A steam engine would not work if there was a constant pressure of steam on the piston. Because the flow of steam is periodically interrupted by the valve the piston is able to move backwards and forwards and so generate motion and useful power. The power of a permanent magnet cannot be turned into a useful engine because there is no way of switching it on or off, so once the pull has been exerted the attracted metal remains stuck to the magnet. If we could switch this magnetic attraction on and off in a cycle then we should have a useful engine. This is what is done in the electric
motor.
On/offcycles seem to be a characteristic of nature because they provide the
simplest form of a dynamic system. The electromagnetic waves that form the
basis of radio, light or X-rays can all be described in terms of cycles of energy
or a wave motion. The ordinary waves in the sea transmit energy over long distances although we have not yet succeeded in harnessing this. A cork or buoy floating in a harbour goes up and down as each wave passes. There is a cycle of movement: up to a peak height then down to a trough. The leg that turns the pedal on a bicycle goes through the same sort of up and down cyclical motion. The rotation of a wheel is also a cycle insofar as a point on the rim moves to a point as far distant as possible on the other side of the wheel and then comes back to the original point.
There are cycles in fashion: skirts get longer and then shorter and then longer again. There are cycles in morals from Victorian to permissive and then back again. In any system where there is change and yet the direction of change is strictly limited there is likely to be a cycle. This follows because people are bored with what exists or react against it. People who are bored with short skirts can only make them longer and when they have reached the ground they can only be made shorter again.
Business and economic cycles arise for two reasons. The first is the operation of greed and confidence. People buy property because it is doing well so it does better and better until a point is reached when the increase in price slows down and the second part of the cycle (decline) takes over. The second reason is the mismatch between supply and need. Whenever things are out of phase a cycle results: investment followed by overcapacity, followed by a fall in investment and eventual undercapacity and so on.
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