452 



THE EARTH. 



ance that are observed, and it has been demonstrated accordingly to be the 

 true one. 



On examining the change of the apparent diameter of the sun, it is found 

 that it is least on the 1st of July, and greatest on the 31st of December ; that 

 from December to July, it regularly decreases ; and from July to December, it 

 regularly increases. By observing the rate of its variation through these inter- 

 vals, it will be found that the path of the earth around the sun is an ellipse, 

 having the sun in one of the fuci. 



In the annexed figure, 5, if S represent the place of the sun, A will represent 

 that of the earth when at that place called perihelion, or that point where it is 

 nearest the sun ; and B its position at aphelion, or the point where it is most 

 distant from the sun. The elliptic path of the earth is represented by the figure 

 A D B O ; C being its centre, and S its focus. 



Fig. 5. 





It is proper to observe here that the earth's orbit departs infinitely less from the 

 circular shape than the oval exhibited in the annexed diagram. In fact, the real 

 figure of the orbit of the earth is so slightly oval, and so little different from a 

 circle, that if it were delineated on paper in its true proportions, the eye conld 

 not discover its difference from a circle ; actual instrumental measure alone 

 could detect it. If the greatest distance of the earth from the sun were ex- 

 pressed by 1,000, its least distance would be expressed by 983. 



It i& worthy of observation that the earth is most remote from the sun at 

 midsummer, and nearest to it at midwinter. 



It was not until the date of the revival of letters that the annual motion of 

 ^ the earth was admitted. The apparent stability of our globe was, until that 

 epoch, generally maintained ; and even now, when so universal is the assent 

 .jriVen to this fundamental principle of astronomy, it may still perhaps be useful 

 briefly to state the leading arguments by which it is established. 



When the sun is observed in the firmament, it appears to move among the 

 siurs from west to east, following a course in the heavens which has been called 

 the KC.UPTIC ; and at the end of a year its centre returns, after a complete cir- 

 cuit of the heavens, to the point from which it set out. This is an effect which 

 uo'ild lie produced by a reai motion of the sun round the earth in a year. Bv 



