Unity of the General Forces of JVaiure. 315 



tions of the parts of space to one another as absolutely 

 adjacent, that which occupies one part of space may be 

 shifted to another; in other words, it possesses (2) mobility. 



II. Under the second aspect, as occupying space, matter 

 may be said to have (1) Divisibility ; (2) Magnitude ; (3) 

 Form; (4) iJltimate incompressibility , or the impossibility 

 of being compressed by pressure from an extended to an 

 absolutely unextended thing, from what is, to what is not, 

 extended. 



Now, when these general properties of matter are exam- 

 ined, it is at once seen that no one of them, except the last, 

 has any relation to force. Position, mobility, form, magni- 

 tude, these are not proj^erties of force, nor do they result 

 from force. They can all be conceived ideally. But 

 . incompressibility, however ultimate, has direct relation to a 

 resisting force in the body itself. The atom in the last 

 analysis is incompressible ; it cannot be so compressed that 

 it ceases to occupy space, and to repel other matter from the 

 space which it fills. So far as there are pores or vacuities 

 in any kind of matter, so far other matter may permeate 

 a given mass, as the air permeates cork, or as one gas 

 diffuses itself between the molecules of another. But the 

 atom is ultimately, incompressible, it resists all compression 

 which would destroy its integrity. It evermore asserts its 

 own existence, against every other particle with which it can 

 come into contact. 



In resisting compression, however, the atom manifests 

 Itself as possessing a true force ; for resistance to our own 

 voluntary motion is, in the last analysis, the only form in 

 which any force manifests itself to us. Gravitation we know 

 as a force, because it resists our own efforts to support a 

 falling body. It is through the same means that we come 

 to the knowledge of any other force. Cohesion is known to 

 us as a force, only by its resistance to our endeavor to sepa- 

 rate the parts of one united body, or mass. 



There is, then, in every atom of matter a resistance to 



