Once upon a time, in the days of sundials and pendulum clocks, people needed a way to agree on the time. For instance, if my watch says 11:13 and your watch says 1:32, who's right? One way to coordinate time in a city or a sea port was a time ball placed somewhere highly visible. People could use the ball to set their pocket watches, and use their pocket watches to set their other clocks.
Here's how time balls worked, from the Cincinnati Observatory:
Precisely 15 minutes before noon, the ball was raised, using a windlass, to half-mast, and, at 5 minutes to noon, the ball was lifted to the top, providing viewers with 15-minute and 5-minute advance notices. At astronomical noon in Cincinnati, the ball dropped free- fall style. A hand-operated Prony friction brake allowed the ball to stop gently before the end of its 30-foot travel.
Set your pocket watch to precisely noon with the stem out. When the ball drops, drop the stem. If you kept your watch wound, you'd have fairly accurate time for a few months.
New York City used the ball-drop method of time coordination to ring the new year and to promote Edison's lightbulbs. Since the whole point of the ball drop was visibility, there'd be no value to a midnight ball-drop unless the ball was lighted.
The first NYC New Year's ball was covered in 100 lightbulbs. You could set your watch by it.
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