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Sometimes selenium comes in crystal forms, and again it is combined with various metals for different uses." "There's one good thing about it. There are several varieties, and I'll try them all before I give up." "That's the way to talk!" cried Ned. "Never say die! Don't give up the ship, and all that. But, Tom, what you need now is a little fun. You've been poking away at this too long.
A scale must be prepared, with the zero point at the greatest possible resistance of the selenium, which corresponds with absolute darkness. The greatest effect of the light would be to annul the resistance of the selenium. Consequently, the cylinder must be withdrawn from the circuit to represent this effect; and the maximum deviation of the galvanometer is then to be observed, and marked 100.
It therefore occurred to Professor Bell that if a telephone were connected in circuit with the current, and the ray of light falling on the selenium was eclipsed by means of the vibrations of sound, the current would undulate in keeping with the light, and the telephone would emit a corresponding note. In this way it might be literally possible 'to hear a shadow fall athwart the stillness.
Tom was the first to enter the telephone booth where Eradicate had played the part of the Angel Gabriel. He looked at the wires and apparatus, but could see nothing wrong. Then he glanced at the selenium plate, on which he hoped, some day, to imprint an image from over the wire. And, as he saw the smooth surface he started, and cried. "Ned! Ned, come here quick!"
The whole is placed upon a stand, and shielded from reflected light, but fully exposed to that which is to be measured for actinic intensity. If now a constant current of electricity is passed through the apparatus, as indicated by a galvanometer, the variations of the latter will show the effect produced upon the selenium.
By constructing sensitive selenium cells through which the current passed, then directing a powerful beam of light upon them, and occulting it by a rotary screen, he was able to vary the strength of the current in such a manner as to elicit musical tones from the telephone in circuit with the cells.
Siemens had been trained as a mechanical engineer, and, although he became an eminent electrician in later life, his most important work at this early stage was non-electrical; indeed, the greatest achievement of his life was non-electrical, for we must regard the regenerative furnace as his MAGNUM OPUS. Though in 1847 he published a paper in Liebig's ANNALEN DER CHEMIE on the 'Mercaptan of Selenium, his mind was busy with the new ideas upon the nature of heat which were promulgated by Carnot, Clayperon, Joule, Clausius, Mayer, Thomson, and Rankine.
Korn's apparatus depends on the ability of the element selenium to vary the strength of an electric current passing through it in proportion to the brightness with which the selenium is illuminated. A new field has been opened by these inventions which are now becoming more and more numerous, since the Korn system did the pioneering.
At length he fell into a fitful doze, and he had a wild dream that he was sliding down hill on a big mirror in which all sorts of reflections were seen reflections that he could not get to show in the selenium plates. Then Tom felt the mirror bobbing up and down like a motor boat in a storm. He felt the vibration, and he heard a voice calling in his ear: "Get up, Tom! Get up!" "Yes!
They are connected in the like order with those of disk, A, and with those of receiver, so that the wire bearing the No. 5 from the selenium will correspond identically with like contact No. 5 of receiver. The receptive plate must be smaller than the plate whereon the light impinges.
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