120 



SCIENCE OF HOME AND COMMUNITY 



that the speed should be uniform, and this is controlled by 

 means of a governor consisting of balls attached to wires 

 and all rotating with the machine. The faster this rotates, 

 the more these balls are thrown out by centrifugal force; 

 and this brings a disk on the axle into contact with a friction 

 pad, so that the speed is lessened. The speed may be reg- 

 ulated by means of a screw which controls the position of 

 these pads. 



To JRe 'sounding 

 Chamber 



Wex/b/e Core/ 

 Diam on d fb/n t 



FIG. 38. Section of a phonograph. 



The tones are strengthened by means of horns. Some- 

 times these are visible and attached on the outside ; in the 

 box form the horn is hidden by the sides of the box. 



The making of records is now a large industry. Two 

 kinds of records are in use, the cylinder and the disk. The 

 original records for the cylinder are made in wax, from 

 which a sharp point cuts out a thin shaving, leaving 

 the record engraved on the wax. The groove thus formed 

 is very shallow, varying from .01 inch in depth to .001 or 

 even less. In order that many copies of records may be 

 made from this original, it is electroplated with gold and 

 copper and from this mold many copies are made in 

 wax. 



