Explanation of the Mirage. 35 



hedge, so as to obtain a better view from the mound, 

 the cause of the ilhision was at once visible. 



Looking through the gap was like looking through 

 a narrow window, only a short section of the hill 

 being within sight ; from the elevation of the mound 

 the whole range of hills could be seen at the same 

 time. Then it became immediately apparent that on 

 either side of this great mountain the continuation of 

 the down right and left remained still at its former 

 level. Upon the central hill a cloud was resting, and 

 had for the time taken its exact shape. The ridge 

 itself was dark, and the dark gray vapor harmonized 

 precisel}^ with its hue ; so that the real hill and the 

 cloud merged into each other. Either the barn and 

 clump of trees were reproduced or perhaps enlarged 

 and distorted by the refraction : the seeming column 

 of smoke w\as a fragment of a blacker color which 

 chanced to be in a nearly perpendicular position. 

 Even when recognized as such, the illusion was still 

 perfect ; nor could the eye separate the hill from the 

 unsubstantial vapor. 



As I watched it, the apparent column of smoke 

 bent, and its upper part floated awaj^, enlarging just 

 as smoke, its upward motion overcome by the wind, 

 slowly yields to the current. Soon afterwards the 

 light breeze stretched out one end of the mass of 

 cloud, began to roll up the other, and presently 

 lifted it, revealing the real ridge beneath, which 

 grew momentarily more distinctly defined. Finally, 

 the mist}^ bank hung suspended over the down, and 

 slowly sailed eastwards with the wind. Some time 

 afterwards I saw a similar mirage-like enlargement 

 of the down by cloudy vapor resting on it and as- 



