dered as
representing the pole. But such does not appear to me to be the view of
those who have written on the subject, certainly not of some of them, and
is inconsistent with the supposed laws which they have assumed, as
governing the diminution of power at increased distances from the poles.

499. Grotthuss, for instance, describes the poles as centres of attractive
and repulsive forces (481.), these forces varying inversely as the squares
of the distances, and says, therefore, that a particle placed anywhere
between the poles will be acted upon by a constant force. But the compound
force, resulting from such a combination as he supposes, would be anything
but a constant force; it would evidently be a force greatest at the poles,
and diminishing to the middle distance. Grotthuss is right, however, _in
the fact_, according to my experiments (502. 505.), that the particles are
acted upon by equal force everywhere in the circuit, when the conditions of
the experiment are the simplest possible; but the fact is against his
theory, and is also, I think, against all theories that place the
decomposing effect in the attractive power of the poles.

500. Sir Humphry Davy, who also speaks of the _diminution_ of power with
increase of distance from the poles[A] (483.), supposes, that when both
poles are acting on substances to decompose them, still the power of
decomposition _diminishes_ to the middle distance. In this statement of
fact he is opposed to Grotthuss, and quotes an experiment in which sulphate
of potassa, placed at different distances from the poles in a humid
conductor of constant length, decomposed when near the pole, but not when
at a distance. Such a consequence would necessarily result theoretically
from considering the poles as centres of attraction and repulsion; but I
have not found the statement borne out by other experiments (505.); and in
the one quoted by him the effect was doubtless due to some of the many
interfering causes of variation which attend such investigations.

[A] Philosophical Transactions, 1807, p. 42.

501. A glass vessel had a platina plate fixed perpendicularly across it, so
as to divide it into two cells: a head of mica was fixed over it, so as to
collect the gas it might evolve during experiments; then each cell, and the
space beneath the mica, was filled with dilute sulphuric acid. Two poles
were provided, consisting each of a platina wire terminated by a plate of
the same metal;