| Photos below show the escapement based on Thomas Reid's concept. This
design is a type of gravity escapement and belongs to a category of escapements called remontoire escapements. Where an escapement acts to
lift a small weight or bend a small spring always by equal amounts with each cycle of the
escapement. This differs from train remontoire that act independent of the escapement. The
escape wheel looks just like a conventional Graham type deadbeat escape wheel. The third
photo shows an exploded view. The two triangular shaped steel pallets each act to
alternatively lock the escape wheel and lift each gravity arm. The pendulum acts against
the lower portion of the gravity arms causing them to unlock the escape wheel. The flat
springs which hold the gravity arms require careful adjustment. They are not a passive
holding system, but exert a bit of downward force. However, adjusting too much force (by
straightening the spring) causes the escape wheel to occasionally jam up. Too little, and
the gravity arms will tend to bounce upon the impact of the escape wheel locking against
the pallet. This is especially dangerous with this kind of escapement as a slip of the
pallet could result in a 'runaway' causing damage to the escapement. The delicate springs
that hold the locking pallets are also subject to damage from a pendulum over-swing. This
was also a concern in Hardy's famous escapement. Overall, this was one of many attempts
that were made by many horologists in this period before Dennison has perfected his design
in 1860. It is not particularly distinguished as it still needs oil on the pallets, is
subject to tripping and catastrophic runaway. All of these which were overcome in
Dennison's design. For another pre-Dennison example of gravity escapement see Dent exhibition clock. This clock also employs
another type of remontoire known as a train remontoire. The second to the last photo shows the bell system hidden under the hood of the clock. The last photo shows the signature on the reverse of the porcelain dial. Anyone who can shed light on this signature would be most appreciated.
Notice the identical configuration of the locking pallets in the photo above and the drawing below. These perform the dual function of locking the escape wheel as well as the lifting of the gravity arm.
Escapement illustration by E.A. Ayres for C. Allix, 1949. Published in Horological Journal, August 1992, pp. 56 |
