DESIGN FOR A BRAIN 16/3 



of the first dial going to R on the movement of the bolt is con- 

 ditional on the positions of all the other six; and similarly for 

 the second and remaining letters. 



A second example is given by a set of simultaneous equations, 

 which can legitimately be regarded as the temporary environment 

 of a professional computer if he is paid simply to get correct 

 answers. Sometimes they come in the simplest form, e.g. 



2x = 8 ^| 

 3y = -7\ 



iz = S J 



Then they correspond to the iterated form ; and each line can 

 be treated without reference to the others, as in S. 15/4. 

 Sometimes they are rather more complex, e.g. 



2x = 3^ 



3x — 2y = 2 



x + y — z = 0. 



This form can be solved serially, as in S. 15/8; for the first line 

 can be treated without reference to the other two; then when 

 the first process has been successful the second line can be treated 

 without reference to the last; and so to the end. The peculiarity 

 of this form is that the value of x is not conditional on the values 

 of the coefficients in the second and third lines. 

 Sometimes the forms are more complex, e.g. 



2x + y — 3z = 2^ 



x — y + 2z = 



- x _ sy + 2 = 1. 



Now the value of x is conditional on the values of all the coeffi- 

 cients; and in finding x, no coefficient can be ignored. The same 

 is true of y and z. Thus if we regard the coefficients as the 

 environment and the values of x, y and z as output, correctness 

 in the answer demands that, in getting any part of the answer 

 (any one of the three values), all the environment must be taken 

 into account. 



A third, and more practical, example of a richly connected 

 environment (now, thank goodness, no more) faced the experi- 

 menter in the early days of the cathode-ray oscilloscope. Adjust- 

 ing the first experimental models was a matter of considerable 

 complexity. An attempt to improve the brightness of the spot 



200 



