August, 1912. 



KNOWLEDGE. 



effect upon inertia. This is the law of the conserva- 

 tion of inertia. 



This law is very frequently- termed the law of the 

 conservation of mass. It used to be known as the 

 law of the conservation or indestructibilitv of matter, 

 and this expression is still occasionally met with. 

 The first of these expressions is objectionable 

 because, although " mass " is generally used by 

 modern physicists in the sense of " inertia " as 

 defined above, at one time it was held to signify 

 the '■ quantity of matter in a body."' " Mass," 

 therefore, is an ambiguous term, and ought to be 

 avoided, since the word " inertia" accurately expresses 

 its modern connotation without ambiguity.* 



With the second of the above expressions we have 

 now to deal. The word " matter " is exceedingly 

 ambiguous. + Bv a certain school of metaphysicians, 

 who may be termed materialists, the word "matter" 

 is used to denote a hypothetical thing-in-itself, a 

 "substance" supposed to underlie all the phenomena 

 of the phvsical universe. This metaphysical use of 

 the word at once places it outside the domain of 

 pure science, since science is only concerned with 

 phenomena as such. ^ It is, of course, obvious that 

 the law of the conservation of inertia affords no 

 ground for asserting the indestructibility of matter 

 so defined. .According to the materialistic hypo- 

 thesis, matter is known to us not onl\- bv its inertia, 

 but by all those other phenomena w hich are termed 

 (in accordance with this hypothesis, and loosely by 

 those w ho do not hold it) "" properties of matter." 

 Surely, then, the " quantity of matter "" in a body is 

 not to be measured merelv bv the inertia of the 

 body, but rather bv the sum of all its " properties." 

 The argument that the " quantitv of matter" must 

 be measured only by the inertia, since all the other 

 " properties " of a closed material system are 

 variable, the inertia of such alone being constant, 

 is a flagrant petitio priiicipii, since it assumes the 

 very point at issue, namely, the indestructibility of 

 matter. Indeed, since materialistic pliilosophers 

 always postulate extension, or the projierty of 

 occupying space, as the most fundamental "pro[)erty 

 of matter," it would seem that the " quantity of 

 matter " in a body ought to be measured, if by 

 one "property" alone, by its volume: and the 

 volume of a body is by no means constant. The 

 volume of bodies, as is well known, can readily 

 be altered merely by the application of pressure 

 or by a change in temperature : moreover, the 

 volume of a reacting svstem is not usually constant 

 during a chemical change. 



B)- another, and less speculative, school of philo- 

 sophers the term " matter " is used merely to 

 connote the fact or, perhaps we should say, law that 

 certain phenomena (the so-called " properties of 

 matter") are always found grouped together so as to 



form a complex, which may be termed a " material 

 body " ; and it is now becoming more completely 

 realised that the term "matter" ought to be employed 

 in purely scientific writings only with some non- 

 metaphysical meaning such as this. If the term 

 is used in this sense, there is evidently no justi- 

 fication for supposing tha;t matter is indestructible 

 because inertia is conserved. For, thus employed, 

 "matter" stands for many phenomena, or "proper- 

 ties," or rather for the fact or law of their connec- 

 tion ; not merely for that particular phenomena 

 or property termed "inertia." 



No alleged scientific evidence has ever been 

 brought forward in favour of the doctrine of the 

 indestructibilit\' of matter, save the facts generalised 

 under the expression " the law of the conservation 

 of inertia." Now it is evident that these facts can 

 only be regarded as evidence of the truth of this 

 doctrine, if it can be proved that the matter of a 

 body (in whatever sense the word "matter" is used) 

 is identical with, or measured by, the inertia of the 

 body. Nothing, however, has ever been advanced 

 to prove this, and as must be evident from what has 

 been already said, it is most unlikely that any such 

 relation between matter and inertia holds good. 

 Moreover, if it were maintained that " matter " 

 ought to be defined as " inertia," the obvious reply 

 is that this would be contrar\-, not only to the 

 ordinar\- usage of the word, but also to its use by 

 philosophical writers generalh-. 



But to consider even unlikely possibilities, were it 

 proved that the inertia of a body does, in fact, 

 measure the " quantity of matter " it contains, or 

 were it generally agreed that the word " matter " 

 ought to be employed as synonymous with " inertia," 

 the case for the doctrine of the indestructibility of 

 matter would in no way be improved. For Professor 

 Sir J. J. Thomson has proved mathematically that 

 an electrically-charged particle in motion possesses 

 inertia in virtue of this motion, and that if its 

 velocity is sufficiently high, an increase in the velocity 

 produces a considerable increase in its inertia. 

 This has been experimentally verified by Kaufmann, 

 who measured the inertias and velocities of the 

 small particles emitted by the disruption of the atoms 

 of radium. He found that the greater the veloci- 

 ties of these particles the greater were their 

 inertias, the observed increment in every case 

 agreeing with that calculated according to Thomson's 

 reasoning. It is evident, therefore, that although 

 inertia is conserved during chemical action, the 

 inertia of an electrically-charged body may be 

 ahered by sufficiently accelerating it. If then, 

 " matter " is the same thing as inertia, or is measured 

 thereby, it is evident that matter may be created 

 by sufficiently accelerating such a body, or destroyed 

 bv retarding it. 



'■' For a further discussion of the ambiguity of tlie word " mass," and its bearing on the philosophical doctrine of materialism, 

 see the chapter " On the IndestructibiHty of Matter " in the present writer's " Matter, .Spirit, and the Cosmos " (Rider, lylO). 



t Compare Professor Ostwald's remarks on the use of the word " matter " in his "• The Fundamental Principles of Chemistry " 



(trans, by H. W. Morse, 1909), i? 7 and 10. 



