362 



NATURE 



[May 20, 1920 



with regard to D3, for no substance was found in 

 the laboratory which could produce this line. 



By studying the behaviour of D3 in relation to 

 the hydrogen lines, throwing the image of ihe 

 sun's limb on to the slit of a spectroscope, Lockyer 

 found that the lines were distorted — i.e. there 

 were changes of wave-length due to movements 

 of the material in the sun. The orange line was, 

 however, observed to behave quite differently 

 from either of the hydrogen lines, showing that 

 a different substance was in question. 



Hence [as Lockyer remarks] we had to do with 

 an element which we could not get in our laboratories, 

 and therefore I took upon myself the responsibility of 

 coining the word helium, in the first instance for 

 laboratory use. At the time I gave the name I did 

 not know whether the substance which gave us the 

 D3, was a metal like calcium or a gas like hydrogen, 

 but I did know that it behaved like hydrogen, and 

 that hydrogen, as Dumas had stated, behaved as a 

 metal ("Sun's Place in Nature," p. 33). 



In the following years numerous other lines in 

 the sun and stars were found associated with the 

 yellow line, but the origins of these were all 

 unknown and designated as such. 



It was not until the year 1895 that the terres- 

 trial equivalent of this well-known yellow and 

 other lines was discovered. " In the course of 

 investigations on argon," so wrote Sir William 

 Ramsay in a communication to the Royal Society 

 (Proc. Roy. Soc, vol. Iviii., p. 65) on March 26, 

 1895, "some clue was sought for which would 

 lead to the selection of one out o'f almost innumer- 

 able compounds with which chemists are 

 acquainted with which to attempt to induce 

 argon to combine." 



Acting on a suggestion by Sir Henry Miers, 

 who directed attention to the work of Dr. Hille- 

 brand in 1888 on the occurrence of nitrogen in 

 uraninite, etc., Sir William Ramsay employed 

 the mineral cl^veite, essentially a uranate of lead 

 containing rare earths. He treated this mineral, 

 and from it extracted a small quantity of gas, 

 which he subjected to spectroscopic examination. 

 To use his own words, as printed in the above- 

 mentioned communication : — 



Several vacuum tubes were filled with this gas and 

 the spectrum was examined, the spectrum of argon 

 being thrown simultaneously into the spectroscope. 

 It was at once evident that a new gas was present 

 along with argon. 



Fortunately, the argon tube was one which had been 

 made to try whether magnesium poles would free the 

 argon from all traces of nitrogen. This it did; but 

 hydrogen was evolved from the magnesium, so that 

 its spectrum was distinctly visible. Moreover, mag- 

 nesium usually contains sodium, and the D line v/as 

 also visible, though faintly, in the argon tube. The 

 gas from cl^veite also showed hydrogen lines dimly, 

 probably through not having been filled with corn- 

 pletely dried gas. 



On comparing the two spectra, I noticed at once 

 that while the hydrogen and argon lines in both tubes 

 accurately coincided, a brilliant line in the yellow, in 

 the clfeveite gas, was nearly, hut not quite, coincident 

 with the sodium line D of the argon tube. Mr. 

 Croakes was so kind as to measure the wave-length 

 of this remarkably brilliant yellow line. It is 587-49 

 NO. 2638, VOL. 105] 



millionths of a millimetre, and is exactly coincident 

 with the line D3 in the solar chromosphere, attributed 

 to the solar element which has been named helium. 



Thus was the terrestrial equivalent of the 

 helium line discovered after an interval of twenty- 

 seven years. 



Solar observations had shown that this line was 

 observed high in the chromosphere, indicating 

 that the density of the gas should be very low. 

 Special interest, therefore, attached to the deter- 

 mination of this important property. In a pre- 

 liminary experiment Sir William Ramsay 

 obtained 39 as a maximum number for the density 

 of helium, oxygen being 16, thus showing that 

 the surmise was correct. Soon after this dis- 

 covery Lockyer prepared some of the gas from 

 broggerite, and established the fact that numerous- 

 lines, designated "unknown," in the spectra of 

 the chromosphere, nebulae, and stars, were due 

 to this gas. 



Thus from an observation of the sun a new 

 terrestrial gas was discovered, and from this 

 terrestrial gas the origins of a host of unknown 

 lines in the spectra of the heavenly bodies were 

 explained. 



Like hydrogen, helium has a wide diffusion irk 

 space, for not only is it in strong evidence in 

 the hot stars, but it also must occur in such 

 cooler stars as Arcturus, since this star is at 

 about the same temperature as our sun, in which, 

 we know helium is present. In bur atmosphere 

 helium is one of the rarer constituents, being 

 present in the proportion of about one volume in 

 250,000. 



Up to the last few years the amount of helium 

 which has been collected has been small, owing 

 to the costly process of obtaining it, but during 

 the war a demand for it in large quantities arose 

 because of its lightness and non-inflammable 

 nature. Helium is the lightest gas known next to 

 hydrogen, of which it has about 92 per cent, of 

 the buoyancy or lifting power. It was intended to 

 supply a fleet of airships with this gas, and great 

 fractionating plants were laid down in the United 

 States of America capable of separating helium 

 from natural gas at a very moderate cost. It was 

 due to the above-mentioned demand that helium 

 became more widely known, and attention was at 

 once paid to bring together all the informa- 

 tion that had been published about it as an fiid 

 to that enterprise. 



The U.S. Department of Commerce took the 

 matter in hand, and under Dr. S. W. Stratton, 

 the director of the Bureau of Standards, a biblio- 

 graphy of scientific literature relating to heliuoT 

 was compiled. The information (more than 400 

 references) thus brought together has since 

 (September 10, 1919) been published in pamphlet 

 form in a Circular of the Bureau of Standards 

 (No. 81), and will be found a very valuable source 

 of reference. 



The importance of helium to-day may be briefly 

 summarised from the following extract from the 

 introduction to this circular : — 



Helium has probably been the most interesting of 



