318 LENZ ON THE VARIOUS CONDUCTING POWERS 



these results in my former memoirs ; where, in many places, the same 

 observations of deviation were successively repeated in order to obtain 

 a greater accuracy, and where the results leave nothing to wish as to 

 their accordance. Convincing proofs may moreover be found in the 

 following series of experiments. 



The reason why the strength of the current cannot depend on the sud- 

 denness of the disruption might also be easily demonstrated by theo- 

 retical considerations. The current in the electromotive spiral arises 

 from this cause, that the magnetic intensity of the keeper of soft iron 

 about which the spiral is coiled diminishes from a maximum to a mini- 

 mum, — the latter approaching nearer to in proportion as the iron pos-^ 

 sesses a less coercitive power. We may imagine this diminution of 

 the magnetic intensity of the keeper to be divided into indefinitely 

 small parts, each of them producing in the spiral an indefinitely small 

 current, and this again exercising an indefinitely small effect on the 

 needle of the multiplier : all these effects taken together produce the 

 entire deviation of the needle. If, therefore, the whole series of inde- 

 finitely small effects act on the needle successively, but in so short a 

 time that they exercise their whole force when the needle is in a posi- 

 tion very little different from the normal one, the sum of the effects will 

 be as great as that which would be produced by the whole force acting 

 at once, or by the iron passing suddenly from the maximum to the mi- 

 nimum ; and within these limits suddenness of disruption will have no 

 influence over the deviation. Experience teaches therefore that the sud- 

 denness I commonly employed was within these limits ; which will be 

 more easily conceivable from the circumstance that the intensity of the 

 keeper diminishes in the beginning much more quickly than at the end : 

 so that we may take it for granted that more than VV of the indefinitely 

 small diminution of intensity takes place during the contact of the magnet 

 with the keeper and within the distance of one inch from it. 



My first experiments refer to the law of conductibility of wires of 

 different lengths. I cut for this purpose a copper wire (0*023 Engl, 

 inch thick), covered with silk, into five pieces, so that each was 7 Engl, 

 feet long, and observed the deviations of the needle produced by the dis- 

 ruption of the keeper, together with the electromotoric spiral from the 

 magnet, by inserting between the wire of the multiplier and the elec- 

 tromotive spiral eitlier no wire at all, or one, two, four, &c. wires suc- 

 cessively. Their extremities were connected by immersion in mercury. 

 The following table shows the results of these experiments ; the signi- 

 fication of the numbers 1,2, 3, 4 will be found in my former Memoir. 



