The Interior of the Earth 



the ground to a depth of more than a hundred 

 yards over a surface of over a hundred square 

 kilometres, while distributed over the surface of 

 the globe it would not have reduced its radius 

 by nrznrth of an inch. Mallet's theory is equally 

 incapable of explaining the enormous outpour- 

 ings of gas which accompany eruptions and 

 transform the vents of volcanoes into regular 

 cannon trained against the sky and discharging 

 their projectiles to a height of several miles. On 

 the contrary it is reasonable to admit that under 

 the pressure of the primitive atmosphere, which 

 must have been three hundred times greater 

 than at present, the molten mass of the globe 

 dissolved these gases which to-day escape 

 through the fissures of the crust. 



A more ingenious and more frequently- 

 advanced hypothesis seeks in chemical reactions 

 the origin of volcanic manifestations. Already 

 at the end of the seventeenth century Nicolas 

 L6mery hit on the idea of burying a mixture of 

 iron filings and flowers of sulphur. When 

 wetted with warm water the sulphur and iron 

 combined with production of heat, the ground 

 swelled and steam could be seen escaping from a 



143 



