E56 – How They Work 1 – The Long History of Escapements (with David Flett)

In this episode, Allen and David finally go beyond the dial and start discussing how watches work. Well, that was the intention but David insists on starting at the beginning…

David explains that measuring time requires a regular, constant or repetitive physical phenomenon that can be counted or recorded in some way. Sundials are a useful starting point but they do not work when it is cloudy nor at night. They are accurate up to around 15 minutes per day which is the maximum deviation of a solar day from a regular day.

The oldest water clocks may have existed as long ago as 3500BC in China but there is clear documentary evidence that they were in use in Egypt by 1500BC. The earliest water clocks were simply large bowls where water flowed from one to the other taking a repeatable time to empty each time. Water clocks gradually became more accurate and more complex. It is as part of water clocks, that we find the first complications to display time visually or by chiming or ringing bells through the use of a waterwheel-type escapement.

The Clock of Andronicus Cyrrhestes, Athens – a three story structure that contained a large water clock and was adorned with multiple sun dials. Image credit: ESA

Water clocks prevailed for at least 3000 years until mechanical clocks were developed. The mechanical clock, like the water clock also used gravity to turn potential energy into kinetic energy but used falling weights instead of falling water. However, to turn the continuous kinetic energy into measurable events, an escapement was needed. The first description of a mechanical escapement comes from a 1327 manuscript describing an escapement created by Richard of Wallingford for the clock in St Albans abbey.

Richard of Wallingford’s ‘verge’ escapement mechanism.Image credit: University of British Columbia

An escapement basically stops and starts a continuous motion so that it can be used to measure time. The first type of mechanical escapement was the Verge escapement that David insists on calling the Burger King escapement because it relied on a distinctive crown wheel being stopped by a horizontal rod with two pallets.

Click to see Ken Kuo’s verge/foliot escapement animation on YouTube.

While the verge escape and foliot beam were popular, they did not provide the precision required. Robert Hooke in the mid-1600’s improves on the accuracy by combining the pendulums being using in Italian astronomy with his own ‘Anchor’ escapement to prove a step change improvement in accuracy. The same pendulum escapement is sometimes attributed to Dutch astronomer Huygens but contemporary reports state Hooke devised his escapement and a rudimentary balance wheel 10 years before Huygens. Modern versions of Hooke’s anchor escapement is still used today in grandfather clocks due to its inherent efficiency and accuracy.

The anchor escapement. Image credit: Wikipedia

In 1755, Thomas Mudge a successful English watchmaker invented the lever escapement and enabling the reduction in size of the pocket watches of the time and ultimately enabling modern watchmaking. Abraham-Louis Breguet improved on Mudge’s design. The lever escapement gave significant improvements in accuracy because it spends the majority of its time not in contact with the balance, thus minimizing the frictional losses.

The modern lever escapement. Image credit: Wikipedia

The image above shows how the red pallet stones alternately lock and then impulse the yellow escape wheel. The blue lever is moved left and right by an roller jewel attached to the balance wheel (not shown) rocking the upper end of the lever