relation to the Fourth Series on a new law of
Electric Conduction, to Franklin's experiments on the non-conduction of
ice, which have been very properly separated and set forth by Professor
Bache (Journal of the Franklin Institute, 1836. xvii. 183.). These, which I
did not at all remember as to the extent of the effect, though they in no
way anticipate the expression of the law I state as to the general effect
of liquefaction on electrolytes, still should never be forgotten when
speaking of that law as applicable to the case of water.

There are two papers which I am anxious to refer to, as corrections or
criticisms of parts of the Experimental Researches. The first of these is
one by Jacobi (Philosophical Magazine, 1838. xiii. 401.), relative to the
possible production of a spark on completing the junction of the two metals
of a single pair of plates (915.). It is an excellent paper, and though I
have not repeated the experiments, the description of them convinces me
that I must have been in error. The second is by that excellent
philosopher, Marianini (Memoria della Societa Italiana di Modena, xxi.
205), and is a critical and experimental examination of Series viii, and of
the question whether metallic contact is or is not _productive_ of a part
of the electricity of the voltaic pile. I see no reason as yet to alter the
opinion I have given; but the paper is so very valuable, comes to the
question so directly, and the point itself is of such great importance,
that I intend at the first opportunity renewing the inquiry, and, if I can,
rendering the proofs either on the one side or the other undeniable to all.

Other parts of these researches have received the honour of critical
attention from various philosophers, to all of whom I am obliged, and some
of whose corrections I have acknowledged in the foot notes. There are, no
doubt, occasions on which I have not felt the force of the remarks, but
time and the progress of science will best settle such cases; and, although
I cannot honestly say that I _wish_ to be found in error, yet I do
fervently hope that the progress of science in the hands of its many
zealous present cultivators will be such, as by giving us new and other
developments, and laws more and more general in their applications, will
even make me think that what is written and illustrated in these
experimental researches, belongs to the by-gone parts of science.

MICHAEL FARADAY.

Royal Institution,
Marc