the Inflection, Reflection, and Colours of Light. 247 
afterwards drew across the image parallel lines ; this operation 
I repeated with the same and different images, at many dis- 
tances from the pin, and on different days, with various sorts 
of pins, and sizes of holes, &c. & c. and all these repetitions 
were made before I once examined the result of any one mea- 
surement, that I might be unprejudiced in trying the thing 
over again. I then compared the sketches of divided images, 
which I thus obtained, and found sufficient reason to conclude^ 
that the differences between the sines of reflection in the diffe- 
rent rays were in the harmonical order. For the divisions 
were nearly as i; T \; ~ ; ^ ; which, when 
compounded with the scale, give 1, yf, t 9 q, -J, \\ 
and these are exactly the change of the notes in an octave, 
obtained by taking the sums of the octave, and a second major, 
a third major, a fourth, a fifth, a sixth major, a seventh major, 
and an eighth, instead of the difference between a double octave, 
and a second major, a third major, and so on. Thus the spec- 
trum by reflection is divided exactly as the spectrum by refrac- 
tion, only that the former is inverted, and the different rays 
have reflexibilities that are inversely as their refrangibilities. 
Having settled this (I flatter myself ) curious and important 
point, I proceeded next to inquire into the absolute reflexi- 
bility of the extreme colours ; for if this be known, the angle 
of incidence being given, the angle of reflection of all the 
different rays may be found. For obtaining a solution of this 
problem I made the following experiment. 
Ohs. 10. The sun shining strongly through the small hole 
in the window-shut, and the rays diverging into a cone, whose 
base fell on an horizontal chart 2- feet from the hole, be- 
tween the hole and chart I placed a screen, which had a plate 
