PHYSIOLOGICAL PARADOXES. 



boat seen on the distant horizon after sunset 

 against the evening sky. The diagram A, 

 Fig. 51, suggests the distance and smallness of 

 the object seen upon the edge of the dark 

 sea. It is too far off and too ill lighted for 

 the set of the sails or the pointing of the boat 

 to be seen ; but a few minutes' observation 

 shows that it is travelling in the direction of 

 the lower arrow-head. As the wind is blowing 

 in the direction of the upper arrow-head, it is 



c 



FIG. 51. -LIABILITY OF INTERPRETATIONS TO ERROR. 



obvious that the boat is tacking, but on which 

 tack it is cannot be seen. A bird's-eye or 

 balloon view of that part of the sea might 

 show that the boat is moving in the direction 

 B or in the direction C ; which of the two 

 the eye cannot distinguish. 



Here comes in the influence of habitual 

 knowledge and unconscious judgment. 



A fisherman fifty miles away, who happened 

 to observe this boat on the horizon, and could 

 only see that she was moving to the right 

 against the wind, but was well acquainted 

 with the fishing customs of that part of the 

 coast, might easily say to himself, without 



236 



