98 



THE POPULAR EDUCATOR. 



iron (armatures), moves in front of a fixed electro-magnet. The 

 current supplied to this magnet is cut off just before each 

 armature approaches the poles, so that the attractive force 

 of the magnet causes each armature in turn to approach it, 

 and pass it by. Were the current to remain unbroken, of 

 course the nearest armature would take up a position close to 

 the magnet, and would rpmain there. Another means of obtain- 

 ing rotary motion from a magnet is taken advantage of in the 

 machine constructed by M. Bourbouze, which, it will be seen 

 from Fig. 78, has much the appearance of an ordinary beam- 

 engine. But the cylinders are represented by hollow coils of 

 wire, which exert an attractive force upon plungers loosely 

 fitting within them, and a repellent force when the current flow- 

 ing through the coils is reversed. It is quite within the bounds 

 of possibility that these machines might have been brought to 

 great perfection, but it very quickly became evident that they 

 were far more expensive to work than even a badly constructed 

 steam motor. No cheaper means of obtaining an electric current 

 was then available than the consumption of zinc in a battery ; 

 and as the energy evolved only amounted to about one-tenth of 

 that obtainable from the same weight of coal, coal at the same 

 time being a much cheaper material, it was evident that the 

 cost of maintenance must be quite out of proportion to the work 

 accomplished. Setting these considerations aside, it is evident 

 that it is much easier to burn coal in a furnace, and to maintain 

 its efficiency, than it is to consume zinc in a battery, with all its 

 attendant troubles and difficulties, which are by no means few. 

 The idea of superseding steam by electricity has once more 

 come to the front, but the question now stands upon quite 

 another footing. The electric battery for such purposes is cast 

 aside (we leave out of consideration for the present the modern 

 accumulator, or secondary battery), and the electricity is ob- 

 tained from quite another source. To understand the significance 

 of this change in the aspects of the matter, we must devote 

 some little attention to the labours of that brilliant philosopher, 

 Michael Faraday. 



The marvellous power exerted by the magnet naturally took 

 a hold of the great mind of Faraday, and he is reported to have 

 expressed the opinion that the more he pondered over it, the 

 more mysterious it seemed to him to be. Notwithstanding this 

 admission, he, of all men in the world, knew most about that 

 mysterious power. That an electric current could invoke mag- 

 netism in a piece of iron was known before his day. It was 

 reserved to him to point out that the converse of this is true, 

 and that a magnet can arouse a current in a wire placed near to 

 it. This is one of the greatest achievements of Faraday, and 

 we shall presently see what an important bearing it has had 

 upon the advancement of electrical science. In Fig. 79 we 

 have an illustration of the famous experiment by which this 

 discovery was demonstrated. A permanent magnet, by which is 

 meant an ordinary steel magnet, either of the bar or horse-shoe 

 shape, is plunged into a coil of wire. The two ends of this coil, 

 seen on the right hand side of the figure, are supposed to be in 

 connection with a delicate galvanometer. At the moment when 

 the magnet is thrust towards the coil, the galvanometer needle 

 is deflected, showing in the most conclusive way that a current 

 of electricity has traversed the wire. The needle immediately 

 returns to its normal position, thus showing that the current is 

 but transient. But upon withdrawing the magnet from the 

 coil, the needle once more moves, but this timo in the opposite 

 direction. Another transient current has been induced in the 

 wire by the magnet, but in the reverse direction to the first 

 one. So we see that by the simple approach to or recession 

 from a coil by a magnet, currents can be induced in that coil, 

 but in opposite directions. Such is the nature of that grand 

 discovery known as magnetic induction. 



We may be quite sure that as soon as it was generally made 

 known that Faraday had indicated a method of invoking a cur- 

 rent of electricity by such apparently simple means, there were 

 plenty of inventors ready to turn it to some practical account. 

 The first idea which was broached was the natural one of causing 

 the magnet to move towards and from coils of wire by means of 

 mechanism. So that we find the pioneer machine to be simply 

 a couple of coils supported on a frame, with a permanent horse- 

 shoe magnet held poles upwards, so that they all but touch the 

 coils above them. This magnet was made to turn rapidly by 

 cog-wheel attachments- and a handle, and the alternating cur- 

 rents so induced in the coils followed one another so rapidly, 



that a comparatively large amount of electricity was poured 

 forth. This machine was due to Pixii. 



In Clarke's machine (Fig. 80), which followed it, we have a 

 similar arrangement, but in a far more compact form. Here the 

 heavy magnet A is wisely a fixture, and the comparatively light 

 coils of wire, B B, are made to revolve close to its poles. By 

 means of a belt across the fly-wheel, R, the motion, too, is much 

 accelerated, and the efficiency of all these machines depends in 

 a remarkable manner upon the speed at which they are driven. 

 Another improvement exhibited by Clarke's machine is in the 

 attachment of a device called a commutator, by which the alter- 

 nating currents are turned into one direction, so as to resemble 

 the current from a battery. This commutator consists of a 

 block, m, from which project three springs, a, b, c, which rub 

 against a little shaft which turns with the coils. The shaft is 

 made of some non-conducting material, such as ivory, but has 

 fixed upon it some pieces of metal which cause currents of one 

 direction only to be gathered up by the springs a and c, whilst 

 the spring 6 will only collect those of the reverse direction. 

 These currents are carried to the handles pp. Exactly the 

 same arrangement as this, except that the magnet lies on its 

 side, is exhibited by those little electric machines sold for medi- 

 cal purposes in the present day. 



After the production of this machine by Clarke, others rapidly 

 followed, some being of vast size, and containing an enormous 

 number of bobbins of wire and stationary magnets. A large 

 one was constructed by M. J. Nollet, and has since become well 

 known as the " Alliance machine." It was used in some of the 

 French lighthouses to produce an electric light in place of the 

 oil lamps formerly employed ; and later on, for the same pur- 

 pose, at our South Foreland lighthouse. Previous to this time 

 the electric light had been attempted merely for special uses, 

 and was scarcely ever seen except on a small scale in the 

 lecture theatre ; but the rapid advance in these magneto-electric 

 machines gave the hope that the light might be brought into 

 more extended use. 



In 1854 Siemens introduced an improvement in magneto- 

 electric machines, which marks a point of distinct advance. 

 Hitherto, as we have seen, the wires were wound in the form of 

 bobbins, very much as reels of cotton are wound. Siemens 

 made the important modification known as Siemens' armature, 

 in which the wire is wound lengthwise, like a weaver's shuttle. 

 By this alteration he was able to cause the shuttle-like coil to 

 be rotated close to, and between, the poles of the magnet, where 

 the force is greatest, and by its adoption he secured much more 

 powerful effects. 



The next notable advance was made by Wilde, of Manchester, 

 who, for the first time in the history of these machines, em- 

 ployed an electro-magnet as well as a battery of permanent 

 magnets. In the jaws of the latter he caused a Siemens' arma- 

 ture to be rotated by a belt from a steam engine, but the current 

 so obtained was not immediately utilised, but was carried to the 

 coils of a large electro-magnet, between the poles of which 

 another Siemens' armature revolved. It was the greatly aug- 

 mented current from this second armature which was carried off 

 for the production of light, or any other purpose required. 



The term " permanent," which, as we have seen, is applied to 

 all ordinary steel magnets, of which the horse-shoe of the toy shops 

 may be taken as the type, is rather misleading ; for such magnets, 

 as a matter of common experience, are not permanent. They 

 gradually lose a certain proportion of their original power. Thus, 

 at some of the lighthouses where machines like the " Alliance " 

 are still in use, the light given is found to be very much short 

 of what it used to be, and this loss of light agrees very nearly 

 with the loss of power experienced by the magnets, amounting, 

 in some cases, to 20 per cent. Still the word permanent is of use 

 as distinguishing that form of magnet from the electro-magnet. 



Wilde's machine, which presented such a notable improve- 

 ment upon those which had before been made, had scarcely been 

 given to the world when another important link in the history 

 of these machines was brought forward simultaneously by two 

 indefatigable workers, Wheatstone and Siemens. They pointed 

 out that the permanent magnets used in Wilde's machine were 

 not really required, because iron always has some residual 

 magnetism in it, which can, by proper precautions, be raised 

 to any amount of intensity. The core of an electro-magnet 

 which has once been magnetised is especially rich in this re- 

 sidual magnetism, and sufficient exists to induce a current in a 



