2-798-502 - The Print Collector/Heritage Images

The Time Ball, Royal Observatory, Greenwich, Fig. 1, 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. 1, exhibits an upright plan of the first, second, and third floors, on which the apparatus is placed...and a section of the turrets which carries the ball...the supporting shaft bearing the ball on its top and terminating below, at b, in a piston, which works in an air cylinder, d, and by which the too sudden descent of the ball is prevented....'. From "Illustrated London News", 1844, Vol V.