Following the experiments made on November 27 the various pieces of film mentioned were carefully examined to determine the cause of the noises heard. Examination of these pieces of film under the low power of the microscope showed that the film base material contained a large number of black specks. These specks may have been dust or dirt which was in the base when it was manufactured. They were however very small and it is thought that they were not the cause of the noises heard. When a piece of film was held up in front of the eye against a dark background and the eye focused upon the surface of the film; if the film was now slowly moved distinct waves in the surface of the film could be noticed. These waves were present both in moving picture film and also the clear film base used in making Kodak films. It seems reasonable that these waves in the film base may be the cause of the noises heard as they would probably have a considerable distorting effect upon the light coming through the slit. Some film base was ordered directly from Eastman’s with the specifications that it come from the first step in manufacture that is before it had been run through the rolls or punches. This material has been received but has not yet been tried in comparison with the ordinary moving picture film base.
The wave effect is visible upon its surface and it also showed the black spots when viewed under the low power of the microscope. A comparison between ordinary motion picture film base and the film base in Kodak film showed that the Kodak film base was much more noisey than the moving picture film base. This was contrary to what one would expect as the Kodak film base was about half the thickness of the moving picture film base and also contained less black specks when viewed under the microscope than did the moving picture film base. Dr. Mees of the Eastman Kodak Co. said that the same material was used in making the base for both films.
For use in working with these moving picture films, a camera described in the notes of November 27 was made up. It consisted of two solid wood drums over which the film could be placed and arranged with a crank so that the film could be passed before a slit. For the slit, a variable slit about one-half inch wide was obtained out of an old spectroscope.
In view of the fact that we had obtained a good voice transmission with a special oxy-acetylene manometric burner, it was decided to photograph the variations from this burner upon a strip of moving picture film. A strip of unexposed film about seven feet long was mounted in the camera. The slit was adjusted to a very narrow width and a picture of the varying flame was taken. The flame was placed just outside the camera and about three inches from the slit. The film was turned past the slit by hand at the speed of about one foot per second. During the taking of thai picture the flame was made to vary by talking into the diaphragm. The film was developed; the exposure proved to be very nearly correct. The voice variations however were very small as there was too much continuous light and not sufficient amplitude of variation.
As this time Dr. Lee DeForest reported to Mr. Case that he had been using small flashlight bulbs for taking pictures of voice variations. To obtain satisfactory results, it was necessary to burn these bulbs very bright, consequently they burned out. Mr. Case had suggested to him several weeks before that he try hydrogen in his small light so that the filament would cool quicker. Dr. DeForest had evidently been thinking this over and on December 12, he requested Mr. Case to fill some of these small lamps for him with hydrogen gas. He desired the filaments to be straight and about one-eighth inches long. A number of flashlight bulbs were obtained and a suitable system set up to fill these bulbs with hydrogen gas. Two or three of these bulbs were sent to DeForest and a few kept here for experiments at this laboratory. Some pictures were taken to the variations produced in the filament of one of these little hydrogen filled bulbs. The bulb was lighted by means of a six volt storage battery potentiometer arrangement and burned to a point where the filament was a bright orange. The voice variations were then impressed upon the filament light taken directly from a four stage amplifier system. A small Federal microphone supplied the variations to the first bulb of this system. The were then amplified by a western Electric loud speaker and the output impressed upon the filament of the small bulb by means of a step-down transformer. The transformer was in series with the flashlight bulb and the storage battery or potentiometer. When one spoke into the microphone, fluctuations in the light from the flashlight bulb were noted. A number of pictures were taken of variations produced in this small flashlight bulb.
A number of experiments were made to get the exposure correct. In most cases the photographs obtained showed as before too much continuous light and not much amplitude of variation. It was thought that the filament in these bulbs was too large and was not responding sufficiently to the impressed voice variations. Some surgical lamps were obtained from the Welch-Allyn company of this city. These were very much smaller and in fact were stated to be the smallest lamps manufactured. Two of the smaller lamps gave very good response to the voice variation. The variations could be reproduced quite perfectly by allowing the light to fall upon a sensitive Thalofide cell and amplifying the electrical change produced. However, upon photographing the variations of the small lights about the same results were obtained as in the case of the small flashlight bulbs. The results were not satisfactory.











