John Ellicott, F.R.S., 1706-1772 is considered one of the greatest 18th. century British clock and watch makers. His highly successful career was attributable to his scientific invention and the consistant high quality of all of his work which can only be said of the great clockmakers. Ellicott is principally remembered for two things, the development of the ruby cylinder escapement and his experiments on the pendulum - in particular the gridiron. In 1752 he presented a paper to the Royal Society Contrivances for preventing the Irregularity of Pendulums Asising from Temperature, published in the Philosophical Transactions. In it he claimed to have originated the principle of compensation. John Harrison, 1693-1776, had the same claim but stated that his idea was first. It was also claimed that George Graham, 1675-1751 was the first. Finally it was adjudged that Graham was the first inventor but that Harrison had constructed a pendulum on a similar principle quite unaware of Graham's own invention. It was further adjudged that Ellicott's version had no resemblance to either of them and was a great improvement!
Despite the excellent results from his pendulum few were made in comparison to the number of regular gridirons used by other contemporaries such as Mudge or Graham. The reason was presumably the cost, for the the bobs were constructed to the most exacting measurements and the micrometer adjustment device was a work of art in itself which one might fancifully like to believe is why Ellicott designed it with a glazed portal.
A similar, slightly later example, was sold in these rooms, The Samuel Messer Collection, 5 December, 1991, lot 35 for £77,000