OBSERVED IN SNOW CRYSTALS. 7 



quite natural for crystalline forms. Some such ice crystals 

 which I observed and figured from Davos in Switzerland*, 

 show a variety of curved lines, the cause of which I found 

 for some time enigmatical ; but the explanation is so 

 extremely simple that I feel surprise that it did not at once 

 present itself to me, and, I believe, shows that such obser- 

 vations may have a scientific utility. 



It is not often in England that there are favourable op- 

 portunities for observation, as the temperature is seldom 

 much below freezing. Frequently in the Swiss mountainous 

 districts, when a very low temperature obtains, there are a 

 great number of the ice-crystals just mentioned floating in 

 the air. These are usually the most beautiful and regular, 

 and are the most readily examined. 



The illumination I used was Wenham^s parabolic re- 

 flector. The lines which I wish to bring before your 

 notice are the curved internal ones, especially such as the 

 meander line in fig. G. 



Fig. Q. 



This crystal I carefully watched during the process of 

 melting. First the external arms melted down as far as 

 this meander line; next the crystal melted down to 



* Klimatologische Notizen u. d. Winter im Hochgebirge von Arthur W. 

 Waters. Basel, 1871. 



