104 



THE MICROSCOPE. 



into its interior, by adopting the following method : 

 A small quantity of balsam, proportioned to the size of 

 the specimen, is to be spread upon a slip of glass, and to 

 be rendered stiffer by boiling, until it becomes nearly 

 solid when cold ; the same is to be done to the thin glass 

 cover ; next, the specimen being placed on the balsamed 

 surface, and being overlaid by the balsamed cover, such a 

 degree of warmth is to be applied as will suffice to liquefy 

 the balsam, without causing it to flow freely ; and the 

 glass cover is then to be quickly pressed down, and the 

 slide to be rapidly cooled, so as to give as little time as 

 possible for the penetration of the liquefied balsam. 



Circular Disc. For the purpose of cutting glass covers 

 or making shallow cells with japanners' gold-size for 

 mounting objects, fig. 70 will be found useful ; it is made 



Fig. 70. Circular Disc Machine. 



of two circular wheels of wood, these being let into a 

 solid block of wood, and secured there by central screws. 

 A handle of wood is fixed into the upper part of one, for 

 the purpose of turning it round, the motion being com- 

 municated to the other by an endless band of catgut 

 running in the grooved edge of each. On the upper sur- 

 face of the wheel, under the right hand, are fixed, by 

 means of screws, two strips of brass, which serve as springs 

 for securing the glass slip ; a camel' s-hair pencil, previously 

 dipped in japanners' gold- size, is then taken between the 



