ON THE LINES OF MAGNETIC FORCE. 
outside of the magnet, was fixed at b, and the portion a, being a separate piece, was 
carried along the axis until it came in contaet with the Fig. fi. 
former at d\ the revolution of one part was thus permitted 
either with or without the other, yet preserving always 
metallic contact and a complete circuit for the induced cur- 
rent. In this case, when the external wire and the magnet 
were fixed, no current was produced by any amount of revolution of the wire a oti 
its axis. Neither was any current produced when the magnet and wire, c d, were 
revolved together, whether the wire a revolved with them or not. When the magnet 
was revolved without the external part of c d, or the latter revolved without the 
magnet, then currents were produced as before (3091.). 
3096. The magnet was now included in the circuit, in the following manner. The 
wire a, fig. 7? was placed in metallic contact on both sides Fig. 7. 
of the interval between the magnets atN (or the pole), and 
the part c was brought into contact with the centre at d. 
The result was in everything the same as when the wire a 
was continued up to d, i. e. no amount of revolution of 
the magnet and part c together could produce any electric current. When c was 
made to terminate at e or the equatorial part of the magnet, the result was precisely 
the same. Also, when c terminated at e, the part a of the wire was continued to the 
centre at d, and there the contact perfected, but the result was still the same. No 
difference, therefore, was produced, by the use between N and d, or d and e, of the 
parts of the magnet in place of an insulated copper wire, for the completion of the 
circuit in which the induced current was to travel. No rotation of the part a pro- 
duced any effect, wherever it was made to terminate. 
3097- In order to obtain the power of rotating the magnet without the external 
part of the wire, a copper ring was fixed round, and in contact with it at the equa- 
torial part, and the wire c, fig. 8, made to bear by spring- 
pressure against this ring, and also against the ring H on 
the axis, fig. 1 (3084.) ; the circuit was examined, and found 
complete. Now when the wire c e was fixed and the 
magnet rotated, a current was produced, and that to the 
same amount for the same number of revolutions, whether the part of the wire a 
terminated at N, or was continued on to the centre of the magnet, or was insulated 
from the magnet and continued up to the copper ring e. When the wire, by expe- 
dients, whieh though rough were sufficient, was made to revolve whilst the magnet 
was still, currents in the contrary direction were produced, in accordance with the 
effect before described (3091.) ; and the results when the wire and magnet rotated 
together (3092.), show that these are in amount exactly equal to the former. When 
the inner and the outer wires were both motionless, and the magnet only revolved, a 
current in the full proportion was produced, and that, whether the axial wire a made 
contact at the pole of the magnet or in the centre. 
Fig. 8. 
MDCCCLII. 
F 
