consists" (p. 162). Yet absolutely the only proof he gives that the caps
are frozen water is the almost frivolous colour-argument above referred
to!

_No Spectroscopic Evidence of Water Vapour._

As Sir William Huggins is the chief authority quoted for this fact, and
is referred to as being almost conclusive in the third edition of Miss
Clerke's _History of Astronomy_ in 1893, I have ascertained that his
opinion at the present time is that "there is no conclusive proof of the
presence of aqueous vapour in the atmosphere of Mars, and that
observations at the Lick Observatory (in 1895), where the conditions and
instruments are of the highest order, were negative." He also informs me
that Marchand at the Pic du Midi Observatory was unable to obtain lines
of aqueous vapour in the spectrum of Mars; and that in 1905, Slipher, at
Mr. Lowell's observatory, was unable to detect any indications of
aqueous vapour in the spectrum of Mars.

It thus appears that spectroscopic observations are quite accordant with
the calculations founded on the molecular theory of gases as to the
absence of aqueous vapour, and therefore presumably of liquid water,
from Mars. It is true that the spectroscopic argument is purely
negative, and this may be due to the extreme delicacy of the
observations required; but that dependent on the inability of the force
of gravity to retain it is positive scientific evidence against its
presence, and, till shown to be erroneous, must be held to be
conclusive.

This absence of water is of itself conclusive against the existence of
animal life, unless we enter the regions of pure conjecture as to the