PHILOSOPHICAL SOCIETY OF WASHINGTON. 155 



placed in an electrical circuit when required. The surface is then 

 smoked until a good film of lamp-black is obtained, filling the inter- 

 stices between the teeth of the silver combs. When the lamp-black 

 cell is connected with a telephone and galvanic battery, and ex- 

 posed to the influence of an intermittent beam of sunlight, a loud 

 musical tone is produced by the telephone. This result seems to be 

 due rather to the physical condition than to the nature of the con- 

 ducting material employed, as metals in a spongy condition pro- 

 duce similar effects. For 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 an 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 lamp-black cell for experi- 

 mental purposes is shown in Fig. 9. When an intermittent current 

 is passed through the lamp-black, (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 simultaneously, 

 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. 



Vpon 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 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 appa- 

 ratus for studying the effects, but as our researches are not yet com- 

 plete, I shall confine myself to a simple description of some of the 

 forms of apparatus we have devised. 



