Clepsydras, or water-clocks, had been tried, but they were deficient in accuracy.

Of one of them, ornamented with the signs of the zodiac, and destroyed by certain primitive Christians, St.Polycarp significantly remarked, "In all these monstrous demons is seen an art hostile to God." Not until about 1680 did the chronometer begin to approach accuracy.

Hooke, the contemporary of Newton, gave it the balance-wheel, with the spiral spring, and various escapements in succession were devised, such as the anchor, the dead-beat, the duplex, the remontoir.

Provisions for the variation of temperature were introduced.

It was brought to perfection eventually by Harrison and Arnold, in their hands becoming an accurate measure of the flight of time.