“It must have been fine,” Dr. Dale commented when Bob had concluded. “I have a personal interest in forestry work for reasons that I will tell you about when I have more time. I’m glad to hear that Mr. Bentley is going to visit you, and I would like to come round and get acquainted with him.”
“I’ll tell you when he comes,” promised Bob.
“One reason that I missed his talk last night,” the doctor went on, “was that for the greater part of the evening I was listening in at WGY. Those, you remember, are the call letters of the Schenectady station. They’ve got a wonderful new contrivance there that’s going to make a sensation in the radio world when it becomes generally known.”
“One more miracle to be put down to the account of radio, I suppose,” replied Bob, with an appreciative smile.
“You might almost call it that,” replied the doctor. “Some weeks ago WGY told its audience that a new device different from the phonograph was being used to talk into the radio transmitter. But at the time they didn’t give any explanation of what the contrivance was. I suppose they wanted to test it out under all conditions before they let the public in on it. But last night they told us all about it. It’s a film that does the talking.”
“A film!” exclaimed Bob, in surprise.
“That’s just what it is,” affirmed Dr. Dale. “They showed it to Edison when he was up there the other day, and he was astonished. And anything that astonishes that wizard must be pretty good.”
“I should say so!” acquiesced Bob. “Please tell me just what it is and how it works.”
“It’s something like this,” replied the doctor. “I’ll try to give it to you as nearly as I can in the very words that were used in explaining it. The purpose of the device is to record sounds on a photographic film so that the sound may later on be exactly reproduced in ordinary telephones and loud speakers. The record is made by causing the sound waves to produce vibrations on a very delicate mirror. A beam of light reflected by this mirror strikes a photographic film which is constantly in motion.
“When the film is developed it shows a band of white with faint markings on the edges which correspond to the sound which has been reproduced. On account of the exceedingly small size of the mirror, it has been found possible to produce a sound record which includes the delicate overtones which give quality to speech and musical sounds. Do you get my meaning?”