The Groundwork of the Universe, Sec. 67 



with entirely different chemical properties. To such atoms, I 

 gave the name isobares, from isos = equal and baros = weight. 

 To illustrate the question of isobarism, the following data will be 

 sufficient : — 



/5-ray ^-ray 



Mesothorium-1 ' Mesothorium-2 ' Radiothorium 



Change Change 



AtomicWeight = 228 Atomic Weight = 228 AtomicAYeight =228 

 Number of Hydrogen Element 



atoms displaced by one 

 atom of element. 



resembles. 



Mesothorium-1 2 Barium 



Mesothorium-2 3 Lanthanum 



Radiothorium 4 Cerium 



From the foregoing, the following possibilities are evident: — 

 Two elements having identical chemical properties are isotopic. 

 Two elements having different chemical properties are heterotopic. 

 Two elements having identical atomic weights are isobaric. 

 Two elements having different atomic weights are heterobm^ic. 

 By taking all the possible combinations of these in turn, the 

 Soddy-Stewart classification of atoms is obtained : — 



Atomic Weights Chemical Properties 

 Isobaric Isotopes Same Same 



Isobaric Heterotopes Same Different 



Heterobaric Isotopes Different Same 



Heterobaric Heterotopes Different Different 



Thus by means of this system we are able to define the relations 

 between any two atoms, whether they are of the same elemental 

 character or not and whether their Aveights are identical or 

 different. 



Leaving the work of the laboratory, it may be well to turn 

 next to phenomena upon a far vaster scale. The resources of 

 energy which the chemist and physicist have at their disposal are 

 limited both in quantity and in intensity ; and it is necessary to 

 examine certain astronomical evidence in order to gain a further 

 knowledge of the behaviour of elementary matter under extreme 



