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Description: | Cast cu-alloy portable or 'pocket' sundial or 'ring dial', slightly damaged, dating from the Late Post-Medieval or Early Modern period, i.e. 16th-18th century. It is complete but broken at the top where it has come apart. The suspension loop is still intact and most of the numbers and letters are still clearly legible. Ring dials are an old and rather inaccurate form of sundial. They work by allowing the rays of the sun to shine through a pinhole onto the hour lines engraved on the inside face of the opposite side of the ring. The dial can be adjusted for date in one of three ways: showing the hour lines as curves crossed by date or declination lines; having two pinholes (one for summer and one for winter); or setting the pinhole in a movable band which can be adjusted against the date scale on the outer surface of the ring. It appears that this ring dial was of the second type, with two pinholes (one for the winter and one for the summer months. The style of ring dials altered little through the centuries and so dating them is often very difficult. The use of the ring dial is explained by Bion (1758): "Plate the moveable Hole at the Degree of the Sign wherein the Sun is; then holding the Ring suspended, turn it towards the Sun, so that his Rays passing thro' the Hole, may fall upon the convenient Circumference of the Sign in the concave part of the Ring, and then you will have the Hour of the Day shewn." Ref: National Maritime Museum (with more images and explanation: http://www.nmm.ac.uk/collections/explore/object.cfm?ID=AST0252)
Original Image | Publisher: | http://finds.org.uk | Source: | Portable Antiquities | Identifier: | http://finds.org.uk/database/artefacts/r... | Go to resource |
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