190 
DR. BREWSTER ON REFLECTED LIGHT. 
disappointments which it occasioned, I was led to the results which I shall now 
proceed to describe. 
The solids which I employed were two prisms of plate glass, which I shall 
call A and 13. The prism A, whose section was an isosceles right-angled tri- 
angle, had its base polished at the plate glass manufactory where it was made. 
The prism B was executed for me by Dollond, and very finely polished, having 
also its section a right-angled isosceles triangle. The refractive indices were 
In A ... m — 1.508 
In B ... m — 1.510 
The fluids which I employed were castor oil and balsam of capivi, the latter 
having a greater and the former a less refractive power than the glass prisms. 
The refractive indices were 
In castor oil m — 1 .490 
In balsam of capivi . . . m = 1.528 
Fig. 1. 
m 
n. 
The prisms A, B were now fixed 
together as in fig. 1, and a film C D 
p of castor oil interposed between 
them. A ray of light R r will after 
refraction at r be reflected in the di- 
rection oqm from the surface CoD 
which separates the prism A and 
the oil ; and another portion of it 
will be reflected in the direction p s m from the surface G/?H which separates 
the prism B and the oil. In order that the two rays qm,sn may be suffi- 
ciently separated, the common sections of the faces which contain the right 
angle are slightly inclined to each other. 
When the angle of incidence RrE is very great, the light suffers total re- 
flection at the surface CoD. Within the limit of total reflection the light oqm 
is yellow ; and by diminishing the angle of incidence gradually, the pencil 
o q m passes through all the tints of nearly three orders of colours, as shown in 
the following Table. 
