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A molecular bombardment from the cathode is, in his opinion, going on, and when the shots, that is to say, the molecules of air, strike the wall of the tube, or any other body within the tube, the shock gives rise to phosphorescence or fluorescence and to heat.
Even in ordinary conditions, certain substances called radioactive emit, quite outside any particular reaction, radiations complex indeed, but which pass through fairly thin layers of minerals, impress photographic plates, excite fluorescence, and ionize gases. In these radiations we again find electrons which thus escape spontaneously from radioactive bodies.
This deportment of fluor spar determined Stokes in his choice of a name for his great discovery: he called this rendering visible of the ultra-violet rays Fluorescence. By means of a deeply coloured violet glass, we cut off almost the whole of the light of our electric beam; but this glass is peculiarly transparent to the violet and ultra-violet rays.
This pure anthracene exhibits the phenomenon of fluorescence, that is, it not only looks white, but when the light falls on it, it seems to reflect a delicate violet or blue light. Our table shows us that from the 12 gallons of tar from 1 ton of coal we may gain 2-1/4 lb. of 20 per cent. Alizarin paste.
On the sixth night, the Air Force sent in an investigator and he saw them. Between the hours of 9:00P.M. and midnight he saw six groups of triangular shaped objects that glowed "with a dull fluorescence, faint but bright enough to see." They passed from horizon to horizon in six seconds.
It drew attention to the fluorescence of minerals placed in the cathode tube; this inspired Becquerel to inquire whether naturally fluorescent substances gave off anything like X-rays, and eventually yet again by accident he came upon certain uranium compounds. These were found to give off a radiation similar to X-rays, and to give it off naturally and all the time.
They gave him some pink fluid with a greenish fluorescence and a meaty taste, and the assurance of returning strength grew. "That that makes me feel better," he said hoarsely, and there were murmurs of respectful approval. He knew now quite clearly. He made to speak again, and again he could not. He pressed his throat and tried a third time. "How long?" he asked in a level voice.
Goethe in his 'Farbenlehre' thus describes the fluorescence of horse-chestnut bark: 'Let a strip of fresh horse-chestnut bark be taken and clipped into a glass of water; the most perfect sky-blue will be immediately produced. Sir John Herschel first noticed and described the fluorescence of the sulphate of quinine, and showed that the light proceeded from a thin stratum of the solution adjacent to the surface where the light enters it.
Chick got his first glimpse here of what lay outside an iridescent landscape, at first view astonishingly like an ocean of opals; for it was of many hues, red and purple and milky white, splashed violantin blue and fluorescence a maze and shimmer of dancing, joyful colours, whirring in an uncertainty of polychromatic harmony. Such was his first fleeting impression.
All animal infusions show this fluorescence. The crystalline lens of the eye exhibits the effect in a very striking manner. When, for example, I plunge my eye into this violet beam, I am conscious of a whitish-blue shimmer filling the space before me. This is caused by fluorescent light generated in the eye itself.
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