3 
a 
: 
. 
; 
A. G. Bell—Production of Sound by Radiant Energy. 487 
the one hand and up as high as the middle of the violet on the 
oy) 
Although the experiments so far made can only be consid- 
ered as preliminary to others of a more refined nature, I think 
we are warranted in concluding that the nature of the rays that 
produce sonorous effects in different substances depends upon the 
ees of the substances that are exposed to the beam, and that the 
ounds are in every case due to those rays of the spectrum that are 
Decrhsa by the body. 
The Spectrophone. 
r experiments upon the range of audibility of different 
Pbatanoes | in the spectrum have led us to the construction of 
anew instrument for use in spectrum analysis, which was de- 
scribed and exhibited to the Philosophical Society of Washing- 
ton last Saturday.* The eye-piece of a spectroscope is re- 
moved, and sensitive substances are placed in the focal point 
of the imstrument behind an opaque diaphragm containing a 
slit. These substances are put in communication with ‘the 
ear by means of a hearing-tube, and thus the instrument is 
ee into a veritable ‘“spectrophone,”’ like that shown in 
g. 13. 
Suppose we smoke the interior of our ages 3 ay receiver, 
and fill the cavity with peroxide of nitrogen e 
then a combination that gives us good sounds in ail parts of 
the spectrum (visible and invisible), except “ate ultra-violet.- 
Now, pass a rapidly-interrupted beam of light through some 
substance whose absorption spectrum is to be Sr causa, and 
bands of sound and silence are observed upon exploring the 
spectrum, the silent positions corresponding to the absorption 
ands. Of course, the ear cannot for one moment compete 
oe the eye in the examination of the visible A oe of the spec- 
um; but in the invisible part beyond the red, where the eye 
is Aend Hire the ear is invaluable. In working in this region of 
t 
(1.) The interrupted beam was filtered through a saturated 
solution of alum. 
Result: The range of audibility in the ultra-red was slightly 
reduced by the absorption of a narrow band of the rays o 
lowest refrangibility. The sounds in the visible part of the 
spectrum seemed to be unaffected. . 
* Proc, of Phil. Soc. of Washington, April 16, 1881. 
