to Electricity and Magnetism. 485 



with three elements the increase was more decided, while the 

 shock at breaking the circuit remained nearly of the same in- 

 tensity as at first, or was comparatively but little increased. 

 When the number of elements was increased to ten, the shock 

 at making contact was found fully equal to that at breaking, 

 and by employing a still greater number, the former was de- 

 cidedly greater than the latter; the difference continually in- 

 creasing until all the thirty elements were introduced into the 

 circuit. 



9. In my last paper, a few experiments are mentioned as 

 being made with a compound battery of Cruickshank's con- 

 struction ; but from the smallness of the plates of this, and 

 the rapidity with which its power declined, I was led into the 

 error of supposing that the induction at the ending of the 

 current, in the case of a short coil, was diminished by increas- 

 ing the intensity of the battery (see paragraph 19. of No, III.) ; 

 but by employing the more perfect instrument of Professor 

 Daniell in the arrangement of the last experiment. I am en- 

 abled to correct this error, and to state that the induction at 

 the ending remains nearly the same when the intensity of the 

 battery is increased. If the induction depends in any degree 

 on the quantity of current electricity in the conductor, then a 

 slight increase in the induction should take place ; since, ac- 

 cording to theory, the current is somewhat increased in quan- 

 tity, in the case of a long coil, by the increase of the intensity 

 of the battery. Although very little, if any, difference could 

 be observed in the intensity of the shock from the secondary 

 current, yet the snap and deflagration of the mercury appeared 

 to be greater from the primary current when ten elements of 

 the battery were included in the circuit, than with a single 

 one. The other results which are mentioned in my last paper, 

 in reference to the compound battery, are, I believe, correctly 

 given. 



10. The intensities of the different shocks in the foregoing 

 experiments were compared by gradually raising the helix 

 from the coil (see Fig. 3.), until, on account of the distance of 

 the conductors, the shock in one case would be so much re- 

 duced as to be scarcely perceptible through the fingers or the 

 tongue, while the shock from another arrangement, but with 

 the same distance of the conductors, would be evident, per- 

 haps, in the hands. The same method was generally cm- 

 ployed in the experiments in which shocks are mentioned as 

 being compared, in the otiier parts of this paper. 



1 1 . Experiments were next made to determine the influence 

 of a variation in the length of the coil, the intensity of the 



