92 



the field, and requires that it be looked for anew with 

 each change. In the rack and pinion the nose-piece 

 has an unvarying relation to the tube, and is not 

 liable to this difficulty, and offers a steady and agree- 

 able adjustment. The advantages of the rack and 

 pinion seem to be generally appreciated in this coun- 

 try, for there are few instruments sold and used with- 

 out it. 



Whether an instrument shall be of japanned iron or 

 lacquered brass is probably largely determined by the 

 amount of money to be expended. As far as the 

 intrinsic suitability of the metals is concerned, there 

 is no difference. Brass, however, oilers the maker a 

 better opportunity for displaying his mechanical 

 skill, and while it is no doubt true that many highly 

 finished instruments are of poor workmanship in their 

 working parts, it is also a fact that a well made instru- 

 ment is always nicely finished. 



The size of instrument is worthy of consideration. 

 If an instrument is to remain stationary in a practi- 

 tioner's office or laboratory, it may be large without 

 being cumbersome. If, however, it is intended to be 

 carried about, it should be of the smaller and more 

 contracted style. 



Another important consideration is the space 

 between the stage and base, or table. While it is 

 advisible to have the stage low on account of the con- 

 venience in manipulating a slide, there should still be 

 sufficient space for the convenient attachment of sub- 

 stage accessories. As a rule the American pattern of 



