Prof. Magnus on the Motion of Fluids. 13 



30. Further on, in § 41, I shall return to the explanation of 

 the fact, that the action of the water against the plate increases 

 with the distance. It appeared to me to be of interest to ascer- 

 tain, in the next place, the manner in which the water of the jet 

 mixes with that into which it is pi'ojected. 



For this purpose I permitted the water to pass horizontally- 

 through an orifice from 2 to 3 millims. in diameter, and under 

 a vertical pressure of 7 feet, into a vessel two of whose sides 

 were glass, and separated from each other by a distance of only 

 0-5 of an inch. As the jet entered the vessel through the middle 

 of its small side, and hence could only spread itself upwards and 

 downwards, there was reason to hope that the inconsiderable 

 thickness of the water would permit of an exact observation of 

 what went on within. 



The friction against the sides of the vessel rendered it neces- 

 sary to sensibly increase its width at some distance from the 

 orifice (see A, fig. 11). The opposite side of the vessel at B was 

 famished with a channel, through which the superfluous water 

 escaped, leaving the surface at a constant height. In order 

 better to observe the jet, I introduced into the water opake 

 bodies of various kinds. Semen lycopodii and milk ; but the mo- 

 tion was always so unsteady and violent, that exact observation 

 was impossible. Another phaenomenon, however, was exhibited 

 in this experiment, which, although it might be immediately 

 inferred from those already described, is still perhaps not without 

 interest. The orifice through which the jet entered the vessel 

 lay about 2 inches under the surface of the water therein con- 

 tained, and 3"5 inches above the bottom. As soon as the jet 

 entered, the surface in the narrow portion of the vessel sunk, 

 and exhibited various depressions, according as the water entered 

 with greater or less powder. The surface near the orifice often 

 sunk below the level of the latter. When this occurred, a vio- 

 lent foaming was the consequence; and as long as the water 

 entered with sufficient force, the surface at this point continued 

 lower than the orifice. When, however, this considerable sinking 

 of the surface was avoided, so that the orifice / remained beneath 

 it, several depressions exhibited themselves, as shown in fig. 11. 

 If the mass of water were increased by completely opening the 

 cock c, the depression at d became smaller; but that at e, on 

 the contrary, about 5 inches distant from the orifice /j remained 

 almost wholly unchanged. In all these cases, the water in the 

 wider portion AB of the vessel, both above and below, moved 

 backwards into the narrower portion, and hence against the 

 direction of the jet, which furnishes a new proof that a pretty 

 considerable portion of the motionless water is constantly carried 

 forward by the jet. This gives rise in the neighboiu'hood of the 



