7 Christiaan Huygens 7apartment in its building. Apart from occasional visits to
Holland, he lived from 1666 to 1681 in Paris, where he
made the acquaintance of the German mathematician and
philosopher Gottfried Wilhelm Leibniz, with whom he
remained on friendly terms for the rest of his life. The
major event of Huygens’s years in Paris was the publication
in 1673 of his Horologium Oscillatorium. That brilliant work
contained a theory on the mathematics of curvatures, as
well as complete solutions to such problems of dynamics
as the derivation of the formula for the time of oscillation
of the simple pendulum, the oscillation of a body about a
stationary axis, and the laws of centrifugal force for uniform
circular motion. Some of the results were given without
proof in an appendix, and Huygens’s complete proofs were
not published until after his death.
The treatment of rotating bodies was partly based on
an ingenious application of the principle that in any system
of bodies the centre of gravity could never rise of its own
accord above its initial position. Earlier Huygens had
applied the same principle to the treatment of the problem
of collisions, for which he had obtained a definitive solution
in the case of perfectly elastic bodies as early as 1656,
although his results remained unpublished until 1669.
The somewhat eulogistic dedication of the Horologium
Oscillatorium to Louis XIV brought to a head murmurs
against Huygens at a time when France was at war with
Holland, but in spite of this he continued to reside in Paris.
Huygens’s health was never good, and he suffered from
recurrent illnesses, including one in 1670 which was so
serious that for a time he despaired of his own life.
A serious illness in 1681 prompted him to return to
Holland, where he intended to stay only temporarily. But
the death in 1683 of his patron, Jean-Baptiste Colbert,
who had been Louis XIV’s chief adviser, and Louis’s
increasingly reactionary policy, which culminated in the