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Updated: June 5, 2025
With contragravity, of course, terms like "escape-velocity" and "mass-ratio" were of purely antiquarian interest. "How long," he asked Pearson, "would it take to fit that vehicle with a full set of detection instruments radar, infrared and ultraviolet vision, electron-telescope, heat and radiation detectors, the whole works and spot it about a hundred to a hundred and fifty miles above Keegark?"
So in taking an ultraviolet photograph a screen must be used which will be opaque to these visible rays and yet will let the ultraviolet rays through to form the image. That gave Professor Wood a lot of trouble. Glass won't do, for glass cuts off the ultraviolet rays entirely. Quartz is a very good medium, but it does not cut off all the visible light.
Dureresque, grimly awful as materialization of a scene of the Dance Macabre and yet vastly comforting. For here was something which was well within the range of human knowledge. It was the light about us that did it; a vibration that even as I conjectured, was within the only partly explored region of the ultraviolet and the comparatively unexplored region above it.
This push developed molecularly from the earth-mass-resultant to the generator; and at the same fractional distance from the rep ray generator to the power plant. The force exerted upward against the ship was, of course, highly concentrated, being confined to the path of the ultraviolet beam.
"But what makes you think that it will penetrate fog?" I queried. "And if it is invisible itself, how will it illumine an object?" "As to your first question," he answered, with a smile, "it is well known to surgeons that ultraviolet light will penetrate the human body to the depth of an inch, while the visible rays are reflected at the surface.
He wasted five precious minutes, scouting an area of several miles, but he could find nothing to protect them on the flat plain. "Better put in the ultraviolet glass shields in our helmets, boys," he called into the jet-boat communicator. "It's going to be mighty hot, and dangerous." "Aye, aye, sir," came the replies from the other two jet boats soaring close by.
As soon as I heard of the first symptom of sunburn, I knew it was caused by the ultraviolet rays, the same as from the sun; and I knew that nothing but my light could produce those rays at night time. And as a physician I knew what I did not know as an inventor the swift amblyopia that follows the impact of this light on the retina.
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