produced by a Fluid in Motion. 101 



discontinue to move in their original direction, are influenced by 

 the adhesion of the glass, which tends to draw them upwards; 

 they are no longer prevented from rising by the accumulation of 

 lycopodium on each side of the descending stream, and they 

 meet with less resistance than if they moved forward at once with 

 the central current, they consequently ascend. To the motions 

 producing the circular currents in the first experiment, we have 

 to add that produced by the adhesion of the glass, acting in a 

 different direction ; as a consequence, the circular motion of the 

 water- particles is changed into an elliptic motion, the major 

 axis of the ellipse being in the direction of the newly added force, 

 as we should expect. 



A jet of water issuing from an orifice 1*5 millim. in diameter 

 with sufficient force to rise to the height of a metre, was caused 

 to enter water at right angles to its surface. A cylindrical 

 copper vessel, *3 metre in diameter by '17 metre deep, was used 

 for the purpose ; and the water-surface (upon which lycopodium 

 was sprinkled) stood at a height of 75 millims. from the bottom 

 of the vessel. The orifice of the delivery-tube was placed 3 mil- 

 lims. above the water-surface, and the jet was allowed to enter 

 near the side of the vessel. The particles of lycopodium beneath 

 the influent jet immediately began to revolve around it in con- 

 centric circles, having the jet for their centre, and currents were 

 produced similar to those shown in fig. 1, but moving in a re- 

 verse direction; that is to say, the side currents moved from the 

 jet, and the central current into which they united moved towards 

 the jet. 



When the influent jet was placed in the centre of the vessel 

 instead of near its side, the lycopodium moved radially to the 

 sides of the vessel, and returned ; after which the course of the 

 currents could not be traced, because they met each other in 

 various positions, producing spiral and circular eddies. If in- 

 stead of allowing the jet to enter the water by its clear portion, 

 that is to say, above the vena contracta, it was caused to enter by 

 its opake and agitated portion, the particles of lycopodium, in- 

 stead of revolving around the jet, were drawn towards it by a 

 spiral current and carried beneath the water-surface, 



A jet of water, similar in all respects to that employed in the 

 last experiment, was allowed to escape 1 millim. beneath the 

 surface of water ; it issued from the water at right angles to its 

 surface, and in contact with the side of the containing vessel. 

 After ascending to the height of about 100 millims. the jet 

 divided and returned in two parabolas, one on each side of the 

 ascending jet. Lycopodium entered the ascending jet with 

 great velocity, followed the path of the parabolas, and reentered 

 the jet by currents moving in a parabola, which started from 



