Prof. Tyndall on some Physical Properties of Ice. 343 



it is not because the air gets rid of its heat by radiation, but 

 simply because its power of absorption is infinitely behind that 

 supposed by the hypothesis of M. Agassiz and the Messrs. 

 Schlagintweit, that animal and vegetable existence at the earth's 

 surface is possible. 



When air-bubbles occurred in those portions of the ice where 

 the liquid discs appeared, the associated water spread out on 

 planes parallel to those of the discs, evidently in consequence of 

 the freer yielding of the ice in these planes. Keeping this remark 

 in view, and comparing fig. 1 with fig. 10, plate 4 of M. Agassiz' 

 Atlas, the resemblance of both phsenomena will at once be per- 

 ceived. The glacier ice, like the Norway ice with which I ex- 

 pei'imented, is divided into segments by surfaces of discontinuity. 

 The air- and water-cavities are represented as flattened ; but, as 

 in the lake ice, they seemed flattened in all directions. M. 

 Agassiz regards the flattening of the cavities as a certain proof 

 that they have been squeezed flat by pressure ; and he attributes 

 the difi'erent directions of flattening to a power of independent 

 motion possessed by each fragment. The perfect similarity, 

 however, of the phaenomena presented by the two kinds of ice 

 must render us cautious in accepting an explanation which may 

 apply to the one, but excludes the other. 



§ IV. 



30. But the question still remains, how are the water-chambers 

 produced within the ice ? Mr. Huxley throws out the suggestion 

 which our knowledge at the time of his observations rendered 

 most probable, namely, that the water had never been frozen at 

 all, but had preserved itself, like the liquid in the cavities of a 

 Gruyere cheese, from the neve downwai'ds. 



31. One simple test will, I think, decide the question whether 

 the liquid is or is not the product of melted ice. If it be, its 

 volume must be less than that of the ice which produced it, and 

 the bubble associated with the water must be composed of rarefied 

 air. Hence, if on establishing a liquid connexion between this 

 bubble and the atmosphere a diminution of volume be observed, 

 this will indicate that the water has been produced by the melting 

 of the ice. 



32. From a block of Norway ice, containing such compound 

 bubbles, I cut a prism, and immersing it in warm water, con- 

 tained in a glass vessel, I carefully watched through the side of 

 the vessel the efi"ect of the melting upon the bubbles. They 

 invariably shrunk in volume at the moment the surrounding ice was 

 melted, and the diminished globule of air rose to the surface of 

 the water. I then arranged matters so that the wall of the cavity 

 might be melted away underneath, without permitting the bubble 



