will be most felt by those who are best trained in ordinary
theoretic conceptions. He does not know the reader's needs, and he
therefore does not meet them. For instance he speaks over and over
again of the impossibility of charging a body with one electricity,
though the impossibility is by no means evident. The key to the
difficulty is this. He looks upon every insulated conductor as the
inner coating of a Leyden jar. An insulated sphere in the middle of
a room is to his mind such a coating; the walls are the outer coating,
while the air between both is the insulator, across which the charge
acts by induction. Without this reaction of the walls upon the
sphere you could no more, according to Faraday, charge it with
electricity than you could charge a Leyden jar, if its outer coating
were removed. Distance with him is immaterial. His strength as a
generalizer enables him to dissolve the idea of magnitude; and if
you abolish the walls of the room--even the earth itself--he would
make the sun and planets the outer coating of his jar. I dare not
contend that Faraday in these memoirs made all his theoretic
positions good. But a pure vein of philosophy runs through these
writings; while his experiments and reasonings on the forms and
phenomena of electrical discharge are of imperishable importance.

Footnotes to Chapter 8

[1] Newton's third letter to Bentley.

[2] Had Sir Charles Wheatstone been induced to resume his measurements,
varying the substances through which, and the conditions under which,
the current is propagated, he might have rendered great service to
science, both theoretic and experimental.