110 



and contraction of glass and metal may cause the 

 cement between the lenses to crack. Also keep them 

 from direct sunlight. 



Screw them into the nose-piece and unscrew, by 

 grasping the milled edge. 



Avoid any violent contact of the front lens with 

 the cover-glass. Usually the latter suffers, but it is as 

 liable to occur to the former. 



Above all, it should be made a rule that no one but 

 the owner handle the microscope and accessories. 

 One person may be expert in the manipulation of one 

 instrument and still find it difficult to work with 

 another. The fine adjustment particularly causes the 

 greatest difficulty as in some instruments it corres- 

 ponds with the movement of the micrometer screw, 

 while in others it is contrary and thus the objective 

 as well as object are endangered. 



