Phonograph

Phonograph is an instrument for recording and reproducing sounds, originally devised by Edison. Sounds, being vibrations of the air, will, if produced near an elastic diaphragm, cause it to vibrate similarly. If the diaphragm be provided with a sharp but smooth point projecting from its centre, and if this point just touch a sheet of tinfoil supported in a suitable way and moved at right angles to it, it series of indentations will be produced. When the diaphragm is moved towards the tinfoil it will make a small hollow, but will leave a little hill when it moves in the other direction. In tbis way the sheet of foil forms a record of the sounds. If the foil is again moved past the point, the latter will be pushed back and forth by the indentations, and as the diaphragm moves with the point it will be thrown into vibration and the original sounds will be more or less accurately reproduced. In the original instrument the foil was wrapped round a cylinder having on its surface a spiral groove and turning on an axle on which was cut a screw-thread of the same pitch as the spiral; this axle turned in a. nut, so that the cylinder moved longitudinally while it was being turned. By this means the point on the diaphragm was always kept opposite the groove. If words were shouted into a mouthpiece attached to the diaphragm while the cylinder was rotated by clockwork, and if the cylinder were afterwards put back to its original position and again rotated, sounds were emitted which bore some resemblance to their original, so that if one had heard them spoken into the instrument one could generally recognise them. A much-improved instrument has more recently been made by Tainter and Edison, in which a cylinder of wax replaces the tinfoil, a groove of varying depth being cut on it by a sharp point shaped after the manner of a turning-tool. When the machine is required to talk, another diaphragm, provided with tubes for insertion in the ears, is put in position. The cylinder is rotated by an electric motor, and the details have been worked out with much care. By these improvements the articulation has been made very much better, but the volume of sound has been reduced. The original pattern produced plenty of sound, such as it was - it could, indeed, be heard by the whole of a small audience - but the new model requires tubes from the diaphragm to the ears. It is suggested by the inventors that the phonograph can be used as a means of correspondence, the wax cylinder being transmitted through the post; but it seems much more probable that it will continue to be interesting only as a scientific toy.