Categories: Chemistry in History , My Hero |  Comments
Guest post by Chemistry World intern Dan Johnson
It has often been said of Franz Schubert, the great Austrian composer, that if the mark of a genius is an early death, then he can be considered a greater genius than Mozart. Mozart died at 35; Schubert at 31. But perhaps we should cast the net wider than music. On this scale of genius cut short, the death of Henry Moseley on 10 August 1915, at the age of only 27, might make his life the most fleetingly brilliant of all. His death is all the more poignant for what he might have achieved. In a few short years he laid out the basis for the modern periodic table, predicted the elements that would fill in the gaps and showed that x-rays could be a supreme analytical tool. Few achieve in a lifetime of research what he achieved in a career of just 40 months.
— Henry Moseley in his lab
Moseley, known as Harry to his family, came from strong scientific stock. His father, Henry Nottidge Moseley, was a naturalist and professor at Oxford who journeyed on the Challenger expedition; his grandfather was a conchologist and fellow of the Royal Society. As a child it seemed that he would follow his father –Harry and his sister scoured the surrounding countryside, cataloguing as much of the native flora and fauna as they could find.
In the end experimental physics was to be his path. According to John Heilbron – author of a biography about Moseley – a physics master at Harry’s prep school, Summer Fields, steered him towards the fastest-paced discipline of the day. But in light of his wider interest in science, it is perhaps fitting that he was to make such an impact on another discipline: chemistry.
From Summer Fields, he gained a scholarship to Eton, and from Eton he proceeded to Oxford. Oxford in Harry’s time was not the intellectual powerhouse it is today. In fact, where the still youthful disciplines of science were concerned, it was something of an intellectual backwater. The old dons and their belief in the primacy of classical antiquity had conspired to stem the funding available for new laboratories. A large part of the problem was the professor in charge of physics, a man named Robert Bellamy Clifton. He had spent vast sums of university money designing and building the Clarendon laboratory, but appears to have allowed no-one to use it. However, Harry was lucky enough to have use of the shared laboratory of Balliol and Trinity colleges during his undergraduate years. Here he honed his exceptional talents for experiment, before moving to one of the research hothouses of the day, the Victoria University of Manchester, where he would work under the great Ernest Rutherford.
His first experiments for Rutherford were on radioactivity, which, according to Heilbron, was ‘about the only thing you could study at Manchester’. It is a topic he does not appear to have found all that interesting. When the equipment for one of his experiments – the development of a radium battery – did not arrive, he set about looking for fresh research, and happened upon the fashionable area of x-rays. Foreseeing many prickly thickets of mathematics ahead (many will know how he felt), he enlisted the help of C G Darwin, the grandson of Charles Darwin and mathematical reader at Manchester.
With this collaboration came Harry’s first great successes. Keeping pace with W H Bragg – an expert on x-rays at Leeds University who was both their tutor and rival – they refined their experiments to the extent that a role reversal was possible: the clarity of the spectra allowed atomic structure to become the subject, rather than the x-rays themselves.
Like so much of his career, the next stage of Moseley’s research was a happy combination of being in the right place at the right time and natural ability. Moseley, who had recently parted ways with Darwin, was by now a virtuoso experimentalist, and onto this perfectly prepared platform landed Niels Bohr. According to Heilbron, Bohr was in Manchester towards the end of the first week of July 1913. After a long conversation with Bohr in the first week of July, in which they discussed whether the frequency of x-rays would depend on the atomic number or atomic weight, Moseley saw his opportunity. Bohr’s theory of the atom suggested that it would be atomic number that the x-rays corresponded to, as their energy depended on the outermost electron and the nature of this electron depended on the atomic number.
Using his talent for engineering he put together apparatus whereby multiple elements could be used to create x-rays. By 19 October 1913 he had surmounted most of the experimental challenges, and in only four days he collected the spectra of titanium, chromium, manganese, iron, cobalt, nickel and, for good measure, copper and silver. In a fortnight he had all the spectra from calcium to zinc. Moseley was taken aback by how easy it all was – he was into his stride.
What Moseley did next would have a huge effect on chemistry, and the periodic table in particular. Since Mendeleev’s time, the table had been ordered on the concept of atomic weight. Mendeleev and his contemporaries forensically examined the chemical properties of each element, and grouped those with similar properties together. However, in a few notable cases – such as that of argon and potassium – Mendeleev had to break the sequence of atomic weight to keep similar properties in the same groups. These ‘pair reversals’ called into question the principle of atomic weight as the basis of the periodic table.
— Moseley’s ‘step ladder’ of x-ray emission specta
Moseley’s research provided the solution. Through his ground breaking experiments he formulated a law (later called Moseley’s law) which proved what Bohr and others had suspected – that the frequency of x-rays is proportional to the atomic charge. The elements could now be ordered according to atomic number and the mystery of the pair reversals was solved. Nevertheless, some more conservative chemists, such as Arthur Smithells at Leeds, refused to accept Moseley’s law as the new basis of the periodic table. They thought it an isolated trend and were unwilling to concede that the search for new elements was almost at an end.
At the end of November he published his famous step ladder, showing the increasing frequency of the x-rays from calcium to copper. Conscious of being overtaken by another researcher, he published his law on what he called the ‘slenderest of evidence’; he later vindicated the law with investigation of further elements. Ordering the elements in this way meant he could now see the gaps in the periodic table, where elements of a certain atomic number were missing. Moseley had laid the groundwork for a vast treasure hunt, and chemists would spend more than 30 years searching for the missing elements his method had predicted.
On the 28 July 1914, a gunshot in Sarajevo sealed the fate of Harry and thousands of other young men like him. At the start of the first world war Moseley was in Australia for a meeting of the British Association for the Advancement of Science. Confident that he was some distance ahead of his competitors (‘those hungry Germans,’ as he called them), he had planned to stay until October. But once news of the declaration of war reached the Antipodes, Moseley felt it was his duty to fight. Friends and family tried to persuade him not to join up, but it appears that he never considered it. He left on a ship for San Francisco, where he caught the first train to New York. From there the ill-fated Lusitania took him home and he was in England training with the Royal Engineers by October.
The Gallipoli campaign, the failure of which would consign Churchill to two decades in the political wilderness, needed reinforcements. Hundreds of troops had died in an effort to secure a sea passage through the Dardanelles to Britain and France’s ally, Russia. It was here that Harry and his men were sent. Unwilling to admit that the campaign had failed, generals ordered Harry’s force to the strategic high ground of Chunuk Bair, to relieve a tired battalion of New Zealanders. Having marched cross-country, over river beds and through thick woods, they were overwhelmed by a Turkish counter-attack. Heilbron quotes one of the soldiers there saying: ‘The Turks came again and again … calling upon the name of God.’ He continues: ‘Our men stood to it and maintained, by many a deed of daring, the old traditions of their race. There was no flinching. They died in the ranks where they stood.’ Among the carnage Henry Moseley was cut down, three months before his 28th birthday. Isaac Asimov called it ‘the single most costly death of the war’.
It is impossible to predict what else he might have turned his penetrating mind to, but Joseph Nordgren, an x-ray specialist at Uppsala University, thinks Moseley could have counted on a Nobel prize. Indeed, he was nominated for the 1914 prize for physics. Further evidence for this can be found in the choice of the 1924 prize for physics. Alfred Nobel’s will states that the prize for physics ‘shall go to person who shall have made the most important discovery or invention within the field’. But Nordgren says that Manne Siegbahn, who was awarded the 1924 prize for his work on x-rays, didn’t make a tangible discovery. ‘Siegbahn’s improvements made other discoveries possible. But if you want to find a distinct discovery [by Siegbahn], a paper for example, it’s very hard’. This was discussed by the committee of 1924, before they eventually awarded Siegbahn the prize anyway. His improvements, impressive as they were, were built on an earlier discovery. The discovery was Moseley’s.
Moseley then, was both lucky and tragically unlucky. Lucky that he lived in an age where science became more open and more exciting with each new discovery. Unlucky that he also lived in an age where war was seen as a game, and years of relative peace had erased the pain of bloodshed from the collective memory.