146 Report of the Researches of M. Agassiz. 



ice in assuming the liquid form, diminishing its volume, and 

 thus occasioning the ascent of the mercury in the tube. Next 

 morning, when all the ice was melted, the mercury was found 

 to have still ascended ; but on this occasion it was due solely 

 to the contraction which the water and the air had undergone 

 from the cold of the night, for as the heat of day prevailed, 

 the mercury recommenced its descent ; and these variations 

 continued, after the same fashion, for many consecutive days. 

 Hence it follows that the effect of the external temperature is 

 very different, accordingas it acts upon water and uponice. The 

 ice in melting diminishes in volume, and hence the apparatus 

 indicated a contraction of the mass during the day, so long as 

 there was any ice in the jar. But the ice once thoroughly 

 melted, this same temperature, which before caused the melt- 

 ing of the ice, now dilates the water produced by that melting, 

 and causes a fall of the mercury during the day, and a rise 

 during the night. It necessarily follows from this, that what- 

 soever of a mysterious character M. Hugi imagined he dis- 

 covered in these facts, assigning a species of vitality to the 

 glaciers, is to be viewed as wholly chimerical. 



M. Hugi moreover alleged, that, during the night, ice ab- 

 sorbed the humidity of the air, and disengaged it during the 

 day ; and in this phenomenon he perceived another proof of 

 the vitality of glaciers. On the contrary, however, M. Vogt 

 has determined, by accurately weighing it, that ice exposed 

 to the air, in a hot day, when the hygrometer indicates great 

 dryness of the air, loses much by evaporation ; which evapo- 

 ration is in the direct ratio of the surface exposed to the at- 

 mosphere, and is equal in all kinds of congealed water, 

 whether it be snow or the matter of the neve, whether it be 

 white ice or blue. On the other hand, when the dew is abund- 

 ant, by the occurrence of nights at once cold and clear, ice is 

 decidedly increased in weight, but in the direct ratio of the 

 surface, and this increase is more considerable in propor- 

 tion as the dew has been more abundant. Every morning, 

 after a clear night, the surface of the glacier is found covered 

 with a coat of dew. When the cold is severe, this dew is 

 transformed into a coat of rime or hoar-frost reposing on the 

 moraine, whilst on the surface of the ice it produces a delicate 



