readers is, that the author has here, for the first time, fully set
forth his views both as to the habitability of Mars and as to its being
actually inhabited by beings comparable with ourselves in intellect. The
larger part of the work is in fact devoted to a detailed description of
what he terms the 'Non-natural Features' of the planet's surface,
including especially a full account of the 'Canals,' single and double;
the 'Oases,' as he terms the dark spots at their intersections; and the
varying visibility of both, depending partly on the Martian seasons;
while the five concluding chapters deal with the possibility of animal
life and the evidence in favour of it. He also upholds the theory of the
canals having been constructed for the purpose of 'husbanding' the
scanty water-supply that exists; and throughout the whole of this
argument he clearly shows that he considers the evidence to be
satisfactory, and that the only intelligible explanation of the whole of
the phenomena he so clearly sets forth is, that the inhabitants of Mars
have carried out on their small and naturally inhospitable planet a vast
system of irrigation-works, far greater both in its extent, in its
utility, and its effect upon their world as a habitation for civilised
beings, than anything we have yet done upon our earth, where our
destructive agencies are perhaps more prominent than those of an
improving and recuperative character.

_A Challenge to the Thinking World._

This volume is therefore in the nature of a challenge, not so much to
astronomers as to the educated world at large, to investigate the
evidence for so portentous a conclusion. To do this requires only a
general acquaintance with modern science, more especially with mechanics
and physics, while the main contention (with which I shall chiefly deal)
that the features termed 'canals' are really works of art and