284 THE GRAMMAR OF SCIENCE 



when applied to particles are confirmed by our perceptual 

 experience of bodies. Ought we to assert that these laws 

 hold in their entirety for all the downward scale from 

 particle to ether-element ? Shall we find our conceptual 

 description of the universe simplified, or the reverse, by 

 supposing complete mechanism to extend from particle to 

 ether-element? Or will it be more advantageous to 

 postulate that mechanism in whole or part flows from the 

 ascending complexity of our structures, that the ether- 

 element is largely the source of mechanism, but is not 

 completely mechanical^ in the sense of obeying the laws 

 of motion as given in dynamical text-books ? The question 

 is undoubtedly an important one, but one which cannot be 

 answered off-hand. Nor, indeed, till we have much clearer 

 conceptions of the structure of the prime-atom than we 

 have at present reached, will it be possible to say how 

 far the mechanism we postulate of particles may be 

 conceived to flow from its structure. 



In order to remind the reader that the general laws of 

 motion we are about to discuss may either entirely or 

 only in part hold for the whole series of physical concepts 

 from particle to ether-element, we will class the whole 

 series together as corpuscles, a word simply signifying 

 little elementary bodies. We shall then have to ask in 

 each case to which of the ideal corpuscles we are to 

 suppose our laws to apply. The test will always be the 

 same, namely : How far is the assumption necessary in 

 order to obtain a model which will enable us to describe 

 briefly the routine of perception ? 



^ 3. — The First Law of Motion 



Let us now return to our conception of the universe 

 as the regulated dance of the elemental groups which we 

 have termed prime-atoms, chemical atoms, molecules, and 

 particles. Individual corpuscles dance in groups, groups 



1 For example, as will be shown in the sequel, the "mass" of a particle 

 must be considered as in all probability very different from the "mass" of 

 an ether-element (see § 1 1 of this chapter). 



