The Identification and Attribution
of CHRISTIAAN HUYGENS'
First Pendulum Clock. ^(a

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INTRODUCTION

It is an awkward irony, to be obliged to begin by advancing a proposition which contradicts some of the studies on which it itself is based. Here, in identifying and attributing Christiaan Huygens’ first pendulum clock, it is necessary to dismiss the notion that his first clockmaker was Salomon Coster (1620-1659) or that he developed his invention without using a clockmaker at all. Both assumptions, though flawed, are revealing and examination of them provides the best introduction.

NOT ALONE

Huygens mentions no clockmaker in connection with the development of his innovation. However, it is most unlikely that he would have launched his paradigm change in a centuries-old craft without experimenting on the purpose- made product of a practitioner. To have done so would be contrary to the quantitative method of this great empiricist. He required precise values. In this case he needed to know the scope and limits of his invention before divulging it. Huygens dates his invention to December 25 1656.(1  This date should not be regarded as marking an Archimedean inspiration on the basic principle of pendulum control. In fact, although it has often been said that he applied the pendulum to clockwork, it is perhaps truer to say that he brought clockwork to the pendulum. His original intention was, in part, to relieve astronomers from the task of impelling and counting the oscillations of the manual pendulum then in use for timing observations(2 Having realised how this could transform clockwork he would surely have commissioned a specially transformed clock. Christmas day 1656 therefore, probably signifies the completion of the last missing element of a tried and tested machine. Nothing less than the high performance of such a machine would have allowed Huygens to reveal immediately to others, his hopes of solving the longitude problem(3. By the beginning of 1657 he must have achieved a roughly two orders of magnitude increase in accuracy over pre-pendulum timepieces, obtaining results to within a few seconds per day. How else could a mathematician flatter himself that his invention was immanently relevant to maritime longitude? Apart from longitude he urgently required the best possible timepiece for his astronomical observations, for his studies of accelerated motion and his search for the constant of gravitational acceleration where his conical pendulum later provided the key. Logic alone therefore suggests that when Huygens realised the potential of a pendulum escapement, he commissioned the finest machines possible with which to experiment further.

● There is evidence that confirms what logic supposes. Firstly there are the material results of this experimentation in the refinements he developed before obtaining a patent: maintaining power, optimal gear train, pendulum crutch with flexible suspension and isochronal cheeks(4. These considerable intricacies required professionally made machinery and lengthy experimentation. Many months would be needed to evaluate the Flemish astronomer GodefroyWendelin’s (1589- 1667) proposition of seasonal variations alone(5. Secondly there is written evidence.
On the 1” November 1658, he distantly recalls in a letter to Pierre Petit, (1598-1677):

It is tempting to speculate that it was the empirical perfection of these isochronal cheeks that was commemorated on the 25 December 1656. To one of the finest geometers of his age, the resolution of what must have been for him the ugly inconsonance of the tautochrone and the circle would have been particularly pleasing. However, it is clear from this passage that he shaped his isochronal cheeks by experimenting with (at least) two weight-driven, seconds indicating clocks. Since the profile of these cheeks was part of Huygens’ invention, these experiments must have taken place in 1656. In April 1657, two months before the patent application, Claude Mylon (1618-1660) expresses in a letter, the wish that Huygens’ clock will go as well with a spring as it does with weights, ‘one could wish for nothing more for the longitude.(7

NOT WITH COSTER

So who made these clocks? And indeed who made the clock drawn in Huygens’ patent application of 14 June 1657, which was approved 2 days later, after the actual timepiece was inspected by a committee of the States General of the United Netherlands? It has been assumed that the answer to both questions is Huygens’ assignee Salomon Coster. Before considering why Huygens would have forsaken his original clockmaker, the evidence against Coster’s involvement at the experimental stage will be set out.

● Firstly, a passage that has been cited as pointing to Coster’s priority is ambiguous and problematic. In Horologium Huygens wrote:(8

Who, apart from Coster, were these artificers who had been able to do much to Huygens’ invention? Why use the phrase ‘him whose labours I first employed’ if, as has always been assumed, Huygens had only one licensee at the time of writing? Fond as Huygens may have been of the personal metonym, he could have referred to Coster as he did in his letter to Pierre Petit of November 1” 1658, as ‘my worker’ or, for example, my licensee ?

Also, the words, ‘I have indeed seen in the workshop(9 are an unlikely description of Coster’s clocks which he describes in the opening chapter as, ‘having had many copies ... already for sale and for sending forth in all directions’. Is it the clocks, made long ago in the old style, which Huygens had indeed seen, (now converted to pendulum) in the clockmaker’s workshop? This interpretation better accommodates the words ‘indeed’ (or ‘truly’, ‘quidem’) and ‘completed clocks’ (‘talia quoque confecta’). One can imagine the memorable sight of, say, a horizontal table clock put on its side and converted to pendulum. The last part of the above passage beginning, ‘now these are disused’ (i.e. fusee and chains) and describing going and tandem barrel clocks, may quite properly be interpreted as referring to Coster’s spring clocks. However, they may not be the clocks ‘seen in the workshop of him’ whom Huygens first employed. Lastly, the identity of that first employee depends on a precise identification of ‘these constructions’ which may refer only to the commercially available clocks and not his experimental clocks.

● The circumstances of the patent application may be very significant. Huygens allowed Coster to present the patent request on his behalf. This would appear uncharacteristically trusting of Huygens and suggests that the scientist felt in complete control. It is known that the design was Huygens’ own and that the Committee of the States General went to inspect the actual clock before consenting two days later.(10 They subsequently refer to the invention as ‘done by Huygens’ (‘gepractiseert’ by’(11) with permission for Coster to copy (‘naer te maeken’). This re enforces the impression that Coster introduced the committee to a clock not made by him.

● In summary, no surviving written reference points to Coster as having been anything other than the sudden and fortunate recipient of Huygens’ commercial assignment.

● The tangible evidence supports this view. None of the seven surviving examples of Coster’s work exhibit the slightest rigour of Huyghenian science. The simple going barrels, hinge swinging movements, inferior box pillars and cycloidal cheeks are led by the lack of a seconds dial, in denying any pride in this horological revolution. Admittedly Huygens considered their design fit for domestic purpose and they justify the very high antiquarian affection that they currently enjoy. Much significance has been attached to their dated plaques. It is unusual for clocks of any period to be dated. However, it is possible that these plaques were originally tokens, purchased by Coster from Huygens and representing paid dues on the licence for each clock sold. The plaque would have been provided with ‘met privilege’ and perhaps the date, etched in facsimile on them, but otherwise blank for Coster or his nominee to engrave as they wished.(12 Coster partisans may blame misfortune for leaving us only examples of his pendulum clocks intended for modest domestic use. However, there is no indication in Coster’s price list of work more worthy of the original maker and the appetite of time’s consumption is not usually so selective.


 REASONS FOR CHANGING CLOCKMAKERS

Why would Huygens overlook his original clockmaker when licensing his patent? There are at least three plausible reasons for so doing. Firstly, he himself tells us at the beginning of Horologium that he wished to give his native country, Holland, the benefit of his invention. Were that country not the domicile or nationality of his clockmaker, then eventual disfranchisement would have been inevitable.
The very fact that Huygens mentions this wish could indicate that there was an unusual option in a matter, like patriotism itself, normally taken for granted. Secondly, Huygens’ most treasured possession was his intellectual property. He may well have thought this would be better protected by separating development from commercial production. Thirdly, being in the vanguard of research in the physical sciences, it was clearly to his advantage to have a more accurate timepiece than anyone else. He may well have deliberately confined readily available production to the inferior models of a separate clockmaker. The question then arises as to whether or not there was an aggrieved clockmaker and if so, why there are no recorded repercussions. The obvious explanation is that this clockmaker had little or no creational input, and accepted from the onset strict conditions of secrecy and the absence of potential patent rights. Perhaps a notary was involved. However it should also here be remembered that there is at least one reference to a counter claim by a clockmaker. Jean Chapelain (1595-1674) mentions in a letter to Huygens of 20 August 1659, a clockmaker of Paris, (‘de notre’), ‘who has tried to rob you of your claim’. The editors of the Oeuvres Completes conclude that this is probably a reference to Isaac Thuret (c.1 However they produce no evidence to support this supposition.(13

● The document that could well settle the mystery of Huygens’ first clockmaker is the design submitted through Coster to the Committee of The States General. Sadly, as Drummond Robison(14 lamented 77 years ago, this has been lost and there are no known copies; or are there?

THE NEGLECTED EVIDENCE

It has long been assumed that the earliest surviving illustration of a clock by Huygens is that contained in his Horologium of 1658. This illustration shows his second type of clock, with vertical verge escapement, ‘O-P’ gearing to narrow the pendulum amplitude, and lack of isochronal cheeks. This clock beats half-seconds (Fig. 1). The other published illustration of a conventional pendulum clock by Huygens is the more famous illustration in Horologium Oscillatorium published 15 years later in 1673.

Fig. 1 (click to enlarge)
Christiaan Huygens’ earliest published illustration
of a clock, showing his second type of clock
with 0-P gearing, Horologium, (1658).
(view high res. picture)

This shows a seconds beating clock with isochronal cheeks and horizontal escapement Fig. 2. It has been assumed that this is an illustration of a regulator made for Huygens sometime in the middle or late 1660s. In fact, this is an illustration of Huygens’ first pendulum clock of 1656/7. In all probability it is copied from the original design that accompanied his patent application. The proof for this is fortunately preserved in Benjamin Martin’s (1705-1782) book of 1764, Newtonian Mathesis(15 original woodcut of 1657 and illustrated it Mathesis) Martin somehow obtained Huygens’ (Fig. 3) along with the following description:

Fig. 2 (click to enlarge)
Horologium Oscillatorium, (1673).
The plate from Benjamin Martin's copy.
(view high res. picture)

This woodcut is the same side view of the movement illustrated in Horologium Oscillatorium, though of a different size and without the pendulum weight or fine adjustment weight. Martin was so taken by this discovery that he annotated his own copy of Horologium Oscillatorium with the words, ‘Huygenius’s

Fig. 3 (click to enlarge)
Newtonian Mathesis (1754).
A copy of Huygen's woodcut of 1657
(view high res. picture)

Original Clock’ above the illustration (Fig. 4).(16 He also reckoned the date described by Huygens noting, ‘1657 first published his clock’ no doubt delighted that Huygens’ opening words, ‘Ann us agitur sextus decimus ex quo fabri cam horologiorum’ tallied with the date of his woodcut (Fig. 5).

Fig. 4 (click to enlarge)
Benjamin Martin’s annotation above the plate of his copy of Horo/ogium Oscillalorium.

Fig. 5 (click to enlarge)
 Benjamin Martin’s reckoning of the date on the title page of his copy of Horologium Oscilatorium.

Since Martin states that the woodcut has never to his knowledge been seen by an English reader, one wonders whether it was part of the auction in Holland in 1754 of Huygens’ effects. This auction included lenses, a planetarium and a clock which were purchased by Huygens’ great nephew A.J. Royer, and left in 1809 to Leiden University.(17

● The fact that Huygens chose to illustrate his first clock in a work published 16 years later should not come as a surprise to Huyghenian scholars. It has been known for some time that all but the last part of Horologium Oscillatorium was drafted by the end of 1659.(18 In all probability the first chapter was started in October 1659 (although information on sea trials was appended later). It is obvious that Huygens would not have commenced his description of the clock without an annotated diagram. By 1659, with his discovery and proof of the cycloidal tautochrone, he had discarded his second type of clock with ‘O-P’ gearing (illustrated in Horologium).
There would have been every reason to illustrate his original clock, probably supplying the diagram of his patent application. The o improvement on the original clock was an invisible one; the cheeks were now cycloidal. This was left to the text to explain. There is further evidence to show that Horologium Oscillatorium used an early diagram which was later modified.
The theory and shape of the fine adjustment weight which was developed in the early 1660's is given a non sequential Greek letter ‘Δ' indicating that it was not part of the original diagram. The linear scales from which the theory of this weight was derived, on the far right (fig. liv in the plate) appear also to be a later addition.(19 Their description is contained in part 4, written in 1664. It is interesting to note that Martin’s woodcut does not include this fine adjustment weight.

Fig. 6 (click to enlarge)
A French engraving of 1671 showing Huygens’ clock which appeared 2 years later in Horologium Oscillatorium.

There is other evidence that a drawing of Huygens’ first clock had some circulation before Horologium Oscillatorium. It is included in a French engraving of 1671 (Fig. 6).(20 A similar clock with a great wheel of 96 teeth, is illustrated in a letter Huygens wrote to Canon Estienne (?- 1723), in 1669.(21 Martin’s description therefore, must be considered conclusive and the identity of Huygens’ first clock established beyond doubt. Since the thesis of this article was largely written before discovery of this description, it is not with the benefit of hindsight to note that the Horologium Oscillatorium clock shows all the signs of being the prototype.
There are elements which do not flourish in subsequent production; the boat-shaped pendulum bob, the large diameter escape wheel pinion, the seconds disc. Being a weight-driven clock beating seconds, it has the specifications that one would imagine Huygens required to test pendulum theory. The introduction to the clock and its detailed description in the text of Horologium Oscillatorium, make more sense as a celebration of the original movement than the random inclusion of a subsequent model. Had Huigens wished to be up to date with developments in 1673, he would presumably have illustrated the anchor escapement.

End of this section, click here to continue.

	Notes:
A	Reprinted from the December 2008 issue of Antiquarian Horology’. (back to text)
1.	M. Nijhoff, Oeuvres Completes de Christiaan Huygens (The Hague, 1932), vol.2, p.l Huygens gives this date for the ‘first model of that type of clock’ in a letter he sent to Ismail Boulliau (1605-1694).     (back to text) Ismail Boulliau
2.	Christiaan Huygens, Horologium (The Hague, 1658), P.4. (back to text)
3.	Nijhoff, Op. Cit. vol.2 p. Letter from C.H. to van Schooten, 121 Jan 1657, see also p.7, for letter from Huygens to Mylon, 1” February 1657. Both letters express the hope that the invention will be applied to the determination of longitude. (back to text)
4.	The term ‘isochronal’ is here used to describe the purpose and not the strict qualification. Huygens shaped his cheeks empirically at this time. (back to text)
5.	Huygens, op. cit. p.1 ‘to me certainly it was not given to observe anything of this kind ...‘ is Huygens’ comment on Wendelin’s proposition of variations, (presumably caused, in part by temperature change) and indicating that he had tested his invention through the seasons. (back to text)
6.	Nijhoff, op. cit. vol.2, p. (back to text)
7.	Nijhoff, O cit. vol.2, p. (back to text)
8.	Huygens, O Cit. p.1 (back to text)
9.	The word ‘workshop’ is a translation by Ernest L. Edwards, of the Latin ‘apud’ which is a preposition governing the accusative case and has a wide range of meaning including ‘at the house of’, ‘in the works of’, ‘among’, ‘before’, ‘in the presence of’, etc. It is not certain therefore that Huygens specifically saw these clocks in a ‘workshop’ for which he could have used the word ‘officina’. This may become significant with regard to the location of these clocks seen by Huygens. (back to text)
10.	Nijhoff, op. cit. vol.2, pp. (back to text)
11.	The precise definition of the Dutch verb ‘practiseeren’ would here seem to lie somewhere between ‘carry out’ and ‘use’. It gives the impression that what the committee saw was ‘done’ by Huygens and not Coster. A contemporary account of the murder of William the Silent describes the deed as ‘gepractiseert’ by the murderer! (back to text)
12.	Some plaques have ‘met privilege’ and the date etched or scratched on them in script different from the Coster signature; these plaques would appear to be original. Viz: Huygens’ Legacy, Hans van den Ende, et. at (Fromanteel Ltd: Isle of Man, 2004), p. (back to text)
13.	Nijhoff, Op. Cit. vol.2 p.
14.	J. Drummond Robertson, ike Evolution of Clockwork (London, 1931), p. (back to text)
15.	Benjamin Martin, A New Comprehensive System of Mathematical Institutions Agreeable to the Present State of Newtonian Mathesis (London, 1754). Vol. 2. pp.373 For Martin see, JR. Milburn, Retailer of the Sciences (London, 1986). (back to text)
16.	Christiaan Huygens, Horo/ogium Oscillatorium ... (Paris, 1673). Sold Christie’s, London, December 2006, Lot 81. Provenance; Benjamin Martin (double signature on title page, pen drawings, occasional notes and calculations), John Pope, 1784, (book plate), John Jackson (pencil signature). (back to text)
17.	C.A. Crommelin, Descriptive Catalogue of the Huygens Collection .. (Leiden, 1949), PP.
18.	Joella C. Yoder, Unrolling Time (Cambridge, 1988), p.5. (back to text)
19.	It is clear that a smaller script has been used in fig. IV of Plate One of Horologium Oscillatorium. (back to text)
20.	A.E. Bell, Christiaan Huygens and the Development of Science in the 17th. Century (London, 1947), Plate 3. (back to text)
21.	Nijhoff op. cit. vol.6 pp. (back to text)
22.	Johan Lulofs, Waarneeming van Mercurius op de schyf der Zon, den 6Mey 1753, gedaan Ce Leyden (Haarlem, 1754), pp.37 (back to text)
23.	R.H. van Gent & J.H. Leopold, Timekeepers of Leiden Observatory (Leiden, 1992), p. note 37. (back to text)
24.	Reinier Plomp, ‘A pendulum Clock Owned by The Danish Astronomer Ole Rømer (1644-1710)’ Antiquarian Horology 30/5 (March 2008), 624-628. (back to text)
25.	They have been checked with their TPI and, as to be expected, do not conform to any standard threads. They have nor yet been compared to the threads or diameters of the Boerhaave clock. (back to text)
26.	J-D. Augarde, Les Ouvriers do Temps (Geneva, 1996), p. (back to text)
27.	Nijhoff, op. cit. vol. 1V, p.llO. (back to text)
28.	Nijhoff, op. cit. vol.V, p.383. Also RH. van Gent & J.H. Leopold, op. cit. p.l3. (back to text)
29.	Reinier Plomp, ‘A longitude timekeeper by Isaac Thuret .with the Balance Spring Invented by Christiaan Huygens’ Annals of Science’ 56 (1999),   (back to text)
30.	Yoder, op. cit. p  (back to text)

   back  

	By: Sebastian Whitestone & Jean Claude Sabrier.
Reprinted from the December 2008 issue of Antiquarian Horology’.

  Back to end of previous section.

TWO SURVIVING EXAMPLES

Martin’s copy of Huygens’s woodcut, (and of course the plate in Horologium Oscillatorium), show a movement known only in the work of Isaac Thuret. There are at least two examples of this exact movement. One is a hitherto unpublished example discovered 30 years ago by Jean-Claude Sabrier. The other example is now in the Boerhaave Museum, Leiden (Figs 7 & 8) and is held by long tradition to have been the personal property of Christiaan Huygens. In 1754 Johan Lulofs (1711-1768) wrote of his observations at Leiden, ‘the timepiece that I used was made in Paris by Thuret under the supervision of Mr. Huigens... ‘.(22 Leopold and van Gent(23 believe this clock was one of two first mentioned in an inventory of the Observatory in 1706. If so, then the clock left to Leiden University by the Royer bequest in 1809, is another clock. The gearing in the Leiden clock is identical with Huygens’ diagrams apart from the 40/20 contrate to escape wheel pinion instead of 48/24. There is, according to Plomp, another similar Thuret clock in a private collection. There is also a clock with similar train but with only two pillars in the Ole Rømer Museum, Denmark. This clock is unsigned and may be a later Danish copy of the Boerhaave clock.(24

Fig. 7 (click to enlarge)
The clock by Isaac Thuret, Museum Boerhaave, Leiden, inv.no.Vg854.

Fig. 8 (click to enlarge)
The back plate of clock by Isaac Thuret, Museum Boerhaave, Leiden, inv.no.Vg854.

● Thirty years ago Jean-Claude Sabrier was asked while visiting a French Chateau, to examine a clock kept in a cardboard box in the attic.
He informed the owners of the great importance of this clock and persuaded them not to restore it. A few months ago, in preparation for this article, he persuaded the current owners to release the clock for thorough examination and restoration and full details of it follow in Figs 9-23.

Fig. 9 (click to enlarge)
The Thuret clock discovered by Jean-Claude Sabrier, the case with opening door.
(view high res picture)

● The case is made of brass with hinged and glazed front door and sliding back panel. It is attached to the dial by four screws inserted in right-angle brackets attached to the back of the dial. The case is hung on the wall by rings at the side and not on the top. Large pyramidal headed screws adjust the distance from the wall. The dimensions are: 175 x 132 x 108 mm.

● The dial is gilded brass with silvered chapter rings and original steel hands. The chapter rings are now screwed to the dial plate. The signature has two small unused holes at either end suggesting a covering plaque. The dimensions are: 235 x 192 mm.

● The movement has exactly the same train as in Huygens’ diagram (see Fig. 2). The train count corresponds to a 1 second pendulum.

Fig. 10 (click to enlarge)
Original hands.  (view high res. picture)



Fig. 11 (click to enlarge)
of the metal box case and dial.
(view high res. picture)

Fig. 12 (click to enlarge)
 Thuret clock, side view, metal box case,
hanging loops riveted to case sides.
 (view high res. picture)

Fig. 13 (click to enlarge)
Thuret clock, back view, box case removed.
(view high res. picture)

Fig. 14 (click to enlarge)
Thuret clock, back of dial, case and movement removed.
(view high res. picture)

Fig. 15 (click to enlarge)
View of movement, note the crown wheel and large diameter pinion. Also note the hole in the first arbor originally used for the pin securing the driving pulley
(now missing)
(view high res. picture)

● The dimensions of the movement plates are:
back 148.5 x 77 mm, front 167.5 x 77 mm. The first-wheel arbor was originally fitted with a driving pulley. Assuming the dimensions of the movement plates in the drawing of Fig. 2 are the same as this clock then one can determine that the diameter of the pulley was about 25 mm. This diameter would give a drop of 188 cm per 24 hours. The height of the clock centre for 30 hours would be at least 235 cm or 7 ft 10 in.

Fig. 16 (click to enlarge)
The outer sides of the back (left) and front (right) movement plates.
(view high res. picture)

Fig. 17 (click to enlarge)
The inner sides of the back (left)
and front (right) movement plates.
(view high res. picture)

Fig. 18 (click to enlarge)
Thuret clock. The wheels and pinions.
(view high res. picture)

Fig. 19  (view high res. picture

● To increase the duration between windings and allow for a lower positioning on the wall this pulley has subsequently been removed and the first wheel arbor extended through the back plate for an additional pinion. This pinion was driven by an extra wheel (now missing) situated between the bracket and the backplane, its arbor pivoted at the front in a small cock secured to the inside of the front plate. The arbor of this extra wheel carried the new, and probably larger, driving pulley. The lower position of this pulley was only accommodated by filing flats on the insides of the two lower pillars. The ratchet pulley mounted on the back of the dial may still be the original, but reversed.

Fig. 20 (click to enlarge)
The back-cock would have originally held a silk suspension (two threads) and the cycloidal cheeks.
(view high res. picture)

There is a section of partly threaded square brass rod which was found with the clock and has been recorded in case it was part of the original pendulum. It is too large to pass through the pendulum crutch however it may have been part of a lower section of the pendulum. The pulleys, weights and pendulum are missing.

Fig. 21 (click to enlarge)
Pyramidal headed screws for adjusting
 the vertical position of the clock on the wall.
(view high res. picture)

Fig. 22 (click to enlarge)
Back-cock screws.
(view high res. picture)



Fig. 23 (click to enlarge)
Case securing screws.
(view high res. picture)

● The two screw holes in the dial plate either side of the signature are interesting. The only explanation for these holes is that they once held a plate covering the signature. The hiding of Thuret’s name would very much resonate with Huygens’ secretive behaviour. It is quite possible therefore that both clocks belonged to Huygens and there is no reason to believe that they are not of the same date as the 1657 woodcut.

● With regard to their description in previous articles as astronomical regulators it is important to remember that any experimental clock of this period that was designed to be tested accurately would be regulated with reference to astronomical observation and therefore likely to have regulator dials.

ISAAC THURET

Isaac Thuret was born into a Protestant family at Senlis in France, around 1630. He acquired impressive social connections. His sister Susanne married Charles Francois de Sylvestre, Maître de dessin des Enfants de France and his son Jacques married the daughter of the famous designer to the court of Louis XIV, Jean Bérain.(26 
A 25 year- old Thuret, rapidly becoming France’s greatest seventeenth century clockmaker, would have been a natural contact for his contemporary Huygens, when the latter visited Paris in 1655. Huygens spent 4 to 5 months in France in the autumn of that year, mainly in Paris. There is no mention of Thuret’s name in Huygens’ correspondence published in the Oeuvres Completes until 1662 when the latter is informed that his father was impressed by Thuret’s clocks and asks his brother Lodewijk, in a letter of April l2 ‘how are these Thuret clocks made, for which my father pays 10 or 12 pistoles and prefers to his own? If we could know the form it could be used to instruct the clockmakers here...'.(27 This reference has been taken as indicating Huygens’ lack of acquaintance with Thuret, sometimes giving the impression that it is a general enquiry about Thuret’s work. However the complete passage clearly shows that it is an enquiry about a specific type of clock with which Huygens’ compatriots, under his patronage, were in direct competition. Huygens is responding here to a previous comment and taking advantage of his brother’s location in Paris. Given also Huygens’ conflict of interest, the request in this letter is not surprising and does not preclude previous close cooperation between Thuret and himself.

● The next reference to Thuret, again in family correspondence, occurs several times in 1664 and concerns the sending of clocks made by Claude Pascal to Thuret for repair.

Jean Chapelain (1595-1674)

In 1665, Jean Chapelain writes to Huygens on the subject of the latter’s remontoire clock for which a French patent was granted, ‘that excellent clockmaker Monsieur Thuret, of whom you yourself have told me much good, visited me yesterday and asked me to offer you his services for the construction of clocks to be used on ships and for their sale and distribution.. ‘.(28  Chapelaine was authorised to dispose of the patent on the inventor’s behalf and it was probably that fact, or the chance that a random visit presented, that caused Thuret to make this indirect approach. Huygens agreed to this request 2 weeks later.

● In 1666 Huygens moved to Paris and presumably continued to employ Thuret. However the next episode involving the two that appears in Oeuvres Completes is their collaboration and subsequent contention over the balance spring which took place in 1675 and is outside the scope of this article

CONCLUSION

The clock illustrated in Horologium Oscillatorium has up to now been attributed without dispute to Isaac Thuret(29 albeit without realising its early date. There is no need to withdraw this attribution. To the contrary, Huygens had ample opportunity to meet Thuret in Paris in the autumn of 1655. Huygens himself is linked to one of the surviving Thuret clocks and both examples described here, certainly look as early, if not earlier than the Coster clocks. For the sake of completeness it may be asked whether Thuret clocks could be later copied from this illustration rather than visa-versa. However, the clock in the illustration, like Huygens’ research in early 1657 reveal the work of a clockmaker, and the search for someone else would be at the expense of plausibility. It is probable that Thuret did not initially have permission to make these clocks for anyone other then Huygens and by the time that restriction had ceased, clock design had progressed beyond the need to reproduce the original model.

● The remaining problem concerns the fact that the first mention of Thuret’s name in the Oeuvres Completes is 7 years after Huygens’ first visit to Paris. The likelihood is that Huygens went to great lengths to keep Thuret and his contribution secret. However, it is also very important here to recognise the limits of the Oeuvres Completes in general and Huygens’ surviving correspondence in particular. This is a classic example of where absence of evidence is not, of itself, evidence of absence. As is so often the case, it is not known how Huygens compiled or subsequently edited his own correspondence. It is far from complete. Where is the trade correspondence? Did he later remove contentious or awkward material with a view to posterity?

● Apart from his alleged secrecy there is an aspect of Huygens’ character which is relevant to the changing dynamic of his relationship both with his invention and with Thuret; and that is the rapidity with which he progressed through successive projects.

● This progression should be viewed against the backdrop of his many simultaneous scientific enquiries. Naturally his first horological priority was to eliminate variation and this meant, among other things, that he had to start with weight drive. By early 1657, while preparing to franchise various imprecise domestic models, he was working, almost certainly in secrecy, on a maritime pendulum clock with spring drive as mentioned in the Mylon letter quoted previously. Huygens was clearly confident of overcoming the problems of pendulums at sea. For ships’ chronometers he favoured a going barrel without fusee. Although he vaunted the resistance of his isochronal pendulum against the variations of power in a going barrel, the main reason for rejecting the fusee was its lack of maintaining power during winding. However, he found that his isochronal cheeks, fine when stable in a wall clock, changed the pendulum length when even slightly tilted. This led him, in late 1657 or early in 1658 to develop his half-second clock with ‘O-P’ gearing. This gearing avoided the need for isochronal cheeks by lessening the amplitude of the pendulum to that arc where the circular and the tautochrone hardly diverge. This second clock was therefore presumably intended to be developed into a marine clock although the possibility of an increase in pendulum amplitude caused by pitch or roll must have been a concern. Again Huygens commenced by testing a weight driven version and he presumably found that the performance was insufficient for further development in marine use. At this point he probably realised that longitude horology required a radically new approach.

● In November 1659, Huygens developed a conical pendulum clock () which he used to obtain a new value for the constant of gravitational acceleration. It is not known who constructed any of these subsequent clocks. It is established that his conical pendulum clock existed, for he obtained his new value for free fall, ‘ex motu conico penduli’ (30 The lack of any mention of it in the correspondence of the Oeuvres Completes and the editorial speculation that it did not exist, provides a further caveat to regarding such an archive as an audit of events. With his extraordinarily busy life and changing agenda, it is quite possible that Huygens temporarily abandoned his far-off Parisian clockmaker in the first years of the 1660s, if not before. The lack of mention of Thuret in Huygens’ papers is no doubt chiefly due to the fact that Huygens saw no share for the constructor in the celebrity of his invention. At least two Thuret clocks have thus been deprived for 350 years of their proper recognition. They are the sisters of his first pendulum clock and the earliest surviving models of the first complete pendulum theory. And as such they embody what may be, despite modern perspective, the defining achievement of a prolific immortal of the Scientific Revolution.

ACKNOWLEDGEMENTS

I wish to express my gratitude to Jean-Claude Sabrier for discovering and making available a hitherto unpublished Thuret clock. And to Andrew Crisford who provided from his libraries the conclusive evidence of Benjamin Martin.

March 2009, Copyright:

	Sebastian Whitestone.
	Jean Claude Sabrier.

LINKS

Chr. Huygens' Œuvres Complètes. (pdf)

Chr. Huygens Horologium 1658. (pdf)

The Antiquarian Horological Society.

(This article is subject to ongoing revisions.)