DESIGN FOR A BRAIN 8/11 



4* /\-^ 7 n 5u- 



++ 



Time 



Figure 8/10/1 : Record of Homeostat's behaviour when a commutator H 

 was reversed from time to time (at the R's). The first set of uniselector 

 values which gave stability for both commutator positions was terminal. 



uniselector position happened to provide a field which gave 

 stability with both values of H. So afterwards, the changes of 

 H no longer caused changes in the step-mechanisms. The re- 

 sponses to the displacements Z), forced by the operator, show that 

 the system is stable for both values of H. The slight but distinct 

 difference in the behaviour after D at the two values of H show 

 that the two fields are different. 



The ultrastable system is, therefore, selective for step-mechanism 

 values which give stability for both values of an alternating 

 parameter. 



8/11. What will happen if the ultrastable system is given an 

 unusual environment ? Before the question is answered we must 

 be clear about what is meant by ' unusual '. 



In S. 6/2 it was shown that every dynamic system is acted 

 on by an indefinitely large number of parameters, many of which 

 are taken for granted, for they are always given well-understood 

 ' obvious ' values. Thus, in mechanical systems it is taken for 

 granted, unless specially mentioned, that the bodies carry a 

 zero electrostatic charge; in physiological experiments, that the 

 tissues, unless specially mentioned, contain no unusual drug; in 

 biological experiments, that the animal, unless specially mentioned, 

 is in good health. All these parameters, however, are effective 

 in that, had their values been different, the variables would not 

 have followed the same line of behaviour. Clearly the field of 

 a state-determined system depends not only on those para- 

 meters which have been fixed individually and specifically, but 

 on all the great number which have been fixed incidentally. 



116 



