to Electricity and Magnetism. 487 



know that the latter is diminished in a given unit of the con- 

 ductor by increasing the length of the whole. 



14-. We have seen (8.) that, with a circuit composed often 

 elements of the compound battery and the coil No. 2, the 

 shock, at the beginning of the current, was fully equal to 

 that at the ending. It was, however, found, that if, in this 

 case, the length of the coil was increased, this shock was di- 

 minished ; and we may state, as an inference from several ex- 

 periments, that however great may be the intensity of the 

 electricity from the battery, the shock at the beginning may 

 be so reduced, by a sufficient increase of the length of the 

 primary circuit, as to be scarcely perceptible. 



15. It was also found, that when the thickness of the coil 

 was increased, the length and intensity of the circuit remain- 

 ing the same, the shock at the beginning of the battery cur- 

 rent was somewhat increased. This result was produced by 

 using a double coil ; the electricity was made to pass through 

 one strand, and immediately afterward'; through both : the 

 shock from the helix in the latter case was apparently the 

 greater. 



16. By the foregoing results we are evidently furnished 

 with two methods of increasing, at pleasure, the intensity of 

 the induction at the beginning of a battery current; the one 

 consisting in increasing the intensity of the source of the elec- 

 tricity, and the other in diminishing the resistance to conduc- 

 tion of the circuit while the intensity remains the same. 



1 7. The explanation of the effects which we have given, rela- 

 tive to the induction at the beginning, is apparently not diffi- 

 cult. The resistance to conduction in the case of a long con- 

 ductor and a battery of a single element is so great, that the 

 full development of the primary current may be supposed 

 not to take place with sufficient rapidity to produce the in- 

 stantaneous action on which the shock fi'om the secondary 

 current would seem to depend. But when a battery of a 

 number of elements is employed, the poles of this, previous 

 to the moment of completing the circuit, are in a state of elec- 

 trical tension ; and therefore the disciiarge tiirough the con- 

 ductor 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 



