Electro-ballistic apparatus for measuring the speed of cannon-shot, 1864

Electro-ballistic apparatus for measuring the speed of cannon-shot, 1864. Apparatus invented by Major Navez, of the Belgian Artillery. 'Upon the gun being fired, the projectile cuts the wires of the first screen, and thus demagnetises the electro-magnet which holds up the pendulum. This latter commences to fall, and the index-needle with it along the graduated arc. When the second screen is cut through by the shot, the electro-magnet at the top of the conjunctor is demagnetised, and the weight falls into the mercury pressing down the steel blade, and completes another electric circuit, which magnetises the large magnet in rear of the pendulum, and clamps the index-needle against the scale on the arc. The operator then reads off the scale the distance which is marked by the index, and the time thus measured is that which the shot took to pass through the screens, minus the time necessary for the weight to fall in the conjunctor, and which the operator, before commencing, finds by means of the disjunctor...a skilful operator is able to measure...to the three-thousandth part of a second. Such wonderful precision renders this instrument most valuable for artillery scientific purposes'. From "Illustrated London News", 1864. Creator: Unknown. (Photo by The Print Collector/Heritage Images via Getty Images)