DESIGN FOR A BRAIN 



4/11 



4/11. This definition of stability conforms to the requirement 

 of S. 2/10; for the observed behaviour of the system determines 

 the field, and the field determines the stability. 



The diagram of immediate effects 



4/12. The description given in S. 4/1 of the working of the 

 Watt's governor showed that it is arranged in a functional circuit : 

 the chain of cause and effect is re-entrant. Thus if we represent 

 1 A has a direct effect on B ' or ' A directly disturbs B ' by the 

 symbol A — > B, then the construction of the Watt's governor may 

 be represented by the diagram: 



(The number of variables named here is partly optional.) 



I now want to make clear that this type of diagram, if accurately 

 defined, can be derived wholly from the results of primary operations. 

 No metaphysical or borrowed knowledge is necessary for its 

 construction. To show how this is done, take an actual Watt's 

 governor as example: 



Each pair of variables is taken in turn. Suppose the relation 

 between ' speed of engine ' and ' distance between weights ' is 

 first investigated. The experimenter would fix the variable 

 4 velocity of flow of steam ' and all other extraneous variables that 

 might interfere to confuse the direct relation between speed of 

 engine and distance between weights. Then he would try various 

 speeds of the engine, and would observe how these changes affected 

 the behaviour of ' distance between the weights '. He would 

 find that changes in the speed of the engine were regularly followed 

 by changes in the distance between the weights. Thus the transi- 

 tion of the variable 4 distance between weights ' (one distance 

 changing to another) is affected by the value of the speed of the 



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