Chap. 7.] Why a long fir ah Wall appears curved. 245 



why, if we ftand on the fea-fliore, thofe parts of the 

 ocean which are at a great diftance appear elevated; 

 for the globular form of the earth is not perceptible to 

 the eye, and if it was, the apparent elevation of the fea 

 is far greater than the arch which a fegment of the 

 globe would form within any diftance that our eyes are 

 capable of reaching. 



For the fame reafon, if a number of objects are 

 placed on the fame plain and at {he fame height below 

 the eye, the more diftant will appear taller than the, 

 others ; and if the fame objects are placed on a fimilar 

 plain above the eye, the more diftant will appear the 

 loweft. 



The diftant parts of a long wall, for the fame rea- 

 fon, appear to a perfon who ftands near one end to 

 curve or incline towards him. In the fame manner the 

 high wall of a lofty tower, feems to a fpectator placed 

 directly under it to bend over him, and threaten him 

 with inftant deftruction. If any perfon inclined to 

 make the experiment, will lie down on his back in a 

 fituation of this defcription, at the diftance of five 

 or fix feet from the wall of which he contemplates 

 the tremendous height, he will immediately be made 

 fenfible of the phenomenon. 



If the diftance between two objects forms an infen- 

 fible angle, the objects, though in reality at fome dif- 

 tance from each other, will appear contiguous. This 

 is afligned by fome aftronomers, as the reafon why the 

 ring or belt of Saturn appears as one mafs of light, 

 while they contend that it is formed from a number ot 

 little ftars or fatellites ranged within a certain diftance 

 of each other. 



If the eye is carried along, as in a boat, without be- 

 ing fenfible of its own motion, the objects which arc 

 ilationary on each fide, will appear to move in a con- 

 R 3 trary 



