394 THE ADDRESSES, LECTURES, ETC., OF 



Royal Institution, it was a red-letter day in his existence, and he 

 even then thought that it would be a point of departure of some 

 importance, because he said on that occasion : "Although this spark 

 is very small, so that you can hardly perceive it, others will follow 

 who will make this power available for very important purposes." 

 Now that the light is lowered, I will draw your attention to the 

 point of the wire touching this little disk or pan, and you will 

 distinctly observe the spark when I break the connection. This 

 magnet is the very steel magnet which Faraday used, and at that 

 time it was quite a giant amongst magnets. 



Faraday next turned his attention to magneto-electricity, and 

 to what was called by him the magnetic field. I have here a 

 horse-shoe electro-magnet, with its two stems surrounded by coils 

 of wire. If a current is passed through the coils, these extensions 

 become magnetic poles, and if I lay a piece of cardboard upon 

 them, and spread over it some iron filings, you will observe that, 

 under the influence of the electric current, they distribute them- 

 selves in a veiy peculiar way. Most of the iron filings you see 

 have massed upon two spots, exactly corresponding to the two 

 poles ; and all round these spots, lines which are called the lines 

 of magnetic force are shown by the iron filings. It is, of course, 

 difficult, in an experiment of this sort, to show the action as com- 

 pletely as one can in a laboratory ; I have accordingly brought 

 some photographed cards, which are certainly very instructive. In 

 these the result of the attraction of the poles, the outflowing lines, 

 as it were, of force from the magnet running in all directions, are 

 well depicted. In the one that has been reproduced, in Fig. 1, 

 Plate 8, the two half -circles, intensely white, are the magnetic 

 fields of a dynamo-machine such as you see before you, and the 

 diagram enables us to trace the intensity and direction of the 

 magnetic action in every part of the machine. 



Now if a wire forming a closed circuit was taken across these 

 lines of force, although passing only through air (indeed it might 

 be passing through a vacuum), it would encounter resistance due 

 to the magnetism, and this resistance manifests itself as a current 

 of electricity passing through the wire. I shall endeavour to 

 make the experiment in such a way as to render this action 

 visible to you. I have here my magnetic field, that is to say, two 

 polar surfaces opposed to one another, and a framework wound six 



