VIEWS OF RUNNING WATER. 



6 53 



gradual diminution. We have already shown this in the forma- 

 tion of swells by changes of slope in streams. "We have another 

 experiment. Slowly close a faucet till the liquid vein flows in a 

 mere thread (Fig. 11, xv). The orifice in this case being perfect- 

 ly cylindrical, the contraction is due on one side to the adherence 

 of the liquid to the sides of the hole, and on the other side to 

 acceleration, and takes place equally in all directions. Interca- 

 late a solid body or a liquid surface at a few centimetres from the 

 hole. The pressure at the base of the column augmenting by 

 resistance, we might expect the vein to take the continuous form 

 of two reversed cones (Fig. 11, xvi). It does not, but takes the 

 form of swellings, of knots regularly placed, which give the vein 

 the appearance of a chaplet (Fig. 11, xvii). This phenomenon, 

 interesting as a case of action at a distance, and also as a case of 

 vibrating action, has been observed 

 by Savart and is described by him in 

 the second of his memoirs. What the / _ 

 pressure caused by shock produces \-f^T 



>SL 



here, the pressure caused by cohesive \ 

 attraction (capillary pressure or su- 

 perficial tension) produces on the 

 edges of the liquid sheet : a series of FlG> 11# 



knots is formed. The section of the 



jet loses the form of the hole as soon as it leaves it, but the in- 

 crease of thickness at the expense of breadth does not take place 

 continuously ; the central sheet is still thin and even, while the 

 edges are already transformed into thick cords followed by other 

 smaller ones. It is the same system of swells and ripples that we 

 met before. The stria? of one side cross those of the other side, 

 and the tongue is covered with a system of lozenges producing a 

 very pretty effect (Fig. 8, x, and, in section, xviii). 



Now that we know the details of the form and constitution of 

 the upper part of the liquid sheet, let us see what occurs lower 

 down. On issuing from the canal, the lateral molecules of the 

 sheet are subjected to the action of a component of horizontal 

 centripetal velocity which turns them toward the middle. The 

 particles in the middle, on the other hand, thrown toward the 

 outside, acquire also a horizontal component, but centrifugal (Fig. 

 8, xiv). The point of stable equilibrium is where the jet has a 

 cylindrical form. But there are various things to be observed. 



As the rope-walker does not cease oscillating when he reaches 

 the point of stable equilibrium, but by virtue of his inertia goes as 

 far beyond it on the other side, so the horizontal oscillation of the 

 molecules of water, repeating itself, produces a new sheet in a plane 

 perpendicular to the first one, but this time in the form of a double 

 tongue that is, of a disk or lentil. The phenomenon repeating 



