XVIII. Experiments on the directive power of large steel magnets, of bars of magnetized soft iron, and of galvanic coils, in their action on external small magnets. —With appendix, containing an investigation of the attraction of a galvanic coil on a small magnetic mass

Abstract

The only experiments with which I am acquainted tending to throw light upon the distribution of magnetic power in the different parts of a steel magnet are some very imperfect ones by Coulomb in the French Memoirs for 1789 and other years. It appeared to me that it might be desirable to make experiments of a rather more exten­sive character, and to add some measures of the magnetic effect of galvanic currents, both directly by their immediate action, and indirectly by the amount of magnetic power which they produce inductively in soft iron. For the measure of permanent magnetism I selected a bar magnet 14 inches long, 1.4 inch broad, 0.35 inch thick; it has not been touched by a magnet for several years, and is likely to be in a state of very permanent magnetism. For the galvanic currents a cylindrical coil was used 13.4 inches long, 1.4 inch in external diameter, and about 0.9 inch in internal diameter; it has, I believe, four layers of wire, each layer having 160 revolutions of the wire. The battery used with it consisted of three cells, with sulphuric acid diluted in the proportion of 1 to 6; the plates were of zinc and graphite, each exposing on each side about 8 square inches ; the circuit was always completed about half an hour before the experiments were begun, and a delicate galvanometer was placed in circuit by which the steadiness of the current was established. A core of iron 0.8 inch in diameter and of the same length as the coil, removable at pleasure, fits well in the inside of the coil; the iron is quite soft, and can with ease be entirely freed from any sub permanent magnetism.