" ' "' " jm\f Liquid ^mr^fibm Circular Orifices. 291 



portion. On the contrary, however, experiment shows that the 

 length of the continuous portion is nearly proportional to the 

 diameter of the orifice. 



Lastly, it is easy to see, a priori, that the tension due to acce- 

 leration of velocity does not in reality produce any tendency to 

 disunion. In fact, if this tension separated the liquid molecules, 

 the density of the continuous part would diminish from above 

 downwards j now a little reflection on the relative mobility of 

 molecules of liquid will soon convince us that this diminution of 

 density is impossible ; for as soon as two molecules tend to se- 

 parate, another is displaced and steps between them, whence it 

 follows that the only effect of tension will be to lengthen the 

 jet by making it thinner; and as the acceleration is uniform 

 throughout the whole extent of the jet, it is evident that its sole 

 tendency will be to diminish the diameter of the jet from the 

 orifice downwards in a perfectly regular and continuous manner, 

 without occasioning a tendency to rupture at any point. 



Thus theory and experiment unite in proving the complete 

 inadmissibility of the hypothesis of rupture. Let us next con- 

 sider that of pulsations. 



We may at once remark, that the latter appears in itself diffi- 

 cult to justify, seeing that Dejean is not satisfied with Savart^s 

 explanation, and that Maus attempts another. In fact, in the 

 efflux of a jet completely protected against external influences, 

 where everything appears to be in favour of continuity, the only 

 natural manner of conceiving alternate diminutions and augmen- 

 tations in the velocity of efflux to arise, would be to suppose, with 

 Savart, that the friction of the liquid against the edges of the 

 orifice sets the latter in vibration, and that these vibrations are 

 transmitted to the liquid. But Savart assured himself that when 

 the borders of the orifice are touched with a solid and resisting 

 body — which ought to arrest, or at least deaden the vibrations, — 

 no change whatever in the nature of the jet is perceptible. The 

 vibrations of the sides of the orifice therefore cannot occasion the 

 pulsations of the liquid ; but to whatever cause these pulsations 

 may be attributed, they must, if they exist at all, consist of a 

 vibratory motion of the liquid, which motion would necessarily 

 be communicated to the sides of the orifice j so that by hinder- 

 ing, as Savart did, the vibrations of these sides, the pulsations 

 of the liquid ought to be impeded also, and the state of the jet 

 to be modified ; how is it, then, that the jet suffers no appre- 

 ciable modification ? ^'^;;:^^,^ . J';^,^^'^^,^^'!^^ '/ 



Further, Savart, w&n eiEiiimm'g'tlife atinirfar expansions 6i 

 the continuous part of the jet, according to the method he de- 

 scribes, was not able to prove their existence except at a little 

 distance from the orifice ; and Hagen, who discovered a method 



V2 



