SCIENCE. 
1 2 1 
SCIENCE: 
A Weekly Record of Scientific 
Progress. 
JOHN MICHELS, Editor. 
Published at 
229 BROADWAY, NEW YORK. 
P. O. Box 3838. 
SATURDAY, SEPTEMBER n, 1880. 
THE PHOTOPHONE. 
Mr. Alexander Graham Bell, whose contributions 
to electric science have been recognized at home and 
abroad to their fullest value, has written a paper on 
his latest invention, the Photophone, which we repro- 
duce and abundantly illustrate. 
It is a beautiful application of the telephone to the 
registration of the mechanical action of electricity set 
in motion by light ; but it is not (as the world was 
lead to suppose by some ill informed journalist) a me- 
thod of transmuting light pulsations into electrical 
ones, and then changing these back again into light. 
A beam of light is reflected upon a mirror diaphragm, 
which is set in motion by the voice or otherwise; the 
concentrated ray is then reflected so as to affect a 
piece of selenium in a telephonic circuit, which, by 
its varying conductivity, acts intermittently on the 
diaphragm of the telephone, and thus in the usual 
way reproduces the sound. The instrument is sim- 
plicity itself, but the results are of the highest popular 
and scientific interest. 
produce a mechanical effect, was demonstrated when 
Edison used his Tasimeter for measuring the waves 
of radiant energy of Vega. We thought Bell had 
solved the problem, upon which Edison was at work 
when he became interested in the perfection of his 
electric light, but our hope has not been realized, j 
The subject, however, is one of extreme interest, 
and it is not strange for the discoverers of the two 
telephonic systems to be simultaneously engaged in | 
solving the natural corollary to their great proposi- 
tions. But Edison has an advantage in the pursuit. 
His employment of the varying electrical conductivity 
of carbon allows him to introduce any amount of 
reserve power for mechanical purposes. 
It is much to be regretted that Edisrm can not find 
' leisure from the practical applications of his science 
to turn his attention to those problems which he is so 
eminently capable of solving. We vividly recall some 
experiments in this direction which he told us of 
during the Spring of 1878, while on a visit to his 
laboratory at Menlo Park. He allowed a beam 
j of light to fall on the surface of a diaphragm 
connected with his carbon button, in the hope that 
by a surface and molecular action, it would be possi- 
ble to transmit its motion to a receiving diaphragm, 
where a similar molecular tension would result in the 
reproduction of the original vibrations. A faint halo 
is said occasionally to have surrounded the diaphragm. 
We could not^but believe this due to the excited im- 
agination of Mr. Edison, for at the time he was en- 
thusiastically engaged in testing the wondrous 
capacity of the tasimeter, which he was soon to use 
in eclipse observations on the Draper expedition. 
He also tried to observe the effect of a beam acting 
on the diaphragm of a phonograph, whose cylinder re- 
volved at enormous speed, hoping a line of phosphor- 
escence might arise from the tinfoil where it came in 
contact with the needle. Mr. Edison said he em- 
ployed the direct action of the light (in the last case), 
in preference to using electricity as a medium for it, 
because he feared there existed a difference between 
the vibratory periods of light and electricity, al- 
though their velocity was nearly the same. For 
a similar reason he sought to realize the instan- 
taneous translation of light by using his motograph, 
in preference to the magnetic telephone which for this 
purpose is valueless, owing to the time required to 
charge and discharge the iron core. But the most 
interesting of these experiments is to come. He 
threw a beam of lamp light on a small mirror, fast- 
ened to a tuning fork, and reflected a ray upon a strip 
of hard rubber in the tasimeter, the button of the 
latter being in circuit with a telephone and battery. 
On setting the fork in motion, the Lissajous figure 
caused a movement of the rod, which resulted in the 
reproduction of the musical note. 
But all these pretty experiments are but introduc- 
tory to the more subtile question, how to translate 
light through other forms of motion back into light. 
We wish a hearty rivalry between the two discoverers ; 
for Messrs. Bell and Edison will find the fields of 
science (like those of trade) yield best fruit when 
fertilized by competition. 
