456 Professor Tyndall, [Jan. 22, 



tion, because the volume of the liquid is less than that of the ice 

 which produced it ; whereas, if the air be simply that entrapped in 

 the snow of the neve, it will not be thus rarefied. Here, then, we 

 have a test as to whether the water-cells have been produced by 

 the melting of the ice. 



Portions of ice containing these compound cells were immersed 

 in hot water, the ice around the cavities being thus gradually 

 melted away. When a liquid connexion was established between 

 the bubble and the atmosphere, the former collapsed to a smaller 

 bubble. In many cases the residual bubble did not reach the 

 hundredth part of the magnitude of the primitive one. There was 

 no exception to this rule, and it proves that the water of the 

 cavities is really due to the melting of the adjacent ice. 



The first hypothesis above referred to is that of M. Agassiz ;. 

 which has been reproduced and subscribed to by the Messrs. 

 Schlagintweit, and accepted generally as the true one. Let us 

 pursue it to its consequences. 



Comparing equal weights of air and water, experiment proves 

 that to raise a given weight of water one degree in temperature, as 

 much heat would be needed as would raise the same weight of 

 air four degrees. 



Comparing equal volumes of air and water, the water is known 

 to be 770 times heavier than the air ; consequently, for a given 

 volume of air to raise an equal voluine of water one degree in 

 temperature, it must part with 770 x 4 = 3080 degrees. 



Now the quantity of heat necessary to melt a given weight of 

 ice would raise the same weight of water 142*6 Fahr. degrees in 

 temperature. Hence to produce, by the melting of ice, an amount 

 of water equal to itself in bulk, a bubble of air must yield up 

 3080 X 142 '6, or upwards of four hundred thousand degrees 

 Fahrenheit. 



This is the amount of heat which, according to the hypothesis 

 of M. Agassiz and the Messrs. Schlagintweit, is absorbed by the 

 bubble of the air in a short time under the eyes of the observer. 

 That is to say, the air is capable of absorbing an amount of heat 

 which, had it not been communicated to the surrounding ice, would 

 raise the bubble to a temperature 160 times that of fused cast 

 iron. Did air possess this enormous power of absorption it would 

 not be without inconvenience for the animal and vegetable life of 

 our planet. 



The fact is, that a bubble of air at the earth's surface is unable, 

 in the sightest appreciable degree, to absorb the sun's rays ; for 

 those rays before they reach the earth have been perfectly sifted by 

 their passage through the atmosphere. The following experiment 

 illustrative of this point, has been made by the speaker : the rays 

 from an electric lamp were condensed by a lens, and the concen- 

 trated beam sent through the bulb of a differential thermometer. 

 The heat of the beam was intense ; still not the slightest effect was 



