the harvest ripens over huge tracts of country; that is, of
course, if the earth's atmosphere allowed a clear view of the
terrestrial surface--a very doubtful point indeed. Professor Lowell
thinks that the perfect straightness of the lines, and the geometrical
manner in which they are arranged, are clear evidences of artificiality.
On a globe, too, there is plainly no reason why the liquid which results
from the melting of the polar caps should trend at all in the direction
of the equator. Upon our earth, for instance, the transference of water,
as in rivers, merely follows the slope of the ground, and nothing else.
The Lowell observations show, however, that the Martian liquid is
apparently carried from one pole towards the equator, and then past it
to the other pole, where it once more freezes, only to melt again in due
season, and to reverse the process towards and across the equator as
before. Professor Lowell therefore holds, and it seems a strong point in
favour of his theory, that the liquid must, in some artificial manner,
as by pumping, for instance, be _helped_ in its passage across the
surface of the planet.

A number of attempts have been made to explain the _doubling_ of the
canals merely as effects of refraction or reflection; and it has even
been suggested that it may arise from the telescope not being accurately
focussed.

The actual doubling of the canals once having been doubted, it was an
easy step to the casting of doubt on the reality of the canals
themselves. The idea, indeed, was put forward that the human eye, in
dealing with detail so very close to the limit of visibility, may
unconsciously treat as an actual line several point-like markings which
merely happen to lie in a line. In order to test this theory,
experiments were carried out in 1902 by Mr. E.W. Maunder of Greenwich
Observatory, and Mr. J.E. Evans of the Royal Hospital School at
Greenwich, in which certain schoolboys were set to make drawings of a
white disc with some faint markings upon it. The boys were placed at
various distances from the disc in question; and it was found that the
drawings made by those who were just too far off to see distinctly, bore
out the above theory in a remarkable manner. Recently, however, the
plausibility of the _illusion_ view has been shaken by photographs of
Mars taken during the opposition of 1905 by Mr. Lampland at the Lowell
Observatory, in which a number of the more prominent canals come out as