258 



Essay on Motion and Force. 



confessedly something which our senses perceive, and that 

 something, which is what I mean by matter y moves. I have 

 no desire to step over the strict line of demarkation which 

 seperates the physical from the metaphysical. I have no 

 wish to follow in the track of those, who, standing upon 

 the verge of the precipice which limits human under- 

 standing, and reaching out arms into the unfathomable 

 darkness, have mostly toppled into the abyss of hopeless 

 bewilderment. I shall therefore avoid the discussion of 

 all metaphysical questions, and confine myself strictly to 

 physical phenomena and theories based upon them. 

 I shall also assume the atomic and molecular condition 

 of matter, since whether the truth of the atomic theory, 

 strongly questioned by Grove and others, be admitted 

 or not, it will not effect the doctrines I shall support in 

 this paper, and these terms, in the absence of better 

 terminology, afford a convenient mode of expression. 



I shall divide motion into two general classes. Atomic 

 motion, or motion of ultimate particles, and aggregate motion, 

 or motion of matter in masses ; and make here this first 

 proposition. All change which matter undergoes is motion, and 

 conversely all motion is change. 



I use the word change in the sense of passing from one 

 state to form another, or from one position to another, and 

 not in the sense of the variation of form, quality, or 

 essence, which a body has sustained by previous motions, 

 and which characteristic properties it possesses as a result 

 of those motions ; although if the atomic theory should 

 ever be satisfactorily proven, it will doubtless be discovered 

 that even in the latter meaning of the word, change is 

 motion and motion is change. 



Molecules, if there be molecules, are of course matter 

 in a condition of aggregation, although perhaps not tech- 

 nically so considered ; but as it is necessary to distinguish 

 molecular motion, from the motion of bodies which are 

 sufficiently large to be sensible, I shall further divide 

 aggregate motion into molecular motion, and aggerose 



