II. 



THE EYES AS FALSE WITNESSES, 

 i. Opposite Movements looking Identical. 



A SURPRISINGLY large part of what we believe 

 that we see is not directly seen with the eyes, 

 but inferred, however swiftly and instinctively, 

 by the judgment, from previous knowledge 

 and experience. This explains the well-known 

 frequency with which honest witnesses of the 

 same events see in them things which are 

 different, and even contradictory. 



If a windmill is seen at a distance on a 

 dark and cloudy night, with no light behind 

 the spectator, and only a dull sky behind the 

 mill, no details are visible. Only large masses 

 can be seen, and these without any gradation 

 of shades to help in defining relative distances 

 or obliquity of surfaces. The mill, as seen 

 under these circumstances, may be repre- 

 sented diagrammatically by A in Fig. 50. Of 

 the movement of the sails all that can be 

 seen is that they rise on the left and fall on 

 the right, like the hands of a clock, and that 

 their ends describe an ellipse, not a circle. 

 This shows that their plane of revolution is 

 oblique to the spectator ; but whether they 



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