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Thomas Armstrong Prismatic Marching Compass c.1880

Thomas Armstrong 'RGS' Prismatic Explorers Compass c.1880-1900

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A very unusual early version of the ‘RGS’ type pocket compass, dating from c.1880-1900. This is a particularly rare prismatic design, with elements of both the Schmalcalder designs of the early 19th century, and the Singer’s Patent compasses of the 1860’s. It may well have been intended for military use, as an officer's night marching compass.

The compass features a card with a development of the distinctive Singer’s design and is very similar to one illustrated in the Royal Geographical Society’s explorers manual Hints to Travellers (1871). The ‘RGS’ type was often used by travellers and explorers around the turn of the century, and Ernest Shackleton took several similar compasses with him on his expeditions to the antarctic, including the celebrated 1907-9 British Antarctic Expedition.

Compasses of this type are known to have been manufactured by Francis Barker before 1875. The card is hand-drawn, with a very finely engraved aluminium ring around the outer edge. It would have been painted with a luminous compound (most probably ‘Balmain’s Luminous Paint’), which was activated by exposure to very bright light, often created by burning a strip of magnesium ribbon. Part of the original instructions for rendering the compass luminous in this way can still be seen on the label inside the lid. There is also a small pouch on the front of the leather compass case for the magnesium ribbon. The card is also marked ‘No. 1090’, which may be a serial number, or a registered design number. The compass has an oxidised brass case, folding prismatic sight, a transit lock, and a manual brake. It comes complete with its original fitted leather case.

The compass is signed by 'Thomas Armstrong & Bros., Manchester’. Armstrong’s had been trading in Manchester since 1825, as jewellers and silversmiths. Around 1851 Thomas Armstrong expanded the business to include the manufacture of optical instruments. In 1868 he took his brother George into the business and changed its name to 'Thomas Armstrong & Brother'. This helps to date the compass to sometime after 1868, which also ties in with the Singer’s Patent style design of the card (Singer’s patent expired in 1868). During this period Armstrong's reputation was such that in 1891 the company won the contract to supply the War Office, the Admiralty, the Board of Trade, the India Office and the General Post Office (G.P.O) with scientific instruments.


In very good original condition, and good working order. The compass finds north well, although sometimes a little slowly. The prism, transit lock and brake are all fully functional. The brass case is in good condition, with much of the original oxidised finish still present. The lid fits perfectly and the hinge is strong. There are a couple of minor blemishes to the outer edge of the glass window in the lid, possibly created when the glass was made. Part of the instruction label is still present inside the lid. The compass card is in very good condition. The original leather case is in good condition, with just the usual signs of age and use.

Dimensions: 50mm diameter (85mm inc. prism & loop)