4 



Gee and Adamson, Dioptriemeters. 



In this construction tlie lengths ?/ and v are marked 

 off on each side of the lens A on a scale representin g 

 tenths of a metre, and as before an arbitrary unit AB is 



<, M 



chosen for the scale of dioptrics. The scale reading 

 below o will represent the value i/// and the upper scale 



