Helium’s unusual story attracted attention of many scientists and science historians, but the real sequence of events was distorted in numerous descriptions which overgrew with a lot of fictional details. Even a legend was invented beautiful and impressive–about the discovery of the sun element but it was far from the truth.
The French astronomer J. Janssen and the English astronomer N. Lockyer are considered to be the discoverers of helium. They studied the total solar eclipse of 1868 which was especially convenient to observe on the Indian ocean shores. In letters sent to the Paris Academy of Sciences and read out at one of its sessions they wrote that the spectra of the sun photographed during the eclipse contained a new yellow line D3 corresponding to an unknown element. To commemorate this remarkable event (the discovery of a new element existing on the sun but not on the earth) a special medal was minted.
Everything is wrong in this fascinating story except two dates. First of all, in August 1868, Lockyer was not on the Indian Ocean coast and did not observe the total solar eclipse. Janssen made his observations after the eclipse. They were of great importance for astronomy but not for the history of helium. The French astronomer was the first to observe solar prominences (gigantic ejections of solar matter) not during an eclipse and to describe their nature. Here is the text of the telegram sent by him to the Paris Academy of Science: “the eclipse and prominences were observed, the spectrum is remarkable and unexpected; Prominences are of a gaseous nature.”
Up to that time scientists had known nothing about the nature of prominences. Now it became clear they were clouds of gaseous matter and had a complex chemical composition. A detailed description of his observation was given by Janssen in a letter which reached Paris only 40 days later and was two weeks behind the letter of another French astronomer S. Raye. The latter also observed the prominences and made certain conclusions about them. And what was Lockyer doing at the time? Without leaving England, he observed the prominences with the help of a specially designed spectroscope and determined the positions of lines in their spectra. On October 23 he sent a letter to the Paris Academy of Sciences; by a surprising coincidence it was received on the same day as J. Janssen’s letter.
On October 26 the letters of Janssen and Lockyer were read to the session of the Academy but they did not contain a word about either the hypothetical sun element or the line which was later identified as the characteristic line of the helium spectrum. It was only pointed out in the letters that prominences had been observed when the sun was not eclipsed. And the medal was minted precisely to mark this event. Thus, no helium was discovered on August 18, 1868, either by Janssen or by Lockyer. Their observations provided an impetus for an intensive study of prominences by many astronomers. And only then was it noticed that the spectra of prominences contained a line which could be assigned to none of the elements known on the earth. Most clearly the line was observed by the Italian astronomer A. Secci who later designated it as D3. Secci’s name ought to be placed side by side with those of Janssen and Lockyer. His role in discovering helium was no less than that of his predecessors. Secci, however, assumed that the D3 line could belong to some known element, for instance, hydrogen, under high pressures and temperatures. If this assumption had not been confirmed, Secci would have agreed to consider D3 line as corresponding to some element unknown on Earth. N. Lockyer and E. Frankland tried to solve the problem posed by Secci but they did not notice any changes in the hydrogen spectrum. Therefore, in his article of April 3, 1871, Lockyer already used the expression “a new element X”. There are indications that the name “helium” (from the Greek helios for “solar”) was proposed by Frankland. The word “helium” was first uttered at a British Association Session by its president V. Thomsov (Lord Kelvin) on August 3, of the same year. Even if we regard the discovery of helium as “fait accompli”, then, it still remained unusual. It was the only element which could not be isolated in a material form. What is helium under ordinary conditions–gas, liquid, or solid? What are its properties? What is its atomic mass and where is its place in the natural series of elements?
None of these questions could be answered even approximately. Besides, Secci’s doubt was still not cleared. Thus, a period began in the history of helium when it was only a hypothetical element. There was no consensus on helium. Mendeleev firmly supported Secci’s point of view, feeling that the bright yellow line could belong to some other known element at high temperatures and pressures. W. Crookes, however, completely recognized helium’s independence and considered it to be a primary matter which gave rise to all other elements via successive transformations.
Sometimes it seemed that helium was not unique in its mysteriousness. Astronomers discovered new lines in the spectra of various cosmic objects: the sun, the stars, and nebulae. A number of hypothetical elements appeared, namely coronium, arconium, nebulium, protofluorine. Several years later they were all recognized to be nonexistent and only helium survived.
To receive recognition, helium had to show its “earth face” and its “earth” history began with a chance event.
On February 1, 1895, W. Ramsay received a short letter from K. Miers, a British museum employee. By that time Ramsay had already been acclaimed as the discoverer of argon and we may think Miers did not choose him by chance. Miers wrote about the experiments of the American researcher. W. Hildebrand, performed at the US Geological Institute as early as 1890. Upon heating of some thorium and uranium minerals (for instance, cleveite) a chemically inactive gas was liberated; its spectrum was similar to that of nitrogen and contained new lines.
Later Hilderbrand himself confessed to Ramsay that he had a temptation to attribute these lines to a new element. However, his colleagues were sceptical about the results and Hildebrand stopped his experiments. Miers, however, believed that in the light of numerous cases of nitrogen presence in natural uranates it was reasonable to stage another experiment.
Evidently, Ramsay believed that Hildebrand’s inactive gas could be argon; therefore, he agreed with Miers and on February 5, he acquired a small amount of cleveite. Ramsay himself, however, was busy with studying argon and attempting to prepare its compounds and, therefore, asked his pupil D. Matthews to carry out the experiment. Matthews treated the mineral with hot sulphuric acid and, like Hildebrand, observed the formation of bubbles of a gas resembling nitrogen.
When a sufficient amount of the gas was collected, Ramsay performed its spectral analysis (March 14). The picture was unexpected: the spectrum had a bright band whose lines were not found in the spectra of nitrogen and argon.
Although Ramsay had no sufficient facts to make definitive conclusions he assumed that cleveite contained, in addition to argon, another unknown gas. Ramsay spent a whole week to obtain this gas in as pure a form as possible. On March 22, he compared the spectra of argon and the unknown gas in the presence of B. Brauner. Ramsay provisionally named this gas “krypton” from the Greek for “secret”, “covered”. The name later passed to another inert gas. On March 23. The scientist wrote down in his diary that the bright yellow line of “krypton” did not belong to sodium and was not observed in the argon spectrum. (In the late sixties it was necessary to prove that the D3 line of solar helium was not the bright yellow line of sodium; history, as we see, repeated itself.)
Not quite sure of his result, Ramsay sent an ampoule with the gas to W. Crookes. A day later a telegram was received from Crookes which read: “krypton is helium, 587.49; come and see.” The figure 587.49 corresponded to the wavelength of the solar helium on a specially calibrated scale. Although these data facilitated the identification of helium on the earth, otherwise this discovery was independent. It became possible for the scientists to comprehensively study helium–a new chemical element which was no longer hypothetical. Helium’s complete chemical inactivity was not suspicious: similar inactivity of argon had already been known by that time (1894).
A brief communication about the discovery of helium on the earth was first published by Ramsay on March 29, 1895, in the “Chemical News” edited by Crookes. It is interesting that almost simultaneously terrestrial helium was discovered in cleveite by the Swedish scientist P. Cleve (in whose honour the mineral had been named) and by his assistant. A Lunglet. They, however, were a little too late with their experiments and could only express their disappointment, by no means claiming their priority. Terrestrial helium received full recognition and no attempts were made to refute Ramsay’s results. A little time passed and helium was discovered in other minerals and mineral spring waters. In 1898 helium was found in the earth atmosphere.