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 fiat 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 

 yLth of an inch in diameter, was increased in length by succes- 

 sive 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 constantly increased in intensity, until 

 a length 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 

 a wire of the above diameter. 



19. When the intensity of the electricity of the battery is in- 

 creased, the action of the short riband coil decreases. With a 

 Cruickshank's trough of sixty plates, four inches square, scarcely 

 any peculiar eff'ect 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 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, 



