The gramophone is also another speaking machine. This is the invention of Mr. E. Berliner and covered by him in patent No. 372,786, Nov. 8, 1887. An illustration of the gramophone recorder is given in Fig. 193. Instead of a wax cylinder this machine employs a flat disc on which the record is formed as a volute spiral groove, gradually drawing toward the center. It is produced as follows: A zinc disc is covered by a thin film of acid resisting material, such as wax or grease, and is placed in a horizontal pan, mounted to revolve as a turn table about a vertical axis. A stylus and diaphragm, with speaking tube attached, are arranged above the disc, and when spoken into the vibrations of the diaphragm cause, through the stylus, a record to be traced through the wax, down to the zinc. As the waxed disc and pan are revolved, the stylus and diaphragm are gradually moved by gears toward the center of the disc. While the record is being traced the waxed disc is kept flooded with alcohol from a glass jar, seen in the cut, to soften the film and prevent the clogging of the stylus. The disc, when completed, is then rinsed off and etched with acid, chromic acid being used, to prevent liberation of hydrogen bubbles. The etched disc is then electrotyped to form a matrix, and from this electrotype hard rubber duplicates of the original record are molded, which are capable of giving 1,000 reproductions. These rubber discs are placed on the reproducing instrument, which is arranged to cause the stylus to freely trail along in the spiral groove, and when the disc is rotated under the said stylus its record is converted into articulate speech. Such flat disc records give quite loud reproductions, are not easily destroyed, and may be compactly stored and transported. In the gramophone the diaphragm stands at right angles to the record disc and the stylus does not vibrate endwise to make a path of varying depth, as in the phonograph and graphophone, but the stylus vibrates laterally and traces a little zigzag line. The cost of a talking machine is from $5 to $150. The wax cylinders cost from 25 cents to $3.00, and the cylinders will hold a record of from 800 to 1,200 words, equivalent to about three or four pages of print in an octavo volume. An important part of such machines is the motor, which must maintain a uniform rate of speed, and much ingenuity has been displayed on this part of the machine. Probably the largest use of the phonograph or graphophone is for home amusement and exhibition purpose. The coin operated, or “nickel-in-the-slot” machine, finds a popular demand, while its utilitarian use as an amanuensis, or stenographer, is as yet a subordinate one.