THE PHONOGRAPH.

Globe, Volume IX, Issue 1257, 29 March 1878, Page 3

THE PHONOGRAPH.

(London “ Times.”) Not many weeks have passed since we were startled by the announcement that we could converse audibly with each other, although hundreds of miles apart, by means of so many miles of wire with a little electro magnet at each end, yet we are on the point of realising some of the many advantages promised by the telephone. Another wonder is now promised us—an invention, purely mechanical in its nature, by means of which words spoken by the human voice can he, so to speak, stored up and reproduced at will over and over again, hundreds, it may be thousands, of times. What will be thought of a piece of mechanism by means of which a message of any length can be spoken on to a plate of metal, that plate sent by post to any part of the world and the message absolutely respoken in the very voice of the sender purely by mechanical agency ? What, too, shall be said of a mere machine by means of which the old familiar voice of one who is no longer with us on earth can be heard speaking to us in the very tones and measure to which our ears were once accustomed ?

The highly ingenious apparatus by which this wonder is effected is the invention of Mr Thomas A. Edison, of Manlowe park, New Jersey, U.S.A., the electrical adviser to the Western Union Telegraph Company. Mr Edison is well known in the States, and scarcely less so in England, for several valuable practical applications of electrical science, among Mr Edison’s other inventions being an exceedingly well-arranged telephone. To the present invention Mr Edison has given the name of the Phonograph, and it depends for its action upon certain well-known laws in acoustics.

The Phonograph is composed of three parts mainly—namely, a receiving, a recording, and a transmitting apparatus. The receiving apparatus consists of a curved tube, one end of which is fitted with a mouthpiece for the convenience of speaking into it. The other end is about two inches in diameter, and is closed in with a disc or diaphragm of exceedingly thin metal, capable of being thrust slightly outwards or vibrated upon gentle pressure being applied to it from within the tube. To the centre of this diaphragm —which forms a right angle with the horizon—is fixed a small blunt steel pin, which, of course, partakes of the vibratoi’y motion of the diaphragm. This arrangement is carried on a table and is fitted with a set screw, by means of which it can be adjusted relatively to the second part of the apparatus—the recorder. This is a brass cylinder about four inches in length, and four inches in diameter, cut with a continuous Y groove from one end to the other, so that itm effect represents a large screw. Measuring along the cylinder from one end to the other there are i.O of these grooves to the inch, or about 40 in the whole length. The total length of this continuous groove, or screw thread, is about 42 feet —that is to say, that would be the length of the groove if it were stretched out in a straight lino. The cylinder is mounted on a horizontal axis or shaft carried in bearings at either end, and having its circumferential face presented to the steel point of the receiving apparatus. The shaft is prolonged for four inches or so beyond the ends of the cylinder, and one of the prolongations is cut with a screw thread and works in a screwed bearing. This end terminates in a handle, and as this is turned round the cylinder is not only revolved, but by means of the screwed spindle is caused to travel its whole length in front of the steel point, either backwards or forwards.

We now see that if the pointer bosetjin the groove in the cylinder at its commencement, and tho handle turned, the groove would be travers pd over the point from beginning to

end, or, conversely, the point would always be presented to the groove. A voice speaking in the receiver would produce waves of sound which would cause the point to enter to greater or less depths into this groove, according to the degree of intensity given to the pressure upon the diaphragm set up by the vibrations of the sound produced. This, of course, of itself would mean nothing ; but in order to arrest and preserve these soundpressures, a sheet of tin.foil is interposed, the foil being inelastic and well adapted for receiving impressions. This sheet is placed around the cylinder and its edges lightly fastened together by mouth-glue, forming an endless band, and held on the cylinder at the edges by the indiarubber rings. If a person now speaks into the receiving tube, and the handle of the cylinder be turned, it will be seen that the vibrations of the pointer will be impressed upon that portion of the tin-foil over the hollow groove and retained by it. These impressions will be more or less deeply marked according to the modulations and inflexions of the speaker’s voice. We have now a message verbally'imprinted upon a strip of metal. Sound has, in fact, been converted into visible form, and we have now to translate that message by reconverting it into sound. We are about, in effect, to hear our own voice speaking from a machine the words which have just fallen from our lips. To do this we require the third portion of Mr Edison’s apparatus—-the transmitter. This consists of what may be called a conical metal drum, having its larger end open, the end, which is about 2in, in diameter, being covered with paper, which is stretched taut as is the parchment of a drumhead. Just in front of this paper diaphragm is a light, flat steel spring, hold in a vertical position and terminating in a blunt steel point projecting from it, and corresponding with that on the diaphragm of the receiver. The spring is connected with the paper diaphragm of the transmitter by r means of a silken thread, which is placed just sufficiently in tension to cause the outer face of the diaphragm to assume a slightly convex form. This apparatus is placed on the opposite side of the cylinder to the receiver. Having set the latter apparatus back from the cylinder, and having, by turning the handle in a reverse direction, set the cylinder back to what we may term the zero point, the transmitting apparatus is advanced towards the cylinder by means of a set screw until the steel point rests without absolute pressure in the first indentation made by the point of the receiver. If now the handle be turned at the same speed as it was when the message was being recorded, the steel point will follow the line of impression and will vibrate in periods corresponding to the impressions previously produced on the foil by the point of the receiving apparatus. Vibrations of the requisite number and dept h being thus communicated to the paper diaphragm, there will be produced precisely the same sounds that in the first instance were required to produce the impressions formed on the tinfoil. Thus the words of the speaker will be heard issuing from the conical drum iti his own voice, tinged, however, witli a slight metallic or meohahical tone. If the cylinder be revolved more slowly than when the message was being recorded, the voice assumes a bass tone; if more quickly, the message is given with a childish treble. These variations occur according as the vibrations are more or less frequent.

Such is the apparatus, and it promises to be one of the most remarkable of the receut marvels of science. The machine we have described is the first Mr Edison has made, but he is now constructing one to be set in motion by clockwork, the cylinder being 16 inches long. In the present machine, for recording a long message, as soon as one strip of the tinfoil is filled, it is removed and replaced by others until the communication has been completed. In using the machine for the purpose of correspondence the metal strips are removed from the cylinder and sent to the person with whom the speaker desires to correspond, and who must possess a machine similar to that used by the sender. The person receiving the strips places them in turn on the cylinder of his apparatus, applies the transmitter, and puts the cylinder in motion, when[he hears his friend’s voice speaking to him from the indented metal. And ho can repeat the contents of the missive as often as he pleases until he lias worn the metal through. The sender can make an indefinite number of copies of his communication by taking a plaster of Paris cast of the original strip and rubbing off impressions from it on a clean sheet of foil. It will thus be seen, as we stated at the commencement of this article, that the voices of those who have left us, either for ever or for a season only, can be heard talking with us if wo so desire it. The invention has been so recently and so quickly developed into existence by Mr Edison that he himself can hardly say what its practical value is or will prove to be. Numerous applications suggest themselves, but beyond those to which wc have alluded, it is difficult to say with precision how they would work out in practice. In cases of depositions it might be of the highest importance to have oral evidence mechanically reproduced in a court of justice. Authors, too, may perhaps be saved the trouble of writing their compositions.