DESIGN FOR A BRAIN 



7/14 



^V 



TIME— > 



Figure 7/13/1 : Types of behaviour of a variable : A, the full-function ; 

 B, the part-function ; C, the step-function ; D, the null-function. 



In all cases the type-property is assumed to hold only over 

 the period of observation: what might happen at other times 

 is irrelevant. 



Sometimes physical entities cannot readily be allotted their 

 type. Thus, a steady musical note may be considered either as 

 unvarying in intensity, and therefore a null-function, or as 

 represented by particles of air which move continuously, and 

 therefore a full -function. In all such cases the confusion is at 

 once removed if one ceases to think of the real physical object 

 with its manifold properties, and selects that variable in which 

 one happens to be interested. 



7/14. Step-functions occur abundantly in nature, though the 

 very simplicity of their properties tends to keep them incon- 

 spicuous. ' Things in motion sooner catch the eye than what 

 not stirs '. The following examples approximate to the step- 

 function, and show its ubiquity: 



(1) The electric switch has an electrical resistance which remains 



constant except when it changes by a sudden jump. 



(2) The electrical resistance of a fuse similarly stays at a low 



value for a time and then suddenly changes to a very 

 high value. 



88 



