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
about it. Some impute it wholly to the thinner air being unable to
absorb and retain so much heat as that which is more dense; but if this
were the case the soil at great altitudes not having so much of its heat
taken up by the air should be warmer than below, since it undoubtedly
_receives_ more heat owing to the greater transparency of the air above
it; but it certainly does not become warmer. The more correct view seems
to be that the loss of heat by radiation is increased so much through
the rarity of the air above it as to _more_ than counterbalance the
increased insolation, so that though the surface of the earth at a given
altitude may receive 10 per cent. more direct sun-heat it loses by
direct radiation, combined with diminished air and cloud-radiation,
perhaps 20 or 25 per cent. more, whence there is a resultant cooling
effect of 10 or 15 per cent. This acts by day as well as by night, so
that the greater heat received at high altitudes does not warm the soil
so much as a less amount of heat with a denser atmosphere.
This effect is further intensified by the fact that a less dense cannot
absorb and transmit so much heat as a more dense atmosphere. Here then
we have an absolute law of nature to be observed operating everywhere on
the earth, and the mode of action of which is fairly well understood.
This law is, that reduced atmospheric pressure increases radiation, or
loss of heat, _more rapidly_ than it increases insolation or gain of
heat, so that the result is _always_ a considerable _lowering_ of
temperature. What this lowering is can be seen in the universal fact,
that even within the tropics perpetual snow covers the higher mountain
summits, while on the high plains of the Andes, at 15,000 or 16,000 feet
altitude, where there is very little or no snow, travellers are often
frozen to death when delayed by storms; yet at this elevation the
atmosphere has much more than double the density of that of Mars!
The error in Mr. Lowell's argument is, that he claims for the scanty
atmosphere of Mars that it allows more sun-heat to reach the surface;
but he omits to take account of the enormously increased loss of heat by
direct radiation, as well as by the diminution of air-radiation, which
together necessarily produce a great reduction of temperature.
It is this great principle of the prepotency of radiation over
absorption with a diminishing atmosphere that explains the excessively
low temperature of the moon's surface, a fact which also serves to
indicate a very low temperature for Mars, as I have shown in Chapter VI.
These two independent arguments--from alpine temperatures and from those
of the moon--support and enforce each other, and afford a conclusive
proof (as against anything advanced by Mr. Lowell) that the temperature
of Mars must be far too low to support animal life.
A third independent argument leading to the same result is Dr. Johnstone
Stoney's proof that aqueous vapour cannot exist on Mars; and this fact
Mr. Lowell does not attempt to controvert.
To put the whole case in the fewest possible words:
All physicists are agreed that, owing to the distance of Mars from the
sun, it would have a mean temperature of about-35° F. (= 456° F. abs.)
even if it had an atmosphere as dense as ours.
(2) But the very low temperatures on the earth under the equator, at a
height where the barometer stands at about three times as high as on
Mars, proves, that from scantiness of atmosphere alone Mars cannot
possibly have a temperature as high as the freezing point of water; and
this proof is supported by Langley's determination of the low _maximum_
temperature of the full moon.
The combination of these two results must bring down the temperature of
Mars to a degree wholly incompatible with the existence of animal life.
(3) The quite independent proof that water-vapour cannot exist on Mars,
and that therefore, the first essential of organic life--water--is
non-existent.
The conclusion from these three independent proofs, which enforce each
other in the multiple ratio of their respective weights, is therefore
irresistible--that animal life, especially in its higher forms, cannot
exist on the planet.
Mars, therefore, is not only uninhabited by intelligent beings such as
Mr. Lowell postulates, but is absolutely UNINHABITABLE.
End of Project Gutenberg's Is Mars Habitable?, by Alfred Russel Wallace