A. G. Bell—Production of Sound by Lnght. 3138 
few days afterwards my ideas upon this = received a fresh 
impetus by the announcement made by Mr. Willoughby 
Smith,* before the Society of Telegraph Engineers, that he 
had heard the action of a ray of light falling upon a bar of 
gi bere selenium by listening toa telephone in circuit with it. 
I not unlikely that the publicity given to the speaking 
Ba ih during the last few years, may have suggested to 
many minds, in different parts of the world, somewhat menor 
ideas to my own; indeed, fy i recently come to my kno 
edge that a writer (J. F. W.,t of Kew) on the 13th of Jone, 
1878, asked the readers of “ Nature” through the columns of 
that periodical, whether any experiments had been made with 
a telephone in, circuit with a selenium galvanic element ar- 
ranged as in Sabine’s selenium ware ;f and suggested that it 
was not unlikely that sounds would be produced in a telephone 
by the action of light of variable intensity upon a selenium 
element in circuit with it 
In September or sees 1878, Mr. A. C. Brown, of London, 
submitted to me, confidentially, the details of a most ingenious 
invention of his, of which we may yet hear more: This inven- 
tion, although entirely different from my own, involved the use 
of selenium in circuit with a battery and telephone, and the 
production of articulate speech by the action of a variable light. 
am also aware that Mr. W. D. Sargent, of Philadelphia, has 
had some ideas of a grt! nature, the details of which I do not 
know. I understood from Mr. Sargent that he proposed sub- 
mitting selenium to the “hafta of an oscillating beam of 
light which should be sent on and off the selenium by the 
action of the voice. us this i is so the effect produced would be 
only of an intermittent character and a musical tone, not speech, 
would be heard from ths telephone in eat with the selenium. 
Although the idea of producing and reproducing sound by 
the action of light, as described above, was an entirely original 
and independent conception of my own, I recognize the fact 
that the knowledge necessary for its conception has been dis- 
seminated throughout the civilized world, and that the idea 
may therefore have occurred, independently, to many other 
nds, 
I have stated above the few facts that have come under my 
observation bearing upon the subject. 
ental idea, on which rests the possibility of produc- 
ing ep by the action of hi light, ts the conception of what may be 
termed an undu sigh beam of light in contra-distinction to a merely 
Saieemittend bn 
By an dadnlsiory beam of light I mean a atm that shines 
* See Journ. of Teleg. Engin., May 23, 1878, vii 
+ Nature, xviii, 169. ¢ Nature, xvii, i — 25, 1878, 
