THE CLIMATE AND PHYSIOGRAPHY OF MARS.
Mr. Lowell admits, and indeed urges strongly, that there are no
permanent bodies of water on Mars; that the dark spaces and spots,
thought by the early observers to be seas, are certainly not so now,
though they may have been at an earlier period; that true clouds are
rare, even if they exist, the appearances that have been taken for them
being either dust-storms or a surface haze; that there is consequently
no rain, and that large portions (about two-thirds) of the planet's
surface have all the characteristics of desert regions.
_Snow-caps the only Source of Water._
This state of things is supposed to be ameliorated by the fact of the
polar snows, which in the winter cover the arctic and about half the
temperate regions of each hemisphere alternately. The maximum of the
northern snow-caps is reached at a period of the Martian winter
corresponding to the end of February with us. About the end of March the
cap begins to shrink in size (in the Northern Hemisphere), and this goes
on so rapidly that early in the June of Mars it is reduced to its
minimum. About the same time changes of colour take place in the
adjacent darker portions of the surface, which become at first bluish,
and later a decided blue-green; but by far the larger portion, including
almost all the equatorial regions of the planet, remain always of a
reddish-ochre tint.[4]
[Footnote 4: In 1890 at Mount Wilson, California, Mr. W.H. Pickering's
photographs of Mars on April 9th showed the southern polar cap of
moderate dimensions, but with a large dim adjacent area. Twenty-four
hours later a corresponding plate showed this same area brilliantly
white; the result apparently of a great Martian snowfall. In 1882 the
same observer witnessed the steady disappearance of 1,600,000 square
miles of the southern snow-cap, an area nearly one-third of that
hemisphere of the planet.]
The rapid and comparatively early disappearance of the white covering
is, very reasonably, supposed to prove that it is of small thickness,
corresponding perhaps to about a foot or two of snow in north-temperate
America and Europe, and that by the increasing amount of sun-heat it is
converted, partly into liquid and partly into vapour. Coincident with
this disappearance and as a presumed result of the water (or other
liquid) producing inundations, the bluish-green tinge which appears on
the previously dark portion of the surface is supposed to be due to a
rapid growth of vegetation.
But the evidence on this point does not seem to be clear or harmonious,
for in the four coloured plates showing the planet's surface at
successive Martian dates from December 30th to February 21st, not only
is a considerable extent of the south temperate zone shown to change
rapidly from bluish-green to chocolate-brown and then again to
bluish-green, but the portions furthest from the supposed fertilising
overflow are permanently green, as are also considerable portions in the
opposite or northern hemisphere, which one would think would then be
completely dried up.
_No Hills upon Mars._
The special point to which I here wish to call attention is this. Mr.
Lowell's main contention is, that the surface of Mars is wonderfully
smooth and level. Not only are there no mountains, but there are no
hills or valleys or plateaux. This assumption is absolutely essential to
support the other great assumption, that the wonderful network of
perfectly straight lines over nearly the whole surface of the planet are
irrigation canals. It is not alleged that irregularities or undulations
of a few hundreds or even one or two thousands of feet could possibly be
detected, while certainly all we know of planetary formation or
structure point strongly towards _some_ inequalities of surface. Mr.
Lowell admits that the dark portions of the surface, when examined on
the terminator (the margin of the illuminated portion), do _look_ like
hollows and _may be_ the beds of dried-up seas; yet the supposed canals
run across these old sea-beds in perfect straight lines just as they do
across the many thousand miles of what are admitted to be deserts--which
he describes in these forcible terms: "Pitiless as our deserts are, they
are but faint forecasts of the state of things existent on Mars at the
present time."
It appears, then, that Mr. Lowell has to face this dilemma--_Only if the
whole surface of Mars is an almost perfect level could the enormous
network of straight canals, each from hundreds to thousands of miles
long, have been possibly constructed by intelligent beings for purposes
of irrigation; but, if a complete and universal level surface exists no
such system would be necessary._ For on a level surface--or on a
surface slightly inclined from the poles towards the equator, which
would be advantageous in either case--the melting water would of itself
spread over the ground and naturally irrigate as much of the surface as
it was possible for it to reach. If the surface were not level, but
consisted of slight elevations and expressions to the extent of a few
scores or a few hundreds of feet, then there would be no possible
advantage in cutting straight troughs through these elevations in
various directions with water flowing at the bottom of them. In neither
case, and in hardly any conceivable case, could these perfectly straight
canals, cutting across each other in every direction and at very varying
angles, be of any use, or be the work of an intelligent race, if any
such race could possibly have been developed under the adverse
conditions which exist in Mars.
_The Scanty Water-supply._
But further, if there were any superfluity of water derived from the
melting snow beyond what was sufficient to moisten the hollows indicated
by the darker portions of the surface, which at the time the water
reaches them acquire a green tint (a superfluity under the circumstances
highly improbable), that superfluity could be best utilised by widening,
however little, the borders to which natural overflow had carried it.
Any attempt to make that scanty surplus, by means of overflowing canals,
travel across the equator into the opposite hemisphere, through such a
terrible desert region and exposed to such a cloudless sky as Mr. Lowell
describes, would be the work of a body of madmen rather than of
intelligent beings. It may be safely asserted that not one drop of water
would escape evaporation or insoak at even a hundred miles from its
source. [5]
[Footnote 5: What the evaporation is likely to be in Mars may be
estimated by the fact, stated by Professor J.W. Gregory in his recent
volume on 'Australia' in _Stanford's Compendium_, that in North-West
Victoria evaporation is at the rate of ten feet per annum, while in
Central Australia it is very much more. The greatly diminished
atmospheric pressure in Mars will probably more than balance the loss of
sun-heat in producing rapid evaporation.]
_Miss Clerke on the Scanty Water-supply._
On this point I am supported by no less an authority than the historian
of modern astronomy, the late Miss Agnes Clerke. In the _Edinburgh
Review_ (of October 1896) there is an article entitled 'New Views about
Mars,' exhibiting the writer's characteristic fulness of knowledge and
charm of style. Speaking of Mr. Lowell's idea of the 'canals' carrying
the surplus water across the equator, far into the opposite hemisphere,
for purposes of irrigation there (which we see he again states in the
present volume), Miss Clerke writes: "We can hardly imagine so shrewd a
people as the irrigators of Thule and Hellas[6] wasting labour, and the
life-giving fluid, after so unprofitable a fashion. There is every
reason to believe that the Martian snow-caps are quite flimsy
structures. Their material might be called snow _soufflé_, since, owing
to the small power of gravity on Mars, snow is almost three times
lighter there than here. Consequently, its own weight can have very
little effect in rendering it compact. Nor, indeed, is there time for
much settling down. The calotte does not form until several months after
the winter solstice, and it begins to melt, as a rule, shortly after the
vernal equinox. (The interval between these two epochs in the southern
hemisphere of Mars is 176 days.) The snow lies on the ground, at the
outside, a couple of months. At times it melts while it is still fresh
fallen. Thus, at the opposition of 1881-82 the spreading of the northern
snows was delayed until seven weeks after the equinox: and they had,
accordingly, no sooner reached their maximum than they began to decline.
And Professor Pickering's photographs of April 9th and 10th, 1890,
proved that the southern calotte may assume its definitive proportions
in a single night.
[Footnote 6: Areas on Mars so named.]
"No attempt has yet been made to estimate the quantity of water
derivable from the melting of one of these formations; yet the
experiment is worth trying as a help towards defining ideas. Let us
grant that the average depth of snow in them, of the delicate Martian
kind, is twenty feet, equivalent at the most to one foot of water. The
maximum area covered, of 2,400,000 square miles, is nearly equal to that
of the United States, while the whole globe of Mars measures 55,500,000
square miles, of which one-third, on the present hypothesis, is under
cultivation, and in need of water. Nearly the whole of the dark areas,
as we know, are situated in the southern hemisphere, of which they
extend over, at the very least, 17,000,000 square miles; that is to say,
they cover an area, in round numbers, seven times that of the snow-cap.
Only one-seventh of a foot of water, accordingly, could possibly be
made available for their fertilisation, supposing them to get the entire
advantage of the spring freshet. Upon a stint of less than two inches of
water these fertile lands are expected to flourish and bear abundant
crops; and since they completely enclose the polar area they are
necessarily served first. The great emissaries for carrying off the
surplus of their aqueous riches, would then appear to be superfluous
constructions, nor is it likely that the share in those riches due to
the canals and oases, intricately dividing up the wide, dry, continental
plains, can ever be realised.
"We have assumed, in our little calculation, that the entire contents of
a polar hood turn to water; but in actual fact a considerable proportion
of them must pass directly into vapour, omitting the intermediate stage.
Even with us a large quantity of snow is removed aerially; and in the
rare atmosphere of Mars this cause of waste must be especially
effective. Thus the polar reservoirs are despoiled in the act of being
opened. Further objections might be taken to Mr. Lowell's irrigation
scheme, but enough has been said to show that it is hopelessly
unworkable."
It will be seen that the writer of this article accepted the existence
of water on Mars, on the testimony of Sir W. Huggins, which, in view of
later observations, he has himself acknowledged to be valueless. Dr.
Johnstone Stoney's proof of its absence, derived from the molecular
theory of gases, had not then been made public.
_Description of some of the Canals._
At the end of his volume Mr. Lowell gives a large chart of Mars on
Mercator's projection, showing the canals and other features seen during
the opposition of 1905. This contains many canals not shown on the map
here reproduced (see frontispiece), and some of the differences between
the two are very puzzling. Looking at our map, which shows the
north-polar snow below, so that the south pole is out of the view at the
top of the map, the central feature is the large spot Ascraeeus Lucus,
from which ten canals diverge centrally, and four from the sides,
forming wide double canals, fourteen in all. There is also a canal named
Ulysses, which here passes far to the right of the spot, but in the
large chart enters it centrally. Looking at our map we see, going
downwards a little to the left, the canal Udon, which runs through a
dark area quite to the outer margin. In the dark area, however, there is
shown on the chart a spot Aspledon Lucus, where five canals meet, and if
this is taken as a terminus the Udon canal is almost exactly 2000 miles
long, and another on its right, Lapadon, is the same length, while Ich,
running in a slightly curved line to a large spot (Lucus Castorius on
the chart) is still longer. The Ulysses canal, which (on the chart) runs
straight from the point of the Mare Sirenum to the Astraeeus Lucus is
about 2200 miles long. Others however are even longer, and Mr. Lowell
says: "With them 2000 miles is common; while many exceed 2500; and the
Eumenides-Orcus is 3540 miles from the point where it leaves Lucus
Phoeniceus to where it enters the Trivium Charontis." This last canal is
barely visible on our map, its commencement being indicated by the word
Eumenides.
The Trivium Charontis is situated just beyond the right-hand margin of
our map. It is a triangular dark area, the sides about 200 miles long,
and it is shown on the chart as being the centre from which radiate
thirteen canals. Another centre is Aquae Calidae situated at the point
of a dark area running obliquely from 55° to 35° N. latitude, and, as
shown on a map of the opposite hemisphere to our map, has nearly twenty
canals radiating from it in almost every direction. Here at all events
there seems to be no special connection with the polar snow-caps, and
the radiating lines seem to have no intelligent purpose whatever, but
are such as might result from fractures in a glass globe produced by
firing at it with very small shots one at a time. Taking the whole
series of them, Mr. Lowell very justly compares them to "a network which
triangulates the surface of the planet like a geodetic survey, into
polygons of all shapes and sizes."
At the very lowest estimate the total length of the canals observed and
mapped by Mr. Lowell must be over a hundred thousand miles, while he
assures us that numbers of others have been seen over the whole surface,
but so faintly or on such rare occasions as to elude all attempts to fix
their position with certainty. But these, being of the same character
and evidently forming part of the same system, must also be artificial,
and thus we are led to a system of irrigation of almost unimaginable
magnitude on a planet which has no mountains, no rivers, and no rain to
support it; whose whole water-supply is derived from polar snows, the
amount of which is ludicrously inadequate to need any such world-wide
system; while the low atmospheric pressure would lead to rapid
evaporation, thus greatly diminishing the small amount of moisture that
is available. Everyone must, I think, agree with Miss Clerke, that, even
admitting the assumption that the polar snows consist of frozen water,
the excessively scanty amount of water thus obtained would render any
scheme of world-wide distribution of it hopelessly unworkable.
The very remarkable phenomena of the duplication of many of the lines,
together with the darkspots--the so-called oases--at their
intersections, are doubtless all connected in some unknown way with the
constitution and past history of the planet; but, on the theory of the
whole being works of art, they certainly do _not_ help to remove any of
the difficulties which have been shown to attend the theory that the
single lines represent artificial canals of irrigation with a strip of
verdure on each side of them produced by their overflow.
_Lowell on the Purpose of the Canals._
Before leaving this subject it will be well to quote Mr. Lowell's own
words as to the supposed perfectly level surface of Mars, and his
interpretation of the origin and purpose of the 'canals':
"A body of planetary size, if unrotating, becomes a sphere, except for
solar tidal deformation; if rotating, it takes on a spheroidal form
exactly expressive, so far as observation goes, of the so-called
centrifugal force at work. Mars presents such a figure, being flattened
out to correspond to its axial rotation. Its surface therefore is in
fluid equilibrium, or, in other words, a particle of liquid at any point
of its surface at the present time would stay where it was devoid of
inclination to move elsewhere. Now the water which quickens the verdure
of the canals moves from the pole down to the equator as the season
advances. This it does then irrespective of gravity. No natural force
propels it, and the inference is forthright and inevitable that it is
artificially helped to its end. There seems to be no escape from this
deduction. Water only flows downhill, and there is no such thing as
downhill on a surface already in fluid equilibrium. A few canals might
presumably be so situated that their flow could, by inequality of
terrane, lie equatorward, but not all....Now it is not in particular but
by general consent that the canal-system of Mars develops from pole to
equator. From the respective times at which the minima take place, it
appears that the canal quickening occupies fifty-two days, as evidenced
by the successive vegetal darkenings, to descend from latitude 72° north
to latitude 0°, a journey of 2650 miles. This gives for the water a
speed of fifty-one miles a day, or 2.1 miles an hour. The rate of
progression is remarkably uniform, and this abets the deduction as to
assisted transference. But the fact is more unnatural yet. The growth
pays no regard to the equator, but proceeds across it as if it did not
exist into the planet's other hemisphere. Here is something still more
telling than travel to this point. For even if we suppose, for the sake
of argument, that natural forces took the water down to the equator,
their action must there be certainly reversed, and the equator prove a
dead-line, to pass which were impossible" (pp. 374-5).
I think my readers will agree with me that this whole argument is one of
the most curious ever put forth seriously by an eminent man of science.
Because the polar compression of Mars is about what calculation shows it
ought to be in accordance with its rate of rotation, its surface is in a
state of 'fluid equilibrium,' and must therefore be absolutely level
throughout. But the polar compression of the earth equally agrees with
calculation; therefore its surface is also in 'fluid equilibrium';
therefore it also ought to be as perfectly level on land as it is on the
ocean surface! But as we know this is very far from being the case, why
must it be so in Mars? Are we to suppose Mars to have been formed in
some totally different way from other planets, and that there neither is
nor ever has been any reaction between its interior and exterior forces?
Again, the assumption of perfect flatness is directly opposed to all
observation and all analogy with what we see on the earth and moon. It
gives no account whatever of the numerous and large dark patches, once
termed seas, but now found to be not so, and to be full of detailed
markings and varied depths of shadow. To suppose that these are all the
same dead-level as the light-coloured portions are assumed to be,
implies that the darkness is one of material and colour only, not of
diversified contour, which again is contrary to experience, since
difference of material with us always leads to differences in rate of
degradation, and hence of diversified contour, as these dark spaces
actually show themselves under favourable conditions to independent
observers.
_Lowell on the System of Canals as a whole._
We will now see what Mr. Lowell claims to be the plain teaching of the
'canals' as a whole:
"But last and all-embracing in its import is the system which the canals
form. Instead of running at hap-hazard, the canals are interconnected in
a most remarkable manner. They seek centres instead of avoiding them.
The centres are linked thus perfectly one with another, an arrangement
which could not result from centres, whether of explosion or otherwise,
which were themselves discrete. Furthermore, the system covers the whole
surface of the planet, dark areas and light ones alike, a world-wide
distribution which exceeds the bounds of natural possibility. Any force
which could act longitudinally on such a scale must be limited
latitudinally in its action, as witness the belts of Jupiter and the
spots upon the sun. Rotational, climatic, or other physical cause could
not fail of zonal expression. Yet these lines are grandly indifferent to
such competing influences. Finally, the system, after meshing the
surface in its entirety, runs straight into the polar caps.
"It is, then, a system whose end and aim is the tapping of the snow-cap
for the water there semi-annually let loose; then to distribute it over
the planet's face" (p. 373).
Here, again, we have curiously weak arguments adduced to support the
view that these numerous straight lines imply works of art rather than
of nature, especially in the comparison made with the belts of Jupiter
and the spots on the sun, both purely atmospheric phenomena, whereas the
lines on Mars are on the solid surface of the planet. Why should there
be any resemblance between them? Every fact stated in the above
quotation, always keeping in mind the physical conditions of the
planet--its very tenuous atmosphere and rainless desert-surface--seem
wholly in favour of a purely natural as opposed to an artificial origin;
and at the close of this discussion I shall suggest one which seems to
me to be at least possible, and to explain the whole series of the
phenomena set forth and largely discovered by Mr. Lowell, in a simpler
and more probable manner than does his tremendous assumption of their
being works of art. Readers who may not possess Mr. Lowell's volume will
find three of his most recent maps of the 'canals' reproduced in
_Nature_ of October 11th, 1906.