Trust in Glass: Negotiating the Purchase of the Object Glass for the Airy Transit Circle

Planning the Transit Circle

The first surviving reference to a proposed transit circle at the Observatory can be traced back to 1843. In this year Airy began contemplating the substitution of the meridian instruments (the transit instrument and the mural circle) with one(s) that had greater optical power. As he noted in his autobiography, this work began by contacting opticians about an 8-inch object glass:

In November [1843] I was enquiring about an 8-inch object glass. I had already in mind the furnishing of our meridional instruments with greater optical power. ¹⁵

Between 1843 and the official proposal of the Transit Circle (in 1847), Airy was involved in the supervision and the making of the equatorial and transit instruments for the Liverpool Observatory (for which the object glasses were supplied by George Merz). ¹⁶ Meanwhile, Airy designed and oversaw the construction of a new astronomical instrument (the Altazimuth) for the Royal Observatory, Greenwich by the firms Troughton & Simms and Ransome & May. ¹⁷ These projects served as testing grounds for Airy where he could assess the product quality and the services provided by opticians, engineers, and instrument makers. As we will see, references to these projects and firms were frequent in Airy’s negotiations over the object glass of the Transit Circle. For instance, he argued that his (temporary) distrust in Georg Merz originated from his involvement in the Liverpool Observatory project. ¹⁸

The official publications of the Royal Observatory, Greenwich told a slightly different story about the origin of the Transit Circle. They highlighted the importance of following the historical aim of the Observatory with a focus on positional astronomy and contributing to the ever more precise determination of longitude. ¹⁹ The initial official proposal of a new instrument replacing Troughton’s transit instrument was mentioned in the Annual Report of 1846. ²⁰ It identified the small optical power of other meridian instruments at the Observatory as a general problem. ²¹ With the addition of this note, Airy was already hinting at the possibility of replacing the mural circles too that were used in conjunction with the Troughton transit instrument. The problem of small optical power was repeated in the Annual Report of 1847, but it was contextualised differently. ²² Airy reported that the French instrument maker, Noel Paymal Lerebours offered to make the Observatory “the largest refracting telescope in existence,” but the Astronomer Royal felt obliged to decline this offer. ²³ Airy argued that such an instrument would have distracted the attention of the Observatory from the main plan of operations in meridian astronomy, which was historically defined as its mission. Instead, it was proposed to the Board of Visitors to contemplate whether “meridional instruments carrying larger telescopes should not be substituted for those which [the Observatory] possess.” ²⁴ From these two reports we can already see that the object glass emerged as a crucial point of departure for the construction of the Transit Circle. Its importance was further emphasised by the Visitors’ response to Airy’s proposal:

[the] Astronomer Royal to be requested to make further inquiries with respect to the size and character of new instruments fitted for such purposes [i.e. observation of small objects], and to report thereon to a future meeting of this Board. ²⁵

Airy wasted no time and by the end of the year he was working on the preliminary designs of the Transit Circle from his countryside residence in Playford. ²⁶ There are references to these designs in Airy’s letters to Charles May, but it is difficult to determine whether any of the surviving plans of the instrument are these. Most of the surviving plans seem to have been drawn up by the draughtsman of Ransome & May (and by Charles May himself). ²⁷ However, at least two of the plans were drawn on different types of paper, and with less accuracy, which imply the lack of tools and resources that Airy had available in Playford. ²⁸ All of these plans played a crucial role as they became the basis for the small models that were used to showcase the instrument for the Board of Visitors in order to convince its members about the need for the project and the viability of the instrument’s design. ²⁹

The role of the Board of Visitors in the purchase of the object glass

Before venturing further into the story, it is important to clarify the role of the Board of Visitors under Airy’s directorship. The Board of Visitors oversaw the operations of the Observatory in order to provide the Admiralty (the institution funding the Observatory) with expert advice. ³⁰ Through the Annual Visitations they supervised the work of the Astronomer Royal, and in major projects (such as the construction of the Transit Circle) they provided him with suggestions. The Board also had to approve the Astronomer Royal’s proposals for new research projects (such as the construction of new instruments or the systematic re-calculation of previous observations) and provide the Admiralty with justification for the related expenses. At the time of the Transit Circle’s proposal, the Board consisted of the President of the Royal Society (the Marquess of Northampton), the President of the Royal Astronomical Society (John Herschel), selected Fellows of the Royal Society (John Lubbock, Captain William Smyth, Reverend George Peacock, Dr William Whewell, Reverend Richard Sheepshanks), selected Fellows of the Royal Astronomical Society (Charles Babbage, Samuel Hunter Christie, Sir Francis Beaufort, Manuel J Johnson), former presidents of the two societies (Sir James South and Lord John Wrottesley), the Savilian Professor of Astronomy at the University of Oxford (William Donkin), and the Plumian Professor of Astronomy at the University of Cambridge (Professor James Challis).

As can be seen from these names, the Visitors included established members of the scientific community, who were not in an agreement on every issue. In fact, personal grievances against each other often affected their meetings. For example, James South and Richard Sheepshanks engaged in one of the most dramatic disagreements on the quality of British craftsmanship, which in turn divided many members of astronomical community, including Charles Babbage and George Airy. ³¹ Babbage also had more reason to nurture his disapproval of the Airy. While Airy was still living in Cambridge, he was appointed instead of Babbage as the Lucasian Professor of Mathematics in 1826. ³² Furthermore, after becoming Astronomer Royal, Airy acted as a scientific advisor to the government, through which he did not support the renewal of funding for Babbage’s differential engine. ³³ In brief, while the Board of Visitors existed to provide expert advice to both the Admiralty and the Observatory, their members were not in unanimous agreement on every matter. However, one of Airy’s major critics, James South rarely attended the Visitations, which helped to alleviate the major disagreements between the members. ³⁴ With Airy’s appointment as Astronomer Royal, the Board’s function also slightly changed. The Commissioners of the Admiralty were given the ability to issue instructions without the need to consult the Board of Visitors first. ³⁵ With this change, Airy had the opportunity to bypass the Board of Visitors in certain matters. This was rarely exercised, and the members of the Board continued being consulted before making major decisions. However, as we will see, in the case of the object glass of the Transit Circle, Airy did not consult the Board when justifying the choice for its supplier. Instead, he applied directly to the Admiralty for funding with a justification offered in the form of a price comparison. ³⁶

The Annual Visitations where the regular meetings of the Visitors took place were usually held on the first Saturday of every June. Considering the construction of a new instrument a significant issue, Airy called for an extraordinary meeting of the Board to be held in January 1848 to discuss his proposal for a new meridian instrument. ³⁷ Prior to this meeting, Airy circulated among the Visitors a report that was going to be discussed at the meeting. In this document, he outlined his general plans for a transit circle. ³⁸ He received many responses to this circular, which included both support and further suggestions on his plans. ³⁹ Lord Wrottesley pointed out that the approximate cost of constructing the new instrument was not mentioned in the circular. ⁴⁰ James Challis reported back on how he used the Northumberland Equatorial to make meridional observations, thus attempting to direct the conversation towards the procurement of an instrument other than meridian instruments. ⁴¹ Richard Sheepshanks responded in most detail. He was the son of a wealthy textile manufacturer, a Cambridge graduate, and a lawyer by original profession. His background allowed him to devote his time to scientific research and to take active part in the scientific community and to build up close relationships with instrument makers. ⁴² In addition, Airy and Sheepshanks have built up a strong friendship, which was solidified even further after their clash with Babbage and South. ⁴³ This proximity to Airy allowed Sheepshanks to share his personal thoughts on the proposed Transit Circle. His response to Airy’s letter stated that the larger size of the object glass did not always increase the ability of an instrument to observe fainter celestial objects, noting that other variables also had to be taken into account during the construction of the Transit Circle. On the other hand, he also pointed out that if the telescope was well built, then the larger object glass could increase the optical power of the telescope and extended the observing range with about two magnitudes. Finally, he added that in order not to waste the potential of a larger object glass, he preferred to use it as part of a transit instrument as opposed to as part of a transit circle. By doing so, he was arguing that constructing a transit circle instead of a transit instrument was too much of a risk with respect to the quality and size of the proposed object glass. ⁴⁴ The concern of Sheepshanks about wasting the potential of the object glass was not unfounded. Transit circles that combined the designs and functions of transit instruments (used for measuring the right ascension of celestial bodies) and mural circles (used for measuring the declination of celestial bodies) were relatively uncommon at the time. In addition, Airy proposed his own unique design for a transit circle rather than relying on designs previously made by instrument makers. Therefore, the comments by Sheepshanks highlighted the risky nature of the construction project. Besides the Visitors, Airy also asked for the opinion of Heinrich Christian Schumacher, founder and editor of the international astronomical journal Astronomische Nachrichten. He called Airy’s attention to the need to test the errors of the proposed collimating telescopes measuring the deviations of the telescope tube, since the temperature changes were going to affect several parts of the Transit Circle, such as the east-west axis and the piers. ⁴⁵

The responses Airy received allow us to reflect upon two important aspects of the history of the Transit Circle. First, the responses show the active role of the Board of Visitors in the construction process. Its members supported Airy’s proposal by suggesting further improvements to the instrument and offered alternative directions to him at the same time. These suggestions demonstrate that the final design of the Transit Circle was the outcome of a collaborative discussion taking place among several members of the astronomical community, as opposed to the product of a single individual. Second, the responses depict what issues were deemed significant for the members of the Board, and how everyone framed the issue of the object glass differently. For example, while Lord Wrottesley was interested in the financial side of the purchase, Sheepshanks emphasised the need for reliability in relation to the prospective performance of the object glass. Similarly, while Schumacher highlighted the importance of measuring the errors of the telescope, Challis described alternative instruments and methods through which Airy’s aim could be achieved. In brief, the Transit Circle was not an instrument that embodied unanimous consensus; instead, it brought forth the different ways in which the instrument (even at its immaterial form) was interpreted.

While Airy received mixed responses in terms of the direction which he should take with construction of the Transit Circle, the minutes of the January 1848 meeting reveal that there was an agreement among the members of about the need for a new instrument that allowed for the observation of fainter celestial objects. In fact, the meeting finished with emphasis on procuring the object glass for the instrument as the first step to begin the project, and in turn the Astronomer Royal was assigned the task of finding out and deciding who to purchase the object glass from. ⁴⁶

Trust and distrust in glass

The making of high-quality object glasses was a secretive task during the first half of the nineteenth century. The object glasses made by Louis M. Guinand were generally considered to be the highest quality at the time. ⁴⁷ In 1805, he joined the craftsmen and opticians at Benediktbeuern, which establishment later included individuals who rose to prominence as opticians and instrument makers during the nineteenth century: Joseph Fraunhofer, Joseph Utzschneider, Georg von Reichenbach, and Georg Merz. ⁴⁸ Benediktbeuern Abbey was the site for a monastery, which was dissolved in 1803. In 1805 it was bought by the instrument maker Joseph Utzschneider for setting up a workshop dedicated to experimenting with the production of high-quality glass suitable for use in optical instruments. Benediktbeueurn became a highly respected establishment and the making of high quality optical glass in Europe was almost completely monopolised by it until the 1850s. Astronomers sought to order object glasses from Benediktbeuern in order to ensure the reliability of the final product. ⁴⁹ The popularity and secrecy of the manufacturing processes resulted in higher prices and long production times, which factors astronomers like Airy disliked. Louis Guinand did not spend his entire life at Benediktbeuern. He left the workshop in 1814 and returned to his home in Switzerland. Although he gave up object glass manufacturing for a few years, his appetite for the craft returned and supplied various instrument makers and opticians with his own products (such as Jean Lerebours, Robert-Aglae Cauchoix, Charles Tulley, Georges Bontemps, Noel Paymal Lerebours) which resulted in the dissemination of his work into the hands of a new generation of opticians.

While the secrets of Guinand and the opticians at Benediktbeuern were not revealed, other nations were keen to learn the secret manufacturing processes. ⁵⁰ In Britain, astronomers considered the products and skills of the optician Peter Dollond to be superior to his continental competitors during the late eighteenth century. With the emergence of the Guinand-Benediktbeuern axis, the British scientific community gradually concluded that the British opticians produced glasses of inferior quality. To tackle this problem, a government-funded research project was set up to improve object glass production techniques. ⁵¹ While the project was considered a success, the developed process was still unable to achieve the quality of Guinand and Benediktbeuern glasses. In light of this, British men of science made several offers to the Benediktbeuern workshop for the secrets of their manufacturing process, but all were rejected. ⁵² At the same time, the gradual dissemination of the technique to England was helped by the employment of the French optician Georges Bontemps by the Chance Brothers in Smethwick, Birmingham. ⁵³

Given the historical context for object glass manufacturing, it was no surprise that Airy quoted only the price of a Georg Merz object glass (an instrument maker and optician from the Benediktbeuern dynasty) as a guiding estimate in his 20 December 1847 circular to the Board of Visitors. ⁵⁴ Reflective of this, on 18 January, just 3 days after the Board’s meeting, Sheepshanks sent a letter to Airy urging the Astronomer Royal to purchase the object glass from Merz. Sheepshanks had good awareness of the market for object glasses, and listed three alternative opticians: William Simms, “Guinand of Paris” or Henri Guinand – son of Louis M. Guinand –, and Noel Paymal Lerebours. Despite these alternatives, Sheepshanks firmly supported ordering an object glass from Merz, due to the quality of the alternative sources being unreliable. ⁵⁵ Sheepshanks supporting Merz instead of Simms showed that Sheepshanks did not blindly favour the work of the eminent British instrument maker at all times. Instead, he preferred using suppliers who were reliable on crafting high-quality products. In addition, it also showed that William Simms was not yet known as a reliable producer of high quality object glasses, despite being considered an eminent optician.

Opposing Sheepshanks’ advice, Airy declared his determination to order the object glass from William Simms: “[i]f Simms can make a good 8 or 8 ½ inch object glass, in good time, I would prefer it to the one of Merz.” ⁵⁶ He further provided three points for justifying his selection of Simms: “first, on the principle of ostracism, secondly because Merz is confoundedly dear, thirdly because I do not think the he [Merz] is certain.” ⁵⁷ The first reason (“the principle of ostracism”) was not explained by Airy further. It seems to refer to his attempt to exclude Merz from the competition for the object glass. If that was the case, then the statement was as a direct reaction against the monopoly of Merz, and a conscious support for aiding his competitors (especially British ones such as Simms). Airy’s second reason, Merz being “confoundedly dear,” referred to the high price which the Bavarian optician requested for the object glass. ⁵⁸ This reflected Airy’s preference of economy and efficiency as displayed through the introduction of a factory mentality into the management of the Observatory, whereby the cost of a project was given just as much importance as the final reliability of the instrument. ⁵⁹ Lastly, Merz’s uncertainty can be interpreted in various ways. Airy perhaps used it to counter Sheepshanks’ emphasis on the reliability on the quality of the optician’s products, or referred to uncertainty whether Merz was going to agree to the making of the object glass (a point, which later played a crucial role in Airy’s decision). It could have also referred to the uncertainty around the exact time it would take to make the object glass. Despite these points raised by the Astronomer Royal, Sheepshanks stood his ground. He continued trying to convince Airy about the benefits of ordering the object glass from Merz. He further added that continuing negotiations with Simms and thereby creating a rivalry between Merz and Simms would foster a healthy competition and help in elevating the status of Simms as a supplier of object glasses. ⁶⁰ Airy remained set on his decision, and to close the discussion he repeated that he was planning to order the object glass from Simms if he “will make a right good glass of the proper size and in the proper time. . .” ⁶¹

William Simms and the 8-inch object glasses

Sheepshanks’ insistence on Merz was somewhat surprising since he maintained a very close friendship with Simms. It is best exemplified by the South vs. Troughton & Simms debate, in which Sheepshanks offered to defend the instrument makers in the lawsuit brought against them by James South. ⁶² One would have expected Sheepshanks as opposed to Airy to insist on procuring an object glass from Simms. After Sheepshanks’ first letter, Airy wrote to Simms about his availability and willingness to make an object glass for the Transit Circle. In this letter he emphasised that Simms’s advantage at this stage was not his quality of craftsmanship, but rather his ability to prepare the object glass within a short period of time. As Airy stated, “time is a very important element in our arrangements” to such an extent that if there was the “chance of long delay in one quarter [of the arrangements], we must of necessity look to another [supplier].” ⁶³ This emphasis on time pressure is surprising, since the urgency for procuring the object glass was not mentioned in the conclusion that the Board of Visitors reached in relation to the Transit Circle project. Therefore, time pressure was either used here as a response to Sheepshanks’ suggestions, or as Airy’s personal preference in terms of beginning the construction process as soon as possible. It is worth keeping in mind that Airy at this point still maintained the view that the construction of the instrument, could not continue any further until the object glass was finished. ⁶⁴ As a result, in Airy’s understanding of the project, securing an object glass quickly also had the practical advantage of construction on other parts of the instrument beginning sooner.

Simms accepted Airy’s conditions for the order and provided further information about when a new shipment of glass discs was going to arrive at his workshop. ⁶⁵ It is important to note here that while Merz made the object glasses himself, Simms imported the semi-finished discs (or “blanks”) from France and then modified and polished them according to the needs of his clients. Simms’ reliance on other sources for object glass could have been considered as another issue of reliability from Airy’s part, since with an external supplier, Simms could not assure the quality of the new discs he received. Despite this, Airy was adamant that Simms had to be given a chance, which insistence demonstrated the trust and the close connection that existed between the instrument maker and his client. In the same letter, Simms reassured Airy about the quality and the rapidity of the process by describing the high quality of discs received through previous orders. In addition, he promised to work on the object glass personally, so that it could be finished by the end of May the latest. ⁶⁶ Since this answer from Simms was received on 24 January, it explained why Airy decided to close further discussions with Sheepshanks (on 25 January) about alternative suppliers to the object glass.

In light of Airy’s insistence on giving Simms the opportunity to provide the object glass, it is important to discuss where such reliance on the instrument maker originated from. The proximity between the two of them began when Simms became the partner of Edward Troughton’s instrument making business. As a result of the partnership, Simms frequently worked for orders made by Airy, dating as far back as the astronomer’s directorship of the Cambridge Observatory (for the Cambridge Mural Circle (1832) and the Northumberland Equatorial Telescope (1840)). Prior to the proposal of the Transit Circle, Simms also collaborated with Ransomes & May on another one of Airy’s commissions, the Altazimuth. ⁶⁷ Since Airy was pleased with the Altazimuth instrument, that project can be considered as an important testing ground for Simms’s skills as well as his ability to cooperate with other instrument makers. Yet, Airy’s emphasis on his preference for Simms’s craftsmanship (as found in his letter to Sheepshanks) depicted the Astronomer Royal’s reasoning in a different light. Rather than focusing on their previous projects, he highlighted the quick production process, good quality, and low price offered by Simms. These factors resemble the major points that Airy also emphasised in the construction of the Northumberland Equatorial for the Cambridge Observatory, where he summarised them with the concepts of economy and efficiency. ⁶⁸ Such factors demonstrate Airy’s mindset in running the Observatory according to the principles of industrial standards (as a “factory”) where economy and efficiency were the defining principles. ⁶⁹

Simms began work as soon as he received the first shipment of discs from France in late February or early March. When Airy wrote to the optician to ask about the progress made so far, Simms replied with both bad and good news. ⁷⁰ The bad news made it clear that the discs received were so imperfect for the task that the instrument maker had to return them to France. Therefore, Simms’s initial promise about the quality of imported glasses to Airy failed. However, he explained his alternative plan, which was to perfect an object glass that was currently in his possession – a solution that according to the optician promised well. ⁷¹ While Airy’s response to this letter did not survive, Simms’s next letter exclaimed the good progress that he had made: “as soon as the weather clears up, I shall submit an 8 inch object glass to your examination.” The letter also provided additional information about the history of the new object glass: “The flint [glass] is one of those formerly in your hands but it has been reworked and I have obtained it a piece of English crown [glass] by which the performance is greatly improved. . . [The object glass was] intended for a college in America.” ⁷² The college in America referred to in the letter was possibly the University of Alabama, which did not receive its 8-inch equatorial telescope from the instrument maker until 1849 (the only other instrument being prepared by Simms at the time that carried an 8-inch object glass). ⁷³ The way in which Simms decided to solve the problem surrounding the object glass demonstrated both his ability to identify the factors significant to Airy correctly, and his level of commitment to maintaining a good relationship with the Observatory by giving it preference over the purchase and use of products made for other clients. The failure with the original shipment of glasses also showed that the initial promises and work of Simms were not fully reliable. Despite this, Airy maintained his trust in the instrument maker, which ultimately led to Simms prioritising one client over another.

Before testing the object glass, Airy asked Simms to specify the price, which signalled the Astronomer Royal’s equal emphasis on the cost and quality when making the final decision for the purchase. ⁷⁴ Simms’s asking price was £300 which according him was lower than the actual time and resources combined put into its making. ⁷⁵ After the successful trial of the lenses, Airy offered £275, which Simms accepted. The basis for negotiating it further provides us information about a third optician who was also mentioned by Airy to be in competition for the Transit Circle project, Noel Paymal Lerebours: “I may remark that the price of £300 is higher than that held at by Lerebours and lower than that of Merz (who, for saying that he has a monopoly, is very unreasonable).” ⁷⁶ Once again we see that for Airy the price of the object glass was significant factor in its purchase, and he acted upon the basis of his principles of economy and efficiency.

Lerebours and the historical aim of the Observatory

As Sheepshanks pointed out in one of his early letters on the project, having instrument makers competing to become the supplier of the object glass gave Airy a strategic advantage during the negotiations. Airy used this to his advantage by repeatedly relying on the comparison of the prices offered by the different opticians. Therefore, it is important to look at how the interactions and negotiations with both Lerebours and Merz (Simms’s competitors for the object glass) took place. By analysing the unsuccessful negotiations, we get a glimpse into how Airy’s preferences were highlighted in his interactions with other instrument makers, and what factors led to the breakdown of these negotiations.

Noel Paymal Lerebours was a French instrument maker who is best remembered today for his daguerreotypes. ⁷⁷ He was also one of the opticians who was able to procure object glasses made by Louis M Guinand towards the end of his life. As a result, he also engaged in making object glasses for telescopes and other optical instruments. ⁷⁸ The first contact between Airy and Lerebours can be traced back even before the proposal for the Transit Circle. As it was pointed out in this article, in 1846 Lerebours offered the Astronomer Royal to make the largest equatorial telescope in existence for the Observatory, but Airy declined the offer. Despite this, Airy and Lerebours continued to keep in touch through the latter’s London agents. On 4 August 1847 Airy wrote to Lerebours asking whether Lerebours had “an object glass of 6 to 8 inches aperture?” ⁷⁹ Lerebours’ agents responded positively in two consecutive letters, the first one stating the instrument maker was in possession an 8 ¼ inch and a 9 ½ inch object glass, as well as several 6 inch object glasses. ⁸⁰ However, the responses coincided with Airy’s visit to the Pulkovo Observatory, which caused significant delays in his response. ⁸¹ When Airy finally responded on 21 September, there was no more enquiry about the 8-inch object glass, but he asked for more information about the 6 inch object glasses. ⁸²

In these negotiations, it is important to note the sizes of the different object glasses. The sought object glass of the Transit Circle was 8 inches, while the one being negotiated by Airy with Lerebous was 6 inches. There are three possibilities that could explain the differences in sizes. First, Airy wanted to employ different makers for the mechanical parts of the instrument and for its optical parts. This idea was supported by Airy’s letter in which he asked for the price of the object glass in a simple tube with an eye-piece. It highlighted Airy’s intention to construct an astronomical instrument around the object glass, as opposed to ordering an entire instrument from the French instrument maker. If this was the case, then it highlighted that the Astronomer Royal had already in mind the employment of another firm (possibly Ransome & May) for the manufacturing of the mechanical parts of the Transit Circle. The second possibility was that Airy considered purchasing an astronomical instrument different from a transit circle. This possibility was brought up by both Challis and Sheepshanks, and at this point, Airy had not yet specifically proposed the construction of a transit circle to the Board of Visitors. The third possibility was the construction of a transit circle that required a smaller object glass. This would explain why John Herschel later discouraged Airy from beginning work on the construction of the mechanical parts of the instrument, since they argued that the focal length of the lenses was going to determine the size of other parts of the instruments (e.g. the telescope tube or the size of the lifting apparatus).

The negotiations about the 6-inch object glasses progressed as far as discussions about their trial. Airy asked whether they could be tested prior to purchase at the Paris Observatory or in London by either Airy himself or a person appointed/sent by him. While Lerebours agreed to these conditions, there remains no surviving letter whether the trial had taken place or not. The last reference to it was made in a letter dated 6 December, where Lerebours’ agent stated that the foggy weather had limited their ability to send out the object glass for testing at the Paris Observatory. ⁸³

The next time the object glass resurfaced in Airy’s correspondence with Lerebours was in a letter written on 22 February 1848. This was a few days after Airy had declared to Herschel that all negotiations must be stopped with Merz, but before Simms received the first shipment of object glasses from his French supplier. This shows us that Airy was constantly looking for possible alternatives, even when he clearly declared his preference for Simms’ object glass to both Herschel and Sheepshanks. In the letter Airy provided an official rejection of any further negotiations regarding the 6 inch object glass due to “conference with the proper authorities.” Instead, the altered direction of the letters focused on questions about an 8 inch object glass. ⁸⁴ Airy’s next letter to Lerebours was written on 27 March, which was just a bit more than a week before the confirmed purchase of the object glass from Simms. The questions asked from Lerebours reflected Airy’s main concerns: (1) the price of the object glass, (2) the condition for it to be purchased only after trial, (3) the conditions of trial, and (4) the time it would take to finish. ⁸⁵ Despite these questions, Airy’s next letter stated that he had found another supplier in London, and as a result, he was not going to proceed any further with the negotiations. ⁸⁶ The halting of the negotiations was not taken kindly by Lerebours. He accused Airy of backing out from an actual order placed. However, to counter this accusation, Airy provided four pages of evidence referencing their correspondence demonstrating that he never placed an order, and repeatedly specified that he had only made enquiries as opposed placing orders. ⁸⁷ After this exchange, no further letters seem to have survived coming from or going to Lerebours or to his agents.

The negotiations with Lerebours highlighted several significant aspects of the history of the object glass. First, it demonstrated that Airy had been in contact with the French instrument maker about an 8 inch object glass even before he proposed the Transit Circle to the Board of Visitors, thereby showing Airy’s interest in constructing the instrument as far back as August 1847. Second, the story demonstrated Airy’s quest for an alternative supplier. This further showed Airy’s distrust in the work of Merz, as well as the impact of Richard Sheepshanks in encouraging Airy to always have alternative options open for the supplier of the object glass. In addition, since Airy had written to Lerebours only a few days before he finalised his offer to Simms, it questions the extent to which the Astronomer Royal trusted Simms throughout the entire negotiations. In this light, while at the beginning of the project Airy was a strong supporter of Simms, due to the poor quality of the first shipment, and the use of an alternative object glass, Airy’s late contact with Lerebours showed the Astronomer Royal’s diminishing trust in Simms.

Airy’s attempt to look for alternatives serves as a ground for reconceptualising the object glass during this stage of its history. First, it demonstrates that the object glass could have materialised in a different form too, and that between January and April 1848, the object glass of the Airy Transit Circle existed in three alternative (material and immaterial) forms simultaneously: one repolished in Simms’s workshop, one in stock at Lerebours’ workshop, and one on paper waiting to be ordered by Merz. Second, the correspondence with Lerebours further repeated the factors that Airy considered important in relation to purchasing the object glass: price, conditions of trials, trial before purchase, and time necessary for preparing the object glass. The emphasis on these factors highlighted Airy’s managerial mentality towards the making of astronomical instruments, as opposed to being involved only in the quality testing of the object glass.

Negotiations with Merz

Besides Lerebours and Simms, Airy also exchanged letters with Georg Merz. Even though extracts from their correspondence were used in Airy’s letters to other individuals, it is necessary to examine what aspects of the original correspondence were omitted from these second-hand accounts. Furthermore, the analysis of the original letters to Merz allows us to see the differences and the similarities between how Airy approached negotiations with various instrument makers. The Astronomer Royal first wrote to Merz on 31 January 1848, thereby making it the second letter to directly refer to the object glass of the Transit Circle as approved by “the authorities of the Royal Observatory of Greenwich.” ⁸⁸ In this letter, Airy asked three of the four recurring questions relating to aspects of the object glass: (1) how much time it would take to finish an 8 inch object glass (2) whether Airy or one of his deputies could test the object glass either at Munich (possibly at the local workshop of Merz) or at the Bogenhausen Observatory (3) how much would the object glass cost (without the tube or any other mounting). The lack of questions relating to the conditions of the trial of the object glass shows that Airy did not think that it was going to be an issue.

It was Merz’s response to this letter that caused a turmoil around the conditions of the trial, which was later discussed between Airy, Herschel, and Sheepshanks. The optician stated that he only allowed trial on his own mounts (all of which were equatorial mountings) and on terrestrial objects. He argued that this was because they could only guarantee the quality of their own tools during the tests. ⁸⁹ Airy was not satisfied with this response, since the conditions of the trial set by Merz did not take into consideration that the object glass was intended for a transit circle, which required a non-equatorial mounting. Furthermore, Airy wanted to try the object glass on celestial objects as opposed to on terrestrial objects only.

Airy’s response was dated 21 February 1848. Between Merz’s initial answer and this letter, Airy wrote to both Herschel and Sheepshanks, asking them about their opinions on the conditions of the trial set by Merz. Both continued to reassure the Astronomer Royal about the quality of the object glasses made by Merz. Furthermore, Sheepshanks asked Airy to clarify to Merz the intended use of the object glass in order to avoid further miscommunications. Taking up this suggestion, Airy’s letter clarified that “the object glass [was] not required for a parallactic instrument [but] for an instrument of a different class [i.e. transit circle] not usually made by you.” ⁹⁰ By doing so, Airy was attempting to renegotiate the conditions of the trial.

Merz replied confirming that Airy understood clearly the original conditions of the trial set by the instrument makers and, while understanding Airy’s concerns, Merz insisted on a trial only being possible on terrestrial objects as they did not have a proper mounting for trial on celestial objects. Instead, Merz asked for Airy’s trust based on the previous instruments that he received. ⁹¹ Following a month-long hiatus in the correspondence, Airy notified Merz about finding another supplier. However, unlike in the case of Lerebours, the letter left the possibility of future purchases from Merz open. ⁹²

The letters exchanged between Airy and Merz highlight several new aspects of the history of the object glass of the Transit Circle. Most importantly, it shows that Airy seriously considered purchasing the object glass from Merz, thereby illuminating the competition that Airy induced between instrument makers for the Transit Circle. As we have seen in a previous section, this strategy of making instrument makers compete against each other was not Airy’s idea, but rather that of Sheepshanks. Therefore, the Airy-Merz letters show us that Sheepshanks managed to convince Airy about starting negotiations with Merz. The Airy-Merz correspondence also demonstrates what Myles Jackson identified as the diminishing power of Merz by the middle of the nineteenth-century. ⁹³ The high price of his object glasses, the inflexibility regarding trials, and what Airy considered to be poor services, were all factors contributing to the eventual diminishing of his monopoly. Furthermore, Airy’s decision to ostracise Merz showed that at least one member of the astronomical community actively made attempts to counter the monopoly of the optician. Finally, the letters showed the importance that trust played in the purchase of instruments and object glasses. While Airy trusted Simms (even after the bad first shipment of object glasses), he was less patient during his negotiations with Merz. When Merz eventually appealed to Airy’s trust, it showed that the instrument maker was unaware of the distrust that Airy held against him. We can gain a more complete picture on the sources of Airy’s distrust in Merz by looking at the letters exchanged between Airy and another one of his friends, John Herschel.

Herschel’s advice and his support of Merz

Besides Richard Sheepshanks, Airy wrote to John Herschel on several occasions to seek advice on the purchase of the object glass. Being the son of the famous astronomer, William Herschel, John Herschel was brought up in a family and circle of friends closely connected to both men of science and instrument makers of the nineteenth century. ⁹⁴ By 1848 he had published his results of the observations made more than a decade earlier at the Cape of Good Hope in South Africa, which increased his already high reputation in the British astronomical community. ⁹⁵ Educated at the University of Cambridge, he became a core member and role model of the “Cambridge Network” of men of science. ⁹⁶ By the time Airy started his undergraduate studies at Cambridge, Herschel had already left the university, but George Peacock (one of Airy’s close friends) introduced the young Airy to Herschel. ⁹⁷ After their first meeting, a friendship developed, which formalised into even more frequent interactions once Airy was appointed Astronomer Royal.

Herschel was a member of the Board of Visitors as the President of the Royal Astronomical Society when discussions about the Transit Circle began. In the purchase of the object glass, his role went beyond that of an ordinary Visitor. Rather than only asking for his initial and overall thoughts on the project, Airy repeatedly contacted him for advice, or to simply share his own thoughts with someone. ⁹⁸ Besides their friendship, and Herschel’s expertise within the fields of astronomy and optics, Herschel also had prior experience in dealing with both continental and English instrument makers, which allowed Airy to rely on more than just Sheepshanks’ opinion on the quality of Merz’s products. Airy’s desire for a second opinion of Merz and his work was not a straightforward distrust in Sheepshanks’ advice, but rather, a precaution by Airy based on his previous experience with Merz. In 1845 and 1846, Airy was an adviser on the founding of the Liverpool Observatory. One of his roles was to aid in consulting with instrument makers. In this role, Airy ordered an object glass from Merz for the equatorial refractor of the Observatory. ⁹⁹ Airy thought the quality of the object glass received to be worse than expected, but still good enough for use. Furthermore, there were minor complications regarding the payment, as Merz and his English clients calculated with different exchange rates during discussions over the final price of the instruments. As a result, Merz contacted Airy demanding the rest of the money. Airy was only able to settle this with the involvement of Herschel who was also in the process of paying for his own purchase at the time. ¹⁰⁰ In brief, the Airy-Herschel-Merz triad had interacted with each other in the past, which memory Airy seemed to have preserved clearly in his mind.

Airy’s first letter to Herschel concerning the object glass of the Transit Circle was sent on 17 February 1848. In this, Airy copied a long extract from Merz’s letter regarding the conditions of the trial of the object glass. The extract described how Merz only carried out trials on terrestrial objects, and with mountings different from those used for transit circles. Therefore, Merz was only allowing to sell the object glass without the condition of trial. This condition was not in accordance with the terms set by the Board of Visitors who made it clear that the object glass had to be tested before purchase. This was a preference shared by Airy too. Based on these complications, and the unusual conditions set by Merz, Airy directly declared: “. . . I do not trust Merz. Therefore it seems – I think that all proceedings with him must be stopped for the present.” ¹⁰¹

Herschel’s response was very calm and diplomatic. He began by pointing out that if he were to purchase a telescope for private use with an 8-inch object glass he would order one from Merz without hesitation since others have also had dealt with Merz and were well treated. To ease Airy’s worries further, Herschel told him to wait until a recent purchase from Merz by the Royal Observatory at the Cape of Good Hope arrived and Thomas Maclear, the director of that observatory, had tested the object glass. Herschel promised that if Maclear found the object glass to be of poor quality, then he would never say another word in favour of Merz. However, if Maclear found the object glass of good quality, then the word of another director perhaps could change Airy’s opinion. Finally, Herschel finished the letter by emphasising the importance of procuring an object glass before the construction of the Transit Circle started, since he presumed that the tube could not be “exactly constructed so long as any small uncertainty exists as of the focal length [of the object glass].” ¹⁰² In brief, through Herschel’s first response about the object glass we see that neither Herschel nor Sheepshanks shared Airy’s concerns about Merz. Perhaps most surprisingly, Herschel did not mention whether the testing procedure for the object glass quoted by Airy was an unusual way or carrying out the trial or not. Therefore, Herschel seemed to have found Airy’s main concern unfounded. Mentioning Thomas Maclear as a person to test another Merz instrument also highlighted a hierarchy of credibility within the astronomical community, and Herschel’s attempt to increase Airy’s trust in Merz by involving views of another eminent astronomer.

Airy responded to Herschel’s letter the next day. He began by summarising the state of the negotiations and outlined his reasons for distrusting Merz: “Merz will allow trials of object glasses sold as mounted on his equatoreal stand. Merz’s object glasses so sold with the equatoreal mounting are always trustworthy.” On the other hand, “Merz will not allow trial of object glasses which are sold without an equatoreal stand. Merz’s object glasses sold without equatoreal mounting are not always trustworthy.” Based on these four underlying statements, Airy continued by refuting the former side of the argument. Referencing the order for the equatorial telescope for the Liverpool Observatory, he found that the object glass supplied with the telescope was “not so perfect as we expected.” In consequence, for Airy, neither side of the argument (whether the object glass was going to be supplied (a) with or (b) without the telescope) guaranteed the high quality of the object glass, making Merz “untrustworthy.” Therefore, we see the important role that the quality of previous products and services played in long-term interactions between astronomers and instrument makers. The rest of the letter refuted Herschel’s doubts about not having the object glass at hand halting the production process, by highlighting that a “large portion of the work (building, piers, Y’s, transit-axis, clamp circle, graduated circle, microscopes and collimating telescopes)” could begin even without an object glass. ¹⁰³

Airy’s next letter to Herschel about the object glass was written about a month later, just a couple of days before confirming the purchase of the object glass from Simms. In this letter, Airy provided a detailed account of the trial to which he subjected the object glass by Simms. However, the letter’s main aim was already clarified in the first lines:

“I would be glad to have your friendly advice, not for the purpose of relieving me from any responsibility or for of excusing me from the necessity of judging myself, but for my own clarification.” ¹⁰⁴

In these first lines, Airy attempted to change Herschel’s frame of reference so that Herschel could consider the letter as an exchange between two friends as opposed to an official correspondence. The letter continued to describe Airy’s source for his distrust in Merz’s work, which was based not on his own observations, but on the ones made by William Simms who carried out the first trial of the object glass of the Liverpool Equatorial. The letter described how the initial method of the trial was not adequate for Airy, and asked Simms to carry out a trial on celestial objects too. After the second trial, Simms “was very well satisfied with it.” From Airy’s description we now see a third source for his distrust in Merz emerging. Unlike previous ones, this was based entirely on the method with which they did not test the object glasses on celestial bodies, as opposed to on the unreliable quality of their previous final products.

The rest of the letter provided the results of the trial in detail by describing the extent of the visibilities of several celestial bodies. At the end of this description, highlighting the good quality of the object glass, Airy proceeded to ask Herschel the following two questions:

“Now do you not think it would be well to purchase this object glass at once? Or do you suggest any other examination as necessary or desirable?” ¹⁰⁵

In brief, Airy was keen on purchasing the object glass as soon as possible, but wanted a second confirmation from Herschel, in order to ensure that he did not overlook anything during the trials. The letter then finished with two practical solutions that Airy wanted to implement into the Transit Circle: one correcting the chromatic dispersion of the light, the other focusing on a design for the eyepiece that allows it to be tilted so that the chromatic effect caused by the imperfection of its centering could be corrected. This addendum demonstrated that Herschel was not only involved in advising on the supply of the object glass, but also on the optical arrangements of the telescope.

Conclusion

The Airy Transit Circle was finally installed at the Royal Observatory at Greeenwich in 1850 with an object glass supplied by William Simms. The first observation was made with it on 4 January 1851 and it continued being used until 1954. Even though the object glass was cleaned several times during the more than 103 years of its service, it was never replaced with a new one. The story about the negotiations of the purchase of the object glass provides us with new insights into the history of the Transit Circle. It demonstrates that several instrument makers were considered as possible suppliers of the object glass. Therefore, the procurement of the object glass was not as straightforward as it was described in the Annual Reports of the Astronomer Royal, upon which later scholarship based the history of the instrument. ¹⁰⁶ Furthermore, the inclusion of instrument makers from continental Europe showed that the Observatory was not only embedded within the British network of instrument makers, but also within the wider European one. Each one of the possible suppliers excelled in different aspects of their offers: Lerebours offered the cheapest object glass on offer, Merz had a global reputation, while Simms offered to make it in the shortest amount of time. With Simms failing on his initial promise (by not receiving good shipment of glass from France), Airy’s decision to employ him was no longer a straightforward decision. The fact that Airy wrote to Lerebours just a few days before Simms finally prepared the object glass for testing, demonstrated the Astronomer Royal’s gradually diminishing confidence in the work of the British instrument maker. However, Simms understood Airy’s emphasis on time and quality, and the re-use of an object glass from another work in progress showcased the priority that the Observatory (and the Astronomer Royal) enjoyed in the mind of the instrument maker. This act demonstrated Simms’s knowledge based on previous experience on how to interact with the Astronomer Royal in order to secure the production of the object glass. ¹⁰⁷ In relation to the work of Merz, Airy’s distrust based on prior work led him to be hesitant over contacting the instrument maker, which once again demonstrated the important role that the previous interactions with the Astronomer Royal played. Furthermore, Merz’s reluctance to alter the conditions of the trial of his object glass according the wishes of a prospective client, as well as Airy’s distrust in the quality of his work, exhibited the first signs of the loss of the credibility in the products of the instrument maker, which eventually led to his diminishing monopoly over the making of object glasses. ¹⁰⁸

Airy’s preferences for the order brought forward the principles of “economy” and “efficiency,” which factors were also prominent in the running of the Observatory as a factory. He emphasised the inseparability of time, money, and quality when deciding upon the supplier. By doing so, the principles and standards of business were not only implemented into the rules and division of labour set up at the Observatory but were also present within Airy’s approach to negotiating with instrument makers. In consequence, the final form of the object glass of the Transit Circle similarly embodied the features of economy and efficiency. The analysis of the early correspondence relating to the object glass further showed that it was not only Airy and the instrument makers who were involved in its procurement, but several members of the Board of Visitors too. By receiving advice from them, two of its members were able to shape the direction that Airy took with the negotiations. In light of this, the procurement of the object glass was a collaborative enterprise between Airy, the instrument makers, and selected members of the Board of Visitors.