296 On the Laws of lleflexion and Refraction. 



From this we may easily show that 



Hence, assuming 



, .^ ^ — = U , and c^ = -T- x57j 



Q^_.V3l^2^V-i_l A B' 



we find 



CU = jlAs' — J'' v^ — 1} 



and .-. (cU+2J ^"=1)2 = iu^s'''=i^^-i>'; 



and hence, finally, 



Furthermore, if we assume 



we have 



We have, therefore, for vibrations parallel to the plane of 

 incidence. 



Hence, proceeding as before, we find the following real 

 values : 



V = 6cos [nt—k {px+sz)]i 



