Method of determining Curvature of Spherical Surfaces. 221 



The lathe-head is attached by an adjustable screw to a 

 straight-edged board which rests upon tii9 top of the table 



with its straight edge in contact with the scale. The spindle 

 of the lathe-head is screwed at one end to fit a brass face- 

 plate furnished with three screws which serve to adjust a 



Fisr. 2. 



second brass plate to which the lens or mirror to be tested is 

 attached by wax. Each end of the spindle is turne I to a 

 conical point, and the vertex of each cone lies on the axi< of 

 revolution of the spindle. One arm of a steel rod bent at 

 right angles can be secured by a set-screw in a sockel 



