of Magnetism : with Notes hy Mr. Faraday. 405 



most active in the present point of view ; then at a little di- 

 stance 'won {Exp. Res. 207. 212.); afterwards antimony; and 

 finally, bismuth. But in truth the fragility of the two latter 

 only allowed us to give them the spiral figure by fusing them. 

 For this method, which was long and difficult, we supplied 

 another; which was, to make quadrangular spirals of a num- 

 ber of rods of these metals soldered at their extremities, or else 

 merely held and pressed the one against the other, to ensure 

 contact. It is scarcely necessary to say, that in order to obtain 

 comparative results the same quadrangular form was given to 

 the spirals of copper and iron. 



2. Electric Spark {Exp. Res. 32. 57.*). 



The relation placed at the head of this article, says ''that in 

 a particular case Mr. Faraday had obtained a spark " {Exp. 

 Res.32.). Although this expTession gave no light on the sub- 

 ject, and rather rendered doubtful the constancy of so extra- 

 oi'dinary a phsenomenon, we nevertheless did not suspend our 

 researches, and have been so fortunate as to succeed beyond 

 our hopes. The following are the theoretical views which 

 have conducted us to this important result, but which, we 

 fairly say, at first gave us but very little confidence. 



The voltaic pile gives a spark only when composed of a cer- 

 tain number of pairs of plates. A single Wollaston's voltaic 

 element yields it ; and when of a certain activity produces it 



constantly 



[* Being much engaged in the investigation and confirmation of the laws 

 of magneto-electric action, terrestrial magnetic induction, &c. &c. some 

 of the results of which are contained in my second paper (The Bakerian 

 Lecture), it will be seen that in the race which Sig. Nobili and Antinori 

 (probably inadvertently) ran against me (see the last paragraph of their 

 paper), they obtained the electric spark from the common magnet before 

 me. I have great pleasure in bearing witness to the accuracy of their rea- 

 soning on this point, and also to the success of the result. Having made 

 a variation of the experiment by obtaining the spark from the action of a 

 common loadstone, in which their most perfect mode could not be applied, 

 I will take theopportunity of describing the simple adjustment I have devised. 

 A helix was fixed round the lifter,the wire 

 ends were raised upwards; one, which 

 may be called a, was bent into a hook 

 as in the figure; the other, b, after 

 rising was bent at a right angle, and had 

 a thick small circular plate of copper 

 fixed to it, which was made by the 

 spring of the wire to press in the mid- 

 dle slightly against the rounded end of 

 a; this [)late and the end of a were 

 amalgamated. On bringing the lifter 



down suddenly upon the poles in the position figured, the momentum of 

 the plate caused it tt) separate from the end of «, and the spark passed. 

 On lifting it up tlic concussion always separates the end of a from llic plate, 



and 



