24 Mr GREEN, ON THE REFLEXION, &c. OF LIGHT. 



seems sufficient to give the result. Let therefore, here, n = — , also 



7 

 e, e t and 6 as before, then e t — — e, and the accurate value of e is 

 given by 



*. /~n — T75 Tn (m 2 — l) 2 tan 6 



tan e - n Vfi* tan 2 9 - sec 2 - K — — - z - . 



M + 1 



The first term of this expression agrees with the formula of page 362 

 Airy's Tracts, and the second will be scarcely sensible except for highly 

 refracting substances. 



