April 22, 1920I 



NATURE 



231 



is assumed to consist of one a and one v group, 

 with a symmetrical arrangement of the seven positive 

 electrons. Two a particles do not seetn to combine, 

 but from three to eight, and also ten, a particles 

 combine without the inclusion of any cementing 

 electrons ; but when more than ten unite, two or a 



ABUNDANCE OF THE ELEMENT3 



multiple of two negative electrons are used in cement- 

 ing on extra o particles — that is, a particles which do 

 not contribute to the positive charge on the nucleus. 

 Argon and calcium have isomeric atoms, the formula 



C 



J 



Fig. 2. 



of the former being aio/Sjc',, and that of the latter 

 Oioe'i.ej, so both have the general formula 0,0620- 

 The formulae given below represent a few charac- 

 teristic atoms : — 



Even Nuclear Charge 

 C a^'^^i 

 O a,«V« 



Fe 0,4^2^', g^g 



Thorium Series 



1 h ^is^-ii^'m'"* 



ThX ase824^'8,^2 

 Pb(Th) a,^B^',^e, 



Odd Nuclear Charge 



F a^ve'^-, 



CI OgVff'jo^? and a^vfie\(,e-. 



Co Oi4>'32«'l8^9 



Uranium Series 



Ra asaH0-ne'gt/!t 



rb(Ra) ai,ti&to''-!^i 



Here c represents a valency electron, e' a non-nuclear 

 electron in one of the inner shells, and /3 a cementing 

 electron in the nucleus. The evidence for these 

 formulae is good, but cannot be presented here. 



NO. 2634, VOL. IO5I 



It will be seen that this hydrogen-helium-meta- 

 hydrogen theory of atom-building is based upon the 

 atomic weight and atomic number relations ; the 

 Rutherford atom ; the rule of Soddy, F'ajans, and 

 Russell for radio-active changes ; and the atomic 

 weight relations discovered by Rydberg about thirty 

 years ago ; and is dependent for its validity upon the 

 existence of chlorine, magnesium, silicon, and the 

 heavy atoms in isotopic forms. It is a resurrection 

 and an extension of the hypothesis of Prout. 



References. — J. Am. Chem. Soc, xxxvii., pp. 1367- 

 96 (1915); xxxix., pp. 856-79 (1917); Phil. Mag., 

 XXX., pp. 723-34 (1915); Science, N.S., xlvi., pp. 419- 

 27, 443-48 (1917); Proc. Nat. Acad. Sciences, i., p. 276 

 (1915); ii., pp. 216-24 ('916); Physical Review, 

 February, 1920, in press. 



William D. Harkins. 



Department of Chemistry, University of 

 Chicago, March 8. 



I HAVE read Prof. Harkins's letter with great 

 interest. If Prof. Harkins has succeeded in separating 

 the isotopic hydrochloric acids he is certainly to be 

 congratulated. The very meag^'e positive results from 

 my work with neon "described at the British Associa- 

 tion meeting in 1913 convinced me of the extreme 

 difficulty and labour of such diffusion experiments. 

 In the "case of neon I had only to grapple with_ a 

 twentieth root in the diffusion equation, whereas with 

 HCl it is the thirty-sixth root which is involved. In 

 connection with the possibility of a third isotope of 

 chlorine in the full account of my recent analysis of 

 this element, now in the press, I have described a 

 faint line at 39 which mav be this. 



More experimental results will be required befofe the 

 time is ripe for the formulation of a comprehensive 

 theory of atomic structure. I do not propose, there- 

 fore, to discuss the one put forward by Prof. Harkins, 

 but would like to point out that his basal assumpticyi 

 that the positive" electron has a weight I'ooo 15 

 definitely contradicted bv experimental results quoted 

 in mv letter in Nature of March 4. F. W. Aston. 



Cavendish Laboratory, Cambridge, April 20. 



On Atomic and Molecular Structure. 



The statement of Mr. S. C. Bradford in the second 

 paragraph of his letter to Nature of April 8, that I 

 suppose the electrons to revolve in small circles with- 

 out any constraining force, is erroneous. The fact 

 that I reserved an opinion as to the nature of the con- 

 straining force does not imply, as he suggests, that 

 I denv its existence. Thus (cf. Science Progress, 

 April, 1920, and Phil. Trans. Roy. Soc, vol. ccxx,, 

 p. 247, 1920) an electron moving with speed 

 V perpendicular to a magnetic field of intensity H 

 (which may originate in the nucleus) describes a 

 circular orbit of radius p = tnf/He, and the frequency 

 of the electron is v=He/2rrw, which (and this is an 

 advantage in the case of a radiating orbit) is inde- 

 pendent of the speed with which the electron describes 

 the orbit. .\t present we know little about the actual 

 value of T*. If H is of the order 10' gauss, the value 

 ascribed to the molecular field from magnetic con- 

 siderations, the frequency is that of infra-red radia- 

 tion, and the correlation" of the elastic properties of 

 the medium (which are determined by this molecular 

 field) with the infra-red vibrations, as originally 

 pointed out bv Debve, is apparent. Within an atom 

 the controlling field mav be of the order to" gauss, 

 which gives rise to vibrations of optical frequency. 

 Closer to the nucleus a field of 10' gauss gives rise 

 to frequencies comparable with those of a K series. 



Finally, it should be Pointed out that the rifig 

 electron' theory, which Mr. Bradford attributes to 



