Makch 20, 1896.] 



SCIENCE. 



431 



to explain. Let us once more consider 

 what has been said. The atoms of the ball, 

 when all their motions are analyzed and 

 summed, prove to have enormous velocities 

 in enormously composite paths compared 

 with which the molar motion of the ball on 

 the floor sinks into insignificance. 



Every particle in the wooden ball rolling 

 on the floor has telluric motion, molecular 

 motion and molar motion. Consider one of 

 these particles moving with the three kinds of 

 motion, and we realize that its speed is very 

 great and that the path which it traverses 

 is greatly composite. If such a particle 

 had its composite path straightened into a 

 right-line path it would at once pass out of 

 the sphere of the solar system into a region 

 beyond, from whatever point within the 

 system it might start, and in whatever 

 direction the right-line path extended. 

 But the molecule remains within the solar 

 system because its stellar motion is com- 

 posite; and it remains within the ball be- 

 cause its molar motion is composite ; and it 

 remains within the molecule because its 

 molecular motion is complete. 



When the ball was started molar motion 

 began and when it stopped that molar mo- 

 tion ended. But we do not suppose that it 

 came out for nothing and vanished into 

 nothing ; we resort to preexisting molec- 

 ular motion to explain it ; we say that the 

 molar motion was derived from the molec- 

 ular motion of the hand that set the ball 

 rolling and that it was transformed into 

 m.olecular motion in the wall which de- 

 stroyed the molar motion. In making this 

 explanation we assume that motion as speed 

 went out of the hand into the ball and then 

 out of the ball into the wall. Is this true? 

 Was the velocity of the molecular motion 

 in the hand diminished and the velocity of 

 the molecular motion in the wall increased ? 

 If so, action and reaction are not equal ex- 

 cept in the sense that what is lost by one 

 is gained by the other. 



Did motion go out of the hand into the 

 ball, or was the direction of motion existing 

 in the ball changed ? Did motion go out of 

 the ball into the wall, or was the direction 

 of motion existing in the wall changed ? If 

 the law of action and reaction is valid, 

 when the change was made upon the ball 

 by the hand, an equal change was made 

 upon the hand by the ball. Neither of 

 them lost velocity by the changed form, or 

 one lost what the other gained. All of 

 Newton's reasoning on this subject proceeds 

 upon the assumption that the speed of each 

 is unchanged, but that the direction of each 

 is changed and that this deflection is equal 

 in the case now considered. When the 

 ball struck the wall neither ball nor wall 

 lost motion, but the molecular paths were 

 changed by collision. The form or mode of 

 direction of motion was affected, the quan- 

 tity of motion as speed was unaffected, if 

 we follow Newton's reasoning. But there 

 was a change in the hand, in the ball, and 

 in the wall. In what did that change con- 

 sist? We know that in part at least it 

 consisted in a change of paths. The mo- 

 lecular motions in the hand must have had 

 their directions changed ; the molecular 

 motions in the ball must have had their 

 directions changed ; in like manner the 

 molecular motions of the wall were changed 

 in direction. This we know; in every col- 

 lision there is a change of direction in the 

 motion of the particles constituting the 

 bodies colliding. Is this change of direc- 

 tion all? Or is there a transference of 

 speed so that one loses while another gains ? 

 The whole problem is narrowed to this is- 

 sue — that which we call acceleration is 

 wholly deflection or in part deflection and 

 in part loss and gain— loss of speed by one 

 and gain by another, and if there is any 

 loss and gain then action and reaction are 

 not equal, as Newton's law affirms. 



There is still another set of relations 

 which must be considered. A body is con- 



