On the Automatic Temperature Compensation of the Force Magnetometers
. A portion of the funds liberally contributed by the Government for the advancement of science, and placed at the disposal of the President and Council of the Royal Society, having been entrusted to the author for the accomplishment of the above object on a plan which was submitted to the Astronomer Royal and Colonel Sabine in the spring of last year, and by them considered feasible, he considers that he cannot better fulfil the obligation of reporting progress at the present period, than by laying before the Royal Society a description of the instruments now constructed. So long as the results of the variations of magnetic force were deduced from eyeobservation only, at the periods of which the temperature as well as the position of the magnets was recorded, a correction for the influence of change of temperature on the instruments themselves could be readily estimated and applied; but in deducing mean values from the photographic registers, especially those for intervals involving considerable changes of temperature, it is manifest that the greatest degree of accuracy cannot be attained, unless either the apparent values were individually corrected by means of a separate register of the thermometer enclosed in the box with the magnet, or the instrument possessed within itself an approximate automatic correction for the effects of change of temperature.
II. On the automatic registration of magnetometers, and meteorological instruments, by photography. —No. IV
