Page:Is Mars habitable - Wallace 1907.djvu/72

 of the atmosphere—those which the planet 'parts with quickest.' But this is just what water-vapour is, being a little less than two-thirds the weight of air (0.6225), and one of those which the planet would part with the quickest, and which, according to Dr. Johnstone Stoney, it loses altogether.

Note on Professor Lowell's article in the Philosophical Magazine; by J.H. Poynting, F.R.S., Professor of Physics in the University of Birmingham.

" Professor Lowell's results are erroneous through his neglect of the heat stored in the air by its absorption of radiation both from the sun and from the surface. The air thus heated radiates to the surface and keeps up the temperature. I have sent to the Philosophical Magazine a paper in which I think it is shown that when the radiation by the atmosphere is taken into account the results are entirely changed. The temperature of Mars, with Professor Lowell's data, still comes out far below the freezing-point—still further below than the increased distance alone would make it. Indeed, the lower temperature on elevated regions of the earth's surface would lead us to expect this. I think it is impossible to raise the