CAPILLAKY ACTION. 



ii,.l, 0<M BlL * the equUibrium of the disk C is therefore mi- 

 Hem* tho equUibrium of a cylindric film whose length is greater than 

 unstable. Such a film, if ever so little disturbed, will 



l it x'll 'x f 



begin to contract at one section and to expand at another, till its form ceases 

 to iwetnble a cylinder, if it does not break up into two parts which become 

 ultimately portions of spheres. 



INSTABILITY OF A JET OF LIQUID. 



When a liquid flows out of a vessel through a circular opening in the 

 bottom of the vessel, the form of the stream is at first nearly cylindrical though 

 its diameter gradually diminishes from the orifice downwards on account of the 

 ring velocity of the liquid. But the liquid after it leaves the vessel is 



subject to no forces except gravity, the pressure of the air, and its own surface- 

 tension. Of these gravity has no effect on the form of the stream except in 

 drawing asunder its parts in a vertical direction, because the lower parts are 

 moving faster than the upper parts. The resistance of the air produces little 

 disturbance until the velocity becomes very great. But the surface-tension, 

 acting on a cylindric column of liquid whose length exceeds the limit of stability, 

 begins to produce enlargements and contractions in the stream as soon as the 

 liquid has left the orifice, and these inequalities in the figure of the column 

 go on increasing till it is broken up into elongated fragments. These fragments 

 aa they are felling through the air continue to be acted on by surface-tension. 

 They therefore shorten themselves, and after a series of oscillations in which 

 they become alternately elongated and flattened, settle down into the form of 

 spherical drops. 



This process, which we have followed as it takes place on an individual 

 portion of the falling liquid, goes through its several phases at different dis- 

 tances from the orifice, so that if we examine different portions of the stream 

 as it descends, we shall find next the orifice the unbroken column, then a 

 aeries of contractions and enlargements, then elongated drops, then flattened 

 drops, and so on till the drops become spherical. 



