On Electro- Dynamic Induction. 121 



at beginning was slightly increased ; with three elements the in- 

 crease was more decided, while the shock at breaking the circuit 

 remained nearly of the same intensity as at first, or was compar- 

 atively 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 decidedly stronger than the latter, the difference con- 

 tinually increasing 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 construction ; 

 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 increasing the intensity of the bat- 

 tery, (see paragraph 19, of No. Ill,) but by employing the more 

 perfect instrument of Professor Daniell in the arrangement of the 

 last experiment, I am enabled 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 de- 

 pends in any degree on the quantity of current electricity in the 

 conductor, then a slight increase in the induction should take 

 place, since, according to theory, the current is somewhat in- 

 creased in quantity, in the case of a long coil, by the increase of 

 the intensity of the battery. Although very little, if any, diffe- 

 rence 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 ele- 

 ments 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, cor- 

 rectly given. 



10. The intensity of the different shocks in the foregoing ex- 

 periments was compared by gradually raising the helix from the 

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

 ductors, the shock in one case would be so much reduced 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, perhaps, in the hands. The 

 same method was generally employed in the experiments in which 



Vol. xn, No. 1.— April-June, 1841. 16 



