WORK ON RADIUM 159 



The emanation was recognised as possessing the pro- 

 perties of a true gas obeying Boyle's law like other gases. 

 It had been previously shown by Rutherford and Soddy 

 to be chemically inert like argon. This production of 

 helium from the emanation Ramsay speaks of as the 

 first observed case of " transmutation," for radium and 

 its emanation as well as helium must be counted among 

 the substances known as " elements." This idea de- 

 veloped later into the conviction that radio-active 

 change might be made use of to effect the transmutation 

 of the common elements. This subject will be referred 

 to later. 



The important discovery just described gives the clue 

 to the sources of helium in natural spring waters which 

 evidently rise through or from radiferous rocks. As to 

 the homologues of heKum, namely argon and the rest, 

 no corresponding source is known. But if analogy may 

 be relied on it seems probable that argon, neon, krypton 

 and xenon are, like helium, products of radio-active 

 change occurring in substances similar in constitution 

 to radium but having much higher atomic weight and 

 a far more unstable constitution. These have long since 

 disappeared from among the known mineral constituents 

 of this earth's crust. Ramsay does not seem to have 

 occupied himself with this point of view, which obviously 

 cannot be put to the test of experiment. 1 Some years 

 later he seems to have thought it possible that neon and 



1 This speculation is discussed in the pages of a little book, The Elements, 

 by Sir W. A. Tilden (Harpers). 



