spring and contact-point a to the line. At each vibration of the reed the contact between the spring and a is made and broken, and the circuit opened and closed. Whenever the signalling-key is depressed, therefore, an intermittent current enters the line.

Mr. Gray also procures the intermittent current by means of a vibrating bar or string, as in Fig. 14, where a is a thin steel bar stretched by the screw s, and carried by a fixed metal bar or frame, B. The bar A vibrates between upper and lower contact-points, c, d. M M are two electro-magnets whose poles are let through the bar B, so as to act upon the vibrating bar. PP are pillars supporting the whole. In this arrangement a local battery is also employed to set and maintain A in vibration: this is done, however, in the act of signalling. On closing the signalling-key the local current passes to the upper contact c, against which the bar A rests. From thence it passes, by means of the bar B and wire w, through the magnets м M, completing its circuit. These magnets then attract the bar downwards in its middle, plucking it away from contact with c, and bringing it into contact with d underneath. The local circuit being thus broken, however, the bar springs back again into contact with c, to be plucked down again as before. In this way the bar is started vibrating. The line circuit is made through the lower contact d, the bars B and A, and the pillar P. At every vibration of the steel bar A it is interrupted, and an intermittent current set up in the line.

In both of these methods the number of intermissions in the line current will correspond with the number of vibrations of the vibrators. By employing in the first method reeds of different pitch, and in the last bars or strings of different dimensions and tension, distinct intermittent currents will be produced.

The principal receivers for interpreting these currents into distinct audible sounds are represented in Figs. 15 and 16. In Fig. 15 M is a double electro-magnet supported over a resonance pipe closed at one end. The soft-iron armature of the electro-magnet, t T, is rigidly fixed to one pole at t, the other end being free to vibrate in front of the other pole at T. When the intermittent current from the line passes through the electro-magnet the free end of the armature or tongue is set into corresponding vibration, and the aircolumn in the resonance box, vibrating in unison with it, gives out an audible note. It is easy to see how, by employing a number of separate transmitters, such as described, to superimpose separate intermissions in the line current,

and passing the complex current so produced through as many separate receivers of this kind, that each receiver will only respond to its own particular set of intermissions. For the sounding-pipe of each receiver can be so constructed

as to resound only to the vibrations set up in the tongue by a particular series of intermissions. In this way several distinct notes may be simultaneously telegraphed, each note being used for a separate message.

The receiver shown in Fig. 16 has been called the " physiological receiver," since it depends for its action on the

contact of living animal tissue with a conducting surface, It is the most interesting of the two, because its action has not hitherto been explained. If the intermittent current from the line is passed through the tissue to the conductor,

the corresponding note is faintly audible. To intensify the effect the line current, in practice, is simply passed to earth through the "primary," P, of an induction-coil, and the more intense secondary current is used. In the figure, B is a hollow wooden resonance-box, with a bulging zinc face, b. This box is carried by a metal axle, A, supported by a stand, s: it is rotated by turning the handle, E. The zinc face is connected by a wire, w, to the axle; h is merely an air-hole in the face of the box. One end of the "secondary coil," s, is connected by wire to the metal axle at the terminal a ; the other end is connected to a bare wire held in the operator's hand, as shown. The operator lightly presses a finger of this hand on the zinc face, while with the other he rotates the box, and the dry rasp of the skin on the zinc surface is changed into a musical note whenever the current passes.

Like M. la Cour, Gray also provides that the vibratory current shall close a local circuit and record the message in permanent marks, by means of a Morse or other recording instrument. For this purpose he employs a receiver similar to the string-transmitter shown in Fig. 14. The line current, passing through the magnets of this instrument, sets the tense bar in vibration against the upper contact c, thus closing the local circuit and actuating the local recorder.

Mr. Gray's apparatus is now successfully operated over more than 2400 miles of the Western Union Telegraph Company's lines, including distances of several hundred miles. As many as four, and even eight, messages are simultaneously sent. Both he and M. la Cour are still engaged in perfecting their apparatus, and we may reasonably expect that the telephone will ere long do good service as a practical telegraph.

b. The Articulating Telephone.

This ingenious little instrument is the most wonderful of all the forms of telephone, and the latest, as it is the greatest, to use the words of Sir William Thomson, "of all the marvels of the electric telegraph." Its peculiar faculty lies in the transmission of promiscuous sounds. Not only does it convey the blended notes of musical instruments, but it actually reproduces the human speech. It is easy to see how an instrument like this will become practically useful. For domestic or commercial purposes, for reports of lectures and speeches it is especially fit. It has the advantage of quickness over ordinary methods of telegraphing.

In these, each letter of a word is on an average composed of three distinct signals; but in the articulating telephone a whole word is transmitted by the single act of uttering it.

Mr. A. Graham Bell, the inventor of this now-famous instrument, is, we believe, a native of Edinburgh, and is now a Professor of Boston University, and a naturalised

citizen of the United States. In December last he patented it in England.

The articulating telephone consists of two distinct apparatus, a sender and a receiver. Fig. 17 represents the sender, and Fig. 18 the receiver: they are both exceedingly simple. In the sender, M M are two coils of insulated wire

surrounding the two poles of a powerful permanent magnet. These coils are connected up together, and to the terminals tt, on the mahogany stand s. Immediately in front of the poles of a magnet is a membrane stretched on a ring, R. This membrane carries an oblong piece of soft iron cemented to it just opposite the poles of the magnet. A suitable acoustic cavity, or mouthpiece to speak into, o, fitted with three screws for tightening up the membrane, complete the apparatus. The sender speaks into the mouthpiece in an elevated voice, and the membrane, vibrating in unison, carries the piece of soft iron-which is really a movable armature-to and from the poles of the magnet. This has the effect of inducing a magneto-electric current in the coils of wire, M M, which are connected up to the line. The strength of this induced current varies continuously, "as nearly as may be, in simple proportion to the velocity of a particle of air engaged in constituting the sound." It travels along the line, and passes through the receiver at the distant station, evoking there the sounds which gave

rise to it. The receiver is even more simple than the sender, and its action is the reverse. It consists of a tubular electromagnet, m, encased in iron to concentrate its power as much as possible on the circular disk armature, a, which is so fixed as to be free to vibrate over its cavity. It is connected up in circuit with the line by the terminals shown. The induced current coming from the sending station passes through the coil of this electro-magnet, and sets the thin disk armature into sonorous vibrations, which are distinctly and clearly heard as a reproduction of the original sounds.

In his address to the physical section of the British Association at Glasgow last year, Sir William Thomson thus