PHYSIOLOGICAL PARADOXES. 



It would involve too long a digression to go 

 fully into the explanation of this ; and it must 

 suffice for the present to say that the lines of 

 vision for equal spaces enclose smaller angles at 

 the eye when they are remote from it than when 

 they are near to it ; so that the distances 

 between parallel lines look smaller when far off 

 than when close to. 



This law of perspective, illustrated in avenues 

 of trees, long dock-sheds, pier-columns, em- 

 bankments, and numerous other objects, are 

 illustrated also by the clouds. The manner in 

 which clouds are formed frequently results in 

 their being ranged in lines. Even when these 

 lines, owing to their being parts of a cyclonic 

 or anticyclonic system, are in reality parts of 

 the circumferences of concentric circles, or 

 parts of diverging radii, the circles involved 

 are of such enormous size, and the portions of 

 cloud-lines under observation are relatively so 

 small, that they are indistinguishable from lines 

 which are truly straight and truly parallel. 

 So it is possible for a person, in very thick, foggy 

 weather, to follow the fence right round a cir- 

 cular racecourse, under the impression that he 

 has been walking in a straight line ; or for 

 two persons to move away from the fence in 

 lines at right angles to it and not far apart, 

 under the impression that these lines were 

 parallel, whereas they are really lines meeting 

 in the centre. 



240 



