Dr. Tyntlall on some Phanomena of a Water-Jet. 107 



A convenient way of making the, above expei-iment is with a 

 syringe-bottle, such as that nsed by chemists for washing out 

 precipitates, the pressure of the breath being vised instead of the 

 pressure of the steam. The experiment was also modified in the 

 following manner : — A cylindrical tin vessel, about 10 inches in 

 height, had a circular hole punched through its bottom. When 

 filled with water, the limpid portion of the vein which issued from 

 it was of considerable length ; but this, being a function of the 

 pressure, became shorter as the latter, by the sinking of the water 

 in the vessel, decreased. An arrangement similar to the former 

 was made. Wlien the vessel was fuU, a basin of water was 

 brought underneath so that its surface cut the jet above its con- 

 tracted section. As the pressure became less the latter ascended, 

 and immediately after it had crossed the sui'face the bubbles 

 commenced. In this case also the fluid was agitated, but with 

 the same result as before. 



These experiments demonstrate that the entrance of the air is 

 not due to adhesion, and also that a contemporaneous motion of 

 the smface may take place without any bubbles being produced. 

 They urge us to seek the cause of the latter in the structure of 

 the jet on the lower side of its contracted section. Above this 

 point the action of the jet against the water is nearly uniform, 

 resembling in this respect a solid wire drawn quickly downwards 

 through the fluid. The portion, however, below the contracted 

 section is not represented by a wire, but by a string of beads ; 

 the action here is not uniform, but the water opens and closes 

 according as the diameter of a bead or the space between two 

 beads coincides with the plane of the surface. In this manner 

 the impact of each drop causes the fluid to recede on all sides, 

 and creates an interval into which the air enters ; partly by the 

 return of the fluid, and partly by the descent of the succeeding 

 drop, this interval is covered in and the bvibblc formed. If a 

 smooth string be held between the finger and thumb to the bot- 

 tom of a basin filled with water and then drawn quickly through, 

 no bubbles are formed ; but if the same string be knotted, bubbles 

 to any amount may be obtained. The direction of the force 

 exercised by the jet above the contracted section is almost wholly 

 vertical ; but below this point each drop furnishes a lateral com- 

 ponent, which dashes the fluid aside and thus allows s])ace for 

 the air to enter. The same is exhibited when, for the drops of 

 water, we substitute grains of shot. 



All these ))h}enoniena can be very prettily exhibited with oil. 

 Looking through the side of the glass into which the vein de- 

 scends, the bubbles are observed to describe ellipses : the same 

 is the case with water, the eccentricity of the curves being, how- 

 ever, greater. Looking downwards on the surface, the bubbles 



