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THE " PHOTOGRAPHOPHONE."
BY ERNST RUHMER.
The SCIENTIFIC AMERICAN has from time to time presented to its readers different methods of recording and reproducing both musical sounds and human speech.Photographophone Casing Open: Shown is a wooden light blocking case around the photographic film reels.
Of these methods, perhaps the most generally known is that employed by Mr. Edison, in which a stylus attached to a diaphragm engraves upon a rapidly revolving wax cylinder the sound impulses thrown against the diaphragm. Still another system has been devised by the Danish engineer Valdemar Poulsen, who records sounds magnetically by passing a steel ribbon between electromagnets energized with an intensity depending upon the strength of the current which has been telephonically set up in the circuit. In a third, and perhaps a more sensitive method than either of the two mentioned, photography is employed as the recording means.
Photographophone Receiver: The receiver included a selenium cell with two telephone receivers.
Under favorable conditions the variations in the intensity of oscillation of a "speaking" arc light are so appreciable that it is possible to record them upon a moving sensitive film. Upon this possibility the construction of my "photographophone" depends.

The photographophone, as shown in Fig. 1, consists primarily of a light-tight wooden casing in which photographic-film reels are mounted, the film as it is unwound from one reel being received by the other, as in the cinematograph and similar chronophotographic machines. The reel is driven by a small electric motor through the medium of a belt and pulley. Traveling at a uniform rate varying from 2 to 3 meters per second, the film passes the focus of a lens in front of which the source of light, which may be a speaking arc and which is caused to undulate in accordance with the sound waves, is placed at a suitable distance. The film after having been subjected to the action of the undulating light is developed in the ordinary way and fixed. If the record be very long, special developing apparatus is necessary, resembling that employed in the development of cinematograph pictures.
Photographophone Both Parts: Both halfs
The variations of light may be distinctly seen on the film. Fig. 4 shows a film which has been acted upon by the light, and then developed and fixed. In reproducing the recorded sound, an ordinary stereopticon is used in place of the original undulating source of light, the film traveling with the velocity equal to that with which the record is made. Behind the film an exceedingly sensitive selenium cell is removably mounted and connected with two the film or whether the original negative be used. Apart from the extreme sensitiveness of this photographic method of recording sound, the invention is of considerable practical utility in so far as any number of positive copies can be made from the original negative. The film may be so long that the speech or song to be recorded may be almost interminable. Moreover, the films are so compact that even a very long record can be stored in an exceedingly small space.
Photographophone Sound-Record Film
By using an undulating incandescent lamp in place of the speaking arc light in an improved instrument which I have constructed, I succeeded recently in attaining very good results with a film speed of 20 centimeters per second. It is my intention to employ the photographophone in connection with the cinematograph and to ascertain whether it be possible to record the movements of bodies and of sounds (such as music) upon the same film. By means of the many auxiliary apparatus which have been devised in late years for the purpose of magnifying sound, it is to be hoped that the photographic sound-record may be successfully reproduced in a large auditorium.

Berlin, April, 1901.