Page:Is Mars habitable - Wallace 1907.djvu/66

v.] elaborate paper, except on a few points, I will here limit myself to giving a short account of it, so as to explain its method of procedure; after which I may add a few notes on what seem to me doubtful points; while I also hope to be able to give the opinions of some more competent critics than myself.

The author first states, that Professor Young, in his General Astronomy (1898), makes the mean temperature of Mars 223.6° absolute, by using Newton's law of heat being radiated in proportion to temperature, and 363° abs. (=−96°F.) by Dulong and Petit's law; but adds, that a closer determination has been made by Professor Moulton, using Stefan's law, that radiation is as the 4th power of the temperature, whence results a mean temperature of −31° F. These estimates assume identity of atmospheric conditions of Mars and the Earth.

But as none of these estimates take account of the many complex factors which interfere with such direct and simple calculations, Mr. Lowell then proceeds to enunciate them, and work out mathematically the effects they produce:

(1) The whole radiant energy of the sun on striking a planet becomes divided as follows: Part is reflected back into space, part absorbed by the atmosphere, part transmitted to the surface