OP THE MICROSCOPE. 179 



glass slide. A brass ring, of which the interior is the same size 

 as the disc, is then attached to the slide, and the object is fixed 

 to the wax by slightly moistening the surface of the latter by a 

 minute drop of turpentine. When dry, a cover, which exactly 

 fits into the bevel of the ring, is attached with a little cement, 

 and the whole may then be finished off on the turn-table. The 

 appearance is very elegant, and the specimens are perfectly pre- 

 served. 



A cell which we have found very durable, easily and quickly 

 made, and very neat, is constructed as follows: Having pro- 

 cured some good gold size and pure litharge, grind the latter 

 to a very fine powder. Mix the litharge and gold size to the 

 thickness of cream, and color either black or dark olive by 

 adding lamp-black. With this paint, as it may be called, make 

 as many cells as are wanted, and when made, dust finely pow- 

 dered litharge over them until they are covered a sixteenth of 

 an inch deep ; allow them to stand a few minutes, and then 

 shake off all the loose litharge by means of a few smart taps. 

 The surface of the cell will now be quite rough. Allow it to 

 stand a few hours, and then press it against a plate of glass. If 

 this be done carefully, a smooth, solid ring will be left on the 

 slide. If the edges should not be as smooth as they ought to 

 be, it is easy to trim them off on the turn-table by means of a 

 small chisel. Such cells, after a few weeks, become very hard, 

 and may be finished so as to be very neat. By introducing a 

 few obvious and unimportant modifications, we have, in this 

 way, made cells of some depth which held liquids quite well. 



Finishing the Slides. After the objects have been 

 mounted, the slides may be finished in one of two ways: they 

 may be covered with paper, or they may be left without any 

 covering, the labels being attached directly to the slide. In 

 the latter case the edges of the slide must have been previously 

 ground and polished, and, as a general rule the thin cover is 

 circular and not square, and is finished with a neat coat of var- 

 nish on the edge. This varnish serves to do something more 

 than merely ornament the slide; it secures the cover in its 

 place, and prevents the drying up of the medium used for 

 mounting. Even in the case of Canada balsam it is of use, for 



