UNDULATORY FORCES. ELECTRO-MAGNETISM. [MOTION or WUIM, we. 



of a right angle to tlio wins. With a powerful battery 

 the right angle is nearly completed.* 



Whenever a wire conduct* a voltaic current, it mani- 

 fest* magnetic tendencies in a direction at right angles 

 to that of the current : in other words, supposing that 

 a current of electricity be sent through a copper wire in 

 a direction from north to south, or nee vend, the mag- 

 netic effect will bo observed on its east and west sides, 

 and, in fact, all round the wire in any position at right 

 angles to the course of the electric current. By ex- 

 tending this principle practically, we may make a voltaic 

 conducting wire, although of copper, to present all the 

 phenomena afforded by an ordinary piece of magnetised 

 stoel ; that is, it will bo subject to tlio laws of attraction, 

 repulsion, and polarity,t gust as if it were an ordinary 

 magnet. The following experiments will illustrate the 

 fact. Wo shall chooso two simple pieces of apparatus, 

 which may readily be constructed by the reader, and for 

 which wo shall give full directions. 



Experiment 3. Solder to a piece of covered copper 

 wire, of about eighteen inches in length, a narrow strip 

 of zinc and one of copper one at each end and then 

 twist the wire into a spiral form, so as to leave the 

 strips of inetal hanging beneath it. Lot these dip into 

 some sulphuric acid and water, and suspend the spiral 

 by means of a piece of thread, so that tho whole ar- 

 rangement may freely move in any direction. Its entire 

 appearance is represented in tho following engraving. 

 Fig. 5. 



It will bo found that the spiral wire will have become 

 powerfully magnetic. It will assume a direction of 

 nearly north and south, just as a magnetic needle 

 wouid do ; and if a horse-shoo magnet be presented 

 to it, the poles of the spiral and the magnet will either 

 repel or attract each other, dependent on tho poles 

 which are experimented on, and according to the laws 

 which have been previously explained when treating on 

 magnetism. J 



It is thus evident that a most intimate connection 

 exists between magnetic force and a current of electri- 

 city ; mid the next experiment will still more familiarly 

 prove tlio fact. 



Experiment 4. Immerse a wire convoying tho vol- 

 taic current in some irun tiling*. It will bo found that 

 so long as electricity passes, some of the filings will 

 adhere to the wire indicating the existence of magnetic 

 attraction on its surface. 



A great variety of apparatus has been invented for 

 the purpose of illustrating this mutual action of electric 

 currents and magnetised bodies, by means of which 

 motion may be readily produced by their opposition or 

 attraction of each other. We may select two of those 

 as still further illustrative of the laws we have been 

 speaking of ; and we have chosen such as may bo readily 

 constructed by our readers. 



Experiment 6. Fix in a wooden foot, which may be 

 six inches long and throe broad (a Fig. C), an upright 

 brass or copper wire, c, which must be bent round 



Be* ante, p. 193. + Ante, p. 144. t Antr, p. 244. 



at tho top, so as to hang over a hollow trough cut out 

 of tho foot, as seen at 6. From the wire c suspend 

 it 



rig. c. 



\ 



another, so that 



can move freely in 



all directions, and 



fill the trough 6 



with mercury, so 



that it may touch 



the extremity of the 



wire . suspended 



from d. Now, of 



course, as such has 



no force acting on 



it, it will remain 



perpendicular. At- 



tach one of the wires 



of a coll of a voltaic 



battery to c, and dip 



tlio other wire into tlio cistern of mercury b. A current 



of electricity will now pass through tho wires say from 



p to at, thence by e to 6, and so back to the battery. 1 f 



a horse-shoe magnet bo now placed on the wooden foot, 



so that one of its poles shall be on each side of the 



suspended wire e, that will be instantly put into motion, 



and will be rapidly jerked out of tho mercury. By 



this, contact with tho battery will bo broken; and as 



all effects are thus stopped, the wire will fall bock into 



the mercury. Contact and a complete current will 



be again established; and the wire will be again 



jerked from the cistern. Tho direction of this motion, 



as indicated by the dotted lines ; will depend on that ( 



tho current and on the position of the poles of tlio 



magnet, and it may bo continued so long as the battery 



power is sufficiently maintained. 



Wo may just observe, that for the success of all elec- 

 tro-magnetic experiments, it is highly necessary that the 

 ends, <fco., of the wires bo kept perfectly clean. This is 

 best effected by dipping them into a little nitric arid, 

 and then into mercury. By this they will bo slightly 

 amalgamated, and much disappointment will bo pre- 

 vented, which, at all times, arises from carelessness as 

 to this particular. 



Experiment C. The arrangement we ore about to de- 

 scribe, actsm precisely the same principles as the last one ; 

 but instead of a jerking motion, a circular one is ob- 

 tained. In fact, we may regard tho wheel wo shall 

 mention, as made up of an infinite number of wires, or 

 radii, proceeding from a common centre, instead of 

 being suspended from a hook, as shown in our last 

 engraving. To construct this arrangement, cut a circu- 

 lar wheel out of thin sheet copper, and through its 

 centre solder an axle of copper wire, as at a, Fig. 7, 

 so that it may freely turn thereon ; and supported by a 

 brass arm, 6, which is to be fixed to an upright, also of 

 metal, c. This may stand on a wooden foot, hollowed 

 out at c, as in our last arrangement ; and tho rim of tho 

 Rf. 7. 



copper wheel should just touch some mercury contained 

 in tho trough e. One wire of a battery is to bo attached 

 to tho upright c, and tho other is to be immersed in tin- 

 mercury in tho cistern. On placing a horse-shoe magnet, 

 with its poles resting on the foot, on each side of tho 

 wheel, the latter will begin to rotate, and will maintain 

 its motion so long as the current of electricity passos. 

 This arrangement may bo modified by uxing a wheel 



