3/11 DESIGN FOR A BRAIN 



The rider's centre of gravity being at first unmoved, the line 

 vertically downwards from his centre of gravity will strike the 

 ground more and more to the left of the line joining the two 

 points. As a result he will start to fall to the left. This fall will 

 excite nerve-endings in the organs of balance in the ear, impulses 

 will pass to the nervous system, and will be switched through it, 

 if he is a trained rider, by such a route that they, or the effects 

 set up by them, will excite to activity those muscles which push 

 the right hand forwards. 



We can now specify the variables which must compose the 

 system if it is to be absolute. We must include : the angular 

 position of the handlebar, the velocity of lateral movement of the 

 two points of contact between wheels and road, the distance 

 laterally between the line joining these points and the point 

 vertically below the rider's centre of gravity, and the angular 

 deviation of the rider from the vertical. These four variables are 

 denned by S. 3/8 to be the 4 environment ' of the rider. (Whether 

 the fourth variable is allotted to ' rider ' or to i environment ' is 

 optional (S. 3/12) ). To make the system absolute, there must be 

 added the variables of the nervous system, of the relevant muscles, 

 and of the bone and joint positions. 



As a second example, consider a butterfly and a bird in the air, 

 the bird chasing the butterfly, and the butterfly evading the bird. 

 Both use the air around them. Every movement of the bird 

 stimulates the butterfly's eye and this stimulation, acting through 

 the butterfly's nervous system, will cause changes in the butter- 

 fly's wing movements. These movements act on the enveloping 

 air and cause changes in the butterfly's position. A change of 

 position immediately changes the excitations in the bird's eye, 

 and this leads through its nervous system to changed movements 

 of the bird's wings. These act on the air and change the bird's 

 position. So the processes go on. The bird has as environment 

 the air and the butterfly, while the butterfly has the bird and the 

 air. The whole may justifiably be assumed absolute. 



3/11. The organism affects the environment, and the environ- 

 ment affects the organism : such a system is said to have 4 feed- 

 back ' (S. 4/12). 



The examples of the previous section provide illustration. 

 The rider's arm moves the handlebars, causing changes in the 



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