482 

NATURE 
[APRIL 7, 1923 
American Association Meeting at Boston. 
“HE seventy-sixth meeting of the American 
Association for the Advancement of Science 
was held at Boston on December 26-30. Several of the 
addresses delivered by presidents of sections have 
appeared in recent issues of Sczence, and briet accounts 
of some of them are subjoined. 
Puysics AND GEOMETRY. 
In his address to Section A (Mathematics) Prof. 
Oswald Veblen discussed some of the aspects of 
postulational geometry in reference to the develop- 
ments of physics during the last twenty years. 
In the classical branches of physics the main 
elements of the abstract point of view have been 
implicit in them for a long time. When it is stated 
with sufficient clearness in physical terms what is 
meant by undefined elements, unproved propositions, 
and so on, it is often found that a physicist classifies 
these as truisms of little importance. So far as 
practical results are concerned he is justified in 
this attitude during the earlier and cruder stages 
of physical theory. But experience is showing that 
when the results of a more refined experimental 
technique force a reconsideration of fundamental 
assumptions, the technique of the study of these 
assumptions must undergo a corresponding refine- 
ment. A recent illustration is afforded by Einstein’s 
theory of gravitation, which accounts for certain 
observed physical phenomena by casting aside the 
familiar conception of space and time in favour of 
a new one, which is just as self-consistent and capable 
of logical development: 
Beginning with elementary geometry, the oldest 
branch of physics, there is a sequence of statements 
arranged ina certain logical order, but void of all 
physical meaning. In order to apply them to 
Nature, the undefined terms (points, lines, etc.) are 
identified as names of recognisable objects. The 
unproved propositions (axioms) are then given a 
meaning, and when this meaning can be identi- 
fied with a true statement the theorems which 
are logical consequences are also true, and the ab- 
stract geometry takes its place as a useful branch of 
physics. 
For kinematics it is necessary to have a theory 
of time: the undefined terms are “ instant’ and 
““ before ’’ or “‘ after,’’ and the postulates one of the 
sets of postulates for the linear continuum. The 
main theorem is that there is a continuous one-to- 
one correspondence between the instants of time and - 
the numbers of a real number system. 
Prof. Veblen has also formulated a set of postulates 
for ‘“mass’”’ or “ substance,’’ observing that the 
postulates proposed may contain both omissions and 
redundancies. They have merely been advanced to 
emphasise the fact that very little work has yet 
been done in this direction. 
ALLUREMENTS IN PuysIcs. 
In his address to Section B (Physics) Prof. G. W. 
Stewart, of the University of Iowa, president of the 
section, dealt with the attractive nature of some of 
the problems of physics at the present time. 
The investigation of atomic structure becomes so 
exciting that we may. easily forget the absence of 
clearness in some of our hypotheses. The static 
theories have the advantage that they give clear 
pictures of the atoms which can be used in discussion 
of the physical and chemical properties of the elements 
as they appear in periodic groups and of the com- 
pounds they form. The orbital theories, on the 
NO. 2788, VoL. 111] 


other hand, have been most successful in explaining 
the spectra of hydrogen and helium, and, by the 
help of a further hypothesis, the spectra of the alkali 
metals. In his most recent work Bohr has departed 
from the simplicity of his original hypotheses and 
has endeavoured, by assuming electron orbits which 
may be circular, elliptical, or highly elliptical, and 
penetrate each other in many ways, to construct 
systems which would have the properties of the 
elements of the periodic table. Although this method 
of attacking the problem is not so rigorous, Prof. 
Stewart thinks it will prove more fruitful than that 
of the statical theories. “ 
Acoustics receives little attention from physicists 
of the present day, but Prof. Stewart points out its 
allurements, and refers with keen appreciation to 
the work of the late Prof. W. C. Sabine of Harvard 
on the acoustics of buildings, which is only just 
becoming known in Great Britain. The problem of 
the best angle for a conical horn seems nearing solution 
and the conception of the instrument as a collector 
of sound replaced by the proper conception of it 
as a resonator. 
Gas IONISATION AND RESONANCE POTENTIALS. 
An address on this subject was given to Section C 
(Chemistry) by Prof. W. A. Noyes of the University 
of Chicago. The ionisation potential is the fall of 
potential through which an electron must move to 
acquire speed enough to drive out of an atom of a gas 
on which it impinges one of its outer electrons, known 
as valence electrons, and the resonance potential is 
the fall through which an electron must move to 
acquire speed enough to displace an electron of an 
atom from an inner to an outer ring of electrons. The 
two potentials should, according to the Bohr theory 
of the atom, be connected in a simple way with the 
spectrum of the gas, and many measurements have 
recently been made to test this theoretical conclusion. 
The agreement is not so satisfactory as one would 
desire, and there is considerable difficulty in inter- 
preting the values ot the potentials found in experi- 
ment in terms of changes in the atoms. Prof. Noyes 
thinks, however, that it is along these lines that our 
knowledge of atomic structure and of the mechanism 
of chemical combination will develop in the future. 
GEOLOGY’s DEBT TO THE MINERAL INDUSTRY. 
Dr. Willet G. Miller, president of the Section E 
(Geology and Geography), selected as the subject of 
his presidential address, ‘“‘ Geology’s Debt to the 
Mineral Industry.’”’ He explained that, throughout 
the history of its development, the progress of the 
science of geology has been helped to a large extent 
by work connected with the mineral industry. 
Werner and his disciples did much for the science of 
geology in its early development by their investiga~ 
tions of earth-structure as revealed in mines. William 
Smith, the English civil engineer, whose great work 
as the “‘ father of geology ”’ is so well known, estab- 
lished the principles of stratigraphical geology as a 
by-product of his work on engineering problems. He 
complained that the theory of geology was in posses- 
sion of one class of men, the practice with another. 
——— oe 
Logan, the great pioneer of field studies in Canada, ~ 
especially in the pre-Cambrian areas, declared that 
for many years he was engaged in coal-mining and 
copper-smelting, and that his connexion with geology 
related largely to its economic aspects. 
After Logan’s time little progress was made in 
