Maech 20, 1896.] 



SCIENCE. 



427 



ground motion seems to be destroyed. 

 When the horse stands he seems to be at 

 rest ; when he moves motion seems to be 

 created ; and when he stops motion seems 

 to be destroyed. The ship is idle in the 

 harbor, and it seems to rest or to be with- 

 out motion ; the winds fill its sail, and it 

 seems that motion is created ; it is becalmed 

 at sea and the motion seems to be destroyed. 

 Without the consideration of other unseen 

 facts, rest seems to be a state without mo- 

 tion, and it appears that motion can be 

 created and destroyed. This is the illusion 

 to be dispelled. It is proposed to demon- 

 strate that acceleration in molar motion is 

 deflection of molecular motion, and in gen- 

 eral that acceleration in any body is deflec- 

 tion in the particles of the body. 



For this purpose it becomes necessary to 

 define what is here meant by the terms 

 body and particle. The universe is discov- 

 ered to be a hierarchy of bodies. The solar 

 system is a group of stars. When the solar 

 system is considered as a unity the parti- 

 cles of which it is composed are the stars, 

 but when one of these is studied as a unity 

 it is found to be composed of particles. 

 When any one of these particles is consid- 

 ered by itself it is a body. A molecule is a 

 body considered as a molecule, but it is 

 composed of many atoms, which are its par- 

 ticles. If, on the other hand, the atoms are 

 compound, then they are bodies. Thus it 

 is that a body is composed of particles, and 

 that which is a body or system in relation 

 to its component particles may be a particle 

 in relation to a body or system of a higher 

 order. It is in this sense that the term 

 must be understood when we affirm that 

 acceleration in a body or system is deflec- 

 tion of its particles. The ball in the hand 

 is not at rest, or without motion in its par- 

 ticles ; the horse has not more motion in its 

 particles when running than when stand- 

 ing ; the ship at anchor has motion still in 

 its particles. These propositions are aU 



simple and can be easily demonstrated, and 

 yet the illusion remains. These seeming 

 paradoxes are to be explained if we afiBrm 

 that motion cannot be created or destroyed. 



]ft has been demonstrated by science that 

 motion is persistent — cannot be created or 

 annihilated, and the demonstration has 

 been accepted by a great body of scientific 

 men. Antecedent to this demonstration 

 Newton had propounded three laws of mo- 

 tion, one of which is that action and reaction 

 are equal and in opposite directions. In 

 this axiom the persistence of motion or the 

 indestructibility of energy was implied, but 

 at first its full significance was not under- 

 stood, perhaps not even by I^ewton himself. 



In ' The Principia ' his first chapter is a 

 series of definitions, the third of which is 

 as follows : 



" The vis insita, or innate force of matter, 

 is a power or resisting by which every body, 

 as much as in it lies, endeavors to persevere 

 in its present state, whether it be of rest or 

 of moving uniformly forward in a right line. 



" This force is ever proportional to the 

 body whose force it is, and differs nothing 

 from the inactivity of the mass, but in our 

 manner of conceiving it. A body, from the 

 inactivity of matter, is not without difiQ- 

 culty put out of its state of rest or motion. 

 Upon which account this vis insita may, by 

 a most significant name, be called vis in- 

 ertiw, or force of inactivity. But a body 

 exerts this force only when another force 

 impressed upon it endeavors to change its 

 condition, and the exercise of this force 

 may be considered both as resistance and 

 impulse; it is resistance, in so far as the 

 body for maintaining its present state with- 

 stands the force impressed; it is impulse, 

 in so far as the body, by not easily giving 

 way to the impressed force of another, en- 

 deavors to change the state of that other. 

 Resistance is usually ascribed to bodies at 

 rest, and impulse to those iu motion; but 

 motion and rest as commonly conceived 



