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