This law was confirmed by several other experi ments.
When the uniting wire is placed in the same horizontal plane as the needle, but perpendicular to its direction, and near one of its poles, this pole will be elevated, if the current comes from the east, but depressed if it comes from the west. This will easily be understood by the inspection of Plate DXXII. Fig. 3. B A represents here the conductor, N S and N' S' two needles. All the parts of the drawing have the same signification as in Fig. 1, only that the dotted lines denote the infe rior parts of the magnetical circles, but the unin terrupted lines the superior parts. It is evident that N (the north end of one of the needles) is here driven upwards by the repelling action from below and the attracting one above it. In the same man ner, S' (the south end of the other needle) is both drawn and pushed upwards.
The effect is on both sides the same, because not only the magnetics] poles, but likewise the oppo site sides have contrary effects. If one of the needles were turned by means of a magnet, so that each side of the wire could act upon a pole of the same kind, one of them would be elevated, when the other was depressed.
When the uniting wire is perpendicular, and the current enters its superior part, a needle, of which one of the poles is very near to the wire, will be thrown westwards; but if the wire is placed over against a point of the needle, situated between one of the poles and the middle, the needle will be turned eastwards. By opposite currents the results are likewise opposite. Fig. 4 will make this easier understood. A B is the uniting wire, the notations the same as in the former figures. It is evident, by the inspection of the figure, that the north end of the needle a, having predominant austral mag netism, must be repelled by the similar magnetism of the conductor; and be turned towards the west. The attraction of the opposite magetism in the conductor tends to give the needle the same direc tion; but as this coincidence of motions, produced by opposite powers, is constant in electromagnet ism, we shall always confine ourselves to mention but one of them. The south end of c, having pre
dominant boreal magnetism, is also repelled by the similar magnetism of the current, which here has the same direction as the austral on the opposite side of the conductor. Thus the north end of the needle is on one side of the conductor turned the same way as the south end on the other side. The north end of c receives the strongest impulses from the west, and must, therefore, be pushed eastward; while the south end of d receives the strongest im pulses from the east, and must move towards the west, and in consequence of this its north end must also turn eastward like that of c. Were the wire placed exactly over against the middle of the nee dle, this would be solicited equally in opposite di rections, and therefore rest at its place.
When the uniting wire is bent in such a manner, that the parts on each side of the flexture are pa rallel, the exterior surfaces of the two branches are similar, and also the interior ones. In Fig. 5, A C D B represents such a wire. As the current enters the superior branch at C, and in the inferior at B, it is obvious that the directions of the powers in the magnetical circles are the same at e and f, at g and h. Suppose that the two branches are in one perpendicular plane, and the north end of the needle is placed in a plane, below the superior and above the inferior branch, the north end will be re pelled, when placed on the west side, and attracted, when placed on the north side of the wire. Above the superior branch, or below the inferior branch the effects are in the opposite direction. All the other cases, belonging to the effects of bent con necting wires upon magnetics] needles, may be easily explained in a similar manner.
These are the principal experiments, by which Professor Oersted endeavoured to establish the fundamental law of electromagnetism. As they all belong to one class, it has been practicable for us here to maintain in our account the historical or der, without impairing the systematical one. In order to have a short term, we shall call the mag netical action of the electrical current, the revolv ing magnetism.