PSYCHOLOGY AND TESTIMONY a^7 



and a commentary of even greater length. Such a procedure would be 

 him to be of the size of a plate, a cart-wheel, or what not, and there's 

 an end. His answer can not be challenged on the score of malobserva- 

 tion; one may impeach either his memory or his truthfulness, but not 

 the accuracy of his observation or even of his judgment. In other 

 words, if the man misunderstood the question, and was really answering 

 this other: "How large does the moon instinctively appear to you?" ; 

 his answer, " as large as a carriage-wheel " or " as large as a one-cent 

 piece," is better than any that either the psychologist or the astronomer 

 can supply for him. If, on the other hand, the student understood the 

 question as it was " carefully explained " by Professor Miinsterberg, 

 he absolutely deceived himself if he imagined that his " perception " 

 of the moon's size had anything to do with the answer. We do not, by 

 direct perception, actually estimate the angle subtended by an object, 

 nor do we perform any equivalent operation. For any object within a 

 small distance, we automatically make absolutely complete compensa- 

 tion for the diminishing angle under which it is seen as the distance 

 increases; a plate, a silver dollar or a pea, held at arm's length, tools 

 precisely as large as it does when held at the distance of a foot — we 

 have no consciousness whatsoever that the angle it subtends is only one 

 third as great in the former case as in the latter. The moon subtends 

 an angle of half a degree; a large pea at arm's length does the same; 

 a large pin's head, perhaps, does the same a foot away from the eye. 

 But the keenest observer in the world is no more aware of these things 

 by direct perception than is the most ill-constructed member of Pro- 

 fessor Miinsterberg's class. Our automatic compensation for dimin- 

 ishing angle becomes very imperfect both at great distances and in 

 unusual circumstances — such as looking down upon the floor of the 

 rotunda of the capitol from the gallery at the top; and for celestial 

 objects, like the sun and the moon, it of course falls infinitely short of 

 requirements. We make some compensation, though immeasurably 

 less than what is required; and the well-known fact that people differ 

 enormously in their feeling of the apparent size of the moon merely 

 shows that the amount of this compensation (which, in any event, has 

 no simple relation to the actual size and actual distance of the moon) 

 is very different with different persons. But, strangely enough. Pro- 

 fessor Miinsterberg seems to lose sight of all these facts, and actually 

 to regard the question of the apparent size of the moon as identical 

 with the mathematical question of the angle that it subtends 

 — or, what comes to the same thing, the size of an object which, held 

 at arm's length, will " just cover " it. For while he " carefully ex- 

 plained " the question as meaning the latter thing, his comments relate 

 to the former; and, in particular, in the closing remarks of his article, 

 he speaks of his students not knowing whether " the moon is small as 

 a pea or large as a man." By "is," he of course means "seems"; 



