Page:The evolution of worlds - Lowell.djvu/133

Rh Jupiter is by all odds first. His mass is 318 times the Earth's and his volume nearly 1400 times hers. From this it appears that his density is very much less. Indeed, his substance is only fractionally denser than water. This and its tremendous spin, carrying a point at its equator two hundred and eighty thousand miles round in less than ten hours, flatten it to a very marked

oval with an ellipticity of $1⁄15.5$. Not the least beautiful of the revelations of astronomy are the geometrical shapes of the heavenly bodies, proceeding from nearly perfect spheres like the Sun or Moon to marked spheroids like Jupiter or Saturn. So enormous are the masses and the forces concerned that the forms assumed under them are mechanically regular. They are the visible expression of gravitation, and so delight the brain while they satisfy the eye.

It is to appreciation of the detail visible on Jupiter's disk that modern advance in the study of the planet is indebted. Examination has shown its features to be of great interest. To Mr. Stanley Williams of Brighton, England, much of our knowledge is due, and Mr. Scriven Bolton has also made some interesting contributions. The big print of the subject, read