122 SCIENTIFIC METHOD IN PHILOSOPHY 



worlds are so correlated as to belong to one momentary 

 " state " of a thing, it would be natural to regard them as 

 simultaneous, and as thus affording a simple means of 

 correlating different private times. But this can only be 

 regarded as a first approximation. What we call one 

 sound will be heard sooner by people near the source of 

 the sound than by people further from it, and the same 

 applies, though in a less degree, to light. Thus two cor- 

 related appearances in different worlds are not necessarily 

 to be regarded as occurring at the same date in physical 

 time, though they will be parts of one momentary state 

 of a thing. The correlation of different private times is 

 regulated by the desire to secure the simplest possible 

 statement of the laws of physics, and thus raises rather 

 complicated technical problems ; but from the point of 

 view of philosophical theory, there is no very serious 

 difficulty of principle involved. 



The above brief outline must not be regarded as more 

 than tentative and suggestive. It is intended merely to 

 show the kind of way in which, given a world with the 

 kind of properties that psychologists find in the world 

 of sense, it may be possible, by means of purely logical 

 constructions, to make it amenable to mathematical treat- 

 ment by defining series or classes of sense-data which can 

 be called respectively particles, points, and instants. If 

 such constructions are possible, then mathematical physics 

 is applicable to the real world, in spite of the fact that 

 its particles, points, and instants are not to be found 

 among actually existing entities. 



The problem which the above considerations are in- 

 tended to elucidate is one whose importance and even 

 existence has been concealed by the unfortunate separa- 

 tion of different studies which prevails throughout the 

 civilised world. Physicists, ignorant and contempt- 



