1858.] on some Physical Properties of Ice, 457 



produced upon the thermometer. In fact, all the rays that glass 

 could absorb had been absorbed by the lens, and the heat con- 

 sequently passed through the thin glass envelope of the thermo- 

 meter, and the air within it, without imparting the slightest sensible 

 heat to either. 



The bubbles observed by the speaker, and those which occur in 

 the deeper portions of glacier ice, he supposes to have been pro- 

 duced by heat which has been conducted through the substance 

 without melting it. Regarding heat as a mode of motion, he 

 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 liquidity. 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 similar to those at the surface ; and they are 

 liberated by an amount of motion which has been transmitted 

 through the ice without prejudice to its solidity. The conception 

 is helped when we call to mind the transmission of motion through 

 a series of elastic balls, by which the last ball of the series is de- 

 tached, while the others do not suffer visible separation. The 

 speaker, moreover, proves, by actual experiment, that the interior 

 portion of a mass of ice may be liquified by an amount of heat 

 which has been conducted through the exterior portions without 

 melting them. 



Now precisely the converse of this takes place when two pieces 

 of ice, at 32° Fahr., with moist surfaces, are brought into contact. 

 Superficial portions are by this act transferred to the centre, where 

 a temperature of 32° is not sufficient to produce liquefaction. The 

 motion of liquidity which the surfaces possessed before contact is 

 now checked, and the pieces of ice freeze together. This appears 

 to furnish a complete explanation of all the cases of this nature 

 which have hitherto been observed. 



The particles of a crushed mass of ice at 32°, or a ball of moist 

 snow, may, it is now well known, be squeezed into slabs or cups of 

 ice. That moisture is necessary here, and that the same agent is 

 necessary in the conversion of snow into glacier ice, was proved by 

 the following experiment. A ball of ice was cooled in a bath of 

 solid carbonic acid and ether, and thus rendered perfectly dry. 

 Placed in a suitable mould, and subjected to hydraulic pressure, 

 the ball was crushed ; but the crushed fragments remained as 

 tvhite and opaque as those of crushed glass. The particles, while 

 thus dry, could not be squeezed so as to form pellucid ice, which is 

 so easily obtained when the compressed mass is at a temperature of 

 32® Fahr. 



[J. T.] 



