Williamson invents the equation clock Even after the invention of the domestic pendulum clock in 1656, all clocks still had to be set locally by referencing a sundial. As the sundial indicated solar time, the clock owner was then obliged to consult an Equation of Time table to calculate the conversion of apparrent solar time to mean time, which facilitated the setting of their clock to the correct local time. These Equation of Time tables were typically printed on paper or engraved upon the pate of a sundial. Eventually, the task of converting solar to mean time was mechanised by clockmakers. Clocks with these early equation mechanisms are called equation clocks, because they include a mechanism that simulates the Equation of Time calculation so that the user can read or calculate solar time. In a letter to the Royal Society, written around 1715, the clockmaker Joseph Williamson (who had worked for Daniel Quare) suggests that he was the father of all equation mechanisms. In it, he claims I have made others for Mr Quar(e), which showed Apparent Time by lengthening and shortening the Pendulum in lifting it up and setting it down again, by a Rowler somewhat in the form of an Ellipsis, through a slit in piece of brass, which the spring at the top of the pendulum went through. Clockmaker John Shelton the Younger made one of the earliest surviving examples of a clock with an equation mechanism in its final and most complicated form. This is the Teiger Shelton Solar Longcase, which is dated to 1736 and exhibited here on Clocktime. Reference Williamson, J. 1753 ‘A Letter of Mr. Joseph Williamson Watchmaker, to the Publisher, Wherein He Asserts His Right to the Curious and Useful Invention of Making Clocks to Keep Time with the Suns Apparent Motion.’ in Philosophical Transactions of the Royal Society of London 30: 1080–1082. https://archive.org/details/philtrans05753149/page/n2/mode/2up?view=theater
