04/25/2026
Weekly Gem #207, Timing is Everything
This hidden gem is located at the intersection of Westminster Bridge and the River Thames in London, England.
When Big Ben was built in the mid 1800s, it was far and away the most massive gear-driven clock in the world. The clock maker himself (a brazen chap named Dent) didn’t know how to make this clock work at the time he submitted a proposal to do so. Fortunately for him, construction delays are nothing new. Building the clock tower took almost 5 years longer than planned, and by the time the clock was installed, a method was invented for his clock to keep time.
The solution was a Denison Double Three-Legged Gravity Escapement.
Thankfully, Denison became Lord Grimthorpe, his invention was renamed the Grimthorpe Escapement, and we need not mull over the "double three legged" part.
Needless to say, this isn’t your grandfather’s clock. But, consider a grandfather clock. It has a pendulum, which turns some gears at a precise pace. Those gears allow a weight to drop at an equally precise rate, and that weight is what turns the hands of the clock. Easy peasy. Of course, your grandfather clock is inside your house, and also inside a closed case. The pendulum and the clock face are enclosed because even a slight wind, or something miniscule resting on the hands, will reduce the accuracy of the clock, or even cause it to stop.
Big Ben has four clocks, each exposed (but differently) to wind, snow, ice, rain, and the occasional perching bird. For example, a west wind presses in on the hands on the west face, blows across the north and south faces turning the hands into ‘wings,’ and the east face is unperturbed (although that is probably where the bird will perch).
How to keep each clock on time, and showing exactly the same time?
The Grimthorpe Escapement was a stroke of genius. Details aside, this device kept the pendulum swinging exactly right, regardless of what outside influences were doing to speed up or slow down the hands.
Good enough, but that's not good enough. In the clock tower are three massive gear mechanisms, each made of dozens of cast metal parts which expand and contract with changes in weather. So, double three legs aside, the clocks were still prone to changing speed with the changing weather.
Dent determined that adding one penny to the pendulum raised the center of gravity ever so slightly, but enough to speed the clock by two fifths of a second per day. One penny equals two fifths.
Nowadays, Big Ben is tracked and monitored electronically, sensors scattered about. When the sensor shows the clock is running a bit off, the clockmaster goes down to the pendulum and places, or removes, one penny.
“The more that you read, the more things you will know. The more that you learn, the more places you'll go.” ~ Dr. Seuss
