60 LIGHTING AND FOCUSING [CH. II 



elin and benzin, equal parts), on a piece of chamois leather or on the 

 lens paper, and rub the parts well, then with a clean dry piece of the 

 chamois or paper wipe off most of the oil. If the mechanical parts 

 are kept clean in this way a lubricator is rarely needed. Where op- 

 posed brass surfaces "cut," i. e., when from the introduction of some 

 gritty material, minute grooves are worn in the opposing surfaces, giv- 

 ing a harsh movement, the opposing parts should be separated, care- 

 fully cleaned as described above and any ridges or prominences scraped 

 down with a knife. Where the tendency to "cut" is marked, a very 

 slight application of equal parts of beeswax and tallow, well melted 

 together, serves a good purpose. 



In cleaning lacquered parts, benzin alone answers well, but it 

 should be quickly wiped off with a clean piece of the lens paper. Do 

 not use alcohol as it dissolves the lacquer. 



§ 113. Care of the Optical Parts. — These must be kept scrupu- 

 lously clean in order that the best results may be obtained. 



Glass surfaces should never be touched with the fingers, for that 

 will soil them. 



The glass of which the lenses are made is quite soft, consequently 

 it is necessary that only soft, clean cloth or paper be used in wiping 

 them. 



Whenever an objective is left in position on a microscope, or when 

 several are attached by means of a revolving nose-piece, an ocular 

 should be left in the upper end of the tube to prevent dust from falling 

 down upon the back lens of the objective. 



§114. Lens Paper. — The so-called Japanese filter paper, which 

 from its use with the microscope, I have designated lens paper, has 

 been used in the author's laboratory for the last sixteen years for clean- 

 ing the lenses of oculars and objectives, and especially for removing 

 the fluid used with immersion objectives. Whenever a piece is used 

 once it is thrown away. It has proved more satisfactory than cloth or 

 chamois, because dust or sand is not present ; and from its bibulous 

 character it is very efficient in removing liquid or semi-liquid substances. 



§ 115. Dust may be removed with a camel's hair brush, or by 

 wiping with the lens paper. 



Cloudiness may be removed from the glass surfaces by breathing 

 on them, then wiping quickly with a soft cloth or the lens paper. 



Cloudiness on the inner surfaces of the ocular lenses may be re- 

 moved by unscrewing them and wiping as directed above. A high 

 objective should never be taken apart by an inexperienced person. 



