Teiger Shelton Solar Longcase The Teiger Shelton Solar Longcase, made by London clockmaker John Shelton the Younger, is a technical feat in early modern clockmaking. Made in 1736, it was produced during the early part of Shelton’s career and is one of the earliest surviving examples of an equation clock in its final and most complicated form. It even includes concentric minute hands to tell solar time. Shelton, who was celebrated for his technical prowess, was the first English maker to apply this feature to an equation clock. While undeniably beautiful, with its break-arch dial, ornate gilt spandrels and clean-lined burr walnut case, the Teiger Shelton’s aesthetic appeal was secondary to its special role as a precision instrument. It was specially created as a regulator, a clock accurate enough to be used for scientific calculations. In this case, it was used for timing the transit of Venus observations to the exact second. No need for a sundial Even after the invention of the domestic pendulum clock by Christiaan Huygens in 1656, all clocks still had to be set locally by reference to a sundial. Relying on a sundial can be tricky because the time indicated on the dial represents solar time. Solar time differs from local mean time (or clock time) by a few minutes throughout the year. This meant that an equation was needed to reliably convert the reading of solar time from a sundial to mean clock time. This conversion equation, known as the Equation of Time, was devised around AD 150 by the Greek astronomer Claudius Ptolemy. In 1672–1673, just after the establishment of the Greenwich Observatory in England, the first Astronomer Royal, John Flamsteed, published his Equation of Time tables for the conversion of apparent solar time to mean clock time. Many sundials, which were often made of bronze, even had an Equation of Time engraved upon them, thereby allowing proud owners of pocket watches to set them to local mean time. For an example, see the Duke of Kent Sundial, made around 1700, by Thomas Tompion, who helpfully engraved a version of these tables on this sundial.[1] Eventually, clockmakers such as Shelton mechanised this task by creating equation clocks.[2] An equation clock is a mechanical clock with an equation mechanism that simulates the Equation of Time calculation, so that the user can read or calculate solar time without the aid of a sundial. Thus, with a clock such as the Teiger Shelton, there was no need for a sundial. Still, in many respects the Teiger Shelton can be read like any traditional clock. Its Greenwich Mean Time (GMT) indications include the traditional silvered chapter ring and outer silvered minute ring seen on all clock faces of the time. It has a GMT minute hand, a GMT hour hand, and a gilt solar hand with sunburst pointer, thus providing indications for both solar time and GMT on its dial. In this way, Shelton aimed to show the Equation of Time in its simplest form with the two GMT hands. Innovatory indications The Teiger Shelton’s solar indications are innovatory because they are technically progressive while still being fairly easy to read. As mentioned above, the clock’s maker, Shelton, was the first English maker to apply a concentric solar hand to an equation clock. The solar hand rotates backwards and gives the same time a sundial would give. Horologist Dr John C Taylor observes that this Shelton method of having the sun hand and the Greenwich Mean Time hands is certainly the easiest way to understand what happens when we convert solar time to mean time. The indication for the Equation of Time can be found on the hood of the Teiger Shelton, in the demicircle-shaped sector in its break arch, just above the XII. This sector displays a silvered year calendar disc engraved with seven concentric rings that are calibrated for the days of the month, the twelve months (in Portuguese), the zodiac, the position of the sun, and the Equation of Time.[3] As explained above, before the invention of the equation clock, the clock and watch owner was expected to undertake the Equation of Time calculation on his or her own. However, the Teiger Shelton can perform this task on its own. Dr Taylor reminds us of how groundbreaking an equation mechanism such as this was for its time: Nowadays, we are utterly immune to the effects of the sun and the moon. We just assume that all time must be Greenwich Mean Time. Very few are even aware of solar (sundial) time, let alone the fact that we must make allowances for it whenever a clock is set. Of course, now, most people have smartphones, and they take for granted that their devices automatically set to their local mean time. Cutting-edge features and playful inversions Shelton also fitted his state-of-the-art solar longcase with other horological innovations, such as the dead-beat escapement. In 1715, master clock- and watchmaker George Graham perfected this type of escapement by eliminating recoil, thereby making the pendulum swing more consistent. The dead-beat escapement increased accuracy to such an extent that it was used for all regulators, such as the Teiger Shelton, going forward. Shelton’s dead-beat escapement is modelled on Graham’s. Shelton also used a temperature-compensating gridiron pendulum, invented by Yorkshire clockmaker and horological hero John Harrison in 1726, just ten years prior to the making of this clock. Shelton’s version has five steel rods and four brass rods to enable differential expansion. Additionally, the Teiger Shelton’s standard GMT hour, minute, and second hands, as well as its solar hand, are all driven by a kidney-shaped cam, which is mounted on the backplate on an arbor. Shelton’s signature, John Shelton fecit. Shoe Lane. 1736 August 25, has been scratched onto the back of the cam. Taylor suggests that Shelton provided the date to proclaim that he’s the first ever to make a concentric solar hand and GMT hand on the same dial. It’s never been done before. So, there he is claiming it for his own invention. Features on this Teiger Shelton are also playfully inverted. For example, in almost all clocks, the escapement is located at the top of the mechanism, but in Shelton’s clock it is in the bottom. Also, the seconds dial is placed in the lower half of the dial, by the VI, whereas this type of dial is usually placed above, by the XII. Finally, the winding holes are by X and II, whereas they usually appear adjacent to the VIII and IIII. These inversions were made because the entirety of the movement is basically upside down when compared with almost all other clocks. A special clock with a special purpose The Teiger Shelton was not meant to grace the drawing room of a stately home. It is a regulator – an accurate clock that was precise enough to be used for scientific calculations. Clocks such as the Teiger Shelton were found in observatories and learned spaces, and used on scientific expeditions around the world. In its case, the Teiger Shelton regulator was used for timing the transit of Venus observations to the exact second. Unfortunately, the details of it use-life as a scientific instrument are not known. A Portuguese connection There is an oral tradition that the Teiger Shelton was commissioned by King João (John) V ‘the Magnanimous’ of Portugal (b. 1689, d. 1750), and that the clock found a home in the Portuguese Palace-Convent Mafra. This possibility of royal provenance is based on the Portuguese notations on the Teiger Shelton’s calendar disc and João’s well-documented investment in astronomical clocks from the best makers in London.[4] Engraved upon the Teiger Shelton’s silvered year calendar disc at the top of it break-arch dial are the names of the calendar months in Portuguese. The use of that language certainly indicates some sort of Portuguese connection. Although there are no clear links between the Teiger Shelton and King João, it is entirely plausible that the Teiger Shelton was acquired by the Portuguese king. First, Shelton had other royal patrons, including the Spanish royal house, as there are two equation clocks by him in the Spanish Royal Collection.[5] Second, João was known for his lavish spending on ambitious architectural works and on commissions and additions for his sizeable art and literary collections.[6] During his reign, he championed the cultural renewal of Portugal, specifically investing in the latest innovations in astronomical clocks and instrumentation. These investments fostered international exchange with the finest makers in Britain and Europe. Ties between the Portuguese court and the London clockmakers, particularly George Graham, are well documented.[7] During the 1720s, Jesuit astronomers working at the Portuguese royal court received several instruments, including astronomical clocks made by Graham. Diplomatic correspondence, in the form of a letter dated to 21 July 1724, confirms that Graham’s clocks arrived in João’s court.[8] There is also a set of instructions for Graham’s clocks in Latin, which are dated to 1726.[9] This is significant, because we know that Shelton worked closely with Graham.[10] Therefore, João easily could have connected with Shelton by way of Graham. João also had other ties to Britain. He was educated under the direction of Catherine of Braganza, King Charles II‘s queen, who had returned to the Portuguese court as a widow. Also, João’s wife, Maria Anna of Austria (b. 1683, d. 1754), was the daughter and sister of the recipients of the Spanish Tompion Clock (No. 381) by Thomas Tompion, which was made around 1702.[11] While it makes perfect sense that João would covet a technically progressive clock such as the Teiger Shelton for his court, there is no firm evidence linking the Teiger Shelton to Portuguese royalty. Still, Shelton’s solar longcase undoubtedly represents an important acheivement in manufacturing and horological innovation: its ingenious equation mechanism paved the way for our experience of instantaneous, precision time-telling today. Dr Kristin Leith, Senior Curator of Clocktime May 2024 End Notes [1] Taylor et al. 2019, 27, Exhibit No. 4:4; Carter 2022, 188–197, Catalogue No. 28; coming soon to Clocktime. [2] Although Shelton was one of the first to produce an equation clock in its most complicated form, it was clockmaker Joseph Williamson who laid claim to this invention in a letter that he wrote to the Royal Society around 1715. [3] The break-arch dial is influenced by master clockmaker George Graham, with whom Shelton worked closely (Carter 2021, 209). [4] Tirapicos 2017; 2023. [5] Carvajal 1987, 41. [6] Carter 2021, 209. [7] Tirapicos 2017. [8] Tirapicos 2017, n. 31. [9] Tirapicos 2023. [10] By the mid 18th century, Shelton was the principal person employed by Graham to make astronomical clocks (Carter 2021, 209). [11] Carter 2021, 189 and 209; coming soon to Clocktime. References Carter, J. 2021. The John C Taylor Collection: Part II (Selling Exhibition Catalogue, Carter Marsh & Co.). Winchester: Carter Marsh & Co. Carter, J. 2022. The John C Taylor Collection: Part III (Selling Exhibition Catalogue, Carter Marsh & Co). Winchester: Carter Marsh & Co. De Carvajal, C. 1987. Catálogo de Reiojes del Patrimonio Nacional. Madrid: Editorial Patrimonio Nacional. Taylor JCT. 2019. Tirapicos, L. 2017. ‘Astronomy and diplomacy at the court of King João V of Portual’ in Cahiers François Viète III-3: 61–79. https://journals.openedition.org/cahierscfv/762 Tirapicos, L. 2023. ‘Directions of precision: George Graham’s instructions for his pendulum astronomical clocks’ in Annals of Science: 1–15. https://pubmed.ncbi.nlm.nih.gov/37983075/
