CHAPTER II, 

 TRACING GRAMOPHONE AND PHONOGRAPH RECORDS. 



A phonograph record may be studied with a microscope, but finer 

 analysis requires that the groove be traced off on paper in great enlarge- 

 ment. For a gramophone record the microscope is useless because the 

 waves are so drawn out in length that the details are lost for the eye ; 

 tracing is always necessary. 



The curves used for my investigations were traced by four pieces 

 of apparatus which have undergone gradual improvement. It will be 

 sufficient to describe only the latest forms. The gramophone tracing ap- 

 paratus is first described because it was the first one made and also because 

 it gave experience for the more difficult phonograph apparatus. 



A top view of the gramophone apparatus is shown in figure 18. An 

 electric motor turns a pulley connected to a series of countershafts by 

 which the speed is reduced before being transmitted to a brass cyhnder 

 termed the " far drum." A band of paper of any desired length transmits 

 the movement to the "near drum." The band of paper is coated with 

 smoke. The axle of the near drum carries two pulleys which drive the 

 " rotator." One pulley has a belt to slowly rotate a horizontal metal plate 

 upon which a gramophone disc is fastened. A steel point fastened near 

 the fulcrum in a very long lever rests in the groove of the gramophone 

 disc. As the disc turns, the vibrations of the sound groove move the 

 steel point back and forth sidewise and the recording point of the lever 

 traces this movement as a white line in the smoke on the band of paper 

 around the two drums. As the sound groove is a spiral running toward 

 the center of the disc, the disc must be moved sidewise in order to have 

 the groove pass continuously under the steel point. This is accomphshed 

 by a " screw for side movement"— run by belt from the second pulley on 

 the axle of the near drum — which shoves the disc sidewise. 



A side view of the rotator (figure 19) shows the metal disc turned by 

 its belt. The disc itself runs on an axle which is fixed to a carriage. 

 This carriage has two projections bored to receive the circular rod indi- 

 cated as " rail" in the figure; the ends of these two projections are shown; 

 one of them carries the " contact support." The other side of the carriage 

 has a single projection which rests on a planed rail (not shown). The 

 carriage is pushed along by the "screw" for side movement. It is held 

 against the end of the screw by the " tension weight." This screw is 



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