£ 56 Mr. Brougham’s Experiments and Observations on 
5. Passing over other phenomena of less note, I come now 
to one that has divided opticians more than any other ; I 
mean the coloured fringes that surround the shadows of bodies. 
I made several observations on these, which enable me to con- 
clude that each fringe is an image of the luminous body ; for 
holding between my eye and a candle two knife blades, as I 
approached the one to the other, the edge of the candle seemed 
multiplied, and soon became coloured, coming wholly away 
from the candle, and as the knives approached still nearer, be- 
came distinct dilated images, highly tinctured with the pris- 
matic colours ; and just before the knives met, the candle, 
whose edges had been all along coloured with red and yellow, 
became much distended, till at last it was divided in the 
middle, one half seeming to be drawn away by each knife, 
and then it wholly disappeared. I have observed three kinds 
of these images ; two without and one within the shadow ; the 
first had its colours in the order from the shadow, red outer- 
most, and violet innermost ; the second and third had the co- 
lours in the contrary order, but the second was so very faint 
that I could never perceive it unless when let fall on my eye. 
All this is easily explained by the different flexibility of the 
rays. In fig. g. let AD be a body, by which the rays SDT 
and S'D'T' pass ; and let SD be within AD’s sphere of inflec- 
tion, and S'D' within its sphere of deflection; then SD will 
be bent into DG, but because of the different inflexibility of 
its parts, the red will be bent into DR, and the violet into DV, 
and the intermediate rays will fall between R and V, the 
whole forming an image RGV, separated into the seven pri- 
mary colours ; and in like manner, by the different deflexibi- 
lity of the parts whereof S'D' consists, an image without the 
