146.  The helix alone was then held permanently in the magnetic direction, and the soft iron cylinder afterwards introduced; the galvanometer needle was instantly deflected; by withdrawing the cylinder as the needle returned, and continuing the two actions simultaneously, the vibrations soon extended through an arc of 180 deg..  The effect was precisely the same as that obtained by using a cylinder magnet with its marked pole downwards; and the direction of motion, &c. was perfectly in accordance with the results of former experiments obtained with such a magnet (39.).  A magnet in that position being used, gave the same deflections, but stronger.  When the helix was put at right angles to the magnetic direction or dip, then the introduction or removal of the soft iron cylinder produced no effect at the needle.  Any inclination to the dip gave results of the same kind as those already described, but increasing in strength as the helix approximated to the direction of the dip.

147.  A cylinder magnet, although it has great power of affecting the galvanometer when moving into or out of the helix, has no power of continuing the deflection (39.); and therefore, though left in, still the magnetic needle comes to its usual place of rest.  But upon repeating (with the magnet) the experiment of inversion in the direction of the dip (141), the needle was affected as powerfully as before; the disturbance of the magnetism in the steel magnet, by the earth’s inductive force upon it, being thus shown to be nearly, if not quite, equal in amount and rapidity to that occurring in soft iron.  It is probable that in this way magneto-electrical arrangements may become very useful in indicating the disturbance of magnetic forces, where other means will not apply; for it is not the whole magnetic power which produces the visible effect, but only the difference due to the disturbing causes.

148.  These favourable results led me to hope that the direct magneto-electric induction of the earth might be rendered sensible; and I ultimately succeeded in obtaining the effect in several ways.  When the helix just referred to (141. 6.) was placed in the magnetic dip, but without any cylinder of iron or steel, and was then inverted, a feeble action at the needle was observed.  Inverting the helix ten or twelve times, and at such periods that the deflecting forces exerted by the currents of electricity produced in it should be added to the momentum of the needle (39.), the latter was soon made to vibrate through an arc of 80 deg. or 90 deg..  Here, therefore, currents of electricity were produced by the direct inductive power of the earth’s magnetism, without the use of any ferruginous matter, and upon a metal not capable of exhibiting any of the ordinary magnetic phenomena.  The experiment in everything represents the effects produced by bringing the same helix to one or both poles of any powerful magnet (50.).