Inventor of the Chronograph
The recent discovery of a hitherto unknown timepiece is rewriting the history of watch development. It turned out to be the first ever chronograph, although its maker, Louis Moinet, called it a Compteur de Tierces. According to hallmarks on the dust cover, the chronograph was started in 1815 and completed the following year.
Setting his sights on the stars
Moinet made the timer for an astronomical transit instrument, originally mounted for use at sea, that he had adapted to track the movement of heavenly bodies from land.
According to a letter he wrote in 1823:
“I came to Paris in 1815 with the sole purpose of devising and making a Compteur de Tierces. The difficult and seldom attempted realisation of this instrument featuring a new construction has achieved my purpose most satisfactorily.”
Why did Moinet need such high frequency ? He was timing the passage of stars, planets and even planetary moons. A frequency of 216,000 v/h imparted 60 vibrations a second, thus dividing the second into sixtieths. He made the compteur initially to set the precise distance between the crosshairs in his telescope, as he describes in his Traité d’Horlogerie (1848):
“ This invention came to me during my observations in the following circumstances. I had acquired a small mobile quadrant by the famous Borda (maker of the repeating circle). This fifinely English-made instrument was balanced on rubies, and its maker supposed that an ingenious system of counterweights would preserve it via its own inertia from the motion of the ship, thereby providing observations at sea almost as exact as those obtained on land. But the project was not successful.”
“ Having acquired the instrument for ano-ther purpose, I added – for terrestrial observations – an azimuth circle with a graduated Vernier scale by the late Fortin, two intersecting levels, a polished mobile axis and a threefooted stand with levelling screws and a scale etc. Nonetheless, the scope’s narrow field of vision put the reticule lines very close together, and it was to remedy this inconvenience of failing to see a line, that I thought up the Compteur de Tierces, which worked very well by giving me a precise distance between the reticule lines.”
Moinet’s compteur had to function for at least 24 hours at an energy-hungry frequency to time successive transits of a star. To minimise energy consumption, his escapement ran on oiled rubies. He reported that it had worked very well for a prolonged period.