Since it is always difficult to fit the tinfoil to the cylinder, Mr. Edison has tried, with good success, to obtain the tracing on a plane surface of tinfoil, by means of the arrangement represented fig. 69. In this new model, the plate on which the tin or copper sheet is to be applied has a spiral grooving, of which one end corresponds to the centre of the plate, and the other to its outer edges. The plate is set in motion by a powerful system of clockwork, of which the velocity is regulated with reference to the length of the turns of the spiral. The vibrating disk is arranged as in the former instrument, and is placed above this plate; the tracing point may, by means of a movement of progression imparted to the system, follow the spiral groove from the centre of the plate to its circumference. 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 definite 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, and M. Puskas was obliged to import some from America to continue his experiments. 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. [Illustration: FIG. 70.] 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 a millimètre 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. The phonograph is still in its infancy, and it is probable that it may soon be enabled to register speech without the necessity of speaking into a mouthpiece. According to the newspapers, Mr. Edison has already discovered a way of collecting, without the aid of an acoustic tube, the sounds uttered at a distance of three or four feet from the instrument, and of printing them on a metallic sheet. From this there is only a step to the power of inscribing a speech uttered in a large hall at any distance from the phonograph; and if this step is taken, phonography may be substituted with advantage for shorthand. We add in a note the instructions given by M. Roosevelt to the purchasers of phonographs, so as to enable them to work the instrument.[20]