ON THE REFLEXION AND REFRACTION OF LIGHT. 269 



reflected wave may readily be found. As the calculation is 

 extremely easy after what precedes, it seems sufficient to give 



the result. Let therefore, here, fju = , also e, e t and 6 as be- 

 fore, then e, = e, and the accurate value of e is given by 



9a 2-. (/u, 2 -l) 2 tan0 



an 2 0-sec 2 0- *- ^ . 



p* + 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. 



* [Airy, uU &up. p. 114, Art. 133.] 



