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night to night. By careful observation on the aspect which they present from hour to hour, and from night to night, it was found that the planet rotates on its axis in about 9 hours 55 minutes. The astronomer may therefore in the course of a single night see every part of the surface of the planet presented to his view in succession.

Two features presented by the planet will at once strike the careful observer with the telescope. One of these is that the disk does not seem uniformly bright, but gradually shades off near the limb. The latter, instead of being bright and hard is somewhat soft and diffuse. In this respect the appearance forms quite a contrast to that presented by the moon or Mars. The shading off toward the edge is sometimes attributed to a dense atmosphere surrounding the planet. While this is possible, it is by no means certain.

The other feature to which we allude is an ellipticity of the disk. Instead of being perfectly round, the planet is flattened at the poles, like our earth, but in a much greater degree. The most careful observer, viewing the earth from another planet, would see no deviation from the spherical form, but, viewing Jupiter, the deviation is very perceptible. This is owing to its rapid rotation on its axis, which causes its equatorial regions to bulge out, as, to a smaller degree, in the case of the earth.

The features of Jupiter, as we see them with a telescope, are almost as varied as those of the clouds which we see in our atmosphere. There are commonly elon-