MOTION, FORCE, MATTER 343 



manded, as has been seen, by the necessity for finding a 

 method of measuring the latter. Mass as a property of 

 particles is preferable to weight, since this varies from point 

 to point on the earth's surface and limits the generality of 

 one's system of mechanics. Mass is the one property of 

 particles which is preserved throughout mechanical trans- 

 formations, hence it becomes their identifying feature. From 

 this point of view matter is commonly defined in science as 

 that which exhibits mass. 



By means of some such postulate scheme as this, the 

 scientific notion of matter receives definition. It is to be 

 noted that all of its properties are expressible in terms of 

 numbers which are obtainable through the medium of clocks, 

 meter rods, and coordinate systems. Time, space, and mass 

 are, in fact, the three basic quantitative notions in physics. 

 Together they define matter, and in various combinations 

 afford the foundation for all other physical measurements. 

 It should be noted, further, that the scientific conception of 

 matter involves no reference to the so-called secondary 

 qualities; particles do not exhibit heat, color, sound, taste, or 

 odor. These are not features in which things act as though 

 they were located at points ; on the contrary they are proper- 

 ties known to be related to qualitatively distinct parts of 

 things, e.g., molecules, atoms, electrons, and neutrons, etc. 

 They are therefore to be accounted for in terms of hypotheses 

 of matter, not in terms of idealized constructions. 



matter: operational derivation 



As in the case of force, matter functions in science only as 

 measured matter. The operational transformation of the 

 empirical concept of matter therefore consists in the introduc- 

 tion of the refinements which are necessary in order to permit 

 the basic properties of matter to be measured. These funda- 

 mental qualities are of three kinds: space, time, and force. 

 Hence the operational route from empirical matter to 

 scientific matter involves the passage from empirical space 

 to geometrical space, from empirical time to scientific time, 



