JULY 19, 1923 PROCEEDINGS: PHILOSOPHICAL SOCIETY 297 
175TH MEETING 
The 175th meeting of the Acaprmy was held jointly with the Philosophical 
Society of Washington in the Assembly Hall of the Cosmos Club the evening 
of Saturday, March 10, 1923. Prof. A. Sommerrenp of Munich, delivered 
an address on Hvidence for the theory of relativity afforded by atomic physics. 
Two branches of modern physics stand in the center of scientific interest, 
the theory of relativity and the theory of atomic structure. They came 
together, as the speaker showed in 1916, in the theory of the fine structure 
of certain spectral lines. 
The theory of relativity (Einstein, 1905 and 1915) is a new foundation of 
our general notions of space, time, matter, and gravitation, based on obser- 
vational facts. The mass of an electron, for example, as well as length, 
time, and energy, is dependent on the relative velocity of the electron with 
respect to the observer. The theory of atomic structure (Bohr, 1913) is 
based on the notion of the nuclear atom (Rutherford, 1911) and on the 
theory of quanta (Planck, 1900). The electrons revolve around the nucleus, 
like the planets in the solar system around the sun. In the simplest atoms 
of hydrogen and of ionized helium we have a Keplerian motion: one electron 
revolving around the nucleus. Bohr succeeded in computing the wave 
lengths of the spectrai lines of these elements and in revealing the laws of 
spectra, widely different from the laws of the oscillations of the usual mechani- 
cal systems. The wave-lengths are given by the energy differences of the 
atom in its initial and final states. 
According to the theory of quanta, a certain state of the atom corresponds - 
to a certain number of electronic orbits, either circular or elliptical. In the 
helium liné \ = 4686, e.g. the initial state of the atom corresponds to four 
different orbits, the final state to three. These four different initial orbits, 
as well as the three different final ones, have the same energy, according to 
the classical mechanics of Newton. Therefore, all the 4 XK 3 = 12 transi- 
tions give the same energy difference and produce the same spectral line. 
But Newton’s mechanics are only a first approximation; the real mechanics 
_ are Einstein’s. According to the relativistic increase of the electronic mass 
with increasing velocity, the energy of the four initial orbits is slightly dif- 
ferent as well as the energy of the three final orbits. So we get 12 components 
very close together, of a so-called fine structure. The photographs taken 
by Paschen in 1916 are projected; they prove themselves to be in best agree- 
ment with the prediction of the theory. 
Fine structure components of the same character occur in the X-ray 
spectra of all elements; they show that the same circular and elliptical orbits 
and the same relativistic increase in the mass of the electron occur in the 
inner parts of all elements. (Auwthor’s abstract.) 
Wiuiiam R. Maxon, Recording Secretary. 
’ 
PHILOSOPHICAL SOCIETY OF WASHINGTON 
883D MEETING 
The 883rd meeting was held in the Cosmos Club Auditorium on Saturday, 
April 7, 1923. It was called to order at 8:15 p.m. by President Wu1tTe with 
42 persons in attendance. 
Owing to some experiments with liquid hydrogen which were in prepara- 
tion by Dr. Kanour, the reading of minutes of previous meetings was de- 
ferred until later in the evening. 
