350 Prof. Bischof on the Natural History of 



been remarked that the shocks most commonly followed the 

 direction of chains of mountains. 



In favour of the hypothesis, that earthquakes are produced 

 by aqueous vapour* penetrating to great depths, the following 

 circumstances may be adduced. Firstly, as aqueous vapour is 

 supposed to produce volcanic action, it must be presumed to 

 be also the cause of earthquakes. Secondly, some hours be- 

 fore the first shock of the tremendous earthquake at Algiers and 

 the neighbourhood, the 2d to 5th March 1825, which entirely 

 destroyed the town of Blisa, all the springs and wells are re- 

 ported to have been dried up.f Thirdly, earthquakes, though 

 undoubtedly felt even in the centre of large continents, seem 

 to produce their most frightful effects in countries not very 

 far removed from the ocean. But, perhaps, earthquakes may 



* A remarkable case which has taken place at the iron-foundiy at Sayn, 

 proves, that shocks of the earth may be several times repeated by the effect 

 of elastic fluids. A cylinder 14 feet in height, and 31,395 pounds in weight, 

 wa'S to be cast. The clay mould having been totally filled up by melted 

 iron, the latter broke through the ground, and penetrated to the depth of 

 25 feet into the sandy soil, consequently 1 1 feet deeper than the lower 

 part of the mould. Some time after an earthquake actually took place, 

 which shook the whole building so violently, that the workmen feared it 

 would be seriously injured. About half an hour after, an equally violent 

 shock happened, and after more than 24 hours a third followed. The local 

 circumstances of that iron-foundry lead to an explanation of these pheno- 

 mena. There are at a depth of 23-24 feet under the ground of the said 

 building, many inclined channels which communicate together, for the pur- 

 pose of collecting the rain-water. Immediately after the shocks, watery 

 vapours issued abundantly from the mouth of the channels. These vapours 

 were evolved by the heat of the melted iron from the water, being in the 

 ground about 2 feet below the bottom of the channels ; and penetrated 

 through the joinings of their brick- work. But these joinings being filled up 

 with mud and sand, offered resistance, and consequently the vapours had to 

 attain a certain elasticity before they were able to penetrate through them. 

 It is, however, very probable that the vapours, bearing mud and sand with 

 them, again stopped up the opening, when their elasticity gradually again 

 decreased. During the shocks, the steam attained its greatest elasticity, 

 and thickened the earth which surrounded the heated mass of iron ; and 

 this circumstance may have imi)eded a new afflux of water. Therefore, after 

 the first shock, half an hour elapsed ; and after the second, which still more 

 obstructed the afflux of the water, even more than 24 hours elapsed before 

 the third and latest shock took place. 



t Berzelius, Jahresbericht, 1827, p. 310. 



