24,6 Mr. Brougham's Experiments and Observations on 
the colours made by the reflecting body, and the manner of 
their formation. At present I shall only caution those who 
may wish to repeat the above experiments, that the hole in the 
window-shut must be small, the room quite dark, the pin well 
polished, and the desk, chart, &c. placed at a distance from the 
pin not greater than three feet, otherwise the images will be 
dilute and dim ; nor, on the other hand, less than six inches, 
otherwise they will be too short, and the colours not far enough 
separated one from another. 
My next object of inquiry was the different degrees of re- 
flexibility belonging to each ray. It appears, not only from 
mathematical considerations sufficiently obvious, but also from 
the experiments I have related, that though the different rays 
have at the same or equal incidences different angles of reflec- 
tion, yet each ray is constant to itself in degree of reflexibi-- 
lity, and that its sine of reflection bears always the same ratio 
to its sine of incidence. The question then is, what are the 
sines of reflection of the different rays, the sine of incidence 
being the same to all ? 
Obs. 9. In summer, at noon, when the sun's light was ex- 
ceedingly strong, and there was not the vestige of a cloud in 
the sky, I produced an uncommonly fine set of images, by 
fixing at an inch from the small hole -^th of an inch diameter, 
a pin -^-th °f an diameter. One of the brightest of these I 
let pass through the desk to the chart below at 2^ feet from 
the pin, and the image was 3 inches from the shadow in a 
straight line. I delineated it carefully, by drawing two paral- 
lel lines for the sides, and marking the semicircular ends. 
Then with the point of a small needle I marked the confines 
of the contiguous colours on one of the parallel sides, and 
