On Electro-Dynamic Induction. © 213 
15. When the electricity is of low 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 more brilliant deflagrations, and louder snaps from 
a surface of mercury, than any other form of conductor. The 
shocks, with this arrangement, are, however, very feeble, and can 
be felt only in the fingers or through the tongue. 
16. The induced current in a short conductor, which thus 
produces deflagration, but not shocks, may, for distinction, be 
called one of quantity. 
_ 17. When the length of the coil is increased, the battery con- 
tinuing the same, the deflagrating power decreases, while the in- 
tensity 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 resistance or 
diminished conduction of the lengthened coil begins to counter- 
act the influence of the increasing length of the current. The 
following experiment illustrates this fact. A coil of copper wire 
7th of an inch in diameter, was increased in length by succes- 
Sive additions of about thirty two feet atatime. After the first 
two lengths, or sixty four feet, the brilliancy of the spark began 
to decline, but the shocks constantly increased in intensity, until 
alength of five hundred and seventy five feet was obtained, when 
the shocks also began to decline. This was then the proper 
length to produce the maximum effect with a single battery, and 
& Wire of the above diameter. : ns 
19. When the intensity of the electricity of the battery is in- 
¢ , the action of the short riband coil decreases. With a 
Cruickshank’s trough of sixty plates, four inches square, scareely 
any peculiar effect can be observed, when the coil forms a part of 
the circuit. If however the length of the coil be inereased in 
Proportion to the intensity of the current, then the inductive in- 
fluence 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, 
