THE EARTH. 



123 



will come most properly under that of the several minerals I'Y 

 which tbey are produced. 



After all, therefore, we must be contented with but an im- 

 pure mixture of our daily beverage. And yet, perhaps, this 

 very mixture may often be more serviceable to our health than 



offered. Wlien they are connected with volcanoes, we naturally ascribe tJie 

 temperature of thet spring to the heat of the volcano ; but when they occur 

 Rt a considerable distance from volcanic countries, such an explanation can- 

 not be applied. Thus, the hot spring at Bath, has continued at a tempera, 

 ture higher than that of the air, for a period not less than 2000 years ; yet it 

 is so far from any volcano, that we cannot, without a very violent and im- 

 probable extension of volcanic fires, ascribe it to their energy. There ara 

 various decompositions of mineral bodies, which generate considerable heat 

 These decompositions are generally brought about by means of water; or to 

 speak more properly, water is itself the substance which is decomposed, and 

 which generates heat by its decomposition. Thus, for example, there are 

 varieties of pyrites, which are converted into sulphate of iron by the contact 

 of water, and such a change is accompanied by an evolution of heat. Were 

 we to suppose the Bath spring to flow through a bed of such pyrites, its heat 

 might be occasioned by such a decomposition. Such probably is the way in 

 which those springs, that contain sulphurated hydrogen ga-s, receive their 

 impregnation. But we are pretty certain, that such a supposition will not 

 apply to Bath water : first, because it does not contain the notable quantity 

 of sulphate, or iron, which would be necessary upon such a supposition ; and, 

 secondly, because instead of sulphurated hydrogen gas, which would infalli. 

 bly result from such a decomposition of pyrites, there is an evolution of azotic 

 gas. This evolution of azotic gas, however, is a decisive proof that the heat 

 of Bathwater is owing to some decomposition or other which takes place 

 witliin the surface of the earth; though from our imperfect acquaintance 

 with the nature of mineral strata, through which the water flows, we cannot 

 give any satisfactory information about what that decomposition actually is 

 In the island of St Miguel, one of the Azores, wliich exhibits, acc.irding to 

 Mr Masson, very obvious marks of having abounded in volcanoes, there are 

 R considerable number of hot springs of various temperatures ; some boiling 

 hot, others cooler, and some so low that they are used as baths, and have ac- 

 quired great celebrity for the wonderful cures they have performed. Mr 

 Masson informs us, that these springs are surrounded with abundance of na. 



live sulphur, which, he affirms, is exhaled by them in abundance a circum. 



stance which renders it probable, that the heat of these springs depends upon 

 the decomposition of pyrites. 



In the island of Amsterdam there are several hot springs ; in one of them 

 was immersed Fahrenheit's Thermometer, which in the air stood at sixty- 

 two degrees, and it ascended immediately to 19S0. In another it rose 204» ■ 

 mid the bulb of the thermometer being applied to a crevice, ascended in less 

 than a minute to the boiling point. Some fish being caught and put into the 

 f pring, were boiled 8t for eating in 15minute3. In the island of Iceland there 

 ore many hot springs, and several magnificent spouting springs, which ara 

 called Geysers 



1^2 



