15 



While certain parts are necessary to make up a 

 modern instrument, no one design of construction is 

 followed. The forms are innumerable, each maker 

 following his own inclination in variety, design, num- 

 ber of parts and material. For the latter brass pre- 

 dominates, although bronze and iron are used to a 

 considerable extent. The first two metals are usually 

 highly finished, and as they easily tarnish in this 

 state, are protected by lacquer, which is not only ser- 

 viceable in this direction when well done, but offers 

 a means of ornamentation. The latter metal is cov- 

 ered with a heavy coating of japan and being an 

 intense black is on this account often recommended 

 by instructors as being agreeable for the eyes. The 

 entire apparatus is called a microscope, whereas, with- 

 out the optical parts, it is termed a stand. 



Description of Parts. As it is necessary for 

 the student to become conversant with the terms of 

 the various parts and to understand their use, we give 

 an illustration (Fig. 6) with letters, and append a list 

 giving the names. 



A. Base on Foot. This is the foundation of 

 the instrument. It usually rests upon three points (or 

 should do so) and is of such a weight that it keeps 

 the instrument firm when it is in an upright or inclined 

 position. The revolving plate, when this is provided, 

 by means of which the upper portion of the instru- 

 ment is revolved, without changing the position of 

 the base, is considered a part of it. 



