World War I, Gallipoli front, the allied forces consisting of the soldiers from Britain, France, Australia, and New Zealand attacked and partly occupied the Gallipoli Peninsula of the Ottoman Empire (present Turkey) starting April 25, 1915. The goal was to control the Straits of the Dardanelles, separating the European part of the Ottoman Empire from its Asian part Anatolia so that the allied battleships can reach Constantinople (Istanbul) and knock out the Ottoman Empire from the war. The other goal was to open a supply line to the Russian Empire that was struggling in battles against Germany on its Western front. Earlier on March 18, 1915, sixteen of the British and French battleships with two ships in reserve had failed to pass through the Dardanelles and retreated with heavy losses. The battles on the Gallipoli front were very bloody and caused heavy casualties totaling to about 250,000 dead or wounded soldiers on each side. One of the bloody battles took place at a hill called Chunuk Bair (Conkbayırı) (280 m high) on August 10, 1915, which was partly occupied by the soldiers from New Zealand, who were later replaced by those from Britain a day earlier. For both sides, this hill was absolutely crucial to the victory or loss of the whole battle of Gallipoli. Early morning, three regiments of the Turkish soldiers attacked the British soldiers and swept them from the hill. Both sides suffered very heavy casualties. Some of the Turkish soldiers reached a place called The Farm about 400 m below the Chunuk Bair, where the 38th Brigade of British soldiers commanded by General Antony Baldwin were trying to attack the hill. The battle was very intense and General Baldwin and his soldiers totaling to about 1,000 were killed. The survivors retreated. Among the soldiers killed, there was a Second Lieutenant by the name of Henry Moseley, who got shot in the head and died instantly. He was 27 years old, about three months short of his 28th birthday.
Who was Henry Moseley and what was his relationship to the Periodic Table of the Elements? I became aware of Moseley’s death at the battle of Gallipoli when I was reading Richard Rhodes’s book “The Making of the Atomic Bomb” in 2008. There was also a picture of Moseley in his military uniform. I became very interested in finding out more about Moseley’s death, his scientific contributions and how he ended up being in the middle of this battle. I had always been interested in the history of the battle of Gallipoli and had previously visited the battlefields four times. My fascination with this battle is an intersection of where I am from and what I do. I’m originally from Turkey and a scientist. My work and the work of many scientists depend on the periodic table, so it’s important for us to remember the work of those who contributed to it. I’ve had the opportunity to give talks about Moseley in a friendship meeting between the Turkish and British organizations dedicated to the remembrance of this battle, as well as to several universities in Turkey. I even wrote a small book about Moseley at the request of the Turkish Academy of Sciences, where I had given a talk about him.
Henry Gwyn Jeffreys Moseley, Jr. was born on November 23, 1887, in Weymouth, Dorset, England. He came from a rich and aristocratic family that included famous scientists. His father Henry Nottidge Moseley was a professor of anatomy and physiology at the Oxford University.He joined the scientific staff of HMS Challenger to study ocean bottoms for four years (1872-1876). On his return, H. N. Moseley wrote an account of his experiences during the voyage on HMS Challenger, “Notes of a Naturalist on the Challenger” (1879). Shortly after receiving a copy, his close friend Charles Darwin wrote to him, “Your volume is a mass of interesting facts and discoveries, with hardly a superfluous word.” Henry was only four years old when his father died at the age of 47 in 1891. His mother was Amabel Gwyn Jeffreys, the daughter of the Welsh biologist John Gwyn Jeffreys. In 1913, she won the British Ladies’ chess championship. At the age of 13, Henry entered Eton College with a King’s Scholarship. This school catered mainly to the sons of the upper-middle class families and furnished a large share of Britain’s politicians, industrial leaders, scientists, etc. He studied mathematics, physics, and chemistry. In 1906, Henry entered the Trinity College at the University of Oxford, where he earned his bachelor’s degree in 1910. Henry received second class honors in physics and always considered it a “failure.” After graduating, Moseley contacted Prof. Ernest Rutherford at the University of Manchester and expressed his desire to work with him. Rutherford, who was awarded the Nobel Prize in Chemistry in 1908, accepted Moseley, and he moved to Manchester in September 1910. The laboratory of Rutherford was a kind of “nursery of genius” with young scientists from different countries who laid the foundations of much of modern atomic physics. Many of them such as Hans Geiger, Ernest Marsden, Frederick Soddy, György von Hevesy, Otto Hahn, and Niels Bohr won their own Nobel Prizes. First, Moseley had a teaching load as a “Lecturer and Demonstrator” for the first year. Then, at the request of Rutherford, he worked on radioactivity and published four papers. Actually, Moseley’s big interest was the nature of X-rays, discovered in 1895 by the German physicist Wilhelm C. Röntgen. Henry believed that such a work would shed light on the nature of the atom. He asked his childhood friend Charles G. Darwin (Charles Darwin’s grandson), who was a mathematician and theoretical physicist, to join him in this work. Rutherford, however, objected and felt that nobody, including himself in Manchester, knew about the techniques to be used in this work. After a short while, he consented to let Moseley and Darwin try. So began Moseley’s revolutionary work on X-rays.
Moseley and Darwin built an apparatus, which consisted of an X-ray source called “Müller tube” with a platinum target, a crystal, and a detector (ionization chamber). Three different crystals were used. They discovered that the radiation from the X-ray tube with a platinum target was of two kinds, (A) radiation of indefinite wavelength analogous to white light, and (B) five types of monochromatic radiation, probably characteristic of platinum. Bragg’s law (nλ = 2d sin θ) was used to calculate the wavelengths of the five types of monochromatic radiations reflected only at special angles. They also found that the X-rays were not manufactured in the crystal because all their properties were independent of the nature of the reflecting three crystals used. Moseley and Darwin published their findings in July 1913 in Philosophical Magazine. Afterwards, Moseley continued working alone and became convinced that the discovery of unique X-ray wavelengths of every known element offers science a powerful tool, which may shed light on the secrets of the atom’s structure. In 1869, the Russian chemist Dmitri Ivanovich Mendeleev declared his discovery in a speech to the Russian Chemical Society that the chemical properties of the elements periodically depend on their atomic weights, inventing the Periodic Table of the Elements that had 63 elements. In addition, he predicted three new elements to complete the table. A few months later, the German chemist Julius Lothar Meyer independently published a paper also describing the periodic properties of the known elements depending on their atomic weights, discovering the same periodicity. In the Mendeleev’s table, there were arbitrary atomic numbers of the elements. This Periodic Table of the Elements served science for almost fifty years. In 1913, Antonius van den Broek, a lawyer and amateur physicist in Amsterdam, proposed in two papers, in Physikalische Zeitung and Nature, that all the chemical and optical (including X-rays) properties of an element were determined by its “atomic number,” that is, by its serial order in the periodic table of Mendeleev, but not by its atomic weight. Broek’s contributions were praised as “very promising” first by Frederick Soddy and a month later by Rutherford in successively published papers in Nature in 1913. However, the “atomic number” was merely an element’s place in the periodic table and somehow related to the positive charge of the nucleus of Rutherford’s atom and was approximately equal to half of the atomic weight. It was not known to be associated with any measurable physical quantity. Chemists had already discovered that, at three places in the periodic table — argon-potassium, cobalt-nickel, and tellurium-iodine — the chemical order inverts the sequence of atomic weights. There was no satisfactory explanation for this phenomenon. Moseley decided to test the “Broek’s hypothesis,” as he called it. He declared, “we will see what quantity determines the X-ray spectra” and began his survey of the high-frequency spectra of the elements.
Moseley made several changes to his X-ray apparatus and substituted a photographic plate for the ionization chamber. He used 12 elements from calcium to zinc (Z [atomic number] = 20 to 30). These elements included one of the critical pairs, cobalt (atomic weight [A = 58.93] [Z = 27]) and nickel (A = 58.69) (Z = 28). As he expressed later: “The inclusion of nickel was of special interest owing to its anomalous position in the periodic system.” In only a fortnight, he got the X-ray spectra. Each element gave two main lines, an α and a β, of which the former was five times more intense than the latter. He made a table for α and β lines with eleven of them where scandium (Z = 21) had no numbers. According to the Bohr’s atomic model, Kα line is produced by an electron dropping from the L-shell (higher energy level) to the K-shell (ground state with the lowest energy level), whereas an electron dropping from the M-shell (higher energy level than the L-shell) to the K-shell gives rise to the Kβ line. The spectra followed Z rather than A. He informed his friend Niels Bohr of his progress, “The results are extremely simple and largely what you expect.” The spectra of some elements contained other lines with low intensity. Moseley thought that these lines may result from impurities in the metal samples. To prove his point, he also analyzed brass (an alloy of copper and zinc) and found the characteristic α and β lines of copper and zinc. Moseley prepared a table that showed the reflection angles of the α and β lines, the wavelengths, and the atomic numbers and atomic weights of the elements. There was a simple formula in this table:
Q = (ν/¾ν0)½ (ν = the frequency of the radiation α)
Q increased by a constant amount from one element to the next, using the chemical orders of the elements in the periodic table. Except in the case of nickel and cobalt, this was also the order of the atomic weights. He then plotted the inverse square roots of the wavelengths of the Kα and Kβlines and obtained a straight line in each case in the exact order of the atomic numbers of the elements (the Kβ line of zinc was missing because it was not found). (I replotted these numbers and found a perfect linear relationship with R2 (coefficient of determination) = 0.9999.)
Moseley generated a diagram using the spectra of the elements in decreasing order of frequencies and atomic numbers from left to right with the spectrum of copper on the bottom and that of calcium on the top. Scandium was missing because he had not examined a sample of it. He used the photographs of the spectra. The spectrum of each element consisted of two lines, the stronger α line and the weaker β line. He stated that the faint lines found besides the α and β lines were almost certainly all due to impurities. Indeed, brass showed the α and β lines of both copper and zinc. It was startling that these lines shifted, as the atomic numbers of the target increased, in the directions of shorter and shorter wavelengths. This diagram is now celebrated as “Moseley’s staircase (or step ladder).” Moseley concluded, “The prevalence of lines due to impurities suggest that this may prove a powerful method of chemical analysis. Its advantage over ordinary spectroscopic methods lies in the simplicity of the spectra and the impossibility of one substance masking the radiation from another. It may even lead to the discovery of missing elements, as it will be possible to predict the position of their characteristic lines.” Time would show that he was absolutely right.
The frequency of the α component was given to within 0.5% by an “extremely simple” formula, where N is the atomic number (N was used for the atomic number at the time, but replaced by Z later) and v0 is the Rydberg fundamental frequency of ordinary line spectra according to Bohr’s explanation of the Balmer series for hydrogen:
ν = ¾ ν0 (N–1)2 or ν = (1/12–1/22) ν0 (N–1)2
Moseley also gave a formula for the radiations of the L series for the results obtained, stating that they are “too meagre to justify any explanation.” He published his results in Philosophical Magazine in December 1913 as “The High-Frequency Spectra of the Elements” with the statement “We have here a proof that there is in the atom a fundamental quantity, which increases by regular steps as we pass from one element to the next. This quantity can only be the charge on the central positive nucleus, of the existence of which we already have definite proof.” With Moseley’s work, it could now be stated: “The properties of the elements are periodic functions of the atomic number of the elements.” In the previous issue of the same journal, a trilogy of Niels Bohr’s papers entitled “On the Constitution of Atoms and Molecules” was published (Phil. Mag. 1-25, 476-502, 857-875, 1913). In 1923, Nobel Laureate György von Hevesy emphasized in one of his papers that Moseley’s results were “amazingly simple” and “the atomic theory would not predict this simplicity.”
In November 1913, Moseley felt the need for a drastic change. He went to Oxford University to work with Prof. J.S. Townsend and to continue his experiments and to be nearer to his mother. Rutherford tried hard to persuade him to stay in Manchester, but without success. In Oxford, he measured the Kα and Kβ lines for the elements from aluminum to silver (Z = 13 to 47), and then Lα and Lβ, Lφ and Lγ lines for the elements from zirconium to gold (Z = 40 to 79). He prepared two tables with the atomic numbers (N) and the wavelengths of the α and β lines in one table, and thewavelengths of α, β, ϕ and γ lines in the other table. There were also two Q values in both tables QK = N–1 and QL = N–7.4, with both being approximate values. Moseley then plotted the square roots of the frequencies of each line versus the atomic weights, with the wavelengths as the scale at the top of the diagram, except in the cases of argon-potassium, cobalt-nickel, and tellurium-iodine, where these clashed with the order of the atomic weights. The graph showed straight lines for all six measured Kα, Kβ, Lα, Lβ, Lφ and Lγ lines. In the case of Lβlines, there was some slight deviation from the linearity in the case of the elements 76 to 79. There were problems in the rare earth element group. He hoped soon to complete the examination of the spectra of this group. Vacant lines were left for three elements with the atomic numbers of 43, 61 and 75, none of which were known. Tellurium, which had been erroneously separated into two constituents by C.A. von Welsbach, was given two lines with the atomic numbers 69 and 70. The elements 71 and 72 were incorrectly designated as ytterbium and lutetium, respectively. These four elements were not measured. He also mixed up the rare earth elements holmium and dysprosium, but later corrected these mistakes in a letter to von Hevesy in April 1914 before distributing reprints except for “celtium,” which the French Chemist Georges Urbain claimed to have discovered in 1911. Moseley made it element 72. Moseley concluded, “There is every reason to suppose that the integer which controls the X-ray spectrum is the same as the number of electrical units in the nucleus, and these experiments therefore give the strongest possible support to the hypothesis of van den Broek.” He then gave the approximate general relation between ν1/2 and N as ν = A (N – b)2 where A and b are constants characteristic of each line: for Kα line, A = (1/12–1/22) ν0 and b =1, and for Lα line, approximately A = (1/22–1/32) ν0 and b =7.4. These equations are known as Moseley’s Law. Moseley summarized his findings:
Mendeleev once admitted, “The position of the rare earths is to be one of the most difficult problems offered to the Periodic Law.” He could find no places for them in his list of the elements. Chemists had great difficulties for isolation and purifying these elements. This problem had occupied chemists for years. William Crookes (inventor of Crookes tube) said, “The rare earths perplex us in our very dreams. They stretch like an unknown sea before us, mocking, mystifying, and murmuring strange revelations and possibilities.” Moseley decided to face this “jungle” with his X-ray method. He obtained samples from various scientists including Crookes. He measured the L rays of these elements, but encountered considerable trouble because most of them were “terrible mixtures.” Moseley’s work showed that the lanthanide series of rare earth elements, i.e., lanthanum through lutetium (Z = 57 to 71), must have 15 members, no more and no less, as Moseley expressed it. A quick look at the modern Periodic Table of the Elements reveals exactly this fact. In May 1914, Prof. Georges Urbain from the University of Paris, who had worked on rare earth elements for many years, came to Oxford to visit Moseley. He wanted to examine the X-ray spectrum of “celtium” that he thought he had discovered as a new element. Urbain also brought several other elements. He handed Moseley an ore containing an unknown number of the rare earth elements mixed in minute amounts and said, “Tell me what elements are present.” After careful measurements with his X-ray spectrometer for a week, Moseley gave Urbain a complete story of the rare earth elements in Urbain’s samples. “Erbium, thulium, ytterbium and lutetium (Z = 68, 69, 70 and 71, respectively) were present, but the element corresponding to No. 61 was absent.” Urbain was astonished by the speed and reliability of Moseley’s analysis, but annoyed that there was no place for his “celtium.”
Following Moseley’s death, the four elements for which Moseley had left vacant lines in the Figure 3 of his last paper were discovered. In 1923, the element with the atomic number 72 was discovered in Niels Bohr’s laboratory by György von Hevesy and Dirk Coster. It was named Hafnium (Hf). The element with the atomic number 75 was discovered in 1925 by Walter Noddack, Ida Tacke and Otto Berg in Germany by using Moseley’s methods. It was named Rhenium (Re). The element with the atomic number 43 was discovered in 1937 by Carlo Perrier ve Emilio Segrè in Italy. It was named Technetium (Tc). This is the first artificially obtained radioactive element. Today, Technetium is the widely used radioactive element in nuclear medicine. The element with the atomic number 61 was discovered in 1945 at the Oak Ridge National Laboratory, USA by Jacob A. Marinsky, Lawrence E. Glendenin and Charles D. Coryell. It was named Promethium (Pm).
When World War I started in July 1914, Moseley was in Australia with his mother attending a meeting of the British Association for the Advancement of Science. On his return, Moseley decided to enlist himself in the military. Rutherford and his mother tried to unsuccessfully dissuade him from enlisting for combat duty. They said he would be better off serving his country’s war effort behind the front lines. Moseley did not budge and decided to enlist himself in the Royal Engineers. They declined and said, “We need engineers, not physicists.” Nevertheless, he then pulled “private strings” and joined the 38th Brigade as a Second Lieutenant responsible for communications with his 26 soldiers under his command. He thought that he would go to France and fight against Germans. In April 1915, General Sir Ian Hamilton was assembling an army for the invasion of the Gallipoli peninsula. Several months after invasion, however, Hamilton requested fresh troops because of the stalemate in Gallipoli following intense battles. Moseley’s unit was attached to the 38th Brigade within the 13th Division of the New Army built by the Secretary of State for War Lord Kitchener. The new army was ordered to deploy to the East. This order would take Moseley to the Gallipoli peninsula rather than to France. In late June, the 13th Division arrived in Alexandria, Egypt. After a week, they sailed to the Dardanelles. Meanwhile, British casualties were mounting. Erasmus Darwin, Charles Darwin’s grandson, was killed in April. William H. Bragg’s second son, Robert, lost his life at Gallipoli.
On that fateful day of August 10, 1915, Henry Moseley died at the young age of 27. When the news of Moseley’s death reached Manchester, Rutherford was deeply shocked and wrote a notice of Moseley’s death to Science and said: “Moseley was one of the best of the young people I ever had, and his death is a severe loss to science.” Before another month had passed, Rutherford was still deeply affected and wrote a letter to Nature: “It is a national tragedy that our military organization at the start was so inelastic as to be unable, with a few exceptions, to utilize the offers of services of our scientific men except as combatants on the firing line. The loss of this young man on the battlefield is striking example of the misuse of scientific talent.” This indictment referred to many soldiers besides Moseley. The lesson of this mistake was learned to some extent during World War II, when somewhat more care and judgment were taken by the British military organization to assign scientists to behind-the-lines work.
When he heard of Moseley’s death, Nobel Laureate Robert A. Millikan wrote in public eulogy: “In a research which is destined to rank as one of the dozen most brilliant in conception, skillful in execution, and illuminating in results in the history of science, a young man twenty-six years old threw open the windows through which we can glimpse the sub-atomic world with a definiteness and certainty never dreamed of before. Had the European War had no other result than the snuffing out of this young life, that alone would make it one of the most hideous and most irreparable crimes in history.”
Nobel Laureate Louis de Broglie said: “Moseley’s law was one of the greatest advances yet made in natural philosophy.”
Nobel Laureate Niels Bohr in 1962 said: “You see actually the Rutherford work [the nuclear atom] was not taken seriously. We cannot understand today, but it was not taken seriously at all. There was no mention of it any place. The great change came from Moseley.”
Georges Urbain of the University of Paris wrote to Rutherford: “I had been very much surprised when I visited Moseley at Oxford to find such a very young man capable of accomplishing such a remarkable piece of work. The Law of Moseley confirmed in a few days the conclusions of my efforts of twenty years of patient work. His law substituted for Mendeleev’s somewhat romantic classification a complete scientific accuracy.”
After the war in 1919, the British returned to the Gallipoli peninsula and found battlefields covered with bones of soldiers. They built cemeteries and buried them. However, most soldiers could not be identified. A cemetery was also built on the Farm Plateau where Moseley lost his life. Bones of the 652 soldiers from General Baldwin’s 38th Brigade were buried there. It is very likely that Moseley is one of those 652 soldiers. Today, there are only seven gravestones with the names of soldiers believed to be buried in the Farm Cemetery. 645 soldiers are unidentified. An obelisk over 30 m high called the Helles Memorial was erected by Britain at the southern part of the Gallipoli Peninsula in memory of 20,956 fallen British soldiers. Their names can be found carved in stone around the memorial. One of those is the name of the Second Lieutenant Henry Gwyn Jeffreys Moseley, Royal Engineers.Gallipoli was a turning point in Turkish history because Colonel Mustafa Kemal (later Mustafa Kemal Atatürk), who led the Turkish soldiers to victory in many battles there, went on to be the founder of the secular Republic of Turkey and became its first president. Many people, including historians, consider Gallipoli a prologue to the Republic of Turkey. In 1934, Atatürk honored all foreign soldiers fallen in Gallipoli with a memorial. In a written speech that was later carved into a stone memorial near the Chunuk Bair, he said: “Those heroes who shed their blood and lost their lives. You are now lying in the soil of a friendly country. Therefore, rest in peace. There is no difference between the Johnnies and the Mehmets to us where they lie side by side here in this country of ours. You, the mothers, who sent their sons from faraway countries wipe away your tears; your sons are now lying in our bosom and are in peace. After having lost their lives on this land they have become our sons as well.”
In his short life, Moseley published eight papers. His last work led to great advances in Physics and Chemistry. Other scientists, who made very important discoveries during the same period, were awarded with the Nobel Prize. Many of Moseley’s colleagues, who were familiar with his extraordinary work, stated that, if he had lived, Moseley would have received the Nobel Prize in a few years. In fact, Karl Manne Siegbahn, the researcher who followed Moseley’s planned work and technique after his death, won the Nobel Prize in Physics in 1924. Prof. Richard Hamer from Pittsburgh University proposed in 1925 that the element 43 be called “Moseleyum” with the symbol “Ms” (Science 61, 208-209, 1925), although it had not been discovered, yet. He said, “It is a name, better and more international in character like true science itself than a latinized name of the discoverer’s own kingdom or republic.” Unfortunately, this proposal has been ignored except for the editors of Nature, who stated “In our view it would be a fitting tribute to the brilliant work of Moseley to perpetuate his name in some such way” (Nature 115, 543-546, 1925).
The following short statement by Ernest Rutherford (Nature, 96, 33, 1915) expresses the great importance of Moseley’s discoveries for Physics and Chemistry and beyond: “Moseley's fame securely rests on this fine series of investigations, and his remarkable record of four brief years’ investigation led those who knew him best to prophesy for him a brilliant scientific career. There can be no doubt that his proof that the properties of an element are defined by its atomic number is a discovery of great and far-reaching importance, both on the theoretical and the experimental side, and is likely to stand out as one of the great landmarks in the growth of our knowledge of the constitution of atoms.”
Moseley’s work is also beautifully summarized on a plaque on Oxford University’s Clarendon Laboratory: “Clarendon Laboratory, where H.G.J. Moseley (1887-1915) completed his pioneering studies on the frequencies of X-rays emitted from the elements. His work established the concept of atomic number and helped reveal the structure of the atom. He predicted several new elements and laid the ground for a major tool in the chemical analysis.”
As far as the Gallipoli Campaign is concerned, the defeated Allies fully evacuated the peninsula on January 6, 1916. Winston Churchill as First Lord of the Admiralty, who was its main architect and proponent, lost his job over the fiasco of the defeat. On the other hand, U.S. and British Navies applied the lessons learned at Gallipoli during the amphibious assaults in Normandy on June 6, 1944 (D-Day), and the Pacific in World War II. Moreover, the Gallipoli campaign fostered the national identity in Australia and New Zealand, and both countries emerged as independent states.
The author used the following sources for information: