DESIGN FOR A BRAIN 



8/2 



fi^hs. 





°<3^ 



Figure 8/2/3 : Wiring diagram of one unit. (The letters are explained 



in the text.) 



Next, the units are joined together so that each sends its 

 output to the other three; and thereby each receives an input 

 from each of the other three. 



These inputs act on the unit's magnet through the coils A, 



B, and C, so that the torque on the magnet is approximately 

 proportional to the algebraic sum of the currents in A, B, and 



C. (D also affects M as a self -feedback.) But before each input 

 current reaches its coil, it passes through a commutator (X), 

 which determines the polarity of entry to the coil, and through 

 a potentiometer (P), which determines what fraction of the input 

 shall reach the coil. 



As soon as the system is switched on, the magnets are moved 

 by the currents from the other units, but these movements change 

 the currents, which modify the movements, and so on. It may 

 be shown (S. 19/11) that if there is sufficient viscosity in the 

 troughs, the four-variable system of the magnet-positions is 

 approximately state-determined. To this system the com- 

 mutators and potentiometers act as parameters. 



When these parameters are given a definite set of values, the 

 magnets show some definite pattern of behaviour; for the para- 

 meters determine the field, and thus the lines of behaviour. If 



102 



