ROTATION OF LIQUIDS. 469 



the magnet is a north pole, the rotation is opposite to the motion of 

 the hands of a watch. Faraday's arrangement gives greater friction, 

 and the rotation is less rapid. 



485. ROTATION OF LIQUIDS. When the current traverses a 

 liquid, the liquid filaments, which coincide with the lines of electrical 

 flow, may be considered as movable circuits, capable of obeying 

 electromagnetic actions, and experiment shows that the liquid is 

 moved along with the current which it carries. 



i st. Davy's Experiment. Two platinum electrodes just pro- 

 ject a very little below the top of the mercury. If the N pole 

 of a magnet is placed over one of them the negative electrode, 

 for example a depression of the mercury is observed ; and, at 

 the same time, a rotation in the same direction as the hands of 

 a watch. 



2nd. M. Jamiris Experiment. The two electrodes of a volta- 

 meter are placed in the same vertical line, and on the axis 

 of the poles of a horseshoe magnet. If the liquid molecules in 

 a filament of the current formed a rigid thread, we should be 

 in the same condition as in Faraday's experiment, in which 

 rotation is impossible. The electromagnetic forces really act inde- 

 pendently, and in the same manner as in Davy's experiment, on 

 the portions of the filaments which diverge as they start from 

 each of the electrodes. The liquid divides them into two super- 

 posed layers which rotate in contrary directions, and the rotation 

 is made visible by the bubbles of gas which result from the 

 decomposition of water. 



3rd. M. Bertiris Experiment. In M. Bertin's experiments the 

 movement of the liquid is made visible by small pieces of cork 

 which float on the surface. The liquid is in an annular dish 

 containing two rings of metal, one inside the other. If these 

 circles are electrodes, a series ot either centripetal or centrifrigal 

 radiating currents is obtained in the liquid. When a magnet is 

 placed in the axis of the current, the liquid acquires a rotation 

 in a definite direction in agreement with theory. The direction 

 of the rotation is not altered, if the central magnet is replaced 

 by a magnetised tube encircling the dish. For if the north 

 pole is at the top in the two cases, the flow of magnetic force is 

 diverted downwards, both inside and outside the hollow magnet. 

 This is not the case when the magnet is replaced by a coil : 

 the rotation of the liquid changes its direction according as the 

 coil is inside or outside the dish, and each of the lines of force 

 constitutes a closed circuit. 



