2-798-505 - The Print Collector/Heritage Images

The Time Ball, Royal Observatory, Greenwich, Fig. 4, 1844. 'The hour of one o'clock is announced by the descent of a large black ball, from the summit of a pole, which surmounts the northwestern turret of the Observatory; a position singularly favourable for its exhibition to mariners on their progress down the adjacent river Thames. The apparatus...may be said to consist of a hoist for raising the ball, a trigger and discharging gear for its liberation, and a clock, regulated by observation, for giving the required moment of time....Fig. 4. Apparatus of the second and third floors: triangular supporting shaft; piston rod; cylinder; a weight, having a collar, which when raised by the chain, elevates the supporting shaft; iron guiding rods; catches for fixing the piston...; rod, by which the piston is set free from the grasp of the catches; cocks for regulating the discharge of air in the cylinder'. From "Illustrated London News", 1844, Vol V.