PRODUCTION OF SOUND BY RADIANT ENERGY. 191 



periment was conducted. The diaphragm of the transmitter (A) was 

 only five centimetres in diameter, the diameter of the receiver (B) was 



CO 



6 



also five centimetres, and the dis- 

 tance between the two was forty 

 metres, or eight hundred times the 

 diameter of the transmitting dia- 

 phragm. We were unable to ex- 

 periment at greater distances with- 

 out a heliostat, on account of the 

 difficulty of keeping the light 

 steadily directed on the receiver. 

 Words and sentences spoken into 

 the transmitter in a low tone of 

 voice were audibly reproduced by 

 the lampblack receiver. 



In Fig. 3 is shown a mode of in- 

 terrupting a beam of sunlight for 

 producing distant effects without 

 the use of lenses. Two similarly- 

 perforated disks are employed, one 

 of which is set in rapid rotation, 

 while the other remains stationary. 

 This form of interrupter is also 

 admirably adapted for work with 

 artificial light. The receiver illus- 

 trated in the drawing: consists of a 

 parabolic reflector, in the focus of 

 which is placed a glass vessel (A) 

 containing lampblack or other sen- 

 sitive substance, and connected with 



