Conservation of Matter 27 



be truly said that if any difference were 

 discovered it would not be expressed by 

 saying that the amount of matter was 

 different, but simply that " weight " was 

 not so fundamental and inalienable a pro- 

 perty of matter as has been sometimes 

 assumed ; in which case it is clear that 

 there must be a more fundamental property 

 to which appeal can be made in favour of 

 constancy or persistency or conservation. 

 Now the most fundamental property of 

 matter known is undoubtedly ' inertia' ; and 

 the law of conservation would therefore 

 come to mean that the inertia of matter 

 was constant, no matter what changes it 

 underwent. But, then, inertia is not an 

 easy property to measure, very difficult 

 to measure with great accuracy : it is in 

 practice nearly always inferred from weight ; 

 and in terms of inertia the law of conserva- 

 tion of matter cannot be considered really 

 an experimental fact ; it is, strictly speaking, 

 a reasonable hypothesis, an empirical law, 

 which we have never seen any reason to 



