light at the surfaces of different media. 



213 



The colour of the pencil p s n produced by the other sepa- 

 rating surface G jo H is at all incidences a faint yellowish gray, 

 (which is best seen by turning the system of prisms upside 

 down ; and receiving the ray Rr upon the prism B, so that 

 the reflected ray p s n may not pass through the oil ;) and its 

 intensity suffers very little change. This fact is a very re- 

 markable one, and arises (as will be presently seen) from some 

 specific property of the glass itself. When the lower prism is 

 of the same glass as A, and produces the colours in the pre- 

 ceding table at different angles of incidence from those of A, 

 the play of colours is particularly fine, and the whole pheno- 

 menon is one of the most beautiful in physical optics. 



AVhen the incident light is homogeneous, no colours of 



This column is calculated from the formula A — 45^ 



sin. I 



being the angles of incidence in the 1st column, A the angles in the 2d, 

 and m '=^ 1.508 the refractive index of the glass. 



