DESIGN FOR A BRAIN 2/8 



as will be seen later (and as has been shown in /. to C), it makes 

 possible a theory that is clear, simple, and coherent. The theories 

 that arise when we consider the more realistic state of affairs in 

 which not all states are accessible, or not all variables controllable, 

 are tangled and complicated, and not suitable as a basis. These 

 complicated variations can all be derived from the basic theory 

 by the addition of complications. For the moment we shall 

 postpone them. 



2/8. The primary operation that wins new knowledge from the 

 * machine ' is as follows : — The experimenter uses his power of 

 control to determine (select, enforce) a particular state in the 

 system. He also determines (selects, enforces) the values of the 

 surrounding conditions of the system. He then allows one unit 

 of time to elapse and he observes to what state the system goes 

 as it moves under the drive of its own dynamic nature. He 

 observes, in other words, a transition, from a particular state, 

 under particular conditions. 



Usually the experimenter wants to know the transitions from 

 many states under many conditions. Then he often saves time 

 by allowing the transitions to occur in chains; having found that 

 A is followed by B, he simply observes what comes next, and thus 

 discovers the transition from B, and so on. 



This description may make the definition sound arbitrary and 

 unnatural ; in fact, it describes only what every experimenter does 

 when investigating an unknown dynamic system. Here are some 

 examples. 



In chemical dynamics the variables are often the concentra- 

 tions of substances. Selected concentrations are brought together, 

 and from a definite moment are allowed to interact while the 

 temperature is held constant. The experimenter records the 

 changes which the concentrations undergo with time. 



In a mechanical experiment the variables might be the positions 

 and momenta of certain bodies. At a definite instant the bodies, 

 started with selected velocities from selected positions, are allowed 

 to interact. The experimenter records the changes which the 

 velocities and positions undergo with time. 



In studies of the conduction of heat, the variables are the 

 temperatures at various places in the heated body. A prescribed 

 distribution of temperatures is enforced, and, while the tempera- 



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