192 Miscellanies. 
water. This inconvenience might have been obviated by mounting 
the helix as in the figure, and allowing its ends 6, 6, to descend into 
separate mercury cells; but the use of mercury is objectionable, and 
by adopting the arrangement described, the polarity of the helix 1s 
exhibited in a convenient and pleasing manner. 
Fig. 3. 
Fig. 3, isa plan for exhibiting the polarity and curious motions of 
De la Rive’s ring, floating in the air instead of acid and water. The 
great advantage of this construction, and that of fig. 2, is that the 
ring and helix, and the batteries, may be of any desired size. a re- 
presents the ring, suspended as in fig. 1. The wire ends descend 
into concentric mercury cells, c,c. ‘These separate cells communi- 
cate with the battery cells d,d, by wires passing along the slight 
lever beam e. The ring and cells are balanced by a small weight, d. 
The magnet, m, supported by its centre, is bent so as to form an arc 
' of the circle described by the ring. Suppose the ring to be in equi- 
librium at the neutral point of the magnet, m. Reverse the bat- 
tery wires in the cells d, d, and the ring starts off from the bar, turns 
round, presents its other face, and passes on to m as before ; so that 
this motion can be produced on a large scale at pleasure, simply by 
changing the battery wires without disturbing the magnet, as in the 
floating apparatus. All this can be done with solid conductors, but 
there being no rapid motion in this experiment, the mercury cells 
are preferable, from their simplicity. 
