formation of language, and are going on still. No doubt the feature
which strikes us first and most forcibly in any phenomenon, is the
pleasure or the pain which accompanies it, and the agreeable or
disagreeable results which follow after it. A theory of nature from
this point of view is embodied in many of our words and phrases, and
is by no means extinct even in our deliberate opinions.

It was a great step in science when men became convinced that, in
order to understand the nature of things, they must begin by asking,
not whether a thing is good or bad, noxious or beneficial, but of what
kind is it? and how much is there of it? Quality and Quantity were
then first recognized as the primary features to be observed in
scientific inquiry.

As science has been developed, the domain of quantity has everywhere
encroached on that of quality, till the process of scientific inquiry
seems to have become simply the measurement and registration of
quantities, combined with a mathematical discussion of the numbers
thus obtained. It is this scientific method of directing our
attention to those features of phenomena which may be regarded as
quantities which brings physical research under the influence of
mathematical reasoning. In the work of the Section we shall have
abundant examples of the successful application of this method to the
most recent conquests of science; but I wish at present to direct your
attention to some of the reciprocal effects of the progress of science
on those elementary conceptions which are sometimes thought to be
beyond the reach of change.

If the skill of the mathematician has enabled the experimentalist to
see that the quantities which he has measured are connected by