140 REPORT—1840. 
violet arcs are already 2° apart, they will overlap, and form a 
whitish ring, whose radius will be that of the red ring of the 
rainbow, or 42°, diminished by 73°, leaving about 35° for the 
radius of the whitish ring, agreeing sufficiently well with ob- 
servation. 
306. I apprehend, however, that there are many difficulties 
in this view of the subject. That light, four times reflected, 
should have intensity enough to produce three or more coronez, 
seems incredible. Again, the ring of 37° to 42° radius, ob- 
served by Kamtz and Scoresby, with faint colours, seems to be 
the rainbow itself, not the superposition of its faded colours, 
for Dr. Young very obscurely hints* as to the non-appearance 
of the real bow. The reason of its variable magnitude and 
faint colour is quite sufficiently explained by Mr. Airy’s in- 
vestigation (271.), in which the deviation of the maximum of in- 
tensity from the geometrical caustic is shown to depend upon 
the size of the drops, and that diminution of size diminishes the 
radius of the bow, and likewise the sharpness of its definition, 
though in every case (as it seems to us) the maximum next the 
caustic must be most intense, and therefore the true bow can 
never vanish so long as any of its subordinate features remain, 
which Dr. Young seems to have thought possible. Finally, 
Dr. Young, in another section of the paper so often referred 
tot, adopts the theory of diffraction as producing the lesser 
glories, and calculates the size of the drops on that hypothesis, 
which size is double that obtained on the other. : 
307. Had not this discussion been already extended further 
than persons more interested in meteorology than in physical 
optics may think suitable, I should have dwelt at some length 
upon certain curious phenomena of shadows with luminous 
borders, and certain vertical trains of light seen in connexion 
with them, which seem not to have received the attention which 
their theoretical importance demands. I wil] state very briefly 
what may serve to instigate further inquiry. 
308. Standing on the tower of Carisbrook Castle with a friend 
one calm hazy summer evening near sunset, I perceived glori- 
fied shadows as from the Rigi, but without colours. So intense 
was the concentration of rays opposite the sun, that the shadow 
of the head of the observer was almost obliterated by the inten- 
sity of the light which seemed to emanate from it. The shadow 
of the body was fringed all round by a luminous but colourless 
border. The shadow of another person standing a short way 
* Chromatics, p. 625, col. i.; p. 638, col. 1. 
+ Chromatics, Sect. xi. 
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