SECTION IV. 



MAGNETISM, AND ITS APPLICATIONS. 



CHAPTER I. 



TUB subjects on which we have already treated, will 

 liiivu prepared the minds of our readers for the study of 

 a very interesting class of phenomena, which, although 

 of a restricted cliaracter, have yet the most im- 

 portant relations, both in a philosophical and social 

 point of view. 



There are few persons who have watched the oscilla- 

 < of the mariner's compass, but who must have 

 ted that some unseen agent is incessantly at work 

 maintaining the needle true in its polarity. Amongst 

 all the curious facts which science or daily experience 

 presents to our notice, none seem more extraordinary 

 than that a small piece of metal should constantly point 

 in one direction, if it have been previously endued with 

 the magnetic f orce. Day and night it ceaselessly obeys 

 some unperceived power : if undisturbed, it truly guides 

 its possessor through the trackless ocean ; and in it he 

 puts an implicit faith, which can only be justified by 

 the fact that Nature is never at fault. 



It may not perhaps be too great an exaggeration if we 

 remark, that many of the political, commercial, and 

 social circumstances of the present age are due, to a 

 large extent, to this application of magnetism. Without 

 it our ships would be compelled to confine their voyages 

 to the coast-line ; our colonies in Australia, New 

 Zealand, etc., would be inaccessible ; the construction of 

 nil roads and the progress of mines, <kc. , would be most 

 difficult ; the intercourse of nations, separated by the 

 ocean, would bo impossible; and commerce itself, with 

 our manufactures, would be confined, for want of raw 

 material, to the narrowest limits. 



Another application of the magnetic needle, to which 

 we may here refer, has become of the most extreme im- 

 portance in every respect. Thirty years ago, the earliest 

 intelligence which could be obtained between our manu- 

 facturing districts and the metropolis, required at least 

 twelve to eighteen hours for its transmission. At the 

 present time, it is possible to receive intelligence of any 

 event which has taken place in any capital of Europe, 

 within a few minutes of its occurrence; and within the 

 space of two or tliroe years, there seems every probability 

 th.it the whole of our Indian possessions will bo, in 

 respect to the power of the electric telegraph, within 

 an hour's time of communication with London, or any 

 city in Great Britain. Wo may also remark on the ex- 

 treme importance which exists in those discoveries of sci- 

 ence that have often been made without any apparent or 

 immediate practical result. Scarcely forty years have 

 elapsed since it was first noticed, that if a current of 

 voltaic electricity were passed by a wire placed over and 

 parallel to a magnetised needle, the latter would be 

 diverged from its usual position, and, according to 

 the direction of the current, the needle deflected to 

 the right or left hand. But we are anticipating the 

 subject on which we shall have to dilate more fully; 

 and, without further preface, we shall proceed to 

 investigate the laws of that force called Magnetism, 

 which we shall subsequently find to bo analogous to the 

 other undulatory forces. 



As a matter of convenience, we shall adopt the follow- 

 ing plan in treating on the subject ; and shall describe 



1. Natural Magnets. 



2. Artificial Magnets. 



3. Magnetic Attraction, Repulsion, and Polarity. 

 After which we shall enter into a variety of phenomena 



which are presented by terrestrial magnetism ; and other 

 phases of the force. 



1. NATURAL MAGNETS. The ancients were well ac- 

 quainted with the fact, that a stone found in Magnesia 

 had the power of attracting metallic iron ; and from this 

 substance, which has since been callod the loadstone, 

 the term ' ' Magnetism" has arisen. It may readily be pro- 

 cured from tho philosophical instrument-makers. It has 

 a black colour, and a close texture ; and if placed 

 amongst iron filings, it immediately attracts them. If 

 a piece of this natural magnet, which is an oxide of 

 iron, be rubbed on a rod of steel, the latter immediately 

 acquires the properties of the loadstone, and becomes, 

 a* it is termed, magnetic. There is a singular peculiarity 

 in reference to the permanence of this force, when it is 

 communicated to ditfcrent kinds of iron. Soft iron is 

 rendered magnetic only so long as it is in communi- 

 cation with a body permanently magnetic. On the re- 

 moval of such influence, the magnetism Immediately 

 ceases. Steel, which is a compound of iron, carbon, and 

 possibly of nitrogen also, has the power of retaining tho 

 magnetic influence, and thus of becoming a permanent 

 magnet. Its power of retaining magnetism, depends, 

 however, on its quality. If the steel bo badly tempered, 

 or of an inferior quality that is, approaching the cha- 

 racter of soft iron its retentive power is greatly dimin- 

 ished. In fact, this power of retaining the magnetic 

 force may, to some extent, be employed as a test of 

 tho quality of steel ; it being borne in mind, that the 

 degree of hardness of the metal also affects tho result. 



Cast-iron which is what we may term an analogue of 

 steel may be often rendered permanently magnetic. 

 Its composition i.s, however, so varied as to leave us in 

 constant doubt as to its character. Indeed, some speci- 

 mens of cast-iron far exceed in hardness those of steel. 

 This is owing to a process of cementation, or partial 

 conversion into steel, which the external surfacn under- 

 goes when in contact with the coal and coke used as 

 moulds in casting the metal. Wo have seen specimens 

 of this nature which were hard enough to cut glass. An 

 artificial loadstone may be prepared by making a paste 

 of oxide ot iron : this, however, deserves notieo simply 

 as a philosophical curiosity. We shall now proceed to 

 the second and more practical division of our subject. 



2. ARTIFICIAL MAGNETS. The most simple manner by 

 which an artificial magnet can be produced, is that of 

 nibbing a piece of the loadstone on a common sewing- 

 needle. It will thus acquire two properties : first, that 

 of attracting any piece of iron ; and, secondly, of pos- 

 sessing polarity, or a tendency to point in the direction 

 nearly of the polo star, in the constellation of Ursa 

 Major. It hence appears that magnetism can be com- 

 municated to any extent ; and not only from a piece of 



