2M 
Prof. J. Henry’s Contributions 
more definitely the conditions which influence the action of 
the spiral conductor. 
15. When the electricity is oflow intensity, as in the case 
of the thermo-electrical pile, or a large single battery weakly 
excited with dilute acid, the flat riband coil No. 1, ninety- 
three feet long, is found to give the most brilliant deflagra- 
tions, and the loudest snaps from a surface of mercury. The 
shocks, with this arrangement, are, however, very feeble, and 
can only be felt in the fingers or through the tongue. 
16. The induced current in a short coil, which thus pro- 
duces deflagration, but not shocks, may, for distinction, be 
called one of quantity. 
1 7. When the length of the coil is increased, the battery 
continuing the same, the deflagrating power decreases, while 
the intensity of the shock continually increases. With five 
riband coils, making an aggregate length of three hundred 
feet, and the small battery, fig. 1, the deflagration is less than 
with coil No. 1, but the shocks are more intense. 
18. There is, however, a limit to this increase of intensity 
of the shock, and this takes place when the increased resist- 
ance or diminished conduction of the lengthened} coil begins 
to counteract the influence of the increasing length of the 
current. The following experiment illustrates this fact. A 
coil of copper wire y^th of an inch in diameter, was increased 
in length by successive additions of about thirty-two feet at 
a time. After the first two lengths, or sixty-four feet, the 
brilliancy of the spark began to decline, but the shocks con- 
stantly increased in intensity, until a length of five hundred 
and seventy-five feet was obtained, when the shocks also be- 
gan to decline. This was then the proper length to produce 
the maximum effect with a single battery, and a wire of the 
above diameter. 
1 9. When the intensity of the electricit}^ of the battery is 
increased, the action of the short riband coil decreases. With 
a Cruickshanks trough of sixty plates, four inches square, 
scarcely any peculiar effect can be observed, when the coil 
forms a part of the circuit. If however the length of the 
coil be increased in proportion to the intensity of the current, 
then the inductive influence becomes apparent. When the 
current, from ten plates of the above-mentioned trough, was 
passed through the wire of the large spool (10.), the induced 
shock was too severe to be taken through the body. Again, 
when a small trough of twenty-five one-inch plates, which 
alone would give but a very feeble shock, was used with helix 
No. 1, an intense shock was received from the induction 
when the contact was broken. Also a slight shock in this 
