1809.] ■'-^ ' [Lowrie. 



curves in the outer half of each revolution, connected together by short 

 curves, some of them loops, in the inner half, and perform journeys im- 

 mensely greater in absolute space in one than in the other. Surely it is 

 impossible that these alternations of fast and slow motion can be account- 

 ed for by the single transient impulse given to each body at the start of 

 the system. Surely we are required to find some constant abiding or 

 constantly renewed force to account for such phenomena. What is it? 



Where shall we find the force that prevents the consolidation and cen- 

 tralization threatened by the force of attraction? Of course we must 

 find the answer in the phenomena of our solar system, that being the 

 only one of which observation gives us any competent knowledge. Phi- 

 losophy cannot go back to find it in the phenomena of creation, for tliat 

 is not phenomenon for us, and therefore that process must ever remain 

 transcendental to us, until we can witness it in some other system and 

 transfer it by analogy to our own; the only way in which we can know 

 anything of our own personal origin. 



All these regulated and phenomenally self-sustaining movements have 

 a sti'ong analogy to life, though we do not conceive of life as a mere 

 property or movement of matter in a system. Phenomenally and stati- 

 cally it is the normal interaction of all the jjarticles of a given system 

 that sustains and constitutes its life; though this definition cannot deter 

 us from our natural seeking after the dynamics of the system, the forces 

 and causes of this interaction. And so it is in our investigation of the 

 solar system. 



We have given to us, by observation of it, over one hundred cosmical 

 bodies, each revolving about some other, which is also moving, and each 

 having a force attractive of all others, and moving at such a distance and 

 with such velocity that it is neither drawn to nor driven from its central 

 body. We find therefore a permanent system of moving and attracting 

 bodies, and for convenience in the study of this fact, we analyse it into 

 two forces — bodies attracting and bodies moving, or, more simply into 

 attraction and motion; though in physics and apart from bodies, these 

 last are nothing but abstract ideas, being the mental instruments by 

 which we handle the actual and concrete forces — bodies moving and 

 attracting. 



We infer that the forces of attraction and of motion balance each 

 other so as to prevent both consolidation and dissolution; but neither, by 

 itself, can maintain the system. Without seeking after the origin of 

 these motions, it is enough for us, that, at any given instant of time, 

 they balanced the force of attraction. Then the question arises — how is 

 this system of motions maintained? Or more definitely thus — given a 

 satellite revolving round a planet, itself round another body and it round 

 another, how is the motion of the satellite maintained? What is there 

 in the forms and forces of this system that constantly restores the proper 

 degree of motion in the satellite amidst the retardations and accelera- 

 tions which we have discovered? 



The readiest illustration of the system is the motion produced when a 



