328 SECTIONAL TRANSACTIONS.—A. 
Prof. J. C. McLennan, F.R.S.—On the Moments of Atomic Nuclei. 
Spectroscopic investigations in progress have already yielded results that enable 
one to calculate the spin moments of the nuclei of the atoms of certain of the 
elements. The values thus obtained are being related now to such factors as atomic 
weight and atomic number. The author, with his collaborators in recent work 
on the fine structure of several prominent lines in the second spark spectrum of lead, 
PbIII, has found that these structures can be given a consistent interpretation by 
assuming the two values, 0 and , for ‘I,’ the quantum number representing the spin 
moment of the nuclei of lead atoms. Intensity relations between the observed 
fine structure components indicate that I=} gives the spin moment corresponding 
to the Pha; isotope and I=O that corresponding to the Pb. and Phyo. isotopes. 
Hyperfine structure data derivable from a study of thallium, lead and bismuth 
spectral lines enable one to show the inadequacy of certain theories now before us. 
Constants of interaction-relationships for nuclear and electronic angular moments 
can be calculated, nuclear magnetic moments can b2 evaluated, and ‘g° values 
(ratios of magnetic to mechanical moments) can be determined from the data accumu- 
lated. These furnish evidence which appears to show that the mechanical moments 
found for atomic nuclei are the resultants of angular momenta originating in the spin 
of the protons within atomic nuclei and in some other motion, probably orbital, of 
these protons. 
Prof. M. N. Sana.—The Interpretation of the Absorption Spectra of Silver 
Halides. (In title.) 
In this paper the view is put forward that the molecules of silver halogenides in 
the vapour state form ionic-compounds, and not atom-compounds, as postulated by 
Franck. The normal state is given by the combination Ag+Cl- where Ag+ is in 
the (4d) state. The excited state is also given by Ag+Cl-, but Ag+ is now in the 
(4d)955 state. 
The [U,,,—1] curve for the neutral combination of AgCl has a hyperbolic shape, 
which accounts for the fact that hog (where vp = limit of absorption frequency) 
is >R, the atomic heat of dissociation. Arguments for and against the two views 
are discussed, and new experiments are proposed to decide between the two views. 
Dr. W. F. G. Swann.—The Significance of Mass in Wave Mechanics. 
In the Hamiltonian Function which forms the basis of the ¥ equation, the constants 
m,, M2, &c., corresponding to the masses of the protons and electrons of an atom in 
the classical sense, make their appearance in a new role which can be seen to be the 
equivalent of their old réle in classical theory only when the motion of the atom as a 
whole is studied in the wave mechanical sense. If, in the Hamiltonian Function, we 
include the scalar and vector potentials of electrodynamics as calculated from the YY 
distributions of the atom regarded as charge densities, the simple mass m,+m.+ .. ., 
&c., of the entity in the dynamical sense becomes increased ( or decreased) by a quantity 
which turns out to be the electromagnetic mass of the YY distributions calculated 
according to electromagnetic principles. In this way, contrary to the ordinary 
electromagnetic theory of mass, the main part of the mass, the part determined by 
my, M2, &c., has a mathematical origin different from that of the mutual mass, and is 
not obtainable, as in classical theory, from a mere extension of the electromagnetic 
principles inherent in mutual mass to the charges as a whole. The phenomena of 
mutual mass and of ‘ packing fractions’ become susceptible of development without 
the assumption of an electron of dimensions comparable with 10-3 cm., with its 
attending difficulties. A certain latitude is open as to the way in which the values 
of ‘YY for the positive and negative charges contribute to the Hamiltonian occurring 
in the Y’ equation ; and, by a reasonable adjustment of these assumptions, it is possible 
to account for the form of the ‘ mass defect ’ curve, and for the numerical change of 
mass defect with atomic number, particularly in the vicinity of the higher atomic 
numbers. 
