height of the instrument. The short tube length of 

 1 60.0 mm. is at the present time in general use. 



Base. The base is an important feature and while 

 it should not be over heavy, should insure steadiness 

 by the proper form and disposition of metal ; it should 

 not rest on more than three points, with the rear one 

 fairly distant from the pillar. 



The Joint for Inclination. This, without 

 question, is an advantage and while it is an inex- 

 pensive addition it will add considerably to the comfort 

 of working and should invariably be present, if 

 pecuniary considerations do not absolutely prohibit it. 



Coarse Adjustment. Almost all reliable instru- 

 ments are provided with both fine and coarse adjust- 

 ments. The choice of the latter lies between the 

 sliding tube and the rack and pinion. The former has 

 only the advantage of economy and is a decided disad- 

 vantage in the hands of students who almost invariably 

 injure objectives and preparations with it. Further 

 than this, it is almost impossible for the maker to center 

 the nose-piece to the tube, so that a change of objective 

 usually throws an object out of the field and requires 

 that it be looked for anew with each change. With 

 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 agreeable adjustment. The 



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