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A gun chronograph is an instrument used to measure the velocity of a projectile fired by a gun. ==History== Benjamin Robins (1707-1751) invented the ballistic pendulum that measures the momentum of the projectile fired by a gun. Dividing the momentum by the projectile mass gives the velocity. Robbins published his results as ''New Principles of Gunnery'' in 1742. The ballistic pendulum could make only one measurement per firing because the device catches the projectile.〔, "only one observation on each round".〕 The gun's accuracy also limited how far down range a measurement could be made.〔, "Beyond 295 feet the gun was not sufficiently accurate".〕 An early chronograph that measures velocity directly was built in 1804 by Grobert, a colonel in the French Army. This used a rapidly rotating axle with two disks mounted on it about 13 feet apart. The bullet was fired parallel to the axle, and the angular displacement of the holes in the two disks, together with the rotational speed of the axle, yielded the bullet velocity.〔 at page 42 abridged from ''Journal des Mines'' No 92 p. 117, May 1804.〕 describes Bashforth's chronograph that could make many measurements over long distances: : In 1865 the Rev. Francis Bashforth, M. A., who had then been recently appointed Professor of Applied Mathematics to the advanced class of artillery officers at Woolwich, began a series of experiments for determining the resistance of the air to the motion of both spherical and oblong projectiles, which he continued from time to time until 1880. As the instruments then in use for measuring velocities were incapable of giving the times occupied by a shot in passing over a series of successive equal spaces, he began his labors by inventing and constructing a chronograph to accomplish this object, which was tried late in 1865 in Woolwich Marshes, with ten screens, and with perfect success. The Bashforth screens were made with several threads and series connected switches. A projectile passing through a screen would break one or more threads, the broken thread caused a switch to momentarily (about 20 ms) interrupt a current as the switch arm moved from its weighted position to its unweighted position, and the momentary interruption would be recorded on a paper chart. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「gun chronograph」の詳細全文を読む スポンサード リンク
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