202 



The National Geographic Magazine 



the new yellow line might possibly be as- 

 cribed to hydrogen, could be maintained ; 

 and hence the line was attributed to the 

 existence of an element in the sun un- 

 known on the earth, and the name 

 "helium" was chosen as an appropriate 

 reminder of the habitat of the element. 



Among the lines visible in the chromo- 

 sphere ten are always observed. Of these 

 four may be seen in the hydrogen spec- 

 trum, one is due to calcium and four to 

 helium ; there is still one unidentified with 

 the spectrum of any known element; it 

 has the wave length 5316.87, and the 

 source has been named "coronium." It 

 appears at a great height in the solar at- 

 mosphere, and it is conjectured that it 

 must be lighter than any known gas. 



Shortly after the discovery of argon, 

 in 1884, the notice of one of the discover- 

 ers was drawn to an account by Dr Hille- 

 brand, of the United States Geological 

 Survey, of the presence in certain ores 

 containing uranium of a gas which could 

 be extracted by an air pump. Hillebrand 

 examined the spectrum of the gas and 

 supposed it to be nitrogen. It is true 

 that he saw in it spectrum lines which 

 could hardly be ascribed to nitrogen ; but 

 on mentioning the fact to his colleagues 

 he was bantered out of his quest and did 

 not follow up the clue. Now, in the 

 spring of 1895 attempts were being made 

 to cause argon to combine, and it was 

 argued that conceivably Hillebrand's gas 

 might turn out to be argon and might 

 give an indication to a possible com- 

 pound. Consequently a specimen of 

 clevite — one of the minerals which Hille- 

 brand had found to give off the supposed 

 nitrogen in largest quantity — was pur- 

 chased and the gas was collected from 

 it. On purification its spectrum showed 

 the presence of a brilliant yellow line 

 almost identical in position with the yel- 

 low lines of sodium. It was soon evident 

 that the solar gas, helium, had been dis- 

 covered on the earth. 



The visible spectrum of helium is com- 

 paratively simple, and many of its lines 

 have been identified among those of the 

 solar chromosphere. It is also to be de- 



•tected in many of the fixed stars, notably 

 Capella, Arcturus, Pollux, Sirius, and 

 Vega. It is one of the lightest of gases, 

 being only twice as heavy as hydrogen, 

 but unlike hydrogen, however, its mole- 

 cules consist of single atoms, whereas 

 those of hydrogen consist of paired 

 atoms, which separate only when hydro- 

 gen enters into combination with oxygen 

 or other elements. This peculiarity ap- 

 pears to render liquefaction of helium 

 almost impossible; for while hydrogen 

 has been liquefied and boils at 422 de- 

 grees Fahrenheit below zero, helium has 

 been cooled to — 438 degrees Fahrenheit 

 and has been compressed to one-sixtieth 

 of its ordinary bulk, and yet has shown 

 no sign of liquefaction. Indeed, it is now 

 the only "permanent" gas, for it has never 

 been condensed into liquid form. 



The minerals which contain helium 

 have one thing in common: they all con- 

 tain uranium, or thorium, or lead, or a 

 mixture of these. Minerals of lead alone 

 do not show the presence of helium ; but 

 it may be stated that helium is an invari- 

 able constituent of ores of uranium and 

 thorium. It was at first supposed that 

 such minerals contain helium in a state of 

 combination; but this view could not be 

 substantiated, for the constituents of these 

 ores do not show any tendency toward 

 combination with helium. The connec- 

 tion of this with what follows is very re- 

 markable. 



The explanation of the fact that com- 

 pounds of radium discovered by Madame 

 Curie in 1901 are permanently at a tem- 

 perature considerably above that of the 

 atmosphere, and that they are continually 

 emitting corpuscules of high velocity, was 

 given by Professor Rutherford and Mr 

 Frederick Soddy in a series of papers com- 

 municated to the Philosophical Magazine. 

 It is that radium and allied bodies are 

 "disintegrating" — that their atoms are 

 spontaneously flying to bits. Now, this 

 view, although new in its application to 

 elements, has long been known to hold 

 for certain compounds. There is a fear- 

 fully explosive compound of nitrogen 

 with chlorine, which on the least touch 



