t the tongue and the eyes, is very characteristic.

280. v. _Spark_.--The brilliant star of light produced by the discharge of
a voltaic battery is known to all as the most beautiful light that man can
produce by art.

* * * * *

281. That these effects may be almost infinitely varied, some being exalted
whilst others are diminished, is universally acknowledged; and yet without
any doubt of the identity of character of the voltaic currents thus made to
differ in their effect. The beautiful explication of these variations
afforded by Cavendish's theory of quantity and intensity requires no
support at present, as it is not supposed to be doubted.

282. In consequence of the comparisons that will hereafter arise between
wires carrying voltaic and ordinary electricities, and also because of
certain views of the condition of a wire or any other conducting substance
connecting the poles of a voltaic apparatus, it will be necessary to give
some definite expression of what is called the voltaic current, in
contradistinction to any supposed peculiar state of arrangement, not
progressive, which the wire or the electricity within it may be supposed to
assume. If two voltaic troughs PN, P'N', fig. 42, be symmetrically arranged
and insulated, and the ends NP' connected by a wire, over which a magnetic
needle is suspended, the wire will exert no effect over the needle; but
immediately that the ends PN' are connected by another wire, the needle
will be deflected, and will remain so as long as the circuit is complete.
Now if the troughs merely act by causing a peculiar arrangement in the wire
either of its particles or its electricity, that arrangement constituting
its electrical and magnetic state, then the wire NP' should be in a similar
state of arrangement _before_ P and N' were connected, to what it is
afterwards, and should have deflected the needle, although less powerfully,
perhaps to one half the extent which would result when the communication is
complete throughout. But if the magnetic effects depend upon a current,
then it is evident why they could not be produced in _any_ degree before
the circuit was complete; because prior to that no current could exist.

283. By _current_, I mean anything progressive, whether it be a fluid of
electricity, or two fluids moving in opposite directions, or merely
vibrations, or, speaking still more generally, progressive forces. By
_arrangement_, I understa