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Description: | The dip circle is built to accomodate three sets of dip needles: three nine inch, three six inch and three three inch and these three sets are in fitted brass boxes. The dip circle is mounted on a horizontal circular base, supported on a tripod stand and engraved in degrees with two vernier scales and double fine adjusting screw and clamp. On the base is a box (glass and gunmetal) encasing the needle and agate bearing, with eight microscopes. A degree scale is engraved on the glass, plus clamp and adjusting screw. A horizontal needle is mounted in a cirular case on top of the box, with a degree scale. Also mounted on the circular base is a gas light and a circular frame carrying glass prisms for directing the light to illuminate the vertical degree scale and level. An empty needle box is marked AST0701.1 and three sets of dip needles in their boxes are marked AST0701.2-8.
A dip circle measures the vertical direction (or dip) in the Earth's magnetic field in the same way that a compass measures the horizontal direction. George Biddell Airy (1801-1892), Astronomer Royal (1835-1881) championed the study of terrestrial magnetism because it improved understanding of the compass and therefore fit in with the role of the Observatory as a compiler of scientific information to aid navigation. Under Airy the Magnetic and meteorological department was established. This dip circle, designed by Airy, and made by Troughton and Simms in 1860, replaced the Robinson dip circle and was used at the Observatory until 1915 to take daily readings to find the variations in the Earth's magnetic field at Greenwich.
The dip circle is built to accomodate 3 sets of dip needles: three 9-inch, three 6-inch & three 3-inch and these three sets are in fitted brass boxes. The dip circle is mounted on a horizontal circular base, supported on a tripod stand & engraved in degrees with 2 vernier scales & double fine adjusting screw & clamp. On the base is a box (glass & gunmetal) encasing the needle & agate bearing, with 8 microscopes. A degree scale is engraved on the glass, plus clamp & adjusting screw. A horizontal needle is mounted in a cirular case on top of the box, with a degree scale. Also mounted on the circular base is a gas light & a circular frame carrying glass prisms for directing the light to illuminate the vertical degree scale & level. An empty needle box is marked AST0701.1 and three sets of dip needles in their boxes are marked AST0701.2-8 and can be found via the Whole/Part toggle.
caption: Airy's magnetic dip circle 1860, with dial boxes
caption: Airy's magnetic dip circle 1860 | Publisher: | "http://collections.rmg.co.uk/" | Rights holder: | "Royal Museums Greenwich" | Subjects: | Airy Science Museum dip circles Vernier The Old Royal Observatory Greenwich Treasures of the National Maritime Museum George Biddell Troughton & Simms London | Source: | Royal Museums Greenwich | Identifier: | http://collections.rmg.co.uk/collections... | Go to resource |
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