NATURAL THEOLOGY. 35 



given. Now, we are able to demonstrate of our 

 law of attraction, what can be demonstrated of 

 no other, and what qualifies the dangers which 

 arise from cross but unavoidable influences ; that 

 the action of the parts of our system upon one 

 another, will not cause permanently increasing 

 irregularities, but merely periodical or vibratory 

 ones ; that is, they will come to a limit, and then 

 go back again. This we can demonstrate only of 

 a system, in which the following properties con- 

 cur, viz. that the force shall be inversely as the 

 square of the distance ; the masses of the revolv- 

 ing bodies small, compared with that of the body 

 at the centre ; the orbits not much inclined to one 

 another ; and their eccentricity little. In such a 

 system, the grand points are secure. The mean 

 distances and periodic times, upon which depend 

 our temperature, and the regularity of our year, 

 are constant. The eccentricities, it is true, will 

 still vary ; but so slowly, and to so small an ex- 

 tent, as to produce no inconveniency from fluctua- 

 tion of temperature and season. The same as to 

 the obliquity of the planes of the orbits. For in- 

 stance, the inclination of the ecliptic to the equa- 

 tor will never change above two degrees, (out of 



