The ('rapbophon.e.—Fig. 2 shows the general arrangement of the Bell-'fainter grapho phone. The instrument is mollified on a table provided with a lid which can be closed and locked when not in use. Underneath this table is fixed a balanced treadle and driving wheel, similar to those of a sewing machine. The cord from the driving wheel passes through the table and around a small pulley, to actuate the governing device, which is arranged to give speed of 160 revolutions per minute. In practice this speed can be maintained within one or two revolutions, no mat ter how fast or how irregularly the treadle is worked. From a pulley, on the other end of the governor, a cord passes to the main pulley of the instrument, which is fixed to the front of the table. This pulley is loose on a spindle which carries the cen tring drum that supports one end of the record cylinder. A simi lar drum, opposite the former, And at a distance from it rorre isponding to the length of the cylinder, runs free in a suitable bearing. This drum and its cyl inder are capable of a lateral motion, controlled by a spring. To mount a cylinder upon its oentres, the drum and its spindle are drawn back, the cylinder is put in position. and the spring is released, so that the cylinder is held tightly by its hearings, and any motion communicated to the driving pulley through the governor is of course imparted to it. In order to provide a means for starting or arresting the movement of the cylinder immediately—an operation absolutely necessary in operating the graphophone—the driving pulley of the instrument, which, as has already been mentioned, runs loose on its spindle, can be made fast with the latter at will by means of a clutch, which can be thrown in and out of gear by means of a system of levers operated by two buttons placed in the position shown in Lhe engraving; by depressing one or other of these buttons or keys, the record cylinder can be stopped and started instantly.
The recording style is carried upon a tube which is fixed parallel to the cylinder, but at a higher level. The lower part of this tube is cut away, to expose a very fine-threaded screw placed within it. This screw is caused to revolve by means of toothed gearing driven from the main pulley, so that when this latter is running idle, the screw. as well as the record cylinder, is stopped. The circular box containing the recording diaphragm is carried at the end of a short arm which terminates in a half-sleeve, of the same diameter as the tube enclos ing the screw. Hinged to this half-sleeve is another similar one, from which projects a short arm carrying at its end a relatively heavy balance weight. Set in a slot made in the half sleeve first referred to, is a portion of a nut, threaded to the same pitch as the screw ; at the back of this nut is a spring which keeps it projecting slightly beyond the face of the sleeve, but which allows it to pass back into the recess if a slight pressure be applied. The position of the parts is so arranged that the style attached to the centre of the diaphragm slightly penetrates the wax film with which the record cylinder is coated, and in this way a very fine screw of 160 threads to the inch, and one-thousandth of an inch in depth. is traced upon the cylinder. We now come to consider the construction of the recording part of the instrument, the function of which is to receive the sound vibrations and to engrave them faithfully upon the wax surface. It consists of the shallow circular box, referred to previously as being at tached to the carrying sleeve. The diaphragm forming a bottom to this box, is made from a piece of very thin and flawless mica; a short distance above, and parallel to it, is fixed in the box a metal plate, pierced with two series of concentric slots ; above this again, but not in contact with it, is a metal cone, the centre of which coincides with the center of the box, and is therefore immediately over the style attached to the mica. All these parts are enclosed
within the box by a metal cover with a central opening, to which is attached a flexible speaking tube, provided with a mouthpiece. In front of the mica diaphragm, and stretching from one side of the box to the other, is a metal bridge, so placed that it is almost in contact with the style. In the centre of this bridge a projection is formed, of such a shape that when the instru ment is in operation it presses upon the wax surface of the recording cylinder and burnishes it in advance of the style, so that the latter may have an absolutely true surface to work upon.
The style is simply a very fine, chisel-pointed cutting tool, capable of forming a perfect thread upon the wax-coated cylinder, of the pitch and depth already mentioned, ht engrav ing. the carrier is placed upon its tube so that the style bears upon the cylinder; the driving pulley is set in motion; the message is delivered through Lhe mouthpiece of the speaking tube, and the air vibrations thus created strike upon the cone within the receiving box, and are distributed uniformly ovot the surface of the mica diaphragm with the aid of the slotted plate, setting up in the latter a series of vibrations corresponding to the sounds produced by the speaker and transmitted through the tube.
The transmitting or repeating mechanism consists of a light carriage for carrying the socket, to which the transmission tube is attached, as well as the diaphragm and its attach ments. On this carriage are four curved arms; the back pair fixed, and the forward pair hinged to the carriage and controlled by springs. A threaded block or nut, similar to that already described as forming part of the receiving mechanism, is fixed between the forward pair of arms; at the back of the carriage, and rigid with it, is another pair of arms with con necting pieces at top and bottom; this serves as a handle for holding the transmitter when it is taken off or put on the instrument. The front part of the carriage terminates in a screwed tubular socket which forms a continuation of the nozzle on which the elastic transmitting tube is fixed; upon this socket is screwed the circular box, containing the transmitting dia phragm. The under side of the box is pierced with holes to prevent the setting up of air currents within, which might interfere with the proper action of the diaphragm. A hollow stein. terminating in a curved beak, forms a part of the bottom of the box. To the centre of the diaphragm, which is of mica, is attached one end of a silk thread, the other end being fastened to a small curved style, which is secured to the beak by a pin in such a way as to give it entire freedom of motion. If now a record has been engraved by the recording style upon the wax-coated cylinder, and the recording diaphragm with its attachments has been removed, the transmitting carriage is slipped over the tube containing the traversing, screw. In doing this the ant between the pair of arms engages with the screw, the point of the curved style enters the groove engraved upon the cylinder, and on the instrument being set in motion the irregularities which had previously been engraved by the recording style give a corresponding motion to the transmitting point, and, by means of the silk thread, which is kept in tension, set up in the transmitting diaphragm a series of vibrations similar in character to those which had been previously created in the recording diaphragm by the message spoken into it. In this way the original sounds are faithfully reproduced as to quality, but not as to intensity, perhaps owing to the smaller diameter of the repeating dia phragm, but they are not audible excepting through the intervention of the transmitting tub. This tube, which is slipped over the nozzle, is bifurcated near its outer end.