METHOD or MOtJN-TlNG OBJECTS IN FLUID. 295 



purpose of either the thin glass cell or the tubular or drilled 

 cell, when these are not a,t hand, may be thus made : Take a 

 piece of glass of the required shape and thickness, say one 

 inch long and three-fourths -wide, and mark out on it, with a 

 writing-diamond or ink, the size of the cell you wish to make, 

 as e in fig. 197, continue the lines to the edge of the glass as 

 shown by dots at a fi e d. Now, with a cutting-diamond, 

 make four cuts in the direction of the lines ah, ac; b d, c d; 

 reject the middle piece, e; and cement the four outside 

 pieces to the slide in the same manner as one of the other 

 forms of cell, taking care always to put the pieces in the order 

 in which they were before they were cut off; this is known 



by making little marks or lines in 

 each corner, so that, when the 

 pieces are separated, one half of the 

 mark may be on one side and the 

 other half on the opposite, as seen 

 in the above figure ; this will serve 

 Fig. 197. as a guide to fit the pieces pro- 



perly together, and when a little 

 marine-glue is placed between the joints, the four pieces will 

 be held as firmly together as if they were a solid mass. Should, 

 however, the pieces not be brought down to a uniform level, 

 the cell may be rubbed on the metal-plate with emery, and be 

 thus reduced to any convenient thinness. Cells made in this 

 way of the thin glass answer exceedingly well, and, when 

 properly cemented, will form an excellent substitute for any 

 of the other kinds ; they may be made of aU thicknesses of 

 glass, from that used for covers up to the thickest plate that 

 the operator can cut slips from with the diamond. 



Thicker cells, as represented by fig. 198, may be made of 

 four narrow strips of stout plate-glass, cemented together as in 

 the preceding specimen, upon a bottom piece of thinner plate; 

 but care must be taken that the ends of the sides, c d, and the 

 edges of « 5 be ground flat, and that the joints be firmly 

 cemented. Strips of plate-glass, from one-eighth to half-an- 

 inch, may be obtained at the looking-glass makers, or may 

 even be cut by the diamond, which will answer very well for 



