Leroy & Cie precision pendulum, 1930

In depth

Based on the fashionable ‘grand boulevard’ de la Madeleine, the Paris firm of Leroy (founded in 1785) specialised in this model of constant pressure regulator, which its maker, P. Rudolf, proudly described as ‘a paragon of precision; the jewel of the workshop’. Enclosed in a bell jar and vacuum tank, these clocks were always intended for astronomical use, their precision partly the result of the modified Reid-type escapement, which acts on the pendulum directly, and partly the remontoire action, which activates a double electric contact, so that both circuits are closed momentarily with each oscillation of the Invar pendulum – except on the 61st swing, which marks the minute.

Despite the beauty of their workmanship, including elaborately damascened plates and typically thin French wheels, these clocks were designed to be sequestered deep underground, isolated from human interference as well as fluctuations in temperature and barometric pressure. Surviving records from Nice Observatory describe their two Leroy regulators sitting in cemented chambers, behind a chain of three insulated doors, more than 10 metres underground. From here, the clocks’ ‘thermometres-avertisseurs’ (‘warning thermometers’) would alert staff remotely to any significant ambient alteration.

The efficiency of the Leroy regulator quickly made it the French standard. From the cellars beneath the Paris Observatory (this time at a depth of 26 metres) three of these clocks serviced the radio time signals distributed from 1910, twice daily, from the Eiffel Tower by the Service de l’Heure – part of France’s (unsuccessful) attempt to wrest control of the international time standard from Greenwich. However, this particular clock – Leroy no. 1403 – was ultimately destined not for scientific use, but for the private apartment of Lieb Harrison Dulles (1899–1971) a wealthy American in Paris. Born in Philadelphia, Dulles had an established taste for precision timepieces; he was a regular customer at the prestigious firm of Breguet, a stone’s throw from Leroy & Cie on the Quai de l’horologe. Dulles paid a deposit of 10,000 francs for this clock on 27 January 1930, settling the balance of 15,000 francs on 8 August. It was delivered on 2 December (in line with Leroy’s standard manufacturing timescale – one year from order to completion).

Number 1403 remained with the Dulles family until the 1990s, when it was sold to William Scolnik, a prominent collector of precision timepieces. It retains its original amplitude microscope, voltage control panel, temperature controlling thermometer, and thermometer signal, and is one of a group of clocks – primarily astronomical-grade regulators – to have entered The Clockworks from the Scolnik collection in 2011.