466 A. G. Bell—Production of Sound by Radiant Energy. 
About a teaspoonful of lamp-black was placed in a. test-tube 
and exposed to an intermittent beam of sunlight. The sound 
produced was much louder than any heard before. 
Upon smoking a piece of plate-glass, and holding it in the 
intermittent beam with the lamp-black surface towards the sun, 
the sound produced was loud enough to be heard, with atten- 
tion, in any part. of the room. ith the lamp-black surface 
Mr. Tainter repeated these experiments for me immediately 
upon my return to Washington, so that I might verify his 
results. : 
Upon smoking the interior of the conical cavity shown in 
figure 1, and then exposing it to the intermittent beam, with 
the glass lid in position as shown, the effect was perfectl 
startling. The sound was so loud as to be actually painful to 
an ear placed closely against the end of the hearing-tube. ‘The 
smoked wire gauze in the receiver, as illustrated in the 
drawing, figure 1. 
When the beam was thrown into a resonator, the interior of 
which had been smoked over a lamp, most curious alternations 
of sound and silence were observed. The interrupting disk 
were constantly occurring, which became more and more 
marked as the true pitch of the resonator was neared. When 
at last the frequency of interraption corresponded to the 
frequency of the fundamental of the resonator, the sound 
was so loud that it might have been heard by an audience of 
hundreds of people. 
The effects produced by lamp-black seemed to me to be very 
extraordinary, especially as I had a distinct recollection of ex- 
periments made in the summer of 1880 with smoked diaphragms, 
in which no such reinforcement was noticed. 
Upon examining the records of our past photophonic experi- 
ments we found in vol. vii, p. 57, the following note : 
“Experiment V.—Mica diaphragm covered with lamp-black on 
side exposed to light. 
“Result: distinct sound about same as without lamp-black.— 
Upon repeating this old experiment we arrived at the same 
result as that noted. Little if any augmentation of sound re- 
