We give here details of Gregory's astronomical clock which hung in the Upper Hall of the University Library. The text was prepared by Turnbull for the occasion of the Tercentenary:-
Gregory's astronomical clock
This astronomical timepiece was made for James Gregory by Joseph Knibb, the well-known London clockmaker, who had worked for a time in Oxford. At Windsor Castle is a clock made by Knibb which bears the date 1677, and on July 3rd, 1682, Charles Il ordered payment of £141 to Knibb for work on the clock. The clock made for James Gregory cannot be dated with absolute certainty but it was probably acquired with the instruments and utensils which the University commissioned him to purchase in London in 1673. Joseph Knibb is mentioned by A J S Brook (Proc. Soc. Ant. Scot. 3 ser., vol. 11, 1901) who alludes to a bracket timepiece belonging to Archbishop Sharp, and also to three timepieces in the University Library, St Andrews.
Originally the clock was a bracket wall timepiece, and no doubt when first brought to St Andrews it hung from the wall of what is now the second window on the south side of the Upper Hall. At an early date, probably before the Upper Hall was heightened and the gallery added, the clock was converted to a long-cased timepiece by the addition of a narrow-waisted trunk measuring 6 3/4 inches in width, and a base.
The hood of the clock-case is square, surmounted by a triangular pediment, and measures over all 15 inches in height. Access to the movement is obtained by sliding up the hood. The dial is of brass, the time being registered on two silverised circles. The smaller circle, enclosed within the other, is engraved with the hours in Roman numerals. The larger circle is divided into sixty seconds, each of which is sub-divided into three, as the pendulum beats thirds of seconds. There is no minute hand. The movement of the clock is of simple construction and contains only three wheels with an ordinary tick-tack escapement driven by a weight, suspended on a slender chain, which requires to be pulled up every twenty-four hours. The pendulum is supported at the back on a knife-edge.
When Gregory left St Andrews for Edinburgh in 1674 the clock must have been almost new. How long it remained in good order after his departure is not known, but it was repaired in 1850 and was then said to have been silent for upwards of a century. It seems likely that in process of being recased the mechanism was affected. It is now in good order but the extreme slenderness of the chain must always be a deterrent to its constant use.