UPHEAVING POWER, OF STEAM. 73 



charges, Bunsen is inclined to adopt the assump- 

 tion, suggested before him by Mackenzie and 

 others, of underground hollows, into which both 

 water and steam find their way at the same time. 

 The water is heated to boiling, by the steam, by 

 the gradually increasing elasticity of which it is 

 forced out : just as the water is driven out of a 

 fire-engine by the expansion of the air condensed 

 in the air-chamber. 



Since the manner in which steam acts in giving 

 rise to the hot springs of Iceland, has been 

 cleared up for us with certainty, we are entitled to 

 conclude, that the same agent has a share in pro- 

 ducing many other hot springs ; such, for instance, 

 as are not in the neighbourhood of high moun- 

 tains, of which the nearly boiling springs of the 

 islands of Ischia, Lipari, and Pantellaria are 

 examples ; near which besides, and that generally 

 in spots lying higher than the springs, jets of steam 

 (fumeroles) are observed. Even many springs 

 that are not quite so hot as these, such as those of 

 Aix-la-Chapelle, Burtscheid, Chaudes-Aigues, 

 &c., seem to depend on the action of underground 

 steam. 



