produced by a Fluid in Motion, 



39 



became more and more base as the flow was diminished, until 

 distinct impulses were heard. 



Suppose the orifices in B closed, and the tube A rilled with 

 water, it is evident that the column of water in A would have 

 no tendency to fall, but would remain suspended in the tube, 

 but directly the orifices were opened the column in A would fall, 

 and air rush in to supply its place in the tube. Now when 

 water is rapidly entering by the tube C, the particles follow each 

 other with such rapidity that air cannot enter by the lateral 

 orifices; but so soon as we diminish the flow, the stream be- 

 comes narrower, consequently its velocity below the orifice of C 

 is less than that above it, because the adhesion of the glass of A 

 causes the stream, although of less diameter, to completely fill it ; 

 air is now able to enter by the lateral orifices, and if water were not 

 constantly flowing from C the whole column would of course fall; 

 but as soon as a small amount of air has entered, the flowing water 

 closes the orifices, so that we get periods during which air enters, 

 alternating with periods during which the orifices are closed. 



The musical notes are produced by the periodic breaking of 

 the continuity of the column of water by air, the regular entry 

 of which causes regular pulses to be given to the air, which, when 

 they follow each other with a certain rapidity, produce a musical 

 note. A slight movement of the tube often stops the produc- 

 tion of the musical note, and the air then enters irregularly, and 

 escapes from the lower orifice of the tube in jerks ; but by 

 pitching the voice to the note previously produced, the air 

 enters regularly, the column assumes the peculiar banded appear- 

 ance, the musical note is produced, and air issues from the lower 

 orifice of the tube in a regular stream. 



When the stream was rapid, y\„ 3, 



the air which entered did not A urn 



completely break its " conti- 

 nuity, but passed down the 

 axis of the tube in small bub- 

 bles (A, fig. 3). No sound was 

 apparent when this occurred. 

 On diminishing the flow the 

 banded appearance set in, and 

 when viewed by means of a 

 moving mirror, was seen to be 

 produced by alternate discs of 

 air and water (B, fig. 3), the 

 former being doubly convex, 

 and the latter doubly concave, 

 as we should expect. When 

 the flow was further dimin- 



