Spectroscopic Observations of the Sun. Received February 2, Read March 19, 1874. Pp. 577-586 in The Philosophical Transactions of the Royal Society, Vol. 165, Pt. 2., 1875. [OFFPRINT of LOCKYER'S DISCOVERY OF HELIUM ON THE SUN. 6 PLATES]

London: Taylor and Sons. 1st Edition. RARE OFFPRINT OF JOSEPH LOCKYER'S DISCOVERY OF HELIUM ON THE SUN. ORIGINAL PAPER WRAPS, FINE CONDITION. 6 PLATES. An "offprint" is a separately published and bound issue of the journal paper in question. Usually these are printed for the given authors and for authors to give to colleagues. Because they are rare, offprints are considered more desirable that either the original issue of the journal in paper wraps or bound.

Helium was the first chemical element discovered on an extraterrestrial body -- in this case, the sun -- prior to its discovery on the Earth. Lockyer's discovery of helium also represents the first element discovered via spectroscopy. Though rare on the Earth, helium is the second most abundant element in the universe, comprising 24% of known baryonic matter by weight.

Lockyer discovered helium on the sun in 1868 when he adapted his 6-inch telescope to utilize a spectroscope and while using it to carry out electromagnetic spectroscopic observations of the sun during an eclipse, he discovered a yellow line never seen before in the laboratory. Unable to reproduce the line in his lab, Lockyer made the bold suggestion that the line was the 'fingerprint' of an element, an element he named 'helium' for Helios, the Greek God of the Sun. Lockyer's finding -- the only element to be discovered in space before it was discovered on Earth -- was the first element to be discovered by spectroscopy.

As Lockyer tried to make sense of his initial discovery of a yellow line, he reasoned that "because the bright yellow line was close to the D1 and D2 lines of sodium, it [should be] designated D3. In order to identify the lines in his spectral data, Lockyer enlisted the help of the prominent British chemist, Edward Frankland. Their laboratory work showed that the majority of the observed solar lines were due to hydrogen, though often modified by changes in temperature and pressure. The D3 line, however, could not be reproduced in the laboratory" (Jensen, "Why Helium Ends in 'ium'?) ...

While Lockyer was ridiculed for his discovery for many years, in 1895, twenty-five years after Lockyer's initial discovery, William Ramsay confirmed the existence of Helium when he managed to isolate it from another mineral. In 1897, Lockyer was finally knighted for his discovery of helium. CONDITION & DETAILS: London: The Royal Society. Offprint from The Philosophical Transactions of the Royal Society, Vol. 165, Pt. 2. 1876. [Printed in 1876]. Continuously paginated, pp. 577-586. 4to. (300 x 225mm; 12 x 9 in.). ILLUSTRATIONS: 6 plates EXTERIOR: Bound in original paper wraps. Tightly bound. Near fine condition.