48 



THE CAMERA,, ETC. 



ser and microscope. The best method, however, is 

 to remove the blue glass, and place a cell having 

 parallel sides, filled with a solution of ammonio- 

 sulphate of copper in a similar position to that 

 recommended for the alum plate. The cell is made as 

 follows : 



A piece of round india-rubber placed between two 

 quarter plates, is made to occupy the same position 

 as the dotted lines in figure 20. A board slightly 

 narrower than the plates and india-rubber, has a 



FIG. 20. 



piece cut out of it 4^ inches wide and about the same 

 length ; four thin stripes are fastened along its edges 

 and the plates with the india-rubber forced down be- 

 tween thfim ; when this has been done the cell is 

 filled with the solution, and the india-rubber pressed 

 down so as to complete the ring and prevent evapor- 

 ation. This cell may with advantage be used on all 

 occasions instead of the blue glass. 



Two plano-convex lenses each about 4J inch focus, 

 when fixed in a shallow tube with their convex sur- 

 faces almost touching, make the best condenser (when 

 high powers are employed) if placed a quarter of an 

 inch in front of the lamp and six inches from the 

 achromatic condenser. 



