490 A. @. Beill— Production of Sound by Radiant Energy. 
(2.) A thin sheet of hard Aibber was interposed in the path 
of the beam 
eo Well-marked sounds in every part of the ultra-red. 
sounds in the visible part of the spectrum, excepting the 
Stich half of the red. 
‘These experiments reveal the cause of the curious fact al- 
luded to in my paper read before the American Association 
last August—that sounds were heard from selenium when the 
beam was filtered through both hard rubber and alum at the 
same time. (See table of results in fig. 14). 
(3.) A solution of ammonia- sulphate of copper was tried. 
Result: When placed in the path of the beam the spectrum 
disappeared, with the exception of the blue and violet end. 
o the eye the spectrum was thus reduced to a single broad 
band of blue-violet light. To the ear, however, the s spectrum 
revealed itself as two bands of sound with a broad space of 
silence between. The ie bet rays sraninkiistad constituted a 
narrow band just outside the 
I think I have said enou % to convince you of the value g 
this new method of examination, but I do not wish you t 
understand that we look upon our results as by any means 
complete. It is often more interesting to observe the first tot- 
terings of a child than to watch the firm tread of a full-grown 
man, and I feel that our first footsteps in this new field of 
science may have more of interest to you than the fuller results 
of mature research. This must be my excuse for having dwelt 
so long upon the details of incomplete experiments. 
I recognize the fact that the spectrophone must ever remain 
a mere adjunct to the spectroscope, but I anticipate that it has 
a wide and independent field of ietilness 3 in the investigation 
of absorption spectra in the ultra-red. 
