554 



Experiments 



It establishes or cuts off communication with the pump, and, when 

 the tube surmounting it is taken away, permits sudden decom- 

 pression of the air in the reservoir, when necessary. 



In the experiments in which I simply compressed the air, the 

 bag pictured in the figure was not present, of course, and the suc- 

 tion of the pump was directly outside. 



