ch. i.] THE RELATIVITY OF KNOWLEDGE. 5 



and a left side, or if spherical, must have a periphery that is 

 conceived as covering some assignable area. Now by no effort 

 of our intelligence can we imagine sides so close together 

 that no plane of cleavage can pass between them ; nor can 

 we imagine a sphere so minute that it cannot be conceived as 

 divisible into hemispheres ; nor can we imagine a cohesive 

 tenacity so great that it might not be overcome by some still 

 greater disruptive force such as we can equally well imagine. 



When we contemplate the mode in which one particle of 

 matter acts upon the adjacent particles by attractive and 

 repulsive forces, we find ourselves equally puzzled. As Mr. 

 Spencer well observes, " matter cannot be conceived except 

 as manifesting forces of attraction and repulsion. Body is 

 distinguished in our consciousness from space, by its opposi- 

 tion 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. Thus 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. Nevertheless, however verbally 

 intelligible may be the proposition that pressure and tension 

 everywhere co-exist, yet we cannot truly represent to ourselves 

 one ultimate unit of matter as drawing another while re- 

 sisting it." 



Nor is this the last of the difficulties which encumber 

 our hypothesis of mutually-attracting and repelling particles 

 separated by tracts of unoccupied space. For this hypothesis 

 requires us to conceive one particle acting upon another 

 through a space that is utterly empty ; and we can in no 

 wise conceive any such action ? How shall we escape this 

 difficulty ? Shall we assume that the intervals between 

 the particles are filled by a fluid of excessive tenuity, like 

 the so-called imponderable ether to which physicists are in 



