222 



ANNUAL EEPORT SMITHSONIAN INSTITUTION, 1908. 



to the cutting point. It must not chip nor flake, as otherwise the 

 recordir.g point will cut a groove with ragged sides, and this will 

 increase the scratching sound made by the needle on subsequently 

 reproducing. The best results are obtained by a tablet of such con- 

 sistency that the cutting point detaches an unbroken thread or shav- 

 ing of wax. 



The diameter of the recording blank varies, but the maximum 

 diameter employed is about 12 inches. It will be clear that the size 

 of the record can not be increased beyond certain limits, when it is 

 remembered that the blank is revolved at a uniform speed, and that 

 consequently the outer portion of the blank is running past the 

 recording point at a much higher speed than the inner portion, when 

 this is brought under the recording sound box. Thus, with a 12-inch 



disk, when the cut- 

 ter is one-half inch 

 from the edge, it 

 will in 1 revolution 

 describe a line on 

 the record of a 

 length approxi- 

 mately equal to the 

 circumference of a 

 circle of 11 inches 

 diameter — that is to 

 say, 34.5 inches. By 

 the time the record- 

 ing point has 

 worked in another 

 3 inches toward the 

 center of the tablet 

 the length of its 

 path over the wax w^ill approximately equal the circumference of a cir- 

 cle of 5 inches diameter, or 15.7 inches. The rate of revolution of the. 

 tablet being iniiform, the sound line at the edge of the tablet is accord- 

 ingly being cut at more than twice the speed that it is cut at nearer the 

 center, and the speed at which the recording point can be made to cut 

 the sound groove satisfactorily can only be varied within certain 

 limits. If the diameter of the tablet is increased the outside speed 

 will be too great for proper recording, and if the speed of the turn- 

 table is correspondingly decreased the ripples in the sound line near 

 the center will be too close together and cramped. There will be too 

 many vibrations per inch of sound line to allow of proper recording 

 and reproduction. The obvious solution would be, of course, gradu- 

 ally to increase the speed of the turntable as the recording point 



Fig. 14. — Recording sound box. A, stylus ; a, stylus bear- 

 ings ; B, diapliragm ; C, diapliragm liolder ; D, tension 

 spring. 



