176 SELECTION AND USE 



dirt adheres more strongly, use fine linen slightly moistened with 

 alcohol, and wipe dry with very fine chamois leather. Remerr- 

 ber, that alcohol, if used profusely, will attack the lacquer of 

 the brass- work, and even dissolve the cement .which holds the 

 lenses together. When objectives are smeared with balsam, 

 the best cleansing agent is said to be kerosene oil. The piece 

 of leather used for wiping lenses should be free from dust, and 

 is best kept in a small box by itself, and used for nothing else. 

 It must be remembered that the glass of which objectives are 

 made is easily scratched, being soft when compared with parti- 

 cles of sand and grit; consequently, when frequently wiped it 

 soon loses that exquisite polish upon which its excellence of 

 performance so much depends. What, then, are we to think 

 of the directions given by the author of a popular work on 

 the microscope, in which we are told to use a piece of leather, 

 slightly impregnated with brick dust ! ! No better method of 

 destroying an objective could possibly be devised. Therefore, 

 see that in wiping, the slightest possible pressure is used, lest 

 any particle of grit should make a scratch. 



The exposed parts of all microscopes, as well as the objectives 

 and their cases, are lacquered, to protect them from being 

 soiled by handling, but the interior of the boxes which hold the 

 object-glasses are rarely so protected, and the black coating of 

 i he interior of bodies, draw-tubes, etc., is frequently not very 

 firmly attached. Therefore, never touch them with the fingers. 



After taking an objective out of its box, either screw on the 

 cover of the box, or place the latter with its open end down, Do 

 not stand it mouth up, so that it may catch all the dust. 



When exhibiting the microscope to others, great care is neces- 

 sary to keep meddlesome fingers from soiling the glasses. Some 

 people are never content when merely allowed to look at things: 

 they insist upon handling them, and feeling them. To the 

 young microscopist, we would say that if any of ^ our friends in- 

 sist upon handling your objectives, eye-pieces, etc., put up the 

 instrument and pack it away. A microscope carefully used is 

 as good after fifty years as when first made, but we have seen 

 an instrument suffer more injury in half an hour at the hands 

 of a thoughtless and dirty person, than it would have sus- 

 tained in twenty years in the hands of a careful microscopist. 



