152 WRITINGS OF JOSEPH HENRY. [1840 



was connected with the compound battery, and helix No. 1, 

 *(No. Ill, 8,) formed of one thousand six hundred and sixty- 

 yards of fine copper wire, was placed on the coil to receive 

 the induction, as is shown in figure 3, which is again inserted 

 here for the convenience of the reader. 



a 



Fig. 3. — a represents coil No. 1, b helix No. 1, and c, d, handles for receiv- 

 ing the shock. 



This arrangement being made, currents of increasing in- 

 tensity were passed through the coil by constantly retaining 

 one of its ends in the cup of mercury forming one extremity 

 of the battery, and successively plunging the other end into 

 the cups which served to form the connections of the several 

 elements of the battery. With the current from one element, 

 the shock at breaking the circuit was quite severe; but at 

 making the same it was very feeble, and could be perceived 

 in the fingers only, or through the tongue. With two ele- 

 ments in the circuit, the shock at the beginning was slightly 

 increased ; with three elements the increase was more decided, 

 while the shock at breaking the circuit remained nearly of 

 the same intensity 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 decidedly stronger than the latter, the differ- 

 ence continually 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 smaliness of its plates, and 

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

 the error of supposing that the induction at the ending of 



