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. 



Glass tank with liquids of unequal density, to 



explain optical effects produced in mirage. See 



"V \ detailed figures following 



,'\ \ 

 ; \ \ 



"? 'J 

 ALCOHOL 



V\/ATER \ \\ \ \ \ PALM\ 



513 



