320 Tainter and Bell— Production of Sound by Light. 
Upon placing the telephone to my ear, I heard distinctly 
from the illuminated receiver the words :—* Mr. Bell, if you 
hear what I say, come to the window and wave your hat.” 
In laboratory experiments the transmitting and receiving 
i CC are necessarily within ear-shot of one another, and 
e have therefore been accustomed to prolong the electric cir- 
ite connected with the selenium receiver, so as to place the 
telephones in another room. 
By such experiments we have found that articulate speech 
can be mbites’ by the oxyhydrogen light, and even by the 
light of a kerosene lamp. ‘The loudest'effects obtained from 
light are produced by rapidly interrupting the beam. 
“A suitable apparatus for doing this is a perforated disc 
which can be rapidly rotated. The great advantage of this 
form of apparatus for experimental work is the noiselessness 
of its operation, admitting of the close approach of the receiver 
without interfering with the audibility of the effect heard from 
the latter—for it will be understood that musical tones are 
emitted from the receiver when no sound has been made at the 
transmitter. A silent motion thus produces a sound. In this 
way musical tones have been heard even from the light of a 
candle 
When distant effects are sought the apparatus can be ar- 
ranged as shown in fig. 7. 
By placing an opaque 
screen near the rotating 
d the beam can be 
entirely cut of a 
hand, and musical sig- 
nals, like the dots and 
dashes of the Morse tel- 
egraph code, can thus 
be produced at the dis- 
tant receiving station 
Such a screen operat ted 
by a key like a ee telegraph key is shown in fig. 8, and has 
been operated very successfully. 
