It appears, then, that Mr. Lowell has to face this dilemma—­Only if the whole surface of Mars is an almost perfect level could the enormous network of straight canals, each from hundreds to thousands of miles long, have been possibly constructed by intelligent beings for purposes of irrigation; but, if a complete and universal level surface exists no such system would be necessary. For on a level surface—­or on a surface slightly inclined from the poles towards the equator, which would be advantageous in either case—­the melting water would of itself spread over the ground and naturally irrigate as much of the surface as it was possible for it to reach.  If the surface were not level, but consisted of slight elevations and expressions to the extent of a few scores or a few hundreds of feet, then there would be no possible advantage in cutting straight troughs through these elevations in various directions with water flowing at the bottom of them.  In neither case, and in hardly any conceivable case, could these perfectly straight canals, cutting across each other in every direction and at very varying angles, be of any use, or be the work of an intelligent race, if any such race could possibly have been developed under the adverse conditions which exist in Mars.

The Scanty Water-supply.

But further, if there were any superfluity of water derived from the melting snow beyond what was sufficient to moisten the hollows indicated by the darker portions of the surface, which at the time the water reaches them acquire a green tint (a superfluity under the circumstances highly improbable), that superfluity could be best utilised by widening, however little, the borders to which natural overflow had carried it.  Any attempt to make that scanty surplus, by means of overflowing canals, travel across the equator into the opposite hemisphere, through such a terrible desert region and exposed to such a cloudless sky as Mr. Lowell describes, would be the work of a body of madmen rather than of 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.