[A] In further illustration of this subject see 855-873 in Series
  VII.—­Dec. 1838.

361.  Believing the point of identity to be satisfactorily established, I next endeavoured to obtain a common measure, or a known relation as to quantity, of the electricity excited by a machine, and that from a voltaic pile; for the purpose not only of confirming their identity (378.), but also of demonstrating certain general principles (366, 377, &c.), and creating an extension of the means of investigating and applying the chemical powers of this wonderful and subtile agent.

362.  The first point to be determined was, whether the same absolute quantity of ordinary electricity, sent through a galvanometer, under different circumstances, would cause the same deflection of the needle.  An arbitrary scale was therefore attached to the galvanometer, each division of which was equal to about 4 deg., and the instrument arranged as in former experiments (296.).  The machine (290.), battery (291.), and other parts of the apparatus were brought into good order, and retained for the time as nearly as possible in the same condition.  The experiments were alternated so as to indicate any change in the condition of the apparatus and supply the necessary corrections.

363.  Seven of the battery jars were removed, and eight retained for present use.  It was found that about forty turns would 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.

364.  The other seven jars were then added to the eight, and the whole fifteen charged by thirty turns of the machine.  The Henley’s 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 with fifteen jars were repeated several times alternately with the same results.

365.  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 (298.).  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.