120 Mr. Willoughhy Smith [June 6, 



one, and close to it, each time the circuit was made or unmade there 

 would be an induced current flowing in this wire, provided it was part 

 of a closed metallic or other conducting circuit. The first experiment 

 was not successful, for the simple reason that the galvanometer was 

 not sufficiently sensitive to be visibly affected by the very small 

 current induced in so short a length of wire as that with which he 

 made the experiment; nor was he prepared to find that induced 

 currents were of such momentary duration. But failures with Faraday 

 were merely stepping-stones to success ; he repeated the experiments 

 with spirals of insulated wire, instead of straight wires parallel to eacl 

 other, thus getting comparatively long lengths in close proximity. B7 

 these means he gained the object of his search, the result of which 

 he called " Volta-Electric Induction." Through the kindness of Tr. 

 Tyndall, I have here the identical spirals which were made and uffid 

 by Faraday on that memorable occasion. One of these Faraday con- 

 nected in circuit with a galvanometer, and placed it on top of the otler 

 spiral, through which intermittent currents from a battery were gent 

 at fixed intervals. On " making " the battery circuit, he noticed :hat 

 the needle of the galvanometer was deflected in one direction, anc on 

 breaking the circuit, the needle was again deflected, but in the opposite 

 direction. Faraday saw, in his mind's eye, each particle of the circuit 

 through which the current was passing, acting as a centre of force, 

 emitting its lines far from it, yet each of these lines returning ^0 its 

 own source ; he in consequence made a series of experiments, by 

 placing various substances in the path of the lines of force, to ascer- 

 tain whether they would in any way be affected or intercepted by the 

 substances so placed. For instance, he found that they were sensibly 

 affected by iron, but with copper no satisfactory effects were perceived, 

 although he felt sure the copper did in some way influence theai, but 

 so imperceptibly that he was unable to detect it. It was this con- 

 viction, and the doubt by Faraday of the result of his experiment 

 with regard to copper, which led me to experiment in this direction. 

 My apparatus and its arrangements being somewhat different from 

 Faraday's, I will more fully describe them. Here are two flat spirals 

 of fine silk-covered copper wire, about twelve inches in diameter, 

 suspended spider-web fashion in separate frames, the two ends of each 

 spiral being attached to terminals at the base of its own frame. These 

 two spirals, which are marked respectively A and B, will now be 

 placed a definite distance apart, and comparatively slow reversals from 

 a battery of ten cells sent through spiral A. You will see the amount 

 of the current induced in B by observing the deflection on the scale of 

 the mirror reflecting galvanometer, which is in circuit with that spiral. 

 These inductive effects vary inversely as the square of the distance 

 between the two spirals when parallel to each other ; the induced 

 current in B being also proportional to the number of reversals of 

 the battery current passing through spiral A, and also to the strength 

 of the inducing current. Spiral A is so connected that reversed 

 currents, at any desired speed per minute, can be passed through it 



