TRACING GRAMOPHONE AND PHONOGRAPH RECORDS. 25 



To allow for variations in the thickness of the gramophone disc the 

 axle of the tracing lever is borne by a short "vertical link." This is a 

 metal bar held on an axle in the same way as the tracing lever. The 

 axle is horizontal; any change in the thickness of the disc raises or lowers 

 the tracing point around this axle. The magnification of this movement 

 at the record is comparatively small, and as the discs are now made with 

 great precision, the main purpose of the vertical link is to maintain con- 

 stant friction at the tracing point. The axle for the vertical link is held 

 on an adjustable "lever holder," which can be fastened by a " fixing screw" 

 in the supporting arm. 



The tracing point should he in a radius of the gramophone disc per- 

 pendicular to the tracing lever; the lever is thus a tangent to the groove 

 being traced. This can be fixed once for all by a non-adjustable point 

 and a hole in the supporting arm for the lever holder, as in figure 21. It 

 is, however, often desiral:)le to vary the magnification of the tracing by 

 changing the distance of the point from the fulcrum; the position of the 

 lever holder must then be changed also. A sliding brass block which 

 can be securely fastened to the supporting arm is then used to carry the 

 lever holder; this is the arrangement indicated in figure 22. 



The gramophone disc must be level, otherwise the tracing point may 

 run up the side of the groove. Considerable pressure is needed in order 

 to make the tracing point remain in the bottom of the groove. A small 

 weight is sometimes of advantage when placed just over it. A larger 

 weight causes the supporting parts to bend and thus diminishes the ampli- 

 tude of the movements, or, if very great, it causes the point to skip over 

 the apexes of sharp waves. 



Both single and compound levers have been used. The single lever 

 is shown in figure 18. The lever itself must be very light and very rigid. 

 In most cases the larger portion near the fulcrum was of Japanese reeds 

 4mm. in diameter, while the other half was of some 2mm. German straws 

 ending in a very light 1mm. French straw.* The tracing point was 

 attached to the end. It was found possible by practice to construct 

 these levers so lightly and rigidly and to adjust the recording point so 

 delicately that a greater magnification could be obtained with the single 

 lever than with a compound one. 



The arrangement with the compound lever is shown in figure 22. 

 The first lever is short; its end repeats the movement of the tracing point 

 with small magnification. Its movement is communicated to the second 



♦The French straws can be obtained of Ch. Verdin, Paris, Rue Linn^ 7, and the German ones of 

 Win. Petzold or E. Zimmerniann, Leipzig. The Japanese reeds can be obtained in America by buying the 

 very smallest Japanese brushes. 



