94 WRITINGS OF JOSEPH HENRY. [1835 



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

 the effect was greater with the larger ; this also appears to 

 depend in some degree on the size of the battery. 



4. A length of about forty feet of the wire used in experi- 

 ments 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 commerce. 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 succession, and always with the same result. 



6. To test still farther 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 doub- 

 ling 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 

 neutralize 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. 



