On the Flow of Elastic Fluids through Orijices. 



187 





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of it through equal orificeS; it will take in that chamber a density 

 somewhere intermediate between that of the atmosphere and that 

 in the receiver. For each relation that may at any moment sub- 

 sist between the density of the atmosphere and that in the re- 

 ceiver, the density in the chamber will have a certain definite 

 and determinate value, such that the chamber may receive 

 through one orifice and discharge through the other simultane- 

 ously the same quantity of air. Now since in order to this equal 

 simultaneous flow the two theories respectively demand quite 

 different densities in the chamber, the object of my experiment 

 was to ascertain the actual densities in such a chamber under 

 various relations of the density in the receiver to the density of 

 the atmosphere, in order to compare the densities thus ascertained 

 experimentally with those demanded by each theory respectively 

 in like circumstances. 



To try the experiment, I con- 

 structed the apparatus shown 

 iti the annexed sketch. A is 

 a vessel or receiver of the ca- 

 pacity of about 50 gallons, so 

 arranged that it may be ex- 

 hausted by the 



otherwise. 



B 



air-pump or 

 is an elbow 



formed of lead pipe of one inch 

 calibre, one branch of which 



opens into the 



and 



A 



C 



receiver, 

 the end of the other branch at 

 C is covered by a brass plate or 

 disc about y'^th of an inch in thickness, through which is an 

 orifice of about yVth of an inch in diameter. Another similar 

 plate with an orifice of the same size intersects the pipe at D, 

 thus forming a chamber between the two plates. Two short 

 tubes are inserted into the lower side of the pipe ; one on each 

 side of the plate D. With these short tubes two glass tubes m 

 and n. each thirty-three inches in length, are connected by means 

 of pieces of India rubber hose. These glass tubes are open at 

 both ends and terminate at the bottom in a vase of mercury. 

 A rod (not shown in the sketch) graduated to inches and tenths 

 IS placed beside the glass tubes, sustained upon a float resting 

 upon the surface of the mercury, so adjusted that zero of the 

 graduation may coincide with the surface of the mercury. 



If the orifice at C be closed by a stopper and the receiver ex- 

 hausted, the mercury will rise in the tubes ; and if the density of 

 the atmosphere at the time of the experiment be expressed in 

 inches of mercury, the height of the mercury in the tubes as 

 read upon the graduated rod will be equal to the difi'erence be- 

 tween the density of the atmosphere and that in the receiver. If 



