CIRCULAR DISC. 209 



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 stiff er 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, Beck's Walmsley's turn-table (fig. 

 143c) is most useful. 



Fia. 143c. Beck's Walmsley's Cell-making Instrument. 



For making cells, take a camel's-hair pencil, pre- 

 viously dipped in japanners' gold-size, hold it firmly 

 between the finger and thumb, and set the wheel in 

 motion, when a perfect circle will be rapidly formed ; 

 it must be put aside to dry. To cut cover-glasses 

 secure a sheet of thin glass under the brass springs, 

 and substituting for the pencil a cutting diamond, 

 a circular cover may be readily cut out. A cutting 

 diamond is not only useful to the microscopist for 

 the above purpose, but also for writing the names of 

 mounted objects on the ends of the glass slides. 



p 



