ANTIIELIA AND CORONA. £83 
come under my observation, however, the shadows 
were evidently reflected from the surface of the 
sea, remaining unaltered after the dispersion of 
the fog, and the consequent disappearance of the 
corona;. 
The anthelion has generally been considered as 
a rare phenomenon; and especially when com¬ 
bined with the concentric crowns, has, I believe, 
been observed by very few individuals. Mr 
Swinton, who saw an anthelion near Oxford, in 
the year 1762, was only able to meet with two 
instances upon record,—one observed near Dant- 
zic, by Hevelius, in 1661; and another seen at 
Wittemberg, 18th January 1738*. 
Dr (Thomas) Young, in his theory of haloes, 
observes, that equilateral prismatic crystals of ice 
(of 60°) produce a deviation of 23° 37', “ for rays 
forming equal angles with its surfaces, and the 
angle of deviation varies at first veiy slowly, as 
the inclination changes, the variation amounting 
to less than 3°, while the inclination changes 
30°.” The effect of such prisms, he conceives, if 
placed at all possible angles in the air, between 
an observer and the sun, would be to produce a 
circle of light at the angular distance of about 23° 
37', or within 3° of it, which is the usual diameter of 
the halo; and the halo of 47° he accounts for on 
* Phil. Trans, vol. lii. p. q 4 . 
