The Ascent of Man (14 page)

It is not accidental that new, iconoclastic ideas in medicine and chemical treatment come cheek by jowl, in time and in place, with the Reformation that Luther started in 1517. A focus of that historic time was Basel. Humanism had flourished there even before the Reformation. There was a university with a democratic tradition, so that, although
its medical men looked askance at Paracelsus, the City Council could insist that he be allowed to teach. The Frobenius family was printing books, among them some by Erasmus, which spread the new outlook
everywhere and in all fields.

A great change was blowing up in Europe, greater perhaps even than the religious and political upheaval that Martin Luther had set going. The symbolic year of destiny
was just ahead, 1543. In that year, three books were published that changed the mind of Europe: the anatomical drawings of Andreas Vesalius; the first translation of the Greek mathematics and physics of Archimedes; and the book by Nicolaus Copernicus,
The Revolution of the Heavenly Orbs
, which put the sun at the centre of the heaven and created what is now called the Scientific Revolution.

All
that battle between past and future was summarised prophetically in 1527 in a single action outside the Winster at Basel. Paracelsus publicly threw into the traditional student bonfire an ancient medical textbook by Avicenna, an Arab follower of Aristotle.

There is something symbolic about that midsummer bonfire which I will try to conjure into the present. Fire is the alchemist’s element by
which man is able to cut deeply into the structure of matter. Then is fire itself a form of matter? If you believe that, you have to give it all sorts of impossible properties – such as, that it is lighter than nothing. Two hundred years after Paracelsus, as late as 1730, that is what chemists tried to do in the theory of phlogiston as a last embodiment of material fire. But there is no such substance
as phlogiston, just as there is no such principle as the vital principle – because fire is not a material, any more than life is material. Fire is a process of transformation and change, by which material elements are rejoined into new combinations. The nature of chemical processes was only understood when fire itself came to be understood as a process.

That gesture of Paracelsus had said, ‘Science
cannot look back to the past. There never was a Golden Age.’ And from the time of Paracelsus it took another two hundred and fifty years to discover the new element, oxygen, which at last explained the nature of fire, and took chemistry forward out of the Middle Ages. The odd thing is that the man who made the discovery, Joseph Priestley, was not studying the nature of fire, but of another
of the Greek elements, the invisible and omnipresent air.

Most of what remains of Joseph Priestley’s laboratory is in the Smithsonian Institution in Washington, D.C. And, of course, it has no business to be there. This apparatus ought to be in Birmingham in England, the centre of the Industrial Revolution, where Priestley did his most splendid work. Why is it here? Because a mob drove Priestley
out of Birmingham in 1791.

Priestley’s story is characteristic of another conflict between originality and tradition. In 1761 he had been invited, at the age of twenty-eight, to teach modern languages at one of the dissenting academies (he was a Unitarian) which took the place of universities for those who were not conformists of the Church of England. Within a year, Priestley was inspired by
the lectures in science of one of his fellow teachers to begin a book about electricity; and from that he turned to chemical experiments. He also became excited about the American Revolution (he had been encouraged by Benjamin Franklin) and later the French Revolution. And so, on the second anniversary of the storming of the Bastille, the loyal citizens burned down what Priestley described as one
of the most carefully assembled laboratories in the world. He went to America, but was not made welcome. Only his intellectual equals appreciated him; when Thomas Jefferson became President, he told Joseph Priestley, ‘Yours is one of the few lives precious to mankind’.

I would like to be able to tell you that the mob that destroyed Priestley’s house in Birmingham shattered the dream of a beautiful,
lovable, charming man. Alas, I doubt if that would really be true. I do not think Priestley was very lovable, any more than Paracelsus. I suspect that he was a rather difficult, cold, cantankerous, precise, prim, puritanical man. But the ascent of man is not made by lovable people. It is made by people who have two qualities: an immense integrity, and at least a little genius. Priestley had
both.

The discovery that he made was that air is not an elementary substance: that it is composed of several gases and that, among those, oxygen – what he called ‘dephlogisticated air’ – is the one that is essential to the life of animals. Priestley was a good experimenter, and he went forward carefully in several steps. On 1 August 1774 he made some oxygen, and saw to his astonishment how brightly
a candle burned in it. In October of that year he went to Paris, where he gave Lavoisier and others news of his finding. But it was not until he himself came back and, on 8 March 1775, put a mouse into oxygen, that he realised how well one breathed in that atmosphere. A day or two after, Priestley wrote a delightful letter in which he said to Franklin: ‘Hitherto only two mice and myself have
had the privilege of breathing it’.

Priestley also discovered that the green plants breathe out oxygen in sunlight, and so make a basis for the animals who breathe it in. The next hundred years were to show this is crucial; the animals would not have evolved at all if the plants had not made the oxygen first. But in the 1770s nobody had thought about that.

The discovery of oxygen was given meaning
by the clear, revolutionary mind of Antoine Lavoisier (who perished in the French Revolution). Lavoisier repeated an experiment of Priestley’s which is almost a caricature of one of the classical experiments of alchemy which I described at the beginning of this essay. Both men heated the red oxide of mercury, using a burning glass (the burning glass was fashionable just then), in a vessel in
which they could see gas being produced, and could collect it. The gas was oxygen. That was the qualitative experiment; but to Lavoisier it was the instant clue to the idea that chemical decomposition can be quantified.

The idea was simple and radical; run the alchemical experiment in both directions, and measure the quantities that are exchanged exactly. First, in the forward direction: burn
mercury (so that it absorbs oxygen) and measure the exact quantity of oxygen that is taken up from a closed vessel between the beginning of the burning and the end. Now turn the process into reverse: take the mercuric oxide that has been made, heat it vigorously and expel the oxygen from it again. Mercury is left behind, oxygen flows into the vessel, and the crucial question is: ‘How much?’ Exactly
the amount that was taken up before. Suddenly the process is revealed for what it is, a material one of coupling and uncoupling fixed quantities of two substances. Essences, principles, phlogiston, have disappeared. Two concrete elements, mercury and oxygen, have really and demonstrably been put together and taken apart.

It might seem a dizzy hope that we can march from the primitive processes
of the first coppersmiths and the magical speculations of the alchemists to the most powerful idea in modern science: the idea of the atoms. Yet the route, the firewalker’s route, is direct. One step remains beyond the notion of chemical elements that Lavoisier quantified, to its expression in atomic terms by the son of a Curnberland hand-loom weaver, John Dalton.

After the fire, the sulphur,
the burning mercury, it was inevitable that the climax of the story should take place in the chill damp of Manchester. Here, between 1803 and 1808, a Quaker schoolmaster called John Dalton turned the vague knowledge of chemical combination, brilliantly illuminated as it had been by Lavoisier, suddenly into the precise modern conception of atomic theory. It was a time of marvellous discovery in chemistry
– in those five years ten new elements were found; and yet Dalton was not interested in any of that. He was, to tell the truth, a somewhat colourless man. (He was certainly colour-blind, and the genetic defect of confusing red with green that he described in himself was long called ‘Daltonism’.)

Dalton was a man of regular habits, who walked out every Thursday afternoon to play bowls in the countryside.
And the things he was interested in were the things of the countryside, the things that still characterise the landscape in Manchester: water, marsh gas, carbon dioxide. Dalton asked himself concrete questions about the way they combine by weight. Why, when water is made of oxygen and hydrogen, do exactly the same amounts always come together to make a given amount of water? Why when carbon
dioxide is made, why when methane is made, are there these constancies of weight?

Throughout the summer of 1803 Dalton worked at the question. He wrote: ‘An enquiry into the relative weights of the ultimate particles is, as far as I know, entirely new. I have lately been prosecuting this enquiry with remarkable success.’ And he thereby realised that the answer must be, Yes, the old-fashioned
Greek atomic theory is true. But the atom is not just an abstraction; in a physical sense, it has a weight which characterises this element or that element. The atoms of one element (Dalton called them ‘ultimate or elementary particles’) are all alike, and are different from the atoms of another element; and one way in which they exhibit the difference between them is physically, as a difference in
weight. ‘I should apprehend there are a considerable number of what may properly be called elementary particles, which can never be metamorphosed one into another.’

In 1805 Dalton published for the first time his conception of atomic theory, and it went like this. If a minimum quantity of carbon, an atom, combines to make carbon dioxide, it does so invariably with a prescribed quantity of oxygen
– two atoms of oxygen.

If water is then constructed from the two atoms of oxygen, each combined with the necessary quantity of hydrogen, it will be one molecule of water from one oxygen atom and one molecule of water from the other.

The weights are right: the weight of oxygen that produces one unit of carbon dioxide will produce two units of water. Now are the
weights right for a compound that has no oxygen in it – for marsh gas or methane, in which carbon combines directly with hydrogen? Yes, exactly. If you remove the two oxygen atoms from the single carbon dioxide molecule, and from the two water molecules, then the material
balance is precise: you have the right quantities of hydrogen and carbon to make methane.

The weighed quantities of different elements that combine with one another express, by their constancy, an underlying scheme of combination between their atoms.

It is the exact arithmetic of the atoms which makes of chemical theory the foundation of modern atomic theory. That is the first profound lesson that comes out of all this multitude of speculation about gold and copper and alchemy, until
it reaches its climax in Dalton.

The other lesson makes a point about scientific method. Dalton was a man of regular habits. For fifty-seven years he walked out of Manchester every day; he measured the rainfall, the temperature – a singularly monotonous enterprise in this climate. Of all that mass of data, nothing whatever came. But of the one searching, almost childlike question about the weights
that enter the construction of these simple molecules – out of that came modern atomic theory. That is the essence of science: ask an impertinent question, and you are on the way to the pertinent answer.