II. The lunar diurnal magnetic variation at Greenwich and other observatories

§ 1. The present research forms part of a wider investigation of terrestrial magnetism, the main object of which is the study of certain electrical phenomena that are associated with solar emissions absorbed in the upper atmosphere, and with the systematic motions of the upper atmosphere. The subject also bears on the electrical conductivity of the solid earth and oceans. The results are briefly discussed from this standpoint in Part IV. The immediate subject of the paper is the lunar diurnal variation of the earth’s magnetic field, and particularly that of the declination at Greenwich, although the results of extensive reductions for other elements, at Batavia, Zikawei, and Pavlovsk, are also included.