INTRODUCTION1

BY JOHN TYNDALL

WHEN from an Alpine height the eye of the climber ranges
over the mountains, he finds that for the most part they
resolve themselves into distinct groups, each consisting of
a dominant mass surrounded by peaks of lesser elevation.
The power which lifted the mightier eminences, in nearly all
cases lifted others to an almost equal height. And so it is
with the discoveries of Faraday. As a general rule, the
dominant result does not stand alone, but forms the culmi-
nating point of a vast and varied mass of inquiry. In this
way, round about his great discovery of magneto-electric
induction, other weighty labours group themselves. His
investigations on the extra current; on the polar and other
condition of diamagnetic bodies; on lines of magnetic force,
their definite character and distribution; on the employment
of the induced magneto-electric current as a measure and test
of magnetic action; on the revulsive phenomena of the
magnetic field, are all, notwithstanding the diversity of title,
researches in the domain of magneto-electric induction.

Faraday's second group of researches and discoveries
embrace the chemical phenomena of the current. The
dominant result here is the great law of definite electro-
chemical decomposition, around which are massed various
researches on electro-chemical conduction and on electrolysis
both with the machine and with the pile. To this group also
belong his analysis of the contact theory, his inquiries as to
the source of voltaic electricity, and his final development
of the chemical theory of the pile.

His third great discovery is the magnetisation of light,
which I should liken to the Weisshorn among mountains—
,dwgh, beautiful, and alone.

•v. The dominant result of his fourth group of researches is the
Discovery of diamagnetism, announced in his memoir as the
These pages form the " Summary " and the concluding passages of

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