Technical: Gears

By Kayleigh Hutchins

07 Jun 2016

The next time you’re out for a stroll this summer, take a closer look at the leaves of the plants you pass along the way and you might catch a glimpse of an insect by the name of Issus coleoptratus. Brownish-black, wingless and seemingly insignificant, this little bug is the owner of a big evolutionary asset. The joints of a juvenile Issus’ hind legs have cog-like teeth—when the insect jumps, the teeth intermesh and rotate, keeping its legs in synch and enabling more energy efficient jumps.

But what’s this common European insect got to do with watches? This isn’t a natural history magazine, I hear you cry. Well, the discovery of the Issus’ leg cogs was the first example of gears that we have found in the natural world. We had previously believed them to be a man-made creation—but as it turns out, evolution had mastered the technique long before we ever could.

Issus coleoptratus

The cog-like hind legs of the Issus coleoptratus are the first example of gears discovered in the natural world

The earliest examples of man-made gears come from 4th century BC China, while over in Europe a century later, legendary polymath Archimedes was developing his own concepts for gears, supposedly inventing an odometer during the First Punic War that featured a gear mechanism. It would take until the 11th century for gears to be applied to clockmaking, when engineer Ibn Khalaf al-Muradi invented a water clock that made use of an intricate gear train. Gears would go on to become an integral part of a watch’s mechanics.

The gear mechanism, in its simplest form, remains the same whether it’s biological or mechanical. The ‘teeth’ of the Issus’ hind legs lock together as it moves, ensuring precise synchronisation of the energy passing through both legs as it launches into a jump. This same principle is used within the movement of a watch, where the gear train is used as means of transferring power from the mainspring to the escapement (which, as we have previously seen, prevents the energy from escaping all at once.)

Gear train

The gear train of a mechanical timepiece, as the gears would be arranged inside of a clock

The gears function to scale up the speed of the slow-turning mainspring, allowing it to power the watch for several days before it needs to be wound again—and it’s to the mainspring that the first wheel in the gear train is attached. The spring turns, causing the wheel to rotate, which then in turn moves three successive wheels.

This is where the second main function of the gears comes into play. The second wheel in the sequence is attached to the minute and hour hands, while the fourth wheel—the last in the train—drives the escapement, which returns the energy in regulated amounts and enables the watch to keep accurate time.

Most mechanical watch movements are standardised, without much variance in the parts and technique used. It’s a feat of engineering that took mankind thousands of years to master; without gears, the earliest clockmakers would have had much more trouble realising their ideas. It’s just a shame we’ve only now realised that Mother Nature got there first.