ON SNOW CRYSTALS. 107 



Art. II. — On someSnoiv Crystals observed on the 14/A of January, 

 1838. By William Thompson, Esq., (V.P.), and Robert 

 Patterson, Esq., Members of the Natural History Society of Bel- 

 fast. 



At Belfast, on the 14th of January, 1838, about half an hour 

 after noon, we remarked among some ordinary snow-flakes 

 which, since the morning, had been falling very sparingly, 

 some of the beautiful lamellar crystals which present so great 

 a diversity of figure. We immediately hastened out of town, 

 that we might have an opportunity of observing them undis- 

 turbed, and for about an hour enjoyed this high gratification. 

 They then ceased to fall, the day became fine, and no return 

 of the phenomenon took place. 



With respect to the means of observation, we were very dif- 

 ferently circumstanced from Dr. Nettis, who states that he 

 w T as "prepared, in the year 1740, to make the most minute 

 observations, and the most exact drawings in his power, of 

 the most perfect figures of snow." — ('Phil. Trans.' 1755, p. 

 645) : and mentions the kind of microscope, and double con- 

 vex glasses employed for this purpose. We were furnished 

 only with the ordinary pocket lenses, and consequently were 

 unable to attain that minute accuracy which is so desirable. 

 However, we most carefully sketched the crystals, either as 

 they fell, or lay undisturbed on pieces of wood or metal ex- 

 posed to the weather ; and thus secured representations of a 

 considerable number. 



On the following day we had the pleasure of comparing 

 and identifying nearly all our figures with those of Hooke, 1 

 Nettis, and Scoresby, 2 but at the same time discovered that 

 some which we had seen, had not been described or delineated 

 by these authors. Nineteen distinct forms at least were 

 distinguished ; and when the limited period of our observa- 

 tions is considered, in connection with the simple lenses em- 

 ployed, we feel satisfied that under more favourable circum- 

 stances, the number of figures might easily have been doubled. 



It was the opinion of Scoresby that the configuration of the 

 crystals "may be referred to the temperature of the air," and 

 in his table some (which we recognised) are mentioned as 

 having been observed at a temperature of 10°, and others at 

 a temperature of 27.26°. From the circumstance of several 

 distinct figures having been detected by us falling simultane- 

 ously, it is obvious that a great diversity of form may be co- 

 existent with the same degree of temperature, and of course 



1 ' Micrograpliia.' 2 'Arctic Regions.' 



