ILLUSIONS 



119 



But there is something more to mirage than 

 this reversed image. The eyes do not see things 

 " in their place," but see them hanging in the 

 air as in the case of ships and caravans. To 

 explain this, in the absence of a diagram, we 

 shall have to take np another illustration. Sup- 

 pose a light-ray so violently bent by the heat 

 lying above a sidewalk that it should come to 

 us around a street corner, and thereby we should 

 see a man coming up a side street that lies at 

 right angles to us. He would appear to our 

 eyes to be coming up, not the side street, but 

 the street we are standing in. The man, to all 

 appearances, would not be "in his place." We 

 should see him where he is not. 



Now suppose again instead of the light-rays 

 bending to right or left (as in the street-corner 

 illustration), we consider them as bending sky- 

 ward or earthward. Suppose yourself at sea 

 and that you are looking up into the sky above 

 the horizon. You see there a ship " out of its 

 place," hanging in the air in an impossible 

 manner something which is equivalent, or at 

 least analogous, to looking down the street and 

 seeing the image of the man around the corner. 

 You are looking straight into the sky, yet see- 

 ing a ship below the verge. The light-rays 



The bent 

 light-ray. 



Ships at 

 sea. 



