ave been the more anxious to assign the true value of this
experiment as a test of electro-chemical action, because I shall have
occasion to refer to it in cases of supposed chemical action by
magneto-electric and other electric currents (336. 346.) and elsewhere.
But, independent of it, there cannot be now a doubt that Dr. Wollaston was
right in his general conclusion; and that voltaic and common electricity
have powers of chemical decomposition, alike in their nature, and governed
by the same law of arrangement.

332. iv. _Physiological effects._--The power of the common electric current
to shock and convulse the animal system, and when weak to affect the tongue
and the eyes, may be considered as the same with the similar power of
voltaic electricity, account being taken of the intensity of the one
electricity and duration of the other. When a wet thread was interposed in
the course of the current of common electricity from the battery (291.)
charged by eight or ten[A] revolutions of the machine in good action
(290.), and the discharge made by platina spatulas through the tongue or
the gums, the effect upon the tongue and eyes was exactly that of a
momentary feeble voltaic circuit.

[A] Or even from thirty to forty.

333. v. _Spark._--The beautiful flash of light attending the discharge of
common electricity is well known. It rivals in brilliancy, if it does not
even very much surpass, the light from the discharge of voltaic
electricity; but it endures for an instant only, and is attended by a sharp
noise like that of a small explosion. Still no difficulty can arise in
recognising it to be the same spark as that from the voltaic battery,
especially under certain circumstances. The eye cannot distinguish the
difference between a voltaic and a common electricity spark, if they be
taken between amalgamated surfaces of metal, at intervals only, and through
the same distance of air.

334. When the Leyden battery (291.) was discharged through a wet string
placed in some part of the circuit away from the place where the spark was
to pass, the spark was yellowish, flamy, having a duration sensibly longer
than if the water had not been interposed, was about three-fourths of an
inch in length, was accompanied by little or no noise, and whilst losing
part of its usual character had approximated in some degree to the voltaic
spark. When the electricity retarded by water was discharged between pieces
of charcoal, it was excee