OBJECTS AND THEIR MOUNTING. 43 



to have a number of these blank sliders with the paper and talc pasted 

 down at one end ready for use, for it often happens that many a 

 valuable object is lost from not having a convenient receptacle for it 

 when it presents itself. 



34. In lieu of glass or ivory, a celebrated Microscopist uses small 

 strips of mahogany veneer, with a hole bored through the centre, into 

 which a piece of glass is fitted to place the object on. In either of these 

 methods, the object is to be fastened to the glass by means of Canada 

 balsam, the glass being warmed previously to its application. This 

 renders objects extremely transparent and beautiful. 



35. There are some objects, such for example as the larger wings of 

 butterflies, which are not sufficiently transparent when mounted in 

 either of the above ways. Mr. Pritchard has, however, devised a 

 plan by which they may be exhibited with singular beauty and inten- 

 sity of colouring. It consists in immersing the object completely in 

 Canada balsam, and pressing it between two slips of thin glass, so as 

 to exclude the air bubbles. The sides of the glass are then to be 

 thoroughly wiped, so as to remove all superfluous moisture, and 

 brushed over either with gold size or marine glue, the composition of 

 which will be found explained further on. By this treatment, many 

 objects which otherwise possess little interest, are rendered highly 

 v aluable, allowing the light to pass freely through them, exhibiting 

 their structure, and presenting the most brilliant and superb colours. 

 By this method also many cylindrical bodies are rendered perfectly 

 distinct, the diffraction at the edges being in a great measure destroyed 

 by the refractive power of the medium. In objects prepared in this 

 way, we are able to perceive whether the cylindrical part be hollow or 

 solid ; for when the former, they are often as finely injected as if by 

 design. 



It may be well to remark, with transparent objects generally, 

 that, to observe all the minutiae of the most delicate, particularly 

 those which are called test objects, they should be placed upon a 

 clear slip of glass without an intervening medium ; but if such must be 

 used, they should be covered by a piece of very thin glass, as mica 

 injures in some degree the rays of light proceeding from minute and 

 delicate objects. It is only for the more common and least delicate 

 forms of objects that the mica is useful. 



