46 T HE YEAR. 



south, and about three or four more on the north side 

 of the equator than on the south, the point of greatest 

 solar action will again arrive at a point in the southern 

 tropic, or latitude 23 28', about six hours in time, or 

 ninety degrees in longitude westward of that at which 

 the year commenced. 



That the motion of this point of greatest solar action 

 is produced not by the motion of the sun, but by the 

 compound motion of the earth, the annual motion in 

 the orbit, and the daily one upon the axis, has not the 

 smallest difference in effect. A person who is cold and 

 wet will be warmed and dried as effectually, and just in 

 the same manner by turning round before the fire as if 

 he stood immoveable and the fire were carried round 

 him ; and, indeed, if there were no fixed object to 

 which he could refer, he would not be able to deter- 

 mine whether himself or the fire were moved, but would 

 remain in the same ignorance of his own motion as 

 many people do of the motions of the earth. The sen- 

 sible perception of a body in motion, is nothing more 

 than the application of different surfaces to the pap- 

 pillse of the fingers, or the shifting of a figure to diffe- 

 rent parts of the retina of the eye ; and when the visible 

 motion is uniform and rapid, we come to very erroneous 

 conclusions respecting the form of the moving body : 

 as a firebrand whirled round in the dark, exhibits lu- 

 minous curves, a falling rain-drop seems a beam or 

 pencil of water, a coach-wheel in rapid motion seems 

 a semi-transparent circle, in which the spokes merely 

 occasion a uniform cloudiness, and if a person wheel 

 rapidly round for some time, the motion is apparently 

 communicated to the surrounding objects, the centre 



