262 Mr. Brougham’s Experiments and Observations on 
luminous body,* I thought that, from this consideration, a 
method of determining the different degrees of flexibility of 
the different rays might be deduced, similar to that which I 
had formerly used for determining their degrees of reflexi- 
bility.-f I therefore made the following experiment. 
Obs. 12. Having let into my darkened chamber a strong 
beam of the sun’s light, through a hole ^th of an inch in dia- 
meter, I held a hair at four feet from the hole, and receiving 
the shadow at two feet from the hair, I drew a line across the 
middle of the coloured images, and pointed off in each the di- 
visions of the colours, as nearly as I could observe ; and repeat- 
ing the observation several times and at different distances, I 
found, by the same way I had formerly done in my experiment 
on reflexibility, that the axis, or line, drawn through the mid- 
dle of each, was divided inversely, according to the intervals 
of the cords which sound the notes in an octave, ut, re , mi, 
sol , la, fa, si, ut. But as the measures in these experiments 
were very minute, and the operations of consequence liable 
to inaccuracy, I thought proper to try the thing by another 
test. 
Obs. 13. The sun shining into the room as before, I placed 
at the hole an hollow prism made of fine plate-glass, and filled 
with pure water, its refracting angle being 55 s ; the spectrum 
was thrown on an horizontal chart eight feet from the win- 
dow, and at four feet from the prism there was placed, in the 
rays, a rough black pin ^th of an inch in diameter. The 
shadow in the spectrum was bounded by hyperbolic sides, as 
before described ; and drawing a line, which might be the axis 
* Page 256. f Page 247. 
