On some Effects produced by a Fluid in Motion. 99 



mult. The utterance of the word "hush/' or "puss/' pro- 

 duces the same effect. This hissing sound contains the precise 

 elements that most forcibly affect the flame. The gas issues 

 from its burner with a hiss, and an external sound of this cha- 

 racter added to that of a gas-jet already on the point of roaring- 

 is equivalent to an augmentation of pressure on the issuing 

 stream of gas. I hold in my hand a metal box containing com- 

 pressed air. I turn the cock for a moment, so as to allow a puff 

 to escape — the flame instantly ducks down, not by any transfer 

 of air from the box to the flame, for I stand at a distance which 

 utterly excludes this idea ; it is the sound of the issuing air that 

 affects the flame. The hiss produced in one orifice precipitates 

 the tumult at the other. 



Note. — Those who wish to repeat these experiments would do 

 well to bear in mind, as an essential condition of complete 

 success, that a free way should be open for the transmission of 

 the vibrations from the flame, backwards, through the gas-pipe 

 which feeds it. The orifices of the stopcocks near the flame 

 ought to be as wide as possible. 



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

 By George Farrer Eodwell, F.C.S.* 



[With a Plate.] 

 No. III. 



1 . Effects produced by a stream of liquid, (a) entering, and (/3) issuing 

 from a liquid mass at right angles to its surface. — 2. Amount of 

 lateral action exercised by (a) a jet of water, and (/3) a jet of 

 steam of known pressure. — 3. Note on the constitution of a de- 

 scending liquid jet. 

 IN the first and second of these papersf I have considered 

 the various modes by which air is carried down by a stream 

 of water; in the present I propose to treat chiefly of some effects 

 more or less directly attributable to the so-called "lateral action " 

 of VenturiJ, which Professor Magnus § has proved to result 

 from the well-ascertained fact (also demonstrated theoretically by 

 Daniel Bernouilli and by Poisson) that the pressure exerted by 

 a fluid in motion is less than its pressure when at rest. As a 

 consequence of this action, a fluid entering or issuing from a 

 fluid mass at rest tends to produce various effects, some of 

 which have been described below. 

 * Communicated by the Author, 

 t Phil. Mag. for January and September 1864. 



X Recherches experiment ales sur le principe de la communication laterale 

 du mouvement dans lesjluides. 



§ " On the Motion of Fluids," Transactions of the Royal Academy of 

 Sciences of Berlin, 1848. Translated in the Philosophical Magazine for 

 Jauuarv 1851. 



H 2 



