562 REPORT— 1902. 



of different substances cannot^ strictly speakinf^, ever be equal, and can only be 

 styled so in the sense of being equivalent ; for were tbey equal in every way 

 the substances would obviously be the same. But this fact, if it ever strikes one, 

 Is ignored by universal custom, and quantities of substances, however unlike — 

 feathers, air, water, salt, and what not — are taken to be all equal, even by chemists 

 as by the world at large, if only they have the same weight, notwithstanding the 

 incongruities of the substances. I proceed now to show the baselessness of this 

 conviction, but only to bring out more strongly the claim of chemical activity to 

 equal rights with weight or mass in determining what are equal quantities of 

 substances, for I am aware that here I have nothing to tell you that you do not 

 already know. Weight being only the gravitational measure of mass, which 

 itself is independent of it, quantities of substances are held to be equal when their 

 masses are equal. Now, mass is quantity of matter. But what then is meant by 

 matter ? The answer must be either that it is a general term for any and all 

 substances, or else that it is the common basis of all substances, which presents 

 itself in all the different forms which are known to us as such, by virtue of a 

 corresponding variety in its intestinal motions. I gladly pass over the latter 

 answer without discussing it, on the ground that it introduces the subject of the 

 intimate constitution of substances, which it is my set purpose to keep independent 

 of in this discourse. I will only say of it that it would probably be the answer of 

 many physicists and chemists, and yet that it gives such a limitation to the nature 

 of matter as makes the common expression ' constitution of matter ' devoid of all 

 meaning. That expression means, and can only mean, the constitution of sub- 

 stances in common ; and this brings me to the first answer, that matter is the term 

 standing for all substances in common. Now, one thing which all substances 

 possess in common is the property of resisting pressures ; pressures not only of 

 moving bodies, but of the motions of the ether and electrons. Measured or 

 quantified, resistance becomes mass, all that can be signified by this term being 

 the quantity of the resistance or inertia a substance exhibits when tested. It is 

 the measure of a property of the substance, that is all ; and there is no other way 

 of quantifying a substance than through some one of its properties. No quantities 

 of different substances can, as such, be commensurable throughout ; and when 

 compared and measured through some common property, such as the possession of 

 mass, the equivalence or pseudo-equality found by this means is not the same as 

 that found when some other common property is taken as the means of measure- 

 ment. But experience has shown that though there are several rational and 

 comprehensive ways of instituting, through some common property, comparisons 

 between quantities of different substances, they all, with the exception of that of 

 weighing, agree more or less exactly in pointing to the same order of equivalence, 

 that of chemical activity ; for with this are colligated those of gaseous volume and 

 the other well-known physical activities, which give nearly the same quantities as 

 it gives of different substances as being molecularly equivalent. There are, 

 therefore, essentially only two measures of quantitative equivalency or pseudo- 

 equality between substances, the dynamical and the chemical or molecular, the 

 one wholly independent of and the other wholly dependent upon the particular 

 nature of the substances compared. The former is the measure of dynamical 

 phenomena, those of changes of bodies, due to their impacts and pressures, which 

 may lead to their deformation and disruption, but do not involve transformations 

 of the substances of the bodies into others ; the latter is the measure of chemical 

 phenomena, those of changes of bodies induced by such of their interactions as 

 do involve transformations of the substances of the interacting bodies into other 

 substances. Since it is already settled for us by custom that quantities of different 

 substances are to be called equal when or because they are equivalent gravimetri- 

 cally, and as it is not to be supposed that we shall ever give up calling 16 kilos, 

 of oxygen, of salt, of chalk, and of every other substance, however unlike, equal 

 quantities of them from the gravimetric point of view, we have no choice but also 

 to call molecular quantities of these substances equal from the chemical point of 

 view, if the claim to coordination in equality of chemical with gravimetric 

 equivalency is to be asserted and maintained. 



