A very rare example of a Schmalcalder's Patent prismatic compass, serial no. 539 B, made in London c.1812-26. The compass card is marked 'Schmalcalder's Patent, No. 82 Strand, London'. With a hand-drawn green compass card, lacquered brass case, prism and vane sights, transit lock, and manual brake. The compass would originally have had a brass lid, but this is missing.
Charles Augustus Schmalcalder (1781-1843) was one of the most significant figures in the development of the compass. His patent design of 1812, which introduced the idea of using an optical prism, combined with a sighting vane, to improve accuracy when taking bearings, is still in use today. Schmalcalder's innovation was a development of the work of Henry Kater. In 1811 Kater developed a design using a mirror and sighting vane. His design was then manufactured by Thomas Jones. Schmalcalder, who also knew Thomas Jones, is believed to have seen Kater's new compass at Jones' premises, and this gave him the idea for his own prismatic version. Schmalcalder moved swiftly to have prototypes of his own design made by Jones, which he then went on to patent. Winning the race to patent his innovation, Schmalcalder's compass completely eclipsed Kater's earlier design. Between 1812 and 1826 (when the patent expired) Schmalcalder's Patent compasses were manufactured by third party makers, like Thomas Jones, and sold from Schmalcalder's premises, first at 82 The Strand, London (1810-1826), and later from 399 The Strand, London. Schmalcalder continued in business until around 1840, with his design being used uncredited by many other makers, such as Simms, Barker, Jones, and Troughton after the patent expired in 1826. No doubt as a result of this, Schmalcalder fell on hard times, dying in poverty in 1843 and being buried in the Strand Union Workhouse cemetery.
All Schmalcalder patent compasses have a serial number in the lid and on the base, with the ones from 82 The Strand having a letter 'B' as the prefix, and the ones from 399 The Strand having a letter 'C' prefix. (This compass has the serial number 539, with the 'B' prefix).
(Much of the above is based on the extensive research and expert knowledge of Paul Crespel at trademarklondon.com, who has always been very generous with his helpful and invaluable advice. For more information on Schmalcalder, Kater and the development of the early prismatic compass, see his excellent trademarklondon.com website).
In good, original condition, and good working order. The compass finds North very well. The glass, sighting vane, and prism are all in good condition. The compass card is in very good condition. Both the manual brake and transit lock are working well. There is wear to the original lacquered finish of the brass case. One of the small filter lenses attached to the prism housing has a small but stable crack. There is a serial number (539B), engraved on the base, along with a name and address 'Douglass, 14 Clifton Terrace, Brighton'.