OF MICROSCOPIC OBJECTS. 93 



for this process except a small thin saw made with a steel blade, 

 for which a piece of watch-spring serves very well ; a fine stone 

 such as is used for sharpening pen-knives ; and two smooth lea- 

 ther strops, one of which is to be used with putty-powder to polish 

 the section after grinding, and the other dry, to give the final sur- 

 face. It is, however, very convenient to have three or four files 

 of different degrees of fineness. The shell, if very thick, may be 

 divided by using the watch-spring saw ; and this section may then 

 with ordinary care be rubbed down with water on the stone until 

 one side of it is perfectly flat. When this is accomplished it must 

 be again rubbed with putty-powder upon the strop, and finally 

 upon the other strop without the powder. This surface will then 

 be finished and must be firmly united to the slide in the position 

 it is intended to occupy. To do this a small quantity of Canada 

 balsam may be dropped upon the middle of the slide and heated 

 over the lamp until on cooling it becomes hard ; but this must be 

 stopped before it is rendered brittle. Upon this the polished sur- 

 face must be laid, and sufficient heat applied to allow the object 

 to fall closely upon the slide, when slight pressure may be used 

 to force aside all bubbles, &c. On cooling, the adherence will be 

 complete enough to allow the same grinding and polishing upon 

 the upper surface which the lower received. Whilst undergoing 

 this, the section must be examined from time to time to ascertain 

 whether the necessary degree of thinness has been reached. When 

 this is the case the section should be washed thoroughly and dried. 

 It must then be covered, which is best done by using the ordinary 

 Canada balsam, as recommended in Chapter III. 



Sections of some exquisitely beautiful objects are cut with much 

 less trouble than the above. The Orbitolite, for instance, may be 

 prepared in this manner. Take the object and by pressure with 

 the finger rub the side upon a flat and smooth sharpening stone 

 with water until the portion is reached which it is wished to show. 

 The strength of the object will easily allow this to be accomplished 

 with ordinary care. This side may then be attached to the glass 

 slide with heated balsam, as above described, and the object may 

 then be gently rubbed down to the degree of thinness required to 

 show it to the best advantage. After removing all disengaged 

 matter from the object by washing and thoroughly drying, it may 



