8/4 THE HOMEOSTAT 



the animal's arm movements were at first grossly inco-ordinated, 

 but improved until an essentially normal mode of progression 

 was re-established. The two examples are typical of a great 

 number of experiments, and will suffice for the discussion. Let 

 us see what the Homeostat will do under a similar operation. 

 Figure 8/4/1 shows the Homeostat simplified to two units 



1 



R i 



u 





°1 °2 



Time 



Figure 8/4/1 : Two units (1 and 2) interacting. Line 1 represents the side- 

 to-side movements of Unit l's needle by vertical changes. Similarly 

 line 2 shows the behaviour of Unit 2's needle. The lowest line (U) shows 

 a mark whenever Unit l's uniselector advanced a step. The dotted lines 

 correspond to critical states. The displacements D were caused by the 

 operator so as to force the system to show its response. 



interacting. The diagram of immediate effects was 1 ^± 2 ; the 

 effect 1 — >- 2 was hand-controlled, and 2 — > 1 was uniselector- 

 controlled. At first the step-mechanism values combined to give 

 stability, shown by the responses to D v (The reader should bear 

 in mind, of course, that this trifling return after displacement is 

 representative of all the complex returns after displacement con- 

 sidered in Chapter 5: Adaptation as stability.) At R v reversal 

 of the commutator by hand rendered the system unstable, a 

 runaway occurred, and the variables transgressed the critical 

 states. The uniselector in Unit 1 changed position and, as it 

 happened, gave at its first trial a' stable field. It will be noticed 

 that whereas before R x the upstroke of D± in 2 caused an up- 

 stroke in 1, it caused a downstroke in 1 after R v showing that the 

 action 2 — > 1 had been reversed by the uniselector. This reversal 

 compensated for the reversal of 1 — > 2 caused at R v 



At R 2 the whole process was repeated. This time three uni- 

 selector changes were required before stability was restored. A 



105 



