dle was now as nearly as possible to the eleventh
division, but the graduation was not accurate enough for me to assert that
the arc was exactly double the former arc; to the eye it appeared to be so.
The probability is, that _the deflecting force of an electric current is
directly proportional to the absolute quantity of electricity passed_, at
whatever intensity that electricity may be[A].

[A] The great and general value of the galvanometer, as an actual
measure of the electricity passing through it, either continuously or
interruptedly, must be evident from a consideration of these two
conclusions. As constructed by Professor Ritchie with glass threads
(see Philosophical Transactions, 1830, p. 218, and Quarterly Journal
of Science, New Series, vol. i. p.29.), it apparently seems to leave
nothing unsupplied in its own department.

368. Dr. Ritchie has shown that in a case where the intensity of the
electricity remained the same, the deflection of the magnetic needle was
directly as the quantity of electricity passed through the galvanometer[A].
Mr. Harris has shown that the _heating_ power of common electricity on
metallic wires is the same for the same quantity of electricity whatever
its intensity might have previously been[B].

[A] Quarterly Journal of Science, New Series, vol. i. p. 33.

[B] Plymouth Transactions, page 22.

369. The next point was to obtain a _voltaic_ arrangement producing an
effect equal to that just described (367.). A platina and a zinc wire were
passed through the same hole of a draw-plate, being then one eighteenth of
an inch in diameter; these were fastened to a support, so that their lower
ends projected, were parallel, and five sixteenths of an inch apart. The
upper ends were well-connected with the galvanometer wires. Some acid was
diluted, and, after various preliminary experiments, that adopted as a
standard which consisted of one drop strong sulphuric acid in four ounces
distilled water. Finally, the time was noted which the needle required in
swinging either from right to left or left to right: it was equal to
seventeen beats of my watch, the latter giving one hundred and fifty in a
minute. The object of these preparations was to arrange a voltaic
apparatus, which, by immersion in a given acid for a given time, much less
than that required by the needle to swing in one direction, should give
equal deflection to the instrument with the discharge of ordinary
elec