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304 _ Description of an Apparatus for , 
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through which by copper rod slides so as to reach above the level 
of the air-pump plate. The end of the rod supports a small hor- 
izontal platform of sheet brass, which receives four upright screws. 
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These, by pressure on brass bars extending from one to the yee’ 
are competent to secure upon the platform a parallelopiped ‘esl 
charcoal. Upon the air-pump plate a glass bell is supported, 
