Footnotes

Literature

Tardy, la Pendule français 5th Edition, vol. 1, p 210

Encyclopédie, ou dictionnaire raisonné des sciences, des arts et des métiers. Paris 1751-1772, edited by Denis Diderot and Jean d'Alembert. Vol. 5, p 587 et seq.

The present clock is described in an article under the heading "Equation, (Horlogerie etc.)" that is separate from the main entry on Horology. Engravings of the movement and its cadrature comprise figures 37 – 41 in the section of plates to accompany the entry "Horlogerie".

The article begins with a lengthy discussion of the types of equation clocks and their construction, noting that the most accurate are those which are cleverly designed to have as few wheels as possible in the train. The present example is cited as one of the first successful Equation clocks with a single dial and concentric hands.

The author then inserts a passionate appeal to the clock making trade condemning those who work only for profit. He goes on to say that to be a great clockmaker, one must be born with a natural talent. The passage is, in fact, a clear statement of LeRoy's own philosophy.

Julien Le Roy (1686-1759) was regarded by his contemporaries, as the most influential horologist of his era. In the words of the historian, Paul Chamberlain , "Le Roy occupies in France very much the same relation to horology that Tompion does in England - a figure that can be looked upon as father of the art at a very interesting period."

Born in Tours and trained by his father, Le Roy arrived in Paris around 1700. Le Roy began his career at a time when the reputation of French clock making was in decline. To remedy this situation, he joined with others to found the Société des Arts to promote horological knowledge. Unlike many, Le Roy freely shared his ideas with his colleagues. His superb craftsmanship influenced the profession and helped reverse the decline. His mechanical improvements to watches were incorporated into virtually all later18th century Continental watches. In the end, the success of the Société prompted a jealous Academie Royale des Sciences to absorb its membership.

Shortly after Le Roy received his freedom in 1713, he set up a workshop in the rue de Harlay, off la place Dauphine, where the most eminent 18th century Parisian clockmakers also worked. In 1739, Julien Le Roy was appointed Valet de Chambre, Horologer du Roi, and granted premises in the Louvre, which he maintained in addition to his atelier in the rue de Harlay.

The Equation of Time

With the invention of the pendulum clock in the late 1650's, the quest for precision became the primary focus of horological research. A clock potentially accurate to within a few seconds appeared by the 1670's in the form of the weight driven longcase clock. The new clocks also revealed a curious phenomenon.

They soon found a significant difference between "true time", the apparent time seen in the shadow of a sundial, and "mean time", the average time measured by a clock. The difference between Solar time and mean time varies daily in a complex way: from over 14 minutes fast in February to over 16 minutes slow in November. The yearly cycle of this variation became known as the "Equation of Time".

In 18th century France, to design a self-adjusting Equation clock became a measure of a clockmaker's abilities. The variable rate required of an Equation mechanism seemed incompatible with the constant rate of a precision clock. The critical part to produce the variation was derived by Christaan Huygens who plotted the yearly course of the Equation as a graph in polar coordinates. The resulting form became the template for a kidney-shaped wheel, or cam, whose profile could mimic the time difference. Mounted on the calendar wheel so that it made a complete revolution once a year its irregular profile guided the Solar minute hand to produce the required time difference.

Provenance

The early history of the clock is unknown. However, Julien LeRoy's work for the French Crown is well documented, so it is worth noting that an "old fashioned" equation timepiece of the same dimensions in a "black case" is in the inventory of clocks in the French Royal Collection made at the time of the Revolution. (see: Verlet, P. Les bronzes doré français du XVIIIe siècle. Paris: Picard 1987, pp 459-465).

The clock came to be part of the Collection of Gabriel Moreau (1891 - 1961), Director of L'École d'Horlogerie d'Anet, founded in 1876 by Alfred Beillard (1850 - 1939) a teacher and scholar who published a series of works on the history of clock making in France. The clock had been in the school's horological museum until it was dispersed at auction in 1986.

There are published examples of two other clocks with LeRoy's 1736 equation mechanism. Both incorporate striking work.
English Royal Collection [RCIN 30036] acquired by George IV in 1824.
Justice Warren Shepro Collection. Sotheby's New York, April 26, 2001, lot 144.