s incessantly
theorising himself. His principal researches are all connected by an
undercurrent of speculation. Theoretic ideas were the very sap of his
intellect--the source from which all his strength as an experimenter was
derived. While once sauntering with him through the Crystal Palace, at
Sydenham, I asked him what directed his attention to the magnetization
of light. It was his theoretic notions. He had certain views regarding
the unity and convertibility of natural forces; certain ideas regarding
the vibrations of light and their relations to the lines of magnetic
force; these views and ideas drove him to investigation. And so it must
always be: the great experimentalist must ever be the habitual theorist,
whether or not he gives to his theories formal enunciation.

Faraday, you have been informed, endeavoured to improve the manufacture
of glass for optical purposes. But though he produced a heavy glass of
great refractive power, its value to optics did not repay him for
the pains and labour bestowed on it. Now, however, we reach a result
established by means of this same heavy glass, which made ample amends
for all.

In November, 1845, he announced his discovery of the 'Magnetization of
Light and the Illumination of the Lines of Magnetic Force.' This title
provoked comment at the time, and caused misapprehension. He therefore
added an explanatory note; but the note left his meaning as entangled as
before. In fact Faraday had notions regarding the magnetization of light
which were peculiar to himself, and untranslatable into the scientific
language of the time. Probably no other philosopher of his day would
have employed the phrases just quoted as appropriate to the discovery
announced in 1845. But Faraday was more than a philosopher; he was
a prophet, and often wrought by an inspiration to be understood by
sympathy alone. The prophetic element in his character occasionally
coloured, and even injured, the utterance of the man of science;
but subtracting that element, though you might have conferred on him
intellectual symmetry, you would have destroyed his motive force.

But let us pass from the label of this casket to the jewel it
contains. 'I have long,' he says, 'held an opinion, almost amounting
to conviction, in common, I believe, with many other lovers of natural
knowledge, that the various forms under which the forces of matter are
made manifest have one common origin; in other words, are so directly