Lesson xxvu.] HALOS AND PARHELIA. 173 



trie to the luminary, having their longest diameter 

 perpendicular to the horizon and extending farther 

 below the luminary than above it : this probably is 

 a deception of vision, arising from the apparent 

 concave of the sky being less than a hemisphere. 

 Those about the moon are often very large, and 

 when seen by the country people, they will com- 

 monly observe, " We shall have a change of 

 weather soon, for there is a bur round the moon :" 

 perhaps their observation may not be altogether 

 void of a reasonable foundation. 



Philosophers sometimes conceive Halos to arise 

 from a refraction of the rays of light in passing 

 through the fine rare vesiculae of a thin vapour to- 

 wards the upper parts of the atmosphere. But an 

 opinion more generally receivrd, is that which 

 supposes Halos to be formed by small round grains 

 of hail, composed of two different parts; the one 

 of which is transparent, inclosing the other which 

 is opaque, and the reflection from these producing 

 the appearances : this is the more probable when it 

 is recollected that they are only seen in frosty, 

 rhimy, or hazy weather. 



There are several ways of exhibiting phaenomena 

 similar to those of Halos : thus, the flame of a can- 

 dle, placed in the midst of a steam in cold weaihrr, 

 or placed at the distance of some feet on the other 

 side of the window, in each of these circumstances 

 will appear to be encompassed by a coloured Halo. 

 Also, when the window of a room is encrusted 

 over with a thin plate of ice, the moon seen 

 1 3 through 



