Page:The fairy tales of science.djvu/215

Rh of about 7800 miles; some 68,000,000 miles distant from the centre of the solar system, she revolves round it in 224 days. Nearly of equal size, mass, and density as the Earth, and with a comparatively trifling difference of some 27,000,000 miles between the respective distances of the two planets from the sun, Venus would be supposed to present the same climatological and meteorological conditions as her sister planet; and this would unquestionably be the case, but that Venus happens to turn most obliquely round her axis, whence it results that snow and ice cannot accumulate at the poles, which are subjected by turns for some four months to the fierce glare of an almost vertical sun, and that there are no temperate zones in that planet as in ours; though an atmosphere, much loaded with clouds, would certainly seem to mitigate in some measure the intense glare and heat of the sunshine.

Mars, the nearest of the superior planets exterior to the Earth, presents more points of similarity to the latter than any of the other. His diameter is about 4100 miles, his distance from the solar centre, round which he revolves in 687 days, 142,000,000 miles; his mass is about one-seventh part of that of the Earth, and his density a trifle smaller. He is evidently surrounded by an atmosphere of considerable density; he shines with a red and fiery light; seen through a good telescope, his disk presents something like a vague delineation of seas and continents. Near the poles a zone of white is seen,