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R. H. Richards—Jet Aspirator for Laboratories. 417 
a) The amount of water column pressure. 
(6) The amount of rarefaction desired. 
(c) The quantity of air desired. 
. 
As ais the scene of contest between the pressure of the 
satisfy all the conditions (a and w being diameters): 
Pxw*=QxXa? 
