Jeremy Evans, Thomas Tompion at the Dial and Three Crowns, AHS, 2006; R.W.Symonds, Thomas Tompion, His Life and Work, Batsford, 1951.
The present clock is unusual and of particular interest in the context of Tompion's wider oeuvre because it is of his phase I design, although it was clearly finished during his phase II period. As such, it is one of a most interesting group of clocks whose finishing post-dated the introduction of his second-phase spring clock. Prior to this momentous advance in design Tompion's most popular spring clock model was the eight day timepiece with pull-quarter repeat, sales of which outnumbered those of striking clocks by a ratio of almost 2:1. All of these earlier phase I items -- clocks and timepieces -- had a simple knife-edge verge escapement with pear-shaped pendulum bob.
The phase II movement was introduced to eliminate the need for an owner to move the clock in order to regulate, silence, or start it. To regulate the phase I movement it had been necessary to turn the clock, open the back door, and screw the pendulum bob up or down its threaded rod. After regulation, or when re-starting the clock at any time, it was necessary to hold the clock and apply a sideways jolt. The new phase II movement incorporated a spring-suspended pendulum with lenticular bob, and with the new phase II dial an owner could regulate the clock via rise-and-fall using one of the subsidiary rings, and silence it from the other. A facility to restart the clock was also provided in the dial -- the mock-pendulum aperture -- whereby a tiny false bob was given a gentle sideways nudge.
Following the introduction of the phase II movement, the eight day spring clock with phase II dial became the standard table clock available to customers -- there was no other standard model available. Thereafter, simple phase I timepieces and phase I clocks -- which did not have subsidiary dials -- were rarely supplied.
Tompion was a prudent businessman as well as a skilled horologist and there is ample evidence that once he had settled upon a design he would remain faithful to it, with little or no modification, for several years. This enabled him to build up stocks of cast brass components -- cocks, bridges, plates and dials, as well as cases -- in the belief they would not be wasted. When the phase II movement, dial and case were introduced, therefore, it is likely that he still had in stock the cases for over a dozen phase I timepieces or clocks, as well as the components of several timepiece movements. It is these components which were used in the finishing of the interesting group of items which includes this clock, No.238.
Whether the finishing of these items was the result of customers asking for clocks of the earlier, less complicated design, or of Tompion's desire to realise the outlay which had already been expended on stock components, is not clear. Either way, it is believed that clocks such as No.238 do incorporate superseded components -- cases, movements and dials -- which had become stranded in stock.
No.238 is closely comparable with another example, No.291, both of which incorporate components intended for use in timepieces. Both of the dials originally had a single winding hole and in both instances, with new sets of winding holes added, the superfluous central hole has been utilised for date indication. These are the only recorded examples of circular date apertures on Tompion's spring clocks, along with that of No.92, another timepiece movement which was not finished as originally intended, and which also had a superfluous winding hole. Perhaps what is most surprising is the fact that it seems that the back plate had not even been drilled and pillared -- only its upper corners had been chamfered -- when it was left in stock, and there is evidence that the front plate had been intended for another movement arrangement. Apart from the going train with knife-edge verge escapement -- incorporating earlier stock components -- the movement, and especially the repeating mechanism, is stylistically closely comparable with the work in his Phase II movements which were finished at about the same time. The engraving of the back plate was by 'Graver 195' whose work is mostly found on clocks numbered between c.220-320.
We are grateful to Mr Jeremy Evans for his assistance with this footnote.