Solid Eyepiece is also a negative eyepiece and is 

 the invention of the late Robert B. Tolles. It is called 

 solid, from the fact that instead of being composed of two 

 lenses, it consists of one piece of glass, Fig. 43, which 

 is cut to a cylindrical form and on the ends of which 

 the proper curvatures are ground and polished. The 

 diaphragm is made by cutting a circular groove into 

 the glass at the proper distance between the two sur- 

 faces, which is then filled up with an opaque pigment. 



Fig. 41. 



Fig. 42. 



These eyepieces are made only in high powers, as 

 optical glass is usually not of sufficient homogeneity 

 to make low powers, and their cost would be too con- 

 siderable without a corresponding advantage. They 

 are usually made only in powers of 1-2 inch and 

 stronger and for this reason have but a limited use. 



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