﻿496 Prof. E. V. Huntington on a Sew 



kinematics without any observer's leaving his own statio n. 

 These definitions wll then be capable of immediate extensio n 

 to the case of a system in uniform motion through the 

 aether. 



The regulating and setting of stationary clocks. 



2. To test whether the clock at any given station A is 

 running at a uniform rate, the observers proceed as follows : 

 a light-signal is sent from A to any second station B, and 

 immediately returned from B to A; if the number of seconds 

 ticked off by the clock at A while the light-signal is making 

 its round trip to B and return is always the same whenever 

 the experiment is repeated, then the clock at A is said to be 

 running at a constant rate. 



3. Each separate clock being regulated to run at a constant 

 rate, the next thing to do is to see that all the clocks run at 

 the same rate. This may be easily accomplished by regulating 

 all the clocks so as to agree with a standard clock in some 

 central station 0, as follows. Light-signals are sent out 

 from 0, at a certain rate per second as measured by the 

 clock at ; if these arrive at station A at the same rate 

 per second as measured by the clock at A, then the clock 

 at A is said to be running at the same rate as the clock at 0. 



Xow it is obviously possible for two clocks to be running at the sara e 

 rate without being synchronous, lor example (supposing for convenience 

 that the clocks read continuously 0, 1, 2, .... seconds, instead of from 

 12 o'clock around to 12 again), we may have two clocks side by side, 

 one reading 



while the other reads 



9,10, 



These clocks are running at the same rate, but they are clearly not 

 synchronous, since the one is alwavs four seconds ahead of the other. 



4. It remains, therefore, to " set " the clocks so that they 

 shall all be synchronous — in other words, so that the " origin 

 of time" shall be the same for all. This maybe readily 

 accomplished by light-signals from the central station *. 

 Let the observer at start a signal towards A when the 

 clock at reads t , and suppose this signal arrives at A 

 when the clock at A reads ^ ; immediately on the receipt 

 of this signal, the observer at A starts a return signal back 

 towards 0, which arrives at when the clock at reads t 2 . 



* Einstein, loc. cit. 



