MECHANISM OF THE TELEPHONE.

Globe, Volume IX, Issue 1220, 31 January 1878, Page 3

MECHANISM OF THE TELEPHONE.

The telephone invented by Professor Bell has been introduced in Adelaide, ns well as in Melbourne. To Mr A. W. Dobbie, of Adelaide, is due the credit of being its first manufacturer. The instrument made by Mr Dobbie is the modification of the original telephone of Professor Grahame Bell, which the latter lias lately produced, and. which overcomes many of the difficulties connected with the original instrument. In its first condition, the apparatus consisted of two large parchment membranes connected together by means of wire and requiring the usual apparatus of batteries to supply the eleetrie current. In its present form the instrument is much less cumbersome and more easily constructed and managed, the batteries being altogether dispensed with. At each end of the wire is a wooden tube with a bell-mouth end, somewhat similar to that of a sthenoecope, but of much more solid construction. The length of'these tubes is only eight inches, arid their diameter does not exceed an inch, the mouth portion being of course somewhat extended. Along the tuba a rod-shaped permanent magnet is carried, at the top of which next the mouthpiece is a disc of soft iron, affected by but not touching the pole of the magnet, and covered by a parchment membrane fitting tightly into the end of the tub\ Immediately below this a coil of fine insulated copper wire is wound round the magnet, the ends of which are attached to two stouter wires, one on each side of the magnet, which pass through the tube, and are connected by means of binding screws to the wires along which the sound is conveyed. The theory of the instrument is the same as that of the one first described, the sound of the voice being conveyed along the wire from one telephone to the other by means of a current of electricity. In the instrument wo are describing, however, the current is induced by means of the magnet. In a state of action —that is When the voice of a speaker impinges upon the parchment-covered iron diaphragm —the latter, ordinarily attracted towards the pole of the magnet, is disturbed, and a change, either strengthening or weakening the normal magnetic field, takes place. This necessarily induces a current ol electricity in tho coil wound round the magnet, whence it flows along the wires. Thus, first of all the vibrations of air caused by tho voice throw the diaphragm into vibration. This produces a disturbance in the normal magnetic connection of the apparatus, and the current of electricity thus induced conveys the sound producing the vibration along the wire. When the current reaches the telephone at the end opposite to that from which it started, a similar disturbance of the diaphragm is caused, and the sound is repeated. Professor Bell ha? succeeded with his instrument in conveying the sound of the human voice with perfect distinctness along a distance of fifty miles. In the first experiment with the instrument we (" Adel tide Observer") witnessed, we had the pleasure of conversing with Mr Dobbie along a wire about a quarter of a mils in length. The voice was perfectly audible, but had a peculiar muffled sound, as if conveyed through an ordinary speaking tube. In speaking into Mr Dobbic's telephone the voice has to be slightly raised above the ordinary conversational key, but in Professor Bell's a whisper can be audibly conveyed, and to this point of perfection Mr Dobbie hopes by some very slight modifications of his tubas to arrive. In the second experiment Mr Debbie increased the length of wire to half a mile, when the voice was conveyed with ecpial distinctness. In fact, as the original inventor proved, up to a certain point the length of the wire makes very little appreciable difference in the distinctness of the vocal sounds.