838 THi: POPULAR SCIENCE MONTHLY. 



ear, and seems to have had no idea of motion communicated continu- 

 ously so as to produce waves. His remarks under this general head 

 are often quite correct, and show that he had some capacity for obser- 

 vation. 



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 jjlaced. On the other hand, in treating this subject he some- 

 times 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 de- 

 cide." 



He next traces the develoi^ment of man from savagism to civiliza- 

 tion ; but, though the account is interesting, it has little to do with his 

 views of physical science, and we therefore pass on to the considera- 

 tion of the remainder of his work, which treats of various natural phe- 

 nomena, and exjilains 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 spe- 

 cially noteworthy, as having been revived of late years by several sci- 

 entists to explain some, if not all, of the phenomena attendant upon 

 such convulsions of nature. He supposes these to be caused by sub- 

 terranean downfalls of large masses of rock. 



This view has not only been accepted by a number of modern ge- 

 ologists, but also, as ^filisee Reclus * remarks, has been corroborated by 

 many observations. To this author we commend the reader who de- 

 sires to know the various reasons for accepting the theory. 



* " The Earth," chapter Ixxiv. 



