258 BULLETIN OP THE 



Society a memoir (comprising the details of his recent verbal 

 conimuuication) "On the Jntlueuce of a ISpiral Conductor in in- 

 creasing the Intensity of Elet-tricity from a galvanic arrangement 

 of a Single pair, etc.," which was read before the iSocieiy, Feb- 

 ruary 6Lh, l8o5. 



After citing his former paper of July, 1S32, the writer remarks 

 that he had been able during the past year to extend his experi- 

 ments on the curious phenomenon. " These though not so 

 complete as 1 could wisli, are now presented to the (Society with 

 the belief that they will be interesting at this time on account of 

 the recent publication of Mr. Faraday on the same subject." He 

 then relates that employing a single pair of his battery (com- 

 prising one and a half square feet of zinc surface), he found as 

 in his earlier experiment in 1832, that the poles being connected 

 by a piece of copper bell-wire five inches long, no spark waa 

 given on making or breaking contact. Fifteen leet of interposed 

 wire gave a very feeble spark ; and with successive additions of 

 fifteen feet, the effect increased until with 120 feet tlie maximum 

 spark appeared to be reached, and beyond this there was no 

 perceptible increase ; while with double this length (or 240 feet) 

 there seemed to be a diminution of intensity. From various 

 trials the inference was drawn that the length required for maxi- 

 mum effect varied with the size of the galvanic element. Thicker 

 wires of the same length produced greater effect, depending in 

 some degree on the size of the battery. A wire of forty feet 

 when coiled into a cylindrical helix " gave a more intense spark 

 than the same wire uncoiled." A ribbon of sheet copper about 

 an inch wide and twenty-eight feet long, being covered with silk 

 and coiled into a flat spiral — like a watch spring — (after the plan 

 of Dr. Richie) gave a vivid spark with a loud snap. When un- 

 coiled, it produced a much feebler spark. With the insulated 

 copper ribbon folded in its middle, and the double thickness 

 coiled into a flat spiral, there was no spark whatever, although 

 the same ribbon unrolled gave a feeble spark: thus showing that 

 the induction of the current upon itself was neutralized by flow- 

 ing equally in opposite directions in the double spiral. With a 

 larger copper ribbon one inch and a half wide, and 90 feet long, 

 spirallv coiled (weighing 15 pounds) the snap of the spark could h& 

 heard in an adjoining room with the door closed. Want of mate- 

 rial prevented the result being pushed further, so as to ascertain 

 the range of maximum effect with this form of conductor. With 

 increased battery surface, the effect was also increased ; so that 

 with eisht elements of his battery arranged as a single pair fof 

 12 square feet) the spark on breaking contact " resembled the 

 discharge of a small Levden jar highly charged." With the flat 

 spiral, no increase of effect was observable on the introduction 

 of a soft iron core into the axis of the spiral, forming a magnet. 

 With a helical or cylindrical coil about nine inches long, enclosing 



32 



