Pendulum the pendulum could be used to measure the force of gravity. During his expedition to Cayenne, French Guiana in 1671, Jean Richer found that a pendulum clock was minutes per day slower at Cayenne than at Paris. From this he deduced that the force of gravity was lower at Cayenne. In 1687, Isaac Newton in "Principia Mathematica" showed that this was because the Earth was not a true sphere but slightly oblate (flattened at the poles) from the effect of centrifugal force due to its rotation, causing gravity to increase with latitude. Portable pendulums began to be taken on voyages
Pierre-François-Victor Foucault Société d'encouragement pour l'industrie nationale, then he showed it at The Great Exhibition (1851) in London. Pierre-François-Victor Foucault Pierre-François-Victor Foucault (1797-1871) was the inventor in 1843 of the first printing machine for braille, the . A pupil of the Institut National des Jeunes Aveugles, Foucault married Thérèse-Adèle Husson, a blind author, in 1826. This marriage gave birth to two daughters. After his wife's death in 1831, following a fire, he married a seamstress (non blind) in 1832, Adélaïde Louise Juteau. This allowed him to become a resident of the Quinze-Vingts (marriages between blind people were prohibited), which gave him the