Page:Popular Science Monthly Volume 18.djvu/858

838 ear, and seems to have had no idea of motion communicated continuously so as to produce waves. His remarks under this general head are often quite correct, and show that he had some capacity for observation.

When treating of the heavenly bodies, he is ordinarily far out of the way. With him the earth is fixed, and the sun and stars revolve about it. With strange perversity, he denies that the orbs of these bodies can be much larger than they appear, no matter at what distance they are placed. On the other hand, in treating this subject he sometimes displays that suspension of judgment which, as opposed to hasty theorizing, is one of the first characteristics of the careful thinker. He himself says: "I assign a number of reasons, one of which must be true; but which among them is true is not for a cautious man to decide."

He next traces the development of man from savagism to civilization; but, though the account is interesting, it has little to do with his views of physical science, and we therefore pass on to the consideration of the remainder of his work, which treats of various natural phenomena, and explains their causes.

He supposes thunder to be produced by the clashing together of clouds, or by the sudden expansion of a volume of air contained in a cloud. This latter action he compares to the bursting of a bladder. Other causes he enumerates, connected with the effects of winds and lightning, whose action on the clouds may produce sound. Lightning, in his view, is struck out like sparks from flint by the friction of the clouds, or it may be caused by the heat generated by the rapid rotation of a hollow cloud.

His views on the cause of water-spouts are similar to those held by many at the present day, namely, that they originate in the vortex of a whirlwind.

His ideas of the nature of clouds are confused, though in one place, at least, he asserts that they are formed by the combination of vapor which is exhaled from the ocean and the earth's surface. The act of raining he ascribes to the compelling force of the winds and the weight of the clouds themselves.

The opinions which he entertains in regard to earthquakes are specially noteworthy, as having been revived of late years by several scientists to explain some, if not all, of the phenomena attendant upon such convulsions of nature. He supposes these to be caused by subterranean downfalls of large masses of rock.

This view has not only been accepted by a number of modern geologists, but also, as Élisée Reclus remarks, has been corroborated by many observations. To this author we commend the reader who desires to know the various reasons for accepting the theory.