Universal equinoctial ring dial, W. & S. Jones
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- Circa 1790
- W & S Jones Holborn London
- 30 cm
- 23 cm
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This brass ring dial is made by William and Samuel Jones, instrument makers based in Holborn, London. The universal equinoctial ring dial consists of four parts: a suspension which can be adjusted to the latitude, a meridian ring with latitudes from 0 to 90, a hinged equator ring with 24-hour indication (two times I-XII) and an engraved centre plate with sliding lens and indication in months and constellations, with declination scale and indicated north and south. The ring dial can be used at different latitudes and is therefore referred to as universal. When in use, one first sets the suspension to the correct latitude, then folds down the equator ring and sets the sliding lens of the central plate to the right month or constellation. The sun falls through the lens onto the hour ring and thus indicates the correct time.
The universal ring dial is also called a 'travel sundial', because when folded up, it can be taken with you. The meridian ring is signed 'W&S Jones Holborn London'. William (1762 - 1831) and his brother Samuel Jones (-1859) were among the most successful instrument makers in London during the late 18th and early 19th centuries. An 1830 catalogue published by them lists several sundials and ring dials: 'A new universal ditto and equatorial, making a very portable angular instrument'.