115 



shows it within a sharply defined border. It is 

 made up in two forms : 



The English type as shown in Fig. 36, which has 

 a large tube fitting into the microscope tube and 

 a neck or smaller tube which is usually arranged 

 with a cap to slide over the eye lens. 



The Continental type has a straight tube which 

 drops entirely into the tube of the microscope and 

 rests upon the mounting of the eye lens. 



Solid Eyepiece. This is also a negative eye- 

 piece and is the invention of the late R. B. Tolles. 

 It is called solid, from the fact that instead of 

 being composed of two lenses, it consists of one 

 piece of glass, 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 surfaces, which is 

 then filled up with an opaque pigment. (Fig. 37.) 



11 



/^ A 



Fig. 37. 



These eyepieces are only made in high powers, 

 as optical glass is usually not of sufficient homo- 



