Thoughts of high frequency radio waves—of X-rays—of Fernand—
"Fernand!" he exclaimed aloud, and with the name coherent thought returned. Putting on all possible speed he covered the distance to his home in a few seconds and dashed up to his laboratory, the while his swiftly-working brain attacked the greatest personal problem that it had ever been called upon to solve.
Having experimented with ultra-short waves, he knew that it was possible to create total transparency of any object if the object could be made to vibrate approximately at the same rate as light. He was familiar with the theory, and although he had worked on it at times, he had never seen a practical demonstration of it.[7] He realized a machine was in the hands of someone, intent on kidnapping Alice. He knew, too, that a police description would be flashed within a radius of thousands of miles instantly, it would be necessary for the abductor to keep Alice invisible for some time to come, for fear of some one seeing and recognizing her. All this flashed through his mind as he assembled a detecting apparatus consisting of a portable aerial and a small box containing a few radio instruments and a pair of headphones.
The aerial, by being rotated, could determine the point from which the waves emanated. In ten minutes Ralph had the apparatus rigged up and began rotating the aerial, until a roaring noise was heard in the telephones. He knew that this must be the apparatus producing the invisibility, and within a few seconds he had dashed from the house on his power skates, carrying the detector in front of him. Two of his assistants accompanied him.
The pursuit was on. As they approached the kidnapper the sounds in the telephones became stronger. They sped along Broadway, while the hastily notified police kept the way open. The rising sound in the 'phones clearly indicated they were headed directly toward the abductor.
They gained steadily on him while the rolling, flying police cleared Ralph's way with their shrieking sirens, while the kidnapper had to pick his way slowly through crowds.
The chase led them into a narrow street on the outskirts of the city.
The sound that came through the telephones was now exceedingly loud, indicating that the quarry was near by. But this very nearness was confusing to Ralph, for the volume of sound prevented him from exactly locating the invisible kidnapper and the girl. In vain he turned the aerial in all directions, seeking one point from which it came louder than another that would determine the course of his pursuit. For the moment he was halted, and, like some hound baffled by the cunning of the fox, he cast about him eagerly, waiting for what he knew must come, the next move of the pursued man.
And then it came—a deepening tone in the telephones, a gradation of sound that to the trained ear of the scientist told him all that he wished to know. With an exultant cry he sprang forward, and dashed through the entrance of a small store.
The proprietor, whose state of mind may best be described by the word "flabbergasted," struggled for some moments in vain for speech while Ralph and his men, with outstretched hands eagerly swept from wall to wall.