The timekeeper method of finding longitude at sea – a shipboard clock that would keep the time at a known location throughout a sea voyage for comparison with observations of local time – was, as Whiston and Ditton said, ‘the easiest to understand and practice’. The huge strides made in the accuracy of pendulum clocks were encouraging but the technical challenges facing their application at sea were huge. Watches, less influenced by the motion of the ship, were much too inexact. As Whiston and Ditton’s 1714 pamphlet put it:
Fig. 17 – The Octagon Room at the Royal Observatory, Greenwich, by Francis Place, c.1676
{National Maritime Museum, Greenwich, London}
Watches are so influenc’d by heat and cold, moisture and drought; and their small Springs, Wheels, and Pevets are so incapable of that degree of exactness, which is here requir’d, that we believe all wise Men give up their Hopes from them in this Matter. Clocks, govern’d by long Pendulum’s, go much truer: But then the difference of Gravity in different Latitudes, the lengthening of the Pendulum-rod by heat, and shortening it by cold; together with the different moisture of the Air, and the tossings of the Ship, all put together, are circumstances so unpromising, that we believe Wise Men are almost out of hope of Success from this Method also.15
It had ‘been so long in vain attempted at Sea, that we see little Hopes of its great usefulness there’.16 Dependence on a single clock was also potentially dangerous if there were no means to check its performance.
Fig. 18 – Marine timekeeper, by Severyn Oosterwijck, c.1662 based on the designs of Alexander Bruce and Christaan Huygens
{National Maritime Museum, Greenwich, London, Private Collection}
Fig. 19 – Frontispiece to Thomas Sprat’s History of the Royal-Society of London (London, 1667); note the triangular maritime timekeeper at the top left and the two navigational instruments hanging on the column behind it
{National Maritime Museum, Greenwich, London}
One of those who had attempted to make functional sea-clocks was the same Christiaan Huygens who had had such success with pendulums. As with others in this story, his attempt to apply this work to the problem of longitude was immediate. Huygens had a deep theoretical understanding of the physical principles behind this practical work, making use of clockmakers and others to construct, test and develop his designs. These collaborations were fruitful but not always easy.
One individual with whom he became involved was Alexander Bruce, Earl of Kincardine, who tested a timekeeper on a voyage between Scotland and The Hague in early 1662. Its performance convinced Huygens to collaborate, and he joined Bruce in making and testing two further clocks on the same model, with the assistance of Severyn Oosterwijck, a clockmaker from The Hague (Fig. 18). Further trial results were sufficiently encouraging for work to be continued, now also in collaboration with Hooke. The clocks were approved at the Royal Society, especially after a very favourable (and probably untrue) report of them was given by Captain Robert Holmes after a voyage to Lisbon. Huygens was made a Fellow of the Royal Society when he visited London in 1663, patents were discussed and the Duke of York expressed interest in the clocks. One of these triangular clocks has been identified on the left of the iconic frontispiece of Thomas Sprat’s 1667 History of the Royal-Society of London (Fig. 19). Despite all this, the clocks were little used.
Huygens continued to develop his ideas. Much of this work was done in relative secrecy and, even once revealed, seems to have made little impact. However, by 1666 he was working within the Académie des Sciences for the French Crown and further sea trials were undertaken, some achieving good results. He published another design in Horologium Oscillatorium in 1673; this timekeeper was spring-driven, set on gimbals (devices designed to keep objects level in unstable conditions), and had a triangular pendulum that was forced to move in only one plane. A later version (Fig. 20) was tried, inconclusively, in the 1680s, this time in collaboration with the Dutch East India Company. Huygens was also one of those who, in the 1670s, were involved with the invention of the balance spring, crucial to the development of accurate watches. There are hints that Huygens saw this as a potential alternative for a timekeeper solution to the longitude problem but, because springs were too greatly affected by changes in temperature, it was not one he pursued.
Fig. 20 – Christiaan Huygens’ design for a marine timekeeper, originally drawn c.1685–86
{National Maritime Museum, Greenwich, London, Courtesy of Jonathan Betts}
Fig. 21 – Longitude timekeeper, designed by Lothar and Conrad Zumbach de Koesfelt, made by Franciscus le Dieu, 1749
{Museum Boerhaave, Leiden}
Fig. 22 – Plate from Henry Sully’s Description Abrégée d’une Horlorge d’une Nouvelle Invention (Paris, 1724)
{National Maritime Museum, Greenwich, London}
Huygens died in 1695, having made some huge practical and theoretical advances but without a clock having yet been taken up as a usable tool at sea. His influence on those who followed, through his publications, manuscripts or collaborators, was enormous. One follower was Lothar Zumbach de Koesfelt, a Dutch physician, mathematician and musician, who described a sea-clock in 1714. It was later improved by his son Conrad, who in 1749 also designed a clock that used a glass container to control its temperature (Fig. 21). Another was Henry Sully, who, trained in England and working on the Continent, experimented with a marine clock and watch (Fig. 22). Sully made ample use of both French and English networks, not least the Royal Society’s chief authority on instruments and timekeepers, George Graham (1673–1751). While Sully’s clock had mechanisms that made it portable and minimized the effects of temperature and gravity, Graham’s report and trials were to show that a ship’s motion in open sea would fatally influence its pendulum.
In 1714, then, there were several potential solutions to the problem of finding longitude at sea. Most of them were theoretically viable and had already been researched by mathematicians, astronomers, artisans and mariners. In many ways the ground had been prepared: the next, crucial step may not have seemed all that distant. However, all of the methods presented practical problems, most particularly due to the conditions under which observers or instruments had to perform at sea. It was a practical and technical set of problems, and the government hoped that these could be met so that the methods ‘true in theory’ might be made ‘Practicable and Useful at Sea’.
While much previous work had taken place in Spain, Holland, Venice and elsewhere, the momentum had decisively shifted towards Britain. Ideas and skills were available, particularly in London with its flourishing instrument trade, maritime interests, places of open discussion, such as coffee-houses, and widespread access to print. These opportunities were seized by many of those with ideas, mechanisms and projects relating to longitude. The Royal Society, Astronomer Royal and Commissioners of Longitude were marked out as the key figures from whom to seek interest, approval and, perhaps,