8 PRINCIPLES OF MOTION. 



material world as a metaphysical bundle of essential 

 properties, and nothing more has led some eminent 

 philosophers to struggle with the task of proving that 

 all the wonderful manifestations of the great physical 

 powers of the universe are but modifications of motion, 

 without the evidence of any antecedent force.* 



The views of metaphyscians regarding motion involve 

 many subtle considerations which need not at present 

 detain us. We can only consider motion as a change of 

 place in a given mass of matter. Now matter cannot 

 effect this of itself, no change of place being possible 

 without a mover ; and, consequently, motion cannot be 

 a property of matter, in the strict sense in which that 

 term should be accepted.f 



even as motionless with regard to each other; since the continual 

 variation of temperature to which all bodies are liable, and the 

 minute agitations arising from the motion of other bodies with 

 which they are connected, will always tend to produce some im- 

 perceptible changes in their distances." Lectures on Natural 

 Philosophy, fyc., by Thomas Young, M.D. Edited by the Rev. P. 

 Kelland. 1845. 



* " The position which I seek to establish in this essay is, that 

 the various imponderable agencies, or the affections of matter 

 which constitute the main objects of experimental physics, viz., 

 heat, light, electricity, magnetism, chemical affinity, and motion, 

 are all correlative, or have a reciprocal dependence ; that neither, 

 taken abstractedly, can be said to be the essential or proximate 

 cause of the others ; but that either may, as a force, produce, or be 

 convertible into, the other : thus heat may mediately or imme- 

 diately produce electricity, electricity may produce heat, and so of 

 the rest. . . . Although strongly inclined to believe that the 

 five other affections of matter, which I have above named, are, and 

 will ultimately be, resolved into modes of motion, it would be 

 going too far at present to assume their identity with it : I, there- 

 fore ase the term force, in reference to them, as meaning that 

 active force inseparable from matter, which induces its various 

 fhanges." On the Correlation of Physical Forces, by W. B. Grove, 

 Esq., M.A., F.E.S. 



f When discussing the hypothesis of Hobbes that no body can 

 possibly be moved but by a body contiguous and moved Boyle asks : 



