COLLIGATIVE RELATIONS AND SCIENTIFIC LAWS 129 



Of course the laws of geometric optics retain all their wonted use- 

 fulness throughout the domain in which they had earlier demon- 

 strated their efficiency. What we have discovered is simply when 

 and where not to apply them and, in Buhem's view, this is the kind 

 of discovery we must expect to make ultimately about any scientific 

 law. 



It is provisional because it represents the fact to which it applies with 

 an approximation that physicists today judge to be sufficient but will 

 some day cease to judge satisfactory. Such a law is always relative; 

 not because it is true for one physicist and false for another, but be- 

 cause the approximation it involves suffices for the use the first 

 physicist wishes to make of it and does not suffice for the use the sec- 

 ond wishes to make of it. 



After this we are forewarned not to use the law when we find our- 

 selves in the position of the second physicist, but we continue to use 

 it, as a limiting law, whenever we are in the position of the first. 



Dalton arrived at his law of partial pressures by way of a theory of 

 the nature of gases we wholly reject, but the law survives. Man-made 

 theories rise and fall; man-made concepts and their denotations prove 

 highly mutable. But colligative relations have generally an immor- 

 tality denied their conceptual formulations. How can tiiis be? Quite 

 simply! The "invention" of human theoreticians who may well be 

 wrong, once "discovered" the law exists independent of their wisdom 

 or folly. By virtue of the denotations attaching to the conceptual 

 terms in which it is formulated, the relation refers to observables that 

 do not change when we change our ideas. Even if a law is given a 

 new conceptual formulation, and new theoretic accommodation, 

 what has correctly been said about the relation of observables by the 

 older law must be said also by the newer. Thus, as Poincare remarks, 

 a law can survive as the imperishable memorial of a theory perhaps 

 long since passed away. 



At first glance it appears to us that theories last but a day and that 

 ruins heap up on ruins. . . . But there is something in them which 

 endures. If one of them has revealed to us a true relation, this relation 

 has been acquired for all time. We shall find it again under a new 

 cloak in the other theories which will reign successively in its place. 



The relation of metals. "Metals, however dissimilar in other re- 

 spects, are generally hard, dense, malleable, ductile, lustrous, in- 



