378 Mr. J. N. Hearder on a powerful Form 



of investigations with my instrument I had occasion to relay the 

 secondary wire, and in doing so I only put on five-sixths of the 

 original quantity, but I have had the satisfaction to find the sta- 

 tical power of the machine nearly doubled. I exhibited this new 

 arrangement at the Royal Cornwall Polytechnic Institution on 

 the 17th of September last, and was honoured by the Society's 

 first silver medal. The main object of the present paper is to 

 detail some of the results of my investigations with it on the 

 character of the induced current, as I have discovered some facts 

 which, as far as I know, are quite new, and which seem to deve- 

 lope a new law of electrical action. 



2. Hitherto, I believe, the only thermal effects observed in 

 metallic conductors by the action of the induced current of the 

 induction coil, have been the incandescence of the end of the 

 negative terminal, w^hich, when made of very fine wire, melts and 

 burns, and the partial combustion of portions of metallic filings 

 when the spark passes between them as they lie strewed upon a 

 non-conducting surface, as is evidenced by the colour of the spark 

 varying with the nature of the metal used. Whilst the spark in 

 its passage through inflammable bad conductors, such as paper, 

 cotton, gunpowder, and even through inflammable non-conduc- 

 tors, such as aether, alcohol, turpentine, &c., readily kindles 

 them, yet the same cun-ent made to pass through an extremely 

 fine wire in a closed circuit docs not sensibly heat it. In this 

 particular the spark of the induction coil resembles that of a dis- 

 charge from a Leyden jar when made to pass through an imper- 

 fectly conducting circuit, such as a wet string, or tube of water ; 

 for it is to be observed, that although a charge from a Leyden 

 jar or battery, when passed at once through a fine wire, may be 

 sufficient to melt and dissipate it, yet it will not sensibly heat 

 the same wire when water is in any way made part of the circuit, 

 though the same spark will in the latter case inflame gunpowder, 

 whilst through the perfectly conducting circuit it disperses it 

 without ignition. There can be very little doubt that the dis- 

 charge requires a certain amount of time to pass through the 

 imperfect conductor, and that the metal is thus able freely to 

 transmit the electricity with its reduced velocity, and is conse-- 

 quently not heated by it. Effects analogous to these are pro- 

 duced by the induction coil ; for although the soft static spark 

 between the terminals will inflame gunpowder, yet the discharge 

 from a Leyden jar, when its coatings are in connexion respects 

 ively with each terminal, merely disperses it, as when charged 

 with frictional electricity. 



3, I had often felt that if any definite thermal results could 

 be obtained from the action of the Leyden jar in connexion with 

 the induction apparatus, a channel would be opened up through 

 which an accurate comparison might be made between the cha- 



