emoir "On the nature of the principle which enters into combination with
metals during calcination" appeared in 1775, and Cavendish's paper on the
composition of water did not see the light until 1784.

During the last quarter of the eighteenth century this new idea of oxygen
and oxidation was struggling into existence. How new was the idea, is
illustrated by the fact that Lavoisier himself at first spoke of that
which he was afterwards, namely, in 1778, led to call oxygen, the name by
which it has since been known, as "the principle which enters into
combination." What difficulties its acceptance met with is illustrated by
the fact that Priestley himself refused to the end of his life to grasp
the true bearings of the discovery which he had made.

In the year 1799 the knowledge of oxygen, of the nature of water and of
air, and indeed the true conception of chemical composition and chemical
change, was hardly more than beginning to be; and the century had to pass
wholly away before the next great chemical idea, which we know by the name
of the atomic theory of John Dalton, was made known. We have only to read
the scientific literature of the time to recognize that a truth which is
now not only woven as a master-thread into all our scientific conceptions,
but even enters largely into the everyday talk and thoughts of educated
people, was, a hundred years ago, struggling into existence among the
philosophers themselves. It was all but absolutely unknown to the large
world outside those select few.

If there be one word of science which is writ large on the life of the
present time, it is the word "electricity." It is, I take it, writ larger
than any other word. The knowledge which it denotes has carried its
practical results far and wide into our daily life, while the theoretical
conceptions which it signifies pierce deep into the nature of things. We
are to-day proud, and justly proud, both of the material triumphs and of
the intellectual gains which it has brought us, and we are full of even
larger hopes of it in the future.

At what time did this bright child of the nineteenth century have its
birth?

He who listened to the small group of philosophers of Dover, who in 1799
might have discoursed of natural knowledge, would perhaps have heard much
of electric machines, of electric sparks, of the electric fluid, and even
of positive and negative electricity; for frictional electricity had long
been known and even care