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_prima facie_ evidence of a corresponding simplicity and uniformity in
its internal structure.

Yet we are not ourselves by any means devoid of 'straight lines'
structurally produced, in spite of every obstacle of diversity of form
and texture, of softness and hardness, of lamination or crystallisation,
which are adverse to such developments. Examples of these are the
numerous 'faults' which occur in the harder rocks, and which often
extend for great distances in almost perfect straight lines. In our own
country we have the Tyneside and Craven faults in the North of England,
which are 30 miles long and often 20 yards wide; but even more striking
is the great Cleveland Dyke - a wall of volcanic rock dipping slightly
towards the south, but sometimes being almost vertical, and stretching
across the country, over hill and dale, in an almost perfect straight
line from a point on the coast ten miles north of Scarborough, in a
west-by-north direction, passing about two miles south of Stockton and
terminating about six miles north-by-east of Barnard Castle, a distance
of very nearly 60 miles. The great fault between the Highlands and
Lowlands of Scotland extends across the country from Stonehaven to near
Helensburgh, a distance of 120 miles; and there are very many more of
less importance.

Much more extensive are some of the great continental dislocations,
often forming valleys of considerable width and length. The Upper Rhine
flows in one of these great valleys of subsidence for about 180 miles,
from Mulhausen to Frankfort, in a generally straight line, though
modified by denudation. Vaster still is the valley of the Jordan through
the Sea of Galilee to the Dead Sea, continued by the Wady Arabah to the
Gulf of Akaba, believed to form one vast geological depression or
fracture extending in a straight line for 400 miles.

Thousands of such faults, dykes, or depressions exist in every part of
the world, all believed to be due to the gradual shrinking of the heated
interior to which the solid crust has to accommodate itself, and they
are especially interesting and instructive for our present purpose as
showing the tendency of such fractures of solid rock-material to extend
to great lengths in straight lines, notwithstanding the extreme
irregularity both in the surface contour as well as in the internal
structures of the varied deposits and formations through which they
pass.

_Probable Origin of the Surface-features of Mars._

Returning now to Mars, let us consider the probable course of events
from the point at which we left it. The heat produced by impact and
condensation would be likely to release gases which had been in
combination with some of the solid matter, or perhaps been itself in a
solid state due to intense cold, and these, escaping outwards to the
surface, would produce on a small scale a certain amount of upheaval and
volcanic disturbance; and as an outer crust rapidly formed, a number of
vents might remain as craters or craterlets in a moderate state of
activity. Owing to the comparatively small force of gravity, the outer
crust would become scoriaceous and more or less permeated by the gases,
which would continue to escape through it, and this would facilitate the
cooling of the whole of the heated outer crust, and allow it to become
rather densely compacted. When the greater portion of the gases had thus
escaped to the outer surface and assisted to form a scanty atmosphere,
such as now exists, there would be no more internal disturbance and the
cooling of the heated outer coating would steadily progress, resulting
at last in a slightly heated, and later in a cold layer of moderate
thickness and great general uniformity. Owing to the absence of rain and
rivers, denudation such as we experience would be unknown, though the
superficial scoriaceous crust might be partially broken up by expansion
and contraction, and suffer a certain amount of atmospheric erosion.

The final result of this mode of aggregation would be, that the planet
would consist of an outer layer of moderate thickness as compared with
the central mass, which outer layer would have cooled from a highly
heated state to a temperature considerably below the freezing-point, and
this would have been all the time _contracting upon a previously cold,
and therefore non-contracting nucleus._ The result would be that very
early in the process great superficial tensions would be produced, which
could only be relieved by cracks or fissures, which would initiate at
points of weakness - probably at the craterlets already referred to - from
which they would radiate in several directions. Each crack thus formed
near the surface would, as cooling progressed, develop in length and
depth; and owing to the general uniformity of the material, and possibly
some amount of crystalline structure due to slow and continuous cooling
down to a very low temperature, the cracks would tend to run on in
straight lines and to extend vertically downwards, which two
circumstances would necessarily result in their forming portions of
'great circles' on the planet's surface - the two great facts which Mr.
Lowell appeals to as being especially 'non-natural.'

_Symmetry of Basaltic Columns._

We have however one quite natural fact on our earth which serves to
illustrate one of these two features, the direction of the downward
fissure. This is, the comparatively common phenomenon of basaltic
columns and 'Giant's Causeways.' The wonderful regularity of these, and
especially the not unfrequent upright pillars in serried ranks, as in
the palisades of the Hudson river, must have always impressed observers
with their appearance of artificiality. Yet they are undoubtedly the
result of the very slow cooling and contraction of melted rocks under
compression by strata _below and above them_, so that, when once
solidified, the mass was held in position and the tension produced by
contraction could only be relieved by numerous very small cracks at
short distances from each other in every direction, resulting in five,
six, or seven-sided polygons, with sides only a few inches long. This
contraction began of course at the coolest surface, generally the upper
one; and observation of these columns in various positions has
established the rule that their direction lengthways _is always at right
angles to the cooling surface_, and thus, whenever this surface was
horizontal, the columns became almost exactly vertical.

_How this applies to Mars._

One of the features of the surface of Mars that Mr. Lowell describes
with much confidence is, that it is wonderfully uniform and level, which
of course it would be if it had once been in a liquid or plastic state,
and not much disturbed since by volcanic or other internal movements.
The result would be that cracks formed by contraction of the hardened
outer crust would be vertical; and, in a generally uniform material at a
very uniform temperature, these cracks would continue almost
indefinitely in straight lines. The hardened and contracting surface
being free to move laterally on account of there being a more heated and
plastic layer below it, the cracks once initiated above would
continually widen at the surface as they penetrated deeper and deeper
into the slightly heated substratum. Now, as basalt begins to soften at
about 1400° F. and the surface of Mars has cooled to at least the
freezing-point - perhaps very much below it - the contraction would be so
great that if the fissures produced were 500 miles apart they might be
three miles wide at the surface, and, if only 100 miles apart, then
about two-thirds of a mile wide.[15] But as the production of the
fissures might have occupied perhaps millions of years, a considerable
amount of atmospheric denudation would result, however slowly it acted.
Expansion and contraction would wear away the edges and sides of the
fissures, fill up many of them with the debris, and widen them at the
surfaces to perhaps double their original size.[16]

[Footnote 15: The coefficient of contraction of basalt is 0.000006 for
1° F., which would lead to the results given here.]

[Footnote 16: Mr. W.H. Pickering observed clouds on Mars 15 miles high;
these are the 'projections' seen on the terminator when the planet is
partially illuminated. They were at first thought to be mountains; but
during the opposition of 1894, more than 400 of them were seen at
Flagstaff during nine months' observation. Usually they are of rare
occurrence. They are seen to change in form and position from day to
day, and Mr. Lowell is strongly of opinion that they are dust-storms,
not what we term clouds. They were mostly about 13 miles high,
indicating considerable aerial disturbance on the planet, and therefore
capable of producing proportional surface denudation.]

_Suggested Explanation of the 'Oases.'_

The numerous round dots seen upon the 'canals,' and especially at points
from which several canals radiate and where they intersect - termed
'oases' by Mr. Lowell and 'craterlets' by Mr. Pickering may be explained
in two ways. Those from which several canals radiate may be true craters
from which the gases imprisoned in the heated surface layers have
gradually escaped. They would be situated at points of weakness in the
crust, and become centres from which cracks would start during
contraction. Those dots which occur at the crossing of two straight
canals or cracks may have originated from the fact that at such
intersections there would be four sharply-projecting angles, which,
being exposed to the influence of alternate heat and cold (during day
and night) on the two opposite surfaces, would inevitably in time become
fractured and crumbled away, resulting in the formation of a roughly
circular chasm which would become partly filled up by the debris. Those
formed by cracks radiating from craterlets would also be subject to the
same process of rounding off to an even greater extent; and thus would
be produced the 'oases' of various sizes up to 50 miles or more in
diameter recorded by Mr. Lowell and other observers.

_Probable Function of the Great Fissures._

Mr. Pickering, as we have seen, supposes that these fissures give out
the gases which, overflowing on each side, favour the growth of the
supposed vegetation which renders the course of the canals visible, and
this no doubt may have been the case during the remote periods when
these cracks gave access to the heated portions of the surface layer.
But it seems more probable that Mars has now cooled down to the almost
uniform mean temperature it derives from solar heat, and that the
fissures - now for the most part broad shallow valleys - serve merely as
channels along which the liquids and heavy gases derived from the
melting of the polar snows naturally flow, and, owing to their nearly
level surfaces, overflow to a certain distance on each side of them.

_Suggested Origin of the Blue Patches._

These heavy gases, mainly perhaps, as has been often suggested,
carbon-dioxide, would, when in large quantity and of considerable depth,
reflect a good deal of light, and, being almost inevitably dust-laden,
might produce that blue tinge adjacent to the melting snow-caps which
Mr. Lowell has erroneously assumed to be itself a proof of the presence
of liquid water. Just as the blue of our sky is undoubtedly due to
reflection from the ultra-minute dust particles in our higher
atmosphere, similar particles brought down by the 'snow' from the higher
Martian atmosphere might produce the blue tinge in the great volumes of
heavy gas produced by its evaporation or liquefaction.

It may be noted that Mr. Lowell objects to the carbon-dioxide theory of
the formation of the snow-caps, that this gas at low pressures does not
liquefy, but passes at once from the solid to the gaseous state, and
that only water remains liquid sufficiently long to produce the blue
colour' which plays so large a part in his argument for the mild climate
essential for an inhabited planet. But this argument, as I have already
shown, is valueless. For only very deep water can possibly show a blue
colour by reflected light, while a dust-laden atmosphere - especially
with a layer of very dense gas at the bottom of it, as would be the case
with the newly evaporated carbon-dioxide from the diminishing snow-cap
- would provide the very conditions likely to produce this blue tinge of
colour.

It may be considered a support to this view that carbonic-acid gas
becomes liquid at - 140° F. and solid at - 162° F., temperatures far
higher than we should expect to prevail in the polar and north temperate
regions of Mars during a considerable part of the year, but such as
might be reached there during the summer solstice when the `snows' so
rapidly disappear, to be re-formed a few months later.

_The Double Canals._

The curious phenomena of the 'double canals' are undoubtedly the most
difficult to explain satisfactorily on any theory that has yet been
suggested. They vary in distance apart from about 100 to 400 miles. In
many cases they appear perfectly parallel, and Mr. Lowell gives us the
impression that they are almost always so. But his maps show, in some
cases, decided differences of width at the two extremities, indicating
considerable want of parallelism. A few of the curved canals are also
double.

There is one drawing in Mr. Lowell's book (p. 219) of the mouths, or
starting points, of the Euphrates and Phison, two widely separated
double canals diverging at an angle of about 40° from the same two
oases, so that the two inner canals cross each other. Now this suggests
two wide bands of weakness in the planet's crust radiating probably from
within the dark tract called the 'Mare Icarium,' and that some
widespread volcanic outburst initiated diverging cracks on either side
of these bands. Something of this kind may have been the cause of most
of the double canals, or they may have been started from two or more
craterlets not far apart, the direction being at first decided by some
local peculiarity of structure; and where begun continuing in straight
lines owing to homogeneity or uniform density of material. This is very
vague, but the phenomena are so remarkable, and so very imperfectly
known at present, that nothing but suggestion can be attempted.

_Concluding Remarks on the 'Canals.'_

In this somewhat detailed exposition of a possible, and, I hope, a
probable explanation of the surface-features of Mars, I have
endeavoured to be guided by known facts or accepted theories both
astronomical and geological. I think I may claim to have shown that
there are some analogous features of terrestrial rock-structure to
serve as guides towards a natural and intelligible explanation of the
strange geometric markings discovered during the last thirty years, and
which have raised this planet from comparative obscurity into a position
of the very first rank both in astronomical and popular interest.

This wide-spread interest is very largely due to Mr. Lowell's devotion
to its study, both in seeking out so admirable a position as regards
altitude and climate, and in establishing there a first-class
observatory; and also in bringing his discoveries before the public in
connection with a theory so startling as to compel attention. I venture
to think that his merit as one of our first astronomical observers will
in no way be diminished by the rejection of his theory, and the
substitution of one more in accordance with the actually observed facts.



APPENDIX.

_A Suggested Experiment to Illustrate the 'Canals' of Mars._

If my explanation of the 'canals' should be substantially correct - that
is, if they were produced by the contraction of a heated outward crust
upon a cold, and therefore non-contracting interior, the result of such
a condition might be shown experimentally.

Several baked clay balls might be formed to serve as cores, say of 8 to
10 inches in diameter. These being fixed within moulds of say half an
inch to an inch greater diameter, the outer layer would be formed by
pouring in some suitable heated liquid material, and releasing it from
the mould as soon as consolidation occurs, so that it may cool rapidly
from the _outside._ Some kinds of impure glass, or the brittle metals
bismuth or antimony or alloys of these might be used, in order to see
what form the resulting fractures would take. It would be well to have
several duplicates of each ball, and, as soon as tension through
contraction manifests itself, to try the effect of firing very small
charges of small shot to ascertain whether such impacts would start
radiating fractures. When taken from the moulds, the balls should be
suspended in a slight current of air, and kept rotating, to reproduce
the planetary condition as nearly as possible.

The exact size and material of the cores, the thickness of the heated
outer crust, the material best suited to show fracture by contraction,
and the details of their treatment, might be modified in various ways as
suggested by the results first obtained. Such a series of experiments
would probably throw further light on the physical conditions which have
produced the gigantic system of fissures or channels we see upon the
surface of Mars, though it would not, of course, prove that such
conditions actually existed there. In such a speculative matter we can
only be guided by probabilities, based upon whatever evidence is
available.



CHAPTER VIII.


SUMMARY AND CONCLUSION.

This little volume has necessarily touched upon a great variety of
subjects, in order to deal in a tolerably complete manner with the very
extraordinary theories by which Mr. Lowell attempts to explain the
unique features of the surface of the planet, which, by long-continued
study, he has almost made his own. It may therefore be well to sum up
the main points of the arguments against his view, introducing a few
other facts and considerations which greatly strengthen my argument.

The one great feature of Mars which led Mr. Lowell to adopt the view of
its being inhabited by a race of highly intelligent beings, and, with
ever-increasing discovery to uphold this theory to the present time, is
undoubtedly that of the so-called 'canals' - their straightness, their
enormous length, their great abundance, and their extension over the
planet's whole surface from one polar snow-cap to the other. The very
immensity of this system, and its constant growth and extension during
fifteen years of persistent observation, have so completely taken
possession of his mind, that, after a very hasty glance at analogous
facts and possibilities, he has declared them to be 'non-natural' -
therefore to be works of art - therefore to necessitate the
presence of highly intelligent beings who have designed and constructed
them. This idea has coloured or governed all his writings on the
subject. The innumerable difficulties which it raises have been either
ignored, or brushed aside on the flimsiest evidence. As examples, he
never even discusses the totally inadequate water-supply for such
worldwide irrigation, or the extreme irrationality of constructing so
vast a canal-system the waste from which, by evaporation, when exposed
to such desert conditions as he himself describes, would use up ten
times the probable supply.

Again, he urges the 'purpose' displayed in these 'canals.' Their being
_all_ so straight, _all_ describing great circles of the 'sphere,' all
being so evidently arranged (as he thinks) either to carry water to some
'oasis' 2000 miles away, or to reach some arid region far over the
equator in the opposite hemisphere! But he never considers the
difficulties this implies. Everywhere these canals run for thousands of
miles across waterless deserts, forming a system and indicating a
purpose, the wonderful perfection of which he is never tired of dwelling
upon (but which I myself can nowhere perceive).

Yet he never even attempts to explain how the Martians could have lived
_before_ this great system was planned and executed, or why they did not
_first_ utilise and render fertile the belt of land adjacent to the
limits of the polar snows - why the method of irrigation did not, as with
all human arts, begin gradually, at home, with terraces and channels to
irrigate the land close to the source of the water. How, with such a
desert as he describes three-fourths of Mars to be, did the inhabitants
ever get to _know_ anything of the equatorial regions and its needs, so
as to start right away to supply those needs? All this, to my mind, is
quite opposed to the idea of their being works of art, and altogether in
favour of their being natural features of a globe as peculiar in origin
and internal structure as it is in its surface-features. The explanation
I have given, though of course hypothetical, is founded on known
cosmical and terrestrial facts, and is, I suggest, far more scientific
as well as more satisfactory than Mr. Lowell's wholly unsupported
speculation. This view I have explained in some detail in the preceding
chapter.

Mr. Lowell never even refers to the important question of loss by
evaporation in these enormous open canals, or considers the undoubted
fact that the only intelligent and practical way to convey a limited
quantity of water such great distances would be by a system of
water-tight and air-tight tubes laid _under the ground._ The mere
attempt to use open canals for such a purpose shows complete ignorance
and stupidity in these alleged very superior beings; while it is certain
that, long before half of them were completed their failure to be of any
use would have led any rational beings to cease constructing them.

He also fails to consider the difficulty, that, if these canals are
necessary for existence in Mars, how did the inhabitants ever reach a
sufficiently large population with surplus food and leisure enabling
them to rise from the low condition of savages to one of civilisation,
and ultimately to scientific knowledge? Here again is a dilemma which is
hard to overcome. Only a _dense_ population with _ample_ means of
subsistence could possibly have constructed such gigantic works; but,
given these two conditions, no adequate motive existed for the
conception and execution of them - even if they were likely to be of any
use, which I have shown they could not be.

_Further Considerations on the Climate of Mars._

Recurring now to the question of climate, which is all-important, Mr.
Lowell never even discusses the essential point - the temperature that
must _necessarily_ result from an atmospheric envelope one-twelfth (or
at most one-seventh) the density of our own; in either case
corresponding to an altitude far greater than that of our highest
mountains.[17] Surely this phenomenon, everywhere manifested on the
earth even under the equator, of a regular decrease of temperature with
altitude, the only cause of which is a less dense atmosphere, should
have been fairly grappled with, and some attempt made to show why it
should not apply to Mars, except the weak remark that on a level surface
it will not have the same effect as on exposed mountain heights. But it
_does_ have the same effect, or very nearly so, on our lofty plateaux
often hundreds of miles in extent, in proportion to their altitude.
Quito, at 9350 ft. above the sea, has a mean temperature of about 57°
F., giving a lowering of 23° from that of Manaos at the mouth of the Rio
Negro. This is about a degree for each 400 feet, while the general fall
for isolated mountains is about one degree in 340 feet according to
Humboldt, who notes the above difference between the rate of cooling for
altitude of the plains - or more usually sheltered valleys in which the
towns are situated - and the exposed mountain sides. It will be seen that
this lower rate would bring the temperature of Mars at the equator down
to 20° F. below the freezing point of water from this cause alone.

[Footnote 17: A four inches barometer is equivalent to a height of
40,000 feet above sea-level with us.]

But all enquirers have admitted, that if conditions as to atmosphere
were the same as on the earth, its greater distance from the sun would
reduce the temperature to-31° F., equal to 63° below the freezing
point. It is therefore certain that the combined effect of both causes
must bring the temperature of Mars down to at least 70° or 80°below the
freezing point.

The cause of this absolute dependence of terrestrial temperatures upon
density of the air-envelope is seldom discussed in text-books either of
geography or of physics, and there seems to be still some uncertainty


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Online LibraryAlfred Russel WallaceIs Mars Habitable? → online text (page 6 of 7)