Prof. Tyudall on some Physical Properties of Ice. 339 



are confined to mere conjectures ; but I hope the coming winter 

 will enable me to investigate this highly interesting question. 

 § III. 

 20. What has been already said will prepare us for the consi- 

 deration of an associated class of phsenomena of great physical 

 interest. The larger masses of ice which I examined exhibited 

 layers in which bubbles of air were collected in unusual quan- 

 tity, marking, no doubt, the limits of successive acts of freezing. 

 These bubbles were usually elongated. Between two such beds 

 of bubbles a clear stratum of ice intervened ; and a clear surface 

 layer, which, from its appearance, seemed to have suffered more 

 from external influences than the rest of the ice, was associated 

 with each block. In this superficial portion 

 I observed detached air-bubbles irregularly 

 distributed, and, associated with each vesicle 

 of air, a bleb of water which had the ap- 

 pearance of a drop of clear oil within the 

 solid. The adjacent figure will give a no- 

 tion of these composite cavities : the un- 

 shaded circle represents the air-bubble, and 

 the shaded space adjacent, the water. 



21. When the quantity of water was sufficiently large, which 

 was usually the case, on turning the ice round, the bubble shifted 

 its position, rising always to the top of the bleb of water. Some- 

 times, however, the cell was very flat ; and the air was then quite 

 surrounded by the liquid. These composite cells often occurred 

 in pellucid ice, which showed inwardly no other sign of disin- 

 tegration. 



This is manifestly the same phsenomenon as that which struck 

 M. Agassiz so forcibly during his earlier investigations on the 

 glacier of the Aar. The same appearances have been described 

 by the brothers Schlagintweit ; and finally attention has been 

 forcibly drawn to the subject in a recent paper by Mr. Huxley, 

 published in the Philosophical Magazine*. 



22. The only explanation of this phsenomenon hitherto given, 

 and adopted apparently without hesitation, is that of M. Agassiz 

 and the Messrs. Schlagintweit. These observers attribute the 

 phsenomenon to the diathermancy of the ice, which permits the 

 radiant heat to pass through the substance, to heat the bubbles 

 of air, and cause them to melt the surrounding icef. 



* October 1857- , ^ • 



t II est e'vident pour quiconque a suivi le progres de la physique mo- 



(leme, que ce phenomene est d<i uniquement a la diathermaneite de la 



glace (Agassiz, Systhne, page 157). 



Das Wasser ist dadurch entstanden, dass die Luft Warmestrahlen absor- 



blrte wek-hc das Eis als diathermaner Korper d\irchliess (Schlagintweit, 



UntfiTSuchunf/en, \i. 17)- 



Z 2 



