functions of angles, were so much simplified that Laplace declared
that by this invention the life-work of an astronomer was doubled.

Jeremiah Horrocks (born 1619, died 1641) was an ardent admirer of
Tycho Brahe and Kepler, and was able to improve the Rudolphine tables
so much that he foretold a transit of Venus, in 1639, which these
tables failed to indicate, and was the only observer of it. His life
was short, but he accomplished a great deal, and rightly ascribed the
lunar inequality called _evection_ to variations in the value of
the eccentricity and in the direction of the line of apses, at the
same time correctly assigning _the disturbing force of the Sun_
as the cause. He discovered the errors in Jupiter's calculated place,
due to what we now know as the long inequality of Jupiter and Saturn,
and measured with considerable accuracy the acceleration at that date
of Jupiter's mean motion, and indicated the retardation of Saturn's
mean motion.

Horrocks' investigations, so far as they could be collected, were
published posthumously in 1672, and seldom, if ever, has a man who
lived only twenty-two years originated so much scientific knowledge.

At this period British science received a lasting impetus by the wise
initiation of a much-abused man, Charles II., who founded the Royal
Society of London, and also the Royal Observatory of Greeenwich, where
he established Flamsteed as first Astronomer Royal, especially for
lunar and stellar observations likely to be useful for navigation. At
the same time the French Academy and the Paris Observatory were
founded. All this within fourteen years, 1662-1675.

Meanwhile gravitation in general terms was being discussed by Hooke,