produced by a Fluid in Motion. 223 



air rushing in to penetrate through the conical cavity, and that 

 same air after having been carried down by the water and col- 

 lected, might be employed separately to produce vibrations in 

 vibrant bodies according to any of the usual methods. 



IV. 



There is one other way in which water passing through a tube 

 may carry down air. 



Suppose a continuous vertical tube with water flowing through 

 it. If now the water is caused to cease flowing, it will remain 

 suspended in the tube by atmospheric pressure ; and such would 

 of course be the case with any tube under 33 feet in length ; but 

 let an orifice be made anywhere in the circumference of the tube, 

 and the whole column beneath that orifice will instantly fall, 

 because it has no longer the weight of the atmosphere on its 

 lower end alone, but also at the orifice ; the influence of the 

 atmosphere is consequently annulled below the orifice, and the 

 column falls by its own weight. 



If water be flowing through such a tube, the column below 

 the orifice will have greater velocity than that above it ; hence 

 rupture of the column will ensue at the orifice, and air will enter ; 

 but as water is continually flowing, the orifice is quickly closed, 

 and we thus obtain an intermittent entry of air. 



In order to see how much air might be carried down by this 

 means, a short glass tube 0, fig. 1, ^ths of an inch diameter, 

 was fitted into the upper orifice of the tube B by means of a 

 cork ; a piece of caoutchouc tubing, P, was adapted to the tube 

 0, and a circular delivery-tube H, ^ths of an inch diameter, 

 was connected with the upper part of the caoutchouc tube. H 

 delivered half a litre of water in 24 seconds. An orifice g^th 

 of an inch diameter was made in the circumference of the caout- 

 chouc tube midway between the orifices of H and ; thus a 

 perfectly continuous tube, with the exception of an orifice ^th 

 of an inch diameter, intervened between the water-cistern and 

 the vessel A. 



Matters being thus arranged, water was allowed to flow from 

 H, and it was found that half a litre of water carried down 218 

 cubic centims. of air. 



When a caoutchouc tube with four orifices in its circum- 

 ference was substituted for that with one orifice, half a litre of 

 water carried down 320 cubic centims. of air : in both instances 

 the water-surface in A was 1 inch below the orifice of B (viz. at 

 b, %. 1). 



We see from the above that there are four modes by which 



