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The American Museum journal (c1900-(1918)) (17973659048)


The American Museum journal (c1900-(1918)) (17973659048)



Title: The American Museum journal
Identifier: americanmuseumjo16amer (find matches)
Year: c1900-(1918) (c190s)
Authors: American Museum of Natural History
Subjects: Natural history
Publisher: New York : American Museum of Natural History
Contributing Library: American Museum of Natural History Library
Digitizing Sponsor: Biodiversity Heritage Library

Text Appearing Before Image:
A Perplexing Phenomenon Mirage Bv CHESTER A. REEDS THK li-ader of the Crocker Lund Exjx'dition, )\Ir. Donnld B. MaeMilhin, states in Harper's Magazine for Noveinl)er, 1915, that Peary's "Crocker Land" is a mirage. Shoiihl we accept the idea tliat Crocker Land is a nn'ra<;e, we nuist l)ear in mind that to produce tlie effect of "innnense lands with hills, valleys and snow-capped peaks" where none exists, there must be objects on the surface of the earth, and certain conditions within the air, which serve to give rise to such illusions. As the immense productions developed in a mirage out of comparatively small objects are most extraordinary, it is not surprising that mirages occur only under abnormal atmospheric conditions. It is essential that layers of air of un- equal density arise and that light waves which traverse them be bent unevenly, so that magnified, distorted, transported and inverted images of distant objects be produced. Mirage is thus a strange optical phenomenon which sometimes en- tertains and helps men, and sometimes leads men astray. Professor C. S. Hastings ^ of Yale Uni- versity has recently reproduced the experiment of Wollaston, an English chemist and physicist of a century ago, to explain the phenomenon of mirage. The apparatus consists of a glass tank with parallel sides filled to a certain depth with thin transparent syrup; upon this a layer of clear water is added so as not to disturb the syrup; finally a layer of alcohol is superimposed on the water. These liquids will mix only slowly by diffusion, producing two transition layers, one above and one below respectively. A small palm in the same horizontal plane, represents a "distant object." If the observer stand eight or ten feet from the tank and view the dis- tant object through it, various images of the palm will appear. At a level where the syrup is unmixed with water as at 1, (upper figure, page 514), an erect image of the object in its true position and size will ' C. S. Hastings, Light, pp. 115-120, Chas. Scribner's Sons, New York, 1901. See p. 117 of this volume for method of conducting experiment.
Text Appearing After Image:
Glass tank with liquids of unequal density, to explain optical effects produced in mirage. See "V \ detailed figures following ,'\ \ ; \ \ "? 'J ALCOHOL V\/ATER \ \\ \ \ \ PALM\





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