52 SECTIONAL ADDRESSES. 
the view that the neutral atom of manganese has an outer system of 
two electrons, and that when this atom loses one of its most loosely 
bound ones another electron from the next inner system comes out to 
take its place in the outermost system, so that the latter again contains 
two electrons. The similarity of the spectra of the neutral and singly 
ionised atoms of manganese would thus be accounted for. By assuming 
that this final configuration of the orbits in the singly ionised atoms 
of manganese was the same as the configuration of the outer orbits 
in the neutral atoms of chromium, the similarity of the are spectrum 
of chromium to those of the singly ionised and neutral atoms of man- 
ganese would also be explained. 
Catalan’s series relations show that the two last acquired electrons 
in the neutral atoms of manganese and chromium are bound in equiva- 
lent orbits of the 4, type, and that as a consequence the ionisation 
potentials of these two elements are given by a frequency of the form 
vy =(1.5), and have the values 7.4 v. and 6.7 v. respectively. 
In some later work Catalan®** has shown that the scheme of series 
in the spectrum of molybdenum is identical with that which applies to 
the spectrum of chromium. With this element he deduced the value 
7.1 volts for the ionisation potential. The two last acquired electrons 
in the atom of molybdenum would appear to be bound in equivalent 
orbits of the 5, type. 
From the considerations that have been presented in regard to the 
atoms and the spectra of chromium and manganese some deductions 
can be made regarding the spectrum and stationary orbits of the un- 
known element of atomic number 48. Its are spectrum, and probably 
that of its singly charged positive ion too, will likely consist of triplet 
series. Its spectrum will also very likely include a set of multiplets, 
and its two outer electrons will probably be found in equivalent 5, orbits. 
Although some considerations recently put forward by Lande** and by 
Back** may lead to modifications in the views expressed above, the 
possibility of making these deductions constitutes a rather remarkable 
testimony to the power of the methods that are being at present applied 
in unravelling the mysteries of atomic structure and of the origin of 
radiations. 
An interesting point in connection with the Kossel-Sommerfeld 
Displacement Law arises in connection with the magnetic properties 
of the neutral atoms of argon, of the singly-charged positive atom ions 
of potassium, and of the singly-charged negative atom ions of chlorine. 
Recent work by W. L. Bragg** and Davey,®” as well as a report by 
Herzfeld,** go to show that the ions referred to and the atom of argon 
have practically the same dimensions, with a radius of about 
1.56x10-*em. It appears also from the work of Kénigsberger,*° 
33 Catalan, C.#., April 16, 1923. 
34 Lande, Zeit. fiir Phys., vol. 15, p. 189, 1923. 
35 Back, Zeit. fiir Phys., vol. 15, p. 206, 1923. 
3% WW. L. Bragg, PAil. Mag., vol. xl., p. 187, 1920. 
81 Davey, Phys. Rev., vol. xvili., p. 103, 1921. 
38 Herzfeld, Jahr. der Rad. und Llek., Bd. 19, p. 259, 1922. 
9 Kénigsberger, Ann. der Phys., vol. 66, p. 713, 1898. 
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