tant friend at the time of the person's death; (4) the performances of certain ‘test mediums,’ especially of one, Mrs. Piper, whose case has been investigated at length by the Society for Psychical Research. (See their Proceedings, 1890, 1892, 1895.) All this evidence rests upon the assertion that the number of coincidences exceeds the number attributible to chance according to the law of probability: e.g. veridical hallucinations are said to be 440 times more numerous than they should be according to chance alone. The verdict of science is still, however, ‘not proven.’
Bibliography. Proceedings Society for Psychical Research, passim; Beard, The Study of Trance, Muscle-Reading, and Allied Nervous Phenomena (New York, 1882); Jastrow, Fact and Fable in Psychology (Boston, 1900); Flammarion, The Unknown (Eng. trans., New York, 1900); Ochorowicz, De la suggestion mentale (Paris, 1887); Parish, Zur Kritik des telepathischen Beweismaterials (Leipzig, 1897); Podmore, Apparitions and Thought-Transference (New York, 1895).
TELEPHONE (from Gk. τῆλε, tēle, afar + φωνή, phōnē, voice, sound). An instrument for the transmission of speech or musical or other sounds by means of electrical vibrations corresponding to the original sounds. The first use of the word telephone is in a description of experiments by Wheatstone where sound was transmitted through wooden rods. In 1837 Page, of Salem, Mass., noticed that an iron rod suddenly magnetized and demagnetized would emit certain sounds which were due to a rearrangement of the molecules, and this phenomenon has since been known as Page's effect. Bourseul of France in 1854 conceived the fundamental idea of the telephone, but did not, however, put it into actual practice. He proposed a device in which a current interrupted by a vibrating disk under the influence of the voice would produce a similar vibration of a disk at the end of a conductor through the agency of an electro-magnet. In 1860 Philipp Reis, of Frankfort, invented an apparatus which he named ‘Telephone,’ with which he was able to reproduce sound at a distance. Reis's telephone, about which there has been much controversy, in his hands at least was able to transmit articulate speech, and he is entitled to credit for the principle of the instrument. For the practical development of the idea and the invention of an actual working telephone the honor must be given to Alexander Graham Bell, who, March 7, 1876, received letters patent for new and useful improvements in telegraphy in which a method for the transmission of vocal sounds is one of the most important of the claims. Few patents for inventions have been subject to more litigation than the telephone, and the literature on the subject is quite exhaustive; but Bell's rights have been sustained by the highest courts, and though he was closely followed by other inventors, notably Elisha Gray, he may fairly be entitled to the honor of the invention.
SECTION OF RECEIVER WITH COMPOUND UNIPOLAR MAGNET.
The Bell telephone, which has survived as the modern receiver, served both as transmitter and receiver in the early apparatus. A reference to the accompanying diagram showing a cross section of a modern unipolar receiver will make clear its action. There is a hard rubber case hollowed at its upper extremity and containing the soft iron diaphragm about 1100 inch thick and two and a quarter inches in diameter, with free part one and three-fourths inches across, which is tightly held at its circumference, but its centre is free to vibrate. A bar magnet, either single or compound, carries at its upper end a coil of fine silk-covered wire (No. 38 B. & S. gauge generally) with resistance of about 75 ohms, whose terminals connect with the binding posts. A more powerful receiver can be constructed by employing instead of a single magnet a horseshoe magnet with coils on each pole. In the Ader bipolar receiver, used extensively in Continental Europe, the horseshoe magnet is ring-shaped and outside of the diaphragm, and in front of the pole pieces a soft iron ring is placed with the object of strengthening the field of force between the poles. The diaphragm of a telephone receiver is in close proximity to the pole or poles of the magnet, but not in contact. When used as a transmitting instrument this diaphragm will vibrate under the influence of the voice, its movement being caused by the movement of the air known as sound waves. The diaphragm rapidly approaching and receding from the magnet consequently produces currents by induction in the wire of the coil. These currents will be transmitted over the line wire, and, flowing through the coil of the receiving instrument, will cause its magnet to become more strongly magnetized and the diaphragm to be attracted. The diaphragm of the receiver will accordingly move in unison with that of the transmitter, and consequently the sound wave which impinges on the latter will be reproduced. The ground can be used as a return or the circuit can be of wire throughout. The currents of electricity that were transmitted
