MEMOIRS ON THE FUNDAMENTAL
fully charge the eight jars. They were then charged by thirty turns of the machine, and discharged through the galvanometer, a thick wet string, about ten inches long, being included in the circuit. The needle was immediately deflected five divisions and a half, on the one side of the zero, and in vibrating passed as nearly as possible through five divisions and a half on the other side.
The other seven jars were then added to the eight, and the whole fifteen charged by thirty turns of the machine. The Henley electrometer stood not quite half as high as before; but when the discharge was made through the galvanometer, previously at rest, the needle immediately vibrated, passing exactly to the same division as in the former instance. These experiments with eight and fifteen jars were repeated several times alternately with the same results.
Other experiments were then made, in which all the battery was used, and its charge (being fifty turns of the machine) sent through the galvanometer: but it was modified by being passed sometimes through a mere wet thread, sometimes through thirty-eight inches of thin string wetted by distilled water, and sometimes through a string of twelve times the thickness, only twelve inches in length, and soaked in dilute acid. With the thick string the charge passed at once; with the thin string it occupied a sensible time; and with the thread it required two or three seconds before the electrometer fell entirely down. The current therefore must have varied extremely in intensity in these different cases, and yet the deflection of the needle was sensibly the same in all of them. If any difference occurred, it was that the thin string and thread caused greatest deflection; and if there is any lateral transmission, as M. Colladon says, through the silk in the galvanometer coil, it ought to have been so, because then the intensity is lower and the lateral transmission less.
Hence it would appear that if the same absolute quantity of electricity passes through the galvanometer, whatever may be its intensity, the deflecting force upon the magnetic needle is the same.
The battery of fifteen jars was then charged by sixty revolutions of the machine, and discharged, as before, through the galvanometer. The deflection of the needle was now as nearly
as possible to the eleventh division, but the graduation was not
4
