70 Dr Daubeny on Thermal Springs, 



itself is curious, I shall avail myself of the kind permission of 

 its author to publish it, and shall afterwards proceed to shew, 

 that though it presses hard against the notion often entertained 

 of the chemical theory *, it cannot operate as an objection to 

 that view of it, which I have adopted in my description of vol- 

 canos, and to which I have ever since found reason to adhere. 



According to Borelli, (See Ferrara, Description de FEtna, 

 p. 200), the lava which proceeded from Etna in 1669 was five 

 miles in breadth, fifteen in length, and from 50 to 1 00 feet in 

 thickness, which gives a bulk equal to about 93,838,950 cubic 

 feet. Let us set it down at 94,000,000 of cubic feet, and as 

 the most compact lava has the specific gravity of 3, let us re- 

 duce the quantity to one-half, or to 47,000,000 of cubic feet, in 

 order that we may be justified in calculating it as having that 

 specific gravity. Now, as a cubic foot of water weighs 70 lb., a 

 cubic foot of lava of the specific gravity of 3. will weigh 210 lb.; 

 and the 47,000,000 cubic feet of lava, multiplied by this latter 

 sum, will give, as the weight of the whole mass emitted during 

 the eruption, 9,870,000,000 lb. 



Now, according to Dr Kennedy, 100 parts of lava consist of 

 the following ingredients : 



containing of Oxygen 25 

 9 



100 41 



Consequently, of these 9,870,000,0001b., two-fifths consist of 

 oxygen, so that 3,938,000,000 lb. of the latter element must 

 have been expended in the process. Now, as water consists of 

 89 by weight of oxygen, and 11 of hydrogen, this quantity of 

 oxygen would require the consumption of 4,437,956,169 lb. of 

 water, equal to 63,798,024 cubic feet. Now this would corres- 

 pond to a depth of nearly four inches of water to a league square. 

 The hydrogen disengaged by the decomposition of this quantity 

 of water would be 487,955,056 lb. ; now, as a cubic foot (1728 



• See, for instance, Dr MacCuUoch's late work. 



