156 WRITINGS OF JOSEPH HENRY. [1840 



of electrical tension; and therefore the discharge through 

 the conductor may be supposed to be more sudden, and 

 hence an induction of more intensity is produced. 



18. That the shock at both making and breaking the cir- 

 cuit in some way depends on the rapidity of formation and 

 diminution of the current is shown by the following experi- 

 ment, in which the tension just mentioned does not take 

 place, and in which also the current appears to diminish more 

 slowly. The two ends of the coil were placed in the two cups 

 which formed the poles of the battery, and permanently re- 

 tained there during the experiment ; also, at the distance of 

 about six inches from — say the right hand end of the coil, a 

 loop was made in the ribbon, which could be plunged into 

 the cup containing the left hand end. With this arrange- 

 ment, and while only the two extreme ends of the coil were 

 in connection with the cups of mercury, of course the cur- 

 rent passed through the entire length of the ribbon of the 

 coil; but by plunging the loop into the left hand cup, the 

 whole length of the coil, except the six inches before men- 

 tioned, was excluded from the battery circuit. 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 bat- 

 tery 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 depends 

 in a considerable degree (if not principally) on the adverse 

 influence of the secondary current, induced in the primary 

 conductor itself, as is shown by the result of the following 

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

 only three spires or turns of copper ribbon; 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 ribbons of coils No. 3 and 4 rolled 



