible to see what causes them; the knob resolves itself into the
illuminated rim of a crater separated from the main body of the visible
moon by the seemingly black void of space. The peak has caught the
sunlight, while its foot and the country between it and the illuminated
surface still lies shrouded in shadow.
From measurement of the distance the sun-tipped peak seems to stand
aloof from the line where the plain itself is touched by the light, the
height of it above that plain may be calculated. In this way have been
found the heights of the mountains of the moon. Incidentally, brain
outstrips brawn. For pinnacles no Lunarian could scale, both for their
precipitous inaccessibility and their loftiness, man has measured
without so much as setting foot upon their globe. At each lunar sunrise
and again at lunar sunset these old crater walls show their crescent
coronets tipped the reverse way; and peaks higher than the Himalayas
make gigantic gnomons of themselves with hands outstretched to grasp
the plains.
In this manner a lunar peak of fifteen thousand feet shows its presence
to the unaided eye. With so much for starting-point we can calculate
how low an elevation could similarly be made out on Mars under a like
phase illumination. Now, in spheres of different diameters the distance
out from the terminator for a given height is as the square root of the
diameter. Mars has about twice the size of the Moon. In consequence, if
we saw the planet at the same distance off as the Moon, the height of a
peak upon it sufficient to cast an equal shadow or be seen at an equal
separation from the terminator need be but two thirds as high. To see
it thus equidistant a power of 250 or 300 is necessary, dependent on
the opposition. Twice this power may at times be used, and by the same
reasoning this would reduce the height sufficient to show by four or to
something like 2500 feet. This, then, would be the theoretic limit of
the visible, a limit needing to be somewhat increased because of the
imperfection of our air.
Having found thus what should be visible on Mars we turn now to see
what is. At once we find ourselves confronted with a very unlunar state
of things. Common upon the face of the Moon, excrescences of the
terminator are rare on Mars. The first ever seen was detected by a
visitor at the Lick Observatory in 1888. Since then they have been
repeatedly noticed both at the Lick and elsewhere. But although
observers are now on the watch for them, they are not very frequently
chronicled because not of everyday occurrence. Much depends upon the
opposition; some approaches of the planet proving more prolific of them
than others. How rare they are, however, may be gathered from the fact
that the last three oppositions have disclosed but one apiece.
An account of the great projection of May 25, 1903, will give an idea
of the extent and interest of the phenomenon and will serve to show to
what cause we must attribute all such that have been visible on Mars,
for the behavior of this one was typical of the class.
[Illustration: Projection on terminator.]
About half past eight o’clock in the evening of May 26, 1903, Mr. V. M.
Slipher, astronomer at Flagstaff, shortly after taking over the
telescope then directed upon Mars, suddenly noticed a large projection
about halfway up the terminator of the planet. He at once sent word of
the fact and the observatory staff turned out to see it, for a
projection has for workers on Mars the like interest that a new comet
possesses for astronomers generally. In this case the phenomenon was
specially potent in that it was the first to be detected that year. Its
singularity was amply seconded by its size. For it was very large, its
extent both in length and height being excessive. When I first saw it,
the projection consisted of an oval patch of light, a little to the
north of the centre of the phase ellipse lying parallel to the
terminator but parted from it by darkness to the extent of half the
projection’s own width. It made thus not simply an excrescence but a
detached islet of light. It was easily seen by all those present and
was carefully studied from that time on by Mr. Slipher and me. Both of
us made drawings of it alternately at intervals, as well as micrometer
measures of its position.
Next to its great size, the most striking feature about it was its
color. This, instead of being white or whitish, was ochre orange, a hue
closely assimilated to the tint of the subjacent parts of the disk,
which was the region known as Chryse. This distinctive complexion it
kept throughout the period of its apparition. At the same time Baltia,
a region to the north of it and synchronously visible close upon the
terminator, showed whitish. The seeing was good enough to disclose the
Phison and Euphrates double, the power a magnification of 310 and the
aperture the full aperture of the 24-inch objective.
From the time it was first seen the detached patch of light crept in
toward the disk, the illuminated body of the planet. Four minutes after
I noted it the dark space separating it from the nearest point of the
terminator had sensibly lessened. So it continued, with some
fluctuations intrinsic to the atmospheric difficulties of observations
generally and to the smallness of the object itself, to become
gradually less and less salient. It lasted for about forty minutes from
the moment it had first appeared to Mr. Slipher and then passed from
sight to leave the edge of the planet smooth and commonplace again.
The measures made on it showed that it lay when first seen in longitude
39°.7, latitude 18°.5 north, and that its highest point stood seventeen
miles above the surface of the planet. It was three hundred miles long.
These are my own figures, from which Mr. Slipher’s do not substantially
differ.
The return of the part of the planet where it had been seen was eagerly
awaited the night after by both observers, to see if it would bring the
projection with it. For only once a day is the same region of Mars
similarly presented. But in order not to miss the projection, should it
be ahead of time, observations were begun before it was due. Shortly
after they were started, there appeared higher up the terminator and
therefore farther north than had been the case the night before, a
small projection. It was with difficulty made out and its position
measured. Without careful watching it must have been missed altogether.
As it was, it differed in every respect from that of the preceding day.
It was not nearly so high, not nearly so large, and lay in a different
place on the planet, being now in longitude 31°.7, latitude 25°.5.
Either the two, therefore, were totally different things or the
projection had moved in the elapsed interval of time over seven degrees
of latitude and eight degrees of longitude, a distance of three hundred
and ninety miles in twenty-four hours. Where the previous projection
had been nothing showed. On the following night, May 28, no trace of
anything unusual could be seen anywhere.
We are now concerned to inquire to what this series of appearances
could have been due. The first observers of projections on Mars had
unhesitatingly attributed them to the same cause that produces
projections on the Moon, to wit, mountains. Such they were held to be
in France and at the Lick. This view, however, was in 1892 disputed by
W. H. Pickering who considered them to be not mountains, but cloud. And
this view was strongly supported by A. E. Douglass in a discussion of a
large number of them observed in 1894 at Flagstaff. The mountain theory
of their generation was finally shown to be untenable and their
ascription to cloud conclusively proved to be the correct solution by
the observations of a remarkable one made in December, 1900, and the
careful study to which by the writer they were subjected. We shall now
explain how this was done and we will begin by pointing out that the
fact that only a single specimen of the phenomenon was visible at each
of the three oppositions of 1900, 1903, and 1905 was itself conclusive,
rightly viewed, of their non-mountainous character. This conclusion
follows at once from the isolateness of the phenomenon. For a mountain
cannot change its place. Now, the shift in the aspect presented by the
planet’s disk from one night to the next is not sufficient to alter
perceptibly the appearance shown by anything upon its edge on the two
occasions. If, then, a peak stood out upon it one evening, the peak
should again show salient when the region reached the same position
upon the succeeding night. That nothing then was seen where something
had previously been visible proved the phenomenon not that of a
mountain peak, since what produced the projection was clearly not fixed
in place and therefore not attached to the soil. Now the only other
thing capable of catching the light before it reached the surface would
be something suspended in the air, that is, a cloud. Deduction,
therefore, from the rarity of the phenomenon alone showed that the
projections must be clouds.
Their behavior in detail entirely corroborates this deduction from
their intermittence. Such was shown by the action of the projection of
December 6, 1900, as set forth in a paper before the American
Philosophical Society and such again by that of the one of May 26,
1903, as we shall now note. To begin with, we notice that the
projection seen on May 26 was not found either _in situ_ or in size on
May 27 and had wholly vanished on May 28, though the seeing was
substantially the same if not better on the two nights succeeding that
of its original detection. Hence in its own instance this projection
proved an alibi irreconcilable with the character of a mountain mass.
But it did more. It not only was not on the second evening what and
where it had been on the first, but the remains of it visible on the
second occasion showed clearly that it had moved in the meantime.
Furthermore it was disappearing as it went, for it was very much
smaller after the lapse of twenty-four hours. The something that caused
it was not only not attached to the soil, but was moving and
dissipating as it moved. Only one class of bodies known to us can
account for these metamorphoses and that is: cloud.
But what kind of cloud are we to conceive it to be? Our ordinary vapor
clouds are whitish and this would be still more their color could they
be looked at from above. The Martian cloud was not white but tawny, of
the tint exhibited by a cloud of dust. Nor could this color have very
well been lent it by its sunrise position, for other places equally
situated to be tinged by the hues of that time of day, Baltia to wit,
showed distinctly white. So that we must suppose it to be what it
looked, a something of the soil, not beholden to atmospheric tinting
for its hue; a vast dust-cloud traveling slowly over the desert and
settling slowly again to the ground.
Precisely the same general course of drifting disappearance was taken
by the projection of December 7 and 8, 1900. And this, too, stood an
unique apparition in the annals of its opposition. Clouds, then, and
not mountains are the explanation of the projections on Mars, differing
thus completely from the lunar ones.
CHAPTER X
THE BLUE-GREEN AREAS
Descending now equatorwards from the polar regions, and their in part
paleocrystic, in part periodic, coating of ice, we come out upon the
general uncovered expanse of the planet which in winter comprises
relatively less surface than on Earth, but in summer relatively more.
Forty degrees and eighty-six degrees may be taken as the mean hiemal
and æstival limits respectively of the snow on Mars; forty-five and
seventy-five as those of the Earth. Whatever ground is thus bared of
superficial covering on Mars lies fully exposed to view, thanks to the
absence of obscuring cloud; and it is at once evident that the terrane
is diversified, patches of blue-green alternating with stretches of
reddish ochre. Of the two opaline tints the reddish ochre predominates,
fully five eighths of the disk being occupied by it.
It was early evident in the study of the surface of Mars that its
ochreish disk was not spotless. Huyghens in 1659 saw the Syrtis Major.
From this first fruit of areography dates, indeed, the initial
recognition of the planet’s rotation; for on noting that the marking
changed its place, he inferred a turning of the planet upon itself in
about twenty-four hours. Thirteen years later he observed and drew it
again and this time in company with the polar cap. Again, after eleven
more years, he depicted it for the third time, and now so changed
because of the different tilt of the planet toward the earth that it
may be doubted whether Huyghens himself recognized it for the same. But
that he drew it correctly a globe of Mars will at once show.
From such small beginning did areography progress to the perception of
permanent patches of a sombre hue distributed more or less irregularly
over the disk. Impressing the observers simply as dark at first, they
later came to be recognized as possessing color, a blue-green, which
contrasted beautifully with the reddish ochre of the rest of the
surface. Cassini, Maraldi, Bianchini, Herschel, Schroeter, all saw
markings which they reproduced. Finally, with Beer and Maedler, came
the first attempt at a complete geography. In and out through the ochre
was traced the blue; commonly in long Mediterraneans of shade, but here
and there in isolated Caspians of color. With our modern telescopic
means the dark patches are easily visible, the very smallest glass
sufficing to disclose them. When thus shown they much resemble in
contour the dark patches on the face of the Moon as seen with the naked
eye. Now these patches were early taken for lunar seas and received
names in keeping with the conception; as the Sea of Serenity, the Sea
of Vapors, and so forth. Following the recognition of a like
appearance, like appellatives were given to the Martian markings; and
the Mare Sirenum, or Sea of the Sirens, the Mare Cimmerium, and others
sufficiently proclaim what was thought of them at the time they were
thus baptized. Indeed, if a general similarity be any warrant for a
generic name they were not at the time ill-termed. For, common to all
three bodies, the Earth, the Moon, and the planet Mars, is the
figuration of their surfaces into light areas and dark. In the Martian
disk, as in the lunar one, we seem to be looking at a cartographic
presentation of some strange geography suspended in the sky; the first
generic difference between the two being that the chart is done in
chiaroscuro for the Moon, in color for Mars. On mundane maps, we know
the dusky washes for oceans; so on the Moon it was only natural to
consider their counterparts as _maria_; and on Mars as ‘seas.’ Nor did
the blue-green hue of the Martian ones detract from the resemblance.
But in something other than color these markings are alike. In fact,
color could hardly be excuse for considering the lunar _maria_ what
their name implies, for distinctive tint is lacking in them, even to
the naked eye. It was in form that the likeness lay. Their figures were
such as our own oceans show; and allowing for a sisterly contrast amid
a sisterly resemblance, the lunar _maria_ or the Martian seas might
well have been of similar origin to those with which our schoolboy
study of atlases had made us familiar. Thus did similarity in look
suggest similarity in origin, and intuitive recognition clothe its
objects with the same specific name.
Considerable assumption, however, underlay the pleasing simplicity of
the correlation on other grounds, consequent not so much upon any lack
of astronomic knowledge as, curiously, upon a dearth of knowledge of
ourselves. We know how other bodies look to us, but we ignore how we
look to them. It is not so easy to see ourselves as others see us; for
a far view may differ from a near one, and a matter of inclination
greatly alter the result. Owing both to distance and to tilt we lack
that practical acquaintance with the aspect of our own oceans viewed
from above, necessary to definite predication of their appearance
across interplanetary space. Our usual idea is that seas show dark, but
it is also quite evident that under some circumstances they appear the
contrary. It all depends upon the position of the observer and upon the
position of the Sun. Their usual ultramarine may become even as molten
brass from indirect reflection; while on direct mirroring, they give
back the Sun with such scarce perceptible purloining of splendor as to
present a dazzling sheen not to be gazed upon without regret. Canopied
by a welkin they assume its leaden hue, while at the same time, their
shores, less impressionable to borrowed lighting, show several tints
darker than themselves. Surfaces so sensitive to illumination hardly
admit of more accusable tint than a chameleon. Nevertheless, we are
probably justified in our conviction that perpendicularly visaged, they
would on the whole outdo in sombreness land round about them, and so be
evident as dusky patches against a brighter ground.
One phenomenon we might with some confidence look to see exhibited by
them were they oceans, and that is the reflected image of the Sun
visible as a burnished glare at a calculable point. Specular reflection
of the sort was early suggested in the case of Mars, and physical
ephemerides for the planet registered for many years the precise spot
where the starlike image should be sought. But it was never seen. Yet
not till the marine character of the Martian seas had been otherwise
disproved was the futile quest for it abandoned. Indeed, it was a tacit
recognition that our knowledge had advanced when this column in the
ephemeris was allowed to lapse.
On this general marine ascription doubt was first cast in the case of
the Moon. So soon as the telescope came to be pointed at our satellite,
it was evident that the darker washes were not water surfaces at all,
but very palpably plains. Long low ridges of elevation stood out upon
them like prairie swells, which grew in visible relief according to the
slanting character of the illumination. Cracks or rills, too, appeared
near their edges and craters showed in their very midst. Patently solid
they betrayed their constitution not only by diverse topography but by
diversified tint. All manner of shades of neutral tone mottled their
surface, from seeming porphyry to chalk. Belief perforce departed when
the telescope thus pricked the bubble, evaporating as the water itself
had done long before.
So much was known before the Mars’ markings were named. Nevertheless,
humanity, true to its instincts, promptly proceeded to commit again the
same mistake, and, cheerfully undeterred by the exposure of its errors
in the case of the Moon, repeated the christening in the case of Mars.
So sure was it of its ground that what it saw was not ground, that
though the particular appellatives of the several seas were constantly
altered, rebaptisms, while changing the personal, kept the generic
name. Dawes’ Ocean, for example, later became l’Ocean Newton and later
still the Mare Erythraeum, but remained set down as much a sea as
before. About thirteen years ago, however, what had befallen the seas
of the Moon, befell those of Mars: the loss of their character. It was
first recognized through a similar exposure; but the fact was led up to
and might have been realized in consequence of quite a different line
of evidence. The initial thing to cast doubt upon the seas being what
they seemed to be was the detection of change in their aspect. That the
detection was not made much earlier than actually happened shows how a
phenomenon may elude observation if scrutiny be not persistent, and its
results from time to time not carefully compared. Schiaparelli was the
one who first noticed variation in the look of the seas, and the
discovery was as much due to the assiduity with which he followed the
planet opposition after opposition as to the keenness with which he
scanned it. The noting of change in the blue-green areas constituted,
in fact, one of the first fruits of systematic study of the planet.
Change in configuration, that is, alteration of area, preceded in
recognition alteration of tint. Thus the Syrtis Major showed larger to
him in 1879 than it had in 1877. This was natural; difference of degree
being a more delicate matter to perceive than its effect upon extent.
From change of area his perception went on to change of tone. In his
own words, what he noticed was this: _Memoria_, VI, 1888, “No less
certain is it that, from one opposition to another, one notices in the
seas, very remarkable alterations of tone. Thus the regions called Mare
Cimmerium, Mare Sirenum, and Solis Lacus, which during the years 1877
to 1879 could be numbered among the most sombre on the planet, during
the succeeding oppositions became less and less black, and in 1888 were
of a light gray hardly sufficient to render them visible in the oblique
position in which all three found themselves.... On the other hand, at
the very same moment, the Mare Acidalium and the Lacus Hyperboreus
showed very dark; the latter indeed appeared nearly black, although
seen as tilted as the Syrtis and the equatorial bays. The condition of
the regions called seas is therefore not constant: so much is
unquestionable. Perhaps the change produced in them has to do with the
season of the planet’s year.”
Holding as he did the then prevailing view that the blue-green regions
were bodies of water, he regarded those of intermediate tint as vast
marshes or swamps, and he accounted for change of hue in them as due to
inundations and occasions of drying up. In consequence of losing their
water, the seas, he thought, had in places become so shallow that the
bottom showed through.
Plausible on the surface, this theory breaks down so soon as it is
subjected to quantitative criticism. For the moment we try to track the
water, we detect the inadequacy of the clew. The enormous areas over
which the phenomenon occurs necessitates the establishing an alibi for
all the lost water that has gone. Drying up on such a scale would mean
the removal of many feet of liquid over hundreds of thousands of miles
in extent. To produce any such change in appearance as we witness, even
on the supposition that these seas were none too deep to start with,
would involve lowering the level of the water by from five to twenty
feet throughout two thirds of the whole surface of the southern
hemisphere. This would leave a heap of waters to be accounted for,
bewildering in its immensity. The myriad tons of it must be disposed
of; either by drainage into other regions or by being caught up into
the sky.
In this emergency it might seem at first as if the polar cap of the
opposite hemisphere offered itself as a possible reservoir for the
momentarily superfluous fluid. But such hoped-for outlet to the problem
is at once closed by the simple fact that when the lightening of the
dark regions of the southern hemisphere takes place, the opposite polar
cap has already attained its maximum; in fact, has already begun to
melt. It, therefore, absolutely refuses to lend itself to any such
service. This was not known to Schiaparelli’s time, the observations
which have established it, by recording more completely the history of
the cap, having since been made. Indeed, it was not known even at the
time when the writer, in 1894, showed the impossibility of the transfer
on other grounds; to wit, on the fact of no commensurate concomitant
darkening of the surface elsewhere and on the manifest non-complicity,
if not impotency, of the Martian atmosphere in the process. The
transference of the water to other dark patches in the northern
hemisphere fails of sufficiency of explanation because of the limited
extent of such areas on that side of the globe; while the air is quite
as incapable of carrying away any such body of liquid, though the whole
of it were at the saturation-point, not to mention that there exists no
sign of the attempt. The reader will find this reasoning set forth in
_Mars_, published eleven years ago. He will now note, from what has
been said above about the northern polar cap, that continued
observations since have resulted in opening up another line of proof
which has only strengthened the conclusion there reached.
[Illustration: Lines in dark area.]
The _coup de grâce_, however, to the old belief was given when the
surface of the dark areas was found to be traversed by permanent lines
by Pickering and Douglass. Continued observation showed these lines to
be unchangeable in place. Now permanent lines cannot exist on bodies of
water, and in consequence the idea that what we looked on there were
water surfaces had to be abandoned.
Thus we now know that the markings on both the Moon and Mars which have
been called _maria_ are not in reality seas. Yet we shall do well still
to keep the old-fashioned sonorous names, Mare Erythraeum, Mare
Sirenum, and their fellows, because it is inconvenient to change;
while, if we please, we may see in their consecrated Latin couching the
fit embalming in a dead language of a conception that itself is dead.
CHAPTER XI
VEGETATION
Since closer acquaintance takes from the _maria_ their character of
seas, we are led to inquire again into their constitution. Now, when we
set ourselves to consider to what such appearances could be due we note
something besides sea, which forms a large part of our earth’s surface,
and would have very much what we suppose the latter’s aspect from afar
to be, not only in tone, but in tint. This something is vegetation.
Seen from a height and mellowed by atmospheric distance, great forests
lose their green to become themselves ultramarine.
To dispossess a previous conception is difficult, but so soon as we
have put the idea of seas out of our heads a vegetal explanation proves
to satisfy the phenomena, even at first glance, better than water
surfaces. In their color, blue-green, the dark areas exactly typify the
distant look of our own forests; whereas we are not at all sure that
seas would. From color alone we are more justified in deeming them
vegetal than marine. But the moment we go farther into the matter the
more certain we become of being upon the right road. With increased
detection the markings they reveal and the metamorphoses they undergo,
while pointing away from water, point as directly to vegetation. All
the inexplicabilities which the supposition of water involves find
instant solution on the theory of vegetal growth. The non-balancing of
the areas of shading in their shift from one part of the disk to
another, no longer becomes a circumstance impossible to explain, but a
necessary consequence of their new-found character, denoting the time
necessary for vegetation to sprout. The change of hue of vast areas
from blue-green to ochre no longer presupposes the bodily transference
of thousands of tons of substance, but the quiet turning of the leaf
under autumnal frosts. Even the fact that they occupy those regions
most fitted by figure to contain oceans fits in with the same
conception. For that the Martian equivalents of forest and moorland,
tree and grass, should grow now in the lowest parts of the planet’s
surface is what might not unreasonably be expected from the very fact
of their being low, since what remained of the water would tend both on
the surface and in the air to drain into them.
[Illustration: Mare Erythræum
Martian date. December 30]
For the change in question to be vegetal it must occur at the proper
season of the planet’s year. This we must now consider. We have said
that Schiaparelli detected change in the blue-green regions and
suspected this change of seasonal affiliation. He inferred this from
piecing together the aspects of different seasons of different years as
shown in consecutive Martian oppositions. To mark it actually take
place in a single Martian year came later. In 1894, at Flagstaff, the
southern hemisphere was presented during its late spring and early
summer; it was observed, too, for many of our months in succession.
During this time the planet was specially well circumstanced for study
of the change in that hemisphere, both by reason of the appositeness of
the season and of the unusual size of the disk. Advantage was taken of
the double event to a recording of the consecutive appearances certain
regions underwent, and the contrasted states thus exhibited were such
as clearly to betoken the action of seasonal change. What Schiaparelli
had thus ably inferred from diverse portions of different Martian years
was in this case shown occurring in one and the same semestral cycle.
Usually the change of hue seems essentially one of tone; the blue-green
fades out, getting less and less pronounced, until in extreme cases
only ochre is left behind. It acts as if the darker color were
superimposed upon the lighter and could be to a greater or less extent
removed. This is what Schiaparelli noted and what was seen in 1894 at
Flagstaff. Three views _en suite_ of the chain of changes then observed
are shown in _Mars_, the region known as Hesperia being central in
each. Comparison of the three discloses a remarkable metamorphosis in
that “promontory,” a rise into visibility by a paling of its
complexion. Nor is the contrast confined to it; changes as salient will
be noticed in the pictures over the other parts of the disk.
There have been instances, however, of a metamorphosis so much more
strange as to deserve exposition in detail; one where not tone simply
is involved, but where a quite new tint has surprisingly appeared.
[Illustration: Mare Erythræum
Martian date. January 16]
On April 19, 1903, when, after being hidden for thirty days, owing to
the different rotation periods of the two planets, the Mare Erythraeum,
the largest blue-green region of the disk and lying in the southern
hemisphere, rounded again into view, a startling transformation stood
revealed in it. Instead of showing blue-green as usual, and as it had
done six weeks before, it was now of a distinct chocolate-brown. It had
been well seen at its previous presentation, so that no doubt existed
of its then tint. At that time the Martian season corresponded to
December 30 in our calendar. Eighteen Martian days had since elapsed,
and it was now January 16 there. The metamorphosis had taken place,
therefore, shortly after the winter solstice of that part of the
planet. The color change that had supervened proved permanent. For the
next night the region showed the same brown hue, and so it continued to
appear throughout the days that it was visible. Two months passed, and
then the chocolate hue had vanished,—gone as it had come,—and the
_mare_ had resumed its usual tint, except for being somewhat pale at
the south. It had come to be February 21 on Mars. Timed and tabulated,
the metamorphosis through which the _mare_ passed stands out thus:—
MARE ERYTHRAEUM 1903
============+================+=============+==================
| DAYS BEFORE OR | |
| AFTER SUMMER | |
MUNDANE | SOLSTICE | MARTIAN |
DATE | (BEFORE = - | DATE | ASPECT
| AFTER = +) | |
------------+----------------+-------------+------------------
February 16 | -10 | December 16 | Blue-green
March 20 | +22 | January 1 | Blue-green
April 19 | 52 | January 16 | Chocolate
April 22 | 55 | January 18 | Chocolate
May 26 | 89 | February 4 | Faint chocolate
May 30 | 93 | February 6 | Faint chocolate
June 30 | 123 | February 22 | Faint blue-green
July 7 | 130 | February 25 | Faint blue-green
============+================+=============+==================
The culmination of the transformation seems to have taken place about
60 days after the southern winter solstice, or in the depth of the
Martian winter of that hemisphere. This is certainly just the time at
which vegetation should be at its deadest.
The northern and southern portions of the _mare_ did not behave alike
in taking on the chocolate tint. From the notes made about them during
the opposition it appears that the latter was later than the former in
undergoing the metamorphosis, as will be seen from the following depth
of the blue green estimated in percentages shown at different dates,
calling the deepest tone ever exhibited by it unity.
=========+==========+=========+=========+==========+==========
MARTIAN | DECEMBER | JANUARY | JANUARY | FEBRUARY | FEBRUARY
DATE, | (16) | (1) | (17) | (5) | (24)
---------+----------+---------+---------+----------+----------
| % | % | % | % | %
Northern | 50 | 50 | 0 | 25 | 50
Southern | 50 | 50 | 0 | 0 | 25
=========+==========+=========+=========+==========+==========
From this table we may place the lowest point of the blue-green tint as
reached about the 22d of January for the northern, the 5th of February
for the southern, part. This would indicate that the wave of returning
growth came from the north, not the south; an important fact, as we
shall see later in studying the action of the canals.
[Illustration: Mare Erythræum
Martian date. February 1]
At the next opposition, in 1905, a recurrence of the transformation was
watched for, and not in vain. It occurred, however, somewhat later in
the Martian season. On December 27 of the planet’s current year the
Mare Erythraeum was still as usual, blue-green, nothing out of the
ordinary being remarked in it; and so it was on its January 17,
although the southern edge was darker than the northern. It looked
certainly as if the metamorphosis were this year to be omitted. But
such was not the case. When the region again came round, on February 1
of the Martian calendar, there the strange tint was as unmistakable as
it had been on its original occurrence. Not only was the Mare
Erythraeum so colored, but on February 5 (Martian) the northern portion
of the Mare Cimmerium was observed to be similarly affected. In the
Mare Erythraeum the anomalous chocolate hue was confined to a belt
between the latitudes of 10° and 20° south of the equator; in the Mare
Cimmerium it stretched a little higher, from 10° at the west to 25° at
the east. It is noteworthy that the southern portion of the latter
showed blue at the time the northern showed brown. Then the
metamorphosis proceeded as shown in the following table:—
MARE ERYTHRAEUM 1905
===========+======================+=============+=================
| DAYS AFTER WINTER | |
MUNDANE | SOLSTICE OF SOUTHERN | MARTIAN | ASPECT
DATE | HEMISPHERE | DATE |
-----------+----------------------+-------------+-----------------
January 25 | 12 | December 27 | Blue-green
March 6 | 52 | January 16 | Blue-green
April 4 | 81 | January 31 | Chocolate
April 12 | 89 | February 4 | Chocolate
April 30 | 107 | February 13 | Faint chocolate
May 8 | 115 | February 17 | Faint chocolate
May 12 | 119 | February 19 | Faint blue-green
June 11 | 149 | March 6 | Faint blue-green
June 15 | 153 | March 8 | Faint blue-green
July 16 | 184 | March 23 | Pale bluish green
===========+======================+=============+==================
Here, as in 1903, a chromatic rise and fall is evident; the culmination
of the change occurring in Martian early February about ninety days
after the winter solstice. That it was not of long duration is also
indicated. If we examine the evidence for the two portions of the
_mare_ separately, the northern and the southern, as in 1903, we find
it as follows:—
=========+==========+=========+==========+==========+=======+========
| | | | | |
MARTIAN | DECEMBER | JANUARY | FEBRUARY | FEBRUARY | MARCH | MARCH
DATE, | (27) | (16) | (2) | (16) | (7) | (23)
---------+----------+---------+----------+----------+-------+--------
| % | % | % | % | % | %
Northern | 50 | 50 | 0 | 10 | 25 | 30
Southern | 50 | 50 | 20 | 20 | 25 | 30
=====================================================================
Here again a slight retardation in the advent of the metamorphosis is
observable in the southern portion.
There would seem to be a difference in the time of the change between
the two years of fifteen days, 1905 being by that much the later. But
with points of reference themselves thirty days apart, it is possible
the two more nearly coincided than here appears.
Unlike the ochre of the light regions generally, which suggest desert
pure and simple, the chocolate-brown precisely mimicked the complexion
of fallow ground. When we consider the vegetal-like blue-green that it
replaced, and remember further the time of year at which it occurred
upon both these Martian years, we can hardly resist the conclusion that
it was something very like fallow field that was there uncovered to our
view.
[Illustration: Mare Erythræum
Martian date. February 21]
From the recurrence of the phenomenon on two successive years, it is
likely that it annually takes place. That it is seasonal can scarcely
be doubted from the timeliness of its occurrence, and that different
portions of its terrane successively underwent their metamorphosis
shows further that it followed a law peculiar to the planet, to which
we shall be introduced when we come to consider the phenomena of the
canals.
Instances of relative hue in different dark patches corroboratory of
seasonal variation, and therefore of vegetal constitution, might easily
be adduced. Thus, in 1905 during the summer of the northern hemisphere,
the Mare Acidalium was notably darker than the Mare Erythraeum to the
north of it, which is what the law of seasonal variation would require,
since it was June in the one, December in the other at the time. But we
need not to add example to example or proof to proof, for there are no
phenomena that contradict it. We conclude, therefore, that the
blue-green areas of Mars are not seas, but areas of vegetation. Just as
reasoning to a negative result drifts us to the first conclusion, so
reasoning to a positive one lands us at the second.
CHAPTER XII
TERRAQUEOUSNESS AND TERRESTRIALITY
With the vanishing of its seas we get for the first time solid ground
on which to build our Martian physiography. The change in _venue_ from
oceans to land has produced a complete alteration in our judgment of
the present state of the planet. It destroys the analogy which was
supposed to exist between Mars and our earth, and by abolishing the
actuality of oceans there, seems, metaphorically, to put us at first
all the more at sea in our attempt to understand the planet. But looked
at more carefully, it turns out to explain much that was obscure, and
in so doing gives us at once a wider view of the history of planetary
evolution.
The trait concerned is cosmic. Study of the several planets of our
solar system, notably the Earth, Moon, and Mars, reveals tolerably
legibly an interesting phase of a planet’s career, which apparently
must happen to all such bodies, and evidently has happened or is
happening to these three: the transition of its surface from a
terraqueous to a purely terrestrial condition. The terraqueous state is
well exhibited by our own earth at the moment, where lands and oceans
share the surface between them. The terrestrial is exemplified by both
the Moon and Mars, on whose surfaces no bodies of water at present
exist. That the one state passes by process of development into the
other I shall now give my reasons for believing.
In the first place the appearance of the dark markings both on the Moon
and Mars hints that though seas no longer, they were seas once upon a
time. On the moon, not only does their shape suggest this previous
condition, but the smooth and even look of their surfaces adds to the
cogency of the inference. More important, however, than either of these
characteristics, and confirmatory of both, is the fact that the great
tracts in question seem to lie below the level of the corrugated
surface, which is thickly strewn with volcanic cones. Their level and
their levelness fay in explanation into one another. The first makes
possible the former presence of water; the second speaks of its effect.
For their flat character hints that these areas were held down at the
time when the other parts of the surface were being violently thrown
up. That they can themselves be cooled lava flows, their extent and
position seem enough to negative; to say nothing of the fact that they
should in that case lie above, not below, the general level. Something,
therefore, covered them during the moon’s eruptive youth and
disappeared later. Such superincumbence may well have been water, under
which the now great plains lay then as ocean bottoms. Deep-sea
soundings in our own oceans betray an ocean floor of the same extensive
sort, diversified as on the moon. To call the lunar _maria_ seas may
not be so complete a misnomer after all; but only a resurrecting in
epitaph what was the truth in its day.
Only doubtfully offered here for the Moon, for Mars the inference seems
more sure. Here again the dark regions not only look as they should had
they had an earlier history, but they, too, seem to lie below the level
of the surface round about. When they pass over the terminator they
invariably show as flattenings upon it, as if a slice of the surface
had been pared off. Such profile in such pass is what ground at a lower
level would present. Undoubtedly a part of the seeming depression is
due to relative absence of irradiation consequent upon a more sombre
tint, but loss of light hardly seems capable of the whole effect. In
the case of Mars, then, as with the Moon, a mistaken inference builded
better than it knew, if, indeed, we should rightly consider an
inference to be mistaken which on half data lands us at the right door.
From the aspects of the dark regions we are led, then, to regard Mars
as having passed through that stage of existence in which the earth
finds itself at the moment, the stage at which oceans and seas form a
feature of its landscape and an impediment to subjugation of its
surface in its entirety. What once were ocean beds have become ocean
bottoms devoid of that which originally filled them.
That the process of parting with a watery envelop is an inevitable
concomitant of the evolution of a planet from chaos to world, we do not
have to go so far afield as Mars and the Moon for testimony. Scrutiny
reveals as much in the history of our own globe. Two signposts of the
past, one geologic, the other paleontologic, point unmistakably in this
direction. The geologic guides us the more directly to the goal.
Study of the earth’s surface reveals the preponderating encroachment of
the land upon the sea since both began to be, and demonstrates that,
except for local losses, the oceans have been contracting in size from
archaic times. So much is evidenced by the successive places upon which
marine beds have been laid down. This suggests itself at once as a
theoretic probability to one considering the matter from a cosmic
standpoint, and it is therefore the more interesting and conclusive
that, from an entirely different departure-point, it should have been
one of the pet propositions of the late Professor Dana, who worked out
conclusively the problem for North America, and published charts
detailing the progressive making of that continent.
[Illustration: Map of North America at the close of Archæan time,
showing approximately the areas of dry land. (From Dana’s “Manual of
Geology.”)]
So telling is this reclaiming by nature of land from the sea that it
will be well to follow Dana a little into detail, as the details show
effectively the continuity of the process acting through æons of
geologic time. At the beginning of the Archæan age, or, in other words,
at the epoch when stratified beds were first laid down, the earth
reached a turning-point in its history. Erosion, superficial and
sub-aërial, then set in to help restrict the domain of the sea. At this
juncture North America consisted of a sickle of terrane inclosing
Hudson’s Bay and coming down at its apex to a point not much removed
from where Ottawa now stands, in about latitude 45°—a Labradorian
North America only. This, the kernel of the future continent, curiously
symbolized the form that continent was later to take. For its eastern
edge was roughly parallel to the present Atlantic coastline, although
much within and to the north of it, while its western one was similarly
aligned afar off to the now Pacific slope. Besides this continent
proper, the Appalachian, Rocky Mountain, Sierra Nevada, and Sierra
Madre chains stood out of the ocean in long, narrow ridges of detached
land, outlining in skeleton the bones of the continent that was to be.
The Black Hills of Dakota and other highlands made here and there
islets in the sea.
Much the same backbone-showing of continents yet to be filled out was
true of Europe, Asia, and South America. In Europe the northern
countries constituted all that could be called continental land. Most
of Norway, Sweden, Finland, Lapland, existed then, while the northern
half of Scotland, the outer Hebrides, portions of Ireland, England,
France, and Germany stood out as detached islands. From this, which is
a fair sample of the proportion of land then to land now over the other
continents so far as they are geologically known, we turn to consider
more in detail the history of North America.
By the time the Upper Silurian period came in, the Appalachian
highlands there had been greatly extended and joined to the Labradorian
mainland by continuous territory; otherwise, no important addition had
occurred, though islands emerged in Ohio, Kentucky, and Missouri.
[Illustration: North America at the opening of the Upper Silurian.
(From Dana’s “Manual of Geology.”)]
At the commencement of the Carbonic era what are now the Middle states
had begun to fill up from the north, and Newfoundland, from a small
island in the Upper Silurian, had become a great promontory of
Labrador, while the Eastern states region and Nova Scotia had risen
into being. The movements closing Paleozoic time upheaved from low
islands the Appalachian chain. The earth’s crust here crumpled by
contraction upon itself; and the movement ended, as Dana says, by
making dry land of the whole eastern half of the continent, along
substantially its present lines.
[Illustration: Map of North America after the Appalachian Revolution.
(From Dana’s “Manual of Geology.”)]
Mesozoic time was the period of the making of the West. It was an era
of deposition and coincident subsidence, when the western land had its
nose just above water at one moment to be submerged the next. Though on
the whole this part of the continent was emerging, the fact was that,
synchronously with the sinking of the sea, much of the land from time
to time sank too. The contraction which raised the Appalachian Mountains
at the beginning of the period and that of the Rockies at its close
overdid the necessities of the case and caused subsidence elsewhere.
The southeastern portion of the continent suffered most, the West on
the whole materially gaining. In the Triassic and Jurassic eras the
gain was pronounced; it occurred in the Cretaceous also, but with much
alternation of loss. Finally, at the close of the Cretaceous, the
continent, except for a prolonged Gulf of Mexico and vast internal
lakes, was substantially complete.
[Illustration: North America in the Cretaceous period. (From Dana’s
“Manual of Geology.”)]
The filling up of these lakes and the reclaiming of land from the Gulf
of Mexico constituted the land-making work of Tertiary times. The
extent of the lakes in the Eocene era is held to show that the general
level of the mountain plateau was low and rose later. So that the gain
by the land at this time was greater than the map allows to appear. By
the beginning of the Quaternary epoch the continents had assumed their
present general area, and since then their internal features have alone
suffered change.
[Illustration: Map of North America, showing the parts under water in
the Tertiary Era; the vertically lined is the Eocene. (From Dana’s
“Manual of Geology.”)]
A similar rising from the sea fell to the lot of Europe, though it has
not been detailed with so much care. The skeleton of that continent was
at the beginning of depositary time much what it is to-day, but a great
inland sea occupied the centre of it, which, as time went on, was
gradually silted in and evaporated away, notably during the Upper
Silurian period.
From all this it is pretty clear that, side by side with alternating
risings and sinkings of the land, there was a tolerably steady gain in
the contest by which dry ground dispossessed the sea. We may, of
course, credit this to a general deepening of the ocean bottoms due to
crumpling of the crust, but we may also impute it to a loss of water,
and that the latter is, at least for a part, in the explanation the
condition of the Moon and Mars makes probable.
Paleontology has the same story of reclamation to tell as geology, and
with as much certainty, though its evidence is circumstantial instead
of direct and speaks for the growing importance of the land in the
globe’s economy since the beginning of depositary time, and thus
inferentially to its increasing extent. Fossil remains of the plants
and creatures that have one after the other inhabited the earth show
that the land has been steadily rising both in floral and faunal
estimation as a habitat from the earliest ages to the present day. The
record lies imprinted in the strata consecutively laid down, and except
for gaps reads as directly on in bettering domicile as in evolutionary
development.
In Archæan times we find no undisputed evidence of life either vegetal
or animal. But beds of graphite and of limestone point to the possible
existence of both. Even anthracite has been found in Archæan rocks in
Norway and also in Rhode Island. Whether Dawson’s Eozoon Canadense be a
rhizopod or a crystal, doctors of science disagree. Dana, while
admitting nothing specific, deems it antecedently probable that algæ
and later microscopic fungi related to bacteria existed then, living in
water well up toward the boiling-point. Indeed, it is practically
certain that invertebrate life existed, because of its already
well-developed character in the next era. The like antedating is
inferable for the whole record of the rocks. Relatively their history
is undoubtedly fairly accurate, but absolutely it must be shifted
bodily backward into the next preceding era to correspond with fact not
yet unearthed.
In the Lower Cambrian, when first the existence of life becomes a
certainty, that life, so far as known, was wholly invertebrate and
wholly marine; rhizopods (probably), sponges and corals, echinoderms,
worms, brachiopods, mollusks, and crustaceans grew amid primitive
seaweed and have left their houses in the shape of shells while
perishing themselves. Their tracks too have thus survived. The
trilobites, crustaceans somewhat resembling our horseshoe crab, were
the lords of the Cambrian seas and marked the point to which organic
evolution had then attained. Their aquatic character as well as their
simple type is shown by their thoracic legs having each a natatory
appendage.
In the next era, the Lower Silurian, the fauna and flora were still
marine, although of a higher order than before, and in the Trenton
period, the upper part of the era, the earliest vertebrates, fishes,
come upon the scene: ganoids and possibly sharks. Nothing terrestrial
of this period has yet with certainty been unearthed in America. Europe
would seem to have either been more advanced then or better studied
since, for there the first plant higher than a seaweed has been dug up,
one of a fresh-water genus betokening the land; while in keeping with
this the first insect, an hemipter, also has been disinterred. Both the
geography and the life of the Eopaleozoic period Dana styles
“thalassic.”
Neopaleozoic time, beginning with the Upper Silurian, marked the
emergence of the continents, and following them the emergence of life
from the water on to this land. In the lower beds of the Upper Silurian
in America we find only the aquatic forms of previous strata, but in a
higher one we come in marshes upon plants related to the equiseta or
horsetails. In England land plants appear for the first time in these
latest Silurian beds and in the schists of Angers have been preserved
ferns. In both the old world and the new fossil fishes are found and
the oldest terrestrial species of scorpions. But the great bulk of
forms was still marine; corals, crinoids, brachiopods, trilobites
constituting the principal inhabitants. At this time the seas were
warm, having much the same temperature between 65° and 80° north as
between 30° and 45°; the prevalence of a general temperate tropicality
being shown by the fact that the common tropical chain corals lived in
latitude 82° north.
In the Devonian era, the Old Red Sandstone, fishes grew and multiplied,
increasing in size apparently through the era, and in the last period
of it reaching their culminating point. These pelagic vertebrates much
surpassed in structure the terrestrial population of the time, which
was of a low type and consisted of invertebrates such as myriapods,
spiders, scorpions, and insects; for the land was only making. In the
mid-Devonian, forests of a primitive kind covered such country as there
was, an amphibious land, composed of jungles and widespread marshes.
Tree ferns made the bulk of the vegetation, but among them grew also
cycads and yews. Mammoth may-flies flitted through the gloom of these
old forests, but no vertebrate as yet had left the sea.
Following upon the Old Red Sandstone were laid down the Carbonic
strata, and with the Carbonic entered upon the scene the advance scouts
of an army of progress evolutionarily impelled to spy out the land—the
first amphibians. They made their début in the Subcarboniferous section
of the era, the oldest of the three periods into which the Carbonic is
divided, crawling out of the sea to return again and leaving but
footprints at first on the sands of time. In the second period, the
Coal-measures proper, they ventured so far as to leave their skeletons
on terra firma, or rather infirma, while their tracks there show them
to have been now in great numbers. In this manner the ancestors of the
oldest land inhabitants began to struggle out of the sea. In the
Permian, the third and latest period of paleozoic times, we find their
descendants established in their new habitat, for in it we come upon
the first reptiles. Such possession marks a distinct step up in
function as in fact, for while amphibians visited dry land, reptiles
made it their home. The getting out of the water had now, in the case
of the more evolved forms, become an accomplished fact. The reptiles
were, indeed, the lowest and most generalized of their class,
Rhynchocephalians, “beak-headed” species that by their teeth proclaim
their marine origin and their relationship to the great amphibians that
still felt undecided where to stay. Meanwhile, in Europe dragon-flies,
two feet across, possessed the air; while amphibians there, as here,
ancestrally preceded reptiles in occupying the land.
Mesozoic times were, _par excellence_, the age of monsters; for the
Triassic (the New Red Sandstone), Jurassic and Cretaceous eras marked
the reign of the reptiles. Great dinosaurs slee
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