246 Mr. Sturgeon on Electro-Magnetism. 



ever, the experiment I am about to describe will confirm this 

 property in a more satisfactory manner. 



The rotation of the magnet on its axis by subjecting both poles 

 at the same time to the influence of similar electric currents. 



Fig. 3 is a representation of the apparatus ; and, with the 

 exception of the magnet NS, is entirely of brass-work. A is 

 a round foot, from which rise the two cheeks BB, for the 

 purpose of supporting the annular cell q holding quicksilver ; 

 and likewise the cross piece R, which is screwed tight down by 

 the knobs kk, and thus the apparatus is kept firm and steady. 

 The magnet passes through the opening in the centre of the 

 cell q, and communicates with the mercury there contained 

 by means of a wire soldered to its equator, and at right angles 

 to its axis. The poles are furnished with pivots ; the lower 

 of which at S runs in a small cup on the top of the foot A ; 

 and the upper one at N runs in the lower extremity of a screw . 

 nail passing through the cross piece R, and whose head is 

 made into the form of a cup for holding mercury. ZC are 

 two wires proceeding respectively from the zinc and copper 

 6ide of a battery : the former communicating with the mer- 

 cury in the cell q, and consequently with the equator of the 

 magnet; the latter communicates with the upper pole N in 

 the manner shown in the figure. Thus, one half of the mag- 

 net forms part of the galvanic circuit. The other half, from 

 its equator to the lower pole S, forms likewise part of another 

 like galvanic circuit, by means of the wires Z' C which pro- 

 ceed respectively from the zinc and copper side of another 

 battery, and communicate with the equator and pole in the 

 same manner as the former. By subjecting the magnet in this 

 manner to the influence of like electric currents, it is rotated 

 with an astonishing velocity, but which may in a moment be 

 retarded by interrupting the circuit of either battery; and 

 again accelerated by renewing the contact. This variation of 

 the experiment proves to demonstration the utility of employ- 

 ing both poles at the same time, and is another proof of the 

 rotations on opposite poles, in the old experiments, being 

 merely relative ; for the poles of the magnet are here both 

 connected with the copper side, and the equator with the zinc 

 side of the respective batteries. Another advantage in the 

 maimer of making this experiment is, that the glass vessel and 

 mercury for floating the magnet are here not used ; therefore 

 the whole of the magnet is in view ; whereas in the old mode 

 only a small portion of the magnet, about the thickness of a 

 quill, was visible above the surface of the mercury. It can be 

 no small gratification to those who are in the habit of giving 



public 



