Quantities concerned can be measured with an accuracy that is
Bounded only by the experimenter’s resources of time and money.)
Ex. 1: An electrical machine that receives potentials on its two input- terminals
Is altered by having the two terminals joined permanently by a wire. To what
Alteration in Tab would this correspond if the machine were represented as in
Ex. 4/3/3.
Ex. 2: “When an organism interacts with its environment, its muscles are the
Environment’s input and Its sensory organs are the environment’s output.”
Do you agree ?
Input and output. The word “transducer” is used by the phys-
Icist, and especially by the electrical engineer, to describe any
Determinate physical system that has certain defined places of
Input, which the experimenter may enforce changes that affect its
Behaviour, and certain defined places of output, at which he
Observes changes of certain variables, either directly or through
Suitable instruments. It will now be clear that the mathematical
System described in S.4/1 is the natural representation of such a
Material system. It will also be clear that the machine’s “input”
Corresponds he set of states provided by its parameters; for as the
Parameters input are altered so is the machine’s or transducer’s
Behaviour affected.
With an electrical system, the input is usually obvious and
Restricted to a few terminals. In biological systems, however, the
Number of parameters is commonly very large and the whole set of
Them is by no means obvious. It is, in fact, co-extensive with the
Set of “all variables whose change directly affects the organism”.
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Transient. The electrical engineer and the biologist tend to test
Their systems by rather different methods. The engineer often
Investigates the nature of some unknown system by submitting it
To an incessant regular change at its input while observing its out-
Put. Thus, in Fourier analysis, he submits it to prolonged stimula-
Tion by a regular sinusoidal potential of a selected frequency, and
He observes certain characteristics in the output; then he repeats the
Test with another frequency, and so on; eventually he deduces
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Something of the system’s properties from the relations between
The input-frequencies and the corresponding output-characteristics.
During this testing, the machine is being disturbed incessantly.
The biologist often uses a method that disturbs the system not at
All, after the initial establishment of the conditions. Thus he may cut
A piece of meat near an ants’ colony and then make no further
Change whatever— keeping the conditions, the parameters, con-
Stant— while watching the whole evolution of the complex patterns
Of behaviour, individual and social, that develop subsequently.
Contrary to what is observed in living systems, the behaviour of
Mechanical and electrical systems often settles to some uniformity
Fairly quickly from the moment when incessant change at the input
Stops. The response shown by the machine after some disturbance,
The input being subsequently held constant, is called a transient. It is
Important to appreciate that, to the engineer, the complex sequence
Of events at the ants’ nest is a transient. It may be defined in more
General terms as the sequence of states produced by a transducer in
Constant conditions before the sequence starts repeating itself.
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A N I N T R O D UC T I O N T O C Y B E R NE T I C S
TH E MA C HI N E WI TH I N PUT
To talk about the transient, as distinct from the repetitive part
That follows, it is convenient to be able to mark, unambiguously,
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