196 
DR. BREWSTER ON REFLECTED LIGHT. 
of each prism in a vessel containing’ each of the three oils, I carefully deter- 
mined that, at a temperature of 50°, they acted on the homogeneous yellow 
light of a monochromatic lamp, in the order in which they are above placed. 
I now combined each of the oils in succession with the two prisms, as shown 
in Fig. 1, and in all the combinations the separating surface of the prism A 
and the oils produced from a white flame, nearly three orders of colours of the 
same intensity, and nearly at the same angles of incidence, as in balsam of 
capivi ; while the separating surface of the prism B and the oils reflected only 
a faint gray image of very little intensity, and generally growing fainter as the 
angle of incidence increased. 
When the homogeneous yellow light of a monochromatic lamp was used, the 
separating surface of the prism A and all the oils produced the first minimum 
at nearly the same angle of incidence ; and though I applied heat gradually to 
the least refractive oil, and cold to the most refractive one, so as to produce a 
perfect compensation of opposite refractions for the yellow rays, yet no per- 
ceptible change appeared either in the place of the first minimum or in the 
intensity of the reflected light. In the case of the mixed oil the compensation 
was effected without any other change of temperature but what was occasioned 
by a change of position in the apartment. 
In the expectation of discovering some solid or fluid medium which would 
produce with plate glass a greater number of orders of colours, I made the ex- 
periments contained in the following Tables. 
Table, Showing the periods of colours produced at the separating surfaces of 
plate glass and oils and other fluids. 
Names of Oils. 
Image at the Surface of Prism A. 
Image at the 
Surface of Prism B. 
Pale red tints at 65° of incidence ; then at less incidences 
pale blue, and then pale red. Heat strengthens the 
tints a little. 
strengthens the 
White and bright. 
Balsam of Peru 
Slight tinges of red ; blue as above. Two faint orders of 
Igllt tlligvd Ol i v U ^ U1 UL uo u IJ 
colours brought out by heat. 
Yellowish white. 
f The tinges of two orders of colours. 
Oil of Anise-seeds < out two good orders of colours. Lir 
L of the first order at an incidence les 
{ 
Balsam of Styrax. . Tinges of two orders of colours. Improved by heat. 
Bright white. 
