all and a conductor (1566.), being here also called into play.

* * * * *

1603. The general analogy and, I think I may say, identity of action found
to exist as to insulation and conduction (1338. 1561.) when bodies, the
best and the worst in the classes of insulators or conductors, were
compared, led me to believe that the phenomena of _convection_ in badly
conducting media were not without their parallel amongst the best
conductors, such even as the metals. Upon consideration, the cones produced
by Davy[A] in fluid metals, as mercury and tin, seemed to be cases in
point, and probably also the elongation of the metallic medium through
which a current of electricity was passing, described by Ampere (1113)[B];
for it is not difficult to conceive, that the diminution of convective
effect, consequent upon the high conducting power of the metallic media
used in these experiments, might be fully compensated for by the enormous
quantity of electricity passing. In fact, it is impossible not to expect
_some_ effect, whether sensible or not, of the kind in question, when such
a current is passing through a fluid offering a sensible resistance to the
passage of the electricity, and, thereby, giving proof of a certain degree
of insulating power (1328.).

[A] Philosophical Transactions, 1823, p. 155.

[B] Bibliotheque Universelle, xxi, 417.

1604. I endeavoured to connect the convective currents in air, oil of
turpentine, &c. and those in metals, by intermediate cases, but found this
not easy to do. On taking bodies, for instance, which, like water, adds,
solutions, fused salts or chlorides, &c., have intermediate conducting
powers, the minute quantity of electricity which the common machine can
supply (371. 861.) is exhausted instantly, so that the cause of the
phenomenon is kept either very low in intensity, or the instant of time
during which the effect lasts is so small, that one cannot hope to observe
the result sought for. If a voltaic battery be used, these bodies are all
electrolytes, and the evolution of gas, or the production of other changes,
interferes and prevents observation of the effect required.

1605. There are, nevertheless, some experiments which illustrate the
connection. Two platina wires, forming the electrodes of a powerful voltaic
battery, were placed side by side, near each other, in distilled water,
hermetically sealed up in a strong glass tube, some minute vegetabl