Absorption on the Resolving/ Power of Prism Trains. 



4 2 



9 

 = l6 



-(?)' 



for B/> 



>= '5754 





1 

 : 4 



-©' 



M 



= 1-3862 





1 



-©" 



•? 



= 2-1972 



ir ~ 



l 



: 16 



=©' 



» 



= 2-7726 



i. 2 



V" 



1 



: ioo 



-&)" 



5? 



= 4-6052 



h 2 



1 

 "2500 



-ft)" 



jj 



= 7-825 



or for the extreme cases the intensity at the edge of the 

 beam traversing the base of the prism-train is fifty-six per 

 cent, and one twenty-fifth of one per cent, respectively, of 

 the intensity at the centre. 



To find the relation between the quantities Bb, ^ , and /3 



the coefficient of absorption of the glass, we have similarly 

 from (5) and (6) 



Also from the geometry of the prism-train 



VI—" 2 sin 2 0/2 



^i-^o~ 2 sin 0/2 



for a single prism of refracting angle placed at minimum 

 deviation. For N similar prisms placed en train we have 

 similarly 



_f_ _ #- _ Vl-^ 2 sin 2 0/2 

 Z-J ;- Nft-Zo) ~ 2N sin 0/2 ' 



and therefore in general 



B=M-=JEi^=, . . . . > m 



v 1— n 2 snr 0/2 



from which we can determine the corresponding values of 

 B6 and /3 for any given spectroscope. Some examples may 

 be of interest. 



For the Bruce spectrograph of the Yerkes Observatory. 



