This section is from the "The New Student's Reference Work Volume 5: How And Why Stories" by Elinor Atkinson.
You remember how, in the telephone, the sound waves made by the voice are caught on an iron disc, or drumhead, and sent on to the wire. Now phone means sound and graph means write. In the phonograph the sound waves of the voice are caught by a drumhead and made to shake a needle that moves over a rolling cylinder, and scratches or writes upon it. Thus a record is made of a dictated letter, a speech or a song. When the cylinder is put into the machine and the needle made to move over the same marks the sounds recorded on the roll are repeated. The sounds are magnified in a trumpet, and so made loud enough to be heard by our ears. On a phonograph record-roll you can see the faint, irregular line made by the needle. A given sound always makes the same kind of mark. Of course, then, it must always give back the same sound.