542 PROF. HENRY ON THE INFLUENCE OF A SPIRAL CONDUCTOR 



constantly remained in the other, the effect was noted. The first length, 

 or fifteen feet, gave a very feeble spark, which was scarcely perceptible. 

 The second, or thirty feet, produced a spark a little more intense, and 

 the effect constantly increased with each additional length, until one 

 hundred and twenty feet were used ; beyond this there was no percep- 

 tible increase ; and a wire of two hundred and forty feet gave a spark 

 of rather less intensity. From other observations I infer, that the length 

 necessary to produce a maximum result, varies with the intensity of the 

 action of the battery, and also with its size. 



3. With equal lengths of copper wire of unequal diameters, the effect 

 was greater with the larger : this also appears to depend in some de- 

 gree on the size of the battery. 



4. A length of about forty feet of the wire used in experiments first 

 and second, was covered with silk, and coiled into a cylindrical helix of 

 about two inches in height and the same in diameter. This gave a more 

 intense spark than the same wire when uncoiled. 



5. A ribbon of sheet copper, nearly an inch wide and twenty-eight 

 and a half feet long, was covered with silk, and rolled into a flat spiral 

 similar to the form in which woollen binding is found in conmierce. 

 With this a vivid spark was produced, accompanied by a loud snap. 

 The same ribbon uncoiled gave a feeble spark, similar in intensity to 

 that produced by the wire in experiment third. When coiled again, the 

 snap was produced as at first. This was repeated many times in suc- 

 cession, and always with the same result. 



6. To test still further the influence of coiling, a second ribbon was 

 procured precisely similar in length and in all other respects to the one 

 used in the last experiment. The effect was noted with one of these 

 coiled into a flat spiral and the other uncoiled, and again with the first 

 uncoiled and the second coiled. When uncoiled, each gave a feeble 

 spark of apparently equal intensity ; when coiled, a loud snap. One of 

 these ribbons was next doubled into two equal strands, and then rolled 

 into a double spiral with the point of doubling at the centre. By this 

 arrangement, the electricity, in passing through the spiral, would move 

 in opposite directions in each contiguous spire, and it was supposed that 

 in this case the opposite actions which might be produced would neu- 

 tralize each other. The result was in accordance with the anticipation : 

 the double spiral gave no spark whatever, while the other ribbon coiled 

 into a single spiral produced as before a loud snap. Lest the effect might 

 be due to some accidental touching of the different spires, the double 

 spiral was covered with an additional coating of silk, and also the other 

 ribbon was coiled in the same manner ; the effect with both was the 

 same. 



7. In order to increase if possible the intensity of the spark wliile the 

 battery remained the same, larger spirals were applied in succession. 



