160 CHEMICAL DISCOVERY AND INVENTION 



For the present it is impossible to do more than mention 

 these facts, which may turn out on further investigation to have 

 a special significance. 



But the elements highest in the scale are all undergoing 

 transformations, attended by radio-active phenomena, into 

 products which are all of smaller atomic weight. The question 

 arises whether uranium with its atomic weight 238-2, is really 

 the limit, or whether there may not be elsewhere in the cosmos 

 elementary substances more complicated in structure and having 

 a greater atomic mass. So far as at present known the evidence 

 is against such a supposition assuming the present conditions 

 prevailing in our solar system. No new elements have been 

 discovered in the meteorites which have fallen on the earth's 

 surface, and the spectroscope directed to the sun, stars, and 

 nebulae, though indicating the presence of elements unknown 

 on the earth, also indicates that they are probably of lower 

 atomic weight than any terrestrial constituent. Nevertheless 

 the possibility of substances of higher atomic weight than 

 uranium being formed, and existing temporarily under other 

 cosmical conditions is not excluded. Helium is known to be 

 expelled by radium and thorium, and helium is the first term of 

 the series of inactive gases, helium, neon, argon, krypton, xenon, 

 with atomic weights gradually increasing up to 130. If helium 

 is the product of the disintegration of uranium it is at least 

 conceivable that the other gases of like character may have 

 resulted from the breaking up of elements of higher atomic 

 weight, which, though temporarily existent, became extinct 

 before the present order of things settled down to a compara- 

 tively stable condition. Uranium, on this view, represents the 

 limit of mass for an atom under present circumstances. 



Such considerations as these lead us to the contemplation of 

 the questions which have so long had a supreme fascination for 

 chemists : How did the present elements come into existence ? 

 Is there a common material out of which all have been evolved 

 an " urstofT " or " protyl " and if so what is its relation to 

 electricity ? And what is electricity, is it a state of matter or 

 matter itself ? 



To such questions there have been many attempts to provide 

 at least partial answers. 



The essential unity of all matter is no modern idea, but the 

 discoveries of the last few years have supplied material which 



