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124 Contributions to Electricity and Magnetism. 
cuit, 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 a? 
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 thé 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 
Toop 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 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, ina 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 
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he 
' was 8 it on a coil consisting of only three spires or turns of 
copper 
tiband ; 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 
making contact with the pole of the battery was so much redu- ae 
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