488 Piof. J. Henry's Contrihilions 



formed the poles of the battery, and permanently retained there 

 during the experiment ; also, at the distance of about six inches 

 I'rom, say the rigiit hand end of the coil, a loop was made in the 

 riband, which could be plunged into the cup containing the 

 left hand end. Witii this arrangement, and while only the 

 two extreme ends of the coil were in connexion with the cups 

 of mercury, of course the current passed through the entire 

 length of the riband of the coil ; but by plunging the loop into 

 the left hand cup, the whole length of the coil, except the six 

 inches before mentioned, was excluded from the battery cir- 

 cuit. And again, when the loop was lifted out of the cup, the 

 whole length was included. In this way the current in the 

 coil could be suddenly formed and interrupted, while the 

 poles of the battery were continually joined by a conductor; 

 but no shock with either a single or a compound battery 

 could be obtained by this method of operation. 



19. The feebleness of the shock at the beginning of the 

 current, with a single battery and a long coil, is not entirely 

 owing to the cause we have stated (17.), namely, the resistance 

 to conduction offered by the long conductor, but also de- 

 pends, in a considerable degree, if not principally, on the ad- 

 verse influence of the secondary current, induced in the pri- 

 mary conductor itself, as is shown by the result of the follow- 

 ing experiment. Helix No. 1. was placed on a coil consisting 

 of only three spires or turns of copper riband ; with this, the 

 shock, both at making and breaking the circuit with a single 

 battery, could be felt in the hands. A compound coil was 

 then formed of the copper ribands of coils No. 3. and 4. rolled 

 together so that the several spires of the two alternated with 

 each other, and when this was introduced into the circuit so 

 as not to act on the helix by its induction, and the battery 

 current passed through, for example, coil No. 3, the shock at 

 making contact with the pole of the battery was so much re- 

 duced as to be imperceptible in the hands, while the shock at 

 breaking the contact M-as about the same as before this addi- 

 tion was made to the length of the circuit. The ends of coil 

 No. 4. were now joined so as to produce a closed circuit, the 

 induced current in which would neutralize the secondary cur- 

 rent in the battery conductor itself; and now the shock at 

 making the contact was nearly as poweriul as in the case 

 where the short conductor alone formed the circuit with the 

 battery. Hence, the principal cause of the feebleness of the 

 effect at the beginning of the battery current, is the adverse 

 action on the helix of the secondary current produced in the 

 conductor of the battery circuit itself. The shock at the 



