of Refraction, Reflexion, and Extinction. 

 From (11) and (12). it appears that 



i(bc+ 1)(W - 1) A (1 >€^+* z ) 



2ttNP 



(bc + lfe mbL -(bc-iy 



■inbZ 



^ (^ + l)V^ Z -(^-l) 2 e-^ Z ' 



287 



(14) 

 (15) 



All this may be corroborated, as a little consideration will 

 show, when our knowledge of magnetic effects is turned to 

 account. We have indeed to assume that the " inoperative 

 terms in the expression of the resultant secondary magnetic 

 effect are destroyed owing to the cooperation of the primary 

 magnetic field ; clearly this is a condition of things which 

 is consistent with steadiness and permanency. To attain our 

 object we need only evaluate (Hf) + and (Hf )_. We find : 



w^-^bn^rH&i] 



_^ JLnit—az) 



2ttNP 



i(bc-l) 



Sn(t-bz) 



2 *-NQ Mi+bg) 



m (2) ) - - <v\ T r - - — - 1 >[*+«(* 



1 u } ~~ "^[iac+i) i[bc-i)] € 



2ttNP 



i(bc + 1) 



InbZ 

 1) 



i(bc+l) 

 nbZ 



1). 



(16) 



•Z)] 



2ttNQ 



i(bc-l) 



,in(t+bz) 



(") 



By application of (2) we conclude that the component along 

 y of the actual 



magnetic field at M is as follows : 



AirNbc 



f{b 2 <--l) 



(P 6 w(^-ft»)_Q e «l(<+te)) j < 



(18) 



and, on the other hand, that our present equations (11) and 

 (12) are fulfilled. Thus, whether electric or magnetic effects 

 are considered, the inference is, as before, that (11), (12), 

 and accordingly (14), (15), must hold true. 



It is of importance to assure ourselves that the intensity 

 of the wave apparently reflected from the interface z -— can 

 be correctly deduced from our investigation. For this 

 purpose we calculate the cumulative electric effect of 

 secondary waves emitted downwards, into the region of 



X2 



