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Inventory no. 44392 - Former Display Label

German HORIZONTAL STRING-GNOMON DIAL etc., on a COVER for WRITING TABLETS
Late 16th century

Gilt copper. Signed, "Pragæ fecit Erasmus Habermehl"; undated.

This 'instrument', shaped like a book, consists of a 'spine' with two hinged covers, between which can be inserted a pad of paper or vellum leaves, or perhaps ivory writing tablets. The pad or tablets are missing. The use of writing tablet covers for sundials and perpetual calendars was not uncommon in the sixteenth, seventeenth and eighteenth centuries, and there are several examples in this Museum.

The covers described here include:

1a. Nomographs for effecting the conversion either between equal (ordinary) hours and unequal (planetary) hours, or between equal hours and Italian hours; also engraved on the upper surface of the top cover is a coat of arms.

1b. A horizontal string-gnomon dial, adjustable for use in latitudes 50°, 48°, 45° and 42° with parallel scales, divided into fifteen minutes, for each of these latitudes; tables of the lengths of day and night, and times of sunrise and sunset; a compass (restored), with sixteen of the points named with the Italian names of the winds.

2a. An astrological table showing the planet ruling over each hour of each day of the week, a Zodiac/calendar scale (Gregorian), arranged as two parallel linear scales; a multiplication table.

2b. An instrumentum sinuum, consisting of a rectangle, the length of the sides of which are in ratio 3:2; the longer sides are divided into 90° equal parts with lines ruled across the rectangle at each division.

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