MAGNETISM. 



619 



By the dispersion of the fluid equally through its 

 surface, it attracted and repelled in the same manner, 

 as if interrupted by a sheet of paper. Nickel, as 

 well as iron, is influenced by the magnet ; but it loses 

 its power of being- attracted or repelled at a much 

 lower temperature ; and in boiling, all its powers 

 cease. Soft iron becomes a powerful magnet, 

 under the influence of voltaic electricity; but re- 

 tains none of the magnetic power, when the cur- 

 rent ceases. Hardened steel acquires less power 

 under the same treatment ; but becomes a permanent 

 magnet, when the connexion is broken. From 

 numerous experiments, he inferred that all the metals 

 have certain properties in common, and magnetism 

 among the rest, which require different circumstances 

 to develope. He infers that all the forty-two metals 

 are susceptible of magnetism, under the influence of 

 extreme cold : the temperature being not less than 

 40 below zero, Fahrenheit. Mr Faraday is still 

 prosecuting this line of inquiry, and daily bringing 

 forth new and interesting facts, a detail of which 

 will be found under Thermo- Electricity, in this 

 work. 



Principles. The term natural magnet, is chiefly 

 applicable to the amorphous granular varieties of 

 iron ore. The natural magnet is of a grey colour, 

 dull metallic lustre, becoming black when pul- 

 verized ; is not malleable. Some varieties have the 

 property of attracting iron, and others of being 

 attracted by the magnet. The specific gravity 

 varies from 4-24 to 4-93. Artificial magnets are 

 commonly bars of tempered steel, to which the mag- 

 netic property has been communicated. When a 

 piece of natural magnet is surrounded with iron 

 filings, they will be attracted to its surface ; but 

 there will be two points of the magnet to which the 

 filings will more particularly adhere, than to any other 

 part. These points of greatest attraction are called 

 the poles of the magnet. 



To form an artificial magnet take a bar of tempered 

 steel, and bring one end of it into contact with one 

 of the poles of the natural magnet, and afterwards 

 bring the other end of the bar into contact with the 

 other pole ; it will be found that the steel bar has 

 acquired the same property of attracting iron, as 

 the natural magnet has. The extremities of the 

 steel magnet are its poles. Form another magnet, 

 in the same way, and suspend both by silk threads 

 from the centre, so that they shall be balanced ; it 

 will be found that they will both arrange themselves, 

 after oscillating a little, in a direction which is nearly 

 north and south. Mark N on the pole of one mag- 

 net which points to the north, and S on the pole 

 which points to the south. Mark, in like manner, 

 n on the north pole of the other magnet, and s on 

 its south pole. It will be found that both magnets 

 incline a little from the horizontal position, the north 

 pole being inclined downwards. This is called the 

 dip of the needle. By comparing the position of the 

 magnet with the true meridian of the place, it will 

 be found that the north pole has either an easterly 

 or westerly direction. This is called the variation 

 of the needle. Both of these last will be more fully 

 discussed hereafter. We shall, in the mean time, 

 draw the attention of the reader to a few experi- 

 ments with the two magnetic bars we have before 

 spoken of. 



Let that magnet marked N S be kept suspended 

 by the silk thread, and bring the pole n of the 

 magnet marked n s near to the N pole of the sus- 

 pended magnet; it will be found that the N pole 

 will move away from, or, in other words, be repelled 

 by the magnet n s. Present the pole n to the pole 

 S, and the suspended magnet will be attracted by 

 the magnet n s. In like manner, present s to S,and 



repulsion will take place ; then * to N, and attrac- 

 tion will ensue : so that it is a general law, that poles 

 having a like direction, repel each other ; and poles 

 having a contrary direction, attract each other. It 

 is in magnetism then, as in electricity, poles simi- 

 larly excited, will repel each other ; and those op- 

 positely excited, will attract ; and, therefore, what- 

 ever it may be at or near the pole of the earth which 

 attracts the north pole of the magnet, it must be in an 

 opposite state of magnetism ; and the same with 

 regard to the south pole. This has led some to pro- 

 pose that they should call the north pole of the 

 magnet, the south pole ; and the south pole, the 

 north. This language would tend sometimes to 

 ambiguity, and therefore we will continue in this 

 article to call that pole which points to the north, 

 the north pole, and that which points to the south, 

 the south pole. 



There being two distinct kinds of action in mag- 

 netical bodies, scientific men have considered that 

 there are two distinct species of magnetic fluid, 

 the particles of the one fluid having the property of 

 attracting the particles of the other ; but when the 

 particles are separate, they repel ; each repels the 

 particles of its own kind, &c. It is supposed, how- 

 ever, that when the particles of the same kind are 

 combined, the action is neutralized, as is the case in 

 simple iron and soft steel bars, which are therefore 

 said to be passively magnetized. 



Soft iron or soft steel cannot be rendered magne- 

 tic for a length of time. Hard steel can be rendered 

 magnetic for a long time ; and if sufficiently hard, 

 the magnetic power will become permanent. The 

 magnetic fluids do not seem to be separated in the 

 middle of the magnetic bar, but both to exist in 

 every particle of the bar, from one end to the other ; 

 a fact proved by the circumstance, that if you cut a 

 bar through the middle, each piece will have its two 

 poles, one pole at each end. From this fact it has 

 been inferred, that in all bodies capable of being- 

 magnetized, both fluids exist, combined in each 

 particle ; but, when by any means they become 

 separated, the body becomes actively magnetic. 

 The cohesion of soft iron opposes little resistance to 

 the separation of the two fluids; and, again, when 

 the separating force is withdrawn, the tendency of 

 the fluids to unite, receives little obstruction from 

 the cohesion of the iron. On the other hand, the 

 cohesion of hardened steel, opposes great resistance 

 to the separation of the two fluids, and also great 

 resistance to their reunion. This lays the foundation 

 of the ordinary methods that have been devised for 

 communicating magnetism. 



When a bar of steel is chosen to be magnetized, 

 the dimensions that ought to be preferred would 

 seem to be, thickness 1, breadth 3, and length 30; 

 the steel being polished, and brought to as hard a 

 temper as possible. 



Different methods have been proposed and prac- 

 tised for magnetizing; but we will confine our 

 selves to the two that have been regarded as the 

 best. The method of Du Hamel consists in placing 

 two steel bars parallel to each other, but an inch or 

 inch and half asunder, being connected at both ends 

 by two cross pieces of soft iron. Let there now be 

 taken two bundles of previously magnetized bars 

 Each bundle must have all its bars, with their like 

 poles, in one direction. Hold now one bundle with 

 the north pole touching the middle of one of the steel 

 bars, and the other bundle beside it, with its south 

 pole touching the bar ; and draw the two bundles 

 along, one to one end of the bar, and the other to 

 the other end, repeating this process until both steel 

 bars are completely magnetized. The advantage of 

 employing the cross pieces of iron consists in this, that 



