problems belonging to the subject may be solved; namely, the determination of the magnetic axis of a needle; the exact determination of the moment of inertia of an oscillating needle; the deviation produced in the direction of the horizontal needle by the neighbourhood of a magnet; and the determination of the absolute intensity of the horizontal magnetic force of the earth. A combination of magnetic observers in different places had been set on foot by M. von Humboldt in 1828; a magnetic observatory was erected at Göttingen in 1833; and in consequence of these circumstances the curious discovery was made in 1834, that the minute momentary changes in the position of the horizontal needle are simultaneous and corresponding at distant places. This led M. Gauss to direct the attention of men of science more particularly to this subject; and the operations of the "Magnetic Union" of observers were carried on with great activity under his guidance. The "Results of the observations of the Magnetic Union" for 1836 and for 1837, published by MM. Gauss and W. Weber, contain an account of the consequences of these exertions. They also contain descriptions of instruments invented by M. Gauss for the purpose of these observations, namely, the magnetometer, and other magnetical apparatus of his construction, which has already been sent to the observatories of Bonn, Dublin, Freiberg, Greenwich, Kasan, Milan, Munich, Naples, Upsala, Krakow, Leipzig, and Marpurg. Also the Bifilar Magnetometer, which determines directly the variation of horizontal intensity. The "Results" further contain various mathematical calculations of great importance, on the subject of the above instruments, and of the observations made by them. And it appears by observations made in March, 1838, at Göttingen and three other places, with the Bifilar apparatus, that there is the same correspondence in the simultaneous changes of intensity at different places which had already been discovered in the declination. The ingenuity shown in the invention of instruments and processes, the mathematical skill employed in treating the observations, and the importance and interest of the results, are well deserving of being honourably marked by the Royal Society, and the adjudication of the Copley Medal to M. Gauss.
The Council have also awarded a Copley Medal to Dr. Faraday for his discovery of Specific Electrical Induction, published in the eleventh series of his Experimental Researches in Electricity.
From the peculiar view which he had taken of the phenomena of induction, Dr. Faraday was led to expect some particular relation of this process to different kinds of matter, through which it might be exerted. This relation he succeeded in establishing by the most decisive experiments.
The phenomena are shown in their simplest form by an instrument which he has named a Differential Inductometer. It consists of three insulated metallic plates, placed facing each other; the centre one being fixed, and the other two moveable upon glides, by which they may be approximated to or withdrawn from the centre.
