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