James Clerk Maxwell (1831-1879)

                  of Edinburgh, Session 1879–80.

335

depending as they do on Laplace’s equation, were best symbolised
by the quaternion notation with Hamilton’s ∇ operator; and in conse-
quence, in his work on electricity, he gives the expressions for all the
more important physical quantities in their quaternion form, though
without employing the calculus itself in their establishment. I have
discussed in another place (“ Nature,” vol. vii. p. 478) the various im-
portant discoveries in this remarkable work, which of itself is suffi-
cient to secure for its author a foremost place among natural philo-
sophers. I may here state that the main object of the work is to do
away with “ action at a distance,” so far at least as electrical and mag-
netic forces are concerned, and to explain these by means of stresses
and motions of the medium which is required to account for the
phenomena of light. Maxwell has shown that, on this hypothesis, the
velocity of light is the ratio of the electro-magnetic and electro-static
units. Since this ratio, and the actual velocity of light, can be
determined by absolutely independent experiments, the theory can
be put at once to an exceedingly severe preliminary test. Neither
quantity is yet fairly known within about 2 or 3 per cent., and the
most probable values of both certainly agree more closely than do the
separate determinations of either. There can now be little doubt
that Maxwell’s theory of electrical phenomena rests upon founda-
tions as secure as those of the undulatory theory of light. But
the life-long work of its creator has left it still in its infancy, and
it will probably require for its proper development the services of
whole generations of mathematicians.

The next in point of date of Maxwell’s greatest works is his
“Essay on the Stability of Saturn’s Rings, ” which obtained the Adams’
Prize in 1859. In this admirable investigation he shows that it is
dynamically impossible that these rings can be solid, and also that
they cannot be continuous liquid masses; the only other available
hypothesis, viz., that they consist of multitudes of discrete parts,
each a satellite, must therefore be the correct one.

Another subject which he treated with great success, as well
from the experimental as from the theoretical point of view, was
the Perception of Colour, the Primary Colour sensations, and
the Nature of Colour Blindness. His earliest paper on these
subjects bears date 1855, and the seventh has the date 1872. He
received the Rumford Medal from the Royal Society in 1860,