212 THE PRINCIPLES OF SCIENCE 



are determined to maintain. But of course all conservation laws do 

 not prove equally adequate. We fail to find conservation of volume, 

 or of motion as such, and even the conservation of mass and energy 

 is not now construed as it was a century ago. E^^en that foundation 

 of all consers^ation laws, the principle of continuity, is not left un- 

 altered by the discovery of quantum phenomena. 



Few, if any, substantive principles are "mere conventions." 

 Whether we suppose the earth moving or at rest is perhaps in part 

 a matter of convention for, as Galileo recognized, 



... all experiments that can be made upon the Earth are insufficient 

 means to conclude for its mobility but are indifferently applicable to 

 the Earth movable or immovable; . . . 



But long before the age of interplanetary rockets we had learned to 

 reject our earlier preference for a stationary earth; and Painleve 

 can, I think, insist with reason that: 



If it is a convention to say that the earth rotates, it is equally a con- 

 vention to say that it exists, and these two conventions are justified 

 by identical reasons. 



We distinguish between "primary" and "secondary" qualities, and 

 seek to explain the second in terms of the first. For example, imput- 

 ing only the first to hypothetical microcosmic particles, we hope to 

 find "emergent" the secondary qualities of ordinary bodies. Newton 

 thought the distinction of primary and secondary qualities of suffi- 

 cient importance to touch on it in his third Rule of Reasoning: 



The qualities of bodies which admit of neither intensification nor 

 remission of degrees, and which are found to belong to all bodies 

 within the reach of our experiments, are to be esteemed the universal 

 [and primary] qualities of all bodies whatsoever. 



Berkeley showed that this distinction, and others like it, fail of ade- 

 quacy, and Ayer comments that: 



The famous distinction which Locke drew between primary and sec- 

 ondary qualities is not a distinction between those perceived qualities 

 that are unaffected by the conditions of obsei-vation and those that are 

 affected. Since all are affected, there is no such distinction, as Berke- 

 ley realized. The primary qualities of the object, those that literally 

 characterize it, are, on this view, just those properties with which sci- 

 ence credits it. 



