APOCHROMATIC LENSES 



35 



Apochromatic Objectives. 



Compensating Eye-pieces for English Bodies. 

 2 4 8 12 18 27 



It is of interest to note that Messrs. Powell and Leal and have 

 since produced a remarkable lens on the same system, having a N.A. 

 of 1'50, with a power of -^ th of an inch. Object-glasses are also now 

 made by other makers, English, European, and American, those 

 having fluorite in them being termed apochromatic, while others 

 made of new kinds of glass are called semi-apochromatic. Semi- 

 apochromats are being daily improved, so much so that some recent 

 objectives nearly equal apochromatic objectives themselves. 



T) 2 



