ROTATION OF A RAY OF LIGHT BY ELECTRIC FORCE. 
9 
specimens of camphine or oil of turpentine, in one of which the rotation was to the 
right-hand, and in the other to the left. In all these cases, as already said (2165.), 
the superinduced magnetic rotation was according - to the general law (2160.), and 
without reference to the previous power of the body. 
2188. Camphor being melted in a tube about an inch in diameter, exhibited high 
natural rotative force, but I could not discover that the magnetic curves induced 
additional force in it. It may be, however, that the shortness of the ray length and 
the quantity of coloured light left, even when the eye-piece was adjusted to the most 
favourable position for darkening the image produced by the naturally rotated ray, 
rendered the small magneto-power of the camphor insensible. 
ii. Action of electric currents on light. 
2189. From a consideration of the nature and position of the lines of magnetic 
and electric force, and the relation of a magnet to a current of electricity, it appeared 
almost certain that an electric current would give the same result of action on light 
as a magnet; and, in the helix, would supply a form of apparatus in which great 
lengths of diamagnetics, and especially of such bodies as appeared to be but little 
affected between the poles of the magnet, might be submitted to examination and 
their effect exalted: this expectation was, by experiment, realized. 
2190. Helices of copper wire were employed, three of which I will refer to. The 
first, or long helix, was 0 - 4 of an inch internal diameter ; the wire was 0 - 03 of an inch 
in diameter, and having gone round the axis from one end of the helix to the other, 
then returned in the same manner, forming a coil sixty-five inches long, double in 
its whole extent, and containing 1240 feet of wire. 
2191. The second, or medium helix, is nineteen inches long, T87 inch internal dia- 
meter, and three inches external diameter. The wire is 0 - 2 of an inch in diameter, 
and eighty feet in length, being disposed in the coil as two concentric spirals. The 
electric current, in passing through it, is not divided, but traverses the whole length 
of the wire. 
2192. The third, or JVoolwich helix, was made under my instruetion for the use of 
Lieut.-Colonel Sabine’s establishment at Woolwich. It is 26 - 5 inches long, 2'5 inches 
internal diameter, and 4 - 75 inches external diameter. The wire is 0T7 of an inch in 
diameter, and 501 feet in length. It is disposed in the coil in four concentric spirals 
connected end to end, so that the whole of the electric current employed passes 
through all the wire. 
2193. The long helix (2190.) acted very feebly on a magnetic needle placed at a 
little distance from it; the medium helix (2191.) acted more powerfully, and the 
Woolwich helix (2192.) very strongly; the same battery of ten pairs of Grove’s plate 
being employed in all cases. 
2194. Solid bodies were easily subjected to the action of these electro-helices, being 
for that purpose merely cut into the form of bars or prisms with flat and polished 
mdcccxlvi. c 
