and neutrons; and both the mass and the charge of all of these particles are each expressed by an extremely small but quite definite number. ‘The precision of this number increases with im- provements in the accuracy of methods of meas- urement, These minute numbers, the socalled universal constants, are in a sense the immutable building blocks of the edifice of theoretic physics. So now we must continue with the question: What is the real meaning of these constants? Are they, in the last analysis, inventions of the in- quiring mind of man, or do they possess a real meaning independent of human intelligence? The first of these two views is professed by the followers of Positivism, or at least by its most extreme partisans, Their theory is that physical science has no other foundation than the measure- ments on which its structure is erected, and that proposition in physics makes any sense only in- sofar as it cn be supported by measurements. But since every measurement presupposes an ob- server, from the positivistic viewpoint the real substance of a Jaw of physics can never be de- ‘ached from the observer, and it loses its meaning as soon as one attempts mentally to eliminate the