IV.] PRIMARY FORCES. 45 



as part of its original constitution, not only the capacity 

 of being acted on by force, but the power to exert force on 

 otlier matter. 



But tlie progress of science has not only made it certain Matter .^^^ 

 that matter lias active dynamical properties as well as ™^^g ^^^ 

 passive ones ; it has made it doubtful whether matter has dyuamical 

 any other than dynamical properties. 



It used to be said that matter was extended and im- 

 penetrable. But what we have learned of general and 

 chemical dynamics makes it possible, and perhaps pro- 

 bable, that matter, in its ultimate constitution, is not 

 extended; for it is as likely a supposition as any other, May nofbe 

 that the ultimate molecules of matter are mere points, extended, 

 having position and mobility, but no magnitude or ex- 

 tension ; which points, however, are the centres of various 

 kinds of attractive forces by which they act on other 

 molecules, and are also endowed with the passive capacity 

 of being acted on by similar forces proceeding from those 

 others. If this is true, it follows also that matter, in its 

 ultimate constitution, is not impenetrable. " The impene- and not 

 trability of matter" means that two portions of matter ^^ble^ 

 cannot occupy the same space. But the facts of chemical 

 combination appear to contradict this ; for in many cases 

 the compound occupies less space than the sum of the 

 spaces occupied by its constituents before combination 

 (in the case of watery vapour, for instance, only two- 

 thirds) ; and the most obvious interpretation of such facts 

 is, that the ultimate atoms of the two constituents coalesce, 

 and occupy the same point in space. On this supposition, 

 the atom of water, for instance, consists of an atom of 

 hydrogen and one of oxygen, which have coalesced and 

 come to occupy the same point.^ 



I do not say that this theory of the nature of matter 

 is true : I say it is possible ; and that we consequently 



1 On this subject of the constitution of matter, see Faraday's Essays on 

 Physics, in which he has revived Boscovich's theory of matter, according 

 to whiph matter consists of mere mathematical points, which are centres 

 of various kinds of force ; and applied it to chemical facts that were 

 unknown to Boscovich. 



