Pagina:Scientia - Vol. VII.djvu/275

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the “canals„ of mars 267

But this general scheme will be profoundly modified by the fact that the polar region is continually presented to the Sun, so that probably there will come a time in the progress of its summer when it will be the hottest part of the entire planet. The pole that is enjoying the summer, therefore, more than even the tropics, will be the centre from which the heated air will radiate. Similarly, the pole in winter will be the ultimate focus towards which these heated currents will direct their course, as it will undoubtedly be the coldest region of the planet — far colder than our extremest earthly experience.

On the Earth, aqueous circulation is carried on both by ocean currents and by the transportation of water through the air. There is nothing on Mars to correspond to the vast ocean surfaces of the Earth and from the ease with which water will pass into vapour, it is clear that we must look to the atmospheric circulation as the chief means for the transference of moisture from one region to another.

And indeed this is readily admitted by all writers on Martian meteorology, so far as it relates to the transfer of moisture to the poles; it is only when the question of the movement in the opposite direction arises that it is assumed to be impossible that the moisture should travel in the form of vapour, and it is found imperative to cover Mars with a Titanic system of irrigation works fitted with mammoth pumping stations at short intervals. Yet the atmospheric circulation of Mars cannot be always in one and the same direction. If anything, one would suppose that the winds blowing in summer time from the melting pole cap, would be more heavily laden with vapour than those blowing in winter towards the freezing. cap.

«Canals», — artificial waterways, — are therefore not necessary in order that the succession of the seasons should mean the transfer of moisture from one region to another, nor has there ever been any valid reason for supposing that such exist on the planet. The only pretext for such a supposition lay in the apparent precise and geometrical regularity of the «canals» and «oases». Yet even as far back as 1884, some of the «canals» were losing their strict rectilinear appearance to Schiaparelli; and later Barnard, Cerulli, Denning, Millochau, Molesworth, Phillips, Stanley Williams, and others