Epact Scientific Instruments of Medieval and Renaissance Europe

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Nocturnal And Sundial
Signed by Girolamo della Volpaia
Dated 1568; Florence
Brass; 147 mm in diameter

The nocturnal is composed of a central circular disc divided with a zodiacal calendar scale (with 0? Aries at 10 March) reading to 1 day and 1?. Within this is a volvelle composed of two discs, the lower carrying a 24 hour scale reading to 10 minutes; the upper with its edge notched with 24 teeth. Half of these are numbered 1 to 12 as in its appropriate place is that for 24. Concentric with the teeth are three scales, that closest to the edge reading from January '7 7 6 6 6 5 5 5 4 4 4 4 4 4 4 5 5 6 6 7 7'. Within this is a further scale reading from January '31 18 57 38 15 53 27 7 46 32 22 20 24 35 54 13 38 0 25 45 9 24 36 19'. Within this is a month scale, and at the centre in a fourth ring is the inscription 'MEDIA NOX PER TOTVM ANNVM' ('the middle of the night for all the year'). An index on the first disc at the 0 point between 1 and 24 is marked MEDIA NOX ('middle of the night'); the solar motion disc has an index set on the division of January and December, and a large rule is mounted so as to rotate round the central sighting hole marked 'HOROLGIVM NOCTVRNVM'.

The second face of the instrument carries at the centre the hour diagram for an Italian hours dial (9 to 24) for latitude 43? 30', flanked on each side by the two halves of a zodiacal calendar scale. Beneath the diagram is a scale of 90? reading to one degree and beneath this a scroll containing the latitude inscription 'AD LATITVDINEM GRADVVM XXXXIII ET M. XXX'. To the left of the diagram is the signature written in a scroll, and to the right, also in a scroll 'LINEE PVNCTORVM POST MERIDIEM'. Above the hour diagram is a shadow square marked 'VMBRA VERSA VMBRA RECTA' divided to 12 by six cumulatively numbered groups of 2; within this is a solar motion table similar to that marked on the centre disc of the volvelle on the nocturnal side. At the centre of the diagram is the number 'XIII'.

Two scrolled pinhole sights are set on the top line of the instrument and above them is a suspension mount/handle similar in form to the 'throne' of an astrolabe made in one piece with the centre plate of the instrument and decoratively engraved.

Anthony J. Turner

Istituto e Museo di Storia della Scienza, Firenze
Inventory no. 2503

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