"In 1851 the astronomer Jean Bernard Leon Foucault, while working
on a conical pendulum clock to regulate a telescope drive, realized that
with an ideal pendulum supported at the north pole "the motion of the
earth, which forever rotates from west to east, will become appreciable in
contrast with the fixity of the plane of oscillation". Although he further
wrote that "when our latitudes are approached, the phenomenon becomes
complicated in a way that is rather difficult to appreciate", he did intuit
that the effect would be proportional to the sine of the latitude. His
first experiments were with a 2 m pendulum in his basement but he quickly
went on to construct a 67 m pendulum at the Pantheon in Paris. This
pendulum created a sensation at the Paris exhibition in 1851 and generated
both a flood of experiments around the world and an enormous scientific
literature. In the autumn of 1995, the 28 kgm iron sphere used by Foucault
was dusted off and again rehung from the Pantheon dome as in 1851."
"In describing his experiments in 1851 Foucault noted he was aware
of a 1837 paper on the deviation of projectiles in which Poisson used the
calculations of his student Coriolis from 1831 on accelerations in rotating
frames of reference. Poisson thought the effect unobservable but Foucault
clearly understood that "a pendulum has the advantage of accumulating the
effects". The experiment was crucial to the development of mechanics; it
established the force concept of Coriolis as useful and the subsequent work
cleared up misconceptions people had on the effect of the rotation of the
earth on air flow in the atmosphere."