486 A. G. Bell—Production of Sound by Radiant Energy. 
(2.) The lamp-blacked wire gauze was then removed and the 
interior of the receiver (G) was filled with red worsted. Upon 
exploring the spectrum as before, entirely different results were 
obtained. The maximum effect was produced in the green at 
that part where the red worsted appeared to be black. 
either side of this point the sound gradually died away, becom- 
ing inaudible on the one side in the middle of the indigo, and 
on the other at a short distance outside the edge of the red. 
(3.) Upon substituting green silk for red worsted the limits 
of audition appeared to be the middle of the blue and a point 
a short distance out in the ultra-red. Maximum in the red. 
(4.) Some hard rubber shavings were now placed in the re- 
ceiver (G). The limits of inaudibility appeared to be on the 
one hand the junction of the green and blue, and on the other 
the outside edge of the red. Maximum in the yellow. Mr. 
Tainter thought he could hear a little way into the ultra-red, 
and to his ear the maximum was about the junction of the red 
and orange. 
(5.) A test-tube containing the vapor of sulphuric ether was 
then substituted for the receiver (G). Commencing at the 
violet end, the test-tube was gradually moved down the spec- 
trum and out into the ultra-red without audible effect, but 
when a certain point far out in the ultra-red was reached a 
distinct musical tone suddenly made its appearance, which 
disappeared as suddenly on moving the test-tube a very little 
further on. 
(6.) Upon exploring the spectrum with a test-tube contain- 
ing the vapor of iodine the limits of audibility appeared to be 
the middle of the red and the junction of the blue and indigo. 
Maximum in the green. 
(7.) A test-tube containing peroxide of nitrogen was substi- 
tuted for that containing iodine. Distinct sounds were ob-. 
tained in all parts of the visible spectrum, but no sounds were 
observed in the ultra-red. The sounds were well marked in‘ 
all parts of the violet, and I even fancied that the audible 
effect extended a little way into the ultra-violet, but of this_ 
I cannot be certain. Upon examining the absorption spectrum | 
of peroxide of nitrogen it was at once observed that the 
maximum sound was produced in that part of the spectrum 
where the greatest number of absorption lines made their. 
appearance. 
8.) The spectrum was now explored by a selenium cell, and: 
the audible effects were observed by means of a telephone in) 
the same galvanic circuit with the cell. The maximum effect 
was produced in the red about its junction with the orange. 
The audible effect extended a little way into the ultra-red on 
* Tn the diagram fig. 14 a mean of these readings is shown. 
