4 CONTRIBUTIONS TO ELECTRICITY AND MAGNETISM. 



8. In the first experiment, coil No. 2, which it will be remembered (III. 7) 

 consists of a copper riband of about sixty feet long, and coiled on itself like the 

 main spring of a watch, was connected with the compound battery and helix 

 No. 1, (III. 8,) formed of one thousand six hundred and sixty yards of fine 

 copper wire, and 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. 



Fig. 3. This arrangement being made, 



'^ currents of increasing intensity 

 I c were passed through the coil by 

 constantly retaining one of its 

 ends in the cup of mercury form- 

 ing one extremity of the battery, 



a represents coil No. 1 , b helix No. 1 , and c, d, handles ^^^^ successively pluncrinS' the 

 for receiving tlie shock. 



other end into the cups which 



served to form the connexions 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 elements in the circuit, the shock 



at bet'inning 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 greater than the latter, the difference 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 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. 3,) but by employing the more perfect instru- 

 ment 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 re- 

 mains 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 



