78 



In a third section the air- and water-cavities observed in ice are 

 examined. These the author observed in lake ice, and they are 

 manifestly the same as those described by M. Agassiz, the Messrs. 

 Schlagintweit, and Mr. Huxley, as occurring in the ice of glaciers. 

 The hypothesis of M. Agassiz and the Messrs. Schlagintweit is, that 

 the air-bubble absorbs the heat which the ice, as a diathermanous 

 body, has permitted to pass, the solid surrounding the bubble being 

 liquefied by the heat thus absorbed. Mr. Huxley makes the suppo- 

 sition most in accordance with the facts known at the time of his 

 observations, namely, that the water in the cavity has never been 

 frozen. It is shown by the author that the water-cavities examined 

 by him have been produced by the melting of the ice. 



But the hypothesis of M. Agassiz and the Messrs. Schlagintweit, 

 which appears to have received general acceptance, leads to the fol- 

 lowing consequences : Taking the specific heat of water and of air 

 into account, the author shows that a bubble of air, in order to raise 

 its own volume of water 1 in temperature, must lose 3080. 



Taking the latent heat of water into account, the author shows 

 that, to melt its own volume of ice, an air-bubble must part with 

 3080X142-6, or 439,208 of temperature. Now M. Agassiz states, 

 that when a piece of ice containing bubbles is exposed to the sun, 

 the water formed soon exceeds the air in volume. Hence, if his 

 hypothesis be correct, the quantity of heat absorbed by the air in 

 the brief time of an observation, would, if it had not been communi- 

 cated to the ice, be sufficient to raise the bubble to a temperature 

 1 60 times that of fused cast iron. The author further infers, from 

 the experiments of Delaroche and Melloni, that the quantity of heat 

 absorbed by a bubble of air at the earth's surface, after the heat has 

 traversed our atmosphere and been sifted by it, is absolutely inap- 

 preciable. This conclusion becomes stronger when the absorption 

 by the ice in the case before us is added to the absorption by the 

 atmosphere. 



Regarding heat as a mode of motion, the author shows that the 

 liberty of liquidity is attained by the molecules at the surface of a 

 mass of ice before the molecules at the centre of the mass can attain 

 this liberty. Within the mass each molecule is controlled in its 

 motion by the surrounding molecules. But if a cavity exist at the 

 interior, the molecules surrounding that cavity are in a condition 



