THE ERROR-CONTROLLED REGULATOR 12/3 



A similar restriction of R's capacity may occur in those cases 

 where R's effect on T is vectorial, i.e. effected through more than 

 one channel or component to T, and some diminution has occurred 

 in the number of T's parameters accessible to R. (Compare S.7/12.) 

 Thus a failure at one of the controls on the dashboard may impair 

 the driver's abihty to keep the car running well. 



The case when R cannot receive full information about T's 

 initial state (discussed in S. 11/19) is really included in the cases 

 mentioned above. Such a difficulty occurs to a railway signalman 

 in a fog. He is well informed that a disturbance "fog" has arrived, 

 but he often has difficulty in ascertaining the present state of the 

 system he is controUing, i.e. the present positions of the trains in 

 his sector. With this restriction in the flow of information from 

 T to R goes the difficulty, or even impossibility, of maintaining full 

 regulation. 



12/3. The basic formulation of S.11/4 assumed that the process of 

 regulation went through its successive stages in the following order: 



(1) a particular disturbance threatens at D; 



(2) it acts on R, which transforms it to a response ; 



(3) the two values, of D and R, act on T simultaneously to produce 

 r's outcome ; 



(4) the outcome is a state in E, or affects E. 



Thus (3) supposes that if R is an actual material system, it performs 

 all its work before T starts to move. We assumed, in other words, 

 that the regulator R moved at a higher order of speed than T. 



This sequence does actually occur in many cases. When the cat 

 approaches, the mouse may react so as to get to its hole before the 

 cat's claws actually strike. We say in general that the organism 

 has reacted to the threat (at D) rather than to the disaster itself (at E), 

 and has thus forestalled the disaster. The formulation is thus 

 properly representative of many important regulations. 



On the other hand, there are many important cases in which this 

 anticipation is not possible — in which R's action cannot be completed 

 before the outcome (at T) starts to be determined. (An example is 

 given in the next section.) In such cases the regulation envisaged in 

 S.l 1/3 is impossible. What then is to be done? 



One method, of course, is to speed up the transmission of informa- 

 tion from D to R; and many regulating systems have various devices 

 specially to this end. Primitive nerve fibres develop myelin sheaths, 

 so that the passage to the brain may be faster. Some organisms 

 develop a sense of smell, so that the appropriate response may be 



221 



