19th century rolling ball chronometer

Unlike the popular pendulum clock 200 years ago, inventor William Congreve's clock measured time by the movement of a small ball.

How the rolling ball clock works. (Video: Vimeo).

In the early 19th century, most clocks measured time through the regular swings of a pendulum. However, English inventor William Congreve (1772-1828) created an unusual clock with the ability to measure time using a small ball.

The Congreve rollerball clock has a brass plate engraved with zigzag lines. A small copper ball rolls along a zigzag groove and follows the tilt of the copper plate. At the end of the groove, the ball hits the lever and the spring causes this end of the copper plate to be raised, reversing the tilt and pushing the ball back. The lever also moves the clock hand a distance equal to the time it takes the ball to roll on the groove. In most versions, this period is 15 seconds, but in some larger watches this period can be as long as a minute.

Although Congreve is often credited with inventing the rolling ball clock, his design was not the first . French inventor Nicolas Grollier de Servière and German watchmaker Johann Sayller each made such clocks in the 17th century.

Rolling ball clock.

Some people believe that Congreve did not know about the existence of these designs, but according to Mark Frank, who operates a website about vintage watches, Congreve may have adopted some details from Johann Sayller's watches, especially since both designs use zigzag lines (Grollier's rolling ball clock uses straight lines). One difference is that Sayller's design uses multiple balls and a fixed flat plate instead of a ball and inclined plate like the Congreve.

The accuracy of rolling ball clocks is easily affected by external factors. Setting the clock requires extreme precision. In 1837, the staff responsible for keeping time with the rolling ball clock at Buckingham Palace described it as the most complicated and troublesome machine.

Darren Cox, a technology conservator at the National Museums of Scotland, also struggled with a watch for two months. "The clock and tilt plate (front and back) need to be perfectly balanced. I found that, even with the temporary cover I made to keep out the dust, the metal ball still needed to be polished for at least two weeks once to remove debris ," he explains.

"However, the biggest task in getting the watch working is to adjust any previously warped and twisted levers and plates. The slightest mistake will stop the ball from rolling, and if it doesn't roll fast enough, it also would not be possible to initiate the chain reaction and lift the inclined plate ," he added.

Dust is also a huge problem. The time it takes the ball to roll downhill varies greatly depending on the cleanliness of the groove and the ball. In addition, the metal expands or contracts as the temperature increases or decreases, causing the groove length and size of the ball to change. Darren Cox found that the ball clock can be off by up to 45 minutes a day. But although they are not reliable time measuring tools, they are beautiful and have an interesting way of working that attracts observers.