H. R. CARLETON. XCI 



p and $ = angles of refraction at A and B. 



xj; = angle of internal incidence of emerging ray CG. 



FA=/ 



sin = ^sin (20 + 8-90°). 



From this equation find by trial. 



fi sin p = sin 6 = /x sin i[/. 



Prob. 4. 



To find equation to true curve of reflecting side of a 

 triangular prism (two refractions and one reflection) 



J/}*-aJ 



t = 



I sin 



V 



I sin /5 



cos {/3 + 7}) = fJL sin e and tan (/? + e - cc ) -= 



x — p cos (?7 + a 



y - p sin (77 + a) 

 y = b + (a-ct) sin /^ + [(a - ct) cos /3 + ( /- as)] x tan (/3 - a. ). 



Mean difference in length of sides of reflecting prisms of a 

 1st order light = 2| per cent. 



The only assumption made, and one which appears to be 

 legitimate, is that the rays of light which fall on the first refracting 

 side are proportionately distributed over the second refracting 

 side. 



