Graphical details: the secret life of Christopher Wren's drawing of the weather clock

Historians have unanimously credited Christopher Wren with having constructed a weather clock (a self-registering instrument) in the early 1660s. This conclusion was based on the account of the French diplomat Balthasar de Monconys, which included a sketch uncannily similar to an undated drawing by Wren of the weather clock. By critically re-examining the available sources, I argue that one can infer that Wren never actually constructed a weather clock. What Monconys saw and sketched was, in fact, a drawing produced by Wren for a meeting of the Royal Society that took place on 8 January 1662. I further show that there is strong evidence to assume that Wren's drawing for the Royal Society is the undated drawing preserved at the Royal Institute of British Architects. The new context in which I place Wren's drawing provides an incentive to look at it with fresh eyes. Though the drawing does not represent a device actually constructed by Wren, it still bears (unexpected) connections to the material world that surrounded him. The analysis of the drawing developed in this article will be relevant for historians interested in the role that images can play as historical evidence.

sketch', and that it might only show a 'sealing-wax and string model', W. E. Knowles Middleton, one of the most authoritative sources on the history of meteorological instruments, concluded that 'The important thing is that what de Monconys saw at Oxford in June 1663 had an actual physical existence.' 2 Jim Bennett reached the similar conclusion that 'The first account we have of a working weather clock comes from the visit the French traveller Balthazar de Monconys made to Wren at All Souls College, Oxford, in June 1663', where 'He was shown a weather clock.' 3 Despite the fact that Monconys never claimed to have seen Wren's weather clock and only remarked that Wren 'spoke most freely' about it, all of Monconys's readers have uncritically assumed that his account must have been based on some physical object that he actually saw. 4 However, in his account Monconys made clear and consistent distinctions between the instruments he saw and those he was only told about. 5 Why, then, the unanimously unquestioned assumption that Monconys's account says more than it actually does?
The reason is found not in the text but rather in Monconys's sketch. It is easier to explain away a word rather than imagine how an elaborate technical scheme could have been drawn based on an oral account alone. No room for doubt seems to be left when considering the undated drawing by Wren himself (figure 2), which, though incomparably superior in draughtsmanship, represents a strikingly similar setup. Details never mentioned in Monconys's text-like the weights and pulleys-appear in both drawings. It has become almost impossible to look at the two drawings side by side without imagining that they ciuils & des plus ouuerts que i'aye trouuez en Angleterre: car quoy qu'il ne veuille pas que ses pensées soient diuulguées, Il ne laissa pas de me dire fort librement celle de son Horologe du temps.   resemble each other because they both represent the same physical object-some version of the weather clock that had actually been constructed. Though often reproduced, Wren's meticulous drawing has thus far been only cursorily examined by historians, who have limited themselves to describing its general setup, most often by citing Monconys's account of Wren's device. The limits of this interpretative approach-of looking at Wren's drawing through the lens of Monconys's text and sketch-are revealed by the failure of commentators to make sense of the double row of boxes below the large funnel (see figure 2). On this point, Monconys offers no help because he only mentions a 'funnel into which it can rain' and his own sketch depicts a single row of vessels. Without Monconys's assistance, some commentators expressed their surprise that the 'rack carries at the right a rain-gauge which appears to be double', while others fully acknowledged their bemusement: 'There seem to be two rows of boxes for the rain, and I do not understand this.' 6 Paradoxically, though Monconys's 'rough sketch' has been deemed less reliable by all commentators, it has become the guide for making sense of Wren's carefully drawn sketch of his own instrument.
In the first part of this paper, I will show that one can infer, with a fair degree of confidence, that Wren produced his drawing for a meeting of the Royal Society that took place on 8 January 1662. Furthermore, one can be confident that this drawing was in Wren's possession when Monconys visited him at Oxford, and that what Monconys saw and sketched was this drawing and not an object that Wren had actually built. These results are important not only because they rectify a unanimously accepted misconception but also because they bring into focus the challenge of interpreting misplaced images. Early modern drawings and prints have often been copied or literally cut out of their original location (letters, books, etc.) to be bound in a collection or archive. 7 These displacements have often obscured the original purpose or circumstances for which an image was produced. 8 The textual sources surrounding Wren's drawing provide a rare glimpse into the life of a drawing: the purpose for which it was created, its movements, particular moments in which it was contemplated, or the impressions it left in the mind of some viewers. Though this approach cannot always be replicated, it should enrich the possible scenarios imagined by historians for a drawing.
In the second part, I will provide a close analysis of Wren's drawing to reveal his graphical strategy of enacting for an audience the construction and operation of a weather clock. Recent scholarship-from historians of science, technology, architecture and art-has carefully investigated the role of images in the production, communication and reception of science at the Royal Society. 9 While these studies have engaged with the broader context of the

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visual culture and the graphical practices of the early modern period, this paper is focused on the close analysis of a single drawing or, even more specifically, of details of a drawing. This narrow choice of focus is deliberate and is a provocation to historians to look at images not only as scientific objects but also as forms of historical evidence.
Though historians have more things than ever to say about images (and, as Lorraine Daston has remarked, 'it is now astonishing to recall how blind historians of science once were to anything but words'), there is a risk that images have little left to show or say to historians. 10 How can one both 'think about images beyond representation', as Daston urges, and also use images as historical evidence? To tackle such a question, Peter Burke proposed a method inspired by Giovanni Morelli, Aby Warburg and Erwin Panofsky, which claims that 'So far as the history of material culture is concerned, the testimony of images seems to be most reliable in the small details.' 11 However, some readers have wondered whether Burke's visual 'traces' truly 'add to existing knowledge rather than reiterate information available from written sources'. 12 This line of criticism could be extended to much of the recent literature on scientific images, which, while talking about images, does not allow the images themselves to talk. This issue has been raised most staunchly by Horst Bredekamp, who insists that one should see an image not just as an instrument, something carrying a message in the manner of speech, but rather as an actor or a 'living image' which can 'seize' the spectator. 13 So far Bredekamp's approach, which emphasizes the autonomy of images and their formal properties, has found little appreciation among historians of science who value the significance of communities, materials and techniques in the making of images. 14 One could say that Bredekamp's 'living images' have not yet given the testimony a historian would hope for.
My analysis of Wren's drawing will navigate these two extremes. My goal is not to use textual sources to explain the image, but rather to produce unknown and unexpected results about the drawing's surrounding world that I can then corroborate, or at least make plausible, using textual sources. This will allow me to connect Wren's world of paper to the material world that surrounded him and that is reflected not so much in the objects that are represented (weather glasses, clocks, etc.) but rather in small graphical details, which are passed over as insignificant ornaments when regarded in isolation, but which can

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6 provide novel insights when contrasted with each other. 15 Though using a different approach, historians of architecture have accomplished a similar goal in connecting Wren's architectural drawings to the buildings constructed after his designs. 16 While some of these insights might come to be established with some degree of certainty, others will challenge historians, within the bounds of historical rigour and method, to imagine new scenarios and ways of looking at a drawing.

THE SECRET LIFE OF A DRAWING
Wren's manuscript drawing of the weather clock is preserved at the Royal Institute of British Architects (RIBA) in the 'heirloom' copy of the Parentalia, or, Memoirs of the family of the Wrens (1750)-a collection of documents compiled by Wren's son and published by his grandson. 17 After a careful analysis of its manuscript versions (the earliest dating back at least to 1719, four years before Wren's death), Jim Bennett concluded 'that in general Parentalia seems to be a fairly accurate record of primary sources'. 18 However, the comments made by the son regarding the primary sources are less reliable, and sometimes completely misleading. 19 One such example is the claim, unanimously accepted by historians though lacking any support in the primary sources, that Wren first imagined the weather clock, or even constructed a version of it, during his teenage years when he

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Though the drawing is undated, its content can be read against textual sources to reconstruct an order of events. One crucial document is an undated address in the form of a letter from Christopher Wren to the president of the Royal Society. 21 The address proposed a plan to the members of the Society for how to become 'benefactors to mankind' by 'advancing 1. knowledge. 2. profit. 3. health; and conveniences of life' through a 'history of the seasons': 'an excellent work … desir'd by all modern philosophers, though no body hath had yet the patience to pursue it'. Such a history, if carried with 'patience for some years', was the only 'certain way of learning to prognosticate' the changes of the weather. The project was 'of little trouble' and 'of no difficulty', though it required 'a little time' and 'patience'; the 'greatest difficulty' was raised by keeping a diary of the winds because 'it seems to require constant attendance'. 22 Luckily, two extant innovations eased such observations. The inconvenience of accurately determining the orientation of a weathercock positioned on top of a building could be resolved by projecting its position onto an ellipsis drawn on the glass of a window. Such a method of observation 'hath been put into execution with very good effect, and some other useful additions at Oxford'. 23 The second innovation allowed one to carry out observations during the night, by using 'a vane as it is at Whitehall, shewing by an index within the room' the changes of the wind. 24 Wren considered that these existing improvements were 'not yet enough, for many changes may happen while the observer is absent or asleep'. To account for such a scenario, he envisioned a further improvement, which 'may be framed', though some might have regarded it as a mere 'promise': I might seem to promise too much, should I say, an Engine may be framed, which if you visit your Chamber but one half Hour in the Day, shall tell you how many Changes of Wind have been in your Absence, though there were Twenty, and at what Hour every

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Change happened, and whether it were soft, stiff, or vehement. Neither shall the Instrument be out of Tune, or if it be, your own Hand may rectify it.
Neither shall the Thermometer need a constant Observance, for after the same Method may that be made to be its own Register. 25 I have analysed this address so closely because it shows the very special context and manner in which Wren's 'engine' was introduced to the Royal Society. First, though Wren acknowledged that he 'might seem to promise too much', he did not mention any previous attempt to build such an 'engine'. Thus, Wren was only describing a conceivable ('may be framed') instrument, not one that was already operational, as those at Oxford and Whitehall. Second, he did not reveal anything about the actual design of the instrument (how it actually operated) and described only its purpose (to register the changes of the wind in the absence of the observer). Third, the need for such an engine was motivated by a specific problem: the difficulty raised by keeping a diary of the wind throughout both day and night. Fourth, Wren only remarked in passing that his engine could incorporate a thermometer, by 'the same method'. Fifth, he did not explicitly mention that his engine could also be used to register the quantity of rain or humidity, though these were quantities of interest in his 'history of the seasons' and he did discuss a novel design for a hygrometer. In contrast to the address, the drawing of the weather clock did include instruments to register both the amount of rain and, as I will show in the next section, humidity.
Though the records of the Royal Society do not make an explicit reference to Wren's address, the minutes of the meetings for the month of January 1662 include the following relevant entries: 1 January Dr Wren intreated to draw up a Scheme for a weather glass clock, against next day. 8 January Dr Wren brought in a Scheme of a weather clock. 22 January Dr Wren shewed his experiment of filing a vessel with water, which emptied itself when filled at a certain height. 29 January Dr Wren read a paper concerning weather-glasses. 26 The initial entry in the Journal Book for 1 January stated that Wren was asked to 'draw up a scheme' for the following meeting, but then an interjection was made in the wide blank margins of the journal that specified the nature of this scheme-'for weather glass'; the margin was then further amended to read 'for a weather clock' (figure 3). This entry in the Journal Book was later transcribed in Birch's History of the Royal Society as 'Dr. Wren to draw up a scheme for a weather-cock [sic], against the next meeting'-a small typo which has probably thrown off historians for more than a century. 27

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What did the members of the Society know about 'a weather clock' to motivate such an abrupt and surprising request? The minutes only show that during the same day some discussions about weather observations had ensued. 28 It is plausible that the Society's interest in weather observations and in the scheme of the newly named instrument was sparked by Wren's address, which could have been read that very day or shortly before. The opening of the address ('Mr. President, We begin a new year, and therefore may pause a little, and look back on what we have done …') makes it clear that it was to be delivered on the occasion of a new calendar or administrative year. 29 While on its own this passage is not sufficient to determine exactly when the address was written and delivered, the naming of the instrument-referred to only as 'an engine' in the address, but as a 'weather clock' in the minutes for 1 and 8 January-does suggest a particular order of events.

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I would like to suggest the possibility that the drawing preserved at RIBA is the 'scheme of a weather clock' brought before the Royal Society on 8 January 1662. That Wren could have drawn such an exquisitely detailed drawing in less than a week should not come as a surprise. After the Great Fire of London swept the city between 2 and 6 September 1666, on or about 11 September, he gave Charles II a plan for totally rebuilding London. 30 Still, it is immediately clear that Wren did not have the opportunity to carefully consider all the implications of the scheme. The row of boxes in which the rainwater was funnelled was placed on top of a horizontal ruler which seems to have rested its whole weight only on a pulley and a pencil. Furthermore, the level of the rainwater in the boxes would have been affected by evaporation, especially when the engine was designed to function unattended for 12 hours or more. This problem was later explicitly acknowledged by Wren: 'I doubt too whether they would not be drie, ere the observer comes to looke in them.' 31 This grave challenge must have become obvious to him soon after he presented the scheme (maybe it was even pointed out during the discussion) because, on 22 January, he presented the Royal Society with an experiment by which a vessel of water could be made to empty itself when filled to a certain level. This mechanism was later developed by Robert Hooke to create a tipping-bucket rain gauge that he incorporated in the weather clock he built for the Royal Society. 32 The following week, on 29 January, Wren read a paper 'concerning weather-glasses'; John Evelyn, who luckily attended the meeting, took note of it in his diary: 'Dr. Wren produced his ingenious Thermometer'-a reference to Wren's circular thermometer (also known as the 'weather-wheel'). 33 Wren was dissatisfied with the construction of the usual thermometers (such as the one depicted in figure 2) because he considered that the liquid that trapped the air in the glass exercised a varying degree of exertion depending on its vertical level. 34 He circumvented this problem by shaping the air reservoir as a drum surrounded by a tube with liquid such that, when the air expanded and pushed the liquid upwards, the drum rotated around its centre to re-balance. On 12 June 1663, Wren informed Monconys about his thermometer design, which Monconys got to see the next day in London, where Wren had left it with Dr Goddard. 35 Thus, by 29 January 1662, three of the four meteorological instruments depicted in the RIBA drawing had been supplanted by new designs. One would guess that, if Wren had to redraw his scheme after this date, the new drawing would have reflected these new changes, something the RIBA drawing fails to take into account. However, this is no counterfactual scenario. After a hiatus of more than a year, Wren's weather clock is mentioned again in the registers of the Royal Society, on 2 September 1663, when a proposal was made to renew the call for a history of the weather. Given the topic, it was 'thought proper, that Dr. Wren should be written to, to send to the society a scheme of his weather-engine, formerly proposed, in order to see whether it needed any addition or not'. While at the next meetings there was some confusion about who was responsible for writing to Wren at Oxford, the request was always for the same thing-a scheme: 'Dr. Wren's scheme for the observation of all the changes of weather' (16 September) or 'his [Wren's] scheme of the instrument for observing all kinds of weather' (23 September). Finally, on 2 December, John Wilkins acquainted the Company, that he had received an answer from Dr Christopher Wren concerning his proposed Weather-Clock, together with the Scheme thereof. The Amanuensis was ordered to draw the Scheme in great, against the next Meeting, at which it should be considered, together with the letter describing it. 36 Though Wilkins announced that the amanuensis would copy and enlarge Wren's scheme, the drawing preserved in the archives of the Royal Society (figure 4) is almost certainly the original one sent by Wren to Wilkins along with his letter, because the fold marks on the drawing identically match those of the letter. 37 Wren's reply to Wilkins is most revealing. It opened with an apology for the delay ('If you will pardon me for being a little late in observing your Commands …'), which would have been unjustified if he had sent the scheme 'formerly proposed' to the Society on 8 January. He further remarked that he 'enclosed the Designe I promised of the Weather Clock, changed a little into a more convenient forme', again referring back to a previous design with which the Society would have been familiar. After describing what was depicted in the drawing (the weather glass had been replaced with the circular thermometer K in figure 4), Wren ended the letter with a note about what the Society might expect to find in this scheme: 'I have willingly in this last contrivance omitted the Boxes, because I thinke they may be better disposed themselves; & I doubt too whether they would not be drie, ere the observer comes to looke in them.' The 'Boxes' present in the previous scheme (and which Wren expected the Society or Wilkins to remember more than a year and a half later) were now 'willingly' omitted: that is, not because of forgetfulness or hastiness, but rather because of a careful consideration that evaporation would render them impractical. This was the contraption that Wren had already considered to be impractical by 22 January 1662, which shows that the Society was familiar with only one drawing.
This exchange proves that Wren did not leave his first drawing with the Society or any of its Fellows, as he did with the second drawing of the weather clock, included in the letter to Wilkins. When writing to Wren, the Society assumed that the drawing was still in his possession, an assumption that was never contradicted by Wren. Thus, one can be fairly certain that, when Monconys visited Oxford in June 1663, Wren had the first drawing that he presented to the Royal Society and that it was a drawing that included a row of boxes-a contraption that is also present in Monconys's sketch. This makes it quite plausible that Wren could have shown Monconys this drawing, or some version of it. An example of such viewing of others' drawings is provided by Wren himself, who, during an eight-month trip to Paris in 1665-1666, was introduced to Gianlorenzo Bernini, who had just arrived in the city to present his designs for the east front façade of the Louvre. In a letter to a friend, Wren confessed that 'I would have given my Skin' to come into the possession of these designs: but the old reserv'd Italian gave me but a few Minutes View … I had only Time to copy it in my Fancy and Memory; I shall be able by Discourse, and a Crayon, to give you a tolerable Account of it. 38 While Wren, a talented draughtsman, might have been able to copy a drawing first in 'fancy and memory' and then on paper, Monconys failed in several revealing ways. His travel notes were only 'jotted down every evening upon arrival at his inn', as his son acknowledged when he published posthumously 'as it was' the 'rather confused rough draft (un brouillon assez confus)' that his father left behind after his sudden death in 1665. 39 In his description of the weather clock, Monconys mentioned that the 'heat & cold Graphical details 13 [are registered] by a thermometer that raises or lowers a tablet', a nonsensical proposition, implausible to have arisen from Wren's description and drawing of the weather clock. 40 However, such a misunderstanding could have easily been caused by a careless sketch by Monconys that used perspective inconsistently. Monconys's carefully phrased description of the weather clock (and his encounter with Wren) were probably written down at a later time and based mainly on a hasty sketch that represented the tablet of the thermometer flat against the page. 41 The reproduction of a drawing from memory, and the changes associated with it, offers a different perspective on the theme of copying images that has preoccupied historians of visual culture and graphical practices. 42 The alternative-that Monconys's sketch was based on a physical version of the weather clock-becomes untenable in light of the exchange between Wren and the Royal Society, in which it was never indicated that Wren took any steps towards constructing such an instrument. This would be an inexplicable omission if Wren had indeed showed Monconys a physical version of the clock on June 1663, but then failed to mention anything about it in his letter to Wilkins from November 1663 (not to mention that by the end of January 1662 Wren had already rejected the use of boxes for rain and had designed a new type of thermometer).
Though one cannot be certain, it is likely that the undated drawing from RIBA is the first drawing that Wren presented to the Royal Society and, most probably, to Monconys. 43 As I have argued above, when closely read, the records of the Royal Society impose certain constraints for when such a drawing could have been made, making it unlikely that Wren would have drawn it after January 1662. The level of detail, which will be discussed below, also suggests that this was not a simple sketch, but rather a vivid make-believe. One can imagine that, if not cautioned about it, Monconys might have believed that this was the drawing of an engine actually built by Wren. This would explain the great ambiguity in the text, where, though Monconys never claimed to have seen Wren's engine, he described and drew it with such a level of detail that several generations of historians could not imagine anything else.

DRAWING DETAILS AND ENACTING CONSTRUCTIONS
Carved pineapple finials on the clock pediment and wind vane, gilded spandrels on the dial, a swan-neck latch and flagged hinges on the longcase, a vase-shaped spindle leg, scrolled brackets on the tablet, beaded strings! It is tempting to assimilate these graphical details to the 'concrete' and 'futile' details that Roland Barthes identified in descriptive passages from realist literature in his essay 'The reality effect'. These 'useless details', Barthes 43 There is no evidence for Wren producing multiple copies of the first drawing he presented to the Royal Society (8 January 1662), or a reason why this should have happened. It is most likely that this drawing stayed in his possession and was passed to his son along with the other papers collected in the Parentalia.
argued, did not represent reality but rather signified it within a system of cultural rules of representation, as if to 'say nothing but this: we are the real'. For Barthes, the 'useless details' were 'irreducible residues of functional analysis', not unlike ornaments in functional architecture. 44 While the seemingly superfluous ornaments in Wren's drawing could be interpreted, following Barthes, as signifying a particular system of representation (i.e. realism rather than reality), disjoint from the function of the drawing, I will argue that these details betray a particular purpose (or function) when they are contrasted with each other. 45 Take the leg that supports the beam on the left end-the seamless integration of shaft, coves and bead is broken abruptly by the flat blocks of discrepant sizes placed below and above it (figure 5). The same goes for the longcase clock, which at the upper end supports an elegant hood, but at the other has been coarsely cut by a beam. While any cabinet maker would have smoothly joined all the pieces, Wren emphasized every protrusion.
These details were no mere fancies, but details of construction that go unnoticed if one reduces the drawing to a mere configuration of objects. Worse still, such a blind interpretation will not even properly identify and make sense of all the instruments. As a careful consideration of the drawing shows, most of Wren's attention and effort was focused not on the general configuration but on the particulars. In what follows, I will start with a couple of examples to show Wren's deep concern with imagining and making visible the subtle construction and operation of his engine. I will then examine the double row of boxes that has so far stumped all commentators. Finally, after the eye has adjusted to connect Wren's scattered details, I will try to make sense of the longcase, which so stunningly resembles seventeenth-century architectural clocks while at the same time breaking with all known cases and patterns.

Pencil holders
The method for registering temperature was ingeniously simple: the clock moved a tablet which was marked by a pencil moved by the changing level of liquid in the thermometer. However, Wren intuited that this straightforward method could fail in practice if the two strings attached to the pencil were misaligned, causing the pencil tip to slip or even flip off the tablet. His solution, enlarged above the tablet, was a special holder that would stabilize the pencil when pulled in two different directions ( figure 6). The pencil marking the changes in wind direction was also placed in a special holder that was attached to the ruler through a mechanism resembling the hinge of a compass-either to make sure that the pencil was pressed against the disc, or to allow for the removal of the disc without any smudges. These were no mere abstractions but rather a variation of the ingenious brass handle that Wren designed for his instrument 'for drawing the out-lines of any object in perspective', such that the pencil 'may be kept very firm, so as alwayes to touch the Paper' (figure 7). 46 A similar concern with details was displayed in his work with astronomical instruments, to which he 'added many sorts of Retes, Screws, and other devises to Telescopes, for taking small distances and apparent diamets to Seconds'. 47

Counterweights
The wind vane had an unusual addition: a protruding rod with a spherical object, whose purpose is revealed by the slanted lines that suggest a screw shaft on which the position of the sphere could be adjusted to counter-balance the weight of the vane ( figure 8). This detail is particularly intriguing because, even in the eighteenth century, few wind vanes were balanced by counterweights. 48

Chains and pulleys
Instead of using a straight line to depict the string that passed over the pulleys, Wren added equally spaced dots to indicate a chain or string of beads, which would be grabbed by the teeth of the pulleys without slipping. This detail was crucial if one considers closely how the long board was actually supposed to move. At first sight, it might seem that the board was pulled by the string to the right, but this assumption is put in doubt by the pulley and the weight below the board. It is more plausible that the string was only attached to the weight below the board; when the clock pulled up the weight, it also rotated the pulley, which would have moved the board to the right (figure 9). 49

Boxes and funnels
The purpose of the double row of 12 boxes has so far bemused all commentators, who have only seen a large funnel and have assumed that it was meant for accumulating rainwater in the boxes below (figure 10). 50 However, Wren's graphical details guide us to imagine a different picture. One should notice the apparently intricate and nonsensical manner in which the large funnel is suspended: it is attached to a tapering pole by a ring that would slide down if it were not for the vertical wire extending upwards. Moreover, it is absurd to imagine that rainwater could be collected inside the space in which the engine was placed. If the wind vane was clearly depicted as being located outside the space of the engine, why would Wren employ a different graphical device for the rain funnel? In fact, the mouth of the actual rain funnel was placed outside the drawing (rendering it invisible to the viewer) and was continued inside the drawing by the tapering pole, which (far from being a support) was used to channel the rainwater into one of the two rows of boxes. The large funnel (which until now has been mistaken for a rain funnel) is in fact a condensation hygrometer, used to measure humidity within the room. This interpretation explains all the graphical details: the system of rings is used to support two funnels; the rain funnel is narrow (a wise choice if one wants to avoid overflooding the rather small boxes), while the funnel of the hygrometer has to be as wide as possible to collect the condensed air; finally, each funnel corresponds to a different row of boxes. This interpretation is further confirmed by textual sources. In his address to the Royal Society, Wren dismissed as unreliable the usual hygrometers (lute strings or oat beards) and promised instead to produce 'a peculiar Manner' to measure humidity 'by collecting the

Clocks
Though to a modern reader the longcase clock is the most familiar object represented by Wren, for his audience, in January 1662, it would have been a rather unusual sight. In June 1657, Salomon Coster, a Dutch clockmaker from The Hague, was granted the first patent to manufacture Christiaan Huygens's recently invented pendulum clock. By October 1658, pendulum clocks were also advertised in England by the clockmaker Ahasuerus Fromanteel, who became for almost a decade the foremost English manufacturer of pendulum clocks. 53 Until the anchor escapement was introduced (around 1670), pendulum clocks relied on a verge escapement with a short pendulum rod (about 4-6 inches), whose movement could be enclosed within the hood. The earliest pendulum clocks were all spring-driven and designed to be placed on tables or hung on walls through hook holes. 54 While the first weight-driven pendulum clocks were similarly suspended on walls, with the weights hanging exposed beneath the hood like many of their pre-pendulum predecessors, they had to be supported by brackets because they were considerably heavier than the spring-driven clocks. The emergence of the longcase, where a trunk rather than a wall bracket supported the hood, is difficult to pinpoint because many of the surviving longcase clocks appear to have 'started life as hooded wall clocks'. 55 One case maker, Joseph Clifton, luckily left a brass token inside the trunk of a longcase dated to 1663. 56 Another surviving longcase ( probably made for Henry Howard, the grandson of the 2nd Earl of Arundel and a generous host of the Royal Society) has been considered by some experts to be 'the earliest known longcase clock', dating to c. 1660-1662. 57 From all available evidence, therefore, Wren's drawing of the weather clock contains the oldest surviving drawing of a longcase clock. 58 The matter becomes even more intriguing if one compares Wren's drawing with some of the earliest surviving examples. The hood of Wren's clock matches almost to a fault the very distinctive style of Fromanteel's clocks, which (irrespective of whether they were spring-or weight-driven, table-top, wall-mounted or longcase) had 'almost from the very beginning' dials with a matted central zone, silvered chapter rings, and spandrels with winged cherub heads; the hoods were commonly decorated with a triangular pediment, side columns and finials. 59 There is only one discrepant and bizarre detail that does not match: the decorations on the sides of Wren's hood; all known exemplars either are decorated by columns or are unadorned. The similarities vanish when one compares the trunks. All surviving longcases have a plinth-a base wider than the trunk which is essential for the overall stability of a structure that stands just over 6 feet high-and, in 'most if not all cases until nearly the end of the seventeenth century', the plinth was supported by bun feet. Only later were the bun feet replaced by a moulded skirting, similar to the base on which Wren's clock rests. 60 The door of the clock provides another jarring difference: while for Wren's clock the door is asymmetrically cut and attached with external strap hinges and a latch, surviving longcases have symmetrical doors, with locks and internal strap hinges, and panels as decorations.
Such asymmetries-between drawing and material objects-show that these graphical details are not representational artefacts, conventions or embellishments, but rather meaningful traces. The most compelling solution of this tension is to assume that a Fromanteel hooded wall clock had been subsequently encased with a trunk. The material record shows that it was not uncommon for hooded wall clocks to be supplemented with trunks of inferior quality (with no decorations) made by joiners and not professional casemakers. 61 One such example is the 'split-seconds' clock commissioned from the clockmaker Joseph Knibb by James Gregory in 1673 for his future astronomical observatory at the University of St Andrews. This clock started life as a wall clock but was subsequently converted into a longcase. 62 A possible trace of such a conversion can be found in Wren's drawing. The side decorations on the hood, which are bizarre and unrecognizable in this context, look strikingly similar to the brackets that would have supported hooded wall clocks (figure 11). Even the size of these decorations, incongruously spanning only two-thirds of the dial, matches the depth of the hood.
It is clear that, for Wren's engine, a clock supported by a longcase was more convenient than a hooded wall clock because it integrated the clock with the instruments as their support and not only as their driving force; thus, one could freely move and orient the engine as required by the meteorological instruments. The longcase was also a more convenient graphical solution as it did not require the backdrop of a wall, nor did it distract the viewer's attention with its hanging weights, which could have then been mistaken for the other weights of the engine. If Wren was indeed representing a novel object convenient for his purpose but unfamiliar to his audience, then the graphical details mentioned above could have been added to retrace the steps by which the familiar hooded wall clock was to be transformed. In this light, Monconys's box suspended in mid-air is not so much the simplified version of a recalled drawing (as one might first think), but rather the drawing of the recalled object with which Monconys would have been most familiar-a hooded wall clock. which probably referred to a longcase (rather than a pendulum with a long rod), might therefore not have fully originated with Fromanteel as all commentators have invariably assumed. Instead, a hooded wall clock could have been fitted with a trunk to allow its use in a space without walls, such as the courtyard of Gresham College, where Wren had mounted a 35-foot-long telescope in 1658. 67 The example of James Gregory's splitseconds clock at the University of St Andrews shows that this would not have been unlikely, especially when such observations were not carried out in a tailor-made space such as an observatory. 68 Placing the wall brackets as side decorations would have been a whimsical solution that allowed one to keep these parts safe in case the clock was to be remounted in the future.

CONCLUSION
Much more than being an embellished depiction of meteorological instruments, Wren's original drawing is the equivalent of a tailored suit that has been inverted to make visible the stitches and the seams. Yet this effect is so subtle that it can easily pass unnoticed. Why not choose more obvious and well-established graphical conventions, such as an exploded view or a cutaway? 69 Unlike drawings or prints of machines that had to be intelligible on their own, or that belonged to well-established genres with particular styles and conventions, Wren's drawing was made for a unique occasion: an oral presentation. Details that might have been lost in a private engagement could now be articulated and emphasized. Even more, one can imagine how Wren would have pointed out details to animate his drawing: how the counterweight could be screwed to assure the vertical stability of the wind vane; how the pencils would be kept pressed on the surface of the tablet; how the pencil or the disc of the wind register could be removed by using a hinge; how the chain would engage the teeth of the pulley to move the main board. It is certain that Wren would have had many things to say about the clock: how long it could work unattended, how precise it would be, etc. Those in the audience would have concluded, if Wren did not explicitly say it, that such an engine could be easily, cheaply and quickly constructed from scraps that were probably available at Gresham College. With the exception of the glasswork, making such an engine did not require an instrument maker but a carpenter. Thus, Wren's drawing was more than a mere plan or design: it was supposed to entice its audience and persuade them of its feasibility by showing how certain technical difficulties could be solved.
In the second drawing of the weather clock presented to the Royal Society (figure 4), instead of details of construction, Wren employed finishing details. Though the gilded spandrels on the dial have been removed, carved floral inlays are distributed around the edges-the horizontal brackets, the legs, the pediment-framing the unembellished instruments. The vase-shaped support legs are now continued by blocks matching them in size. While dotted lines show how the crooked rack enters the hood and is moved by the clock, the circular thermometer, with its intricate drum and surrounding liquid tube, remains opaque. The finishing details are also extended to the shading, the hatching lines being replaced by ink wash. While in the first drawing Wren separated the meteorological instruments from the clock acting as a driving force, the second drawing is centred on the face of the clock, with the two meteorological instruments symmetrically disposed on either side. In this drawing, Wren employs graphical details not only to convey how a finished weather clock might look but also to imagine a scientific instrument that would be worthy to be displayed (or gifted) during a royal visit, such as that for which the Royal Society was preparing in July 1663.
Though I have stressed the importance of the material world that surrounded Wren, the analysis of graphical details could also be taken in a different direction. One last look at Wren's first drawing might leave one wondering about its centre, where, floating in midair, there is a pencil-an appropriate symbol for Wren. However, the careful and measured composition of the overall drawing seems to be put into question by the scrawling on the sides of the pencil: on the left a trefoil knot, on the right a swirling line; the end of both lines is split like the tongue of a serpent. Is this a 'useless' (i.e. meaningless) detail? It is tempting to make a guess and interpret these curlicues as a remembrance by Wren of his father, the Dean of Windsor, who had died only a few years earlier in 1658. The Parentalia note that the 'one thing mentioned by him [Dean Wren] as his own invention', and described in a marginal note in Henry Wotton's Elements of architecture, was 'the Serpentine', a new manner for 'disposing the current of a river to a mighty length in a little space'. 70 Dean Wren, who was 'well skilled in all branches of the mathematics', had similar interests to those of his son, who inclined towards mechanics and practical mathematics. 71 As a sign of gratitude, the young Wren dedicated to his father an 'astronomical instrument' and a 'pneumatic engine' by composing Latin poems which have been preserved, along with the drawing of the weather clock, in the heirloom copy of the Parentalia. 72 The aim of these remarks is not to claim that one can fully know the intent behind these lines, but rather to show how even the most apparently meaningless and superfluous detail may guide historians to see the life hidden beyond the representation.

DATA ACCESSIBILITY
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