NOTES 171 



velocities, revealed the atom as a nebula with a hard point 

 in it. But there was no known property of electricity which 

 would explain how a charge of nearly a hundred units could 

 be concentrated within a volume less than that occupied by 

 an electron. The theory endowed electricity with the attributes 

 of matter rather than explained the attributes of matter in 

 terms of those of electricity. The sequence of radioactive 

 changes and the chemical characterisation of the successive 

 products showed that in the last twelve places of the periodic 

 table, from uranium to thallium, there were nearly forty elements, 

 all those falling in the same place being chemically indistinguish- 

 able, or " isotopic." The presumption was that the same was 

 true in the other parts of the table where no means of detecting 

 it yet existed. The results threw doubt, in particular, on the 

 homogeneity of the element lead, but this point still had to 

 be experimentally settled. Apart from any hypothesis, the 

 radioactive evidence proved that, between thallium and uranium, 

 the successive places in the periodic table corresponded with 

 unit increases in the positive nuclear charge of the atom. A 

 model was shown of the periodic system of the elements 

 embodying, in the well-known "figure of eight" arrangement 

 of Sir William Crookes, many new features in accordance 

 with the actual state of our knowledge of the elements to-day. 

 Mr. Moseley then contributed a most valuable set of entirely 

 new results for the values of the nuclear charges of the elements, 

 as determined from the wave-lengths of their characteristic 

 X-radiation, which fully bore out and extended the conclusions 

 drawn from his initial examination, by this method, of the 

 elements between calcium and zinc, the results of which were 

 published as recently as last December. Accepting the nuclear 

 charge of aluminium as thirteen as the basis, the wave-lengths of 

 the characteristic X-rays of all the others correspond with their 

 atomic numbers, that is, to the number of the place assigned 

 to them by chemists in the Periodic Table. Gaps were indicated 

 in the sequence corresponding with the two missing homo- 

 logues of manganese, between molybdenum and ruthenium 

 and between tungsten and osmium. In the rare-earth group, 

 places for sixteen elements, including lanthanum and cerium, 

 were indicated, instead of the fourteen included in the Inter- 

 national List of Atomic Weights. The work extends our 

 knowledge of the absolute value of the nuclear charge almost 



