12/6 AN INTRODUCTION TO CYBERNETICS 



through rand E. Suppose R is somehow regulating successfully; 

 then this would imply that the variety at E is reduced below that of 

 D — perhaps even reduced to zero. This very reduction makes the 

 channel 



to have a lessened capacity; if E should be held quite constant then 

 the channel is quite blocked. So the more successful R is in keeping 

 £■ constant, the more does R block the channel by which it is receiving 

 its necessary information. Clearly, any success by R can at best 

 be partial. 



12/6. Fortunately, in many cases complete regulation is not 

 necessary. So far, we have rather assumed that the states of the 

 essential variables E were sharply divided into "normal" (17) and 

 "lethal", so occurrence of the "undesirable" states was wholly 

 incompatible with regulation. It often happens, however, that the 

 systems show continuity, so that the states of the essential variables 

 lie along a scale of undesirabiHty. Thus a land animal can pass 

 through many degrees of dehydration before dying of thirst; and 

 a suitable reversal from half way along the scale may justly be 

 called "regulatory" if it saves the animal's hfe, though it may not 

 have saved the animal from discomfort. 



Thus the presence of continuity makes possible a regulation that, 

 though not perfect, is of the greatest practical importance. Small 

 errors are allowed to occur; then, by giving their information to R, 

 they make possible a regulation against great errors. This is the 

 basic theory, in terms of communication, of the simple feedback 

 regulator. 



12/7. The reader may feel that excessive attention has just been 

 given to the error-controlled regulator, in that we have stated with 

 care what is already well known. The accuracy of statement is, 

 however, probably advisable, as we are going now to extend the 

 subject of the error-controlled regulator over a range much wider 

 than usual. 



This type of regulator is already well known when embodied in a 

 determinate machine. Then it gives the servo-mechanism, the 

 thermostat, the homeostatic mechanism in physiology, and so on. 

 It can, however, be embodied in a «on-determinate machine, and it 

 then gives rise to a class of phenomena not yet commonly occurring 



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