Jason Clarke Antiques has dated this piece to the 1850s.
The octant is comprised of an ebony frame with a brass index arms and fittings. It has an inlaid bone scale and inlaid bone plates on the front and back of the frame. The front inlay is engraved with, “Crichton London and Made for G Peterhead”.
Other Crichton octants from the period bear the words “Made for” or “Sold by” to denote an instrument specifically commissioned by an individual or for a retailer to sell on Crichton’s behalf. Given the range of places on his octants from North to South he must have been a prolific and well respected maker of these navigational instruments.

The frame retains its three shades, index glass and horizon glass.
John Crichton is listed as trading between 1831 and 1865 primarily trading from 112 Leadenhall Street, London where he advertised himself as instrument maker to the Honourable East India Company and to Trinity House. He was an exhibitor at the Great Exhibition of 1851 where he was awarded a prize medal for sextants and drawing instruments. The firm continued to trade beyond 1864 as John Crichton & Son
Jason Clarke Antiques has dated this piece to the 1850s.
You can view the stock and full dealer information on the Jason Clarke Antiques Profile Page