DESIGN FOR A BRAIN 2/3 



(2) it must be applicable equally readily (at least in principle) 



to all material 'machines', whether animate or inanimate; 



(3) its procedure for obtaining information from the ' machine ' 



must be wholly objective (i.e. accessible or demonstrable 

 to all observers); 



(4) it must obtain its information solely from the ' machine ' 



itself, no other source being permitted. 



The actual form developed may appear to the practical worker 

 to be clumsy and inferior to methods already in use; it probably 

 is. But it is not intended to compete with the many specialised 

 methods already in use. Such methods are usually adapted to a 

 particular class of dynamic systems: one method is specially suited 

 to electronic circuits, another to rats in mazes, another to solutions 

 of reacting chemicals, another to automatic pilots, another to 

 heart-lung preparations. The method proposed here must have 

 the peculiarity that it is applicable to all; it must, so to speak, 

 specialise in generality. 



Variable and system 



2/3. In /. to C, Chapter 2, is shown how the basic theory can 

 be founded on the concept of unanalysed states, as a mother might 

 distinguish, and react adequately to, three expressions on her 

 baby's face, without analysing them into so much opening of the 

 mouth, so much wrinkling of the nose, etc. In this book, however, 

 we shall be chiefly concerned with the relations between parts, so 

 we will assume that the observer proceeds to record the behaviour 

 of the machine's individual parts. To do this he identifies any 

 number of suitable variables. A variable is a measurable quantity 

 which at every instant has a definite numerical value. A ' grand- 

 father ' clock, for instance, might provide the following variables: 

 — the angular deviation of the pendulum from the vertical; the 

 angular velocity with which the pendulum is moving; the angular 

 position of a particular cog-wheel; the height of a driving weight; 

 the reading of the minute-hand on the scale; and the length of 

 the pendulum. If there is any doubt whether a particular 

 quantity may be admitted as a ' variable ' I shall use the criterion 

 whether it can be represented by a pointer on a dial. 



All the quantities used in physics, chemistry, biology, physio- 

 logy, and objective psychology, are variables in the defined sense. 



14 



