ggo Dr. Young’s Accoun t of some Cases 
When a number of fibres of the same kind, for instance, a 
uniform lock of wool, are held near to the eye, we see an appear- 
ance of halos surrounding a distant candle ; but their brilliancy, 
and even their existence, depends on the uniformity of the 
dimensions of the fibres ; and they are larger as the fibres are 
smaller. It is obvious that they are the immediate consequences 
of the coincidence of a number of fringes of the same size, 
which, as the fibres are arranged in all imaginable directions, 
must necessarily surround the luminous object at equal distances 
on all sides, and constitute circular fringes. 
There can be little doubt that the coloured atmospherical 
halos are of the same kind : their appearance must depend on 
the existence of a number of particles of water, of equal dimen- 
sions, and in a proper position, with respect to the luminary and 
to the eye. As there i's no natural limit to the magnitude of the 
spherules of water, we may expect these halos to vary without 
limit in their diameters; and, accordingly, Mr. Jordan has 
observed that their dimensions are exceedingly various, and 
has remarked that they frequently change during the time of 
observation* 
I first noticed the colours of mixed plates, in looking at a 
candle through two pieces of plate-glass, with a little moisture 
between them. I observed an appearance of fringes resembling 
the common colours of thin plates ; and, upon looking for the 
fringes by reflection, I found that these new fringes were always 
in the same direction as the other fringes, but many times larger. 
By examining the glasses with a magnifier, I perceived that 
wherever these fringes were visible, the moisture was intermixed 
with portions of air, producing an appearance similar to dew. 
I then supposed that the origin of the colours was the same as 
