438 



NAfURE 



[July 26, 1917 



but a very minute proportion of the atoms disintegrat- 

 ing follow the mode followed by the 65 per cent, 

 in the case of thorium-C. The product in this case, 

 radium-D, which, of course, is also an isotope of lead, 

 with atomic weight 210, is not permanently stable, 

 though it has a fairly long period, twenty-four years. 

 The other product is not known to change further, 

 but then, even if it did, it is in such small quantity 

 that it is doubtful whether the change would have 

 been detected. But, so far as is known, it forms a 

 stable isotope of lead of atomic weight 210, formed 

 in the proportion of only 003 per cent, of the whole. 



Now the atomic weight evidence merely shows that 

 one of the two isotopes of lead formed from thorium 

 is stable enough to accumulate over geological epochs, 

 and it does not necessarily follow that both are. Dr. 

 Arthur Holmes has pointed out to me that the 

 analysis I gave of the Ceylon thorite leads to a curi- 

 ously anomalous value for the age of the mineral. 

 The quantity of thorium lead per gram of thorium 

 is 00062, and this, divided by the rate at which the 

 lead is being produced, 472x10-" grams of lead per 

 gram of thorium per year, gives the age as 131 million 

 years. But a Ceylon pitchblende, with uranium 

 72-88 per cent., and lead 465 per cent., and ratio of 

 lead to uranium as 0064, eives the age as 512 million 

 years. Dr. Holmes regards the two minerals as 

 likely to be of the same age, and the pitchblende to 

 be, of all the Ceylon results, the one most trustworthy 

 for age measurement. 



If we suppose that, as in the case of radium-D, 

 the 65 per cent, isotope of lead derived from thorium 

 IS not stable, and that only the 35 per cent, isotope 

 accumulates, the age of the mineral would be 375 

 million years, which the geologists are likely to con- 

 sider much nearer the truth. But the most in- 

 teresting point is that, if we take the atomic weight 

 of the lead isotope derived from uranium as 2060, 

 and that derived from thorium as 2080, and calculate 

 the atomic weight of the lead in Ceylon thorite, 

 assuming it to consist entirely of uranium lead and 

 of only the 35 per cent, isotope from thorium, we get 

 the value 20774, which is exactly what I found from 

 the density, and what Prof. Honigschmid determined 

 (207-77) (compare Nature, May 24, p. 244). 



The question remains : If this is what occurs, what 

 does this unstable lead change into? If an o particle 

 were expelled mercury would result, or if a /3 particle 

 bismuth, two elements of which I could find no trace 

 in the lead group separated from the whole 20 kilos of 

 mineral. But if an o and a /3 panicle were both 

 expelled, the product would be thallium, which is 

 present in amount small, but sufficient for chemical 

 as well as spectroscopic characterisation; If the pro- 

 cess of disintegration does proceed as suggested, it 

 should be possible to trace it, for this particular lead 

 should give a feeble specific a or ji radiation, in addi- 

 tion, of course, to that due to other lead isotopes. 

 So far it has not been possible to test this. In the 

 meantime, the explanation offered is put forward pro- 

 visionally as beinpf consistent with all the known 

 evidence. 



Lookiner for a moment, in conclusion, at the broader 

 aspects of the new ideas of atomic structure, it seems 

 that though a sound basis for further development 

 has been roughed out, almost all the detail remains 

 to be supplied. We have got to know the nucleus, 

 but, beyond the fact that it is constituted, in heavy 

 atoms, of nuclei of helium and electrons, nothing 

 is known; whilst, as regards the separate 

 shells or rings of electrons which neutralise 

 its charge and are supposed to surround it like 

 the shells of an onion, we really know nothing yet at 

 all. The original explanation, in terms of the elec- 



NO. 2491, VOL. 99] 



tron, of the periodicity of properties ' displayed 

 by the elements still remains all that has been at- 

 tempted. We may suppose that as we pass through 

 the successive elements in the table one more electron 

 is added to the outermost ring for each unit increase 

 in the charge on the nucleus, or atomic number, and 

 that when a certain number, 8 in the early part of the 

 table, and 18 in the later, has been added, a complete 

 new shell or ring forms, which no longer participates 

 directly in the chemical activities of the atom. Thanks, 

 however, to Moseley's work^ this, now, is not suffi- 

 ciently precise. For we know the exact number of 

 the elements and the various atomic numbers at 

 which the remarkable changes, in the nature of the 

 periodicity displayed, occur. Any real knowledge in 

 this field will account not only for the two short 

 initial periods, but also for the curious double periodi- 

 city later on, ' in which the abrupt changes of pro- 

 perties in the neighbourhood of the zero family alter- 

 nate with the gradual changes in the neighbourhood 

 of the eighth groups. The extraordinary exception to 

 the principle of the whole scheme presented by the 

 rare-earth elements remains a complete enigma, none 

 the less impressive because, beyond them in the table, 

 the normal course is again resumed and continues to 

 the end. This latter, highly significant, feature of the 

 periodic table is on ^ of the definite conclusions follow- 

 ing from the chemical charactferisations of the 

 numerous radio-elements. 



UNIVERSITY AND EDUCATIONAL 

 INTELLIGENCE. 



London. — Mr. C. O. Blagden has been appointed 

 as from September 1 next to the new University 

 readership in Malay, tenable at the School of Oriental 

 Studies. 



The cordial thanks of the Senate have been voted 

 to Sir Ratan Tata for a further* donation of 1400I. a 

 year for five years in continuation of his previous 

 benefaction for the promotion of the study of the 

 principles and methcnds of preventing and relieving 

 destitution and poverty. This will be expended on 

 behalf of the Ratan Tata Department of Social Science 

 and Administration in the Ix)ndon School of 

 Economics, which will be controlled by a joint com- 

 mittee appointed partly by the Senate and partly by 

 the school. 



The following doctorates in science have been con- 

 ferred : — D.Sc. in Botany, Miss F. A. Mockerldge, 

 an internal student, of King's College, for a thesis 

 entitled " Some Effects of Organic Growth-promoting 

 Substances (Auximones) on the Soil Organisms con- 

 cerned in the Nitrogen Cycle." D.Sc. in Geology, 

 Mr. Arthur Holmes, an internal student, of the Impe- 

 rial College (Royal College of Science), for a thesis 

 entitled "Contributions to the Geology of Mozam- 

 bique." D.Sc. in Mathematics, Mr. G. N. Watson, an 

 internal student, of University College, for a thesis 

 entitled "Various Methods of Approximation, with 

 Special Reference to Bessel Functions and Gamma 

 Functions." D.Sc. in Physics, Mr. W. Wilson, an 

 internal student, of King's College, for a thesis en- 

 titled "The Complete Photo-electric Emission and the 

 Emission of Electrons from Hot Bodies." D.Sc. 

 in Zoology, Miss K. M. Parker, an internal 

 student, of University College, for a thesis 

 entitled "The Development of the Hypophysis Cerebri, 

 the Pre-oral Gut, and Related Structures in the Marsu- 

 pialia." D.Sc. (Economics), Miss Kate Hotblack, an 

 internal student, of the London School of Economics, 

 for a thesis entitled "Chatham's Colonial Policy." 

 Grants have been made out of the Dixon fund for 



