100 Mr. G. F. Rodwell on some Effects 



1. Effects produced by a stream of liquid, (a) entering, and (/3) 

 issuing from a liquid mass at right angles to its surface. 



A stream of water flowing at the rate of 12 cubic centimetres 

 per minute, was allowed to run down the side of a beaker con- 

 taining water, upon the surface of which lycopodium had been 

 sprinkled ; the adhesion of the glass flattened the stream into 

 a thin ribbon of water 6 millims. broad by 1 millim. thick. 

 At the point where the stream entered (A, fig. 1, Plate II.) the 

 particles of lycopodium were driven forward in a straight line to 

 the opposite side of the beaker ; they then returned in the direc- 

 tion of the arrows, and entered the central current immediately 

 beneath the descending stream. At the junctures of the re- 

 turning currents with the central current the lycopodium re- 

 volved with great rapidity in circles moving in opposite direc- 

 tions, as shown in the figure, which represents the water-sur- 

 face. Particles of lycopodium were found to collect together on 

 each side of the descending stream ; when these were dislodged 

 from their position, the circular currents disappeared, and lyco- 

 podium was observed to rise a short distance into the descend- 

 ing stream, and to revolve in ellipses moving in opposite direc- 

 tions. One ellipse was apparent on each side of the descending 

 stream ; and the major axis of each was four or five times as great 

 as the minor. By colouring the descending stream, the main 

 body of liquid entering the beaker was seen to pass between the 

 ellipses, although the space was not more than one tenth of the 

 breadth of the whole stream. In fig. 2 (in which the eye is 

 supposed to be on a level with the water- surface) A represents 

 the descending stream, B the water-surface, and C the stream 

 as it enters the water after passing between the ellipses. 



In the first experiment a central current is produced by the 

 entering stream, which flows across the beaker until it reaches 

 the opposite side, when it divides into two currents, returning 

 by the sides of the vessel. Immediately before the coalescence 

 it is obvious that the side currents move at right angles to the 

 central current; circular currents at the points of juncture are 

 the result. The motions which produce these circular currents 

 are, (a) the motion possessed by the returning currents, directly 

 derived from the motion of the central current, but of less mag- 

 nitude on account of the friction of the sides of the vessel, plus (j3) 

 the motion caused by the lateral action of the central current 

 when the side currents approach it, acting together in one di- 

 rection ; and (7) the motion of the central current acting in a 

 direction at right angles to this. 



In the second experiment the particles of water of the return- 

 ing currents, when they are compelled by the central current to 



