Editor’s Note: Today, we bring you the second part in the new series from Andrew Canter, the Greatest Horological Inventions of All Time. In this installment, Andrew examines the invention of the balance spring, a watchmaking advancement that not only charted a path for the watch industry, but can be said to have legitimately changed the world, enabling accurate, reliable, and portable timekeeping for the first time in human history. Who actually invented it, though, is still a matter of some debate, even after 350 years. 

You can find more of Andrew’s work at the Mr. Watchmaster website here.

Prior to the Balance Spring

Early watches were powered by a verge escapement which was the same type of movement used in the early clocks. The verge is the earliest known type of mechanical escapement that controlled its rate by allowing the gear train to advance at regular intervals or ‘ticks’. Verge escapements were used from the late 13th century until the mid-19th century in clocks and pocket watches.

Drawing of a verge escapement (bottom) and balance wheel (top) from an early pocket watch from an encyclopaedia c.1820

In the earliest watches a plain wheel, known as the balance, was used to control the rate of going of the mechanism. There wasn’t a consistent restoring force (such as a fusee), so consequently, its period of oscillation and, hence, the rate of the timekeeper were dependent on the driving force.

Oval verge escapement watch movement by William Petit, London, c.1630. Science Museum Group/The Clockmakers’ Museum © The Board of Trustees of the Science Museum

This resulted in poor timekeeping which often resulted in watches like the one above running at least +/- 30 minutes per day. Generally, owning a pocket watch in the 1600s was seen as a status symbol and demonstration of wealth.

Portrait of a Gentleman with a watch, c.1675. Science Museum Group/The Clockmakers’ Museum © The Board of Trustees of the Science Museum

This can be seen in the portrait of a Gentleman (above), where he is proudly displaying his pocket watch suggesting his scientific knowledge and wealth. The watch is likely to have been around fifteen-years old by the time the portrait was painted. 

The watch below is a silver astronomical watch made in London by Nathaniel Barrow in around 1660. It is very similar to the watch being shown above. Barrow became a Free Clockmaker in 1660, and Master of the Clockmakers’ Company in 1689.

Silver astronomical watch by Nathaniel Barrow, London, c.1660. Science Museum Group/The Clockmakers’ Museum © The Board of Trustees of the Science Museum

Invention of the Balance Spring

Controlling the oscillations of a balance with a spring was an important step forward in the history of timekeeping. English physicist Robert Hooke designed a watch with a balance spring in the late 1650s. I’ve had the pleasure of reading Robert Hooke’s diary from 1674 at the London Metropolitan Archives. I’ll be honest, it was a little difficult to read, but there were sketches and notes such as ‘Cutting Engine for Clockwork’ (see below). You really felt as if you could get inside his mind and the way he was thinking.

Extract from Robert Hooke’s diary dated. London Metropolitan Archive

There is some dispute as to whether the balance spring was invented by British polymath, physicist and inventor Robert Hooke or Dutch scientist Christiaan Huygens, with the likelihood being that Hooke first had the idea, but Huygens built the first functioning watch that used a balance spring. The discovery in 1991 of this unfinished application for a patent drawn up for Hooke between 1663 and 1665 does much to confirm his claim.

Robert Hooke’s application for a patent for the balance spring, London, c.1663. By kind permission of Bloomsbury Book Auctions

The introduction of the balance spring resulted in an enormous increase in the accuracy of pocket watches, to around 10 minutes per day, making them useful timekeepers for the first time. 

Hooke and Tompion

Thomas Tompion (1639-1713) was one of the greatest horologists of his time and is known as the ‘Father of English Clockmaking’. He came from a family of blacksmiths, but it is not known who taught him his exceptional skills. He joined the Clockmakers’ Company as a specialist turret clockmaker but was soon taken up by Robert Hooke. At this time Hooke was at his most influential as Professor of Geometry at Gresham College, Curator of experiments at the Royal Society, architect and Surveyor of the City after the Great Fire. 

Hooke and Tompion met frequently in coffee houses and at Gresham College, Bishopsgate, where Hooke introduced him to the great intellectuals of the period, including Christopher Wren, Jonas Moore and the Astronomer Royal John Flamsteed. Hooke’s hugely significant invention of the balance spring for watches led to Tompion’s first audience with Charles II. Tompion’s connections, superb craftsmanship, innate business skills and mechanical ingenuity allowed him to build up a substantial business and was elected Master of the Clockmakers’ Company in 1703.

The Balance Spring Effect

The application of a balance spring to a watch, which had the effect of greatly improving its timekeeping, was independently developed by both Robert Hooke and Christiaan Huygens, with Huygens patenting a watch with his design in 1675. Hooke denied Huygen’s invention, claiming that he had devised it in London in 1658.

Robert Hooke’s balance and spring, London, 1675. Guildhall Library

To prove his prior claim to the invention of the balance spring, Robert Hooke immediately commissioned Thomas Tompion to make a watch containing the device, which was signed ‘R. Hooke invenit an. 1658. T. Tompion fecit 1675’. In his diary Hooke drew the sketch shown above, noting “Tompions, I shew’d my way of fixing Double springs to the inside of the Balance wheel thus”.

Early balance spring watch movement with a quarter-repeating mechanism of early design by Thomas Tompion. Science Museum Group/The Clockmakers’ Museum. © The Board of Trustees of the Science Museum

The balance spring, also referred to as the hair spring, works with the balance wheel to regulate the timekeeping mechanism of a watch or clock, providing a consistent oscillatory motion that enhances precision. This invention was a major advancement in horology, laying the groundwork for subsequent developments in timekeeping technology.

Typical components of a mechanical watch with balance spring. Encyclopaedia Brittanica.

The balance spring made it possible to create portable timepieces that could maintain accurate time while being carried around. Also, accurate portable timepieces enabled advancements in navigation, particularly for maritime navigation. Marine chronometers, which relied on balance springs, allowed sailors to determine longitude with greater accuracy, revolutionising sea travel and trade.

The refinement of the balance spring enabled further innovations in horology. It led to the development of more sophisticated escapements and other components that enhanced the performance and reliability of timepieces. It greatly contributed to economic growth and created demand for skilled watchmakers driving the development of watchmaking industries, particularly in countries like Switzerland, which became renowned for their high-quality timepieces.

Accurate timekeepers allowed for the synchronisation of activities, improved punctuality, and played a role in the industrial revolution by enabling the coordination of work schedules. The balance spring facilitated advancements in scientific research that required precise time measurement, such as astronomy and physics with accurate timekeeping being essential for experiments and observations that contributed to our understanding of the natural world.

Let’s Not Forget About Huygens

The debate will rumble on and while Christiaan Huygens is often credited with the balance spring’s invention in 1675, there is strong evidence to suggest that Robert Hooke played a significant role in its development.

Christiaan Huygens (April 14, 1629-July 8, 1695), a Dutch natural scientist

It is probable that Hooke’s work on the balance spring was part of his broader investigations into the mechanics of motion and his interest in improving timekeeping devices. He had a long-standing interest in horology and had communicated his ideas to several contemporaries. Despite these claims, Huygens is generally recognised for the invention due to his published work and successful implementation of the balance spring in practical timepieces. Thus, while Huygens is typically credited with the invention, Hooke’s contributions are acknowledged as an important part of the history of the balance spring.

Overall, the balance spring has had a profound and far-reaching impact on timekeeping technology, navigation, industry, and daily life, driving both technological and social progress.