England · Denison's double three-legged form developed and applied c. 1850s, notably for the Great Clock of Westminster (completed 1854)
Gravity Escapement (Denison Double Three-Legged Form)
Partially verifiedSolved a specific problem — maintaining pendulum regularity despite a variable and sometimes considerable load from external hands and weather — that earlier turret-clock escapements handled poorly.
A gravity escapement lets the pendulum receive its impulse from a small weighted arm that is itself raised by the going train and then allowed to fall onto the pendulum, isolating the pendulum's motion from direct variation in the driving force delivered by the train.
Denison's double three-legged version, developed for turret clocks exposed to variable wind loading on large exterior hands, became the standard escapement for precision tower clocks of significant size.
How to verify this yourself
Denison's own published writings (including his Rudimentary Treatise on Clocks and Watches) describe the escapement's design rationale directly; any specific patent claim should be checked against The National Archives' historical patent index under Denison's name before citation.
Manufacturers known to have used it
- E. J. Dent & Co. (Great Clock of Westminster)
- many subsequent large turret-clock makers
Related photographs
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No confidently matched photograph of this subject has been found yet. These photographs show a closely related record, and are not examples of the type described on this page.
Sources & references
- Denison, E. B. (Lord Grimthorpe), A Rudimentary Treatise on Clocks, Watches and Bells
- Antiquarian Horological Society, articles on the Denison gravity escapement
Where sources disagree, the disagreement is stated rather than resolved silently.