Since these words were spoken by one of the highest authorities in matters telegraphic, Professor Bell has introduced some important modifications in his apparatus. He now employs, not an electro-magnet, but a permanent magnet. That is to say, instead of using at each station such a bar of soft iron as is shown in Fig. 6, which becomes a magnet while the electric current is passing through the coil surrounding it, he uses at each station a bar of iron permanently magnetized (or preferably a powerful magnet made of several horse-shoe bars—that is, a compound magnet), surrounded similarly by coils of wire. No battery is needed. Instead of a current through the coils magnetizing the iron, the iron already magnetized causes a current to traverse the coils whenever it acts, or rather whenever its action changes. If an armature were placed across its ends or poles, at the moment when it drew that armature to the poles by virtue of its magnetic power, a current would traverse the coils; but afterwards, so long as the armature remained there, there would be no current. If an armature placed near the poles were shifted rapidly in front of the poles, currents would traverse the coils, or be induced, their intensity depending on the strength of the magnet, the length of the coil, and the rapidity and range of the motions. In front of the poles of the magnet is a diaphragm of very flexible iron (or else some other flexible material bearing a small piece of iron on the surface nearest the poles). A mouthpiece to converge the sound upon this diaphragm substantially completes the apparatus at each station. Professor Bell thus describes the operation of the instrument:—“The motion of steel or iron in front of the poles of a magnet creates a current of electricity in coils surrounding the poles of the magnet, and the duration of this current of electricity coincides with the duration of the motion of the steel or iron moved or vibrated in the proximity of the magnet. When the human voice causes the diaphragm to vibrate, electrical undulations are induced in the coils around the magnets precisely similar to the undulations of the air produced by the voice. The coils are connected with the line wire, and the undulations induced in them travel through the wire, and, passing through the coils of another instrument of similar construction at the other end of the line, are again resolved into air undulations by the diaphragm of this (other) instrument.”