From the above, it appears then, that a Halo
of 48° diameter may be ascribed to a property
in the doud of refracting certain of the rays at
an angle of 24°. A double Halo, the exterior
ring whereof includes an area of 48°, and the
interior ring whereof inclildes one of 10°, must
be attributed to a property in the cloud of
refracting certain of the rays at an angle of
24°, and certain other rays at an angle of 5°,
and so on of triple ones.
A Corona of 10° diameter appears to be the
consequence of a property in the cloud to refract
certain of the rays at every angle, from the
smallest, say an angle of V to 5% beyond which
the rays are refracted in the cloud, in the usual



Chap. 2. § 20. CAUSE OP THE HALO, &c. 109

manner. A double Corona, the inner one of which
is 5*^ diameter, and the outer 10°, is referrible to
a property in the cloud of refracting certain of
the rays at every angle, from I''' to 2® 30', and
certain other rays, from 2° 30' to 5°, and so on
of triple ones.*

For further particulars relative to these
phaenomena, I refer the reader to the works of
Aristotle,! Newton,:]: Huygens,|| Des Cartes,^
M. Helvetius,^ and to several papers in the
Philosophical Transactions** and Manchester's
Memoires.ff For explanation of the phaeno-
mena of the Rainbow, consult Newton's
Opticks.
By the problem above it appears, that no
two persons standing at any distance from each

* Even the breadth of the ring of a Halo itself must be
caused by a number of rays, refracted at somewhat diflferent
angles ; otherwise the breadth of the ring would equal only
the breadth of one ray.
