Wheatstone’s Microphone to Radiophonic researches. 89 
then explored with the point of the microphone, and sounds 
were obtained in all parts of the illuminated area and in the 
errespand "a area on the other side of the diaphragm. Out- 
e of this area on both sides of the diaphragm the sounds 
baud weaker and weaker, until at a certain distance from the 
center they could no longer be perceived. 
t the points where one would naturally place the supports 
of a yore 2 microphone (see fig. 1) no sound was observed. 
We were also unable to 
against the support to 
which the diaphragm was 
attached. The negative 
results obtained in Ku- 
tion of vibration occurre 
in: the case of a large me- 
tallie mass. An inter- 
mittent beam of santigie 
was focussed upon a brass 
weight (1 kilogram), and - 
the surface of the weight A, stiff wire ; B, diaphragm ; ©, hearing tube; 
was then scplaee with D, perforated handle. Figure reduced one-half. 
ee microphone shown in fig. 2. A feeble but distinct sound 
s heard upon touching the surface within the illumin- 
ited area and for a short satmilas outside, but not in other 
parts 
n this experiment, as in the case of the thin diaphragm, abso- 
tile: contact between the point of the microphone and the sur- 
face brah was necessary in order to obtain audible effects. 
Now I do not mean to deny that sound waves may be origin- 
ated i in the moe suggested by Mr. Preece, but I think that 
our experiments have demonstrated that the kind of action 
described by Lord Raleigh actually occurs, and that it is suffi- 
cient to account for the audible effects observed. 
