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Inventory no. 36708 - Epact entry

Epact number: 14915

Scaphe Dial

Signed by Alexander Ravillius
Dated 1537; Italian
Ivory; 90 mm in diameter

Main text

In this instrument a turned ivory box opens to reveal two instruments, one for surveying, the other for telling the time.

In the lid is a magnetic compass, with a scale of degrees marked with initials of the Mediterranean winds, and gilt decoration beneath the magnetic needle. Sights cut into the ivory rim allow the lid to be used as a surveyor's cross or for taking horizontal angles by the compass.

There is a scaphe sundial in the base, where the hour-lines are engraved on a hemispherical concave surface, with a projecting point to cast the shadow and a small compass for orientation. The system of hours used here is known as Italian hours, reckoned from zero at sunset to 24 at the following sunset. The dial has been projected for latitude 45 degrees.

Source museum: Museum of the History of Science, Oxford
Museum number: Inventory no. 36,708

Detailed text

The compass in the lid has the needle poised above painted and gilt foliate decoration. The circle is divided into 8 winds, marked '|star|' (for north), 'G', '|cross|' (for east), 'S', 'O', 'A', 'P', and 'M', while each wind is divided to 20 and numbered by 5. A glass cover is retained by a brass ring. Slit sights in the ivory rim at the cardinal points form a surveyor's cross, and can be used with the compass to measure magnetic bearings. They have caused open cracks at these points and the rim is now held together by a brass band.

In the scaphe dial in the base the pin-gnomon is set in a turned brass mount at the centre of foliate and circular decorative engraving in the ivory. The glazed magnetic compass at the bottom of the hemisphere is marked with the cardinal points 'O', 'P', 'M' and '|cross|'. The hour lines are numbered 9 to 23, the position of the line for 24 being on the rim, and they are crossed by seven lines for the sun's path between the tropics for the signs of the zodiac, whose symbols are marked on the rim. The hours are marked along the equatorial line. A meridian line within the hemisphere is continued on to the rim, as are the lines for the sun's path. The rim also carried a note of the latitude, 'POLVS G.45' and the signature and date, 'RAVILLIVS M.D.XXXVIII'.

Jim Bennett

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