HOW LUCKY WAS WATT?

The general diagram of a regulated system is shown below. It applies by no means only to mechanical engineering, or indeed to engineering in general (it was mainly electrical engineers who developed it). It may be applied to practically any science. The input is the signal or the fuel flow or any other stimulus that sets the system to work. The output is what the system produces. But the output is measured and the result makes a controller modify the input, that is, a signal from the output is literally fed back to the input. Hence the upper part of the arrangement is called a feedback loop, and if you love English as much as I do (and it's your language, not mine), you will use "feedback" only in this sense (according to the multivolume Oxford Dictionary the word was created in the 1920s by radio engineers); its use in the sense of "response" to a program or a newspaper article is reserved for the lowest dregs of society¾the journalists and editors of the mass media.

To give one of thousands of examples, take the creation of ozone by UV radiation. The regulated system is the ozone layer height (due to the part formed by the disassociation of oxygen), the stimulus or input is the incident UV radiation, the output is the height of the ozone layer. The UV radiation loses its energy (is "absorbed") by disassociating O² into O + O which combines with undisturbed O² to form ozone. Suppose now the UV radia-tion increases, as it does in years of increased solar activity. Then its UV photons will penetrate deeper into the atmosphere before they lose their Energy, and the situation will be the same as before. Only the height, (i.e., the pressure) will have changed. The height/pressure are the controller in the feedback loop. If the UV radiation diminishes, it will spend its energy earlier, and the ozone layer will rise. It is one of thousands of examples of natural self-regulation, and one that does not need the Hon. Gore's advice how to improve it by legislation.