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Article in Museum Publication : Sphaera No. 1 (Spring 1995) 'An Extraordinary Reunion'

'An Extraordinary Reunion'

Among the prized early mathematical instruments in the Museum of the History of Science is a medieval quadrant, of a type known as the 'quadrans vetus', the primary function of which was for telling the time from the altitude of the sun.

This quadrant came to the Museum with the founding collection of Lewis Evans. On its reverse side is a pair of circular scales of a zodiacal calendar, relating dates in the year to the sun's position in the ecliptic, together with a central post or spindle that would originally have taken the components of a volvelle, which would have been used for finding the position of the moon in the zodiac, given the position of the sun (or the date) and the age of the moon. This post also has a slot to receive a wedge for securing the moving parts of a volvelle. Unfortunately, when Lewis Evans purchased the instrument in Paris in 1910, both the volvelle and its wedge were already missing, and they have remained so for some eighty years.

However, in August 1994 the Museum learned that the American instrument dealers 'Tesseract' were in possession of a medieval lunar volvelle plate which had been in a private collection for many years and before that with a London dealer. This plate had a scale of 291/2 divisions, the conventional representation of the lunar cycle, with a pointer at its origin. When in use, it would have rotated at the centre of a zodiacal scale and, with the pointer set to the position of the sun, an index arm moving above the plate would have been rotated to the age of the moon in order to indicate the zodiacal position of the moon on the outer scale.

Since this volvelle was an example of the principal missing component from the Museum's quadrant, and since a similarity in the engraving style had already been noted, the Museum became interested in acquiring the plate to accompany and display alongside its instrument. As Tony Simcock, who was taking care of the Museum's side of the correspondence, gathered more details about the volvelle plate, excitement grew at the increasing convergence of the two sets of photographs and measurements. Even if it was difficult to admit the thought that they really belonged together, it became imperative to purchase the plate for the Museum and this was done with the help of a grant from the PRISM fund of the Museums and Galleries Commission.

On the 26th of October 1994, the volvelle plate was brought to Oxford, and the uppermost gallery, with its celebrated collection of mathematical instruments, was the setting for as theatrical an event as you might ever expect to meet with in a traditional museum. With Tony Simcock as Eamonn Andrews, host of countless unimagined reunions on British television, and David Coffeen of Tesseract as the family friend who has been instrumental in setting up the emotional climax, the anticipated union was finally made.

The fit was precise: the pointer lay just as it should on the outer scale and the hole in the plate neatly fitted the post. But most striking of all was the match between the volvelle plate and a distinct 'shadow' on the quadrant, consistent with the two having previously been together for a great many years. The engraving of the figures on the two plates was also seen to be remarkably close; indeed, the style was judged to be identical. Subsequent examination of the pattern of scratches on both the quadrant face and the post has supported the conclusion that the volvelle and the quadrant belonged together.

It seems impossible to believe this conclusion but, for all that, it appears to be true. Having attracted interest only as an example of a component missing from the Museum's quadrant, the lunar plate is now judged to be an original part of the same instrument. But despite this lucky find, the quadrant still remains incomplete: it is missing half a declination plate from its reverse side and an index arm and securing wedge to complete the volvelle. We live in hope.

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