The legend Onésiphore Pecqueur
THE DIFFERENTIAL WAS INVENTED BY A WATCHMAKER
In 1823 Onésiphore Pecqueur was honoured with the Gold Medal of French Industry by the scientific community. His achievement, in the exact words of the jury, was having found “the solution to a problem of gear transmission, with degrees of speed expressed by prime numbers that exceed the number of teeth that can be cut on the circumference of the same wheel, while maintaining the necessary strength of those teeth.” Pecqueur first implemented this invention in a clock that featured two different dials: one displaying sidereal time and the other, mean time. The differential, invented in 1827, synchronised the rotation of drive wheels on the same axle as they turned a corner. The innovation was patented a year later, marking a pivotal moment for the development of the automobile. The story of a watchmaker who is thus generally considered to be the world’s first automobile engineer.
A child of the French Revolution and heir to the spirit of the Enlightenment, Onésiphore Pecqueur (1792-1852) was also a mechanical genius. While head of the workshop for the Conservatory of Arts and Crafts in Paris, he developed a gear mechanism known as the differential that is still used in countless industrial applications today.
The world’s first automotive engineer was a watchmaker :
Legend has it that he was a precocious student, completing his horological apprenticeship in Paris in just a few months rather than the generally required four years. In 1818 his name appeared on the rolls of the French Academy of Sciences. While there he proposed an ingenious mechanical solution for solving any equation involving two prime numbers, including numbers greater than six figures. This clear proof of talent aroused the interest of a number of academicians.
As he awaited the Academy’s final approval of his “mechanical equation”, he took part in the Exhibition of Products of French Industry of 1819 with a clock that displayed both sidereal time and mean time. The jury, which included one Abraham-Louis Breguet, awarded him a silver medal for inventing a gear that “maintains both communicating movements at acceptable rates of speed”.
Although at first glance it seems banal, this discovery was to have far-reaching repercussions, well beyond the horological sphere.
On 25 August 1823, the Palais du Louvre opened its doors to the fifth Exhibition of Products of French Industry. In the room devoted to “fine and ornamental horology”, the young Onésiphore Pecqueur exhibited his wares alongside Antide Janvier, Lépine, Perrelet and Rieussec. The jury agreed to award him the highest distinction in his category, the gold medal. His competitors had to be content with silver (the Berthoud brothers) and bronze (Rieussec).
As well as rewarding the watchmaker’s achievement, the medal also anticipated the many industrial applications that “Monsieur Pecqueur’s gears” were to have. “One can posit numerous benefits in correcting irregularities in the speed of a steam engine, a waterwheel, in distributing any resistance between two engines according to predetermined proportions; in sum, in solving a host of mechanical problems, the resolution of which is of direct interest to the industrial arts.” Pecqueur unveiled several concrete applications that connected gears to steam power, the new energy source that was to be the cornerstone of the nascent industrial revolution.
On 25 April 1828, “Pecqueur gears” were back in the news once again. Pecqueur registered a patent for a brand new steam carriage, which would earn him a place in the history of the motor car.
In practical terms, the drive of the carriage – a steam engine installed in the front – is transmitted to the two wheels on the rear axle by a central shaft. This is connected to the shafts of the two rear wheels via a “mechanism that directs the power to each wheel without affecting their independence” according to Pecqueur’s own description. And that was to become its most influential application: when rounding a bend, the inside wheel slows down while the outer one increases its speed to compensate.
His invention, later named the “mechanical differential” is widely employed by car manufacturers even today. There are very few inventions that originate in the world of watchmaking that can claim to have had a comparable impact.
