August 26, 1920] 



NATURE 



831 



Sir Norman Lockyer's Contributions to Astrophysics. 



By Prof. A. Fowler, F.R.S. 



BY the death of Sir Norman Lockyer the 

 science of astrophysics has lost the ener- 

 gising' and stimulating influence of the last of the 

 great pioneers whose labours opened the way to 

 so vast an extension of our knowledge of the 

 universe. The science of celestial chemistry and 

 physics had its real beginning in 1859, when 

 Kirchhoff's famous experiment on the reversal of 

 spectral lines furnished the key to the interpreta- ; 

 tion of the dark lines of the solar spectrum, and 1 

 thence to the determination of the composition of 

 the sun and stars. During the earlier years the 

 outstanding features in the development of the 

 new science were the brilliant investigations of 

 Huggins on the spectra of stars and nebulae, and 

 those of Rutherfurd and Secchi on the spectro- i 

 scopic classification of the stars. Curiously 

 enough, the sun had received but little attention ; 

 during this period, and Lockyer was practically I 

 entering a virgin field when, in 1866, he attached 

 a small spectroscope to the modest 6-in. equa- \ 

 torial of his private observatory, and observed the 

 spectrum of a sun-spot independently of the rest | 

 of the solar surface. Simple as it may now seem, 

 this process of "taking the sun to bits," as Sir | 

 Norman used to call it, was an advance of funda- } 

 mental importance. It not only gave an imme- i 

 diate and decisive answer to the question as to the 

 cause of the darkness of sun-spots which was then 

 under vigorous discussion in England and France, 

 but also very soon led to the famous discovery 

 of the method of observing solar prominences ; 

 without an eclipse, with which Lockyer's name, | 

 in conjunction with that of Janssen, will for ever ! 

 be associated. The story of this epoch-making \ 

 observation has been told too often to need repeti- t 

 tion, but it should not be forgotten that the prin- 

 ciple of the method had been clearly recognised 

 by Lockyer two years before he succeeded in J 

 obtaining a spectroscope suitable for the purpose i 

 in view. | 



Those who have become familiar with the beau- j 

 tiful solar phenomena presented by this method of j 

 observation will best understand the enthusiasm 

 and delight with which Lockyer continued his 

 observations whenever the sun was visible. On 

 the first day of observation — October 20, 1868 — 

 he had identified the C and F lines of hydrogen, 

 and a yellow line near D, in the spectra of the 

 prominences, and on November 5 he discovered 

 that the prominences were but local upheavals of 

 an envelope entirely surrounding the photosphere, 

 to which he gave the name of the chromosphere, 

 as being the region in which most of the variously ; 

 coloured effects are seen during total eclipses of 

 the sun. The peculiarities of the bright F line 

 at once suggested to his fertile mind that the ! 

 spectroscope might disclose the physical state, as j 

 well as the chemical composition of the chromo- j 

 NO. 2652, VOL. 105] 



sphere and prominences, through the medium of 

 laboratory experiments, and from this beginning 

 the close association of the laboratory with the 

 observatory became the dominant note in his life's 

 work. His first experiments were made in col- 

 laboration with his friend Frankland, and it was 

 shown that the widening of the F line at the base 

 of the chromosphere was to be accounted for by 

 an increase of pressure. These experiments 

 further demonstrated that the yellow line of the 

 chromosphere, which had been named Dg, was 

 quite distinct from hydrogen, and the then un- 

 known gas to which it was to be attributed was 

 given the now well-known name of helium. Up 

 to the year 1873, however, Lockyer's work was 

 carried on almost entirely in his private observa- 

 tory, and in the laboratory which he had estab- 

 lished in his house at Hampstead. He not only 

 continued his solar observations with conspicuous 

 success, but also commenced his well-known " Re- 

 searches on Spectrum Analysis in Connection with 

 the Spectrum of the Sun," in which he developed 

 experimental methods which afterwards became 

 common practice. 



On his transfer to South Kensington, 

 with which his connection continued for forty 

 years, the facilities at Lockyer's disposal for re- 

 search were at first very meagre, but additions to 

 equipment and staff were made from time to time, 

 and in the later years the observatories and 

 laboratories were well adapted for their special 

 purposes. Lockyer's dream of becoming director 

 of a permanent astrophysical observatory, com- 

 parable with those established by Governments in 

 other countries, however, was never realised, and 

 his work throughout was carried on in temporary 

 buildings, and for the greater part of the time 

 with modest grants in aid from year to year. In 

 1912, on the transfer of the Solar Physics 

 Observatory to the control of the University of 

 Cambridge, Lockyer, in spite of his weight of 

 years, courageously set about the erection of a 

 new observatory at Sidmouth, and continued his 

 work on stellar spectra almost to the close of his 

 life. It is a lamentable fact that much of his 

 time and energy was almost continually taken up 

 with a struggle to obtain adequate means to carry 

 on his researches. 



The contributions to astrophysics made by 

 Lockyer during nearly sixty years of strenuous 

 endeavour in its various fields of investigation 

 form the subject-matter of more than 200 papers 

 and memoirs, and it is only possible here to refer 

 to some of the larger questions in which he was 

 sf>ecially interested. His work, both in the labora- 

 tory and in the observatory, was largely guided 

 by bold speculations, which he was usually careful 

 to regard as working hypotheses, and from time 

 to time the main points were brought t<^ether 



