BEcember 26, 1919] 



SCIENCE 



581 



able to drive hydrogen out of nitrogen atoms, 

 but not out of either Carbon or oxygen. 



THE NEW PERIODIC SYSTEM OF THE ATOMIC 

 NUCLEI 



The ordinary periodic system, when put in 

 a graiphic form, as has been done by Crookes 

 and more correctly by Soddy, and by Harkins 

 and Hall, is a graphic expression of the ar- 



ABVNDAUCE OF THE ELEMEm'S: 



Fe 



C 



Na 



Ni 



Percentage iy Atoms 

 Atomic Number 

 Pig. 1. The Periodic Variation in the Abundance 

 of the Elements as the result 'of Atomic Evolution. 

 The data are given for 350 s,tone and 10 iron meteo- 

 rites, but the relations are true for meteorites in 

 general. Note that ten elements of even atomic 

 numlber makes up 97.59 per cent, of the meteorites, 

 and seven odd-numbered elements, 2.41 per cent., 

 or 100 per cent, in all. Elements of atomic num- 

 J)er greater than 29 are present only in traces. 



rangement of the planetary electrons. The 

 new periodic system of the atomic nuclei was 

 discovered 'by me five years ago in the follow- 

 ing way. I reasoned that if the nuclei of the 

 even numbered atoms are built of helium 

 nuclei alone, while those of odd atomic num- 

 ber contain hydrogen nuclei in addition, that 

 there should be a considerable difference in 



stability hetween the two ■classes of nuclei. I 

 also told my students, before making any 

 further study, that the even numbered atoms 

 would prove to be more stable than the odd 

 numbered. 



'Row there is, unfortunately, no known 

 method of testing directly the stability of the 

 lighter atoms, but it seemed a reasonable hy- 

 pothesis that if the atomic nuclei had ever been 

 built up, that in general the most stable nu- 

 clei would be formed in the greatest abund- 

 ance. An investigation 'brought forth the fol- 

 lowing facts; 



1. The atoms of the even numbered or 

 helium series are 127 times more abundant in 

 the iron meteorites than the atoms of the 

 helium-hydrogen or odd numbered series. 



2. In the stone meteorites they are 47 times 

 more ahundant. 



3. In the surface of the earth the even num- 

 bered atoms are about 10 times more abundant 

 than the odd numbered. 



4. The even numbered rare earth elements 

 are much more abundant than the odd num- 

 bered. 



5. In the meteorites every even numbered 

 element is much more abundant than the two 

 adjacent odd numbered elements. 



6. All of the seven most abundant elements 

 in the meteorites are even numbered, and these 

 seven elements alone make up 98.6 per cent, of 

 all of the material of the meteorites. 



Thus the periodicity of this system is from 

 even to odd, or the periods are two atomic spe- 

 cies in length, while in the MendeleefE system 

 the periods are 2, 8, 18, and 32 elements in 

 length. Dr. N'orris F. Hall, of Harvard Uni- 

 versity, has pointed out that both the isotopic 

 complexity and the number of predominant 

 radiators in a pleiad, follow just this periodic 

 variation. 



THE STABILITY OF THE NUCLEI OF ATOMS 



The most stable nuclei seem to be those ot 

 oxygen, magnesium, silicon, iron, all of them 

 even numbered elements of low atomic num- 

 ber (except that as has been stated the helium 

 nucleus is probably extremely more stable 

 than any of these). 



