322 MANIPULATION. 



only small shells or objects that cannot be damaged by wiping 

 with a camel's-hair pencil, ought to be mounted in this way. 



In Cells. — For this purpose it will be found convenient to 

 use cells not exceeding half-an-inch in diameter, or the size of 

 the largest dark stop ; they may be cut from large barometer 

 tubes of any required thickness, and are to be cemented to 

 the slides with marine-glue in the usual manner. After the 

 cell has been cleaned and the cover and object selected, some 

 black sealing-wax varnish, rather thick, may be dropped into 

 the bottom of the cell, upon this the object is to be laid; the 

 varnish will serve a two-fold purpose — first, as a cement to 

 keep the object in its place, and, secondly, as a stop to prevent 

 the transmission of light. When the seaHng-wax has become 

 hard the cover may be laid on ; this can be effected in one of 

 two ways, either by the plan recommended for the thin dry 

 cells, or by putting a layer of old gold-size upon the walls of 

 the cell, and allowing it to get nearly dry, then laying on the 

 cover, and after the lapse of a day or two, when the size has 

 become hard, filling up the angle between the cover and 

 cell with gold-size laid on in several thin coatings, so that it 

 may not run in and interfere with the object. This plan 

 will be found highly advantageous for most objects ; they may 

 be well seen with the Lieberkuhn, the black cement acts as a 

 stop or dark well, and the small size of the cell allows of the 

 light being readily transmitted on all sides of it, so that no 

 stop under the stage will be required. The glass cover does 

 not at all interfere with correct definition unless the light 

 be thrown upon it very obliquely, when some pencils must 

 necessarily be reflected; but with the vertical light from 

 the Lieberkuhn, nearly as much will pass through as if the 

 cover were not present. The elytra of the diamond and other 

 beetles which still exhibit their rainbow hues when placed 

 in Canada balsam, can be well seen when mounted in this 

 manner; but those objects which require the light to fall 

 upon them at very oblique angles to show their play of 

 colours, must be mounted on discs with the pin, by which 

 means they can with facihty be turned in every direction, and 

 so display their resiJendent tints. 



