Page:The American Cyclopædia (1879) Volume XI.djvu/20

 MAGNETO-ELECTRICITY galvanism around a bar of soft iron ; and since in all cases a mechanical action is accompanies by an equal amount of reaction, it is reasonable to suppose that electricity ought to be evolved by magnetism. Various fruitless attempts were however made to obtain this result ; the form in whi.-h tin- Affect was to appear was unknown, and it was not till 1881 that Faraday succeeded in exhibiting currents of electricity in a v ms of magnetic reaction. It has also been stated in the same article that, In ac< ith the theory of Ampere, the mechanical properties of an ordinary mag- net may be exhibited by currents of electricity transmit! .-.I through spiral conductors; and hence, in order to present the phenomena of lass in the simplest form, we shall begin with stating the fundamental facts of what is called electro-dynamic induction, or electricity i nd need by a galvanic current. 1. Let a por- i a copp-r wire be extended in a straight line horizontally, and the two ends at a dis- tance be connected with a galvanometer so as in a closed circuit in which a current may be induced. Let also a portion of another win-, connect. <! with a galvanic battery, be placed parallel to the first, and a current sent _-h it. If the wire transmitting the bat- irrent be suddenly brought near the wire connected with the galvanometer, during the approach of the second wire toward the first a current of the natural electricity of the latter will pass through the galvanometer in a direc- tion adverse to that of the inducing current. 2. The induced current continues only during the motion of the inducing conductor ; when the motion of this is stopped, the induced cur- rent ceases, and while the current of the bat- tery remains stationary and continues the same in quantity and intensity, no perceptible effect is exhibited in the adjoining wire. 3. When the inducing current is suddenly moved away from the tir-t wire, a current is observed to pass through the galvanometer in the opposite direc- I'oriuer induced current, or in the same direction as the battery current. 4. Let the two wires be placed parallel and near to ach other, while the circuit of the battery current is interrupted. If in this condition the surrent from the battery be suddenly estab- fh the inducing conductor, an in- taced current of electricity will pass through the galvanometer in a direction adverse to that ry current ; or in other words, the effect will I* the same as that of the approach the battery current to the inducing wire as 1. 5. DviQg the continuance of the ' unimpaired strength and <ty no dMurl-aii.-,. (lf the natnral dec _ 'ining wire is perceived: but ie moment the current of the battery is rtopped | l,v a rupture of the circuit, a current .-'h the galvanometer in the same Jon as that of the current of the batterv e phenomena are j,, accordance with the hypothesis that dunii-r the transmission of a current of electricity through a wire, there is exerted in space on every side an inductive action diminishing with the distance which disturbs the natural electricity of any conduct- ing matter which may be brought within its influence ; that while the conductor remains at rest within this influence an abnormal equi- librium exists; and when the conductor is removed from this influence, or when the lat- ter ceases, the usual equilibrium is established by a reverse motion. Since, according to the theory of Ampere, magnetism consists of cur- rents of electricity revolving at right angles to the length of the magnetized bar, it follows that analogous results ought to be produced by magnetism; and for this purpose, instead of the battery current in the last series of ex- periments, let there be substituted a magnetized bar held at right angles to the wire connected with the galvanometer. 1. If this bar be sud- denly brought down upon the wire perpendicu- lar to its length, the galvanometer will indicate a current in an opposite direction to the hy- pothetical current in the lower side of the mag- net. If the wire be E. and W. and the magnet be held across it with its N. pole toward the north, the current in the lower side of the mag- net will be from the E. to the W., while the in- duced current will be in an opposite direction, i. e., from W. to E. 2. When the motion of the magnet toward the wire is stopped, the in- duced current ceases, and no sign of electricity is exhibited so long as the magnet remains at rest. 3. When the magnet is suddenly removed from its proximity to the wire, a current in the opposite direction to that of the first, that is, in the same direction as .the current in the lower side of the magnet, is indicated by the galvan- ometer. 4. When a bar of soft iron is placed across the wire at right angles, and this is sud- denly magnetized, either by a galvanic current or by touching its ends to the poles of a horse- jhoe magnet, a momentary current is produced n the wire in a direction opposite to that of the lypothetical currents of the near side of the magnet. 5. So long as the soft iron bar re- mains at rest and its magnetism suffers no change, no current is indicated by the galvan- ometer^ but the moment the bar is umnag- netized a reverse current takes place. The two series of results we have given above are precisely analogous; the latter being merely a case of the former, in which the hypothetical currents of the magnet are substituted for the real current of the battery. All the effects -hat we have described are produced with nuch more intensity, when, instead of using ctended wires parallel to each other, we em- loy wires in the form of spirals, either flat or ndncal. For example, to obtain an induced rent of considerable intensity by means of tism, we place on a rod of iron, say four nclies long, a spool of long wire covered with ^ ], may OCGU Py two inches of the ph of the middle of the iron. If the two f this rod projecting beyond the spool