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THE POPULAR SCIENCE MONTHLY. 



instance, when an electrical current is passed through spongy platinum 

 while it is exposed to intermittent sunlight, a distinct musical tone is 

 produced by a telephone in the same circuit. In all such cases the 

 effect is increased by the use of an induction-coil ; and the sensitive 

 cells can be employed for the reproduction of articulate speech, as well 

 as for the production of musical sounds. 



We have also found that loud sounds are produced from lamp- 

 black by passing through it an intermittent electrical current ; and 

 that it can be used as a telephonic receiver for the reproduction of 

 articulate speech by electrical means. 



A convenient mode of arranging a lampblack cell for experimental 



purposes is shown in Fio-. 9. When 



Fig 9, . . * 



an intermittent current is passed 

 through the lampblack (A), or when 

 an intermittent beam of sunlight 

 falls upon it through the glass plate 

 (B), a loud musical tone can be 

 heard by applying the ear to the 

 hearing-tube (C). When the light 

 and the electrical current act simul- 

 taneously, two musical tones are 

 perceived, which produce beats when nearly of the 

 same pitch. By proper arrangements a complete 

 interference of sound can undoubtedly be produced. 

 Upon the Measurement of the Sonorous 

 Effects produced by Different Substances. 

 We have observed that different substances produce 

 sounds of very different intensities under similar cir- 

 cumstances of experiment, and it has appeared to us 

 that very valuable information might be obtained if 

 we could measure the audible effects produced. For this purpose we 

 have constructed several different forms of apparatus for studying 

 the effects, but, as our researches are not yet complete, I shall confine 

 myself to a simple description of some of the forms of apparatus we 

 have devised. 



When a beam of lio-ht is broui^ht to a focus bv means of a lens, 

 the beam diverging from the focal point becomes weaker as the dis- 

 tance increases in a calculable degree. Hence, if we can determine 

 the distances from the focal point at which two different substances 

 emit sounds of equal intensity, we can calculate their relative sonorous 

 powers. 



Preliminary experiments were made by ^Nlr. Tainter, during my 

 absence in Europe, to ascertain the distance from the focal point of a 

 lens at which the sound produced by a substance became inaudible. 

 A few of the results obtained will show the enormous differences ex- 

 isting between different substances in this respect. 



