98 MICROSCOPIC OBJECTS. 



rably exliibited under a low magnifjdng power on the 

 screen of the solar or oxyhydrogen microscope; for 

 which purpose proceed as follows : — Procure an aquatic 

 slide whose sides are composed of two parallel pieces of 

 glass two inches wide and four inches long ; let the edges 

 be of cement or some nonmetallic substance, so as to 

 leave a space of ^%ths of an inch between them; let a 

 piece of copper wire be fixed into each edge ; then fill 

 it with clear water, and place it under the microscope ; 

 lastly, connect the outer ends of the wires with a small 

 galvanic trough. The evolution of gas from each pole 

 or inner end of the wires will be shown on the screen by 

 the image of the bubbles in the screen, which will descend 

 (the image being inverted) in rapid succession — thus 

 affording an interesting and instructive spectacle. 



Deut-Ioduret of Mercury. — If a little of this intensely 

 red-colored salt be placed in a watch-glass, with another 

 inverted over it, and then the lower owe heated over the 

 flame of a spirit-lamp, the salt will be sublimed. Now 

 place them on the stage of your microscope, armed with 

 a power of 30 diameters and focus to the inner sm'face of 

 the upper glass, when minute crystals will be formed 

 thereon of a bright yellow colour, which as they cool 

 return to the original red. 



