Gravity Escapement

...belongs to the free escapements of clocks on a tower and is the child of the genius Edmund Beckett Denison. It was first used on the monumental clock of Westminster Abby in London. Many escapements of this kind are equipped with a draught-excluder to reduce the speed of the escape wheel and therefore the strike of the tooth on the locking plates can take place a little smother. The variant shown here has oblique impulse planes on the gravity impulse pallets, to spread the angle of impulse to 45°.

Historical

In his book "Alte Uhren neu entdeckt" (old clocks newly discovered), Horst Landrock wrote about Big-Ben created by Edmund Beckett Denison (later on he called himself Lord Grimpthope!?)
[...]...For the tower of the London Parliament building, Baron Grimpthope constructed the famous Big-Ben-Clock with its Westminster quarter chimes. This clock was build 1859 and for a long time was known to be the most accurate time keeper. The daily allowance is only 1/10 sec. The Pendulum-bob weighs an impressive 310 kg. The diameter of the "face" is almost 7 m and the weight of the hand that shows the minutes weighs 28 kg. Nowadays the winding of the clock is done by an electric winding-mechanism within 40 min. In the olden days, two men had to do this in 5 hours of heavy-labour.