TRACING GRAMOPHONE AND PHONOGRAPH RECORDS. 



27 



Pulley for- 

 'Side Moi'emen t 



the drum, the knob of the recording point, and the apex of the tracing 

 point should be in the same plane. 



If the glass point bears so Hghtly on the paper that the line traced 

 by it is not white enough, it may be weighted by a piece of wax. When 

 the tracing is to be reproduced by photography, the Hne must be whiter 

 than is otherwise necessary. 



The gramophone disc must be accurately centered on the rotator. 

 The tracing point is placed in the groove and the position of the recording 

 point is noticed. The disc is now turned; the point moves to one side, 

 then to the other and back ; the positions of extreme deviation are noted 



and the disc is turned 

 to one of them. It is 

 then carefully shoved 

 until the point takes the 

 middle position. This is 

 repeated until the point 

 rests at the same place 

 during one entire revo- 

 lution. 



The arrangement of 

 the pulleys at the near 

 drum is shown in figure 

 27 ; it is presumably clear 

 without any description. 

 The steps may be on 

 either side; in figure 22 

 they are to the rear, in 

 figure 27 to the front; 

 an improvement has been recently introduced by having more steps 

 to the pulleys. I have lately adopted the plan of replacing the weight 

 belt tighteners by single pulleys carried by heavy supports. The pulley 

 is adjusted till the belt gives a certain tone when snapped; the adjust- 

 ment of the belt for side movement is made once for all and is tested occa- 

 sionally; that for rotation must be made anew at intervals, as the side 

 movement of the disc steadily stretches the belt. The standard of 

 tension can be kept by comparison with a tuning-fork. 



The arrangement shown in figure 18 for the far drum and counter- 

 shafts is now modified by using much smaller worm gears. The reduction 

 of speed can be made very great; with two worm gears of 164 teeth the 

 speed of the drum axle is jii^ = mSo of ^^at of the first countershaft. By 



Fig. 27. — Pulleys and belt tightener. 



