40 SECTIONAL ADDRESSES 



world in which exact measurements may be made and events correctly 

 predicted. He assumes, in fact, in its broad outlines, the thesis of the 

 Grammar of Science. He thus retains the principle of causality, as 

 defined above, in the happenings of the conceptual world, remarking that 

 the relation between events in the perceptual and conceptual worlds is 

 subject to a slight inaccuracy. 



The introduction of Heisenberg's uncertainty principle necessitates a 

 corresponding process in dealing with perceptual problems from the 

 point of view of quantum physics. A conceptual world of quantum 

 physics is framed in which a strict determinism reigns. True, the world 

 has not so many points of resemblance to the perceptual world as had 

 the older schemes — billiard-ball and solar-system atoms have disappeared, 

 and the wave-function, which does not refer to ordinary space, is not so 

 easily interpreted in terms of the world of sense. But the philosophical 

 problem of the transfer is the same. 



Whatever the form of the picture the hard-pressed physicist of to-day 

 remains on firm ground if he refuses to confuse the concept — the world- 

 picture — with the percept ; if, making this distinction, he studies the 

 question of the reality underlying phenomena as philosopher rather than 

 as physicist ; if he is as ready to discard outworn models as ever Maxwell 

 was. 



There is no finality in these matters, and solutions of these difficulties 

 are solutions for a day ; but it is interesting and heartening to know that 

 Planck, the initiator of the movement which has revolutionised physical 

 thought, has, a generation later, pointed a way to a resolution of the funda- 

 mental doubts and difficulties which his genius has raised. 



It must not be assumed that the discussion of uncertainty has passed 

 beyond the region of fundamental criticism. In two recent papers in the 

 Philosophical Magazine, Dr. Japolsky has developed a theory of elementary 

 particles — electrons, protons, positrons, and so forth — which are con- 

 sidered as systems of Maxwellian electromagnetic waves. On this basis, 

 using classical electrodynamics, he develops the usual quantum and 

 relativity relations, including the de Broglie equation. The interaction 

 of the particles follows the inverse square law (breaking down at small 

 distances), and demands a mass-ratio between proton and electron which 

 happens to be that deduced from experiment. 



It is impossible to conclude a sketch of the trend of modern physics 

 without touching upon the remarkable advances made in large-scale and 

 applied physics ; equally impossible is it to do more than mention a 

 selection from such topics. The flotation process for the separation of 

 minerals may be instanced as one, now of large-scale importance, which 

 depends on a knowledge of physical quantities of very academic interest. 

 In the practice of this process the powdered ore is churned in water 

 which contains some substance capable of producing a stable froth. 

 The mineral which it is desired to concentrate must cling to the surface 

 and so remain in the froth, the gangue sinking to the bottom, and a reagent 

 must be added whose action will ensure this. Obviously some very nice 

 physical and physico-chemical problems are involved. In particular, a 



