Collection of documents relating to the Portsmouth-to-Admiralty semaphore line designed by Sir Home Riggs Popham

The Popham semaphore line opened in 1822, replacing the temporary Lord George Murray shutter system that had been used to provide a fast optical telegraph communication link during the Napoleonic Wars. The new line was faster, simpler and more visible, with a capacity to send messages across the 108 km path in approximately 15 minutes.

It traces its origins to 1815, when an act of government was passed giving the Admiralty permission to buy land for a more permanent Semaphore Telegraph Line. Following closure of the shutter stations in 1816, various designs for their replacement were considered by the Admiralty. The design chosen was that of Rear Admiral Sir Home Riggs Popham. It was based on the French Depillon system, but used a simpler two-arm signalling system in place of the three-arm system used by the French, setting them at various heights on a mast 30 feet high. The moveable arms could be placed in any of seven positions, enabling 49 (7 x 7) different signals. Due to its height, the signal pole could not be rigged on a man-of-war, and instead featured two poles with a signal arm on each. This set-up was awkward as it required two men, one on each pole, to work it.

The design was intended for use on land, as was Murray’s system, and aboard ship, where only flag signalling systems had previously been used. Popham's systems are remarkable for their longevity in the service of the British Navy. The first edition of his nook 'Telegraphic Signals' was produced in 1800, and in 1816 the British Admiralty published Popham's manual under its auspices as an official publication, thereby making it applicable to all Royal Navy vessels. Popham died in 1820, but his communication systems continued well into the twentieth century, appearing under government sponsorship in the booklet 'Vocabulary Signal Book'.

In 1818, an experimental Popham semaphore line was built to run from the Admiralty to Chatham as a test of whether the new semaphore system would work. The Semaphores were made by Messrs Maudslay, and the telescopes were supplied by Dollond. The Popham semaphore followed almost the same route as the Murray shutter chain, but did not use the same locations, and reduced the number of the stations from 24 to 15. A fully restored tower station survives at Chatley Heath, and is open to public. The Popham line was operational from 1822 until 1847, when railway and electric telegraph provided a faster means of communication.

The collection describes and illustrates the Popham Semaphore. It comprises a manuscript description of the system addressed to George Spencer, second Earl Spencer (First Lord of the Admiralty 1794–1801 and Home Secretary 1806–1807), accompanied by a card containing the communication key and a drawing of the semaphore. Also included is a manuscript description of the Depillon French semaphore upon which the Popham semaphore was based.