August 5, 1922] 



NA TURE 



l 93 



a telescope in his garden and devoted his spare time 

 to astronomy. The two men were alike in their energy 

 and intense enthusiasm. One sees on nearly every 

 page of his book on " Solar Physics," published in 

 1893, the delight which Sir Norman took in his work. 

 He makes one feel that the years following Kirchhoff's 

 explanation of the dark lines in the solar spectrum 

 were glorious times for astronomers, who suddenly 

 found a way to explore the chemical and physical 

 constitution of the heavenly bodies. One could 

 scarcely say that each day brought a new victory, but 

 new victories and new problems followed one another 

 very rapidly. 



When Sir Norman Lockyer commenced his work in 

 1866, current views on the constitution of the sun 

 were very different from those we now hold. Although 

 Herschefs idea of the cool dark interior had been 

 given up, some traces of its influence still remained. 

 Faye conceived of the interior of the sun as a nebulous 

 gas of feeble radiating power at a temperature of dis- 

 sociation : the photosphere, on the other hand, being of a 

 high radiating power and at a temperature sufficiently 

 low to permit of chemical action. In the sunspot we 

 see the interior nebulous mass. Balfour Stewart and 

 De la Rue were opposed to this view and explained a 

 sunspot as due to an inrush of matter from the sun's 

 atmosphere into the photosphere. With a small 

 direct-vision spectroscope on a 6-J-inch equatorial, 

 Sir Norman Lockyer examined the spectrum of a sun- 

 spot and compared it with that of the surrounding 

 photosphere. He found no bright lines, but the same 

 absorption lines as in the solar spectrum, and so far 

 as he could judge with his small dispersion' rather 

 broadened. This supported Balfour Stewart rather 

 than Faye. In a paper communicated to the Royal 

 Society he laid stress on the importance of detailed 

 spectroscopic study of the sun's surface. He also 

 puts the question, "Slay not the spectroscope afford us 

 evidence of the existence of the ' red flames ' which 

 total eclipses have revealed in the sun's atmosphere ; 

 although they escape all other methods of observa- 

 tion at other times ? " 



With the aid of funds from the Government Grant 

 Committee he proceeded to construct a solar spectro- 

 scope of sufficient dispersion, and on October 20, 1868, 

 wrote to the Royal Society : " After a number of 

 failures which made the attempt seem hopeless I have 

 this morning perfectly succeeded in obtaining and 

 observing part of the spectrum of a solar prominence. 

 As a result I have established the existence of three 

 bright lines in the following positions : 



I. Absolutely coincident with C. 

 II. Nearly coincident with F. 

 III. Near'D. 

 The third line is more refrangible than the more 

 refrangible of the two darkest lines by eight or nine 

 degrees of Kirchhoff's scale." 



A. similar communication was made to the French 

 Academy of Sciences, and in addition, the form of the 

 prominence was roughly drawn. The letter to the 

 French Academy was followed by a communication 

 received the same day from M. Jannsen reporting the 

 success of an expedition to observe a total solar 

 eclipse. During the eclipse the idea had occurred to 

 him of how the red flames could be made visible with- 

 out an eclipse, and he carried it out on the following 

 day. In this dramatic manner the observations of 

 prominences was started, and their gaseous nature 

 proved. The French Government struck a special 

 medal in memory of the discovery and in honour of 

 the discoverers. 



Observation of prominences was after this success 

 carried on with renewed vigour. By the simple 

 device of widening the slit the forms of the promin- 

 ences were seen in C or F light. A further important 



NO. 2753, VOL. I IO] 



discovery was made almost at once. Sir Norman 

 Lockyer found that bright C and F lines were visible 

 all round the sun. In this way was discovered the 

 existence of a continuous envelope round the sun of 

 fairly uniform height except where it was heaped with 

 prominences. This envelope was named the chromo- 

 sphere and it was estimated to be about 5000 miles 

 thi( k. 



The behaviour of the F line, which is described as 

 sometimes exceedingly brilliant and widening out so 

 as to present a bulbous appearance above the chromo- 

 sphere, and the existence of the line near D with no 

 corresponding Fraunhofer line, suggested work in 

 the laboratory. This was undertaken in conjunc- 

 tion with Edward Frankland. These investigations 

 showed that the yellow D 3 line could not be obtained 

 in the spectrum of hydrogen, however the conditions 

 were varied. It was attributed by them to a new 

 element, a light gas, as yet undiscovered on the earth, 

 and the name helium was given to the element producing 

 the line. As is well known, the D 3 line and allied 

 lines were found to have great importance in stellar 

 spectra, and in 1895 was found by Ramsay in a gas 

 from the mineral cleveite. The subsequent history 

 of helium and the prominent part it has played in 

 physical science makes its initial discovery by 

 Lockyer in the sun, twenty-six years before it was 

 found on the earth, a most interesting episode in the 

 history of science. 



These labbratory experiments of. Lockyer 's and 

 Frankland 's are of great importance. Sir Norman 

 had a strong conviction, at this early date, that 

 research should be carried on concurrently in the 

 observatory and the laboratory. The spectra found 

 in the observatory were to be interpreted by experi- 

 ments on the differences produced by temperature, 

 pressure, and varied methods of electric excitation! 

 In this way spectroscopy would lead to knowledge 

 not merely of the chemistry, but of the physical 

 conditions of the heavenly bodies. One immediate 

 conclusion was that the continuous spectrum did not 

 necessitate a solid or liquid photosphere but could 

 arise from a gaseous body. Further, that the absorp- 

 tion indicated by the Fraunhofer lines may take place 

 in the photosphere itself, or very near it, and not in an 

 extensive outer absorbing atmosphere. How fruitful 

 this method of research became in his hands and those 

 of his pupils we all know. 



At South Kensington his work was to a large 

 extent a natural development and exposition of the 

 views he had previously formed. The idea of the dis- 

 sociation of elements at increasing temperature led to a 

 very extensive comparison of the arc spectra of metals 

 with those obtained in the higher temperature or more 

 intense electric conditions of the spark. In 1881 he 

 found that the iron lines 4924-1 and 5018-6 were greatly 

 enhanced in brightness when one changed from the 

 arc to the spark spectrum. The lines of iron, titanium, 

 manganese, chromium, and many other metals were 

 exhaustively investigated at South Kensington. 

 The names of Proto-Iron, Proto-Titanium, etc., 

 were given the metals when in condition to give 

 these enhanced lines. We know now more definitely 

 that what was described as dissociation is loss of an 

 electron, and that when this occurs the enhanced lines 

 appear. 



It is scarcely possible to exaggerate the important 

 results which have accrued from the study of enhanced 

 lines. They have contributed greatly to the inter- 

 pretation of solar and stellar spectra, and have assisted 

 in the sorting out of lines of different elements into 

 series. 



In the course of his life Sir Norman Lockyer made 

 observations of no less than eight total eclipses of the 

 sun. His use of a spectroscope without slit led to a 



