54 



it is a mistake to condemn an instrument for this 

 cause as is sometimes done. If the object will 

 remain in focus under a high power with a fair 

 amount of exertion above that which is required in 

 moving the object about, the stability may be con- 

 sidered ample. In fact in this, as well as other 

 directions, the writer considers it unwise for a 

 user of a microscope with, in most cases, a neces- 

 sarily limited knowledge of its construction, to 

 make assertions, as is often done, as to supposed 

 defects against the long experience of the micro- 

 scope maker, although it is the purpose of this 

 book to aid the reader in judging of defects when 

 such exist. In older instruments the fault often 

 occurred of making the stage unnecessarily thick, 

 which interfered with the proper use of substage 

 accessories and the mistake has in recent years 

 been made by some makers of having it too thin, 

 so that a slide could not be moved except with 

 the utmost care without depressing it and thus put- 

 ting the object out of focus. At the present time, 

 however, the writer believes that in instruments of 

 the best makers the thickness is ample, although 

 in cheap foreign ones he knows that it is some- 

 times not the case. It is of the greatest impor- 

 tance however, that the surface of the stage 

 should be square with the tube in all directions. 



The lower surface is generally blackened and 

 the upper surface brightly polished and lacqiiered 



