on, not rising
more than the fourth of an inch above the latter, whilst the water between
it and the negative pole was perfectly clear. On continuing the action, the
bubbles of hydrogen rising upwards from the negative pole impressed a
circulatory movement on the stratum of water, upwards in the middle, and
downwards at the side, which gradually gave an ascending form to the cloud
of magnesia in the part just under the pole, having an appearance as if it
were there attracted to it; but this was altogether an effect of the
currents, and did not occur until long after the phenomena looked for were
satisfactorily ascertained.

496. After a little while the voltaic communication was broken, and the
platina poles removed with as little agitation as possible from the water
and solution, for the purpose of examining the liquid adhering to them. The
pole _c_, when touched by turmeric paper, gave no traces of alkali, nor
could anything but pure water be found upon it. The pole _b_, though drawn
through a much greater depth and quantity of fluid, was found so acid as to
give abundant evidence to litmus paper, the tongue, and other tests. Hence
there had been no interference of alkaline salts in any way, undergoing
first decomposition, and then causing the separation of the magnesia at a
distance from the pole by mere chemical agencies. This experiment was
repeated again and again, and always successfully.

497. As, therefore, the substances evolved in cases of electrochemical
decomposition may be made to appear against air (465. 469.),--which,
according to common language, is not a conductor, nor is decomposed, or
against water (495.), which is a conductor, and can be decomposed,--as well
as against the metal poles, which are excellent conductors, but
undecomposable, there appears but little reason to consider the phenomena
generally, as due to the _attraction_ or attractive powers of the latter,
when used in the ordinary way, since similar attractions can hardly be
imagined in the former instances.

498. It may be said that the surfaces of air or of water in these cases
become the poles, and exert attractive powers; but what proof is there of
that, except the fact that the matters evolved collect there, which is the
point to be explained, and cannot be justly quoted as its own explanation?
Or it may be said, that any section of the humid conductor, as that in the
present case, where the solution and the water meet, may be consi