The author, after referring to his paper in the Philosophical Transactions for 1868 on the comparison of Magnetic Disturbances inferred from Galvanic Currents recorded by the Self-registering Galvanometers of the Royal Observatory of Greenwich with the Magnetic Disturbances registered by the Magnetometers, on 17 days, states that he had now undertaken the examination of the whole of the Galvanic Currents recorded during the establishment of the Croydon and Dartford wires (from 1865 April 1 to 1867 October 24). The days of observation were divided into three groups,—No. I containing days of considerable magnetic disturbance, and therein including not only the 17 days above mentioned, but also 36 additional days, No. 2 containing days of moderate disturbance, of which no further use was made, and No. 3 containing the days of tranquil magnetism. The comparisons of the additional 36 disturbed days were made in the same manner as those of the preceding 17 days, and the inferences were the same. The results were shown in the same manner, by comparison of curves, which were exhibited to the Society. The points most worthy of notice are, that the general agreement of the strong irregularities, Galvanic and Magnetic, is very close, that the galvanic irregularities usually precede the magnetic, in time, and that the northerly magnetic force appears to be increased. The author remarks that no records appeared open to doubt as regards instrumental error, except those of western declination; and to remove this he had compared the Greenwich Curves with the Kew Curves, and had found them absolutely identical.
I. Note on an extension of the comparison of magnetic disturbances with magnetic effects inferred from observed terrestrial galvanic currents; and discussion of the magnetic effects inferred from galvanic currents on days of tranquil magnetism