Magnetic observations made on board HMS Erebus, including at the Falkland Islands, by [James Clark Ross?] Daily magnetic observations made on the vessel HMS Erebus, using a declination magnetometer, a bifilar [horizontal force] magnetometer, and a vertical force magnetometer. The readings are plotted against Gottingen mean time, at [most often] hourly intervals. For the 'term days' of each month, readngs were taken more frequently during the 24 hour period. With thermometer readings and an end column with occasional weather observations, usually wind direction and force. The ship's positions are not given, although there are occasional indications within the text: notably [p.222] 'Falkland Islands'. 24 June 1841-20 November 1842