The phonograph is an instrument by which sounds can be imprinted on soft metal, such as tinfoil, and reproduced with distinctness and accuracy of tone any number of times. It consists of 3 parts: a receiver, a recorder, and a reproducer.

The receiver consists of a curved tube, one end of which is fitted with a mouthpiece, and the other end closed by an exceedingly thin metallic plate or diaphragm, which vibrates with the least Bound. On the centre of the outer side of this metallic diaphragm is a small blunt steel pin. The recorder is a brass cylinder 4 in. long and 4 in. in diameter, with a continuous V - shaped groove cut into it from end to end, like a large screw; 2 pins 4 in. long are fixed in the ends of the cylinder, one of which is cut with a screw thread, corresponding to .that of the V - groove in the cylinder, and these pins are fitted into appropriate bearings, 8 in. apart. By turning a handle fixed on to one of the pins just referred to, the cylinder is not only rotated, but traverses from one support to the other. In using this instrument, the recorder is covered with a sheet of tinfoil, and is placed in front of the vibrating diaphragm of the receiver, the blunt pin of which just touches the surface of the tinfoil, and is opposite the commencement of the groove of the brass cylinder.

If now a person speaks into the mouth piece of the receiver, and the handle of the recorder be turned, a spiral series of indentations will be made on the tinfoil by the pin of the vibrating diaphragm, these indentations corresponding to the groove in the brass cylinder under the tinfoil. The sounds that have been uttered are now recorded on the tinfoil. The reproducer, which forms the third part, consists of a conical metallic drum, having its larger end open; the smaller, which is about 2 in. in diameter, being covered by a sheet of paper stretched tight like a drum. In front of this paper diaphragm is a light, flat steel spring, held in a vertical position, and from the end of which a blunt steel point projects. The spring is connected with the paper diaphragm by 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. In order to reproduce the sounds received on the tinfoil, the receiver is placed in front of the " reproducer," so that the blunt pin is just over the first indentation; the handle of the receiver is turned in a reverse direction to what it was before, and this causes the spring of the reproducer to vibrate.

The movements of the spring are communicated to the paper, diaphragm by the silken thread, and the words spoken into the receiver are heard issuing from the open end of the reproducer. (Dyer.)

It must not be supposed that all the tinfoil used for phonographic registration is equally good. The foil must be of a definite thickness, and combined with a certain amount of lead. That which is used for wrapping chocolate, and indeed all foil of French manufacture, is too thin and too exclusively made of tin to produce good results. The relative proportion of lead and tin has not yet been defined, and the selection of foil has been made empirically; but as the use of the phonograph becomes more general, this proportion must be ascertained, and it may easily be done by analysing the composition of the foil which gives the best results.

The arrangement of the tracing - point is also of much importance for the successful action of the phonograph. It must be very slender and very short (not exceeding 1 millimetre in length), so as to register distinctly the smallest vibrations of the vibrating disk without deviating from the normal direction of the cylinder, which might be the case, if it were long, on account of the unequal friction exerted on the tinfoil. It must also be made of a metal which has no tendency to tear the metallic sheet. Iron appears to combine most of the conditions demanded. (Hedges.)

Shelford Bidwell gives the following description of how to construct a phonograph. He says the most important part of it is the cylinder. This, in his phonograph, is a hollow brass casting, 4 1/2 in. long and 4 1/2 in. in diameter. It is mounted upon an iron spindle f in. in diameter and 16 in. long, at one end of which is a winch handle. Upon that part of the spindle which lies between the handle and the cylinder, a screw is cut, having 8 threads to the inch. The other end of the spindle is left plain. The cylinder having been turned perfectly true, a screw is cut upon its surface of exactly the same pitch as the screw upon the spindle - i.e. 8 threads to the inch. The depth of the spiral groove thus formed is 1/16 in., and its breadth is 1/16 in. It is better to cut it square, and not V-shaped. Two brass bearings for the spindle are made of the following dimensions - length, 2 1/4 in.; thickness, 1 1/2 in.; height, 1 1/2 in. One of these has an inside screw corresponding to the screw upon the spindle. Each bearing has 2 holes for screwing it to the support.

The cylinder, spindle, and bearings being completed, 10 pieces of wood must be prepared as follows:-

A is 12 in. x 9 1/2 in. X 1 1/8 in.

B is 3 in. x 3 in. x 1 1/8 in.

C is similar to B.

D is 5 1/2 in. x 5 1/2 in. X J in., and has a circular hole, 2f in. in diameter, cut in its centre.

£ is similar to D.

F is 5 1/2 in. x 5 1/2 in. X 1/2 in., and has a hole, 1 in. in diameter, in its centre.

G is 5 1/2 in. X 2 1/2 in. X J in.

H is similar to G.

I is 8 in. X 2 1/2 in. X 1/2 in.

K is similar to I.

There are 2 upright supports for the bearings. The position is indicated by the letters corresponding to them in Figs. 98, 99. The uprights are fixed near the ends of the base - board A by means of 2 1/2 in. screws. D and F are screwed together, and the 2 are then fixed perpendicularly upon G. G is joined to I by a pair of hinges. The 2 ends of I are screwed to the base - board, but the holes in I are J in. larger in diameter than the screws which pass through them. The heads of the screws are effectively enlarged by iron washers f in. in outside diameter. The object in this arrangement is to allow a certain amount of play in the board I for purposes of adjustment. When properly adjusted, the screws may be tightened, and the board firmly fixed in position. £ is attached perpendicularly to H, and made rigid with 2 small triangular pieces, not shown. H is hinged to K, and K is fixed to the base in exactly the same manner as I. Through the middle of I is passed a brass screw - bolt, the square head of which is fixed in I. The screw goes through an elongated hole in G, and is fitted with a round milled brass nut. It is well to place a washer under the nut.