58 LIGHTING AND FOCUSING. [CH. II. 



§ 108. 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 removed 

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

 should never be taken apart by an inexperienced person. 



If the cloudiness cannot be removed as directed above, moisten one cor- 

 ner of the cloth or paper with 95 per cent, alcohol, wipe the glass first 

 with this, then with the dry cloth or the paper. 



Water may be removed with soft cloth or the paper. 



Glycerin max be removed with cloth or paper saturated with distilled 

 water ; remove the water as above. 



Blood or other albuminous material may be removed while fresh with 

 a moist cloth or paper, the same as glycerin. If the material has dried 

 to the glass, it may be removed more readily by adding a small quan- 

 tity of ammonia to the water in which the cloth is moistened, (water 

 ioocc, ammonia 1 cc). 



Canada Balsam, damar, paraffin, or any oily substance, may be re- 

 moved with a cloth or paper wet with chloroform, benzin or xylene. 

 The application of these liquids and their removal with a soft, dry cloth 

 or paper should be as rapid as possible, so that none of the liquid will 

 have time to soften the setting of the lenses. 



Shellac Cement may be removed by the paper or a cloth moistened in 

 95 per cent, alcohol. 



Brunswick Black, Gold Size, and all other substances soluble in chlo- 

 roform, etc., may be removed as directed for balsam and damar. 



In general, use a solvent of the substance on the glass and wipe it off 

 quickly with a fresh piece of the lens paper. 



It frequently happens that the upper surface of the back combination 

 of the objective becomes dusty. This may be removed in part by a 

 brush, but more satisfactorily by using a piece of the soft paper loosely 

 twisted. When most of the dust is removed some of the paper may be 

 put over the end of a pine stick (like a match stick) and the glass sur- 

 face carefully wiped. 



CARE OF THE EYES. 



§ 109. Keep both eyes open, using the eye-screen if necessary (Fig. 

 59, 60) ; and divide the labor between the two eyes, i. e.. use one eye 

 for observing the image awhile and then the other. In the beginning 



