Pair of horizontal force magnetometers (declination variometers) used on the Polar Expedition of 1875-6 undertaken by Sir George Strong Nares and later owned by the Royal Greenwich Observatory, Herstmonceux. A magnetometer measures the intensity of the Earth's magnetic forces by the number of oscillations of the needle - the more oscillations the greater the intensity. The two magnetometers and their 5 inch magnets have four separate part numbers. Both objects have a suspension magnet and mirror, but both without the tube for housing the suspension thread and each has a differng tripod stand. One is missing its shutter.

Each is labelled with a government-issue symbol and "POLAR EXPEDITION. 1875." and "M.P. TENCH. LONDON". They are numbered 1 and 2, number 1 being the one missing its shutter.