THE LODESTONE 105 



force is so feeble that the chain of filings breaks. " The adherent tufts of iron-filings are apparently not only subject 

 to the influence of gravity, but are themselves the seat of some special kind of influence. Between the separate 

 particles some modifjdng cause is evidently at work ; they possess a certain rigidity. If we try to separate them 

 from the lodestone they become drawn out into chains, the filings adhering one to another in succession : the 

 magnetic influence is taken up by the chains of particles, and transmitted from one to another." In fact each 

 particle of iron becomes a separate magnet. 



The power exerted by the lodestone differs from that exerted by other bodies. If the finger or other substance 

 be presented to the fihngs, some may adhere, but they do so in quite a different way, and in a smaller degree. If 

 the lodestone be dipped in sand, or in fihngs of copper or brass, there is no special action of the lodestone in 

 these cases, but only that form of cohesion which exists between all bodies in contact. It is not to be inferred 

 from the last experiment that sand, copper, and brass cannot be brought under the magnetic influence : only this, 

 that they are feebly magnetic when compared with the iron-fiUngs, which are strongly magnetic, and are conse- 

 quently the most convenient for illustration and the construction of magnetic diagrams and pictures. 



Faraday pointed out that all bodies (even gases) are magnetic, and he divided them into dia-magnetic and para- 

 magnetic, according as they arranged themselves across the poles or parallel with the poles of a horse-shoe magnet. 



The lodestone or natural magnet can convey its properties to other substances. Thus, if a piece of steel, say 

 a sewing or knitting needle, or the blade of a knife, be stroked in a given direction and for a certain time by a 

 magnet, the needle and the knife become magnetised. The magnetic properties of the lodestone are conveyed to 

 the needle and knife, and they become artificial magnets. Similarly, in the case of frictional electricity, if a stick 

 of seaUng-wax or a piece of amber be vigorously rubbed with a piece of silk, the seahng-wax and amber attract 

 fight substances, such as hairs, feathers, and cork, to them. They acquire properties not previously possessed by 

 them. It is thus possible to produce artificial magnets. The most common forms of artificial magnets are those 

 known as bar-magnets and horse-shoe magnets : the former consisting of a straight bar of steel with a north pole 

 at one end or extremity, and a south pole at the other end or extremity ; the latter consisting of a bar of steel 

 bent like a horse-shoe with its poles approximated. The horse-shoe magnet is the more powerful. In both forms 

 of magnet the fines of force pass from north to south pole and consequently the north pole attracts the south pole 

 and vice versd. To the bar and horse-shoe magnets, the important electro-magnet is to be added. 



By means of iron-filings the influence exerted by the different parts of a magnet and the lines of force generated 

 in each particular locaUty can be traced. 



Magnetic and electric currents are produced in various other ways — by the action of acids on different metals 

 united by a wire, by the appfication of heat and cold to different metals joined at two points, by friction, by induction. 



Magnetism, electricity, heat, and fight are now regarded as forms of motion, and are closely aUied to each other. 

 They are all dependent for their manifestation on matter in a highly minute state of division ; the particles and 

 forces inhering in them acting and reacting on each other in rapid and constant succession. ^ 



In estimating the fines of force it is of primary importance to eliminate, as far as possible, the effect of gravity 

 in the particles, and this is most readily done by scattering the iron-fifings over a sheet of white paper placed on a 

 horizontal support in the region of magnetic influence. The filings are best distributed from a sieve held above 

 the paper, as this ensures a greater or less degree of uniformity. When the magnet is placed on the paper with 

 the iron-fifings, and the paper gently tapped, the fifings arrange themselves in beautiful curved lines known as 

 Faraday's lities of force. 



The pictxires produced by the action of magnets on iron-filings had been observed prior to Faraday's time, but 

 he was the first to determine their true nature and value. 



These pictures supply, as it were, a chart of the fines of force generated by the magnet in the first instance, 

 and by the particles of iron in the second instance. 



Very satisfactory pictures of iron-filings can be obtained by employing ferrum fulveratum or ferrum redactum 

 shaken from a smaU Unen bag on a horizontal sheet of smooth white cartridge paper. When the lodestone is appfied 

 and the picture completed, the iron particles indicating the fines of force can be fixed by spraying the paper with 

 a thin solution of white sheUac varnish. The picture so produced and fixed can be photographed and preserved for 

 future study and reference. 



1 " When a Leyden jar is discharged the knobs of the jar become alternately positive and negative. The medium around the jar is therefore 

 polarised alternately in opposite directions. This polarisation starts from the knob and spreads through space, at each pomt of which there are 

 to-and-fro motions, and waves of opposite polarisations are sent through the medium, carrying the energy which had been stored up m the Leyden 

 jar. There is a periodic or to-and-fro movement in the ether, and if we could make a Leyden jar of molecular dimensions, charge it, and discharge 

 it, we could produce a periodic movement in the ether which is analogous to that which occurs in the propagation of light. Maxwell's electro- 

 magnetic theory of light supposes that the periodic motions which constitute light are of the same nature as those which arise when the positive 

 and negative conditions of the ether are rapidly alternated in the case of the discharge of a Leyden jar. Light, heat, and electricity are therefore 

 manifestations of electro-magnetic waves which come to us from the sun." ( " What is Electricity ? " By John Trowbridge, Rumford Professor, 

 Harvard University. International Science Series, 1897, pp. 265, 266.) 



VOL. I. ° 



