of the Eye-pieces of Telescopes. 33 



For refraction at the second surface, therefore, instead of using 



DR = X- V-, 



we must use 



1 1 



and instead of using 



s^C 



we must use 



1 1 



RG = a- -, 



1 1 



s + 1 



1 1_ 



Rg = a I +Sa. 



S^^ 



Prom this -^- =n-\ - +-v+vT-i, 

 /tm s A X^ 2 



w Vr 67 1 1 Vr a / 



1 1 



Vs x/ Vs nx y \ \ 1 



1- + ■?= 





5^^ 



Vol.n\. Parti. 



