244 



CLASS DEMONSTRATIONS 



[ CH. IX 



it. The objective is screwed into a sliding tube, and for roughly focus- 

 ing the sliding motion suffices ; for fine adjustment, the sheath is made 

 to turn on a fine screw thread on a cylindrical tube, which serves also 

 as a socket-carrier for the stage. The compound microscope is here 

 reduced to the simplest form I have met with to be a really serviceable 

 instrument for the purpose in view ; and the mechanism is of thor- 

 oughly substantial character. I commend this model to the notice of 

 our opticians. " 



Fig. 196. Demonstration compound 

 microscope of Leitz. Leitz now furnishes 

 a fine adjustment in the form of an inter- 

 mediate piece between the objective and 

 the tube. This has in it a screw which is 

 turned by a milled ring. For the object- 

 ives employed it makes an efficient fine 

 adjustment and renders it possible for each 

 person to adjust the microscope slightly 

 without endangering the loss of the field. 



Fig. 196. 



Since its introduction by Tolles many opticians have produced ex- 

 cellent demonstration microscopes of this type, but most of them have 

 not preserved a special mechanism for fine adjustment. With it one 

 can demonstrate with an objective of 6 mm. satisfactorily. It has a lock 

 so that once the specimen is in the right position and the instrument fo- 

 cused it may be passed around the class. For observation it is onl}' 

 necessary for each student to point the microscope toward a window or 

 a lamp. 



