The Wallace Collection in London is renowned amongst other things for its magnificent collection of French eighteenth-century furniture, much of which has a royal provenance and once furnished the palaces of the ancien régime. However, the royal family was but one source of patronage in the decorative arts of the eighteenth century and the Wallace Collection also contains splendid and costly furniture that was commissioned by the super-rich of their day: wealthy bankers and financiers. One such piece is the magnificent pendule à planisphère, or astronomical clock, which dates from c. 1750 and was commissioned by the king’s banker, Jean Paris de Montmartel (1690-1766); this clock is testament not only to Montmartel’s enormous wealth, but also to his interest in scientific and technological developments of the time – indeed similar to many collectors of watches and timepieces today.
An important feature
Montmartel kept his clock in his Parisian home, the Hôtel Mazarin, in his grand cabinet (study). This is a room where he would have conducted business and held meetings with his fellow financiers and this clock was no doubt an important feature designed to impress his peers – we know that he was proud of it because it features prominently in a portrait of him sitting at his desk in the study. Not only was the clock able to tell him the time in Paris down to the last second (both solar and mean), it was also possible for him to read off the times in any part of the northern hemisphere; from this clock he could also tell his visitors the day and date of the month, the sign of the zodiac and the times of the rising and setting of the sun and moon.
The clock’s mechanisms are housed in a fabulously extravagant case, veneered with amaranth and other woods and mounted with gilt bronze. Surmounting the clock face at the top is the familiar motif of Love Triumphing over Time, a sculptural group in patinated bronze that had been a popular decorative feature of clocks since the early eighteenth century. Time, portrayed as an old man, is seated on a gilt-bronze cloud and has his left hand tied behind his back; one of two winged infants, representing Love, has stolen his gilt-bronze scythe. We do not know who made the case but the design of the bronze mounts has been attributed to Jacques Caffieri (1678-1755), a bronzier of great distinction who worked for the Bâtiments du Roi for many years and whose work furnished many of the royal palaces. At some time in its history various small alterations have been made to the decorative detail of the case, and the plinth has been added to raise it up; in Montmartel’s day the dials would have been much more in line with a standing man’s eyesight.
The movement, a masterpiece of design
We know more about the movement, which is a masterpiece of design. It was designed by Alexandre Fortier, a Parisian notary and inventor who is known to have worked with the clock-maker, Michel Stollewercke (made a maître in 1746, died 1768) on a number of occasions. The bottom of the dial plate is engraved: Alexandre fortier invenit/Stollewerck fecit Aparis. The brass dial plate comprises five main dials and four segmental apertures, each one displaying different pieces of information, and is decorated with engraving. The movement itself is enclosed behind the dial plate but the sides and back of the case are formed from shaped glass panels, allowing sight of the movement within.
The clock comprises a two-week, weight driven going train and a spring-driven count-wheel striking train, which strikes the hours and half hours according to apparent solar time on a bell directly above the movement. The movement now has a Brocot escapement. The solar day, as defined by the sun returning to the meridian, is subject to variation because the earth moves at variable speed round the sun and because the equator is differently inclined towards the sun at different seasons. Mean time overcomes this variation by a uniform division of time, but as a result you get a variation between mean time and solar time, which can rise up to a quarter hour fast or a quarter hour slow. By the eighteenth century, clock-makers knew how to show this variation, or to give it the correct name, equation of time. The clock movement runs in mean time, but the pierced and gilt hands are driven by a moveable carriage, the position of which is governed by a kidney-shaped cam which gives a variable motion, and is able to achieve the equation of time. Thus the clock strikes the hours according to solar time, when the gilt minute hand is on the hour, not when the blued steel hand reaches XII; there is also a dial displaying the seconds.
All information beautifully represented
The astronomical train incorporates a perpetual calendar mechanism. As the date wheel is advanced it winds up a spiral spring at its centre, and when it reaches the end of the month it is unlocked by a lever and returned by the spring to the beginning. Small openings on the dial plate indicate the date, days and months of the year.
Yet more information is available from this clock, all of it beautifully represented. The centre of the dial plate is taken up with the planisphere, an engraved representation of the northern hemisphere with the North Pole at the centre and the degrees of longitude around the circumference. The silvered ring at the outer edge is divided into the different signs of the Zodiac and a sun-shaped gilt disc revolves anti-clockwise through them, pointing to the correct sign for that month. A painted blue space representing the heavens divides this sun from the moon, which takes the form of a silvered disc, charmingly engraved with a face. The moon disc revolves around an inner ring which revolves once in a year and is calibrated from 1 to 29½, thus showing the age of the moon in days. Visually this is represented by the blued steel disc accompanying the moon disc which obscures or reveals it to reflect the different phases of the moon.
The silvered ring closest to the planisphere is engraved with the hours in Arabic numerals in two sequences of 1 to 12, representing the ante-meridian (A.M.) and post-meridian (P.M.) hours. The planisphere itself – a brass disc – revolves against this ring, thus indicating the time at any degree of longitude.
A work of art and technology
It is interesting to note that the 0 degree meridian on the planisphere does not run through Greenwich, or even Paris which was used in France for many years, but through Ferro (Hierro) in the Canaries. The notion of longitude was discovered by the Greeks but it was Ptolemy who first used a consistent meridian for his Geographia (c. AD150). He used a location fairly close to the Canary Islands; the important thing was to be comfortably off the western-most tip of Africa. It was calculated slightly differently over the centuries, but by the sixteenth and seventeenth centuries a similar location was in general use and it was Louis XIII and Richelieu who decided that Ferro should be 0 degree. By 1750 Paris had evolved as the meridian generally used, so it is perhaps surprising to find this clock – so modern in many ways – still utilising Ferro. Montmartel had investments in international trading companies which may offer another explanation of why he was so interested in having such a complex timepiece.
Below the planisphere are two dials indicating the rising and setting of the sun and moon and painted to represent the skies at day and night. In the centre of the bottom of the dial plate are two small openings displaying the month and the date. They are driven by the silvered brass wheels of the perpetual calendar mechanism which is self-adjusting; as the wheel advances, it winds up a spring and when the wheel reaches the last day of the month it is unlocked by a lever and returns, under the pressure of the spring, to the first of the month. The point at which the wheel is released is governed by a cam, with steps of different depths to allow for the variation in length of the different months. The only thing the calendar mechanism cannot do is a leap year! However, a later clock is known by Fortier and Stollewerck that has a more sophisticated leap year adjustment, thus correcting this small deficiency.
At the Wallace Collection we keep this clock running, to the enjoyment and fascination of our visitors. After 260 years it still keeps excellent time, and it can still be used to predict the phases of the moon, the time of the setting sun and indeed to tell us what the time might be in Japan. It is a truly remarkable object – as much a work of art as a work of technology – and one that has brought enormous pleasure to thousands of people over the years. Above all, it pays tribute to Man’s continuing quest over the centuries to understand, measure, and even control time. ■
The ancient art of time measurement
The art of time measurement is one of the great advances of humankind. This centuries-old heritage is rightfully conserved in numerous, though often little-known, museums. So as to bring these riches to life, HH Magazine presents some of the most exceptional pieces, chosen for their technical significance, historical importance, or for their beauty. This regular feature trains the spotlight on a timepiece which has been chosen and described by the curator of the horological collection of one of the approximately two hundred public or private museums which conserve clocks and watches in their collections.