Gilt-brass cased clock-watch with alarm, sundials and lunar volvelle in the form of a book

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  • Handbook text

    In the 16th and 17th centuries, there was a fashion for the ownership of scientific instruments. The astronomical compendium, a number of different instruments combined in one case and small enough to be portable, became a highly desirable object; the more sophisticated it was, the more status it carried. This rare combination of a calendrical compendium and an hour-striking clock-watch with alarm was made by Hans Koch, one of the leading makers in South Germany at the time. His mark ‘HK’ conjoined within a shield, and a separate right-facing monk's head, the town mark of Munich, are punched on the back of the movement.

    Two sundials and a lunar volvelle make up the compendium. The cast gilt-brass case in the form of a book has two closing latches on the open edge and a spine partially pierced and decorated with scrolling foliage and flowers. On the outside of the lid is a large manual volvelle within a fixed circle engraved with degrees and signs of the zodiac. Around the volvelle are several place names in separate circles appropriate for their latitudes, numbered 42, 44, 46, 48, 50 and 52 and inscribed: GRAD:ELEVATIO:POLI (degree of polar elevation [latitude] Around the centre is the inscription: QVANT: DIEI * QVANT: NOCT * (amount of day – amount of night). Two large apertures in the volvelle reveal concentric circles engraved with the number of hours of daylight and darkness. On the solid area between the apertures three points enclose the inscription: MOVEATVR INDEX . AD GRADVM SOLIS (move the index for the degree of the sun). In use, the volvelle is rotated until the index points to the appropriate date expressed in terms of degrees of a zodiac sign. The hours of daylight and darkness for that day can then be read next to the circle in which the required location is listed. At the top, a smaller roundel is inscribed: GRADVS. DECLINATIO. MAGNETIS (degree of magnetic declination) and calibrated with a scale. The central area of the roundel is formed by the base of a compass box which is rotated to comply with the required magnetic declination.

    The inside of the lid has an adjustable horizontal sundial for use between latitudes 45o N and 52o N. and below is a lunar volvelle with an aspectarium engraved in the middle of a manually adjusted central disc inscribed INDEX DIERVM AETATIS LVNAE (daily index of the age of the moon). The scale beneath the disc is divided 1-29½ for the age of the moon. A fixed scale around the outside is divided I-XII twice and the scale around the edge of the disc is calibrated 3-12-9 (the range of dark hours at latitude 48o N). A circular aperture in the disc shows the phase of the moon.

    The main dial has a pin-gnomon sundial in the upper part, with signs of the zodiac to the left and right showing unequal hours, with lines for the two tropics and the equator, each named, and a dial inscribed DIEI HORAE PLANET (planetary hours of the day). In the lower part, the clock dial has a chapter ring with hours I-XII twice, T-shaped half-hour marks, and alternate hatched and plain rectangles for the quarters. There are also touch pins at the hours. Within the fixed chapter ring is a manually adjusted ring numbered 1-24 to show Bohemian or Nuremberg hours, where the day begins at sunset or sunrise respectively. In the centre, a disc numbered 1-12 twice allows for setting the alarm. The blued-steel hand is not original.

    The watch movement has two quite separate mechanisms. The first is circular with gilt-brass plates and shaped pillars. The going train is powered by a fixed barrel with stackfreed. The four wheel going-train of steel wheels drives a verge escapement with a steel dumb-bell balance. The rate of the balance is regulated by a hog's bristle regulator. The bristles are mounted on a long gilt-brass angled arm moved by turning the blued steel hand on the gilt brass drum on the back plate, calibrated 1-9 for regulation. Also mounted in this movement is the simple alarm mechanism. In a separate shaped movement at the top is the hour striking mechanism controlled by a gilt-brass count-wheel numbered 1-12.

    In: Thompson, David, Watches in the Ashmolean Museum, Ashmolean Handbooks (Oxford: Ashmolean Museum, 2007)

Further reading

Baillie, G.H., Watchmakers and Clockmakers of the World, Connoisseur's Library (London: Methuen, 1929), pl. XXVIII and XXIX, p.124.

Thompson, David, ‘Watches in the Ashmolean Museum, Oxford’, Antiquarian Horology, 25, (2000), p.505.

Thompson, David, Watches in the Ashmolean Museum, Ashmolean Handbooks (Oxford: Ashmolean Museum, 2007), no. 4

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