12/14 TEMPORARY INDEPENDENCE 



pendence show a remarkable variety. Thus, in C, 1 dominates 

 3; but in D, 3 dominates 1. As the variables become more 

 numerous so does the variety increase rapidly. 



12/13. The multiplicity of inter-connexions possible in a tele- 

 phone exchange is due primarily to the widespread use of 

 temporary constancies. The example serves to remind us that 

 ' switching ' is merely one of the changes producible by a re- 

 distribution of constancies. For suppose a system has the 



->• 



>.D 



^« 



B 



Figure 12/13/1. 



diagram of immediate effects shown in Figure 12/13/1. If an 

 effect coming from C goes down the branch AD only, then, for 

 the branch BE to be independent, B must be constant. How the 

 constancy is obtained is here irrelevant. When the effect from 

 C is to be ' switched ' to the BE branch, B must be freed and A 

 must become constant. Any system with a i switching ' process 

 must use, therefore, an alterable distribution of constancies. 

 Conversely, a system whose variables can be sometimes fluctuating 

 and sometimes constant is adequately equipped for switching. 



The effects of local stabilities 



12/14. The last few sections have shown how important, in any 

 system that is to have temporary independencies, are variables 

 that temporarily go constant. As such- variables play a funda- 

 mental part in what follows, let us examine them more closely. 



Any subsystem (including the case of the single variable) that 

 stays constant is, by definition, at a state of equilibrium. If the 

 subsystem's surrounding conditions (parameters) are constant, the 

 subsystem evidently has a state of equilibrium in the corresponding 

 field ; if it stays constant while its parameters are changing, then 

 that state is evidently one of equilibrium in all the fields occurring. 

 Thus, constancy in a subsystem's state implies that the state is 



167 



