Thurston's topic reminds us of a common metaphor for this kind of apparently simultaneous invention: steam engine time. When it's steam engine time, suddenly everyone is making steam engines. When it's evolution time, everyone is inventing a theory of evolution. When it's VCR time, everyone is making video cassette recorders. When it's Dotcom time, everyone is setting up Internet trading systems. And when it's Dotcom-going-bust time, all the Dotcoms are going bust.
There are times when human affairs really do seem to run on preconstructed tracks. Some development becomes inevitable, and suddenly it's everywhere. Yet, just before that propitious moment, it wasn't inevitable at all, otherwise it would have happened already. `Steam engine time' is a convenient metaphor for this curious process. The invention of the steam engine wasn't the first example, and it certainly wasn't the last, but it is one of the best known, and it's quite well documented.
Thurston distinguishes invention from discovery. He says that inventions are never the creation of a single individual, whereas great discoveries seldom are. However, the distinction isn't always clearcut. Did ancient humans discover fire as a phenomenon of nature, or did they invent fire as a technology to keep predators away, light the cave, and cook food? The natural phenomenon surely came first, in the form of brush- or forest fires triggered by lightning, or possibly a droplet of water accidentally acting as a lens to concentrate the Sun's rays on to a piece of dry grass[46].
However, that kind of `discovery' doesn't go anywhere until someone finds a use for it. It was the idea of controlling fire that made the difference, and that seems more of an invention than a discovery. Except ... you find out how to control fire by discovering that fires don't spread (so easily) across bare soil, that they can be spread very easily indeed by picking up a burning stick and dropping it into dry brushwood, or taking it home to the cave ...
The inventive step, if there is such a thing, consists of putting together several independent discoveries so that what emerges has genuine novelty.
Dry grass and drops of water are not commonly associated, but perhaps a damp elephant had just emerged from a river crossing on to dry savannah ... Oh, invent your own explanation.
So inventions are often preceded by a series of discoveries. Similarly, discoveries are often preceded by inventions. The discovery of sunspots rested on the invention of the telescope, the discovery of amoebas and parameciums in pond water rested on the invention of the microscope. In short, invention and discovery are intimately entwined, and it's probably pointless to try to separate them. Moreover, the significant instances of both are much easier to spot in retrospect than they were at the time they first happened. Hindsight is a wondrous thing, but it does have the virtue of providing an explicit context for working out what did, or did not, matter. Hindsight lets us organise the remarkably messy process of invention/discovery, and tell convincing stories about it.
The problem is, most of those stories aren't true.
As children, many of us learned how the steam engine was invented. The young James Watt, aged about six, was watching a kettle boil, and he noticed that the pressure of the steam could lift the lid. In a classic `eureka' moment, it dawned on him that a really big kettle could lift really heavy bits of metal, and the steam engine was born.
The original teller of this story was the French mathematician Francois Arago, author of one of the first biographies of Watt. For all we know, the story may be true, though it is more likely a `lie-tochildren', or educational aid,* like Newton's apple. Even if the young Watt was indeed suddenly inspired by a boiling kettle, he was by no means the first person to make the connection between steam and motive power. He wasn't even the first person to build a working steam engine. His claim to fame rests on something more complex, yet more significant. In Watt's hands, the steam engine became an effective and reliable tool. He didn't `perfect' it - many smaller improvements were made after Watt - but he brought it into pretty much its final form.
Watt wrote in 1774: `The fire engine (= steam engine) that I have invented is now going, and answers much better than any other that has yet been made.' In conjunction with his business partner Matthew Boulton, Watt made himself the household name of the steam engine. And it has done his reputation no harm that, in the words of Thurston: `Of the personal history of the earlier inventors and improvers of the steam-engine, very little is ascertained; but that of Watt has become well known.'
Was Darwin just another Watt? Did he get credit for evolution because he brought it into a polished, effective form? Is he famous because we happen to know so much about his personal history? Darwin was an obsessive record-keeper, he hardly threw away a single scrap of paper. Biographers were able to document his life in exceptional detail. It certainly did his reputation no harm that such a wealth of historical material was available.
In order to make comparisons, let's review the history of the steam engine, avoiding lies-to-children as much as we can. Then we'll look at Darwin's intellectual predecessors, and see whether a common pattern emerges. How does steam engine time work? What factors lead to a cultural explosion, as an apparently radical idea `takes off and the world changes for ever? Does the idea change the world, or does a changing world generate the idea?
Watt completed his first significant steam engine in 1768, and patented it in 1769. It was preceded by various prototypes. But the first recorded reference to steam as a source of motive power occurs in the civilisation of ancient Egypt, during the Late Kingdom when that country was under Roman rule. Around 150 BC (the date is very approximate) Hero of Alexandria wrote a manuscript Spiritalia seu Pneumatica. Only partial copies have survived to the present day, but from them we learn that the manuscript referred to dozens of steam-driven machines. We even know that several of them predated Hero, because he tells us so; some were the previous work of the inventor Cestesibus, celebrated for the great number and variety of his ingenious pneumatic machines. So we can see the beginnings of steam engine time long ago, but initial progress was so quiet and slow that steam engine time itself was still far in the future.
One of Hero's devices was a hollow airtight altar, with the figure of a god or goddess on top, and a tube running through the figure. Unknown to the punters, the altar contains water. When a worshipper lights a fire on top of the altar, the water heats up and produces steam. The pressure of the steam drives some of the remaining liquid water up the pipe, and the god offers a libation. (As miracles go this one is quite effective, and distinctly more convincing than a statue of a cow that oozes milk or one of a saint that weeps.) Similar devices were commonplace from the 1960s to make tea at the bedside and pour it out automatically. They still exist today, but are harder to find.
Another of Hero's machines used the same principle to open a temple door when someone lit a fire on an altar. The device is quite complicated, and we describe it to show that these ancient machines went far beyond being mere toys. The altar and door are above ground, the machinery is concealed beneath. The altar is hollow, filled with air. A pipe runs vertically down from the altar into a metal sphere full of water, and a second inverted U-shaped pipe acts like a siphon, with one end inside the sphere and the other inside a bucket. The bucket hangs over a pulley, and ropes from the bucket wind round two vertical cylinders, in line with the hinges of the door and attached to the door's edge. They then run over a second pulley and terminate in a heavy weight which acts as a counterbalance. When a priest lights the fire, the air inside the altar expands, and the pressure drives water out of the sphere, through the siphon, and into the bucket. As the bucket descends under the weight of water, the ropes cause the cylinders to turn, opening the doors.