2-798-506 - The Print Collector/Heritage Images

The Time Ball, Royal Observatory, Greenwich, Fig. 5, 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. 5. The discharging trigger, placed in the first floor of the Time-ball apartments. m, iron discharging rod; n, trigger; o, axis of the trigger; p, spring for holding the trigger till the ball is dropped'. From "Illustrated London News", 1844, Vol V.