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Updated: May 4, 2025
Connection is made by conductors, on opposite sides, with the odd and even numbers of the disks, which diminishes the resistance of the selenium. The cylinder thus formed is insulated by glass supports in the inside of a vacuum tube, for the purpose of preserving it from the disturbing influence of dark rays.
"No," he said with a twinkle of scientific mischief, "no, I'm going to sleep it off." "Thank heaven!" I muttered. "Because," he went on seriously, "that case interrupted a long series of tests I am making on the sensitiveness of selenium to light, and I want to finish them up soon. There's no telling when I shall be called on to use the information." I swallowed hard. He really meant it.
The luminous rays, in falling upon the selenium plates, z', modify the resistance that these offered to the passage of the current produced by the battery, B'. As this resistance diminishes, the intensity of the current in the circuit supplied by the battery, B', increases, the attractive action of the polar pieces of the magnet, M', diminishes, the equilibrium is destroyed, and the piece, A, revolves around the axis, i.
"It actually enables the blind to locate many things, purely by the light reflected by them. Its action is based on the peculiar property of selenium, which, you probably know, changes its electrical conductivity under the influence of light. Selenium in the dark is a poor conductor of electricity; in the light it, strange to say, becomes a good conductor.
And finally for I must be brief we have the remarkable action of light on selenium. This fact was discovered accidentally by an assistant in the laboratory of Mr. Willoughby Smith, who noticed that a piece of selenium conducted electricity very much better when light was falling upon it than when it was in the dark.
"If you ever have any idea, Walter, of going into the burglary business, it would be well to ascertain if the safes have any of these little selenium cells as suggested by my friend, Mr. Hammer, the inventor. For by them an alarm can be given miles away the moment an intruder's bull's-eye falls on a hidden cell sensitive to light."
"And don't you realize that this is the answer to the solar power problem? Why, mirrors and selenium are, at best, ten per cent efficient! Think of big pumping stations on the Sahara! All that heat, all that need for power, for irrigation!" I paused a moment for effect. "Farnsworth, this can change the very shape of the Earth!" Farnsworth seemed to be lost in thought.
From 400,000 pounds of silver and 5,000 pounds of gold were obtained twelve pounds of platinum, two pounds of palladium, and several pounds of selenium. To obtain these the gold is first precipitated from the solution by ferrous chloride, all the other metals by iron turnings.
The rays from this flame were then directed by mirrors to a distant receiving station and there concentrated on a photo-electric selenium cell, which has the strange property of varying its resistance according to the illumination. Thus a telephone receiver arranged in series with it was made to reproduce the sounds.
"If the thing works at all it will send a black man's face over the wire as well as a white man's. I guess the truth of it is that you're like Koku. You're getting tired. I don't know as I blame you. I'm getting a bit weary myself. I'm going to take a rest. I'll send for another kind of selenium crystals I've heard of, and we'll try them. In the meanwhile I'll take a little vacation."
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