136 REPORT—1840. 
(1). They are much smaller, their radii (when several series 
of their colours appear at once) being from 1° to 6°. 
(2). The radins of any ring is not constant at different times. 
(3). The red occupies the owter ring, instead of the inner one 
as in the true halo. 
293. These coloured rings have a manifest analogy to those 
which bear Newton’s name ; and that great man, in his Optics*, 
has given an explanation, which, translated into modern lan- 
guage, would express the interference of the light reflected 
from the different parts of the drop. In June, 1692, he ob- 
served three rings or orders of colours round the sun of the 
diameters of 5° or 6°, 9°20! and 12°; on the 19th February, 
1662 (so early had he begun to speculate on these subjects), be 
had observed the two inner corone round the moon to have di- 
ameters of 3° and 52°, little more than half the dimensions of 
the others. 
294. The true explanation was unequivocally given by Young 
in 1802, in his paper “On some cases of the production of 
colours not hitherto described+,’’ amongst the consequences of 
the fertile principle of interferences, though in a different way 
from what Newton had imagined, or Jordan, who had attributed 
these colours to the inflection of light. Young had practically 
shown that the interposition of uniform strie or powder be- 
tween the eye and a luminous object produces coloured images 
of that object, depending for their position upon the dimensions 
of such striz or powder ; and he had theoretically given that 
beautiful explanation which was afterwards put in a more 
popular form by Fresnel and Fraunhofer. Yet it is remarkable, 
that the latter author (Fraunhofer), in describing the experi- 
ments on which he grounds the very same explanation of co- 
ronz, never mentions the name of Young. 
295. The explanation in effect amounts to this,—that on 
the wave-theory of light, a luminous point is seen only in 
one direction, because the diverging wave produced propagates 
from its surface at any moment impulses which, when they 
reach the eye with any sensible obliquity, have their effect 
compensated by the opposite displacements caused by the ad- 
jacent portions of the wave. By the interposition of particles, 
opake or of a certain refractive power, and of nearly uniform 
size, portions of light become sensible in an oblique direction, 
by the stoppage of the other portions whose different length of 
path would have caused them to annihilate the action of the 
* Book ii. part iv. obs. 13. +t Philosophical Transactions, 1802. 
} Entstehung der Héfe kleiner, Art. Schumacher, Astr. Abhandl., iii. 56. 
