402 THE CANADIAN NATURALIST. [Vol. ix. 



beam of light, and the undulatory beam emerging from the ap- 

 paratus could be received at some distant place upon a lens, or 

 other apparatus, by, means of which it could be condensed upon 

 a sensitive piece of selenium placed in a local circuit with a tele- 

 phone and galvanic battery. The variations in the light produced 

 by the voice of the speaker should cause corresponding variations 

 in the electrical resistance of the selenium employed : and the 

 telephone in circuit with it should reproduce audibly the tones 

 and articulations of the speaker's voice. I obtained some selenium 

 for the purpose of producing the apparatus shown ; but found that 

 its resistance was almost infinitely greater than that of any tele- 

 phone that had been constructed, and I was unable to obtain any 

 audible effects by the action of light. I believed, however, that 

 the obstacle could be overcome by devising mechanical arrange- 

 ments for reducing the resistance of the selenium, and by con- 

 structing special telephones for the purpose. I felt so much 

 confidence in this that, in a lecture delivered before the Royal 

 Institute of Great Britain, upon the 17th of May, 1878, I 

 announced the possibility of hearing a shadow by interrupting 

 the action of light upon selenium. A few days afterwards my 

 ideas upon this subject received a fresh impetus by the anounce- 

 ment made by Mr. Willoughby Smith before the Society of 

 Telegraph Engineers that he had heard the action of a ray of 

 lio-ht falling upon a bar of crystalline selenium, by listening to a 

 telephone in circuit with it. 



It is not unlikely that the publicity given to the speaking 

 telephone during the last few years may have suggested to many 

 minds in different parts of the world somewhat similiar ideas to 

 my own. 



Although the idea of producing and reproducing sound by the 

 action of light, as described above, was ail entirely original and 

 independent conception of my own, I recognize the fact that the 

 knowledge necessary for its conception has been disseminated 

 throughout the civilized world, and that the idea may therefore 

 have occurred to ma))y other minds. The fundamental idea, on 

 wliicli rests the possibility of producing speech by the action of 

 light, is the conception of what may be termed an undulatory 

 beam of light in contradistinction to a merely intermittent one. 

 By an undulatory beam of light, I mean a beam that shines 

 continuously upon the selenium receiver, but the intensity of which 

 upon that receiver is subject to rapid changes, corresponding to the- 



