Screw - bolts of this description are used for fixing the expanding bodies of ordinary photographic cameras, and may be had of any optician. H and £ are fitted with a similar bolt. Two rather stiff pieces of steel spring are attached to the ends of I, and extend for a little distance underneath G. These springs tend to separate G and I, or rather to cause G to turn backwards, like the lid of a box when opened. The nut, of course, works against the springs. When the nut is screwed up tight, G and I approach, and may be made almost to touch each other. When the nut is loosened, the spring causes G to rise. Very delicate adjustment is thus rendered possible. H and K are fitted with similar springs for a similar purpose. The diaphragm which receives the voice is fixed over the circular hole in D, as shown in Fig. 98. It consists of a circular plate of very thin iron 4 in. in diameter. Ferrotype plate will answer the purpose very well, but thin charcoal iron is better. It is, however, possible to have the iron too thin. About two - thirds the thickness of an ordinary ferrotype plate is the best. The point is made from a knitting - needle about 1/20 in. in diameter, which must be very hard - one which can be bent is of no use.

The original point had better be broken off, and a new one ground upon an oilstone. For this purpose, the needle is held at an angle of about 30° with the stone, and is constantly turned round. The point, having been made tolerably sharp, is polished and cut off with a file. The part so cut off is 3/16 in. long. This has now to be attached, perpendicularly to the centre of the diaphragm, and the method of doing so is as follows: - The diaphragm is laid upon a sheet of glass, and a little spot in its centre - about 1/8 in. in diameter - is scraped clean with a knife. This must be done carefully and gently, or a bulge will be produced. The fragment of knitting - needle is then taken up with pliers, and its blunt end, having been moistened with soldering fluid, is held above the flame of a spirit - lamp, and touched with a piece of tinfoil. With a little manipulation, a small bead or globule of tin may thus be made to adhere to the end. The scraped spot on the diaphragm is now moistened with soldering fluid, and the diaphragm is supported at some distance above a small spirit flame. The ring of a retort stand forms a convenient support. The butt end of the point, with tin globule attached, is then applied to the scraped spot with pliers.

In a few seconds the globule melts, when the lamp is instantly removed, and the point manipulated with the pliers, so as to be perfectly upright when the tin hardens, which will take place in a few seconds more. The point will then be found to be firmly attached. The diaphragm and point must, after this operation, be thoroughly washed with soap and water, and slightly oiled - otherwise they will rust. The only precaution to be observed is to apply no more heat than is just necessary for melting the tin. Too much heat will warp the disc, and, if it is a ferrotype, blister the japan. The soldering fluid consists of equal parts of hydrochloric acid and water, in which is dissolved as much zinc as possible. A pile of books will be found useful for steadying the arm while manipulating the point. The diaphragm is fixed in its place by means of a brass flange (like a camera flange), 4 in. in outside diameter, with a 2 3/4 in. opening. Four screws are used. The second diaphragm is made of parchment paper, like that used for covering jampots. It is 4 in. in diameter, and is gummed over the hole in £ on the side remote from the cylinder (see Fig. 98). When the gum is dry, the diaphragm is moistened, and again allowed to dry, when it will be found to be as tight as a drum.

The second point is exactly like the first, though it may with advantage be a trifle sharper. It is not attached directly to the paper diaphragm, but to a steel spring, which may be seen in Figs. 98 and 99. This is a piece of mainspring - 5/16 in. wide and 2j in. long. It is fixed above the hole in £ by means of 2 strips of brass, as shown in Fig. 99, and is just so much bent that the end of it, when free, is | in. distant from the plane of £. The power of this spring may, however, be varied within considerable limits without appreciable difference in its performance. The point is fixed to the spring in the same manner as to the iron disc, but the same care as to over - heating is not requisite, and the operation is consequently easier. Before the spring is screwed in its place, a loop of sewing silk is attached to the centre of the paper diaphragm by means of a piece of court plaister 1/4 in. square (see Fig. 99, where A is the piece of plaister, B the loop). The length of the loop must be such that when it is drawn Over the spring just above the point, the end of the spring may be nearly in the plane of £. The spring is thus caused to draw the paper drum even tighter than before, and its inner surface is rendered slightly convex.

Another flauge carrying a short rim or spout is now screwed round the paper drum. A paper resonator is made to slip over the short rim or spout. It is a cone made of 2 or 3 thicknesses of stout drawing - paper. Its length is 18 in.; diameter at small end, 2J in., and at large end, 7 in. The resonator greatly reinforces the sound when the phonograph is speaking. A wooden mouthpiece like those used for speaking - tubes is inserted into the hole F. The instrument is now complete, but it will require careful adjustment before it can be used. In the first place, the screws which attach I to the base must be loosened, the milled nut on G screwed up tight, and the piece I shifted about until the point on the iron disc is exactly in the middle of one of the grooves on the cylinder, and barely touches the bottom of it. Then the screws must be tightened, and this part of the apparatus is finally adjusted. The same process is repeated on the other side, but in this case the adjustment is not quite final, as will hereafter be seen. The next thing is to procure suitable tinfoil. This should be rather stout - about 15 sq. ft. to the lb. - and should be cut into pieces 14 1/2 in. by 4 1/2 in.