Laurie, who was busy shortening a bit of wire, glanced up with interest.
"I can't for the life of me understand how he knew what he wanted to do, can you?" he mused. "Think of starting out to make something perfectly new—a machine for which you had no pattern! I can imagine working out improvements on something already on the market. But to produce something nobody had ever seen before—that beats me! How did he ever get the idea in the first place?"
The tutor smiled.
"Mr. Bell did not set out to make a telephone, Laurie," he answered. "What he was aiming to do was to perfect a harmonic telegraph, a scheme to which he had been devoting a good deal of his time. He and his father had studied carefully the miracle of speech—how the sounds of the human voice were produced and carried to others—and as a result of this training Mr. Bell had become an expert teacher of the deaf. He was also professor of Vocal Physiology at Boston University where he had courses in lip reading, or a system of visible speech, which his father had evolved. This work kept him busy through the day so whatever experimenting he did with sounds and their vibrations had to be done at night."
"So he stole time for electrical work, too, did he?" observed Ted.
"I'm afraid that his interest in sound vibration caused him a sorry loss of sleep," said the tutor. "But certainly his later results were worth the amount of rest he sacrificed. One of the first agencies he employed to work upon was a piano. Have you ever tried singing a note into this instrument when the sustaining pedal is depressed? Do it some time and notice what happens. You will find that the string tuned to the pitch of your voice will start vibrating while all the others remain quiet. You can even go farther and try the experiment of uttering several different pitches, if you want to, and the corresponding strings will give back your notes, each one singling out its own particular vibration from the air. Now the results reached in these experiments with the piano strings meant a great deal more to Alexander Graham Bell than they would have meant to you or to me. In the first place, his training had given him a very acute ear; and in the next place, he was able to see in the facts presented a significance which an unskilled listener would not have detected. He found that this law of sympathetic vibration could be repeated electrically and, if desired, from a distance by means of electromagnets placed under a group of piano strings; and if afterward a circuit was made by connecting the magnets with an electric battery, you immediately had the same singing of the keys and a similar searching of each for its own pitch."
"I'd like to try that trick some time," exclaimed Ted, leaning forward eagerly.
"So should I!" echoed Laurie.
"I think we could quite easily make the experiment if Laurie's mother would not object to our rigging up an attachment to her piano," Mr. Hazen responded.
"Oh, Mater wouldn't mind," answered Laurie confidently. "She never minds anything I want to do."