MATTER 261 



geometrical ideals with certain relative positions, velocities, 

 and accelerations, the relationships of which are expressible 

 in certain simple laws termed the laws of motion (see the 

 following Chapter). If we choose to term the moving 

 things of the conceptual chart matter, there can be no 

 objection to the term, provided we carefully distinguish 

 this conceptual matter from any metaphysical ideas of 

 matter as the substratum of sense- impression, as that 

 which perceptually moves, as that which fills space, or as 

 that which can be defined as heavy, hard, and impene- 

 trable. Conceptual matter is thus merely a name for the 

 geometrical ideals endowed with certain correlated motions 

 by aid of which we describe the routine of our external 

 perceptions. It is in this sense that we shall use the term 

 matter for the remainder of this work, unless we are 

 expressly referring to the matter of the metaphysicians. 

 " Heavy " matter will be a name for the conceptual symbol 

 by which we represent what we have termed material 

 groups of sense-impressions united in single individuals, 

 while ether-matter will be a name for the symbol by which 

 we describe other phases of sense-impression, especially 

 the relationship in space and time of sense-impressions 

 belonging to different material groups. We shall not 

 project our conceptions into imperceptibles ^ in the field of 

 perception (!) — except in so far as it may be necessary in 

 order to criticise current physical notions. We shall try 

 and preserve throughout the standpoint that science is 

 description of perceptual experience by aid of conceptual 

 shorthand, the symbols of this shorthand being in general 

 ideal limits to perceptual processes, and as such having 

 no exact perceptual equivalents. 



The reduction of " matter to non-matter in motion," of 

 heavy-matter to ether-matter in motion, is so important as 



1 The reader may perhaps expect the words " unperceived things" rather 

 than " imperceptibles." But as every external perception is a group of sense- 

 impressions, and as our senses are limited, the atom, if a real phenomena, 

 could only appear sensible by colour, hardness, temperature, etc., the very 

 sense -impressions it is conceived to describe. Hence, if the ultimate 

 atom is to be 7iot these things but their source, it may be truly termed 

 itnperceptible. 



