It is written in Genesis:

The elemental power of water calls to mind the floods and disasters underlying the various Creation myths. Water is life, abundance, God's blessing all in one. 'Be praised, O Lord, because of the water,' St Francis of Assisi proclaims. 'It is so needful, pliant, precious and fragile.'  The word water connotes sea, river, ice, rain, snow, blood and sap, fecundity and floods, boons and perils. It is of water that many of the chapters of the history of creation, of our planet and its inhabitants, speak. 

Water is a liquid without smell, colour or taste, a compound of hydrogen and oxygen which boils at the temperature of 100° C., and whose freezing point is zero centigrade.  Water is indispensable: more than seven-tenths of the globe's surface is covered with water and nine- tenths of animal life is found in it. Lower animals and vegetable life contain 90 per cent water, and higher animals, including man, between 60 and 70 per cent. Ceaselessly water irrigates the human body, nourishes its cells; it is the prime mover in those manifold and complex physical processes which we call Life.

Falling from the sky as rain, water nourishes the soil, passes through animal and vegetable creation, unites into streams and rivers and lakes, vaporizes, forms clouds, condenses and falls again in droplets, a vital circuit constantly begun again. A waterless globe would be no more than a mass of dead rock.

Thus it is hardly surprising that, two thousand five hundred years ago, there was born the idea that water, the prime source of all life, was the basic substance from which other forms of matter derived; an idea which from that time onward has never ceased to fascinate poets, philosophers and scientists. Today we all realize that this notion, by no means misconceived, accords in part with the fact that hydrogen, the element H with atomic weight of 1-00813 and of such prominence in the modern world, is indeed the fundamental ingredient of matter.

This theory of water as the primary source of all things was propounded first by Thales, a Greek, who did not know what hydrogen was—less still had he any idea of nuclear fusion. He lived about 595 b.c. at Miletus, a coastal town in Asia Minor, and historians are unanimous in regarding him as the father of philosophy. The degree to which Thales and the other pre- Socratic thinkers of Miletus were philosophers in the modern sense is a matter of opinion. The Greeks called them physiologists, meaning naturalists. This they truly were—thinking and theorizing scientists like Galileo, Laplace, Darwin and Einstein.  We can well understand how Thales describes the apparently omnipotent water as 'the beginning of all'.

A fortunate age! The various sciences and speculative disciplines were not yet divided by impassable gulfs. The wide-ranging curiosity of Thales led him to study the nature of water, and to see in it the basis of everything. He could do so with impunity, for nobody had then thought of requiring scientists to keep to their facts and leave philosophy to the philosophers. In the same way, no one desired the philosopher to stay in his world of ideology and not disturb the scientists at their tasks. The result was that Miletus, a port and commercial town at the mouth of the Meander, became the cradle of western physics and philosophy.

We learn a good deal about Thales from scattered pieces of evidence. Various entertaining anecdotes reveal him as a shrewd politician, an astute merchant and a successful speculator in oil, though others reproach him for professional aloofness. One story in particular recounts that once, while gazing at the heavenly bodies, he fell into a well, amid the jeers of the bystanders. Adept at geometry, he calculated the height of the pyramids during a journey in Egypt and brought back to Greece the mathematical knowledge of the Egyptians. He held that all matter was animate, and he may well have suspected the existence of magnetism and electricity. From all points of view he seems to have had a truly encyclopaedic mind.

As has been mentioned, the pre-Socratic Greeks were first and foremost naturalists and rationalists. In seeking the prime substance they were looking not for some abstract principle but for tangible matter. Philosophers of the period could choose among four, the traditional elements of ancient chemistry: earth, water, fire and air. These were not, of course, 'elements' in the sense of modern chemistry, immutable components of matter, for their form changed and could be changed. Must one of them have been progenitor of the other three? If so, which? Thales unhesitatingly chose water.

'What is water?' was also the question asked in the Middle Ages by the alchemists of Europe and the Arab world as, amid the fumes of sulphur, they sought in their sanctums the 'philosophers' stone' and tried to transmute base metals into gold. Yet it would be wrong to ridicule those wizards and their disciples, for the chemists of today descend from them in a direct line.

For a whole millennium the cauldrons and retorts of the alchemists glowed and hissed. Countless salts, metals, liquids, mixtures and tinctures, bases and substances, simmered upon wayward fires. Did those materials derive, as the Greeks had maintained, from a small number of basic elements? The alchemists replied in the affirmative and, like the Greek physiologists, believed in the trans-mutability of the elements. They too, emulating Thales, were searching for prime matter, the root of everything. And most of them inclined towards water.

Boiling turned water into steam, frost made it ice. Salts could be obtained from sea water, and did not miraculous mercury suggest a metal in liquid form—or a metallic liquid? Some of the alchemists even supposed that all salts, ores, metals, minerals and crystals had emerged from water which had been subjected to colossal pressure and incalculable heat in the centre of the earth.

Even on the threshold of modern times many of the best minds still considered that the systematic distillation of water would produce soil and that quartz was evidently crystallized water. It was only in the second half of the eighteenth century—between 1766 and 1783 to be precise—that four scientific inquirers noted independently that water was not an element but a composite substance. Admittedly, none of them deduced the consequences of his discovery; that remained to a fifth man, a master of chemistry, a few years later.

Throughout the eighteenth century men of science had been inquiring into the properties of gases and liquids and into the nature of combustion. Combustion was believed to depend upon the action of an agent which was named 'phlogiston', and for over a century this theory prevailed. This was just at the time when the classical belief in earth, air, fire and water was being replaced by the concept of elements—fundamental substances which defy analysis. Such was the case of gold, of silver, copper, iron, sulphur, phosphorus and chlorine, but not of earth. Were fire, air and water like that too?

Lord Henry Cavendish, grandson of the second Duke of Devonshire. He was a wealthy amateur who dedicated almost his whole fortune to experiments in chemistry and physics. Cavendish was particularly interested in the composition of the atmosphere and in 1766 he submitted to the Royal Society a paper entitled ' Factitious Airs', in which he touched on hydrogen and its explosive effect when mixed with air. Cavendish has been named as the discoverer of hydrogen but he did not make this claim himself and indeed mentions that the explosive effect was known to Robert Boyle and others. Cavendish thought that this gas was in fact 'phlogiston'. He continued his experiments for many years and eventually reached the conclusion, about 1782 or 1783, that water was 'dephlogisticated air combined with phlogiston'. Meanwhile, in 1774, our second inquirer, Joseph Priestley, had isolated oxygen—which was none other than 'dephlogisticated air'. He had settled at Birmingham in 1780 and had immediately joined the Lunar Society there, with many of whose members he had been in correspondence for several years. These included many men of inquiring spirit, among them James Watt, inventor of the condensing steam engine, who had a very practical interest in the nature of water and steam and their properties. Cavendish and Priestley certainly corresponded with each other and it was thus that in 1783 all these men were forming ideas on the exact nature of water and the part played in its constitution by 'phlogiston' (hydrogen), and 'dephlogisticated air' (oxygen). In January 1784 Cavendish communicated to the Royal Society his finding that water was a combination of these two elements, much to the annoyance of Watt, who felt that he had arrived first at the proper conclusion. Both men, however, were too great to remain at loggerheads for long over a question of priority, and as Watt later said: 'It matters little whether Cavendish or I discovered the composition of water; the great thing is that it is discovered.'

Meanwhile the Swedish chemist Wilhelm Scheele had independently established the main constituents of the atmosphere, and reached the conclusion that there were two predominant gases, one of them aiding combustion, the other preventing it.

It required the genius of the fifth man, Antoine Laurent Lavoisier, to appreciate the full consequences of these discoveries and arrive at the true nature of combustion. Lavoisier, who was also in touch with members of the Birmingham Lunar Society, lived in Paris, that Mecca of the natural philosophers of the time. On the very eve of the French Revolution Lavoisier described in his Elemental Treatise on Chemistrythe marvel of combustion. Rejecting the phlogistic theory he revealed the true nature of the process: combination of a substance with the oxygen of the air, the proof of which is said to have cost him over 50,000 livres. In addition Lavoisier set down the fundamental principles of the conservation of matter, and his many deductions and observations earned him the title 'father of modern chemistry'.

In Paris there is a sealed tube containing 45 g. of the water synthesized by Lavoisier, and this carefully preserved relic is doubly precious. For Lavoisier had the misfortune to be not only a scientist. He was a civil servant too: a head tax-collector, inspector-general of explosives, member of the board set up to establish the new weights and measures, director of the tobacco monopoly and, finally, secretary of the treasury. Large sums thus passed through his hands, affording sufficient grounds for the revolutionaries to treat him as a profiteer of the ancien regime. He was arrested on the pretext that tobacco, bad enough before, had under his control become unsmokable. Arraigned before the tribunal Lavoisier was condemned to death. The defence dwelt upon his scientific merits, but the judges rejected their arguments with the lapidary phrase: 'The Republic has no need of scholars!' On 8th May 1794 the father of modern chemistry died upon the guillotine.

Eleven years after the death of Lavoisier two of the greatest savants of the time, Louis Joseph Gay- Lussac, physicist and chemist, and Alexander von Humboldt, traveller and naturalist, proved that water contains two parts of hydrogen to one part of oxygen.

In 1932 the American chemist Harold Clayton Urey discovered that there is, in addition to normal water, a 'heavy' water (with the formula D₂O); and he identified the hydrogen isotope D, deuterium, with an atomic weight of 2-0147, of which ordinary water contains a proportion of about 0-02 per cent. Shortly afterwards a second hydrogen isotope, tritium, was created artificially in a nuclear reactor: it is not found in ordinary water. 'Heavy water' would be of no special interest to us—unlike fish, for whom a stronger mixture of D₂O is fatal—were it not that deuterium and tritium have one surprising property. When subjected in a nuclear reactor to a temperature above fourteen million degrees C., by nuclear fusion they transmute into helium and give off a vast amount of energy in the process.

The H-bomb was already on the horizon.

In the American 'atomic city' of Los Alamos, in the 1950s, the phantasm took shape. It was not without grave misgivings that the project was undertaken. Some protested that the explosion of a hydrogen bomb might start a chain reaction of world dimensions: the hydrogen within the atmosphere and the waters of the Earth would be transformed into helium, the planet would become a flaming star and disappear into the void. Albert Einstein gave warning in these terms: 'The spectre of universal ruin takes ever clearer shape upon the horizon.' Edward Teller, the father of the H-bomb, nevertheless brought his project to fruition, and on 1 November 1952 a ball of fire of a diameter of three and a half miles arose above the island of Eniwetok in the Marshall Islands. There was a crater two hundred feet deep: man had brought off for the first time what was the prerogative of the Sun—with the one distinction that at Eniwetok there had been only destruction and nothing had been created.

There is a long thread linking Thales of Miletus and Edward Teller, the primordial element of water and the H-bomb.