474 A. G. Bell—Production of Sound by Radiant Energy. 
strip (D) was now interrupted as before by the rapid rotation 
of a perforated disk, which was allowed to come gradually to 
rest. 
No sound was heard excepting at a certain speed of rotation, 
when a feeble musical tone became audible. 
This result is confirmatory of the first. 
Fig. 6. 
The audibility of the effect at a particular rate of interrup- 
tion suggests the explanation that the strip D had a normal 
rate of vibration of its own. 
When the frequency of the interruption of the light corre- 
sponded to this, the strip was probably thrown into vibration 
after the manner of a tuning-fork, in which case a to-and fro 
vibration would be propagated down its stem or central sup- 
port to the strip (A). | 
This indirectly proves the value of the experiment. 
The list of solid substances that have been submitted to ex- 
periment in my laboratory is too long to be quoted here, and I 
shall merely say that we have not yet fuund one solid bod 
that has failed to become sonorous under proper conditions of 
experiment.* 
Experiments with Liquids. 
The sounds produced by liquids are much more difficult to 
observe than those produced by solids. The high absorptive 
power possessed by most liquids would lead one to expect in- 
tense vibrations from the action of intermittent light, but the 
