36 



NATURAL THEOLOGY. 



ninety,) and that will require many thousand years 

 in performing." 



" This cut represents the oval A B, nearly circular, in which 

 the Earth moves round the Sun O in one of the foci — while 

 the Moon, E, moves round the Earth in a similar curve, E F. 

 These curves vary, (a? do the paths of all the planets and their 

 satellites, becoming more and more bulged, till they bulge out by 

 a certain quantity, GD, so as to be AGB, and then the curve they 

 describe flattens constantly, till it becomes ADB, but never more, 

 in consequence of the four circumstances mentioned in the text. 



The celebrated proposition of Laplace, respecting the eccentri- 

 cities of the planetary orbits, and their deviation from a nearly cir- 

 cular form, — that upon which the stabihty of the system mainly 

 rests, — may be comprehended by this illustration. Suppose 

 three vessels of different burthen sail from one port to another, and 

 take such courses, that, multiplying the tonnage of each by the 

 square of the deviation in miles which it makes from the straight 

 line, or shortest distance, between the two ports, and adding the 

 three products together, the sum is at every instant of the voyage 

 the same, — say 90 — the vessels being of 10, 22 J and 90 ton* 

 burthens, respectively. It is clear that none of them can ever dc- 



