Invention of the Balance Spring On 20 January 1675, Dutch scientist Christiaan Huygens published a letter in the the Journal des sçavans that provided details and a diagram of his invention, the flat balance spring. His design was made of a spiral spring that attached to the balance wheel of a watch. It achieved true oscillation by controlling the speed at which the wheels turn and regulating the movement of the hands. This was a breakthrough in watchmaking as Huygens’ design greatly increased the accuracy of portable timepieces. When Huygens’ letter was published, English polymath Robert Hooke was enraged, as he had been independently grappling with the design of a spiral balance for the same purpose. Hooke insisted that he had revealed this very invention to the Royal Society five years earlier and accused Huygens of stealing his idea. Yet, Hooke could not substantiate his claim because his notes of the Royal Society meetings during that period could not be found. Without proof to support his assertions, Huygens was credited for the invention of the balance spring for roughly 300 years. In 2006, Hooke’s notes of the minutes of the Royal Society meetings for the years 1660–1682 were found in a cupboard during a house valuation in Hampshire, England. The entry for 23 June 1670 reads: The curator [Hooke] produced a pocketwatch of a new contrivance devized by himself, which he affirmed should goe as equally as a pendulum, and without stopping, and might be made to goe for 8 days. While this proves that Hooke was indeed working on his own design to improve the accuracy of watches, Hooke’s spiral balance design theoretically had great potential but did not have practical application; theory did not meet practice in this instance. Thus, it is Huygens who is still widely credited with the invention. Image Credits Balance wheel of watch with spiral balance spring. PRIVAT-DESCHANEL et FOCILLON. Uploaded by Jean-Jacques MILAN, Public domain, via Wikimedia Commons Note on pocketwatch by Robert Hooke, 23 June 1670. Taken from the Hooke Folio, draft and copy minutes of Royal Society meetings. MS/847 page 81 ©The Royal Society
