The word, ‘barometer’ derives from the Greek, ‘baros’, which means ‘weight’. Observations in the 16th Century and experiments by Galileo in the early 17th century with water as the recording medium were precursors of barometers. Mercury was first used in a barometric experiment in 1643 by Vincenzio Viviani in collaboration with a student of Galileo’s, Evangelista Torrecelli. They filled a thin glass tube with mercury, placed a finger over one end and submerged the other end into a pan of mercury. When the finger was removed, the mercury in the tube settled to a lower height in response to atmospheric pressure. The earliest mercury barometers are called, collectively, cistern or stick barometers, which are simply long glass tubes with the bottoms submerged in a cup filled with mercury. To improve precision, the angle tube barometer, also called the yardarm, diagonal, or sign post type was invented in 1670. The tube on this instrument extended 36 inches at a slight angle to the horizontal, thus a 3 inch vertical variation in the mercury level was recorded over a much greater vector, horizontally. The ‘aneroid’ was invented in 1843, revolutionizing barometer instrumentation. Lucien Vidie created a metallic pressure indicator in 1843 he called an ‘aneroid’, which means ‘dry’ or ‘without liquid', and effectively revolutionized the barometer. For the sensitive pressure detector he used a sealed brass box with a corrugated diaphragm supported by helical springs. A popular pocket-sized version, only 2.5 inches in diameter, was developed by Negretti & Zambra in 1860, and a type of aneroid barometer that graphs changes in barometric pressure on paper - the barograph - was developed about the same time.