Page:The evolution of worlds - Lowell.djvu/204

168 Jupiter's equator lies almost in the plane of his orbit, and on a hasty view the Sun might be credited with the ordering of the belts, as was indeed long the case. But Saturn's inclination to his orbital plane is 27°; yet his belts fit his figure as neatly as his rings, and never get displaced, no matter how his body be turned.

Uranus and Neptune are in the same self-centred attitude at present as the faint traces of belts on their disk, otherwise of the same albedo as cloud, lead us to conclude. Yet both their densities and their situation give us to believe them further advanced than the giant planets, and still they lie wrapped in cloud.

These planets, then, are quite unbeholden to the Sun for all their present internal economies. What goes on under that veil of clouds with which they discreetly hide their doings from the too curious astronomic eye—we can only conjecture. But we discern enough to know that it is no placid uneventfulness. That it will continue, too, we are assured. For whether these clouds are largely water-vapor now, or not, to watery ones they must come as the last of all the wrappers they will eventually put off.

The major planets are the only ones at the present moment in this self-centred and self-sustained stage. Their great size has kept them young. In the smaller terrestrial planets we could not expect to witness any such condition to-day. If they experienced an ebullient