Table Of ContentTHE PAGE-BARBOUR LECTURES FOR
1956 AT THE UNIVERSITY OF VIRGINIA
ATOMIC STRUCTURE
AND THE STRENGTH
OF METALS
An account for the nonscientist of recent
researches aimed at understanding zvhy
metals have their characteristic
strength and ductility
by
N. F. MOTT
Cavendish Professor of Experimental Physics in
the University of Cambridge
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First published 1956
Second impression i960
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PREFACE
THESE three lectures are an attempt to present to an
audience of nonspecialists the results of recent re-
searches in one small part of physics. Most writing
and lecturing at this level has aimed at exciting the
interest of men and women who are not scientists by
describing those features of science which are most
calculated to produce wonder. Of this kind there are
excellent books on astronomy, on the size and dis-
tance of the spiral nebulae and on the age and origins
of our universe. There are also books in plenty about
the nucleus, how small *t is and what incredible
amounts of energy are bound within it, and how this
is released in the atomic bomb. Yet other books
describe the philosophical implications of modern
physics and the breakdown of causality that some
scientists believe to be inherent in it. The aim of this
book is different. It is about metals. In it certain of
the most familiar properties of metals are described,
properties that were known to smiths and metallur-
gists before the days of written history. It is pointed
out that no attempt was made by scientists to under-
stand these properties in terms of the behaviour of
PREFACE
atoms until very recently, until in fact just before
and after the war of 1939-45. The explanation, as
described in these lectures, does not require any
sophisticated model of an atom with a nucleus and
electrons, or any difficult mathematical theory like
wave mechanics. An atomic model like that of
Lucretius is enough—atoms pictured as hard but
slightly compressible spheres and able to stick to each
other. It is curious that in an age which discovered
so much that was totally unexpected it took so long to
provide the relatively simple explanations of facts
known since antiquity.
The lectures were prepared in response to an
invitation to give the Page-Barbour lectures before
the University of Virginia, which the author hopes to
give in October 1956. They are based also in part on
two unpublished lectures given in the University of
Cambridge as part of a course designed to present
some of the ideas of physics to students of the
humanities.
N. F. Μοττ
April 1956
LECTURE ONE
MY aim in these three lectures is to describe a certain
branch of science in nontechnical language, and to
show its interest and importance both to those of
you who are or who intend to be professional
scientists and those of you who do not. The branch
of science which I have chosen is the science of
metals, and particularly of their mechanical proper-
ties, their strength and ductility. I shall speak not so
much of the long history of metallurgy by which
mankind in the course of history and prehistory has
discovered how to prepare metals and alloys suited
to his ever-expanding needs, but rather of a much
more recent field of research, the physics of metals, of
which the aim is to explain and understand these
properties of metals and to relate them to the proper-
ties of atoms. I shall talk to you, therefore, about a
field of pure or fundamental research, but one which
is closely related to a large and important part of
technology.
First of all, however, and by way of introduction,
may I say how glad I am to have the opportunity m
address a mixed audience, largely of nonspecialists,
2 THE PAGE-BARBOUR LECTURES
on this subject? Let me also tell you wThy. It is only
too clear that, in this age of nuclear energy, anti-
biotics and space travel, science is your business,
whoever you may be. Too much of your money is
spent on it, and the results affect you too much, for
you to be indifferent to what is done. Now Ï am a
university professor and, in the phrase used by my
University of Cambridge, my job is to promote
education, religion, learning and research. We whose
business is education have to concern ourselves with
this problem, how7 we are to ensure that the new
generation, who grow up to be administrators, po-
litical leaders and businessmen shall have a proper
understanding of this science which affects their
world so profoundly. We discuss this problem only
too frequently, when we meet together, in your
country I believe as well as in mine. What we want to
avoid, surely, and what to some extent we have, is a
society of two mutually suspicious classes; the
scientists, engineers and technologists who do the
work and set the rate of advance, and the adminis-
trators, soldiers, salesmen, security officers and
common men and women who know that we have to
have science but who do not understand how the
community should use it.
I think that in our two countries we set about this
problem in different ways, You in the United States
give all boys and girls a general education up to the
THE PAGE-BARBOUR LECTURES 3
end of the high school course, and indeed in the first
year or two of the university. In English schools we
start to specialize much earlier, usually at 16, and in
the universities we tend to leave the problem of
general education to the assumed effects of residence
together in colleges, it being hoped that students in
science and in the liberal arts will talk together
about their respective problems. With the exception
of an experiment at the new university of North
Staffordshire, there is very little attempt at formal
instruction in British universities in subjects outside
that of each student's speciality. There are I believe
no courses that are examined or evaluated. I think
that within the framework of British education,
insisting as it does on the educative value of deep and
profound studies on a narrow front, such courses are
not likely to be tried widely. Many of us would like
to see our problem solved in another way, as would
I believe many of you in the United States. This is
by more emphasis in a man's specialized education
on those other subjects which are closely related to
the subject of his specialization.
This point has been very well put by Sir Eric
Ashby, the Vice-Chancellor of the Queen's Univer-
sity of Belfast. He is writing of general education and
trying to define what he means by the educated or
cultured man* He writes1 that he considers that the
path to culture is through a man's specialism, not
4 THE PAGE-BARBOUR LECTURES
by bypassing it through undue attendance at courses
which have no relation to it. "Suppose", he writes,
"a student decides to take up the study of brewing:
his way to acquire general culture is not by diluting
his brewing courses with popular lectures on archi-
tecture, social history, and ethics, but by making
brewing the core of his studies. The sine qua non for a
man who desires to be cultured is a deep and en-
during enthusiasm to do one thing excellently. So
there must first of all be an assurance that the student
genuinely wants to make beer. From this it is a
natural step to the study of biology, microbiology,
and chemistry, all subjects which can be studied not
as techniques to be practised but as ideas to be
understood. As his studies gain momentum the
student will naturally become interested in the
economics of marketing beer, in public houses, in
their design, in architecture; or in the history of
beer drinking from the time of the early Egyptian
inscriptions, and so in social history; or in the un-
happy moral effects of drinking too much beer,
and so in religion and ethics/'
If then this is how we would hope to bring culture
and breadth to the technologist and the scientist, how
shall we do the opposite? How shall we bring some
understanding of the scientific way of thought, the
major achievement of our age, to the nonscientist?
It seems to me that there are two ways. One cnn seek
THE PAGE-BARBOUR LECTURES 5
to excite his wonder, by stories of the emptiness of
space, the size of the spiral nebulae, the smallness
of the atom and the latent energy of the nucleus.
This is one way and in the hands of a master it can
be very effective. But in these lectures I want to
try another method, a method more like the approach
of Sir Eric Ashby to his students of brewing. This is
to take a familiar property of matter, a property which
plays its role in history, in archaeology, in art and in
common experience, and to see how it looks to a
physicist. In this way, just as the student of tech-
nology can be led to pure science, to sociology,
ethics and religion, so I believe that the student of
the liberal arts can learn to feel that his studies
impinge on science.
Now my subject, from which I have wandered, is
the science of metals. It is a good subject, I think,
with which to introduce the student of liberal arts
or humanities to the concepts of science. I believe
that this is true particularly for students of history,
of the classical languages, of archaeology and of art.
This is because of the obvious and profound effect
that the development of metallurgy has had both on
the history of man and on his artistic expression.
This I need not elaborate. But it also seems to me
that the study of metals and their history illustrates
in a very profound way that very important point for
the educated layman, the difference between pure and
6 THE PAGE-BARBOUR LECTURES
applied research and the importance of both. Let me
show you why.
We are apt to think that science and particularly
physics deals with the new and unexpected aspects
of nature that our ancestors knew nothing about,
electricity, radioactivity and nuclear phenomena, and
that it is for these that university scientists must seek
an explanation. We are apt to forget that there are
other much more familiar properties of matter which
are just as much proper subjects for investigation,
and which may be just as difficult to understand, if a
detailed understanding in terms of atomic movement
is required. The fluidity of ordinary water is one, and
the subject of these lectures, strength and ductUity
of metals, is another. Moreover, these properties,
though familiar to us, have not always been so. You
know from your childhood that you can wind a wire
round your finger, that you can shape and deform
metals by bending and hammering. But this know-
ledge has not always been familiar. As we know,
quite complex civilisations with towns, writing and
large buildings existed before mankind knew how to
smelt metals from their ores. Tools were then made
of hard unductile stone, and the materials that man
knew besides were skins, clay, wood and earth.
None of them had this ductility, this capacity to be
hammered and forged into the shape desired. But
there was always gold, malleable and shiny, tö be
