12/4 



AN INTRODUCTION TO CYBERNETICS 



prepared in time for the actual bodily encounter. And economic 

 systems send messages by cable rather than by messenger so that 

 the arrival in port of a ship with a perishable cargo can be prepared 

 for. 



Sometimes, however, the available resources do not include a 

 speeding-up of the transmission through R; i?'s reaction cannot be 

 got to T before the outcome commences. In that case, the best 

 that can be done is that the imperfect regulation should at least be 

 as good as it can be made in the circumstances. The succeeding 

 sections will discuss how this can be done. 



12/4. Regulation by error. A well-known regulator that cannot 

 react directly to the original disturbance D is the thermostat- 

 controlled water-bath, which is unable to say "I see someone coming 

 with a cold flask that is to be immersed in me — I must act now". 

 On the contrary, the regulator gets no information about the disturb- 

 ance until the temperature of the water (E) actually begins to drop. 

 And the same limitation applies to the other possible disturbances, 

 such as the approach of a patch of sunlight that will warm it, or the 

 leaving open of a door that will bring a draught to cool it. 



The same limitation holds over many important regulators. 

 There is, for instance, a mechanism that helps to keep constant 

 the oxygen supply to the tissues : any long-continued lack of oxygen 

 causes eventually an increase in the number of red corpuscles 

 contained in the blood. So people with certain types of heart 

 disease, and those living at high altitudes, where the air is thin, 

 tend to develop such an increase. This regulation draws its informa- 

 tion from the harmful eff"ect (the lack of oxygen) itself, not from the 

 cause (D) of the heart disease, or from the decision to live at a higher 

 altitude. 



From the point of view of communication, the new phenomena 

 are easily related to those of the old. The difference is simply that 

 now the information from D to R (which must pass if the regulator 

 R is to play any useful part whatever) comes through T. Instead of 



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