stead of the ordinary mouth-piece. Instead of a bell to call attention, Gower uses a small vibrating reed, contained in a tube, the mouth of which opens in front of the diaphragm, and the other end at the side of the case. By blowing into this tube, the reed is set in vibration, and FIG. 2.-Receiver of Bell's Telephone, at the Philadelphia its movement communicated to the diaphragm Exhibition. the strength of which varies with the movement of the membrane. This varying current, acting upon the electro-magnet of the receiver, causes this to exert a varying attraction upon its thin disk armature. This latter, therefore, vibrates in unison with the membrane of the sending instrument, and consequently reproduces the sound vibrations acting upon the transmitting membrane. As the function of the battery current traversing the coils of the electro-magnets in both instruments is simply to magnetize them, it may evidently be dispensed with and permanent magnets substituted for the soft-iron cores of the electro-magnets. This change was made by Mr. Bell early in 1877, when he produced the form of instrument shown in fig. 3. This had the advantage by the air. The vibrations thus set up are sufficiently powerful to produce a sound in the receiving instrument loud enough to attract attention to it. Another modification is the crown telephone of Phelps, shown in fig. 7, in which six ring-shaped magnets are substituted for the single straight one of Bell. The "Pony crown" instrument of the same inventor, Fig. 8, has a single magnet bent in a circular form. In the telephone transmitter above described, the electrical impulses are produced by induction, and the strength of the currents sent to line are therefore limited by the power of the aerial vibrations which set the diaphragm in motion. It is, however, possible to make the vibrating disk vary the strength of a battery current, and thus FIG. 8.-Bell's Telephone, Model with Identical Speaker and Receiver, tested at Salem, Feb. 12, 1877. of the former apparatus, that the same instru- | ment could be used either as a transmitter or receiver. Later the very compact and conven obtain much more powerful results. Bell, early in his experiments in telephony, constructed a transmitter of this kind, which is shown in fig. 9. A platinum wire is attached to the vibrating diaphragm and dips into a small cup of FIG. 6.-Gower's Telephone. acidulated water. The circuit is completed through the water, so that the resistance, and consequently the current flowing, varies with the depth of immersion of the platinum wire. In a caveat filed the same day as Bell's application (Feb. 14, 1876), Elisha Gray described an instrument of similar construction, and stated of battery telephone that has been thoroughly successful. It is due to Thomas A. Edison, who was conducting experiments, as mentioned above, with a view to transmitting speech, at the same time that Bell was carrying on his re searches. These experiments were begun in the autumn of 1875, and resulted in the production of the carbon telephone in 1877. Its construction is shown in fig. 10. A small disk of compressed lampblack is held between two plates, the one nearer the diaphragm being of platinum. A little ivory button, resting on the platinum plate, touches the diaphragm and serves to communicate the varying pressure exerted by it in its excursions to the lampblack disk. The carbon disk is included in the circuit of a battery, the current of which is varied by the greater or less resistance offered to its passage by the carbon as the pressure on this varies. The carbon is but slightly compressed, just enough to hold together, so that a very slight pressure on it by the diaphragm serves to alter its resistance materially. The battery current, instead of being sent to line, traverses the primary circuit of an induction-coil, the secondary coil of which has one end grounded and the other connected with the line-wire. The receiving instrument ordinarily employed with this transmitter is the Bell magneto-telephone, E under slight pressure were noticed by Mr. | experiments made by him were described in a Hughes, an American living in London, about FIG. 9.-First Model of Bell's Speaker. a year after the production of the carbon telephone, and some very simple and remarkable paper before the royal society. He gave his instrument the name of microphone (see MICROPHONE), and since then it has been common to designate carbon telephones by that name. -In recent years a great many experiments have been made with the telephone, and a great variety of instruments produced. These have shown that it is possible to dispense with the diaphragm, magnet, and coil in the receiving instrument, and still reproduce speech. It will be noticed that, in all the forms of telephone above described, the electric circuit remains closed, and that there take place simply an increase and decrease of the current. The instrument of Reiss, mentioned above, has been claimed to differ fundamentally from present telephones in that it was a make-and-break instrument, and that, as constructed by Reiss, it was incapable of transmitting speech. Prof. Sylvanus Thomson, who has made a thorough FIG. 10.-Edison's Carbon Transmitter, Model of 1879-in Section and Perspective. examination of the work of Reiss, and experi- | claims that, used as it was intended to be, the mented with the instruments constructed from transmitter is not a make-and-break instrument, but that its action is due to the variations in resistance of a loose contact, the same as in the case of modern carbon transmitters. One form of the instrument of Reiss is shown in FIG. 11.-Transmission Apparatus of Reiss's Telephone. 1861 to 1863, asserts that these are capable of transmitting and reproducing speech, and FIG. 12.-Receiving Apparatus of Reiss's Telephone. figs. 11 and 12, the former being the transmitter and the latter the receiver. The transmitter consists of a membrane stretched across the upper side of the box K, to which is attached a light metallic arm, that touches a platinum point when the diaphragm moves upward in its vibrations. A mouth-piece, T, is placed at the side of the box. The receiver consists of a thin electro-magnet mounted upon a sounding-board. The increase and decrease of the current cause the central iron rod, which is supported free of the coil, to vibrate in harmony with the movements of the transmitting membrane.-The telephone has gone very rapidly into extensive use as a means of business communication in cities. The method of operation consists in providing a central office or exchange, to which all the subscribers are connected, and at which point one subscriber is connected with another by an attendant. There is a call-bell in the office of the subscriber and one at the central office. In this country every considerable town is provided with the telephone exchange, and in Europe, though not in as general use as here, it is being rapidly extended. Early experiments with the telephone showed that speech could be heard through lengths of wire corresponding to a distance of 1,000 m. or more; but trials on actual lines speedily showed that, owing to the retarding effects of static induction, such distances were impracticable, and that 100 to 150 m. was about as far as distinct articulation could be obtained. Within this year, however, conversation has been carried on between New York and Chicago, a distance as great as that above mentioned. But this was over a special wire of low resistance, and the result seems to be wholly due to the wire, as the Edison transmitter, made in 1878, gave as good results as any of the newer instruments tried. See Du Moncel's "The Telephone, the Microphone, and the Phonograph;' Prescott's "The Speaking Telephone, Electric Light, &c. ;) and Hospitalier's "Modern Applications of Electricity." TELESCOPES. One of the largest recent reflecting telescopes is that made by M. Martins for the Paris observatory. Its aperture is 120 centimetres (almost 4 ft.). Its mirror is made of silvered glass. Its mounting is somewhat different from the common one, and appears to have good points. (See engraving, page 916.) So far this telescope has not been successful, probably in consequence of an improper method of supporting the speculum during the process of grinding and polishing. A new reflector of 136 inches aperture was constructed and mounted in 1879 by Mr. A. A. Common of England. It has been used but a short time, and its excellence is highly spoken of by competent judges. If we may judge of it by its successful application in the observations of the faint satellites of Mars in 1879, it is by no means a more powerful instrument than the refracting telescope by which these bodies were originally discovered, viz., the 26-inch telescope of the United States naval observatory at Washington. Many more observations were made by the latter telescope than by the former of the faint satellites of both Mars and Saturn. Mr. Common has obtained photographs of Jupiter's satellites with an exposure of 20m. Saturn and Mars can be photographed in 5 to 8, and Jupiter in 1" to 2". An exposure of 20m on the nebula of Orion produced no result. Dr. Henry Draper photographed this nebula, Sept. 30, 1880, with an 11-inch Clark refractor, with an exposure of 50m. The refracting telescope for the Vienna observatory, made by Grubb of Dublin, has an aperture of 27 inches and a length of 334 feet. The tube is of steel, 3 feet in diameter in the middle, tapering to the The 26-inch Refractor at Washington. ends. The circles can all be read through a single reader-telescope. The accompanying table gives a list of the principal telescopes of the world. Reflectors of less than 13 inches |