Page:Mars - Lowell.djvu/54

32 of decay, must come to a stand-still, when once what was friable had crumbled to pieces under the alternate roasting and refrigerating, relatively speaking, to which the body's surface would be exposed as it turned round on its axis into and out of the Sun's rays. Such disintegration once accomplished, the planet would roll thenceforth a mummy world through space.

An instance of this death in life we have exemplified by the nearest of the heavenly bodies, our own Moon. That cataclysmic changes once occurred there is still legible on her face, while the present well-nigh complete immutability of that face shows that next to nothing happens there now. Except for the possible tumbling in of a crater wall, such as seems to have taken place in the case of Linné a few years ago, all is now deathly still. But atmosphere is as absent as change. Whatever it may have had in the past, there is at present no perceptible air upon the surface of the Moon. And change pro tanto knows it no more.

With Mars it is otherwise. Over the surface of that planet changes do occur, changes upon a scale vast enough to be visible from the Earth. To appreciate the character and extent of these changes we will begin with the appearance of the planet last June. From the drawings it will be seen that the general aspect of the