iments on optics. It is specially to be
noted that at this time, at the age of twenty-four, Newton had laid the
foundations of all his greatest discoveries:--

[Illustration: FIG. 66.--Newton's telescope.]

The Theory of Fluxions; or, the Differential Calculus.

The Law of Gravitation; or, the complete theory of astronomy.

The compound nature of white light; or, the beginning of Spectrum
Analysis.

[Illustration: FIG. 67.--The sextant, as now made.]

His later life was to be occupied in working these incipient discoveries
out. But the most remarkable thing is that no one knew about any one of
them. However, he was known as an accomplished young mathematician, and
was made a fellow of his college. You remember that he had a friend
there in the person of Dr. Isaac Barrow, first Lucasian Professor of
Mathematics in the University. It happened, about 1669, that a
mathematical discovery of some interest was being much discussed, and
Dr. Barrow happened to mention it to Newton, who said yes, he had worked
out that and a few other similar things some time ago. He accordingly
went and fetched some papers to Dr. Barrow, who forwarded them to other
distinguished mathematicians, and it thus appeared that Newton had
discovered theorems much more general than this special case that was
exciting so much interest. Dr. Barrow, being anxious to devote his time
more particularly to theology, resigned his chair the same year in
favour of Newton, who was accordingly elected to the Lucasian
Professorship, which he held for thirty years. This chair is now the
most famous in the University, and it is commonly referred to as the
chair of Newton.

Still, however, his method of fluxions was unknown, and still he did not
publish it. He lectured first on optics, giving an account of his
experiments. His lectures were afterwards published both in Latin and
English, and are highly valued to this day.

The fame of his mathematical genius came to the ears of the Royal
Society, and a motion was made to get him elected a fellow of that body.
The Royal Society, the oldest and most famous of all scientific
societies with a continuous existence, took its origin in some private
meetings, got up in London by the Hon. Robert Boyle and a few scientific
friends, during all the trouble of the Commonwealth.

After the restoration, Charles II. in 1662 incorporated it under Royal
Charter; among the original members being Boyle, Hooke, Christopher
Wren,