386 Mr Bevan, The Influence on Light reflected from and 



values (loc. cit. p. 43) both a and 26 for several metals are greater 

 than 10. For a rough approximation we can, in the expressions 

 for v x and v 2 , neglect l~ compared with a/ 2 and bf 2 , and write 



v 2 2 = ^(-a+^a 2 +b 2 ), 



or z>! =fn, 



Vz =fn'k. 



That is, p lt v 2 have approximately the same values as for light 

 incident perpendicularly on the surface. 

 We thus obtain 



_ 2n<f> {1 - n' 2 (1 - fc) + 2n' 2 k 2 } 



™ ~ n'pf 3 (l + k 2 )[{l - n' 2 (1 - A; 2 )} 2 + 4w' 4 & 2 ] 



_ \Pln 1 - n' 2 (1 - k 2 ) + 2n' 2 k 2 



~~pf*<rV ¥(l + k 2 )[{l-n' 2 (l-k 2 )} 2 +WW\ ' 



If now ^ is the angle of incidence, / =/sinS-, n =/cosS-, f=^., 



2tt 

 and p — , where t is the period of the vibration. 



T 



We obtain therefore 



XE> = -T—J P sin S- cos S-, . 



l-n 2 (l-l<?) + 2n' 2 k 2 

 where A = 



V 



n (1 + k 2 ) [{1 - ri* (1 - A; 2 )} 2 + 4V 4 & 2 ] ' 



The fraction of the time of vibration or the fraction of the 

 wave-length, if we regard the change of phase as a length, is owing 

 to the current 



A\t 



4<7r 2 <r 



P sin ^ cos Sr. 



The units adopted so far are Gaussian ; to express this result 

 in electromagnetic units we observe that o- is in these units 

 the same as in electrostatic units, and the unit of resistance in 

 the electrostatic system is v 2 the electromagnetic unit ; if then a 

 is the number expressing the specific resistance in electromagnetic 



units — is the number expressing the same quantity in Gaussian 



