298 es; Halos. 
in the atmosphere is concerned in their production ; in the case of 
hail, he supposes that the spherical drops of water congeal into the 
same form, and that the spicular, prismatic and stellar form of snow 
flakes, depends on crystallization from the state of vapor. The 
light which comes to the eye, in cases like that described above, 
passes through a compound medium. 
A cloud of rain, snow or ice intervenes between the eye and the 
luminous body. The cloud is near or distant. 
It will be large in direct proportion to the angle of vision which it 
subtends, and the diameter will be in an exact ratio to the visual an- 
gle. The various sizes of these halos are explained by the case of 
a rainbow, the continuity of whose are depends on the continuity of 
the cloud, and the edge of the cloud limits the extent of the refrac- 
tion (for there the medium is broken off, and is at an end); 80 it 
follows that the size of the cloud will control the limits of the reflec- 
_ tion in the corresponding case of a halo, or simple corona. Sup- 
pose the sun elevated, and acloud of dry, glistening snow inter 
__venes between it and the spectator.. The whole mass. 
flective like water, or like glass, or like a semi-opaque body. 4 
extremity of the cloud, or at the densest part, the rays will be most 
strongly attracted and reflected, since it is proved that light is subject 
to this general law, and they will représent a circular image, for they 
proceed in right lines from a spherical body. 
Although refracted by the earth’s atmosphere, they move in equal | 
parallelism, as well after as before refraction. All the direct ae 
P, 
he sun passing through the cloud would represent that objects 
those striking the cloud, in other angles, would have the angles 
acidence and reflection equal, or in other words, would be reflect- 
ed to different points of sight, and give to other spectators at the other 
positions a similar image. If the circle be white, the rays, 25 P& 
sessing equal refrangibility, are called homogencous, if colored, het- 
erogeneous, because unequally refrangible. The halo seen oP the 
7th of February was of pure white, the rays were homogeneous. 
and the medium transmitting them was consequently of the sc 
refracting and reflecting power throughout, a fact which goes very 
far to support the theory already projected. 
We have heard of many facts which show that entire clouds be- 
come the media of reflection.. On the Alps the figure of a man 
is seen by the wondering shepherds. In Sicily the Fata Morgan? 
are well authenticated, and within our own knowledge a fact exists 
ae 
