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_Is Mars Habitable?_

A CRITICAL EXAMINATION OF PROFESSOR PERCIVAL LOWELL'S BOOK
"MARS AND ITS CANALS," WITH AN ALTERNATIVE EXPLANATION

BY ALFRED RUSSEL WALLACE F.R.S., ETC.



PREFACE.

This small volume was commenced as a review article on Professor
Percival Lowell's book, _Mars and its Canals_, with the object of
showing that the large amount of new and interesting facts contained in
this work did not invalidate the conclusion I had reached in 1902, and
stated in my book on _Man's Place in the Universe_, that Mars was not
habitable.

But the more complete presentation of the opposite view in the volume
now under discussion required a more detailed examination of the various
physical problems involved, and as the subject is one of great, popular,
as well as scientific interest, I determined to undertake the task.

This was rendered the more necessary by the fact that in July last
Professor Lowell published in the _Philosophical Magazine_ an elaborate
mathematical article claiming to demonstrate that, notwithstanding its
much greater distance from the sun and its excessively thin atmosphere,
Mars possessed a climate on the average equal to that of the south of
England, and in its polar and sub-polar regions even less severe than
that of the earth. Such a contention of course required to be dealt
with, and led me to collect information bearing upon temperature in all
its aspects, and so enlarging my criticism that I saw it would be
necessary to issue it in book form.

Two of my mathematical friends have pointed out the chief omission which
vitiates Professor Lowell's mathematical conclusions--that of a failure
to recognise the very large conservative and _cumulative_ effect of a
dense atmosphere. This very point however I had already myself discussed
in Chapter VI., and by means of some remarkable researches on the heat
of the moon and an investigation of the causes of its very low
temperature, I have, I think, demonstrated the incorrectness of Mr.
Lowell's results. In my last chapter, in which I briefly summarise the
whole argument, I have further strengthened the case for very severe
cold in Mars, by adducing the rapid lowering of temperature universally
caused by diminution of atmospheric pressure, as manifested in the
well-known phenomenon of temperate climates at moderate heights even
close to the equator, cold climates at greater heights even on extensive
plateaux, culminating in arctic climates and perpetual snow at heights
where the air is still far denser than it is on the surface of Mars.
This argument itself is, in my opinion, conclusive; but it is enforced
by two others equally complete, neither of which is adequately met by
Mr. Lowell.

The careful examination which I have been led to give to the whole of
the phenomena which Mars presents, and especially to the discoveries of
Mr. Lowell, has led me to what I hope will be considered a satisfactory
physical explanation of them. This explanation, which occupies the whole
of my seventh chapter, is founded upon a special mode of origin for
Mars, derived from the Meteoritic Hypothesis, now very widely adopted by
astronomers and physicists. Then, by a comparison with certain
well-known and widely spread geological phenomena, I show how the great
features of Mars--the 'canals' and 'oases'--may have been caused. This
chapter will perhaps be the most interesting to the general reader, as
furnishing a quite natural explanation of features of the planet which
have been termed 'non-natural' by Mr. Lowell.

Incidentally, also, I have been led to an explanation of the highly
volcanic nature of the moon's surface. This seems to me absolutely to
require some such origin as Sir George Darwin has given it, and thus
furnishes corroborative proof of the accuracy of the hypothesis that our
moon has had an unique origin among the known satellites, in having been
thrown off from the earth itself.

I am indebted to Professor J. H. Poynting, of the University of
Birmingham, for valuable suggestions on some of the more difficult
points of mathematical physics here discussed, and also for the critical
note (at the end of Chapter V.) on Professor Lowell's estimate of the
temperature of Mars.

BROADSTONE, DORSET, _October_ 1907.



TABLE OF CONTENTS.


CHAPTER I.

EARLY OBSERVERS OF MARS,
--Mars the only planet the surface of which is
  distinctly visible
--Early observation of the snow-caps and seas
--The 'canals' seen by Schiaparelli in 1877
--Double canals first seen in 1881
--Round spots at intersection of canals seen
  by Pickering in 1892
--Confirmed by Lowell in 1894
--Changes of colour seen in 1892 and 1894
--Existence of seas doubted by Pickering and
  Barnard in 1894.


CHAPTER II.

MR. LOWELL'S DISCOVERIES AND THEORIES,
--Observatory at Flagstaff, Arizona
--Illustrated book on his observations of
  Mars
--Volume on Mars and its canals, 1906
--Non-natural features
--The canals as irrigation works of an intelligent
  race
--A challenge to the thinking world
--The canals as described and mapped by Mr. Lowell
--The double canals
--Dimensions of the canals
--They cross the supposed seas
--Circular black spots termed oases
--An interesting volume.


CHAPTER III.

THE CLIMATE AND PHYSIOGRAPHY OF MARS,
--No permanent water on Mars
--Rarely any clouds and no rain
--Snow-caps the only source of water
--No mountains, hills, or valleys on Mars
--Two-thirds of the surface a desert
--Water from the