294 



MANIPULATION. 



be cemented together, either with the marine-glue or Canada 

 balsam; figs. 191, 192, 19.3, represent three convenient shapes, 

 and figs. 194, 195, 196, one of each 

 cemented to a slide or bottom plate 

 of glass ; these cells have many advan- 

 tages over others, as any number may 

 be made of one thickness, they may 

 also be made perfectly square outside, 

 and yet the cavity or cell within may 

 be either oval or circular, which is 

 _ often desirable. 



I ' """"^^ fjjg method of cementing them to 



I ' m the bottom glass is the same as that for 



IB»iiiii iiiiiiw II III 



Fig. 192. 



Fiff. 191. 



Fig. 193. 



Fig. 196. 



other forms of cells. Being made of plate-glass they are very 

 flat, and from not being ground their surfaces will allow light 

 to pass through when Canada balsam or very thin marine - 

 glue is the cement, hence they may be employed with the 

 Lieberkuhn. This and the succeeding form of cell were first 

 suggested and used by Mr. Goadby. 



Built-up Cells. — These consist of four pieces of glass of con- 

 venient size, which are cemented to form an oblong or square 

 cell. The simplest form, and one which will answer the 



