Page:Heroes of the telegraph (IA cu31924031222494).djvu/242

 tinfoil is indicated, and it is chiefly to the adoption of this material that the success of the 'perfected phonograph' is due. Wax is also employed in the 'graphophone' of Mr. Tainter and Professor Bell, which is merely a phonograph under another name. Numerous experiments have been made by Edison to find the bees-wax which is best adapted to receive the record, and he has recently discovered a new material or mixture which is stated to yield better results than white wax.

The wax is moulded into the form of a tube or hollow cylinder, usually 4$1⁄4$ inches long by 2 inches in diameter, and $1⁄8$ inch thick. Such a size is capable of taking a thousand words on its surface along a delicate spiral trace; and by paring off one record after another can be used fifteen times. There are a hundred or more lines of the trace in the width of an inch, and they are hardly visible to the naked eye. Only with a magnifying glass can the undulations caused by the vibrating stylus be distinguished. This tube of wax is filed upon a metal barrel like a sleeve, and the barrel, which forms part of a horizontal spindle, is rotated by means of a silent electro-motor, controlled by a very sensitive governor. A motion of translation is also given to the barrel as it revolves, so that the marking stylus held over it describes a spiral path upon its surface. In front of the wax two small metal tympanums are supported, each carrying a fine needle point or stylus on its under centre. One of these is the recording diaphragm, which prints the sounds in the first place; the other is the reproducing diaphragm, which emits the sounds recorded on the wax. They are used, one at a time, as the machine is required, to take down or to render back a phonographic message.

The recording tympanum, which is about the size