French corvette Aurore (1766)  Aurore was a corvette or snow, designed by Nicolas Ozanne. Built privately on the personal funds of François-César Le Tellier de Courtanvaux, she was commissioned by the French Navy and used for scientific purposes. She performed the first measurement of longitude using Marine chronometer. During the 18th century, measure of longitude was performed by comparing the solar time of the ship with that of a know point, the difference in time being in relation with displacement on the globe. In practice, this was achieved by keeping the time of the latest point of departure by mean of hourglasses, and by tracking the moment the sun was seen at its zenith. However, hourglasses had a poor precision because they needed to be turned by hand at exact intervals, because sand tended aggregate due to humidity, and because its flow eroded the thin section of the bulb, accelerating the flow. Mechanical clocks were seen as the logical next step in technology, and in 1722, eight years after the British introduced Longitude rewards, the French Academy of Sciences started offering a prize every two year for the best chronometer for sea navigation. In 1766, clockmaker Pierre Le Roy submitted a marine chronometer for consideration for the 1767 prize. At the time, several other clockmakers in France were trying to develop similar instruments, notably Ferdinand Berthoud, Étienne Tavernier and Jean Romilly, but being unfinished or damaged at the time, their prototypes could not contest. Finding Le Roy's invention promising, the Academy started studying ways to test it in real conditions at sea. Courtanvaux, who sat at the Academy, then proposed to shoulder the cost of the tests himself by having a ship built specially for the occasion. The expedition was to depart Le Havre and cruise off the Northern coast of France, sailing to various harbours — Calais, Dunkirk, Rotterdam, Brielle and Amsterdam — before returning to Boulogne and Le Havre. A second journey was to be undertaken in 1768 to the South up to A Coruña. The frequent calls were to allow recalibrating the chronometer often, entailing that the ship had to be specially chartered for the purpose and be small and manoeuverable enough to enter all the ports; this precluded use of a regular merchantman, which would in any case have been slow and whose accommodations would have been ill-suited to the purpose.