40 TIME 



of that feeling is time lived, which we have just seen 

 may be 70 years for one individual and 1 year for 

 another between their two meetings. We can reckon 

 "time lived' 5 quite scientifically, e.g. by a watch travel- 

 ling with the individual concerned and sharing his 

 changes of inertia with velocity. But there are obvious 

 drawbacks to the general adoption of "time lived". It 

 might be useful for each individual to have a private 

 time exactly proportioned to his time lived; but it would 

 be extremely inconvenient for making appointments. 

 Therefore the Astronomer Royal has adopted a uni- 

 versal time-reckoning which does not follow at all strictly 

 the time lived. According to it the time-lapse does not 

 depend on how the object under consideration has 

 moved in the meanwhile. I admit that this reckoning 

 is a little hard on our returned traveller, who will be 

 counted by it as an octogenarian although he is to all 

 appearances still a boy in his teens. But sacrifices must 

 be made for the general benefit. In practice we have 

 not to deal with human beings travelling at any great 

 speed; but we have to deal with atoms and electrons 

 travelling at terrific speed, so that the question of pri- 

 vate time-reckoning versus general time-reckoning is a 

 very practical one. 



Thus in physical time (or Astronomer Royal's time) 

 two people are deemed to have lived the same time 

 between two meetings, whether or not that accords with 

 their actual experience. The consequent deviation from 

 the time of experience is responsible for the mixing 

 up of time and space, which, of course, would be 

 impossible if the time of direct experience had been 

 rigidly adhered to. Physical time is, like space, a kind 

 of frame in which we locate the events of the external 

 world. We are now going to consider how in practice 



