hotels, etc., the useful telautograph, automatic self-adjusting relays, private-line printers--leading up to his famous "harmonic" system. This was based upon the principle that a sound produced in the presence of a reed or tuning-fork responding to the sound, and acting as the armature of a magnet in a closed circuit, would, by induction, set up electric impulses in the circuit and cause a distant magnet having a similarly tuned armature to produce the same tone or note. He also found that over the same wire at the same time another series of impulses corresponding to another note could be sent through the agency of a second set of magnets without in any way interfering with the first series of impulses. Building the principle into apparatus, with a keyboard and vibrating "reeds" before his magnets, Doctor Gray was able not only to transmit music by his harmonic telegraph, but went so far as to send nine different telegraph messages at the same instant, each set of instruments depending on its selective note, while any intermediate office could pick up the message for itself by simply tuning its relays to the keynote required. Theoretically the system could be split up into any number of notes and semi-tones. Practically it served as the basis of some real telegraphic work, but is not now in use. Any one can realize, however, that it did not take so acute and ingenious a mind very long to push forward to the telephone, as a dangerous competitor with Bell, who had also, like Edison, been working assiduously in the field of acoustic and multiple telegraphs. Seen in the retrospect, the struggle for the goal at this moment was one of the memorable incidents in electrical history.