DESIGN FOR A BRAIN 



4/14 



that day in 1888 when Heinrich Hertz gave his famous demon- 

 stration. He had two pieces of apparatus (A and B, say) that 

 manifestly were not connected in any material way ; yet whenever 

 at any arbitrarily selected moment he closed a switch in A a 

 spark jumped in B, i.e. B's behaviour depended at any moment 

 on the position of A's switch. Here was a flat contradiction: 

 materially the two systems were not connected, yet functionally 

 their behaviours were connected. All scientists accepted that 

 the behavioural evidence was final — that some linkage was 

 demonstrated. 



Feedback 

 4/14. A gas thermostat also shows a functional circuit or feed- 

 back ; for it is controlled by a capsule which by its swelling moves 

 a lever which controls the flow of gas to the heating flame, so the 

 diagram of immediate effects would be : 



The reader should verify that each arrow represents a physical 

 action which can be demonstrated if all variables other than the 

 pair are kept constant. 



Another example is provided by ' reaction ' in a radio receiver. 

 We can represent the action by two variables linked in two ways : 



The lower arrow represents the grid-potential's effect within the 

 valve on the anode-current. The upper arrow represents some 

 arrangement of the circuit by which fluctuation in the anode 



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