395 
Natural Philosophy.— Optics, 
that equilateral prisms of ice, with angles of 60°, float in the 
air with their angles in all possible directions, and thus produce 
the halo. More numerous and recent observations have establish- 
ed the truth of this hypothesis beyond a doubt. Dr Brewster has 
shewn, that the crystals of ice always belong to the rhomboidal 
series of Mohs, including the six-sided prism of Haiiy, whose 
angles are 60° ; and Sir Charles Giesecke, in the article Green- 
land , in the Edinburgh Encyclopaedia, vol. x., p. 387, and 
other travellers, have put it beyond a doubt, that particles of 
ice float in the air, and actually prick and blister the skin, with 
the same sensation that would be produced by needles, during 
the prevalence of what is called the Frost Smoke. The singular 
compound figures, which are almost always hexagonal combina- 
tions, drawn by Captain Scoresby, in his interesting Account of 
the Arctic Regions , shew what a variety of forms are likely to be 
produced in the circles which surround the sun and moon, by 
the combination of elementary prisms of ice. 
8. Parhelia. — Two beautiful parhelia or mock suns were 
observed from York, for the space of three quarters of an hour, 
between two and three o’clock in the afternoon of Saturday the 
8th March, at the distance of 24 degrees from the sun, and in 
a line parallel with the horizon. The brilliancy, which for one 
or two short periods became distressing to the eye, was occa- 
sionally impaired by the intervention of some light fleecy clouds 
moving slowly and at a considerable altitude, but was not affect- 
ed whenever the same clouds passed over, and sometimes nearly 
obscured, the face of the sun. The sky, in other directions 
clear and serene, was slightly tinged by a whitish vapour float- 
ing apparently at a great elevation above the surface of the 
earth at the place of their appearance, — the sun itself being 
partially obscured by the same vapour. The sides of the par- 
helia nearest the sun were of a red tint, shaded into orange and 
yellow, and for a short interval two segments of a whitish halo 
passing through the parhelia were perceptible. Altitude of the ' 
sun and parhelia, at the time of their greatest brilliancy, 22 f : 
Barometer 29.736 : Thermometer in shade 41°. Wind brisk 
from NNW. This meteor, of very unfrequent occurrence in 
England, appears to have been similar in many respects to one 
described in Parry’s Voyage, p. 156. 
