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.