THE DIRECTION OF MOTION. 233 



selves one ultimate unit of matter as drawing another while 

 resisting it. 



Nevertheless, this last belief is one which we are com- 

 pelled to entertain. Matter cannot be conceived except as 

 manifesting forces of attraction and repulsion. Body is dis- 

 tinguished in our consciousness from Space, by its opposition 

 to our muscular energies; and this opposition we feel under 

 the twofold form of a cohesion that hinders our efforts to 

 rend, and a resistance that hinders our efforts to compress. 

 Without resistance there can be merely empty extension. 

 Without cohesion there can be no resistance. Probably this 

 conception of antagonistic forces, is originally derived from 

 the antagonism of onr flexor and extensor muscles. But be 

 this as it may, we are obliged to think of all objects as made 

 up of parts that attract and repel each other; since this is the 

 form of our experience of all objects. 



By a higher abstraction results the conception of attrac- 

 tive and repulsive forces pervading space. We cannot dis- 

 sociate force from occupied extension, or occupied extension 

 from force ; because we have never an immediate conscious- 

 ness of either in the absence of the other. Nevertheless, we 

 have abundant proof that force is exercised through what 

 appears to our senses a vacuity. Mentally to represent this 

 exercise, we are hence obliged to fill the apparent vacuity 

 with a species of matter — an etherial medium. The consti- 

 tution we assign to this etherial medium, however, like the 

 constitution we assign to solid substance, is necessarily an 

 abstract of the impressions received from tangible bodies. 

 The opposition to pressure which a tangible body offers to us, 

 is not shown in one direction only, but in all directions ; and 

 so likewise is its tenacity. Suppose countless lines radiating 

 from its centre on every side, and it resists along each of 

 these lines and coheres along each of these lines. Hence the 

 constitution of those ultimate units through the instrumen- 

 tality of which phenomena are interpreted. Be they atoms 

 of ponderable matter or molecules of ether, the properties 

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