The Science of Discworld IV

a circuit that includes a lamp bulb, possibly with a filament which instantly heats up to about 3000˚ Celsius, emitting lots of heat and quite a lot of light. It might instead be a fluorescent tube, or an LED that produces light more efficiently, that is, with less heat.
    We need to think about you causing your finger to press the switch – but we also need to understand how the electrical system is just sitting there waiting for you to work it.
    Jack has a friend who’s an electrician, a pleasant, helpful guy that you can phone up and he’ll sort your electrical problem out. The electrician has many friends and acquaintances who are academics, and he has, at least
three times
, been in the following situation. Someone has rung up to ask why a socket that they have bought and put into the wall isn’t working an appliance that they’ve plugged into it. When the electrician turns up … well, he discovers that they genuinely didn’t know that there have to be wires in the wall connecting the socket to the electricity supply. They thought the socket alone would be enough.
    Part of the problem is the old arts/science division, but one of the people concerned was a biologist. What is it about electricity that’s so mysterious? We don’t think the problem is electricity, or even understanding how it works. It’s about cryptic investment. There was a time, quite long ago, when there were gas pipes to many public buildings, to power the lamps so that people could work when it was dark outside, but no electric supply, yet. Jack’s mother took over the fifth floor of an old factory in Middlesex Street in the East End of London. There were rotating belts going up through the floors, turning long rods to which her sewing machines were attached, worked by great electric motors in the basement. Jack was amazed, when he went down to see these in the 1960s, that there were also remains of an old hydraulic system: water was piped to the building from a central pumping station, and returned when it had done its work, probably between the 1880s and 1910.
    Such investments have been fossilised now, replaced by electric cables; but there had been a succession of power supplies to that building, invisible from outside, just made explicit by a series of bills from The London Hydraulic Power Company. The London Hydraulic Power Company had
181 miles
of cast-iron pipes under Londonproviding power to factories. Who’d have thought that we would have forgotten that? The electric cables to houses are ever so discreet now, but they used to be a pair of wires from a local transformer, draped over the gardens. They still are in many rural districts, but a lot of cables to houses are now underground in British cities and suburbs. (Less so in America and Japan.)
    So it’s no longer obvious, to anyone who bothers to look, just how much investment there has been in energy distribution. Since the wires are invisible, people aren’t always aware that they are present, let alone
necessary
. But that hidden wiring is the reason why we have only to lift an arm to turn the light on.
    Our third example, as promised, is biological, and involves the meddling of humans: orchids.
    Pick up a flower and look at it. Admire its petals. There were no petals 120 million years ago, just leaves. Some of the leaves may have been coloured, to attract insects, but they weren’t petals. Leaves held their own wonders, however: they were flat areas on plants, making photosynthesis more effective. They helped to collect sunlight and to shade other competing plants. Before big leaves evolved, many plants had tiny leaves like scales on their stems; before that, plants were mostly in the seas, with flat ‘stems’ to collect more sunlight.
    Petals are a trick that advanced land plants – angiosperms – use to attract insects (sometimes hummingbirds or even bats) so that they can reproduce sexually when pollen is carried from plant to plant. Originally, petals were leaves, with no reproductive role, sexual or not. But leaves have evolved into colourful arrays – which appeal to the human urge to tinker.
    Look at a standard domestic rose; not the ones in hedgerows, which are often ‘normal’. The sepals, anthers, perhaps even stigmas, have all been turned into petals. The flower of a cultivated rose is a monstrous concoction that has undone millions of years of evolution by selecting genetic differences over the generations. In any plantnursery there are