7 On the history of the discovery of helium

In view of the misrepresentation given in many books on astronomy, (see for example Payne-Gaposhkin & Haramundanis 1970; Celnikier 1986; Zirin 1988; Phillips 1992), we feel it is worthwhile saying a few words here on the subject of who discovered helium. The British astronomer Joseph Norman Lockyer gives the first documented account (Lockyer 1869a,b,c) of a hitherto unknown bright chromospheric yellow line which was later known to have been produced by helium. Lockyer observed the chromosphere in October 1868 and not during the solar eclipse of 18 August 1868; he labelled the yellow line $\rm D^3$ but was unable to identify the element giving rise to it. Lockyer used a technique devised independently by himself and by the French astronomer Pierre Jules César Janssen to observe the chromospheric spectrum outside of an eclipse. Janssen made observations in India during the August eclipse of 1868 but did not record the yellow line that Lockyer saw 2 months later. So credit for the discovery of helium in the Sun should go to Lockyer, not to Janssen. Aubin (1999) has given a detailed account of this fascinating episode in the history of astronomy.

Acknowledgements

David G. Hummer of Boulder (Colorado) gave the initial encouragement for undertaking the present investigation. Klaus Bartschat of Des Moines (Indiana) kindly provided us with his cross sections and details of the model helium atom he used. Jean-Claude Bouret of Toulouse (France) pointed out to us the astronomical importance of electron-helium rate coefficients at temperatures in excess of 30000 degrees, while Hugh P. Summers of Glasgow (Scotland) drew our attention to the needs of those working in the field of Controlled Thermonuclear Energy. We drew all of the figures using the software package TVB developed by Georges Gonczi at the Observatoire de la Côte d'Azur; this is freely available at http://www.obs-nice.fr/tvb/tvb.html with instructions now given in English. Robert P. McEachran of Toronto (Canada) provided the frozen-core Hartree-Fock energies in Table 1. Thanks to the painstaking care with which our anonymous referee examined the original draft, we were alerted of some slip-ups in Table 3 and so able to correct them prior to publication.