The first mechanical device that accurately measured time in seconds was the marine chronometer. Invented by John Harrison in the 18th century, specifically around 1730, the marine chronometer was designed to provide accurate timekeeping for maritime navigation. It was an essential instrument for determining longitude at sea.
The marine chronometer consisted of a highly precise mechanical clock that was resistant to the motion and variations in temperature encountered on ships. By using a balance wheel or a pendulum to regulate its movement, the chronometer provided a reliable reference for measuring time with seconds accuracy.
Before the invention of the marine chronometer, various other devices were used to measure time, but they were not as accurate or portable. Sundials, water clocks, and hourglasses were among the earliest timekeeping devices used by humans. These devices could track hours, but not seconds, and were less precise compared to the marine chronometer.