WORLDS OF PHYSICS AND OF SENSE 123 



uous of philosophy, have been content to assume their 

 particles, points, and instants in practice, while conceding, 

 with ironical politeness, that their concepts laid no claim 

 to metaphysical validity. Metaphysicians, obsessed by 

 the idealistic opinion that only mind is real, and the 

 Parmenidean belief that the real is unchanging, repeated 

 one after another the supposed contradictions in the 

 notions of matter, space, and time, and therefore naturally 

 made no endeavour to invent a tenable theory of particles, 

 points, and instants. Psychologists, who have done in- 

 valuable work in bringing to light the chaotic nature of 

 the crude materials supplied by unmanipulated sensation, 

 have been ignorant of mathematics and modern logic, 

 and have therefore been content to say that matter, space, 

 and time are " intellectual constructions," without making 

 any attempt to show in detail either how the intellect 

 can construct them, or what secures the practical validity 

 which physics shows them to possess. Philosophers, it 

 is to be hoped, will come to recognise that they cannot 

 achieve any solid success in such problems without some 

 slight knowledge of logic, mathematics, and physics ; mean- 

 while, for want of students with the necessary equipment, 

 this vital problem remains unattempted and unknown. 



There are, it is true, two authors, both physicists, who 

 have done something, though not much, to bring about 

 a recognition of the problem as one demanding study. 

 These two authors are Poincare and Mach, Poincare 

 especially in his Science and Hypothesis^ Mach especially 

 in his Analysis of Sensations. Both of them, however, 

 admirable as their work is, seem to me to suffer from a 

 general philosophical bias. Poincare is Kantian, while 

 Mach is ultra-empiricist ; with Poincare almost all the 

 mathematical part of physics is merely conventional, while 

 with Mach the sensation as a mental event is identified 



