110 



ON SNOW CRYSTALS. 



respecting the state of the atmosphere at the time any pecu- 

 liar configuration was distinguished. Mr. Scoresby on the 

 contrary has referred almost every figure to a table, exhibit- 

 ing the most obvious atmospheric phenomena at the time each 

 crystal was observed. The portion of this table which relates 

 to the varieties noticed by us, is here extracted for the conve- 

 nience of reference in our remarks on the several forms here- 

 after recorded. 



State of the atmosphere as observed at the Belfast Museum, Jan. 14th, 1838. 

 9 A.M. Therm. 31.50. Bar. 29.95. Wind E.S.E. calm.) Sky generally 



3 P.M. 



32.95. 



■29.86. 



S.E. 



) overcast. 



No. I. This is identical with No. 1 of Scoresby. In speaking of it he re- 

 marks, — " It is the most general form met with. It varies in size 

 from the smallest speck to ^ of an inch diameter. It seems in great- 

 est profusion when the temperature approaches the freezing point." 

 This figure with its various modifications, forming No. 1 to 8 in our 

 list, was by far the most abundant. Its size varied from 2 to 4 lines 

 in diameter. Its radii, with their attendant ramifications, recal im- 

 mediately to the mind the appearance of some vegetable productions. 

 This idea occurred nearly two centuries ago to Hooke; who remarks, 

 "there is a vegetable which does exceedingly imitate these branches, 

 and that is Feam, where the main stem may be observed to shoot out 

 branches, and the stems of each of these lateral branches, to send 

 forth collateral," &c. 



No. 2. In this the lines diverging from each ray increase in length as they 

 approach the extremity, so that those from the adjacent radii come 

 nearly into contact. It does not appear among the numerous figures 

 of Nettis or Scoresby. 



No. 3. In this on the contrary the lines gradually decrease as they approach 

 the extremity, and the figure precisely resembles one given in Hooke's 

 Micrographia (the largest in the second line), except that the six ra- 

 dii presented a more pointed appearance. 



No. 4. Here the lines diverging from the radii were extremely irregular in 

 length. It is not figured by the authors above referred to.* 



