834 



ELECTRO-MAGNETISM. 



effects that accompany its action ; the heat excite* 

 not diminishing or interfering with the mnguelism 

 but apparently increasing it ; for n fine platina wire 

 so intensely ignited as to be near the point of 1'nsion 

 is observed to attract larger quantities of iron filings 

 than when at a lower temperature. To coimmmi 

 cate magnetic properties to steel needles, which be- 

 fore did not exhibit them, it is necessary merely to 

 place them in contact with, or near to the conjunc- 

 tive wire. The position in which they are to be 

 placed, with regard to the wire, is important, as the 

 permanence of i heir magnetic quality depends upon 

 it. If they are placed parallel with it, they lose 

 their magnetism when the connexion with the bat- 

 tery is broken, which shows that their magnetism 

 arose only from their forming part of the electric 

 circuit, like the connecting wire itself. But if they 

 are placet! across the wire, they become permanently 

 monetized, and retain their power equally with 

 needles prepared in the ordinary way. The polarity 

 is different, however, according as the needle is 

 placed above or below the wire. When a needle is 

 placed under the uniting wire, the positive end of 

 the battery being on the right hand of the operator, 

 the end of the needle next to him becomes the north 

 pole, and the other end the south pole. On the 

 contrary, when a needle is held above the wire, the 

 reverse of this takes place ; the end next to the ob- 

 server becomes the south,and the other the north pole. 

 Even the same opposition is observed when needles 

 are placed in a perpendicular position, on different 

 sides of the wire : in those on one side, all the lower 

 ends are found to be north poles, while, in those 

 on the opposite side of the wire, the upper ends 

 are all north poles, and the lower extremities all 

 south poles. Direct contact of the steel needles 

 with the conjunctive wire is not necessary, for they 

 become instantly magnetic when brought near it, 

 even though thick plates of glass are interposed. As 

 was remarked with regard to the connecting wire, 

 galvanic batteries, consisting of large plates, are 

 most powerful in communicating the magnetic 

 influence. When the conjunctive wires of two dis- 

 tinct galvanic arrangements are made to approach 

 each other, we observe magnetic attractions and 

 repulsions. Two wires of copper, silver, or any other 

 metal, connecting the extremities of two galvanic 

 troughs, being placed parallel to each other, and 

 suspended so as to move freely, immediately attract 

 and repel each other, according as the directions of 

 the currents of electricity flowing through them, are 

 the same or different. When both the negative or 

 both the positive extremities of the troughs are turn- 

 ed to the same quarter, so that the electric current 

 passes along each wire in the same direction, the two 

 wires attract each other ; but when the position of 

 one of the troughs is reversed, so that the electric 

 currents in the two wires flow in opposite directions, 

 tlie wires repel each other. Upon this experiment is 

 founded the most plausible theory of magnetism, viz., 

 that it arises from the attractions and repulsions of 

 currents of electricity, constantly circulating around 

 every magnet. This is conceived to explain the 

 reason why the magnetic needle places itself at right 

 angles to a wire conducting electricity, namely, that 

 the electric current passing along tlie wire may coin- 

 cide with that circulating round the magnet. The 

 magnetic effects produced by galvanic arrangements 

 are obtained also by electricity evolved from the 

 common machine, and still more from this power 

 concentrated in the Leyden jar ; the magnetism 

 communicated agreeing in every respect as to the 

 permanence of the polarity, the variations when the 

 needle is placed placed above or below the wire, &c., 

 with that produced by the voltaic pile. Magnetism 



is communicated to needles in a different manner 

 from that of placing them across the conjunctive 

 wire. The wire is funned into a hollow screw, or 

 helix, by rolling it round a solid rod, and tlie needle 

 to be magnetized, wrapped in a paper, or put into ;i 

 glass tube, is placed hi the centre of it, and the com- 

 munication with the galvanic battery est;il>li-hc,l. 

 This arrangement (according to the theory of M . 

 Ampere) conveys the electric current by the spiral 

 convolutions, round and round the needle, and com- 

 municates to it, or dev elopes in it, tlie electric circula- 

 tion constituting magnetism. By Uiis contriva ce, 

 it is found that a maximum effect is obtained in a 

 shorter time than by any other method. The position 

 of the north and south pole varies according as either 

 end of the helix is connected with tlie positive or the 

 negative pole, which shows that the electric current 

 flows along the uniting wire from the positive or zinc 

 extremity to the negative or copper end of the pile. 

 The electricity of a common machine produces the 

 same effect. 



Having alluded to the principal facts relating to 

 electro-magnetic phenomena, the ingenious theory of 

 M. Ampdre, by which they are explained more 

 extensively and with more precision than by any 

 other hitherto advanced, deserves to be stated. It 

 is the more deserving of attention, as having led its 

 author to the discovery of some of the most remarka- 

 ble facts detailed above ; and, if future researches 

 shall continue to increase its probability, it will no 

 doubt be regarded as one of the finest instances of 

 correct induction, supported by minute experiment, 

 wliich the history of any science can exhibit. The 

 first principle of tlu's theory lias been already stated ; 

 that two currents of electricity attract when they 

 move parallel to each other and in the same direc- 

 tion, and repel when they move parallel to each other 

 in contrary directions. This fact is directly the 

 reverse of the usually observed phenomena of electri- 

 city ; for it is well known that bodies in the same 

 state of electricity repel each other, and in opposite 

 states attract. Hence M. Ampere infers, that these 

 results are not produced by electricity in its known 

 and common state of tension, but are dependent on 

 properties belonging to electricity, previously unsus- 

 pected, and peculiar to it when in motion, or flowing 

 in currents. Electricity, when accumulated, has the 

 power of causing certain effects, particularly attrac- 

 ,ions and repulsions, which are familiar to us, and 

 are called electrical ; but when moving in currents, 

 t exerts new powers, and these constitute magnetism. 

 Reviewing the various experiments which have been 

 enumerated, we find, that tlie connecting wires of two 

 latteries attract and repel each other, according to 

 the directions of the electric currents flowing through 

 them ; that the magnetic needle is, exactly in the 

 same manner, attracted and repelled by a connecting 

 wire, according to the direction of the current of 

 electricity moving through the wire ; that the position 

 of the needle may be varied, in almost any degree, 

 jy clianging the position of the connecting wire ; 

 hat whenever the electric circuit is broken, this 

 influence on the needle ceases, and is renewed when- 

 ever the communication between the poles of the 

 >attery is restored ; that the connecting wire, of 

 whatever metal it may consist, becomes a perfect 

 magnet, as long as the current flows along it, so as 

 to attract iron filings and small steel needles, without 

 attracting copper filings, or any other metal but 

 ron ; that steel needles may be converted into per- 

 manent magnets, by simply placing them across the 

 connecting wire ; that tlie electric currents having 

 his magnetizing power are not, like accumulated 

 electricity, confined by glass, or other non-conductors, 

 but pass through all bodies with facility, as magnet 



