THE CANALS OF MARS
Then there are the so-called canals of Mars, about which so much is
written and relatively little known. Faint markings which resemble them
in character were first drawn in 1840 and later in 1864, but
Schiaparelli, the famous Italian astronomer, is probably their original
discoverer, when Mars was at its least distance from the earth in 1877.
He made the first accurate detailed map of Mars at this time, and most
of the important or more conspicuous canals (_canali_, he called them in
Italian, that is, channels merely, without any reference whatever to
their being watercourses) were accurately charted by him.
At all the subsequent close approaches of Mars, the canals have been
critically studied by a wide range of astronomical observers, and their
conclusions as to the nature and visibility of the canals have been
equally wide and varied. The most favorable oppositions have occurred in
1892 and 1894, also in 1907 and 1909. On these occasions a close minimum
distance of Mars was reached, that is, about 35 millions of miles; but
in 1924 the planet makes the closest approach in a period of nearly a
thousand years. Its distance will not much exceed 34 millions of miles.
But although this is a minimum distance for Mars, it must not be
forgotten that it is a really vast distance, absolutely speaking; it is
something like 150 times greater than the distance of the moon. With no
telescopic power at our command could we possibly see anything on the
moon of the size of the largest buildings or other works of human
intelligence; so that we seem forever barred from detecting anything of
the sort on Mars.
Nevertheless, the closest scrutiny of the ruddy planet by observers of
great enthusiasm and intelligence, coupled with imagination and
persistence, have built up a system of canals on Mars, covering the
surface of the planet like spider webs over a printed page, crossing
each other at intersecting spots known as "lakes," and embodying a
wealth of detail which challenges criticism and explanation.
To see the canals at all requires a favorable presentation of Mars, a
steady atmosphere and a perfect telescope, with a trained eye behind it.
Not even then are they sure to be visible. The training of the eye has
no doubt much to do with it. So photography has been called in, and very
excellent pictures of Mars have already been taken, some nearly half as
large as a dime, showing plainly the lights and shades of the grander
divisions of the Martian surface, but only in a few instances revealing
the actual canals more unmistakably than they are seen at the eyepiece.
The appearance and degree of visibility of the canals are variable:
possibly clouds temporarily obscure them. But there is a certain
capriciousness about their visibility that is little understood. In
consequence of the changing physical aspects, as to season, on Mars and
his orbital position with reference to the earth, some of the canals
remain for a long time invisible, adding to the intricacy of the
puzzle.
For the most part the canals are straight in their course and do not
swerve much from a great circle on the planet. But their lengths are
very different, some as short as 250 miles, some as long as 4,000 miles;
and they often join one another like spokes in the hub of a wheel,
though at various angles. As depicted by Lowell and his corps of
observers at Flagstaff, Arizona, the canal system is a truly marvelous
network of fine darkish stripes. Their color is represented as a bluish
green.
Each marking maintains its own breadth throughout its entire length, but
the breadth of all the canals is by no means the same: the narrowest are
perhaps fifteen to twenty miles wide, and the broadest probably ten
times that. At least that must be the breadth of the Nilosyrtis, which
is generally regarded as the most conspicuous of all the canals. The
Lowell Observatory has outstripped all others in the number of canals
seen and charted, now about 500.
What may be the true significance of this remarkable system of markings
it is impossible to conclude at present. Schiaparelli from his long and
critical study of them, their changes of width and color, was led to
think that they may be a veritable hydrographic system for distributing
the liquid from the melting polar snows. In this case it would be
difficult to escape the conviction that the canals have, at least in
part, been designed and executed with a definite end in view.
Lowell went even farther and built upon their behavior an elaborate
theory of life on the planet, with intelligent beings constructing and
opening new canals on Mars at the present epoch. Pickering propounded
the theory that the canals are not water-bearing channels at all, but
that they are due to vegetation, starting in the spring when first seen
and vitalized by the progress of the season poleward, the intensity of
color of the vegetation coinciding with the progress of the season as we
observe it.
Extensive irrigation schemes for conducting agricultural operations on a
large scale seem a very plausible explanation of the canals, especially
if we regard Mars as a world farther advanced in its life history than
our own. Erosion may have worn the continents down to their minimum
elevation, rendering artificial waterways not difficult to build; while
with the vanishing Martian atmosphere and absence of rains, the
necessity of water for the support of animal and vegetal life could only
be met by conducting it in artificial channels from one region of the
planet to another.
Interesting as this speculative interpretation is, however, we cannot
pass by the fact that many competent astronomers with excellent
instruments finely located have been unable to see the canals, and
therefore think the astronomers who do see them are deceived in some
way. Also many other astronomers, perhaps on insufficient grounds, deny
their existence _in toto_.
Many patient years of labor would be required to consult all the
literature of investigation of the planet Mars, but much of the detail
has been critically embodied in maps at different epochs, by Kayser,
Proctor, Green, and Dreyer. And Flammarion in two classic volumes on
Mars has presented all the observations from the earliest time, together
with his own interpretation of them. Areography is a term sometimes
applied to a description of the surface of Mars, and it is scarcely an
exaggeration to say that areography is now better known than the
geography of immense tracts of the earth.
For some reason well recognized, though not at all well understood, Mars
although the nearest of all the planets, Venus alone excepted, is an
object by no means easy to observe with the telescope. Possibly its
unusual tint has something to do with this. With an ordinary opera glass
examine the moon very closely, and try to settle precise markings,
colors, and the nature of objects on her surface; Mars under the best
conditions, scrutinized with our largest and best telescope, presents a
problem of about the same order of difficulty. There are delicate and
changing local colors that add much uncertainty. Nevertheless, the
planet's leading features are well made out, and their stability since
the time of the earliest observers leaves no room to doubt their reality
as parts of a permanent planetary crust.
The border of the Martian disk is brighter than the interior, but this
brightness is far from uniform. Variations in the color of the markings
often depend on the planet's turning round on its axis, and the relation
of the surface to our angle of vision. If we keep in mind these
obstacles to perfect vision in our own day, it is easy to see why the
early users of very imperfect telescopes failed to see very much, and
were misled by much that they thought they saw. Then, too, they had to
contend, as we do, with unsteadiness of atmosphere, which is least
troublesome near the zenith.
As their telescopes were all located in the northern hemisphere, the
northern hemisphere of Mars is the one best circumstanced for their
investigation; because at the remote oppositions of Mars, which always
happen in our northern winter with the planet in high north declination,
it is always the north pole of Mars which is presented to our view.
Whereas the close oppositions of the planet always come in our northern
midsummer, with Mars in south declination and therefore passing through
the zenith of places in corresponding south latitude.
With Mars near opposition, high up from the horizon, a fairly steady
atmosphere, and a magnifying power of at least 200 diameters, even the
most casual observer could not fail to notice the striking difference in
brightness of the two hemispheres: the northern chiefly bright and the
southern markedly dark. Formerly this was thought to indicate that the
southern hemisphere of Mars was chiefly water and the northern land,
much as is the case on the earth: with this difference, however, that
water and land on the earth are proportioned about as eleven to four.
But Mars in its general topography presents no analogy with the present
relation of land and water on the earth. There seems no reason to doubt
that the northern regions with their prevailing orange tint, in some
places a dark red and in others fading to yellow and white, are really
continental in character. Other vast regions of the Martian surface are
possibly marshy, the varying depth of water causing the diversity of
color. If we could ever catch a reflection of sunlight from any part of
the surface of Mars, we might conclude that deep water exists on the
planet; but the farther research progresses, the more complete becomes
the evidence that permanent water areas on Mars, if they exist at all,
are extremely limited.
Since 1877 Mars has been known to possess two satellites, which were
discovered in August of that year by Hall at Washington. Moons of this
planet had long been suspected to exist and on one or two previous
occasions critically looked for, though without success. In the writings
of Dean Swift there is a fanciful allusion to the two moons of Mars; and
if astronomers had chanced to give serious attention to this, Phobos and
Deimos, as Hall named them, might have been discovered long before.
They are very small bodies, not only faint in the telescope, but
actually of only ten or twenty miles diameter; and from the strange
relation that Phobos, the inner moon, moves round Mars three times while
the planet itself is turning round only once on its axis, some
astronomers incline to the hypothesis that this moon at least was never
part of Mars itself, but that it was originally an inner or very
eccentric member of the asteroid group, which ventured within the sphere
of gravitation of Mars, was captured by that planet, and has ever since
been tributary to it as a secondary body or satellite.