MAGNETISM. 



15 



(the same author observes), such as 

 chisels, punches, and drills for metal, 

 acquires magnetism still more slowly 

 by induction, and receives less of it while 

 in contact with the magnet ; but it is 

 less disposed to lose it, and finally re- 

 tains a larger portion of what it had ac- 

 quired. Steel made as hard as possible 

 is still longer in acquiring all the mag- 

 netism which simple juxtaposition can 

 give to it. It acquires Jess than the 

 former ; but ultimately retains a much 

 greater proportion. The loadstone, or 

 native ore of iron, resembles very hard 

 steel in these respects ; that is, in the 

 time necessary for its greatest impreg- 

 nation, and in the dm ability of the ac- 

 quired magnetism. 



(60.) We have seen that iron, or any 

 of its compounds, when free from mag- 

 netism, is attracted by a magnet only in 

 consequence of the induction of mag- 

 netism upon it by the magnet which 

 attracts it. It follows, therefore, that 

 the degree of susceptibility to induc- 

 tion may be accurately measured by 

 the attraction which results from this 

 property. With this view Mr. Barlow 

 made a series of experiments to ascer- 

 tain the relative attraction which dif- 

 ferent species of iron and steel had for 

 the magnet ; and obtained the following 

 specific results, the relative magnetic 

 power of each substance being expressed 

 by numbers*. 



Malleable iron 100 



Soft cast steel 74 



Soft blistered steel . 67 



Soft shear steel 



Hard blistered steel. 



Soft shear steel .... 



Hard cast steel. . . . 



66 

 53 

 53 



49 

 Cast-iron.. 48 



$ 7- Fracture- 



(61.) We have hitherto been able to 

 trace a very close analogy between the 

 phenomena of magnetism and electri- 

 city, us far at least'as relates to the law 

 of action, and the influence of induc- 

 tion ; but in pursuing it beyond this point 

 it fails us entirely. Electricity, whether 

 positive or negative, is not only capable 

 of being excited by induction, but may 

 be actually transferred from one body 

 to another ; but the transference of the 

 magnetic polarities is a phenomenon 

 which was never, in a single instance, 

 known to take place. A body may, 



* Philosophical Transactions for 1822, p, 117. 



without difficulty, be rendered positively 

 or negatively electrified ; that is, it may 

 be charged with a redundance of one or 

 other of the two kinds of electricity ; and 

 the influence or agency, call it by what 

 name we please, that has been gained 

 by one body, is the same as that which 

 has been lost by the other. It is not so 

 with magnetism. There is never any 

 transfer of properties, but only the ex- 

 citation of those which were already in- 

 herent in the body operated upon. We 

 always find in the same magnet, that the 

 intensities of the two polarities, although 

 each may occupy different portions of 

 it, or be concentrated in some points, 

 and diffused over others, yet still on the 

 whole exactly compensate each other. 

 We never can obtain a portion of iron 

 or steel endowed wholly with either the 

 northern or the southern polarity. Each 

 appears to be strictly confined within the 

 boundary of the surface of the body 

 which contains it. 



(62.) When a conductor of electricity, 

 of an oblong shape, is placed near an 

 electrified body, but not sufficiently near 

 to receive any part of its electricity, it 

 becomes electric by induction, the two 

 ends of the body having opposite electri- 

 cities. If, under these circumstances, 

 the conductor be divided across the mid- 

 dle, and the two portions removed to a 

 distance from one another, we obtain the 

 two electricities separate; each por- 

 tion retaining the electricity that had 

 been induced upon it. The condition of 

 a magnet appears to be exactly analo- 

 gous to this in reference to the distribu- 

 tion of magnetic power; for the northern 

 polarity appears 'to be collected in one 

 half of its length, and the southern po- 

 larity in the other; and each of these 

 agencies seems, indeed, to be almost 

 entirely concentrated in the very extre- 

 mities of the bar. What, then, ought 

 to happen conformably with this analogy, 

 were we to break a magnet (A., fig. 25,) 



Fig. 25. 



across its middle ? Might we not expect 

 by this means to obtain the two polari- 

 ties separate, each still contained in the 

 same portions where they had before re- 

 sided ? 



(63.) The result of this experiment is 

 exceedingly curious, and what certainly 



