^Ofi THE WORLD'S WONDERS. 



common perspective-glass, and the summits of mountains are 

 visible at the distance of from sixty to a hundred miles. 



MIRAGE. 



NOTHING can be more wonderful than the phenomena of the 

 atmosphere, dependent upon reflection and refraction, which are 

 frequently observed in the Arctic seas. They are probably occa- 

 sioned by the commixture of two currents of air of different 

 temperature, so as to create an irregular deposition of imper- 

 fectly condensed vapor, which, when passing the verge of the 

 horizon, apparently raises the objects there situated to a consid- 

 erable distance above 't, or extends their height beyond their 

 natural dimensions. Ice, land, ships, boats, and other objects, 

 when thus enlarged and elevated, are said to loom. The lower 

 portions of looming objects are sometimes connected with the 

 horizon by an apparent fibrous or columnar extension of their 

 parts ; at other times they appear to be quite lifted into the air, 

 a void space being seen between them and the horizon. 



A most remarkable delusion of this kind was observed by 

 Scoresby while sailing through the open ice, far from land. Sud- 

 denly an immense amphitheater, inclosed by high walls of basaltic 

 ice, so like natural rock as to deceive one of his most experi- 

 enced officers, rose around the ship. Sometimes the refraction 

 produced on all sides a similar effect, but still more frequently 

 remarkable contrasts. Single ice-blocks expanded into architec- 

 tural figures of an extraordinary height, and sometimes the dis- 

 tant, deeply-indented ice-border looked like a number of towers 

 or minarets, or like a dense forest of naked trees. Scarcely had 

 an object acquired a distinct form, when it began to dissolve into 

 another. 



It is well known that similar causes produce similar effects in 

 the warmer regions of the earth. In the midst of the tropical 

 ocean the mariner sees verdent islands rise from the waters, and 

 in the treeless desert fantastic palm-groves wave their fronds, as 

 if in mockery of the thirsty caravan. 



