APPARENT AND REAL MOTIONS. 4y 



of gravity lost command of, and the person tumbles to 

 the ground. 



Although, therefore, a knowledge of the real motions 

 of the earth be absolutely necessary, in order to under- 

 stand the solar system, to form anything like an ade- 

 quate notion of the stupendous universe of which that 

 system forms a part but, in reference to the whole of 

 it, it is but a mere spot, less in comparison than the 

 most tiny moth, that the microscope can discover, is, 

 compared with the mass of the earth ; and although the 

 laws that were revealed by the discovery of their real 

 motions, are found to be the laws of all matter down 

 to its smallest fragment ; yet, as the influence which 

 the sun has upon the earth, as a source of light and 

 heat, and of all the seasonal changes and their pro- 

 ductions that thence result, is not an action of ponder- 

 able matter, but in fact an action counteractive of gra- 

 vitation, it is of very little consequence, in considering 

 the seasonal influence of the sun, whether we refer the 

 motion, to that of the earth as real, or to that of the 

 sun as apparent. 



The sun is in succession over all the points in the 

 365J curves, that have been noticed as extending from 

 tropic to tropic, in the course of the year; and as one 

 half of these are made from south declining to north, 

 and the other from north declining to south, it follows 

 that to all places within or between the tropics, the sun 

 will be twice vertical in the course of the year ; that, at 

 the equator, those days of the vertical sun will be the 

 winter and the summer half year distant from each 

 other, or that the interval between them from March 

 to September will be three or four days longer than 



