In 1826 Eli Terry installed a $200 clock in the town hall of New Haven, Connecticut. All went well until townspeople noticed that the Terry clock was falling further and further behind the nearby Yale College clock. At first the Terry clock lagged, gradually losing some 15 minutes. Then it began to gain, eventually racing ahead of the Yale clock by 15 minutes before, over the course of weeks, gradually falling behind again.
Broken? Not likely. Terry was arguably the most distinguished clockmaker in America and among the earliest practitioners of uniform, interchangeable parts. Meanwhile, Yale’s clock had been designed by the talented Simeon Jocelyn, another favored son of Connecticut, and had been telling seemingly reliable time for years.
The difference—and it’s one we rarely consider today—is that Terry’s clock offered mean time—solid, consistent hours that reflected an average of the sun’s daily variation—while Jocelyn’s clock followed the sun itself. As Michael O’Malley writes in his book, Keeping Watch: A History of American Time, the question among the puzzled New Haven community was not “what time is it,” but “what is time?”