Antique Octant by Thompson, Yarmouth.
ANTIQUE OCTANT.
A superb early 19th Century antique navigator’s Octant engraved THOMPSON, YARMOUTH. - The early features found on this Octant probably date it from 1810 to 1820. - Simon Thompson is recorded as working from two addresses in Yarmouth from 1805 to 1844.
The Octant’s ‘T’ shaped frame is constructed from ebony with brass fittings and ivory scales. The arc scale is finely engraved and crisp, reading from -2 degrees to 99 degrees. It is further divided into 20 minutes of arc and can measure angles of up to 90 degrees. The arc scale is also engraved with the fouled anchor mark, this was a trade mark for scales divided by JESSE RAMSDEN who was recognised by the Board of Longitude for the accuracy of his scales.
The ivory makers plaque is situated on the crossbar of the octant frame and is engraved THOMPSON, YARMOUTH.
This Octant has the early flat and unbraced brass index arm, which is fitted with an ivory Vernier scale engraved from 0 to 20 and reading 1 minute of arc. There is a clamping screw to the reverse side and there is also a pivoting brass index arm back stop fitted to the frame.
On the front of the Octant there is a double peep hole fore sight pinnula, to be used in conjunction with the fore sight horizon mirror. This Octant is also fitted with a back sight peep hole pinnula and back sight mirror. ( the back sight was used to measure angles greater than 90 degrees ) There is also a set of three brass framed coloured glass sun filters that are interchangeable between the index mirror and the horizon mirror.
On the reverse side of the Octant there are two butterfly cam levers for adjusting the mirrors. There is a square ivory plaque inlaid into the frame, this is used to note down sight angles and readings. The Octant also has three brass support legs or feet.
This antique Octant is complete with its original wooden, stepped keystone shaped oak box (some repairs to the box are present) - Height of Octant: 14 inches / 35.5 cm Radius of Octant: 11.5 inches / 29.5 cm.
A superb example of this mariner’s navigation instrument and it is in excellent condition considering that it is well over 200 years old.
