8 Prof. Maguus on the Motion of Fluids. 



jet to issue in a perpendicular direction from a vessel through a 

 tube, and brought the surface of the water which the jet was to 

 enter almost into contact Math the end of this tube. Here air- 

 bubbles were also formed in the interior of the fluid ; but in this 

 case the short space of air through which the jet had to pass, 

 about 1 millim., could not possibly have a motion imparted to 

 it by friction suflicient to cause it to penetrate deep under the 

 surface of the water. 



18. Savart has asserted, that a jet of fluid up to its maximum 

 contraction forms a single continuous mass ; but from this point 

 forwards portions are detached, which, owing to the frequent 

 alteration of their shape, give rise to those periodic swellings. 

 It might be imagined that the air-bubbles observed when a jet 

 enters a mass of fluid are due to the air inclosed between those 

 small detached masses; but if a jet be allowed to project itself 

 against a fluid, even before it has attained its maximum con- 

 traction, the bubbles will still appear. Thus, without reference to 

 other objections, is the opinion under question completely refuted. 



19. This phenomenon appears to be caused in the following 

 manner : — A concavity is foi-med by the jet at the point where it 

 strikes the water ; this closes in as soon as the least motion has 

 been imparted to the surface, and the air within it is carried 

 downwards. 



20. If a jet strikes continuously against the surface of a fluid, 

 the concavity formed at the point of contact is distinctly visible ; 

 but in general it closes so quickly, and a new one so speedily 

 occupies its place, that the manner in which the air is inclosed 

 eludes exact observation. 



21. I have had opportunity, however, to observe, that when 

 a jet strikes a tranquil surface placed at some distance from the 

 orifice, but before it has attained its maximum contraction, a 

 considerable concavity is sometimes formed round the jet with- 

 out the entrance of any air. As soon, however, as the least 

 motion is imparted to the surface, the air is observed to enter 

 immediately. Let the surface, for instance, be put in motion 

 by permitting water-drops to fall upon it from a height of a few 

 inches, and at a small distance from the jet. The drops M'ould 

 of themselves carry no air downwards ; but as soon as they meet 

 the surface a peculiar sound is heard proceeding from the point 

 where the jet strikes the fluid, and at the same moment air- 

 bubbles are formed and carried downwards. 



22. The same takes place when the continuity of the jet is 

 broken, as, for example, when a solid body is caused to pass 

 through it ; even when a little bubble is inclosed l)y the jet the 

 noise is heard, and at the same time a considerable quantity of 

 air is carried downwards. The like occurs when an irregular 



