On 20 October 1868, Norman Lockyer discovered helium. Associate Curator of Chemistry Rupert Cole tells the story.
'At last!' exclaimed a weary Norman Lockyer to himself, as his fatigued eye finally accepted what it had witnessed.
Looking down his spectroscope, seeing a rogue yellow line in a spectrum of light from the sun, Lockyer realised he had discovered a new element - helium.
He then, according to the dramatic account of his discovery in the Royal Society's Philosophical Transactions, 'quitted the observatory to fetch my wife to endorse my observation'.
Lockyer's wife Winifred was an active member of the Victorian scientific world, often translating popular science books from French to English. As well as confirming her husband's famous observations, she also accompanied him on an 1870 solar eclipse expedition to Sicily.
Winifred had married Norman Lockyer - a civil servant working for the War Office - in 1858. They moved to in Wimbledon in south London and raised seven children together, but sadly she died in 1878.
Lockyer published her obituary in Nature, the scientific journal he founded. In it he wrote: 'her husband's scientific work for the last eleven years owes whatever it may possess of merit to her constant interest, encouragement, and assistance'.
Lockyer named the new element he discovered 'helium', after the Greek sun god Helios. It's often considered a special discovery as the first and only element to be identified outside Earth.
He used this spectroscope to make the discovery (now part of the Science Museum Group Collection).
The spectroscope combined glass prisms with a telescope to analyse the spectra - lines of colour unique to each chemical element which look like a multicoloured barcode.
German scientists Gustav Robert Kirchhoff and Robert Bunsen (of burner fame) pioneered this technique in 1860, known as spectroscopy.
They discovered two elements by this method, the metals rubidium and caesium.
While Kirchhoff and Bunsen had heated their elements under a flame to dissect their signature spectrums of light, Lockyer held his spectroscope up to a telescope which was pointed at the outer edge of the sun.
The level of accuracy needed for this discovery required an extraordinary spectroscope, containing no less than seven prisms.
It was made by John Browning, a London specialist in scientific instruments, who completed it just four days before Lockyer's discovery after much delay.
On 18 August 1868, during a total solar eclipse observed from India, a French astronomer Pierre Janssen saw the same signature lines of colour through his spectroscope as Lockyer would two months later.
The postal transit time from India to Paris meant Janssen's letter announcing his discovery of a new element did not reach the hands of the President of the French Academy of Sciences until just a few minutes before Lockyer's did via a French scientist.
There was no priority dispute, with both scientists receiving joint credit in France and becoming friends.
However, in the following years, there remained much doubt (and even mockery) over Lockyer's discovery.
Even Lockyer's chemist collaborator in the discovery, Edward Frankland, publicly renounced his involvement in the work.
The question of helium would finally be settled when in 1895 the chemist William Ramsay isolated helium gas from heating the radioactive mineral cleveite.
Ramsay sent Lockyer a sample and this tube used by Ramsay is in the collection.
The discovery of helium is certainly unusual in the history of science, combining both chemistry and astronomy.
The history of science is not just about winners and successes. Lockyer's announcement was made amidst other (now spurious) element discoveries by solar spectroscopy, from Coronium in 1869 (that in 1939 was found to be plain old Iron) to Occultum in 1895, put forward by two eccentric scientifically-minded occultists.
Was Lockyer lucky? He was a man of many theories, many of which were highly controversial and outlandish, including his suggestion of ley lines at Stonehenge. But, rightly or wrongly, he is now remembered for his correct discovery. We do like a hero.
With absolutely no bias from my curatorial remit, the message I am taking home from this episode: it takes a chemist to tidy up the notions of astronomers...