A. G. Bell—Production of Sound by Radiant Knergy. 478 
test the point at issue, for Lord Rayleigh has shown (Proce. of 
Roy. Soe., 1877) that an audible sound can be produced by a 
vibration whose amplitude is less than a ten millionth of a centi- 
meter, and certainly such a vibration as that would not have 
sufficed to operate a ‘ make-and-break contact” like that used 
by Mr. Preece. The negative results obtained by him cannot, 
therefore, be considered conclusive. 
The following experiments ‘(devised by Mr. Tainter) have 
given results decidedly more favorable to the theory of Lord 
Rayleigh than to that of Mr. Preece: 
1. A strip (A) similar to that used in Mr. Preece’s experi- 
ment was attached firmly to the center of an iron diaphragm (B,) 
as shown in figure 5, and was then pulled taut at right angles 
Fig. 5. 
to the plane of the diaphragm. 
was focussed upon the strip (A) a clear musical tone could be 
heard by applying the ear to the hearing-tube (C). 
This seemed to indicate a rapid expansion and contraction of the 
substance under trial. 
ut a vibration of the diaphragm (B) would also have re- 
sulted if the thin strip (A) had pare a to-and-fro motion, 
due either to the direct impact of the beam or to the sudden 
expansion of the air in contact with the strip. 
2. To test whether this had been the case an additional strip 
(D) was attached by its central point only to the strip under 
trial, and was then submitted to the action of the beam, as 
shown in fig. 6. : 
It was presumed that if the vibration of the diaphragm (B) 
had been due to a pushing force acting on the strip (A), that 
the addition of the strip (D) would not interfere with the effect. 
But if, on the other hand, it had been due to the longitudinal 
expansion and contraction of the strip (A), the sound would 
cease, or at least be reduced. The beam of light falling upon 
Am. Jour, oe oor Von. XXI, No. 126.—June, 1881. 
