1840] WRITINGS OF JOSEPH HENRY. 153 



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

 creasing the intensity of the battery; (see paragraph 19, of 

 No. HI;) 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 in- 

 duction 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 some- 

 what increased in quantity, 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 in- 

 cluded in the circuit, than with a single one. The other re- 

 sults 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 em- 

 ployed in the experiments in which shocks are mentioned 

 as being compared, in the other parts of this paper. 



11. Experiments were next made to determine the in- 

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

 of the battery remaining the same. For this purpose, the 

 battery consisting of a single element, and the arrangement 

 of the apparatus as represented in Fig. 3, the coil was di- 

 minished in length from sixty feet to forty-five, then to 

 thirty, and so on. With the first mentioned length the 

 shock, at making contact with the battery, was of course 

 very feeble, and could be felt only in the tongue; with the 



