t 36 ] 



III. On some Effects produced by a Fluid in Motion. 

 By George F. Rodwell, F.C.S.* 



IN the Philosophical Magazine for January 1851, Professor 

 Magnus has given an account of the " Troinpe," or Water- 

 bellows, in which a continuous blast of air is produced by a 

 stream of water, passing down the axis of a vertical tube, of 

 greater diameter than the stream, and in free communication 

 with the atmosphere, by orifices placed just below, or on a level 

 with, the orifice from which the stream issues. 



According to Magnus, air is carried down by the stream owing 

 to the formation of concavities, which close and entrap air within 

 them, and which are produced at the point where collision be- 

 tween the stream and a surface of water takes place 



The following experiments were made to determine the quan- 

 tity of air carried down by a known quantity of water. 



The water used in the experiments detailed below was sup- 

 plied by a cistern 3 feet deep, the bottom of which was 5 \ feet 

 from the ground. 



I. A glass tube A,fig. 1, 

 ^-Jths of an inch diameter, 

 was bent as shown in the 

 figure, so that its length 

 from the upper orifice to 

 the bend was 14 inches, 

 and the length of the 

 bent portion 2 inches ; it 

 was firmly fixed in a ver- 

 tical position, and the 

 curved end placed in a 

 vessel B containing water 

 to a depth of 3 inches. 



A tube C communicat- 

 ing with the water-cistern, 

 ^ths of an inch dia- 

 meter, was placed so that 

 its orifice was level with 

 that of the tube A, an 

 open annular space being left between the two tubes. 



C delivered half a litre of water in 20 seconds, and the jet 

 broke up at 8 inches from the orifice. The stream was allowed 

 to flow down the axis of the tube A, and the air collected in a 

 half-litre flask D, previously filled with water, and inverted over 

 the lower orifice of A. 



A violent foaming attended with a kind of roaring took place 

 in A, at the point where the descending stream came into col- 

 * Communicated by the Author. 



