340 Prof. Tyndall on some Physical Properties of Ice. 



The apparent simplicity of this explanation contributed to 

 ensure its general acceptance ; and yet I think a little reflection 

 will show that the hypothesis, simple as it may appear, is attended 

 with grave difficulties. 



23. For the sake of distinctness I will here refer to a most inter- 

 esting fact, observed first by M. Agassiz, and afterwards by the 

 JMcssrs. Schlagintweit. In the Si/steme Gluciaire'^' it is described 

 in these words : " I ought also to mention a singular property of 

 those air-bubbles, which at first struck us forcibly, but which 

 has since received a very satisfactory explanation. When a frag- 

 ment containing air-bubbles is exposed to the action of the sun, 

 the bubbles augment insensibly. Soon, in proportion as they 

 enlarge, a transparent drop shows itself at some point of the 

 bubble. This drop, in enlarging, contributes, on its part, to the 

 enlargement of the cavity, and following its progress a little, it 

 finishes by predominating over the bubble of air. The latter 

 then swims in the midst of a zone of water, and tends incessantly 

 to reach the most elevated point, at least if the flatness of the 

 cavity docs not hinder it." 



24. The satisfactory explanation here spoken of is that already 

 mentioned : let us now endeavour to follow the hypothesis to its 

 consequences. Comparing equal weights of both substances, 

 the specific heat of water being 1, that of air is 0"25. Hence to 

 raise a pound of water one degree in temperature, a pound of air 

 would have to lose four degrees. 



25. Let us next compare equal volumes of the substances. 

 The specific gravity of water being 1 , that of air is ^y ^ ; hence 

 a pound of air is 770 times the volume of a pound of water ; 

 and hence for a quantity of air to raise its oivn volume of water 

 1 degree, it must part with 770 x 4, or 3080 degrees of tempe- 

 rature. 



26. Now the latent heat of water is 142°-6 F. ; hence the quan- 

 tity of heat required to melt a certain weight of ice is 142*6 

 times the quantity required to raise the same weight of water 

 1 degree in temperature ; hence a measure of air, in order to 

 reduce its own volume of ice to the liquid condition, must lose 

 3080 X 142-6, or 439,208 degrees of temperature. 



27. This then gives us an idea of the amount of heat which, 

 according to the above hypothesis, is absorbed by the bubble and 



* Page 168. The figures to which M. Agassiz refers in the note to this 

 l)age seem to be correctly drawn; but his descriptive reference to them, 

 though in part correct, is in part unintelligible to me. He uses the term 

 Indies for the bubbles of air, and gouttelettes for the drops of water ; and I 

 believe the latter term is ahvays restricted to a liquid. But if we restrict 

 the term thus throughout the passage in question, there is no escape from 

 Mr. Huxley's conclusion, that M. Agassiz has taken the air-bubbles for 

 dfops of water, and the drops of water for air-bubbles. 



