484 A. G. Bell—Production of Sound by Rodiant Energy. 
meaning we bave uniformly attached to the words “ photo- 
phone” and “light” will be obvious from the following passage, 
quoted from my Boston paper: 
“Although effects are produced as above shown by forms of 
for the producti ion and reproduction of sound in this way the 
‘photophone’ because an ordinary beam of light contains the 
rays which are operative.’ 
To avoid in future any misunderstandings upon this point 
we have decided to adopt the term ‘‘radiophone,” proposed by 
M. Mercadier, as a general term signifying an apparatus for the 
production of sound by any form of radiant energy, limiting 
the words thermophone, photophone, and uactinophone to appa- 
ratus for the production of sound by thermal, luminous or 
actinic rays respective y- 
M. Mereadier, in the course of his researches in radiophony, 
sed an intermittent beam from an electric lamp through a 
sie and then examined the audible effects produced in dif- 
rent parts of the spectrum. (Comptes Rendus, Dec. 6th, 1880.) 
We have repeated this experiment, using the sun as our 
source of radiation, and have ae results cid HE differ- 
ent from those note y M. Mercadi 
(1L.) A beam of sunlight was rottoci from a heliostat (A, 
fig. 12) through an achromatic lens (B), so as to form an 
image of the sun upon the slit (C). 
The beam then passed through another achromatic lens (D) 
and through a bisulphide of carbon prism (E), forming a spec- 
trum of great intensity, which, when focussed upon a screen, 
was toutid to be sufficiently es to show the principal absorp- 
tion lines of the solar spectrum 
he disk-interrupter (F) was then turned with sufficient 
rapidity to produce from five to six hundred interruptions of 
the light per second, and the spectrum was explored with the 
receiver (G), which was so arranged that rt lamp-black sur- 
ace exposed was limited by a slit, as show 
Under these circumstances sounds were Pahiined in every 
part of the visible spectrum (excepting the extreme half of the 
violet), as well as in the ultra-red. A continuous increase in 
the loudness of the sound was observed upon moving the re- 
ceiver (G) gradually from the violet into the ultra- red. The 
point of maximum sound lay very far out in the ultra-red. 
ma? bet this point the sound began to decrease, and then sto 
ped so suddenly that a very slight motion of the receiver (G) 
made all the difference between almost maximum sound and 
complete silence.* 
*The results obtained in this and subsequent experiments are shown in a 
tabulated form in fig. 14. 
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