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Ever since in 1888 the first volume of Oeuvres Complètes was published, much has been written about Christiaan Huygens’s invention on Christmas Day 25 December 1656 of the application of a pendulum to a clock movement and the further developments of the early pendulum clock.

By copying information, taking assumptions for granted as true evidence and through misinterpretation, the story of the pendulum clock threatens to get out of proportion.

To put the history and the involvement of the protagonists back into perspective, renewed independent research was needed, based on original documents in the archives and libraries.

This article covers the most important developments up to and including Huygens’s publication of Horologium
 on 6 September 1658.

PUBLISHED ARTICLES

In recent decades, several authors have published articles on the history of the introduction of the pendulum clock. The most important source of these publications is, almost inevitably, the extensive standard work Oeuvres Complètes de Christiaan Huygens,(1 for which the editors deserve our respect and gratitude. We recently found that not all documents kept in the archives have been noticed or recorded by the editors. This prompted us to re-study the first period of the pendulum clock on the basis of our own extensive archive research independent from Oeuvres Complètes, Spring-Driven Dutch pendulum clocks 1657–1710,(2 Catalogue of the Manuscripts of Christiaan Huygens,(3 and all other publications. Original documents were examined in the reading room of the University Library of Leiden,(4 in combination with the Codices Hugeniani in the digital archive of publisher Koninklijke Brill N.V. in Leiden.(5 New, not previously published, finds were made. Time to entrust our findings to this paper.

THE NOTES OF CHRISTIAAN HUYGENS

The notes of Christiaan Huygens
Shortly before his death in 1695, Huygens donated a significant part of his scientific treatises to the University Library in Leiden. After 1800 this legacy was further enriched with family-owned manuscripts and letters. The personal archive of Christiaan Huygens has been brought together in the Leiden University Library in the so-called Codices Hugeniani and is digitally available. These Codices Hugeniani are collected in fifty-two volumes and contain notes and folders with loose texts in the fields of astronomy, mechanics, mathematics and music, as well as annotated books and sent / received correspondence. At the top of the pages of the original letters of Huygens the editors of Oeuvres Complètes added in pencil their own method of numbering the letters, which matches the letter numbers in Oeuvres Complètes as contained therein. For clarification and traceability we added the OC numbering in the footnotes as well.
In order to gain a better understanding of the following, it is important to know that before Huygens sent a letter to one of his contacts, he first wrote a draft or working copy. The primary purpose of this working copy was to organize his thoughts and make improvements when necessary. Once this was to his liking, Huygens wrote the letter in a final version to send it out. He kept the working copy for himself so that he could reread it later. The working copies of Huygens’s outgoing correspondence are thus located in Leiden, while the same letter in the final version may be kept elsewhere, for instance in Paris.
The original documents of the University Library in Leiden show that Huygens consistently and frequently used his working copies of letters as scrap paper for notes, sketches and points of interest. Especially the back, but also the margin of the copy was used (Fig. 1). These notes are not always included in Oeuvres Complètes and can provide new presumptive evidence to the history of the development of the pendulum clock.

 December 1656 – June 1657

Huygens’s correspondence and notes

On Christmas Day 1656, Huygens invented the simple and ingenious way of applying a pendulum to the escapement of a clock movement. This date can be determined accurately because Huygens wrote in a letter to the astronomer Boulliau on 26 December 1657:

It was yesterday exactly a year ago that I made the first model of this kind of clockwork. (Il y eust hier un an justement que je fis le premier modelle de cette sorte d’horloges.) (6

Almost one year earlier, on 12 January 1657, Huygens first mentioned in the last paragraph of his letter to his mentor Frans van Schooten that he had recently invented a new construction of a clock driven by weight, which runs so regularly that he has high hopes it will make the determination of longitude at sea possible.(7

In a letter to Claude Mylon, dated 1 February 1657, Huygens writes:

I really like the news you tell me about Mr Bulliaut’s (8 arrival in these countries, because in addition to what I had to show him in the field of optics, I have a great desire to discuss some specific opinions I find in his work about the astronomy, namely, the comparison of days; I will also share with him a new invention which should be of great use in astronomy and which I hope to use successfully in the search for longitudes. You might hear about it soon.(9

In a letter to Huygens, dated 12 April 1657, Mylon writes that everyone he spoke with about Huygens’s invention of the pendulum clock found it very beautiful. Also that it will be even more so if he makes it invariable with weights as much as with a spring.(10.

Another, undated,(11. letter from Huygens to the manager of the Leiden Observatory Samuel Karl Kechel, also known as Kechelius, is very interesting. Huygens informs Kechel of the following: (12

The occasion for the invention was provided by the pendulums you have been using for several years. Seeing that, because of the amazing equality of their oscillations, these were ideally suited for measuring time, I started to ask myself whether I could somehow keep their movement continuous and at the same time could take away the inconvenience of counting. I finally came up with the simplest of several ways in which this could be done. I connected the pendulum to the part that regulates the motion through its oscillating movement, called ‘onrust’(13 in our language. However, I did not place this part horizontally, but upright, and let the pendulum hang from a rigid iron bar. When I had done this and then put the weight on the clock, it turned out, just as I expected, that the force of the clockwork aided the individual oscillations of the pendulum, so that instead of gradually weakening into smaller oscillations and finally turning off, they kept going on in a certain deflection. Due to the fact that the oscillations remain equal, the motion of the movement remains equal as well.(14

It is now established that Huygens’s very first design of his invention is a weight-driven pendulum clock with a vertical balance, contrary to previous assumptions of a spring-driven balance clock.(15
The question is when Huygens owned a working pendulum clock. The answer can be found in a letter from the French mathematician Claude Mylon to Huygens dated 18 May 1657.(16

I am glad that you are perfecting your new clock more and more, and I do not despair that you will make it as good at sea as in your own room, and that the changes of humidity will not alter it more than the change of weights.

(Je suis bien aise que vous perfectionniez de plus en plus vostre nouuelle horloge et ne desespere que vous ne la rendiez aussi bonne sur la mer que dans vostre chambre, et que les changements du sec a l’humide, ne l’alteront pas plus que le changement des poids).

In addition to the correspondence to and from Huygens, there is also an early note by Huygens to be found in the Codices Hugeniani. This note states:

From 31 May till 6 June, this is in 6 days, found 2 min. too slow, which is daily 1⁄3 min. Therefore 1⁄6 of a turn added. (Van den 31 Maj. tot den 6 Jun. Dat is in 6 daeghen, bevonden 2' te langhsaem, dat is daeghs 1⁄3 min. Daerom 1⁄6 van een draeij opgezet).(17

This means that a working pendulum clock had been constructed at least by 18 May 1657 and that Huygens was fine-tuning the pendulum. Secondly, it is remarkable that the period between the invention of Huygens on 25 December 1656 and a proven working pendulum clock on 18 May 1657 at the latest was very short. This does not surprise us, because it must have been relatively easy for a clockmaker to turn Huygens’s invention into a working model. If a clockmaker was able to make watches or complicated horizontal table clocks with striking mechanism in the pre-pendulum period, the Huygens pendulum clock with only three wheels (excluding the OP-construction and motion work) is very easy to build. Although Huygens ground his lenses himself, no indication has been found in his extensive oeuvre that he was also capable of making a clock himself. During the above-mentioned period, Huygens lived in The Hague and also stayed there. To construct his clock, it is likely that he collaborated with a local clockmaker with whom he communicated regularly to discuss the progress. In the period 25 December 1656 until the patent was filed, between 1 and 15 May 1657 (see below), there is no indication in Huygens’s correspondence or in his workbooks which clockmaker it might be.

The patent

In the first half of 1657, master-clockmaker Salomon Coster applied for a patent at the States-General in which Coster stood proxy for the inventor Huygens.(18 In the seventeenth century it often happened that a patent was granted to someone standing proxy for the inventor.(19 For example, a patent was granted to Jan Andriesz Moerbeeck for printing textiles with figures, while the actual inventors were Aert Duyffkens and Herman Becx. Another patent was granted for a ribbon mill to Gabriel Hanedous, Pieter Bodje and Jan Veecken, while Willem Dircxz Sonneveldt was the inventor.(20
With the assistance of employees of the National Archives in The Hague, we have extensively researched the period between 1 January 1657 and 1 July 1657 in the letters and patent applications in the archives of the States-General and the States of Holland. Unfortunately, this search did not lead to any results. In consultation with the National Archives, it can be finally established that Coster’s patent application is unfortunately no longer there. However, we have been able to determine that, in view of other patent applications from the same period, it took a period of four to six weeks from receipt of an application to processing and ultimately granting. Therefore we can conclude that Coster must have filed the patent application between 1 and 15 May 1657. In addition, it has been confirmed that it was common practice that appendices to a patent application (e.g. an illustration) would be returned to the applicant after processing. Appendices were attached to the official patent document of the patentee for legal reasons in case the patentee had to rely on his patent before a judge. In this way the content of the invention could be clarified.(21
From the minutes of the meeting of the States-General of 14 June 1657 it appears that Coster’s request was read in this meeting. It was decided to instruct the deputies Messrs. Glas and Mauregnault to ‘inspect the invention and submit the report’.(22 (Fig. 2)

Fig. 2
Instruction to inspect the clock
supplied by Salomon Coster
for the patent procedure.
National Archives The Hague,
resolutien Staten Generaal
14 June 1657.

 ‘[...] te versoecken
ende te committeren de heeren
Glas ende Mauregnault om
de voors. inventie t’inspecteren
ende daer van rapport te doen’.

Obviously, they had to inspect a working Salomon Coster pendulum clock, given the simple fact that Coster was the applicant for the patent and thus provided the working invention. As shown in the minutes of the meeting of the States-General of 16 June 1657 the report of Messrs. Glas and Mauregnault was heard, after which the application was approved. The patent (privilege or sole right) was granted to Coster and he received the privilege for 21 years.(23
To practice the patent in the Provinces, Coster had to apply for an attachment. On 16 July 1657 the States of Holland and West-Friesland granted this attachment for twenty years. From that moment Coster was the only one allowed to make and sell pendulum clocks. Coster’s patent was strictly demarcated and even pendulum clocks made outside Holland were not allowed to be sold or traded. The delivery of pendulum clocks therefore always had to take place under the auspices of Coster.(24
At the request of Christiaan Huygens another attachment to the States-General patent was granted by the Province Gelderland in their meeting of 19 October 1658 to Salomon Coster in collaboration with Jan van Call.(25 As a clockmaker, Coster needed a turret-clock maker to forge the necessary large parts for the conversion of turret clocks. Cooperation with turret-clock maker Van Call was obvious, since Huygens writes in his letter to his cousin W. Pieck in October 1658 that he thinks Jan van Call is an honest man and a renowned master.(26

[...] horologij mei edita anno 1657

In the Codices Hugeniani we found a drawing in ink of the profile of a pendulum clock with all elements labelled with a letter.(27 (Fig. 3)The drawing is severely darkened. This drawing has apparently escaped the attention of the editors of Oeuvres Complètes and consequently is not included in it. Joella Yoder has seen this drawing and noted that on the top right hand side Huygens had written ‘[illegible word] horologij mei edita anno 1657.’ (28 She could not decipher the first word. Despite the fact that Yoder noticed this drawing, the document itself has never been published or used by anyone else. The right hand corner at the bottom has been torn off. An identical drawing, exactly positioned over the recto drawing, created in pencil, is found in verso (now the torn off corner is on the left). The elements on this drawing however are not labelled, unlike on the drawing on recto. In another handwriting is added Tabula haec iteri incisa reperitur in Hugenii Horologio, which means that this drawing has been copied into Huygens’s Horologium.

Fig. 3
The recto side of Codices Hugeniani,
Hug 32 folio 188, in Leiden
University Library, showing a
drawing in ink of the profile
of a pendulum clock with
 all elements labelled with
 a letter, and top right
 the inscription […] horologij
 mei edita anno 1657.

Dr Mart van Duijn of Leiden University Libraries(29 has examined this document. His conclusions are:

1. The dark side is caused by rubbing with a dark fabric, which may be dirty but looks like pencil smudges. My suspicion is that this was caused after the pen drawing has been applied, possibly because the sheet lay at the bottom of a pile or was very deliberately swept over it. I don’t think wiping away an existing drawing created the dark colour.
2. There are no signs of correction, wiping or anything to that effect. It is more like hiding the entire page altogether, by making dark streaks on it.
3. The pen note is complete and does not appear to be part of anything that has been corrected or deleted. The fact that the note is difficult to read is most likely due to what caused the dark smudges. It may have been the intention to conceal not only the pen drawing, but also the inscription.
4. There are no indications that there was a pencil drawing underneath the pen drawing. At least that is not visible. On the other side of the sheet there is a pencil drawing of exactly the same clock and it seems that the pencil drawing has been traced from the pen drawing on the other side, or vice versa (see also Yoder).

Examination of the illegible part of the inscription on top of the pen drawing with UV-light is unfortunately inconclusive.

After learning of Dr Mart van Duijn’s findings, we examined a high-resolution image of the drawing with specialized professional software and discovered the ‘illegible’ word Figura. The complete text of the inscription is Figura horologij mei edita anno 1657 (‘Figure/drawing of my clock made known(30 in 1657’) (Fig. 4).

Fig.4
Examinion of a high-resolution
 image of the drawing with
 specialized professional
 software revealed the previously
 illegible word ‘Figura’. The complete
 text is Figura horologij mei
 edita anno 1657
 (‘Figure/drawing of my clock
 made known in 1657’).
Edited by Tom Memel ©.

We also compared the handwriting of the inscription with Huygens’s handwriting in original documents. For instance the letter ‘h’ of the word horologij looks like a letter ‘E’. And in a letter to Boulliau of 1 January 1660,(31 Huygens writes the letter ‘h’ of the word horoscope in exactly the same way. We can establish that the handwriting of the inscription is the genuine handwriting of Christiaan Huygens. (Fig. 5) 

Fig. 5
Comparison of Huygens’s handwriting.
Edited by Tom Memel ©.

So, this is a drawing of Huygens’s pendulum clock with an inscription in his own handwriting and is identical to the illustration that Huygens published in the following year on 6 September 1658 in his Horologium. The darkened drawing shows a weight-driven pendulum clock with hour, second and minute indication, a vertical crown wheel, OP-construction,(32 no cheeks and a ½ second pendulum without a sliding weight.

June 1657 – December 1657

After obtaining the patent in June 1657, Coster immediately noticed he had to expand the working capacity in his workshop. The further development with the matching demand for the much more accurate pendulum clock was expected to become great. In addition, the regular production as well as the repair of non-pendulum clocks and watches had to be maintained. At least during this period the apprentice Christiaan Reijnaerts and of course John Fromanteel worked for Coster. John Fromanteel is mentioned as a master-servant,(33 but according to the rules of The Worshipful Company of Clockmakers was still apprenticed to his father.(34 Fromanteel worked for Coster from September 1657 till May 1658.

Fromanteel was commissioned and supervised by Coster to make horologien. The Coster-Fromanteel contract unfortunately does not give any information about what type of timepiece is meant by horologien, because further specification is lacking. Nor does the contract explicitly refer to Huygens’s invention which makes timepieces much more accurate. It is therefore uncertain whether John Fromanteel, at Coster’s workshop, worked exclusively on the production of pendulum clocks or assisted in the ongoing production of non-pendulum clocks.

In the summer of 1658, the French master clockmaker Nicolas Hanet arrived in The Hague and worked for some time in Coster’s workshop.(35 As Coster’s agent, Hanet left for Paris in September 1658 with two or three pendulum clocks.(36

The first delivery of a pendulum clock

The very first evidence of a delivery of a pendulum clock can be found in the Archives of Florence. Twenty years after the death of Grand Duke Ferdinand II de’ Medici, an inventory of the Grand Duke’s assets was drawn up because of the appointment of a new Guardaroba, a new officer in charge of the Guardaroba office. This inventory of the objects in the private collection of the Grand Duke, dated 12 July 1690, is kept in the Archives of Florence.(37
Described is a clock with a small pendulum in an ebony case with a profiled door with glass, on a velvet-covered dial, a silver hour circle and a silver nameplate signed Salomon Croster [sic], present in the salon. This clock was sent on 25 September 1657 by Signor Titio Livio Burattini to the Grand Duke Ferdinand of glorious memory, was made in The Hague in Holland, and was the first pendulum clock brought to Italy (Fig. 6).(38 Given the production and shipping time, Salomon Coster will have started working on this clock in July or August 1657, shortly after obtaining the patent. Unfortunately this clock has disappeared.

Fig. 6
Detail from Guardaroba Medicea,
 number 959, folio c.29v, in
the State Archive of Florence.
 It describes the Coster clock
 in the inventory list of the
 assets of Grand Duke Ferdinand II
 de’ Medici, drawn up in 1690.

‘Un oriuolo da attaccare al muro
 a dondolo piccolo, con cassa
d’ebano e cristallo avanti,
 con una cornice a onde,
 alto braccia 1/2, largo soldi 8,
 con fascia d’argento delle ore sopra
 del velluto, con una cartellina
 d’argento, similmente scrittovi
 Salomon Croster, sta presentemente
 nel salone, e questo oriuolo fu
 mandato dal sig.re Tito Livio
 Burattini al Serenissimo Gran Duca
 Ferdinando di gloriosa memoria
 ne’ 25 settembre 1657,
fatto all’ Aia in Olanda,
 e fu il primo oriuolo a dondolo
 che fusse portato in Italia’.