372 Mr. Brougham's Experiments and Observations 
a lens; nor was a very excellent one belonging to a Dollond’s 
telescope free from them. The rings with their dark intervals 
resembled those floating specks so often observed on the surface 
of the eye, and called “ muscce volitantes ,” only that the muscae 
are transparent in the middle, because formed by drops of hu- 
mor : they will, however, be found to be compassed by rings 
of faint colours, which will become exceedingly vivid if the eyes 
be shut and slowly opened in the sun’s light, so that the hu- 
mor may be collected ; they also appear by reflexion, mixed 
with the colours described in Phil. Trans, for 1796, p. 268. 
Observation 10. The sun shining strongly on the concave 
metal speculum, placed at such a distance from the hole in the 
window that it was wholly covered with the light ; upon in- 
clining it a little, the image on the chart was bordered on the 
inside with three fringes similar to those already described ; on 
increasing the inclination these were distended, becoming very 
bright and beautiful ; when the inclination was great, and when 
it was still increased, another set of colours emerged from the 
side next the speculum, and was concave to that side. Here 
I stopped the motion, and the image on both sides of the focus 
had three sets of fringes, and four fringes in each set; but 
when viewed through a prism (as before described), the num- 
bers greatly increased, both the fringes and the dark intervals 
decreasing regularly. The appearance to the naked eye is re- 
presented in fig. 6 . where ADC being the image, A and C are 
the sets of fringes at the edges, and B the third set, there being 
none at E and D the sides, since the light which illuminates 
these quarters comes not from the edges of the speculum in so 
great inclinations. I now viewed the surface of the speculum, 
and saw it, in the place answering toB in the image, covered with 
