410 Prof. Erman on the Stnicture, the Melting, 



Peculiar influence of sun-rai/s upon snotv, when they cannot heat it 

 up to the temperature of melting. 



(Raise um die Erde, u. s. w., Histor. Abth, vol. i, p. 704. 

 Ti-avels in Siberia &c., vol. ii. p. 79.) 



December 13. Ou the Obdorian Mountains ; lat. 67° 13', 

 long. 64° 39' east from Paris, at about 1700 Par. feet (1812 

 English) above the level of the sea, the air being very dry, and 

 its temperature varying from — 26° to — 30° R The in- 

 clined strata (of hornblende slate) were quite bare, and it was 

 only on their eastern borders that snow had accumulated into 

 little hillocks It was curious to observe how the perpen- 

 dicular surface of the heaps of snow behind the rocks had become 

 changed in every instance into hard and mirror-like ice; for 

 this could not have been effected by an ordinary thawing. It is 

 true that the sunbeams, which (in this spot and at this time of 

 the year) played but horizontally over the plain, fell perpendicu- 

 larly on these walls of snow ; but as their intensity was weakened 

 by their passing through the densest strata of the air, they would 

 surely not have elevated the temperature of a substance less 

 fusible than ice from —28° R. to 0° R. The undoubted evapo- 

 ration which it undergoes even at the lowest temperatures, seems 

 also to prove a continuous liquefaction of its surface ; and as 

 this takes place when the surrounding bodies are far from being 

 warmed up to zero (of Reaumur), it seems that the extreme sur- 

 face of ice appropriates to itself the heat of liquefaction, not 

 according to the law of radiation, but perhaps to that of a che- 

 mical affinity. 



Additional remark {April 1859). — I am well aware that this 

 question is connected with the more general one — whether the 

 evaporation of any solid body takes place without a liquefaction 

 of the particles which form its surface ? The just-mentioned 

 phsenomenon seems to answer it in the negative. 



Wonderful transformations which snow-crystals were seen to undergo 

 from causes still to be explained. 



(Reise um die Erde, u. s. w., Histor. Abth. vol. ii. p. 395. 

 Travels in Siberia, &c. vol. ii. p. 501.) 



May 13. Lat. 60° 40', long. 138° 57' east from Paris, at 2580 

 Par. feet (2749 English) above the sea. — I had begun immedi- 

 ately after noon to measure solar altitudes, wheu a number of 

 light clouds began to form and then to be driven fast by the 

 west wind. The air cooled down (from about + 3° R.) to + 1°R., 

 and snow fell for sixteen minutes; then the clouds dissolved 

 again, the evening became clear, and the cold increased in the 



