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 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 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 while the 
battery remained the same, larger spirals were applied in succession. 
(itt, he ae eC 
