Masterpieces of Science 



permanent change in its form. Nevertheless, 

 the wave is often accompanied by movements of 

 elevation, or of depression, which produce perma- 

 nent alterations of level of considerable magnitude. 

 An earthquake is just such a disturbance of the 

 ground as would result from a sudden shock, or 

 blow, given upward in the interior of the earth, 

 from which, as from a centre, waves or tremors 

 may be propagated in all directions through the 

 solid ground. In many cases, the shock is pre- 

 ceded or accompanied by a rumbling noise, like 

 that of distant thunder, or by other sounds pro- 

 duced by the subterranean disturbance. The 

 earthquake- wave, as it travels along, causes the 

 ground to rise and fall, and frequently produces 

 irregular fissures, which may close again and thus 

 bury whatever has been engulfed, or may re- 

 main open as yawning chasms, and thus modify 

 the drainage of the country. The impulse may 

 be transmitted through the earth to an enormous 

 distance; the great earthquake which destroyed 

 Lisbon in 1755, having made itself felt, directly 

 or indirectly, on the waters of Loch Lomond in 

 Scotland. If the centre of disturbance is near 

 the sea, the water is affected even more than the 

 land, and the water-waves may be far more de- 

 structive than the earth- waves. News has re- 

 cently reached this country of the terrible devas- 

 tation wrought by the great tidal wave which 

 followed the earthquake at Lima, Arica, Iquique 

 and other points of the coast of South America 

 in May, 1877. 



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