SCIENCE. 



121 



SCIENCE: 



A Weekly Record of Scientific 

 Progress. 



JOHN MICHELS, Editor. 



Published at 



229 BROADWAY, NEW YORK. 



P. O. Box 3838. 



SATURDAY, SEPTEMBER u, i{ 



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. 



That it is possible for even the ray of a star to 

 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. 

 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 EdisDn 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 

 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 

 chirge 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. 



