THE SUN'S DESTINATION. 193 



law itself in its most complete form. A heavenly body like the sun 

 is often said to govern the motions of its family of planets; but such 

 a statement is not strictly accurate. The governing body is no despot; 

 'tis an abject slave of law and order, as much as the tiniest of attendant 

 planets. The action of gravitation is mutual, and no cosmic body can 

 attract another without being itself in turn subject to that other's 

 gravitational action. If there were in our solar system but two bodies, 

 sun and planet, we should find each one pursuing a path in space under 

 the influence of the other's attraction. These two paths or orbits 

 would be oval, and if the sun and planet were equally massive, the 

 orbits would be exactly alike, both in shape and size. But if the sun 

 were far larger than the planet, the orbits would still be similar in 

 form, but the one traversed by the larger body would be small. For 

 it is not reasonable to expect a little planet to keep the big sun moving 

 with a velocity as great as that derived by itself from the attraction 

 of the larger orb. Whenever the preponderance of the larger body is 

 extremely great, its orbit will be correspondingly insignificant in size. 

 This is in fact the case with our own sun. So massive is it in com- 

 parison with the planets, that the orbit is too small to reveal its actual 

 existence without the aid of our most refined instruments. The path 

 traced out by the sun's center would not fill a space as large as the 

 sun's own bulk. Nevertheless, true orbital motion is there. 



So we may conclude that as a necessary consequence of the law of 

 gravitation every object within the solar system is in motion. To 

 say that planets revolve about the sun is to neglect as unimportant the 

 small orbit of the sun itself. This may be sufficiently accurate for 

 ordinary purposes; but it is unquestionably necessary to neglect no 

 factor, however small, if we propose to extend our reasoning to a con- 

 sideration of the stellar universe. For we shall then have to deal with 

 systems in which the planets are of a size comparable with the sun; 

 and in such systems all the orbits will also be of comparatively equal 

 importance. 



Mathematical analysis has derived another fact from discussion 

 of the law of gravitation which perhaps transcends in simple grandeur 

 everything we have as yet mentioned. It matters not how great may 

 be the number of massive orbs threading their countless interlacing 

 curved paths in space, there yet must be in every cosmic system one 

 single point immovable. This point is called the Center of Gravity. 

 If it should so happen that in the beginning of things, some particle 

 of matter were situated at this center, then would that atom ever 

 remain unmoved and imperturbable throughout all the successive 

 vicissitudes of cosmic evolution. It is doubtful whether the mind of 

 man can form a conception of anything grander than such an im- 

 movable atom within the mysterious intricacies of cosmic motion. 



