Royal Microscopical Society. 53 



Ex. 3. — Magnifying power of E eye-piece, whose focal length 

 is £, is for 10 inches, 



m = — - 1 = 80 - 1 = 79. 



"8 



Ex. 4. — Focal length of an eye-piece E when the object at 100 

 inches is diminished 798 times by measurement on the stage of the 

 miniature of disk 10 inches diameter can be similarly found as 

 follows : — 



Neglecting — , 



TP _ 100 100 , 



* - 798 + 2 + ri* ~ 798~+2 Dearly - 

 100 



= 8oo = « nearl y- 



Magnifying power at 10 inches, 



10 10 



= ¥ - l = ~ - 1 = 80 - 1 = 79. 



Focal lengths of objectives and their magnifying powers can be 

 similarly found. 



