8/10 DESIGN FOR A BRAIN 



made by joining the front two magnets by a light glass fibre 

 so that they had to move together. Figure 8/10/1 shows a 

 typical record of the changes. Three units were joined together 

 and were at first stable, as shown by the response when the 

 operator displaced magnet 1 at D v At J, the magnets of 1 and 

 2 were joined so that they could move only together. The result 

 of the constraint in this case was to make the system unstable. 

 But the instability evoked step-function changes, and a new 

 terminal field was found. This was, of course, stable, as was 

 shown by its response to the displacement, made by the operator, 

 at D 2 . But it should be noticed that the new set of step-function 

 values was adjusted to, or 'took notice of, the constraint and, 

 in fact, used it in the maintenance of stability ; for when, at R, 

 the operator gently lifted the fibre away the system became 

 unstable. 



References 



Ashby, W. Ross. Design for a brain. Electronic Engineering, 20, 379 ; 1948. 

 Idem. The cerebral mechanisms of intelligent behaviour, in Perspectives in 



Neuropsychiatry, edited D. Richter. London, 1950. 

 Idem. Can a mechanical chess-player outplay its designer? British Journal 



for the Philosophy of Science, 3, 44 ; 1952. 

 Fisher, R. A., and Yates, F. Statistical tables. Edinburgh, 1943. 



102 



