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SCIENCE. 



[N. S. Vol. III. No. 64. 



are only relatively distinguished, nor are 

 those bodies always truly at rest which commonly 

 are taken to be so." 



In the last sentence quoted it is apparent 

 that Newton himself was conscious of an 

 illusion in the common conception of the 

 term rest, and it is plain from his entire 

 discussion that his term inertia stood for 

 real force, although many scholars since 

 his time have denied this proposition. 

 Had Newton discovered the real nature 

 of what he called vis inertice ' The Prin- 

 eipia ' would have been simplified, as it has 

 been since his time, by definitions given to 

 momentum, energy, force and power. But 

 even these newer definitions can be revised 

 and the subject presented in a simpler man- 

 ner. The purpose in view in this chapter 

 is to re-define vis inertice, and to explain the 

 phenomenon of rest in molar bodies by 

 showing that it is not annihilation of mo- 

 tion, but change in the direction of motion, 

 and that the ordinary concept of rest in 

 molar bodies is an illusion, and that this 

 illusion has been carried into the realms of 

 molecular and stellar motions. 



Vis inertise or inertia is a component of 

 real force, inherent in every particle of 

 matter as speed of motion, which can be 

 changed in direction only through the agency 

 of collision. The explanation of Newton's 

 third law of motion in this manner changes 

 the ideas of motion as they have heretofore 

 existed in philosophy. Motion as speed is 

 inherent, and not something imposed from 

 without. If indeed, this be true, then 

 much reasoning in scientific circles must 

 be revised, for it has far-reaching results. 



The correlation of forces through the per- 

 sistence of motion or the persistence of en- 

 ergy is not universally accepted, but is 

 widely accepted, and it seems to be grow- 

 ing in favor by reason of its great simplic- 

 ity, and because it furnishes an explanation 

 of many facts and a conceivable explanation 

 for many more, but chiefly from the all-im- 



portant consideration, attested again and 

 again by observation, that motion is a real 

 cause or antecedent of force and that no 

 other cause is known. A second explana- 

 tion of force is never even propounded ex- 

 cept as a reification of abstractions inherited 

 from the age of metaphysics, and still found 

 as an atavism in science. 



In the consideration of motion it is ne- 

 cessary to consider the two elements, 

 namely, speed and direction, or path, for 

 each term posits the other. The persistence 

 of motion inheres in the element of speed. 

 While the body in motion must have a path 

 its direction is variable, i. e., not persistent 

 as a right line. It must therefore be un- 

 derstood that in speaking of the persistence 

 of motion it is the element of speed to 

 which reference is made. To afiirm that 

 motion is persistent is equivalent to the af- 

 firmation that speed is persistent, though 

 the path of motion may change. It is not 

 proposed here to discuss the conservation 

 of energy nor the kinetic hypothesis that 

 force is the collision of matter in motion, 

 but to assume these theories for the pur- 

 pose of exhibiting their logical conse- 

 quences. 



In every collision of one particle or body 

 with another there is a double correlative 

 involved. When A and B collide, A acts 

 on B and B on A, so that there is both ac- 

 tion and passion in A and B which are co- 

 existent. Then we have to consider A be- 

 fore the collision and A after the collision, 

 and B before the collision and B after the 

 collision. There is thus a double cause and 

 a double efiect which are sequent. The mat- 

 ter may be expressed in another way. A 

 and B cooperate in producing effects on 

 each other. In this cooperation action and 

 reaction are involved. The action is the 

 cause and the reaction is the effect. How is 

 the cause quantitatively related to the effect 

 and how is the efiect divided between them ? 

 It is proposed to prove that collision does 



