406 SCIENTIFIC WRITINGS. 



between the fluid interior and the surface. The still 

 fluid terrestrial mass must then penetrate into these 

 cracks, and as it is hot and therefore lighter than the 

 superincumbent rock, it must burst forth and form a 

 mountain, with a height corresponding to the difference 

 of the specific gravity. As with the diminution of the 

 pressure, exerted on the hot fluid ascending in the 

 fissures, the gases and vapours contained in the magma 

 must be set free, the bubbles of gas in the column 

 of fluid rock will still further considerably diminish 

 its specific gravity, and the height to which the fluid 

 interior is raised in volcanoes is thereby explained, 

 without the necessity of assuming a mysterious pressure 

 in the interior overbalancing the hydraulic force. 



It is surprising that professional geologists have 

 left these views, modifying in such essential points the 

 foundations of their traditional doctrines, unnoticed and 

 unrefuted for now more than a decennium. 



In an essay "On the luminosity of flame" I de- 

 scribed a series of experiments on the problem of the 

 radiation of light of gaseous bodies, which I partly 

 instituted in the large glass furnaces, provided with 

 regenerative heating, of my brother Frederick in Dresden 

 and in conjunction with him. It appeared from these 

 experiments that permanent gases, if entirely free of 

 dust, are not luminous even at a very high temperature. 

 As they at the same time possess a remarkable power 

 of radiating heat, it is doubtless to be assumed, that 

 with further increase of heat they must nevertheless 

 at last begin to be luminous, because rays of light and 



