Product images of Universal equinoctial dial and armillary trigonometer
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Universal equinoctial dial and armillary trigonometer
Universal equinoctial dial for all latitudes. It has a shaped wooden base and back support. The main brass disc of the instrument is bolted through its centre to the support and is free to revolve in a vertical plane. This disc has another rotatable disc set within it. One semicircle of the outer disc is hinged and can be moved to measure the azimuth of the sun. Behind this semicircle are scales for correcting the observed altitude of the sun and for the equation of time. This instrument was designed by Mungo Murray, a shipwright, and was first seen by James Ferguson in 1757. Ferguson later made his own version and wrote a short tract about its use. The tract explains many uses for solving problems of astronomy and spherical trigonometry, and for constructing pedestal horizontal dials and mural dials.
- Image reference: D8943
- National Maritime Museum, Greenwich, London