A similar arrangement, though not precisely for the same purpose, has already been suggested and tried by Messrs. Deprez, Carpentier, Ayrton, and Perry, in galvanometers with permanent steel magnets. If the coil, D D, be so placed, the deflecting force which now acts obliquely can be considered as the resultant of two forces, one acting at right angles to the line, S N, as in an ordinary galvanometer, and the other parallel to this line, but in a sense opposed to the action of the electro magnet and its exciting coils. If the angle of obliquity be so chosen that this latter component exactly equals the magnetic effect of the exciting coils _per se_, an equality which holds good for all currents, then we shall have an almost perfect imitation of a tangent galvanometer with permanent magnets. But we can go a step further than this; we can overbalance the exciting coils by setting the deflecting coil at a greater angle than necessary for the mere elimination of the former, and thus attain that an increase of current results in a slight weakening of the field in which the needle swings, thus allowing the increment of the angle of deflection to be comparatively large even for large currents. In this way it is possible to obtain a more evenly divided scale than in the case when the deflection follows the law of tangents, as in an ordinary tangent galvanometer. This principle of overbalancing the exciting coils is shown on diagram, Fig. 2. The straight line, O G, represents the magnetic effect on the needle of that component of the deflecting force which is parallel, but in sense opposed to S N; as mentioned above, the magnetic effect of the exciting coils is represented by the straight line, O E. The combined effect of these two forces on the needle is represented by the line, O K, the ordinates of which must be deducted from those of the curve, O A B, in order to obtain the total directing force due to each current. This is shown by the curve, O P Q, shown in a thick full line. This curve shows how the directing force or strength of field in which the needle swings decreases with an increasing current. That this does actually take place can easily be proved by experiment. Fig. 4 shows two curves; the one drawn in a full line is obtained by plotting the deflection in degrees of the needle of a potential indicator as abscissae, and the corresponding electromotive forces measured simultaneously on a standard instrument as ordinates; the dotted line shows what this curve would be with an ordinary tangent galvanometer.