Experimental Researches in Electricity | Page 3

1343 ---- ? 9. Disruptive discharge 1359 ---- ---- ---- Insulation 1362 ---- ---- ---- as spark 1406 ---- ---- ---- as brush 1425 ---- ---- ---- positive and negative 1465 Series XIII. ---- ---- ---- as glow 1526 ---- ---- ---- dark 1544 ---- ? 10. Convection; or carrying discharge 1562 ---- ? 11. Relation of a vacuum to electrical phenomena 1613 §. 19. Nature of the electric current 1617 ---- ---- its transverse forces 1653 Series XIV. §. 20. Nature of the electric force or forces 1667 §. 21. Relation of the electric and magnetic forces 1709 §. 22. Note on electrical excitation 1737 Index Notes

EXPERIMENTAL RESEARCHES IN ELECTRICITY.

FIRST SERIES.
§ 1. _On the Induction of Electric Currents._ § 2. _On the Evolution of Electricity from Magnetism._ § 3. _On a new Electrical Condition of Matter._ § 4. On Arago's _Magnetic Phenomena._
[Read November 24, 1831.]
1. The power which electricity of tension possesses of causing an opposite electrical state in its vicinity has been expressed by the general term Induction; which, as it has been received into scientific language, may also, with propriety, be used in the same general sense to express the power which electrical currents may possess of inducing any particular state upon matter in their immediate neighbourhood, otherwise indifferent. It is with this meaning that I purpose using it in the present paper.
2. Certain effects of the induction of electrical currents have already been recognised and described: as those of magnetization; Ampère's experiments of bringing a copper disc near to a flat spiral; his repetition with electro-magnets of Arago's extraordinary experiments, and perhaps a few others. Still it appeared unlikely that these could be all the effects which induction by currents could produce; especially as, upon dispensing with iron, almost the whole of them disappear, whilst yet an infinity of bodies, exhibiting definite phenomena of induction with electricity of tension, still remain to be acted upon by the induction of electricity in motion.
3. Further: Whether Ampère's beautiful theory were adopted, or any other, or whatever reservation were mentally made, still it appeared very extraordinary, that as every electric current was accompanied by a corresponding intensity of magnetic action at right angles to the current, good conductors of electricity, when placed within the sphere of this action, should not have any current induced through them, or some sensible effect produced equivalent in force to such a current.
4. These considerations, with their consequence, the hope of obtaining electricity from ordinary magnetism, have stimulated me at various times to investigate experimentally the inductive effect of electric currents. I lately arrived at positive results; and not only had my hopes fulfilled, but obtained a key which appeared to me to open out a full explanation of Arago's magnetic phenomena, and also to discover a new state, which may probably have great influence in some of the most important effects of electric currents.
5. These results I purpose describing, not as they were obtained, but in such a manner as to give the most concise view of the whole.
§ 1. _Induction of Electric Currents._
6. About twenty-six feet of copper wire one twentieth of an inch in diameter were wound round a cylinder of wood as a helix, the different spires of which were prevented from touching by a thin interposed twine. This helix was covered with calico, and then a second wire applied in the same manner. In this way twelve helices were superposed, each containing an average length of wire of twenty-seven feet, and all in the same direction. The first, third, fifth, seventh, ninth, and eleventh of these helices were connected at their extremities end to end, so as to form one helix; the others were connected in a similar manner; and thus two principal helices were produced, closely interposed, having the same direction, not touching anywhere, and each containing one hundred and fifty-five feet in length of wire.
7. One of these helices was connected with a galvanometer, the other with a voltaic battery of ten pairs of plates four inches square, with double coppers and well charged; yet not the slightest sensible reflection of the galvanometer-needle could be observed.
8. A similar compound helix, consisting of six lengths of copper and six of soft iron wire, was constructed. The resulting iron helix contained two hundred and fourteen feet of wire, the resulting copper helix two hundred and eight feet; but whether the current from the trough was passed through the copper or the iron helix, no effect upon the other could be perceived at the galvanometer.
9. In these and many similar experiments no difference in action of any kind appeared between iron and other metals.
10. Two hundred and three feet of copper wire in one length were coiled round a large block of wood; other two hundred and three feet of