Page:Popular Science Monthly Volume 51.djvu/375

Rh, and it may not be uninteresting to consider some of their peculiarities.

In considering the climatic conditions of a planet we find they depend principally upon three factors: the distance of the planet from the sun, the inclination of its axis, and the length of its year, with incidentally the length of its day. What the results of this combination may lead us to expect in the case of Saturn we will point out by using the earth, naturally, for analogy or contrast.

In the first place, as affecting animal and vegetable life, the greater distance of the sun, and the corresponding decrease in its lighting and heating power compared with the same effects on the earth, would materially change in itself the character of such life on Saturn. As already noted, the heat and light are reduced to nearly one one-hundredth of their intensity here, but no one can tell what compensating features may ultimately be provided for retaining the internal heat of the globe or storing up the sun's heat. As an instance of such adaptation we have only to turn to the planet Mars, where we have visual proof, in the melting of its polar "snows," of a much milder climate than the earth possesses, although the intensity of the sun's heat there is reduced by half.

In connection with the foregoing is the question of the composition of the atmosphere, and whether it could support such organisms as we are familiar with in terrestrial life. The spectroscope has told us but little about Saturn's atmosphere, but it is known that the planet is provided with one of considerable extent, and apparently of a similar constitution to our own. The presence of water vapor has been detected, according to some observers, but not positively; yet it is fair to suppose from other considerations that this most necessary adjunct of all life is plentifully supplied.

The change in the seasons will, of course, depend upon the inclination of the axis, which in Saturn's case is twenty-six and a half degrees from the perpendicular to its orbit. When we remember that the corresponding inclination of the earth's axis is twenty-three and a half degrees, it will be apparent that the change of seasons would be quite similar to ours, the sun merely rising three degrees higher in the heavens at the summer solstice and three degrees lower at the winter solstice. But the length of the seasons, determined by Saturn's long journey around the sun, will be, on the average, nearly seven and a half years, a fact which would render unlikely much similarity in organic life to the forms found on the earth. If we add to this the rapid succession of day and night, each being at the equator of but five and a quarter hours' duration, we may look for still further