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THE PLANET VENUS.
We have already mentioned that the size of Venus does notgreatly differ from that of the Earth . It is also found, fromcalculations of its mass, that the attraction of gravity upon itssurface is within one-fifth part of being the same. In thisrespect Venus would therefore be much better suited thanMercury (upon which the attraction of gravity is only aboutone-half as great) for the habitation of beings like ourselves.Nor wordd the intensity of the Solar heat be nearly so fierce asupon Mercury, since the Sun would only have an apparent dia-meter two-fifths larger than that which it presents to us ; whileits apparent area, although nearly double that which we see,would only be of one-fourth of its average size as seen fromMercury.* The heat and light received would, in like manner,be about twice that received by the Earth , and about one-fourthof that received by Mercury. We have, moreover, shown thatthere is much more reason to believe, in the case of Venus thanin that of Mercury, in the existence of a dense envelope ofcloud, which might possibly in some degree mitigate the Solarheat. But, if the observations of Schroter, or even the morerecent observations of De Vico and of those who assisted himin 1839-1841 be correct, it would seem, that the tilt of the axisof the planet to the plane of its orbit is such, that the climaticconditions upon it would be very greatly opposed to itshabitability.
Schroter considers the tilt of the axis to the plane of the orbitto be about 15°, and De Vico about 37°, while in the case of theEarth the corresponding inclination is 664°. As a consequencethe arctic zones of the Earth extend to a distance of 234° fromits poles, i.e., to a latitude of 661° from its equator, while thet ropics extend to 231° on each side of the equator, or 661° fromthe poles. Upon Venus , if Schroter were correct, the arcticregions would extend to 75° from the poles, and the tropics to75° from the equator ; while about 53° would be the limit ineither case, according to De Vico.
But even on this latter more moderate supposition the arcticcircles would come down below the half-way parallel of lati-tude of 45°, and the tropics would reach to 8° beyond it. A