Re: Sphaera Nr.10

[G�nther Faltlhansl]

Dear Giles,
I appreciate your  quick response and attaching the interesting article. I
don't think your will mind, if I spread it to the sundialists group, where I
found your address in the first place.
Thanks very much also for putting me on the SPAERA mailing list.
Best regards,
Günther Faltlhansl

-----Ursprüngliche Nachricht-----
Von: Museum of the History of Science, Oxford <[EMAIL PROTECTED]>
An: Günther Faltlhansl <[EMAIL PROTECTED]>
Datum: Freitag, 21. Jänner 2000 11:47
Betreff: Re: Sphaera Nr.10


>At 21:38 20/01/00 +0100, you wrote:
>>   Hello,  My attention has just been directed to Mathsyear 2000 by Peter
>>Ransom via a sundialists' discussion group on the Internet. He also
pointed
>>out  the fact that in Sphaera Nr.10 there would be an interesting article
>>on a 16th  century astronomical compendium, which could be obtained
through
>>you. I am not  sure if he meant by regualr or by e-mail. In any case, I
>>would be interested in  receiving this article, if possible. Please inform
>>me about the  cost. Thank you. Günther Faltlhansl
>
>
>Dear Gunther,
>
>The article on the compendium will be in SPhaera, out printed newsletter,
>which will be put up on the web at some point. Meanwhile, here is a copy of
>the text. I will get you put on the Sphaera mailing list.
>
>Regards
>
>Giles Hudson,
>Curatorial Assistant,
>Museum of the History of Science, Oxford.
>
>
>PREVIOUS articles about Epact – the Museum’s collaborative electronic
>catalogue of medieval and Renaissance instruments – have used individual
>pieces as a starting point to explore the identity of particular instrument
>makers. A sixteenth-century English astronomical compendium, which carries
>the initials ‘V. C.’, provides an instance where the maker remains a
>shadowy figure, but where fresh information has emerged about the
>instrument itself.The many leaves of this gilt brass compendium are
>crammed with features: a nocturnal, a universal equinoctial sun and moon
>dial, a horizontal sundial, a compass and a quadratum nauticum, as well as
>calendrical, astrological, tide and latitude tables. These devices and
>tables are hinged within a square box, the covers of which are decorated
>with strapwork, heads, foliage and fruit, while the remaining free surfaces
>carry foliate engraving. The box is surmounted by a triangular pediment
>decorated with pairs of heads, as well as representations of an armillary
>sphere, two quadrants and the reverse of an astrolabe.The initials ‘V. C’.
>appear on the (now broken) hinged support for the nocturnal disc. That they
>represent the instrument’s maker is clear on two counts. Firstly, the
>compendium carries another pair of initials as part of a motto prominently
>displayed in an oval on the back cover: ‘+ Aske + me + not + for + ye +
>Gett + me + not + + R + P +’. Matched by a coat of arms on the front cover,
>the initials ‘R. P.’ presumably represent the instrument’s first owner.
>Secondly, the initials ‘V. C.’ also appear on a closely related compendium
>now held at the Adler Planetarium in Chicago.The identity of ‘V. C.’ has
>long been a puzzle. In the 1920s R. T. Gunther was inclined to accept the
>existence of an otherwise unknown early maker; in his later years he was
>tempted to identify V. C. as the youthful Humphrey Cole, the best known of
>the Elizabethan instrument makers. This identification was also assumed by
>Louis Janin, who published a copiously illustrated article about the Adler
>compendium in 1976.Although expressed in a tentative manner, the Museum
>has previously acknowledged this possible identification. Until the recent
>closure, the compendium was displayed alongside a group of Humphrey Cole
>instruments together with a label which identified V. C. as ‘? = Vmfredus
>Cole’.However, the identification has not commanded universal assent.
>There is both a stylistic and a chronological gap between the two V. C.
>instruments and the earliest instruments by Cole. From such disparities,
>Gerard Turner was led to argue more than fifteen years ago that V. C. was
>not Cole but most likely a Flemish craftsman, probably employed by the
>publisher and engraver Thomas Gemini, who was himself a Flemish immigrant
>based in London.In 1556 Gemini had published Leonard Digges’s Tectonicon,
>a text on practical mathematics and surveying. The title page advertised
>Gemini’s readiness to supply the instruments featured in the book. Gemini
>had already been responsible for Digges’s other principal publication, the
>Prognostication Everlasting of Right Good Effect. Published under a number
>of titles from at least 1553 onwards, this almanac provided calendrical,
>meteorological and astrological rules, together with basic astronomical
>information and material on tides and time-telling.The Museum’s V. C.
>compendium is very closely related to material in Leonard Digges’s
>Prognostication and it seems that, as well as providing the instruments of
>Tectonicon, Gemini also ensured that he could meet any commission that
>might be forthcoming as a result of the earlier work by Digges.The
>compendium’s quadratum nauticum is similar to Digges’s and the instrument
>also incorporates copies of the general calendar as well as tables for the
>moon, the moveable feasts and tides. A further table with the time of
>daybreak and sunrise, the length of the day and night, and the time of
>sunset and twilight for the first, tenth and twentieth of every month also
>follows Digges’s pattern.The connection with Leonard Digges’s book, and
>with the business activities of Thomas Gemini, is thus strongly suggested
>by the instrument itself. The dates of the two V. C. instruments also
>exactly fit the context of this early mathematical publishing in England.
>The Adler compendium is dated 1557 while the Museum’s undated example must
>have been made around 1554, since it carries two tables for the period 1554
>to 1579.Suggestive as this evidence is, the identity of V. C. may never be
>conclusively established. Turner’s suggestion of a Flemish maker
>nevertheless provides the most plausible answer currently available and
>certainly requires a good deal less interpretative ingenuity than the
>identification with Humphrey Cole.Whatever the final merits of such
>competing claims, it might have been expected that the form and structure
>of the V. C. compendium would now be well understood. However, when
>catalogued for Epact, the instrument provided a surprise by giving up an
>additional unexpected secret.The compendium’s equinoctial dial is of an
>unusual design. The dial is universal, with a hinged plate which can be
>adjusted to any inclination and can therefore serve for any latitude. The
>plate itself is straightforward with a circular scale of hours on the upper
>and lower faces. The provision of lunar volvelles within the hour scales on
>both faces allows the instrument to serve as a moon dial, though each
>volvelle is presently mounted on the wrong side of the leaf so that its
>scale of hours from 4 to 12 to 8  increases in the wrong direction.There
>have been two common solutions devised to register and fix the inclination
>of equinoctial dials: a graduated arc of degrees (which often folds flat
>for portability) providing a friction-tight surface against which the dial
>plate is set; and a folding strut fitting into a notched scale of degrees
>used to elevate the plate.The V. C. compendium incorporates a different
>design. On the upper surface of the dial plate is a square clinometer with
>a quadrant scale and a small plummet (illustrated left). The clinometer
>folds flat across the dial plate and on its reverse carries a circular
>scale of degrees enclosing a depiction of an armillary sphere.The plummet
>no longer swings freely but it does, in principle, indicate the elevation
>of the dial plate. To set the plate for the correct latitude, its
>inclination is adjusted until the plummet indicates the appropriate point
>on the quadrant scale. With the clinometer set carefully in the vertical
>plane its leading edge sits perpendicular to the centre of the dial plate
>and therefore also serves as the gnomon for the upper face of the
>dial.While the operation of the equinoctial dial is clear enough in
>outline, practical problems apparently remain. Firstly, there is no obvious
>way to hold the dial at a particular elevation: the plate has no support or
>strut. Moreover, how can the clinometer be reliably held in the vertical
>plane essential both for the operation of the plummet and the clinometer’s
>role as a gnomon? Finally, while there is a gnomon for the upper face,
>there is no equivalent projection for the lower face, which therefore
>renders the instrument ineffective for half of the year.These practical
>difficulties seemed to imply that a component was missing from the
>instrument. The form of the clinometer itself suggested what the missing
>piece might be. Rather than a sharp, shadow-casting line, the leading edge
>of the clinometer square is shaped as a hollow sleeve with an open slit
>running along its length.Gunther noticed this feature and thought that the
>hollow edge was perhaps intended to receive a wind vane. Such devices are
>found, for example, on the contemporary astronomical compendia of the
>Augsburg master Christoph Schissler. But Gunther’s suggestion scarcely
>seems plausible: rather than being in the plane of the horizon, the plate
>is meant to be set at an angle parallel to the equinoctial; neither is
>there any wind rose against which wind directions could be read.A more
>likely candidate for the missing insertion would be a pin, slipping into
>the clinometer sleeve and passing through a hole in the centre of the dial
>plate. This would provide not only a continuous gnomon for the northern and
>southern declination of the sun but also a rigid means of ensuring that the
>clinometer remained in the vertical plane.  Although partly obscured by
>subsequent restoration, a hole is indeed visible in the centre of the
>plate.Unfortunately, while Janin’s article on the V. C. compendium at the
>Adler illustrates an equinoctial dial of the same type, there is no
>discussion of its gnomon or the elevation of its dial plate. Only direct
>contact with the Adler revealed that a solution to all these problems had
>already been found – within the instrument itself.Though not noted by
>Janin, there is indeed a pin provided with the Adler example, hidden away
>in the dial plate. Housed in a hollowed edge of the plate, this pin is
>keyed to fit the open profile of the clinometer edge and to pass through a
>hole at the centre of the dial plate. Circular in section, with a
>projecting ridge running along its length, the pin fits the sleeve of the
>clinometer while also giving a clean gnomon edge for both the upper and
>lower faces of the dial. When pushed through the plate, the end of the pin
>rests on the next leaf of the compendium, holding the dial plate up at an
>angle. Inserting the pin to a variable distance therefore allows the dial
>to be set for a wide range of latitudes, effectively (if rather
>inelegantly) solving the remaining practical problem of the dial’s
>operation.Armed with this news from the Adler, the Museum’s compendium was
>quickly re-examined. Overlooked and apparently unnoticed, the same solution
>was immediately discovered. One edge of the dial plate bulges slightly and,
>once alerted to its existence, the head of a pin was indeed discernible.
>Extricated with some difficulty and illustrated above projecting from its
>housing, this pin then successfully emerged from what was presumably a long
>period of hiding.The Museum’s gnomon pin is shaped slightly differently
>from the Adler example: rather than a circular section with a projecting
>ridge, it is in the form of a thin rod, the cross section of which is a
>rounded wedge. The sharp edge of the wedge projects through the slit in the
>clinometer sleeve to serve as the gnomon for the upper face. Its other
>functions also match those of the Adler example: pushed through the hole in
>the dial plate the rod ensures that the clinometer remains perpendicular to
>the dial plate and also acts both as the gnomon for the lower face and as
>the support for elevating the dial plate above the next leaf of the
>instrument. In practice, damage to the clinometer sleeve prevents the rod
>being fully inserted, but the principle is clear.The discovery of this
>secret part of the V. C. compendium, despite being a small feature in
>itself, indicates how the cataloguing of instruments for Epact has not only
>led outwards to a broader context, but also to new revelations about the
>structure and use of instruments which might otherwise have been considered
>to be already exhaustively studied. –   S. A. J.
>