184 



Lord Kelvin on the Reflexion 



gives to the medium. The inclinations of the fronts and rears 

 to OX, being what are ordinarily called the angle of incidence 



FiK. 2. 



and the angles of reflexion or refraction of the several waves, 

 will be denoted by i, i', i n j,j r The value of 7 for each of 

 the five waves is zero, and the values of a and ft are as shown 

 in the following table :— 





a. 



|S. 



I 



-j- sin i 



— cos i 





r 



+ sin i 



+ cos i 

 — cos i, 





1 



+ sin i t 





L 



+ siiy" 



+ cos^' 



j 



+ sinj?; 



- cosj>*, 





The section of the five waves by OX is the same for all, 

 being expressed by ur/sin i for I, and by corresponding 

 formulas for the four others. Hence if we denote r-times its 



