square miles; that is to say,
they cover an area, in round numbers, seven times that of the snow-cap.
Only one-seventh of a foot of water, accordingly, could possibly be
made available for their fertilisation, supposing them to get the entire
advantage of the spring freshet. Upon a stint of less than two inches of
water these fertile lands are expected to flourish and bear abundant
crops; and since they completely enclose the polar area they are
necessarily served first. The great emissaries for carrying off the
surplus of their aqueous riches, would then appear to be superfluous
constructions, nor is it likely that the share in those riches due to
the canals and oases, intricately dividing up the wide, dry, continental
plains, can ever be realised.

"We have assumed, in our little calculation, that the entire contents of
a polar hood turn to water; but in actual fact a considerable proportion
of them must pass directly into vapour, omitting the intermediate stage.
Even with us a large quantity of snow is removed aerially; and in the
rare atmosphere of Mars this cause of waste must be especially
effective. Thus the polar reservoirs are despoiled in the act of being
opened. Further objections might be taken to Mr. Lowell's irrigation
scheme, but enough has been said to show that it is hopelessly
unworkable."

It will be seen that the writer of this article accepted the existence
of water on Mars, on the testimony of Sir W. Huggins, which, in view of
later observations, he has himself acknowledged to be valueless. Dr.
Johnstone Stoney's proof of its absence, derived from the molecular
theory of gases, had not then been made public.

_Description of some of the Canals._

At the end of his volume Mr. Lowell gives a large chart of Mars on
Mercator's projection, showing the canals and other features seen during
the opposition of 1905. This contains many canals not shown on the map
here reproduced (see frontispiece), and some of the differences between
the two are very puzzling. Looking at our map, which shows the
north-polar snow below, so that the south pole is out of the view at the
top of the map, the central feature is the large spot Ascraeeus Lucus,
from which ten canals diverge centrally, and four from the sides,
forming wide double canals, fourteen in all. There is also a canal named
Ulysses, which here passes far to the right of the spot, but in the
large chart enters it centrally. Looking at our map we see, goin