This device, known as a circumferentor, was used by surveyors to measure horizontal angles before the general adoption of the theodolite. This example is probably missing a ranging device that fitted across the top of the dial and was located in the holes in the lugs on either side.
Engraved in the centre of the dial is the name ‘Walker Dublin’ with the date 1797. In 1805, W. Walker & Son were trading as mathematical instrument makers at 17 Temple Bar, Dublin and they were still at the same premises in 1824. Fred and George Walker are recorded as mathematical instrument makers in the 1840s.
- NMI Accession Number DM:1990/27
- David Hall, Irish Brass, Bronze and Copper, 1600-1900, National Museum of Ireland, Dublin, 2014, ISBN 978-0-901777-98-0
The following pictures of more complete examples of these instruments were supplied by Mr Dale Beeks.
The following reference gives dates for William Walker’s work in Dublin as: