588 STUDIES IN ADVANCED PHYSIOLOGY. 



can be seen and a comparison with objects lying near it. 

 These inferences are frequently deceptive. A mountain 

 which on account of its immense size stands out so clearly 

 seems for that reason to be very close, and many a deceived 

 tourist has walked miles to find that his mountain remained 

 about as far away as ever. A person unaccustomed to the 

 sea seems helpless in judging distance, and therefore size, 

 and the guesses made by a group of passengers on board of 

 an ocean steamer as to the distance and size of a certain 

 vessel on the horizon will sometimes vary from one mile to 

 twenty-five in the matter of distance, and from a small fish- 

 ing smack to an ocean steamer in size. 



Fig:. 188. OPTICAL ILLUSION OF LENGTH. 



A rather interesting deception occurs in connection with 

 the moon. The moon seems larger near the horizon than 

 near its zenith. Very frequently the comparison is made as 

 between a wagon wheel at the horizon and a cheese-box at 

 the zenith. This apparent change in the size of the moon 

 arises for two reasons. First, we imagine the moon to be 

 farther away when near the horizon that when directly 

 overhead. The globe of the heavens seems to us in fact, 

 a flattened inverted bowl. The moon, however, having the 

 same size at the horizon but being judged by us farther 

 away, we think it larger. It is like the boy in the fable 

 who projected a spider hanging from his hat rim against 

 the distant heavens, and imagined it therefore a spectre 

 reaching from the earth to the skies. The spider appeared 

 no larger than it really was, but under the belief that it 



