_Description of Phonograph, and mode of using it._--The first and best known model of this instrument, which we represent in fig. 66, simply consists of a registering cylinder R, set in motion with the hand by a winch M, before which a vibrating plate is placed, furnished on its face with a telephone mouthpiece E, and on the reverse side with a tracing point. This tracing point, which is seen at _s_ in the section of the instrument given in fig. 68, is not fixed directly on the plate; it rests on a spring _r_, and a caoutchouc pad _c_ is placed between it and the vibrating disk. This pad is formed of the end of a tube which is designed to send the vibrations of the plate to the point _s_ without stifling them. Another pad _a_, placed between the plate L L and the rigid support of the point, moderates in some degree these vibrations, which, without this precaution, would generally be too powerful. [Illustration: FIG. 66.] The cylinder, of which the axis A A (fig. 66) is cut at one end like a screw, to enable it to make a lateral progressive movement simultaneously with the rotatory movement effected on itself, has on its surface a narrow screw-thread coinciding with that of the axis, and when the tracing point is inserted, it is able to pass along it for a distance corresponding to the time occupied in turning the cylinder. A sheet of tinfoil or of very thin copper is carefully applied to the surface of the cylinder, and it should be slightly pressed down upon it, so as to show a faint tracing of the groove, and to allow the point of the vibrating disk to be placed in a proper position. The point rests on the foil under a pressure which must be regulated, and for this purpose, as well as to detach the cylinder when it is desired to place or take away the tinfoil, there is the articulated system S N which sustains the support S of the vibrating disk. This system consists of a jointed lever in which there is a nut screw for the screw R. The handle N at the end of the lever allows the tracing system to be turned aside when the screw R is loosened. In order to regulate the pressure of the tracing point on the sheet of tinfoil, it is enough to turn the screw R loosely in its socket, and to tighten it as soon as the right degree of pressure is obtained. This is the simple system by which speech can engrave itself on a plate in durable characters, and it works in the following manner. [Illustration: FIG. 67.]