366 Mr, Brougham’s Experiments and Observations 
side of v o’s shadow opposite to r' v'. Also when v o is convex 
instead of concave, the like fringes will be produced by the rays 
being deflected in passing by its sides. Lastly, when v o is 
a polished streak, images by reflexion will be produced, as 
described Phil. Trans, for 1796, p. 269. The same passage 
will also shew the reason why, on great inclinations, colours 
by reflexion should be produced. And the second proposition, 
with respect to flexion, follows from what was demonstrated in 
this paper (p. 357 and 358); it being that case where the rays 
either leave or fall on the speculum at such an inclination, as to 
come only within the sphere of inflexion, without being de- 
flected. The fourth proposition is merely a simple case of 
flexion. And the two last require no illustration. I shall now 
relate how I inquired into the truth of these things a posteriori. 
Observation 1. Looking at a plane glass mirror exposed to 
the sun’s light, I observed that up and down its surface there 
were minute scratches (called hairs by workmen), and that 
each of these reflected a bright colour, some red, others green, 
and others blue. On moving the mirror to a different inclina- 
tion, or my eye to a different position with respect to the mir- 
ror, I saw the species of the colours change ; the red, for in- 
stance, became green, and the green blue. I applied my eye 
close to the mirror, and received on it the light reflected from 
one hair. I observed several distinct images of the sun much 
distended and regularly coloured, just like those described above ; 
the same appearances were observable in all specula, metal and 
glass, which had these hairs, and I never saw any metal one 
without some : their size is exceedingly small, not above l 
of an inch. Rubbing a minute particle of grease on the sur- 
face of the speculum, images were seen on the fibrous surface : 
