138 REPORT— 1840. 
station I have seen a single compound circle, of which the red 
ring had a diameter of 18°; but when I entered the cloud on 
the surface of which it had been formed, it contracted to about 
10°. In the Jura Mountains I once perceived traces of a faint 
ring of from 75° to 80° in diameter.* 
300. Accompanying the coloured rings, there is an appear- 
ance of white light, more intense towards the centre (corre- 
sponding to the prolongation of a line drawn through the sun 
and the eye of the spectator), which would give evidently the 
brightest illumination in the middle point, but for the shadow 
of the observer’s head, which, however, is wonderfully di- 
minished by the nebulous light. 
301. That crystals of ice should have anything to do with 
these appearances, as conjectured by Bouguer and Scoresby, 
is altogether incompatible with the circumstances under which 
other observers have seen them. It is equally impossible to 
refer these rings to the diffraction of the solar light falling 
upon particles of vapour surrounding the observer's head, as 
Fraunhofer supposed, and reflected back to his eye from the 
surface of the cloud; for I have observed these rings distinctly 
from a height of fifteen hundred feet above the cloudy screen, 
under a brilliant sky. But the common theory of diffraction of 
particles reflecting as well as stopping light, affords a plausible 
account of some of the phenomena. We have only to suppose 
the constituent materials of the cloud to be spherules (however 
composed) of nearly equal size which reflect innumerable images 
of the sun from their surfaces, backwards to the eye. Some of 
these must be placed at distances which shall re-inforce each 
other’s effect, and some which shall annihilate that effect ; and 
hence periodic colours will result, as in transmitted light (the 
case of corona). 
302. This opinion is confirmed (1) by the order of colours 
being that of diffraction rings (the red outermost); (2) by the 
arithmetical progression of the diameters observed by Bouguer 
and Scoresby; (3) by the curious fact noticed by myself, that 
on immersion in the cloud the rings suddenly shrink in size 
(due, no doubt, to an increase in the magnitude of the cloudy 
particles in the interior); (4) from the comparison made by 
Professor Kamtz, between the diameter of the Corona by 
* Haygarth, in the Manchester Memoirs (Ist Series, iii.), gives rather an 
unsatisfactory account of a glory which must have resembled those seen by 
Bouguer and others. The greatest faint circle at a distance from the smaller 
ones, is distinctly shown in the bad plate which accompanies the paper. 
+ Schumacher, Abhandl., iii. 63. 
