THE MICROSCOPE AND ITS PARTS. 15 



is the master ; his objective is a masterpiece. The own- 

 er of a good objective must not treat it carelessly. He 

 should treasure it, for it is not a common thing. "When 

 not on the stand in use, it should be kept in the brass 

 box supplied for that purpose, and it should never be 

 left on the stand when not in actual employment. 



That part of the brass mounting of the objective 

 which bears the screw is the back ; the opposite end that 

 shows a small flat surface of glass is the front, or, as it is 

 often styled, the front lens. The glass of this part is 

 soft and easily scratched, therefore take care not to 

 let it touch anything hard ; especially avoid any gritty 

 substance, or dirty rag that may hold a minute parti- 

 cle of sand or hard dust.; and never touch it with the 

 lingers, as the oily exudation from the skin will soil 

 it and interfere with the clearness and beauty of the 

 image. If the front lens becomes accidentally stained, 

 or soiled by long use, the objective should be sent to its 

 maker, who can clean it without the great risk that its 

 owner would expose it to if an attempt should be made 

 to wipe the glass. If fine dust adheres too closely to 

 be dislodged by the breath, ravel out the edge of a piece 

 of very clean old linen or muslin, and with the fringe 

 thus obtained gently sweep the surface. 



"When the objective is to be taken from its box, un- 

 screw the cover and tip the lens into the palm of the 

 left hand, supporting it with the fingers ; pick it up 

 with the thumb and finger of the right hand against the 

 sides of the tube or brass mounting, and it will be ready, 



