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Updated: May 4, 2025
Under the influence of the luminous rays, the resistance that the selenium offers to the passage of an electric current instantly changes. At M and M' are placed two horseshoe magnets whose poles are provided with pieces of soft iron that serve as cores to exceedingly fine wire bobbins, d. These polarized pieces are arranged in the shape of a St.
It is on this principle, too, that the small concentrated residues of great operations in the arts are almost sure to be the lurking places of new chemical ingredients: witness iodine, brome, selenium, and the new metals accompanying platina in the experiments of Wollaston and Tennant. It was a happy thought of Glauber to examine what everybody else threw away.”
"Well, sometimes selenium is found in combination with metals, in the form of selenides, the more important minerals of that kind being eucharite, crooksite, clausthalite, naumannite and zorgite " "Good night!" interrupted Ned, with a laugh, holding up his hands. "Stop it, Tom!" he pleaded. "You'll give me a headache with all those big words."
Such modification of the physical properties of selenium, moreover, occurs without the perceptible development of any mechanical work.
Selenium even emits notes under a vibratory beam of light, the pitch depending on the frequency. Changes in the intensity of the light focused by the reflector on the cell alter its electrical resistance and vary the current from the dry batteries. Hence the telephone receiver over there is affected. Bell used the photophone or radiophone over several hundred feet, Ruhmer over several miles.
"Now," he went on, "this property of selenium is used for producing or rather allowing to be transmitted an electric current which is interrupted by a special clockwork interrupter, and so is made audible in this wireless telephone receiver which I have here connected with this second box. The eye is replaced by the ear as the detector of light that is all."
"Well, since we can't go motor boating, I guess I may as well go back and see if that new supply of selenium has come. I do want to get my photo telephone working, Ned." "And that's all the outing you're going to take less than an hour!" exclaimed Ned, reproachfully. "Oh, well, all you wanted to do was to get me out of a rut, as you called it," laughed Tom. "And you've done it you and Mr.
Pursuing these researches, Professor Bell discovered that not only the selenium cell, but simple discs of wood, glass, metal, ivory, india-rubber, and so on, yielded a distinct note when the intermittent ray of light fell upon them. Crystals of sulphate of copper, chips of pine, and even tobacco-smoke, in a test-tube held before the beam, emitted a musical tone.
A Morse apparatus interposed in this annexed circuit will therefore give an automatic inscription of the correspondence exchanged. Such is the principle. But, practically, very great difficulties present themselves, these being connected with the rapid weakening of the electric properties of the selenium, and with the necessity of having recourse to infinitely small mechanical actions only.
In the third case are Tellurium and Tellurets. In the fourth are samples of native Arsenic, and its combinations with nickel and cobalt; Carbon in its various forms, pure as in the diamonds, which the visitor will notice attentively, some imbedded in the earth in which they were discovered, and models of celebrated diamonds; Black Lead in porcelain earth, for which Cumberland is celebrated; Selenium in its combinations with lead, mercury, sulphur, and other metals; and a medallion, in selenium, of Berzelius, who discovered this metal in 1818.
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