522 Trof. A. G. Boll on the Production of 



similar effects. For instance, when an electrical current is 

 passed through spongy platinum while it is exposed to inter- 

 mittent sunlight, a distinct musical sound 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 

 lampblack by passing through it an intermittent electrical 

 current, and that it can be used as a telephonic receiver for 

 the reproduction of articular speech by electrical means. 



A convenient mode of arranging a lampblack cell for ex- 

 perimental purposes is shown in fig. 9. When an intermittent 

 current is passed through the lampblack (A), or when an in- 

 termittent 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 cur- 

 rent act simultaneously, two musical tones are perceived, which 

 produce beats when nearly of the same pitch. By proper ar- 

 rangements 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 circumstances of ex- 

 periment ; and it has appeared to us that very valuable infor- 

 mation 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 appa- 

 ratus we have devised. 



When a beam of light is brought to a focus by means of a 

 lens, the beam diverging from the focal point becomes weaker 

 as the distance 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 Mr. 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 existing between different substances 

 in this respect. 



