ASTRONOMER ROYAL'S TIME 37 



space must be of entirely different nature. They cannot 

 possibly be mixed up." The Astronomer Royal com- 

 placently retorts, "It is not impossible. / have mixed 

 them up." Well, that settles it. If the Astronomer 

 Royal has mixed them, then his mixture will be the 

 groundwork of present-day physics. 



We have to distinguish two questions which are not 

 necessarily identical. First, what is the true nature of 

 time? Second, what is the nature of that quantity which 

 has under the name of time become a fundamental part 

 of the structure of classical physics? By long history 

 of experiment and theory the results of physical inves- 

 tigation have been woven into a scheme which has on 

 the whole proved wonderfully successful. Time — the 

 Astronomer Royal's time — has its importance from the 

 fact that it is a constituent of that scheme, the binding 

 material or mortar of it. That importance is not les- 

 sened if it should prove to be only imperfectly repre- 

 sentative of the time familiar to our consciousness. We 

 therefore give priority to the second question. 



But I may add that Einstein's theory, having cleared 

 up the second question, having found that physical 

 time is incongruously mixed with space, is able to pass 

 on to the first question. There is a quantity, unrecog- 

 nised in pre-relativity physics, which more directly 

 represents the time known to consciousness. This is 

 called proper-time or interval. It is definitely separate 

 from and unlike proper-space. Your protest in the 

 name of commonsense against a mixing of time and 

 space is a feeling which I desire to encourage. Time and 

 space ought to be separated. The current representa- 

 tion of the enduring world as a three-dimensional space 

 leaping from instant to instant through time is an 

 unsuccessful attempt to separate them. Come back with 



