Contributions to Electricity and Magnetism. 



ciiit, are in a state of electrical tension ; and therefore the dis- 

 charge through the conductor may be supposed to be more sud- 

 den, and hence an induction of more intensity is produced. 



18. That the shock at both making and breaking the circuit 

 in some way depends on the rapidity of formation and diminu- 

 tion of the current is shown by the following experiment, 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 retained 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 riband, 

 which could be plunged into the cup containing the left hand 

 end. With 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 circuit. And again, when the 

 loop was hfted 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 join- 

 ed by a conductor, but no shock with either a single or a com- 

 pound battery could be obtained by this method of operation. 



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

 rent, with a single battery and a long coil, is not entirely owing 

 to the cause we have stated, (17,) namely, the resistance to con- 

 duction offered by the long conductor, but also depends, in a con- 

 siderable degre, 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 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 bat- 

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

 makmg contact with the pole of the battery was so much redu- 



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