MAGNETO-ELECTRICITY. If a wire which joins the twn ends of a voltaic battery (GALvAetsu) and consequently through which a voltaic-current is passing, be arranged in such a manner as to be parallel with a second wire, the two ends of which are con nected with a sensitive galvanometer, no action on the second wire will be perceived so long as the current is allowed to pass uninter ruptedly through the first ; but if the current through the first wire, called the primary current, be suddenly arrested by breaking off its connection with the battery, a current of momentary duration will be produced in the second wire ; this which is called the secondary current is said to be direct, or iu the same direction as that of the battery wire. On again connecting the first wire with the battery a momentary current or electric wave is again sent through the second wire; but it is now inverse or in a direction opposite to that of the primary current.
The term voila-electric-induction was applied by Faraday to these phenomena. Their effects may be augmented by employing coils in such a way that that which conveys the primary current, known as the primary coil, shall be placed in the axis of the coil in which the secondary current is generated, the ends of this the weeder" coil being connectiel with the rude of the galvanometer. The moment the primary coil is con nected with the battery the needle will receive a powerful impulse; but will regain its original position after a few oscillations, although the currant through the primary coil is kept up; but no 'sooner is the primary coil disconnected from the battery than the needle will be powerfully impelled in an opposite direction. Similar phenomena may be produced it the primary coil, while connected with the battery, be made suddenly to approach to, or be removed from the secondary coil, in connection with the galvanometer. In approaching the coil the second ary current is inverse ; but In withdrawing it, it is direct. If instead of the galvanometer, a small helix be connected with the secondary coil, a steel wire may be magnetised by the Induction of these hustan. taneous secondary currents. If a Leyden jar be discharged through an insulatesd primary coil a secondary current will be in the other helix. Since then voltaic and frictional electricity may be made to produce magnetism, it was natural to suppose that magnetism could be made to produce electricity. We owe to Faraday the method of producing this result. An experiment will illustrate the conditions required to produce It. The curia of a copper helix are connected with a galvanometer by wires several feet in length in order that the instruusent may not be directly acted on by the magnet which is to be employed. Now if a permanent magnet be introduced into the axis of the hells, a current in the wire is Instantly produced, as marked by the deflexion of the galvanometer needle ; if the magnet be kept at rest with in the helix, the needle after a few oscillation, returns to sera; but the act of withdrawing the magnet is sufficient to deflect the galvanometer needle in the opposite direction and to the carne extent as before. the throatier) of the current depends on which pole of the magnet is introduced into the helix, and also upon whether the helix be left handed or right-handed. On placing a bar of soft iron iu the helix no current is produced; but if the opposite poles of two bar-magnets be brought In contact with the ends of the soft iron, a rumneutary cur rent Is produced.
The secondary currents thus obtained by magneticinduction have considerable intensity, end if when the current. is passing the circuit be broken a bright spark will be seen at the point of interruption. Ituhtnkorffs coil in An improved form of apparatus for exhihitiug these secondary currents. The primary or inner coil A A' Is a stouter and shorter wire than the secondary coil, D B ; this is a very long thin wire insulated by silk, each layer of coils being carefully insulated from the adjacent ones. In a ten-inch coil the primary wire is 132 feet long, and the secondary wire 26,246 feet long. A bundle of soft iron wire, n, is placed in the axis of the coils, while at + and—aro binding screws for connecting the primary coil with a voltaic battery.
The primary coil is broken at c anal d, d being a small armature of soft iron, faced below with platinum, the upper surface of c being ale o faced with platinum. When c and d are in contact the current cir culates through A A ; but in doing so the iron core m becomes magnetic, attracts d, the effect of which is to interrupt the current through A A, and the magnetism in me disappears ; whereupon the hammer d fella upon e, the current through A A is again made to flow, d is again attracted, the current is again interrupted, and in this way the voltaic battery serves as a means for making and breaking the con tact, and so rapid is the action that the hammer rises and falls several hundred times in a minute, and a powerful current is induced in the secondary coil B B by each of these momentary currents in A A, the effect of which is a continuous stream of sparks between the Insulated ends of the secondary wire e f, and shocks of the most painful and dangerous character are produced. The power of the instrument may be greatly increased by connecting the primary wire with an arrange ment called the condenser, consisting of oiled silk covered with tin-foil, folded between two other surfaces of silk and packed in a flat wooden case ; the two coatings are connected with binding screws attached to c and d in the primary current. The effect of this condenser is to increase the intensity of the secondary current, so that with a large coil and careful attention to the insulation of the conducting wires, powerful sparks ten or eleven inches in length have been obtained. By means of this coil, electricity of low tension may be made to equal in intensity that of an ordinary plate machine, while the quantity is greatly increased. If the secondary coil be allowed to discharge in an exit:mated receiver the phenonicuon of the auroral light may be obtained in a very beautiful manner, through an interval of several feet. By arranging the discharge in various ways, as explained by Mr. Garetiot (Phil. Trans., 1858, 1859) in Imig tubes partially exhausted or containing gases of different kinds, the luminous portion is traversed by a series of dark hands, which are rendered much more distinct by the presence of a small portion of phosphorus vapour. [ELECTRICAI. EGO.] The magnet has a powerful action on there stratified bands and luminous discharge& When the terminal plates of a voltaic battery are connected by means of a long wire coiled into a helix, a brilliant spark is produced on breaking contact, arising front a current passing through the wire in the same direction as that from the battery. The inductive action of the battery on the wire may be diverted by placing it second helix within the primary coil or exterior to it. By placing an iron core within the heliacal conducting wire the current becomes sufficiently intense on breaking contact to give a powerful shock, although the battery be of very small pewee. Professor Henry has shown (' Philosophical Maga zine,' 1840) that a succession of induced currents may be formed by the action of coils upon each other. If, for example, the coil In con nection with the battery be in the form of a flat spiral, and we call this A, And two other flat coils running into each other, namely, D and c, be arranged 60 that /1 shall rest on A and o on the table, there will be a momentary current in n and c every time the connection of the coil A with the battery le broken. If two other coils n and z, be arranged so that n shall rest on o and r. on the table, the indliced current in o will produce a current of the third order in n r.. If a flat coil r be placed over E with RS ends united by a small helix a, a current of the fourth order will be obtained. In this arrruigemeut the secondary current n o will be direct ; the current of the third order n is inverse ; the current of the fourth order r direct. The coils must, be carefully insulated, and with care currents even up to the seventh order may be obtained, the currents being alternately direct and invents. Similar currents are generated when ever the printery circuit is completed, but in such mac the direction of the current is reversed. These induced currents give shocks, magnetise steel, and effect chemical decompositions.