Jean PicardDied 12 Jul 1682 at age 61 (born 21 Jul 1620). French astronomer, cartographer and hydraulic engineer who is regarded as the founder of modern astronomy in France. He introduced new methods, improved the old instruments, and added new devices, such as Huygens' pendulum clock to record times and time intervals. Picard was the first to put the telescope to use for the accurate measurement of small angles, making use of Gascoigne's micrometer. He devised a movable-wire micrometer to measure the diameters of celestial objects such as the Sun, Moon and planets. For land surveying and leveling, he designed instruments that incorporated the astronomical telescope. Picard was one of the first to apply scientific methods to the making of maps. Among his other skills were hydraulics; he solved the problem of supplying the fountains at Versailles with water. His most important work was the first measurement of the circumference of the earth. He used the method of Eratosthenes, but with greater accuracy. He greatly increased the accuracy of measurements of the Earth, using Snell's method of triangulation (Mesure de la Terre, 1671). This data was used by Newton in his gravitational theory. The concept behind neon signs began in 1675, when Picard observed a glow in a barometer. |
