ATMOSPHEROLOGY. PAKHELIA. 393 



ler dimensions. At two of the intersections of the 

 coloured with the white circle, were exhibited bril- 

 liant parhelia of an irregular form. 



Huygens accounts for these phenomena, on the 

 supposition that the sun's rays are refracted by cy- 

 lindrical hail. It is, however, probable, that such 

 a form of hail does not occur in nature, though 

 snow or hail of a prismatic or spicular form is not 

 uncommon in the jjolar regions. These prisms or 

 spiculse are so slender, that they assume the appear- 

 ance of white hair chopped into portions of one- 

 twentieth to one-fourth of an inch in length. They 

 fall most frequently when the temperature is about 

 the freezing point, and sometimes in great profu- 

 sion. 



Several appearances resembling the rainbow, pro- 

 duced by the refraction and reflection of the sun's 

 rays, in particles of congealed vapour, have been 

 observed. On the 5th of June 1817, in particular, 

 a beautiful iris was produced in a snow-shower ; and 

 on the 1st of June in the same year, in latitude 

 78° 29', a similar arch was impressed on a shower of 

 a kind of frozen fog. The colours, however, were 

 not so brilliant as those of the rainbow, and the 

 arch was much broader. The chord of this arch 

 at midday, measured 50°, and its versed sine or al- 

 titude 9°. 



The rainhow itself is an appearance so common, 

 that there is no need of dwelling upon it. The 



