ch. y/i] 



CLASS DEMONSTRATIONS 



193 



DEMONSTRATION MICROSCOPES AND INDICATORS 



§ 265. Simple Microscope. — Holding the simple microscope 

 in one hand and the specimen in the other, has always been used 

 for demonstration, but for class demonstration it is necessary to 

 have microscope and specimen together or the part to be observed 

 b3' the class is frequently missed. Originally blocks of various 

 kinds to hold both microscope and specimen were devised, but with- 

 in the last few years excellent pieces of apparatus have been devised 

 by several opticians for the purpose. The accompanying figure 

 shows one of the best forms. 



Fig. 14S. Demonstration com- 

 pound microscope of Leilz. Leitz 

 now furnishes a fine adjustment in 

 the form of an intermediate piece be- 

 tween the objective and the tube. This 

 has in it a screw ivhieh is turned by a 

 milled ring. For the objectives em- 

 ployed it makes an efficient fine ad- 

 justment and retiders it possible for 

 each person to adjust the microscope 

 slightly without endangering the loss 

 of field. 



§ 266. Compound Demonstration Microscope. — This was 

 originally called a clinical or pocket microscope. It is thus 

 described by Mayall in his Canton Lectures on the history of the 

 microscope : "A small microscope was devised by Tolles for clini- 

 cal purposes which seems to me so good in every way that I must 

 ask special attention for it. The objective is screwed into a sliding 



