258 THE GRAMMAR OF SCIENCE 



S 7. — Hardness not Characteristic of Matter 



It remains for us now to deal with the other character- 

 istic, hardness, which is popularly attributed to matter. 

 There are certain persons who are content, when men's 

 ignorance as to the nature of matter is suggested to them, 

 to remark that one has only to knock one's head against a 

 stone wall in order to have a valid demonstration of the 

 existence and the nature of matter. Now if this state- 

 ment be of any value, it can only mean that the sense- 

 impression of hardness is the essential test of the presence 

 of matter in these persons' opinion. But none of us doubt 

 the existence of the sense-impression hardness associated 

 with other sense-impressions in certain permanent groups ; 

 we have been aware of it from childhood's days, and do 

 not require its existence to be experimentally demon- 

 strated now. It is one of those muscular sense-impressions 

 which we shall see are conceived by science to be 

 describable in terms of the relative acceleration of certain 

 parts of our body and of external bodies. But it is 

 difficult to grasp how the sense-impression of hardness 

 can tell us more of the nature of matter than the sense- 

 impression of softness might be supposed to do. There 

 are clearly many things which are popularly termed 

 matter and are certainly not hard. Further, there are 

 things which satisfy the definitions of matter as that 

 which moves or as that which fills space, but which are 

 very far indeed from producing any sense-impression of 

 the nature of hardness or softness ; nor would they even 

 satisfy our definition if we said that matter is that which 

 is heavy, heaviness being certainly a more widely-spread 

 factor of material groups of sense-impressions than hard- 

 ness. Between the sun and planets, between the atoms 

 of bodies, physicists conceive the ether to exist, a medium 

 whose vibrations constitute the channel by means of which 

 electro -magnetic and optical energy is transferred from 

 one body to another. In the first place, the ether is a 

 pure conception by aid of which we correlate in conceptual 

 space various motions. These motions are the symbols 



