In present-day sound recording the operation is briefly as follows: A recording machine is employed on which is mounted a rotating turntable carrying a wax-like disc blank. Suspended above, but in contact with the surface of the blank, is a recording needle or stylus, attached to a diaphragm which, in turn, is connected to an amplifying horn. The horn extends beyond the machine and the singer, band or orchestra is stationed in front of the mouth of this horn. As the singer interprets the song the vibrations set up by the singer’s voice are communicated to the diaphragm by the passage of the sound through the horn. These vibrations, striking upon the diaphragm, set in motion the recording needle or stylus, causing it to move rapidly, and its motion is traced upon the surface of the rotating disc in a line which is known as the sound line. Looked at with the naked eye this line has the appearance of a spiral traced upon the surface of the wax-like blank, but examined under a magnifying glass it shows myriad little indentations or grooves in the wall of the sound line. These indentations correspond to the vibrations imparted to the needle through the diaphragm, and are the recorded sounds made by the singer or band. When the song or selection is finished the surface of the wax-like blank has been covered over with this spiral sound line. The blank has become the “master record,” and the first stage of producing a talking-machine record has been passed. The next step is to secure from this master record a metallic counterpart or shell. This is done by the electro-plating process. When the shell is secured the next step is to provide a matrix which serves as a die or stamp from which to press copies or duplicates of the master record. These copies or duplicates are the talking-machine records which the public ultimately purchases. The matrix or die is placed in a power press and the records pressed from the material used in making the sound records. This material is prepared in a plastic form so that it can be forced under pressure into every line and indentation on the face of the matrix. [Illustration: INSTRUMENTAL MUSIC IS RECORDED AS FAITHFULLY AS VOCAL Barrere, the great flute player and orchestra leader, is shown making a popular record.] The discovery of the art of recording and reproducing sound; the development of that art into a giant industry, and the present-day universal sovereignty of the talking machine are tributes to American inventive genius and American industrial enterprise. The contributions to the art and the improvements in the manufacture of talking machines and talking-machine records from sources outside of the United States have been very unimportant. The industry employs many thousands of people in the manufacture of these instruments and records which afford entertainment, instruction and amusement to the entire world. * * * * * What are Petrified Forests?