Notices respecting Xew Books. 391 



metaphysics in Professor Whitehead's meaning of: the term. Eor 

 according to Einstein, not only is it impossible to denote any reality 

 save in the terms of some observer's observation, but also when 

 you abstract from the observer and his system of reference there 

 is nothing to denote. If there be, what is it ? Shall we say, for 

 example, that colour is sense-awareness and relative to the 

 observer, while the conceptual entity, the light waves of a certain 

 amplitude and frequency, is not relative ? We are at once 

 brought to book by the fact that the essential character of this 

 entity is its dimensions, and dimensions depend on the relative 

 movement of systems of reference and vary with their acceleration. 

 If it is not the dimensions what is it that is absolute in this 

 entity ? Ton find you must answer and you can give no definite 

 answer. You fall back on the indefinite something or other I 

 know not what. Einstein says there is nothing. 



I find in Professor Whitehead's discussion of the theory he 

 accepts, namely, that space-time is four-dimensional, a great deal 

 that puzzles me and even seems at times incongruous. It suggests 

 to me that he is putting new wine into old bottles. A four- 

 dimensional space-time is the groundwork of his concept of nature. 

 Yet he is continually talking about " instantaneous space " "time- 

 less spaces " " time systems,"' these last being apparently inter- 

 changeable without affecting the space. It leaves me wondering 

 whether his four dimensions mean anything more than that time 

 and space are never dissociated. I will give an actual illustration. 

 On p. 97 he says " the meaniug of saying that Cambridge in the 

 appropriate instantaneous space at 10 o'clock this morning for 

 that instant is 52 miles from London at 11 o'clock this morning 

 in the appropriate instantaneous space for that instant beats me 

 entirely." A little further on, after discussing the boundaries of 

 events, he says (p. 100) "Thus the boundary of a duration consists 

 of two momentary three-dimensional spaces." Now have we not 

 here precisely the difference between Professor Whitehead and 

 Einstein ? It could hardly be more complete. For Einstein there 

 is no appropriate instantaneous space for any moment, and no 

 momentary three-dimensional space boundary of any duration. 

 Time and space are solidary. The only meaning you can give to 

 the statement that 52 miles in space separate Cambridge from 

 London is that the train journey occupies an hour, the light 

 journey (if you are in a position to see London from Cambridge) 

 an infinitesimal fraction of a second. In fact I find in this 

 example the essential meaning of Einstein. Reduce the time 

 interval to zero and there is nothing, not only no time but also 

 no space. 



I will conclude with one word concerning the relation of meta- 

 physics to physical science. Probably I have already given 

 myself away and shown that I come under Professor Whitehead's 

 censure as one who confuses the problem of the thing perceived 

 with the problem of the perceiver. The philosophy of science 



