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 Quadrant The back of the quadrant has a rotating volvelle with brass arm. On the plate outside the volvelle are two concentric circles divided in 12 equal parts, each further divided [0] to 30 by 5, numbered by 10. The circular brass plate is divided in 15 concentric circles. Starting from the external, they are engraved with: '...16 32 48 64.....800' in equal parts; '1 2 3 4 5' then every 5 to 100, in unequal parts; '1 2...[29.5]' in equal parts; '1 2 ....[18.5]' in equal parts; '1 2 ...[12]' in equal parts; the following 6 have the names of the months and the total days in different lengths, equal and unequal parts; '2 4 6 8 10' then each 10 to [116] in equal parts; '1 2 3...[27.2]' in equal parts; '1 2 3...[27.5]' in equal parts; '1 2 3...[15]' in equal parts. The brass arm bears the indication of the use of the scales: corresponding to the circles on the brass plate, are engraved: 'an mo aug z stel', 'an access z recesse', 'an me mo [lunarnode]', 'an me mo [Jupiter]', 'an me mo [Mars]', 'an me mo [Sun] [Mercury] [Venus]', 'an me arm [Saturn]', 'an me ar [Jupiter], 'an me ar [Mars]', 'an me ar [Venus]', 'an me ar [Mercury]', 'die me mo [Moon]', 'die me ar [Moon]', 'die me cent [Moon]'. They indicate respectively the precession, the trepidation, the medius motus of Saturn, the lunar node, Jupiter, Mars, and the Sun - Mercury - Venus, the medium argumentum for the year for Saturn, Jupiter, Mars, Venus and Mercury, and the medius motus, medium argumentum and medium centrum for the moon. On this side of the quadrant are also engraved the initials 'T [N]', probably of an owner, and, very faintly, 'Pointer', the collector who bequeathed it to St. John's College, Oxford. See R. T. Gunther, Early Science in Oxford, (14 vols, Oxford, 1923-45). Ilaria Meliconi |