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 pi-ism 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 pei-- 

 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. 



Image at the 

 Names of Oils. Image at the Surface of Prism A. Surface of Prism B. 



rPale red tints at 65° of incidence; then at less incidences'] 

 Oil of Cassia ....< pale blue, and then pale red. Heat strengthens the > White and bright. 

 L tints a little. J 



Balsam of Peru . . ( ^^^S^' *'"gf "^ '^^'^ ' ^\^'^ f ^ ^^°^''- ^^^^ f^'"* ^''^^'^ "^ 1 Yellowish white. 

 l^ colours brought out by heat. J 



"The tinges of two orders of colours. Heat of 200° brings"} p . , ki • i. 



Oil of Anise-seeds «{ out two good orders of colours. Limit of nink and blue C.^rayisn or Dluisn 



white. 



rXhe tinges of two orders of colours. Heat of 200° brings"] , 

 < out two good orders of colours. Limit of pink and blue > 

 L of the first order at an incidence less than 65°. J 



Balsam of Styrax. . Tinges of two orders of colours. Improved by heat. Bright white. 



