MAGNETISM. 



are capable of exhibiting magnetic phe- 

 nomena. Nickel, and also cobalt, have 

 occasionally been found obedient to the 

 action of the magnet ; and sometimes to 

 possess considerable degrees of polarity. 

 Brass, which is a compound of copper 

 and zinc, has likewise been observed to 

 be magnetic under certain circum- 

 stances, especially after it has been ham- 

 mered. Cavallo states* that, when 

 quite soft, brass has generally no per- 

 ceptible degree of magnetism ; and even 

 those pieces which have acquired this 

 property by hammering, again lose it by 

 annealing or softening in the fire. He 

 seems to have ascertained that the mag- 

 netism acquired in the former state, is 

 not owing to any particles of iron or 

 steel imparted to the brass by the tools 

 employed in the hammering; and that 

 those pieces of brass which have that 

 property retain it without any diminu- 

 tion after having been hardened and 

 softened several times in succession. If 

 one end only of a large piece of brass be 

 hammered, that end alone is rendered 

 magnetic. He found, however, that the 

 magnetic power which brass acquires by 

 hammering has a certain limit, beyond 

 which it cannot be increased by further 

 hammering ; and that this limit is dif- 

 ferent in pieces of brass of different 

 quality or thickness. 



(348.) Cavallo next examined various 

 pieces of copper by means of a delicately 

 suspended needle ; but never found them 

 magnetical, except occasionally in those 

 parts where a file had been applied, and 

 where, consequently, some particles of 

 steel, detached from the file, may have 

 adhered to the copper. On hammering 

 other pieces, both in the usual way, and 

 also between flints, he failed in obtain- 

 ing any decisive result. Zinc, whether 

 hammered or not, showed no sign of 

 magnetism whatever. Platina was found 

 to possess a degree of magnetic power 

 nearly equal to that of brass. 



(349.) The magnetic power of brass 

 is sometimes so considerable as to in- 

 terfere very sensibly with the movements 

 of the needle in compasses, in the con- 

 struction of which brass is employed. 

 A remarkable instance of this is given 

 by Mr. Barlow f. Seebeck has recom- 

 mended an alloy of two parts copper 

 with one of nickel, as admirably adapted 

 for the manufacture of compasses, from 



* Philosophical Transactions for 1786, p. 82; and 

 also in his Treatise on Magnetism. 



t Essay on Magnetic Attractions, second edition, 

 J?-17. 



its being 'entirely void 'of magnetism*. 

 We have seen, in the case of brass, that 

 two ingredients, which in themselves, 

 when separate, are devoid of magnetic 

 susceptibility, acquire that property by 

 combination. Mr. Hatchet ascertained 

 that a large proportion of either carbon, 

 sulphur, or phosphorus, combined with 

 iron, enables it fully to receive and to 

 retain the magnetic properties : but that 

 there is a limit beyond which an excess 

 of either of these substances renders the 

 compound totally insusceptible of mag- 

 netism t. On the other hand, instances 

 occur where the admixture of the mi- 

 nutest quantity of another body will 

 entirely destroy the magnetic power of 

 a metal possessing that power when in 

 a pure state. Mr. Chenevix found that 

 the addition of arsenic, in very small 

 proportion, deprived a mass of nickel, 

 which had previously manifested strong 

 magnetic power, of the whole of its mag- 

 netism $. Dr. Matthew Young states 

 that the smallest admixture of antimony 

 is sufficient to destroy the polarity of 

 iron . 



(350.) In the mineral kingdom a great 

 variety of substances, and even some of 

 the precious stones, as the emerald, the 

 ruby, and the garnet, exert a feeble yet 

 sensible attraction on the magnetic 

 needle; and sometimes even acquire a 

 slight degree of polarity ||. 



(351.) Later inquiries appear to have 

 established the fact that all bodies what- 

 soever are, in a greater or less degree, 

 susceptible of magnetism. We owe this 

 discovery to Coulomb, who exhibited his 

 experiments in proof of it at a sitting of 

 the French Institute, in 1802. The 

 bodies examined were cut into small 

 cylinders, or bars, about a third of an 

 inch in length, and about the thirtieth 

 of an inch in thickness : but those which 

 were metallic were formed into needles 

 of about the hundredth of an inch in 

 diameter. Each of these cylinders was 

 suspended by a thread of taw silk, which, 

 being exceedingly fine, could scarcely 

 support more than from 100 to 150 

 grains without breaking: on this ac- 

 count it was necessary to reduce the 

 needles to very small dimensions. They 

 were placed, when thus suspended, be- 

 tween the opposite poles of two steel 



* Annales de Physique, 1826. 



t Philosophical Transactions for 1804, p. 315. 



Nicholson's Journal, 8vo. vol. iii. p. 28?.' 

 Seebeck discovered that an alloy of one part 

 iron with four parts of antimony exercised no power 

 over the magnetic needle, even when in motion. 

 II Cavallo's Treatise on Magnetism, p. ?3. 



