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Excursions

in
Science

Edited by NEIL B. REYNOLDS
and ELLIS L. MANNING

IN Excursions in Science, thirty scien-
tists present, in simple language,
thirty-five stories of their respective
sciences. The subjects range from organic
chemistry to atomic physics, from arch-
eology to astronomy. But instead of
rules and definitions, they tell us what
happens to the food we eat, what causes
lightning, how the vacuum tubes in
our radios work, what causes the tides.
They take us, as the title indicates, on
excursions into the world around us,
showing how the light of science gives
new meaning to the everyday things of
life.

Unlike most scientific books for lay-
men, these Excursions have not under-
gone a translation-like process at the
hand of an interpreter. Each Excursion
is the work of a scientist who has been
trained in his particular field, who has
worked in it, who has almost literally
eaten and slept with it. The eniphasis
is on what he, himself, thinks important,
not what someone else thinks should be
important.

Many of the contributors are well
known, and a number have recently
gained special recognition in tn%ir sci-
ences. Dr.'Langmuir, of course, is famous

(Continued on back flap)

(Continued from front flap)

for his work in electronics and surface
films. Dr. Blodgett's work in "invisible
glass" has recently gained wide atten-
tion. Dr. McEachron's studies of light-
ning led to the artificial lightning
exhibit which has been one of the most
popular features of the General Electric
exhibit at the New York World's Fair.
Dr. Raskins is the author of a recent
book, Of Ants and Men, which has been
well reviewed.

The editors, Neil B. Reynolds and
Ellis L. Manning, are respectively Special
Writer for the General Electric Company
and Supervisor of Science, New York
State Department of Education. Both
were formerly Physicists in the Research
Laboratory of the General Electric
Company.

" Engrossing reading." - Book-of-the-
Month Club News.

" Fascinating." Nature Magazine.

"Some of the most interesting stories
of this year "--Cleveland Plain Dealer.

"Admirable clarity and concretcness.
, . . Excellent."- Baltimore Sun.

"Should win a wide popularity."
Hartford Courant.

W'hittlesey House

McGRAW-HiLL BOOK COMPANY, INC.
330 West 42nd Street, New York

EXCURSIONS IN SCIENCE

'Somebody is always reflectively monkeying
with some of the parts of an infinite universe."

W. R. W.

EXCURSIONS
IN SCIENCE

EDITED BY

NEIL B. REYNOLDS

General Electric Company
AND

ELLIS L. MANNING

Supervisor of Science , New Fork State Department of Education

New Tork WHITTLESEY HOUSE London
MCGRAW-HILL BOOK COMPANY, ING.

PUBLISHED BY WHITTLESEY HOUSE
A division of the McGraw-Hill Book Company, Inc.

Printed in the United States of America by the Maple Press Co., Tork,Po.

To
WILLIS RODNEY WHITNEY

VICE-PRESIDENT IN CHARGE OF RESEARCH

OF THE GENERAL ELECTRIC COMPANY, THE

EDITORS AFFECTIONATELY DEDICATE THIS

VOLUME

PREFACE

rnrio APPRECIATE music, one does not have to be a
-*- virtuoso, or a performer at all for that matter.
Indeed, it may be that the informed but nonprofes-
sional listener gains as much pure enjoyment from a
concert as does the more critical student of musical
technique.

What is true of music, and of the other arts, may be,
in its own fashion, equally true of science. We cannot
ignore the results of science; they lap us round, they
shape and alter increasingly the course of our activi-
ties. Yet their origin is, to most of us, a mystery.
This is our loss, for just as a layman's knowledge of
the instruments that make up a symphony orchestra
may sharpen his appreciation of its rendition
whether of Beethoven's Eroica or of the Rhapsody in
Blue so a little knowledge of the scientist's problems,
his tools, and most of all his mental outlook may serve
to sharpen our appreciation of the gifts science has to
offer.

Such knowledge is not beyond the grasp of anyone,
for the materials with which the scientist deals are,
after all, the things with which we are all most familiar.

[vii]

Preface

Laboratory examination is only an extension in degree
of intelligent observation. Scientific reasoning is
nothing more than systematized common sense.

In May, 1936, the General Electric Company
instituted a radio program, called The Science Forum,
designed to present the meaning, scope, and several
purposes of modern scientific research and engineering
in language that could be understood by the intelligent
layman. As part of that program, workers in many
fields of science were invited to present short talks on
their particular fields of study.

Because the material presented seemed too valuable
to serve only the ephemeral purposes of the radio, the
editors have gathered a selected group of these talks
into this present form. Because, in each section that
follows, we shall be venturing into a different field of
scientific study under the guidance of a writer experi-
enced in that field, the name Excursions in Science has
been chosen. These excursions follow no fixed itiner-
ary; by intent they range from astronomy to physi-
ology, from atomic physics to archeology. The world
about us is filled with interesting things to explore,
and we want to visit as wide a variety of them as
time and our appetite for adventure permit.

A manuscript prepared for broadcasting is not
always in a form most suitable for publication. The

[ viii ]

Preface

talks have, therefore, in certain cases, been somewhat
altered and abridged. But in every case it is the original
author who speaks; the opinions expressed are his.
The editors are pleased to acknowledge their indebted-
ness to these authors, to the General Electric Company,
and in particular to the General Electric Research
Laboratory for aid in making possible these Excursions
in Science.

NEIL B. REYNOLDS,
ELLIS L. MANNING.

SCHENECTADY, N. Y.

[ix]

CONTENTS

PAGE

PREFACE vii

SIMPLE EXPERIMENTS IN SCIENCE 3

by DR. IRVING LANGMUIR

ATOMS AND THEIR FAMILY RELATIONS 1 1

by DR. E. G. ROCHOW

WHERE HUMAN ENERGY COMES FROM 20

by- DR. JAMES W. MAYOR

TIME 27

by DR. LEWI TONKS

THE NATURE OF LIGHTNING 35

by DR. KARL B. MCEAGHRON

THE MARKS ON YOUR THERMOMETER 43

by DR. FRANK R. ELDER

METEORITES 50

by EDWARD S. C. SMITH

ANIMAL LIGHT 57

by DR. LEWIS R. KOLLER

EARS, HUMAN AND ELECTRIC 64

by ALBERT J. MUCHOW

VACUUM 73

by EDWARD F. HENNELLY

THE RED PLANET MARS 80

by DR. FREDERICK W. GROVER
[Xi]

Contents

PAGE

CHEMICAL REACTIONS IN THE HUMAN BODY 86

by DR. MURRAY M. SPRUNG

POWER FROM THE SUN 96

by DR. CLARENCE W. HEWLETT
ODORS AND THEIR DETECTION 103

by DR. NEWELL T. GORDON

LILLIPUTIAN CHEMISTRY 112

by DR. HERMAN A. LIEBHAFSKY

How EARTHQUAKES GIVE Us THE INSIDE FACTS 118

by EDWARD S. C. SMITH

OZONE 127

by DR. FRANCIS J. NORTON

THE EARTH AS A DIARY 135

by KARL A. PAULY

ADVENTURES WITHIN THE ATOMS 143

by DR. Louis N. RIDENOUR

I. What Atoms Are 143

II. How to Change Atoms into Other Atoms 151

PROBABILITIES AND IMPROBABILITIES 162

by FRANK BENFORD

MEN AND METALS 168

by EARL R. PARKER

THE USE OF LIGHT IN CHEMISTRY 176

by DR. GORTON R. FONDA

THE TIDES 184

by DR. FREDERICK W. GROVER

[xii]

Contents

PAOX

WHAT HAPPENS IN A GAS-DISCHARGE LAMP? 194

by CUFTON G. FOUND

SCIENCE AND SUPERSTITION 200

by NEIL B. REYNOLDS

STONES PRECIOUS AND OTHERWISE 206

by DR. E. G. ROCHOW

CHASING THE MOON'S SHADOW 215

by DOROTHY A. BENNETT

How YOUR RADIO TUBES WORK 225

by ELMER D. MCARTHUR
THE MACHINERY OF HEREDITY 234

by DR. CARYL P. HASKINS

FLUORESCENCE AND PHOSPHORESCENCE 244

by DR. GORTON R. FONDA

A GAUGE THAT MEASURES MILLJONTHS OF AN
INCH 255

by DR. KATHARINE B. BLODOETT

AN AMATEUR LOOKS AT ARCHEOLOGY 264

by P. SCHUYLER MILLER

IDENTIFYING MOLECULES 274

by DR. MURRAY M. SPRUNG

ELECTRON OPTICS 284

by DR. RALPH P. JOHNSON

THE LIMITATIONS OF SCIENCE 292

by LAURENCE A. HAWKINS

INDEX 299

[ i
xm]

EXCURSIONS IN SCIENCE

SIMPLE EXPERIMENTS IN SCIENCE
by DR. IRVING LANGMUIR

TTVR. LANGMUIR, born in Brooklyn, New York, was graduated
-*-^ from Columbia University with the degree of Metallurgical
Engineer. He received his Doctor of Philosophy degree, in the
field of physical chemistry, from the University of Gottingen,
Germany. After teaching for three years at the Stevens Institute of
Technology, he went to Schenectady, in 1909, to join the staff of
the General Electric Research Laboratory. Since 1932 he has been
associate director of that laboratory. Dr. Langmuir's investigations
have embraced many fields of science. His study of hot filaments
in gases produced important improvements in incandescent
lighting, and his work on the behavior of electrons in vacuum laid
the foundation for our present knowledge of vacuum tubes and
their applications to radio. His more recent work on molecular
films won for him, in 1932, the coveted Nobel Prize in Chemistry.

SOME people have the feeling that the task of the
scientist a hundred years ago was much easier
than it is now, because in those days it was possible to
make simple experiments that would lead to important
discoveries. They claim that the day of the simple
experiment is now gone forever, and that today no one
can hope to make contributions to science unless he is
equipped with very expensive and elaborate apparatus.

[3]

Excursions in Science

I think this is a mistaken attitude. I believe there
never was a time when there were so many simple
experiments that could be made that can lead to
important results. Of course, it is perfectly true that
many of the problems that scientists have to face today
require apparatus that would be quite beyond the
means of the ordinary individual scientist. Such
problems as these are best attacked in university
laboratories or in big industrial laboratories where
extensive facilities are available.

But I want to describe some of the simple problems
which used to interest me when I was a boy problems
which can be experimented on in a very simple way
and yet which require a great deal of thought to
explain.

For example, I have in my pocket a fountain pen
and a pencil. The pencil is a round one, and the pen
has a considerably larger diameter than the pencil.
If I sit down at a table and place the pencil across the
pen, I find that I can balance the pencil on the pen by
carefully moving the pencil back and forth until the
center of gravity comes just over the point at which it
touches the pen. When I balance the pencil in this
way, and then displace it a little by pushing one end
down, the pencil, instead of falling off the pen,

[4]

Simple Experiments in Science

oscillates back and forth with a definite period of
oscillation, like a pendulum.

Yet, if you try to do the thing the other way around
and put the pen on top of the pencil, you will find that
you cannot obtain a balance. I used to wonder about
this when I was a young boy, so I made experiments
with pencils of different sizes. And I came to the con-
clusion that one pencil can be balanced on another
only if the top one has a smaller diameter than the
lower one. I wasn't able to figure out the reason for
this, but later on when I was a sophomore in college
and began to study mechanics I was able to work
out the solution by myself, and had a lot of fun in
doing it.

Here is another simple experiment that anyone can
try. Take a glass of water and sprinkle into it some
crumbs of dry bread or toast that have been broken
into fine particles by rubbing between the fingers.
Then stir the water in the glass with a spoon and watch
what happens. The crumbs circulate around with the
water, being pretty uniformly distributed through the
whole mass of liquid. Gradually you see the crumbs
settle to the bottom and heap up in a little conical
pile in the center of the glass. The same thing happens
to some extent when you put sugar in a cup of clear
tea and stir it.

[5]

Excursions in Science

Now, why do the bread crumbs collect in the middle
at the bottom of the glass? Different people will give
you many different explanations. The most common
one is that the crumbs cannot settle near the edge
because there the water is moving over the surface of
the glass so fast that the particles are swept along by
the current. At first that seems a reasonable explana-
tion. But in a case like this it is better to try to settle the
question by experiment rather than to argue over the
pros and cons of different possible explanations.

Suppose, instead of rotating the water in the glass
by stirring it, we try to rotate the glass around the
water that is, to have a glass full of water containing
some bread crumbs in suspension and then start
turning the glass at a uniform speed. If the explanation
just given is correct, then we should naturally expect
that the crumbs would again collect in a little cone in
the middle of the glass, because when the water is still
and the glass is rotating the relative motion of the
water and the glass is the same as before.

If you try to think of a method for rotating the glass,
you will probably find it difficult to do in a simple way.
The simplest way that Pve been able to think of is to
take a large mixing bowl, such as can be found in every
kitchen, and fill it with water and float in the middle of
it a smaller, empty bowl. Then give the inner bowl a

[6]

Simple Experiments in Science

spin and it will turn very nicely at any speed you want.

Next, take the glass that has the bread crumbs in it,
agitate the water with a spoon so as to bring the
crumbs into suspension, taking care not to make the
water rotate as a whole in either direction. Then,
before the crumbs have settled, put the glass into the
bottom of the smaller bowl and set this in rotation.
If you try this, you will find that all the crumbs will
settle in a nice ring heaped up against the outer edge
of the glass, and there will be no crumbs in the center.
So evidently the explanation suggested in the begin-
ning is not right.

If you sit down carefully at a table and watch the
motion of the bread crumbs and the water in both of
the experiments, you will, I think, begin to under-
stand what it is that makes the bread crumbs pile in a
cone at the center in one case and spread out in a ring
in the other case. What seems the key to the solution is
found by watching the top surface of the water. In
the first experiment, when you rotate the water while
the glass is still, you find that there is a little depres-
sion in the surface of the water near the middle. But
in the second experiment, when you rotate the glass
while the water is still, you do not see this depression.

Now I am not going to give the answer to this
problem. I suggest that those who are interested try to

[7]

Excursions in Science

work it out for themselves and see whether they can
reach a satisfactory explanation of the things they
observe.

There are many interesting experiments that you
can make with soap-bubble films that will give you a
lot to think about. One of the prettiest is to make an
open framework of wire that has the form of the 12
edges of a cube, with an extra wire to serve as a handle.
Now make up a soap solution. (You will get bubbles
that last longer if you put a little glycerin into the
solution.) Dip the whole wire frame down into the
soap solution and bring it up slowly. You will see
some very interesting geometrical figures, especially
if you dip it a second and third time.

Just before the soap films break you'll notice some
beautiful iridescent colors. To explain these you need
to understand the wave theory of light. The colors are
due to the interference of light reflected from the front
and from the back side of the films. The particular
colors that you get depend upon the relation of the
thickness of the film to the wave length of the light.
If you use light of a known wave length, such as from
sodium-vapor lamps, then, instead of colors, you will
see alternating light and black bands which run across
the films. From these bands, it is possible to calculate
the exact thickness of the films.

[8]

Simple Experiments in Science

Dr. Katharine Blodgett and I have been using just
such a simple method, which does not require expen-
sive or complicated apparatus, to measure the sizes of
molecules that are only one ten-millionth of an inch
in diameter. We can also use this method to detect
extremely small amounts of many chemical substances.
In fact, we can in this simple way find the presence
of many substances, such as copper, in water, even if
they are present only to the extent of one part in a
billion. We hope that these methods are going to
enable biologists and doctors to detect and measure
such substances as toxins and antitoxins in even smaller
quantities than can now be detected by injecting these
substances into animals.

Protein forms an essential part of all living things.
It consists of molecules that are very large in compari-
son with those of most other substances. For example,
some proteins have been found that have a molecular
weight of several millions, although some other pro-
teins have weights of only 30,000. The methods of
measuring these weights have involved the use of
centrifugal force about a million times as great as
the force of gravity. Such methods often require
apparatus that costs hundreds of thousands of dollars,
and each investigation is an elaborate research taking
days or weeks of preparation.

[9]

Excursions in Science

By using the colors that we see in soap bubbles, and
with apparatus that costs only a few dollars, and in a
time of less than half an hour, it now becomes possible
to make measurements of the sizes of these molecules
and to get many other characteristics of these sub-
stances that it was not possible to get before. I mention
these points as illustrations of the fact that it is still
possible today to find very simple methods for obtain-
ing scientific results.

[10]

ATOMS AND THEIR
FAMILY RELATIONS

by DR. E. G. ROCHOW

"p\R. ROCHOW, born in Newark, New Jersey, was graduated in
^~^ chemistry from Cornell University, worked as a research
chemist for the Holowax Corporation, and returned to Cornell to
take his Doctor's degree. In 1935 he joined the General Electric
Research Laboratory, where he is at present working in the field
of ceramics and inorganic insulating materials.

IF YOU have read a good detective story recently, you
may have admired the way the brilliant investi-
gator unraveled a knotty mystery with such unruffled
finesse. And we, too, are about to pay our respects to a
man who solved a longstanding mystery in a very
unusual way. Just as truth is stranger than fiction, so
the solution that this man proposed, and the way he
proved his case, are far more remarkable than the pre-
fabricated tales of the story writers. Moreover, this
particular problem that we shall consider is not
remote or unimportant; it concerns us and the world
around us. Specifically, it concerns the atoms of which
we and our homes are made.

[in

Excursions in Science

Just as you find is the case in most detective stories,
someone had to do the groundwork and uncover a
great many facts before even a start could be made on
this problem of atoms and how they are related. Of
course, the earliest men had started tinkering with
stones and metals and fire and water, and they soon
began to take things apart out of curiosity.

Several hundred years ago, when the art of alchemy
was developing into the service of chemistry, chemists
were learning how to take apart wood and water and
stones, just as an inquisitive youngster takes apart an
old alarm clock. Through the years it gradually
became evident that the familiar objects around us, as
well as our own bodies, were made of a rather limited
number of elementary substances, which in turn
could not be taken apart into simpler materials. It
was encouraging to find that everything contained one
or more of these elementary substances, for here at
last were the building blocks of nature, out of which
the world was fashioned.

These elementary substances were called elements
for short, and they were studied alone in order to
find out how they behaved and how they joined with
other elements to make familiar materials. Then, about
150 years ago, men began to learn how much of one
element would join with a fixed weight of another.

[12]

Atoms and Their Family Relations

It had been surprising to find that water, when
taken apart, always contained the two elements
hydrogen and oxygen, and never any others. Now it
was equally surprising to find that in 9 pounds of
water there were 8 pounds of oxygen and 1 pound of
hydrogen never any more or any less. Water was
water. It always contained just the same proportions
of these two elements, or else it wasn't water.

From this point it was easy to reach the third step
in experience. Water could be synthesized, or put
together, by combining eight parts of oxygen with one
part of hydrogen. Moreover, it now became possible
to take apart water and put it back together again, the
whole process being easier than taking apart a clock
and putting it together again.

The next big advance was the idea of atoms. When a
definite amount of one element combines with a
fixed amount of another, this immediately suggests
that a number of chunks of one element are combining
with a number of chunks of the second element, the
numbers being limited and definite because the chunks
combine in only one way. The chunks were politely
called atoms, because the ancient Greeks had argued
about the existence of atoms without being able to
prove that they existed. An atom, then, is simply the
smallest part of an element that can be depended on

[13]

Excursions in Science

to behave like the element, and so of course all atoms
of a given element are chemically alike.

Now, an atom is very small and very light. It takes
some 1700 million billion hydrogen atoms to make 1
ounce hydrogen atoms being the lightest ones we
know. Even the heaviest atoms would run 18 million
billion to the ounce, and you can see that chemists
would be driven to distraction if they had to juggle
such figures in order to make a simple calculation. For
most work, chemists do not care about the weight of
an atom in ounces, and a century ago they did not
even know it. Since the hydrogen atom is the lightest,
and the oxygen atom is found by experiment to be 16
times as heavy, it is possible simply to call the weight
of the hydrogen atom 1, and the weight of the oxygen
atom 16. This number is just a shorthand notation;
all it can tell us about an atom is that the single atom
is thus-and-so times as heavy as the hydrogen atom.
This gives us a scale of relative atomic weights, and
as you have seen, there is nothing mysterious about
them.

We have followed the method used by the chemists
to learn about matter and what it is made of, and we
have seen how they tracked down the common ele-
ments and found the weight of their atoms. These
early fact-finding chemists thought they were getting

[14]

Atoms and Their Family Relations

at the root of things. Actually, they were creating a
mysterious puzzle since no one knew what con-
nection there was among all these elements, what
order there was in all this chaos of facts. It was
all very well to reduce things to atoms, but unless
there was some common relationship the chemist was
really just as badly off as before. Instead of learning
about the properties of every material, he now had to
learn the individual behavior of every isolated element.
Furthermore, new elements were discovered now and
then, and there was as yet no reason to think that
more new discoveries might not keep on coming
indefinitely.

Thus the stage was set for a master mind to step in
and show some sort of connection among all these
facts. The man who did so was not a detective, and
perhaps he was more of a philosopher than a chemist.
But he found a solution that was so startling, so unu-
sual, that even the most credulous people found it
impossible to believe him at first.

This man was an obscure Russian professor named
Dmitri Ivanovitch Mendelyeev. He took the 58 ele-
ments that were known, and he tagged each one with
the atomic weight that he considered the most
reliable. His problem was then to find the link that
connected all of them.

[15]

Excursions in Science

Mendelyeev finally hit upon a radical idea: that the
properties of an element depend upon its atomic weight. If
the atoms were arranged in the order of their weights,
they showed distinct changes in going from one to the
next, but every so often they repeated some general
properties. Their behavior changed in waves or cycles
which repeated regularly, and so the atomic weight of
an element automatically placed it in a certain wave
or cycle where its neighbors were known, and its
relatives occupying the same place on other waves
could be seen very easily. Because of this cyclic be-
havior, Mendelyeev called his scheme the periodic
system.

Now, to say that the behavior of an element depends
upon its weight alone is a very unusual thing. We do
not have a parallel in everyday life. Suppose that all
the suspects involved in a murder mystery were
gathered together in one room at the police station
58 of them. In walks the detective and says, "If you
arrange these people according to their weights, you
will see that they divide naturally into eight families,
and I can tell from this family arrangement just how
each one will act in a given situation. 35 You would
call the detective crazy.

Mendelyeev published his idea, and people did call
him crazy. For two years he struggled to get his

[16]

Atoms and Their Family Relations

scheme published in a well-known scientific journal,
where the best minds could judge it. Eventually it did
appear in German, and immediately some of the best
minds set out to prove him wrong. Because Mendel-
yeev' s scheme was very weak in spots, this did not seem
difficult.

To picture his plan, Mendelyeev had written down
the elements in a horizontal row, starting with the
lightest and proceeding in order. The eighth element
resembled the first, so he began another row under-
neath the top row. The fifteenth element again re-
sembled the first, so he began still another row. This
went on until the result looked very much like your
monthly calendar the elements were in rows of seven,
like the days of the week, and the similar elements fell
into vertical groups like all the Sundays or all the
Mondays.

But unlike your calendar, this so-called periodic
table had empty spaces in it. Mendelyeev had tried to
put the elements in the exact order of their weights, but
occasionally one did not fit, so he blithely skipped a
space or two and placed the element where he thought
it belonged. There were half as many blank spaces as
there were filled spaces, so the thing was not very
convincing.

[171

Excursions in Science

It was easy for the critics to point out that the
then known elements didn't fall into families; they
said that Mendelyeev had simply arranged them that
way and then had claimed that the arrangement was a
natural law. In other words, they accused him of
cheating at his own game of solitaire.

To this Mendelyeev answered that the empty
spaces represented undiscovered elements, and that his
faith in the periodic system was so great that he would
use the system itself to predict the properties of these,
unknown elements. Picking out three important empty
spaces, he thereupon told the world at large where
these elements might be found, how they would act,
what their atomic weights would be in short, he
seemed to know as much about the unknown elements
as about the known ones.

Very wisely, Mendelyeev did not seek these un-
known elements himself. There were plenty of chemists
anxious to prove him right or wrong, and the search
went on in dozens of places. It was not long before
signs of the missing elements began to appear, and
eventually some of the severest critics were the very
ones who proved that the Russian professor was right.
The predicted elements were found where he said
they would be, and they behaved just as he said they

[18]

Atoms and Their Family Relations

would. The periodic system triumphed, and its
author was vindicated.

Let us see how good a job this detective had done.
For the element which later was named germanium,
he predicted an atomic weight of 72; the weight was
found to be 72%. He said that its density would be 5K>
and it was 5^. He predicted a compound with
chlorine that would boil below 100 and have a
density of l%o- This compound was made; it boiled
at 86, and its density was 1% o- He even predicted
that the element would combine with the ethyl group
of ordinary alcohol to give a liquid boiling at 160.
When such a compound was made, it did boil at 160.

There could be no doubt that Mendelyeev was right
and that he had found law and order among the
elements. The faults of the scheme were cleared up in
time, and at present all but a very few of the 92
elements of the periodic table are well known. A host
of confusing chemical questions have been answered
by the table, and today it is one of the best established
and most useful things in the whole field of chemistry.

[19]

WHERE HUMAN ENERGY
COMES FROM

by DR. JAMES W. MAYOR

R. MAYOR, a native of Glasgow, Scotland, attended Trinity
College, Cambridge University, England. He received his
degree of Doctor of Philosophy from Harvard University. He
was Austin Teaching Fellow at Harvard, was Instructor in Zoology
at the University of Wisconsin, and went to Union College as
Assistant Professor in 1916. Since 1924 he has been Professor of
Biology and head of that department. He is the author of General
Biology y published by The Macmillan Company in 1936.

THE human body, or the body of any animal, for
that matter, may be looked upon as a machine
that does a certain amount of work as a result of being
supplied with a certain amount of fuel in the form of
carbohydrates, fats, and proteins. The energy to do the
work comes from the oxidation, or burning, of these
materials in the body.

It is important to distinguish between the external
work done by the body and the internal work that
goes to maintaining the body temperature and to
carrying on the various internal vital functions. The
external work may be useful, as when the individual is

[20]

Where Human Energy Comes From

engaged in pumping water from a well; or it may lead
to no particular accomplishment, as when the individ-
ual uses a rowing machine. In the first case a certain
amount of water is lifted through a certain height;
in the second case the work on the rowing machine
goes in friction and is dissipated as heat. In both cases
the body may be said to do external work. The internal
work, whether it goes to maintaining the body tem-
perature, to pumping the blood round the body, or to
taking the air into the lungs, either goes to building
up the body or becomes dissipated as heat given off.
Energy is usually measured in units called calories.
The kilogram calorie, or larger Calorie, is the energy
required to raise the temperature of 1 liter, or approx-
imately 1 quart, of water 1 centigrade, or 1^
Fahrenheit. The amount of energy which a given
amount of food yields when oxidized can be deter-
mined in an apparatus called a calorimeter, or calorie-
measurer, which absorbs and measures the heat
generated. By making calorimetric determinations of
the food eaten by a man, and similar calorimetric
determinations of the materials excreted, it is possible
to determine exactly how many Calories of chemical
energy the man actually takes into his body. If
the body is a machine so far as the energy transforma-
tions in it are concerned, it ought to be possible, if

[21]

Excursions in Science

there is no increase in the body weight during the
time of the experiment that is, if there is no energy
stored in the body to account for the Calories taken
into it in terms of work done.

Such experiments have been carried out on the
human subject. Large calorimeters have been built
in which men have lived for weeks, with the amount of
energy supplied to them as food carefully measured,
and the amount of energy given off in the form of body
heat and work also measured. One method of measur-
ing the amount of work done is to have the man ride a
stationary bicycle, the back wheel working against
a brake. From the number of revolutions of the wheel
and the force on the brake, the amount of work done
can be calculated. The results of many such experi-
ments carefully performed with more or less elaborate
apparatus have shown that, in respect to the energy
transformations within it, the human body does be-
have like a machine.

The average working man requires about 3000
Calories per day. But we should like to know the
amount of energy needed just to maintain a person's
vital activities in the resting condition, that is, when he
is doing no outside work. This is called the basal
metabolism. The determination is usually made before
breakfast and with the person lying in bed, and the

[22]

Where Human Energy Comes From

calculation is based on the carbon dioxide given
off rather than on the food taken in. Since under the
conditions no external work is done, all of the energy
liberated goes into heat. The average rate at which
this heat is produced in a normal adult is 1500 to 1800
Calories per day. Thus, in a normal man, somewhat
over one-half of the energy value of the food substances
taken into his body goes to maintaining his body
temperature and for such essential vital activities as
breathing and the beat of the heart. The other part
is available for the performance of external work.

Man is notoriously fussy about what he eats, but the
walls of his intestine are even more particular about
what they absorb. Carbohydrates, fats, and proteins
must be broken down or digested before they can pass
through the delicate cell membranes to enter his body.
As a result, the energy comes to him only in certain
special substances. These are a simple sugar (glucose),
a few fatty acids, glycerin, and some 20 amino acids.
Water, a number of mineral salts, and the much-
publicized vitamins are also required; but while these
are necessary, they do not contribute any appreciable
amount of energy.

The idea crops up from time to time, usually in the
comic supplements, that some chemical genius may
discover a mixture of synthetic products which could

[23]

Excursions in Science

be made into a small pill and which would provide
a substitute for a square meal. Thus one might get his
lunch at the back of the drugstore instead of in the
front. It is a myth. The question may be put as fol-
lows: what is the smallest form or least weight in
which 3000 Calories can be made available for absorp-
tion in the human intestine? It cannot be dynamite,
simply because we are not made that way. Practically,
it must be in the form of carbohydrates, fats, and
proteins. Now, one gram of carbohydrate or a gram of
protein yields approximately 4.1 Calories, and one
gram of fat yields approximately 9.3 Calories. A
simple calculation shows that if the food consisted
entirely of fat, the daily ration would weigh 323 grams,
about two-thirds of a pound, and if it contained a
balanced diet it would weigh at least a pound. No
small pill ! Do what we may, we cannot get away from
the fact that we are human.

Man is therefore entirely dependent on plants and
other animals for his food materials. In the ultimate
analysis, green plants are the only manufacturers of
food substances, and they depend on the sun for the
energy to carry on the process. The average amount of
radiant energy received by one square yard of the
earth's surface in our latitude, taken over the year and
allowing for dull days and bright days, is about 3000

[24]

Where Human Energy Comes From

Calories per day. So, if all the energy that comes to one
square yard of the earth's surface in our latitude could
be used to manufacture food substances, the amount
would supply the needs of one man. This would
seem to suggest that the kind of Utopia in which
efficiency is made the ideal may be one in which there
is standing room only.

One may ask: Just how efficient is modern agri-
culture? Looked upon as a machine for manufacturing
food materials, how efficient is the green plant and
how efficiently is the green plant used by man? When a
green leaf is exposed to the sun under conditions
favorable for photosynthesis, approximately 1 per cent
of the radiant energy received by it is transformed into
chemical energy in the form of sugar or starch. Not all
of this sugar or starch indeed, only a small portion
is available for human food. In the first place the plant
must feed itself and provide the materials for its own
tissues, including the cellulose of its cell walls. In the
second place, the food materials must be in a form that
can be utilized by man. We are unable to make a meal
of grass, like a horse, bark like a deer, or wood like a
termite. True, we can feed the grass to cattle and get
milk or beef in return, but we cannot eat all of a steer.

The result is that it requires on the average at least
one acre to produce the food required by one man for

[25]

Excursions in Science

one year. Recorded in terms of the radiant energy
received from the sun and the Calories in the food, the
efficiency is about Koo of 1 per cent. This is, of course,
nothing for an engineer to boast about. But one must
remember that no other commercial method is really
available for the manufacture of food on a large scale,
and that the end product, human protoplasm, is
unique.

[26]

TIME

by DR. LEWI TONKS

R. TONKS was born in New York City and attended Columbia
University. After holding fellowships and serving as Assistant
in Physics, he received his degree of Doctor of Philosophy from that
University. During the World War he served as special government
expert at New London, Connecticut. Since 1923 he has been a
member of the staff of the General Electric Research Laboratory,
where he has carried on theoretical and experimental investigations
in the fields of electronics and magnetism.

ONCE a year, in New York, gay crowds assemble
with all the paraphernalia of merrymaking to
greet the New Year. On the stroke of 12 the flood of
tumult is loosed. How many of those taking part in the
jubilation consider for a moment that in Chicago and
St. Louis the new year is not to begin for another hour,
and that in San Francisco, Seattle, and Los Angeles it
is only 9 P.M. and celebrants are only beginning to
dress for their good time?

What an opportunity Commander Byrd missed in
the Antarctic by not being within a few hundred feet
of the South Pole on December 31, 1929! There the
meridians, radiating from the pole, are not far sepa-

[27]

Excursions in Science

rated from each other, so that, starting on the 180th
meridian, where each day is born, and circling west-
ward, moving 15 degrees of longitude just before each
succeeding hour, he could have celebrated the coming
of the new year 24 separate and distinct times.

For the astronomers the new year begins at the
instant when the earth reaches a certain point in its
orbit relative to the stars. If we celebrated the begin-
ning of the new astronomical year, there would be a
simultaneous outburst all over the earth morning,
noon, afternoon, or in the wee small hours, whatever
the local time of day happened to be. But people are
determined that the new year shall begin for each of us
approximately at midnight at the time that the earth,
whirling on its axis, has placed us farthest from the sun.
Since it requires 24 hours for all parts of the earth to
traverse this position, the instants for the popular
initiation of New Year's Day last this long.

In passing, it is interesting to note that the point
on the earth's orbit which has been selected by the
astronomers to mark the new year is the earth's
position not on January 1 but on March 21 not
New Year's Day but the vernal equinox.

To measure time, some recurring phenomenon is
indispensable. As examples we have the pulse, a
pendulum, the phases of the moon, sunrise, the vibra-

[28]

Time

tion of an organ pipe or a quartz plate. Galileo used
his pulse in discovering that the period of oscillation of
the chandelier in the church at Pisa did not change as
it swung through a wide or a narrow arc. This dis-
covery led to the invention of the pendulum clock.
The American Indian used the moon to mark the
passage of time. We base our time division of hours,
minutes, and seconds on an average apparent daily
motion of the sun around the earth; but our year, as I
have said, is based on the earth's returning to the same
position in its orbit around the sun. When it does
return, it is almost 6 hours later in the day from year
to year, so that every fourth year we would begin the
year a whole day early if we didn't put in February 29
to compensate.

The fact is that the rotation of the earth on its axis
and its revolution about the sun are quite independent
of each other. As the sun loses mass by radiating energy
and the rotation of the earth slows down because of
tidal friction, we may expect in thousands of
centuries that the year will have a different number
of days in it.

Our daily life is ordered by the rotation of the earth
with respect to the sun. The majority of us sleep at
night, work by day, and play a little near the border
line. Thus, from the workaday point of view, the dura-

[29]

Excursions in Science

tion of time from noon till noon would seem to be the
logical unit of time. This would be solar time and could
be measured by a sundial. But in September such a
day would be 22 seconds shorter than the average, and
in December it would be 28 seconds longer. That
would not do even as a practical matter, for clocks
would require continual readjustment. Therefore, the
variations are averaged out over the year to give us
mean solar time, which is the time in everyday use.

But an averaging is only the last resort in standard- .
ization. We might better use for a standard some
modern pendulum clock, running in vacuum and
driven by a so-called slave clock, for it can be far more
constant than the earth-sun combination. The astrono-
mers have, however, in the rotation of the earth with
respect to the stars, a clock which surpasses all others
in reliability. Each such rotation measures a sidereal
day, as it is called, of 24 sidereal hours.

If sidereal time is so much better as a measure, then
why shouldn't we use it for everyday? Because, as I
have said, our daily activities are regulated by the sun
and not the stars, astrologers to the contrary not-
withstanding. The motion of the earth in its orbit
requires that the earth turn about 361 for noon to
recur at a given terrestrial point, for in its travel it
has left the sun slightly behind, so to speak, and has to

[30]

Time

turn a bit more and face a little backward. That
extra degree of rotation takes 4 minutes, so that the
sidereal day is about 4 minutes shorter than the mean
solar day. The woes of Daylight Saving would be as
naught compared to those of the sidereal addict.
Setting his sidereal alarm clock for 6 A.M., he would
be awakened at 6 A.M. mean solar time on March 21.
But day by day, as spring advanced, it would be
darker and darker when he rose. By June 21 he would
be getting up at midnight with breakfast still 7 hours
away. By September 21 he would sleep through lunch
and arise in time for supper. Only when March came
around again would he enjoy a brief interval of normal
life.

Now I want to turn from the measurement of time,
which is what we really have been discussing, to
inquire briefly into the nature of time. It is one of the
fundamental things of our experience, which we
therefore accept on the whole as a matter of course.

We find ourselves in a complicated, changing world
of matter and consciousness which has its existence
in a framework of space and time. We are conscious
of a here and a there, and of a then and a now. What
goes on is describable in its simplest and most ele-
mentary terms as happening somewhere at some time.
Time and space cannot be explained in the sense that

[31]

Excursions in Science

we attempt to find out what they really are, because
they constitute the reference frame without which
nothing else has meaning. I venture to say that we
shall come closer to explaining consciousness than we
ever shall to explaining space and time.

But We can discover the properties of space and
time. We recognize that space has three dimensions,
meaning that to fix the position of an object with
respect to its environment we must specify three
space-things or coordinates. For instance, to locate
an airplane we have to know how far north of us it is,
how far east, and how high. Time has only one
dimension. We have only to know when the airplane
is in the position already described. Any other arrange-
ment is, I think you will agree, inconceivable.

In one important and definite respect time differs
from space. It is a one-way affair. You can go down-
town and come back with the loaf of bread you forgot
to get, but you cannot go back to New Year's Day to
make that resolution you had intended to. Neither
can you have Johnnie go back to early this afternoon
and not eat that green apple which is now distressing
him.

Ridiculous? And yet, when we examine the mathe-
matical equations that describe the motions of parti-
cles and their interactions with each other, we find

[32]

Time

in them no hint that time points one way. The further
pursuit of this inquiry leads, however, to one of the
most difficult concepts of science, called entropy, and
ends at best in a highly speculative connection be-
tween the one-way nature of time and the inevitable
and continuous increase of entropy in the universe.

The time magnitudes that we familiarly encounter
extend from the ^f second, which is the smallest
interval on a stop watch, up to the span of one's life.
The flicker of a motion picture driven at the original
rate of 16 frames a second represents the smallest
time interval directly perceptible as such. Thus, ^6
second to some 2 billion seconds is the range of our
direct experience of time. But indirectly we can, by
means of instruments, extend our experience in one
direction to far shorter intervals, and in the other
direction, by written records, extend our knowledge to
longer periods.

Shorter time intervals of the order of Ho 00 second
can be obtained by direct mechanical means. Motion
pictures showing what happens in intervals of 1/10,000
second have been obtained by using electrical light
flashes of that frequency. The limit to observation of
single time intervals lies at about one ten-millionth
of a second, which is the fastest speed at which an
electron beam can be swept across a fluorescent

[33]

Excursions in Science

screen and still produce light enough to photograph.
But beyond this we still think of time of shorter
intervals, even though these intervals are strung
together in the successive oscillations of a light wave
and cannot be separated from each other or subdivided
for examination. It is not that we have reached a
point beyond which time is not divisible for rays
oscillating one million times faster are known but
that we are in a region where the physical laws of
atoms apply, our ordinary large-scale physical laws
being a sort of average over larger distances and longer
times.

It is no exaggeration to say that in that region time
has lost its fundamental quality in the world of experi-
ence, because we no longer experience it not even
vicariously through instruments. It is true that we
put a t into the mathematical equations, but that
need have no more time significance than the pen
with which it is written.

[34]

THE NATURE OF LIGHTNING

by DR. KARL B. MCEACHRON

R. MCEACHRON, a native of Hoosick Falls, New York, at-
tended Ohio Northern University and, later, Purdue Uni-
versity, where he took a graduate degree in electrical engineering.
After teaching at Ohio Northern and Purdue, he went to the
General Electric Company, in 1922, to supervise research on
lightning arresters. Since 1 933 he has been Research Engineer in
High-voltage Practice in charge of the Company's High-voltage
Engineering Laboratory, at Pittsfield, Massachusetts. His investi-
gations of natural lightning and his work with artificial lightning
have made him an authority on high-voltage electricity.

SINCE the time of Benjamin Franklin, it has been
known that lightning is electricity the same
kind that is produced when you rub a cat's fur on a
dry day, so-called static, or frictional, electricity.
Static electricity is no different from any other kind,
but it is called frictional because it is frequently
obtained by friction between certain nonconductors
of electricity.

Under proper conditions of humidity and tempera-
ture, the frictional action of air currents causes a
separation of electric charges on drops of condensed

[35]

Excursions in Science

moisture. The droplets unite and fall; they are again
broken up and raised to higher regions by rising air
currents. The electrical potentials become higher and
higher, and at last a lightning discharge takes place,
either to another cloud or to the ground.

Why does lightning want to go to the earth?
Because, as the lower portion of the cloud becomes
charged to one potential, a charge of opposite poten-
tial is induced on the earth beneath. When the
potential, or voltage, at the cloud becomes high
enough, a streamer begins to form. It progresses
toward the earth in a series of starts and stops. In
some cases, it takes as long as Moo second to reach
the earth. It is not visible to the eye because, along
the same path and immediately following the contact
of the streamer with the earth, the brilliant lightning
flash, which we see, builds up from the ground. This
flash travels from the ground toward the cloud at a rate
of about 18,000 miles a second.

Interesting things are happening on the ground
while the streamer is approaching. The streamer
carries with it electric charges of the same sign as the
cloud from which it came. Therefore, on the earth,
directly under the end of the streamer, there is an
intensification of charge. This concentration of charge,
at the surface of the earth, may be sufficient to produce

[36]

The Nature of Lightning

streamers rising upward from the earth. I have a
photograph of streamers 4 to 8 feet long extending
upward from a beach which was struck by lightning.

Many lightning strokes are multiple in character.
They are made up of successive discharges which
follow the initial discharge over substantially the
same path. It is possible to photograph these succes-
sive discharges by using either a moving camera or a
moving film. This principle has been used by many
observers; a variety of cameras have been built, and
they have yielded valuable information on the
mechanism of lightning.

High-speed-camera photographs indicate that all
but the first of a series of discharges will have a leader
stroke, which proceeds from the cloud to the earth
without hesitating. As many as 40 of these successive
discharges have been reported in less than a second,
while 8 to 10 are quite common.

Lightning often strikes electric transmission towers
and lines. Formerly, this usually caused interruptions
to electric service. But as the result of studies of light-
ning, means are now available for preventing these
interruptions, and service is seldom seriously dis-
turbed. Since engineers are interested in the values
of current and potential found on transmission lines
as the result of lightning strokes, many measuring

[37]

Excursions in Science

instruments have been connected to transmission
towers and lines to learn more about lightning. As a
result, it is now known that the currents to be expected
from lightning may be as great as 200,000 amperes,
or as little as 5000 amperes. The voltage has been
variously estimated from 100 million to 10 billion
volts.

The question is often asked: Why does lightning not
follow the field of force between the cloud and the
earth? If it did, in general it would take a smooth
curved path. The answer is that lightning follows the
path of least resistance, which it determines for. itself
as it progresses. One might compare the situation
with that which a schoolboy faces when the bell
rings after recess and the yard is filled with children.
He is on his way to the door, but the path of least
resistance may not be a straight line to the door. So
it is with lightning the path is determined by local
ionization conditions just ahead of the progressing
streamer. In fact, in one investigation, we photo-
graphed lightning which came within a few hundred
feet of the earth and then changed its course and more
or less paralleled the surface of the earth for nearly
2 miles.

Sometimes multiple strokes are very close together.
The shortest time of which I have a record is 700

[38]

The Nature of Lightning

millionths of a second. A millionth of a second is hard
to visualize. An object moving at the great speed of
1000 miles an hour would not move as much as He
inch in a millionth of a second. So when we say, "as
quick as a flash," it is really pretty fast. Individual
discharges may rise to crest current in from five to
ten millionths of a second, but the duration of a
series of discharges may be quite long as much as a
second.

The electric energy in a single lightning flash is
really quite small. It would not make many slices
of toast in your toaster. But the power, or the rate of
dissipation of energy, may be enormous because of
the short time during which the flash occurs. For
illustration, in our laboratory in Pittsfield, Massa-
chusetts, we have an impulse or lightning generator
which produces a 10 million- volt flash, 30 feet long,
with a current of approximately 25,000 amperes.
The total energy is 125,000 watt-seconds. Translated
into terms more familiar that of our electric light bill
this energy is equivalent to a little more than three
one-hundredths of a kilowatt-hour which, at a rate
of 5 cents, is less than two-tenths of a cent's worth.

However, when it is considered that the discharge
is completed in about 10 millionths of a second, the
rate of delivering energy (the power) is about 12,500,000

[39]

Excursions in Science

kilowatts. This is about the average kilowatt load of
all the power systems of the United States for the
month of June.

Natural lightning will frequently have a kilowatt
output many times that of our apparatus. It is easy,
then, to understand the damage done by lightning.
The forces involved may be very great, though the
time of application is extremely short.

Much has been said and written about the queer
pranks of lightning. To understand these it is necessary
to consider for a moment the flow of electricity both
through the air as a spark, and through conductors.
It has been known for many years that mechanical
pressure appears around a rapid discharge in air.
This effect is nicely illustrated by passing our labora-
tory discharge through the small hole in a thick-
walled glass or porcelain tube. The pressure evolved
with high current will destroy the tube just as though
an explosive had been set off in it. This pressure effect
produces the thunder that we hear.

On the other hand, if the high-current discharge is
sent through a conductor, the magnetic forces set up
within the conductor may crush it. Thin-walled metal
tubes, and flat strips of copper, have been crushed in
the laboratory in this manner. If the conductor is too
small to carry the current, it may be vaporized. The

[40]

The Nature of Lightning

largest conductor melted by a lightning discharge of
which I have a record is an iron conductor slightly
more than J inch in diameter.

When wood is struck, a certain amount of the wood
is turned into vapor, which adds to the pressure
created by the spark inside the wood. Trees sometimes
explode very violently when struck, scattering debris
over a large area. This is one of the good reasons why
being under a tree during a lightning storm is likely
to be dangerous.

Buildings are frequently struck, but if they are of
steel-frame construction, with metal parts projecting
from the top, no harm is done. When wood or brick
buildings are struck, the damage at times is very
considerable. However, lightning-rod systems, prop-
erly installed, are very efficient in protecting houses
and trees from the effects of lightning.

Electric transmission systems use a modified light-
ning rod in the form of an overhead ground wire,
strung over the conductors and connected to ground
at each tower. The spacing from the live power con-
ductors in midspan must be sufficient so that while
the lightning is traveling along the ground wire to the
near-by towers, flashover will not take place to the
power conductors. A similar scheme is also used for
the protection of oil storage tanks.

[41]

Excursions in Science

You may have noticed sometimes a statement in
the newspaper to the effect that lightning struck a
concrete highway, ripping it up at several points
some distance away from the point struck. This
effect is due, of course, to the lack of continuity of
the metal reinforcing the concrete. Where the elec-
trical connection is poor between successive pieces of
reinforcing, the concrete punctures, and the ensuing
spark blows a hole in the surface of the road.

As you understand lightning better, your fear of it
largely disappears, especially if you can bring yourself
to find a point of vantage and watch the storm. Many
of the discharges are between clouds, and although
these produce the same thunder as discharges to
ground, they are harmless. High storms will, as a
rule, have a greater number of cloud-to-cloud strokes.
If you are timid, remember that if you hear the
thunder, the lightning did not hit you. In fact, if
you see the lightning, it did not hit you. Furthermore,
if you remember that the number of fatal accidents
from lightning in the United States does not average
more than 500 a year, while automobiles yearly kill
more than 30,000, then you will not crawl under the
bed when the thunder begins to roll. Instead, you
will look for a front seat at a wonderful show of nature.

[42]

THE MARKS ON YOUR
THERMOMETER

by DR. FRANK R. ELDER

IpVR. ELDER was born in Rochester, Minnesota, was graduated
*~^ from Amherst College, and received his Doctor of Philosophy
degree from Columbia University. He was for three years Associate
Professor of Chemistry at the University of Richmond, and from
1917 to 1919 was a first lieutenant in the U. S. Army Signal Corps.
Since 1919 he has been a member of the staff of the General Electric
Research Laboratory.

T A TE ALL know that when the temperature drops
* * below 32 Fahrenheit, it is time to put anti-
freeze in our automobile radiators. Most of us know
that when water reaches a temperature of 212
Fahrenheit, it boils. But in scientific books we often
see temperatures expressed in degrees centigrade.
And when we read that some laboratory has suc-
ceeded in reaching a new low limit of temperature,
that temperature is usually expressed in degrees
absolute. In order to straighten out these appar-
ently confusing temperature scales, we have to get
down to fundamentals. Just what do we mean by
temperature?

[43]

Excursions in Science

Our simplest idea of the meaning of temperature
comes through the sense of feeling. We can feel that
one body is cold, or that one body is hotter than
another. If we take several pieces of the same material,
at different temperatures, we can arrange them in
order, so that each one is hotter than all that precede
it, and colder than all that come after it. This scale
of hotness or coldness is really a scale of temperature.
The idea of temperature, like the idea of length, is
one of the fundamental ideas of nature, and by it we
can describe natural phenomena.

But we still have to obtain a standard scale, or
measuring stick of temperature. And the instrument
with which we are most familiar is the thermometer.
A fluid thermometer is a glass tube partly filled with
liquid. The liquid expands when it gets hotter; it
then fills more of the tube that is, the upper edge
of the liquid column climbs up the tube. When the
liquid gets colder, it contracts takes up less room
and the level falls in the tube. We could put a scale
of inches beside the tube and have a temperature
scale, of a kind, for that particular thermometer.
But what is needed, of course, is a scale for all ther-
mometers on which a certain reading will always
mean a certain definite temperature.

[44]

The Marks on Your Thermometer

Our ordinary thermometer, for use around the
house, has a Fahrenheit scale. It was devised by
Daniel Gabriel Fahrenheit, a renowned German
instrument maker who lived between 1686 and 1736.
Ever since his scale began to be generally accepted,
people have wondered why he chose 32 as the freez-
ing point of water, and 212 as the boiling point.
They are fairly inconvenient numbers to use.

Recently, fresh light has been thrown on the
problem by the discovery, in the Military Academy
at Leningrad, of letters sent by Fahrenheit to Boer-
haave between 1718 and 1729. These letters show
that, actually, Fahrenheit did not pick 32 and 212 as
the freezing and boiling points of water. These tem-
peratures were incidental to two other fixed points.
The zero was obtained by immersing a thermometer
in a mixture of snow and sal ammoniac. The upper
calibration point was the temperature of the human
blood, which in those days was supposed to be strictly
constant for a healthy person, and to which Fahren-
heit gave the arbitrary figure of 96. Fahrenheit gave
no reasons for adopting 96 degrees as blood heat. He
may have chosen the figure because it was divisible
by multiples of 2 and 3, and therefore by 12. The
decimal system was not in general scientific use in

[45]

Excursions in Science

his time, while the duodecimal system based on
multiples of 12 was used.

Today we retain the Fahrenheit scale, but it is a
slightly different scale from the one devised by its
inventor. The fixed points for calibration are deliber-
ately chosen as 32 for the freezing point of water, and
212 for the boiling point. And on this basis blood heat,
as we all know, comes out to be 98.6.

A French scientist, Ren6 de R6aumur, showed by
experiment that various mixtures of water and alcohol
have different expansions. For simplicity he chose a
mixture that gave an expansion of 80 parts between
melting ice and boiling water. You may occasionally
come across European thermometers which are
marked in degrees R for R6aumur and which
give the temperature of boiling water as 80.

In 1736 Celsius, who favored a decimal system
that is, a system of measurement based on the number
10 divided his thermometer scale into 100 parts.
This produced the centigrade scale, the one now
used in most scientific work.

We have now discussed most of the common
thermometer scales, and have seen how they were
developed; but there is one more. In the laboratory
and in industry very wide ranges of temperature are
encountered, and suitable means must be found to

[46]

The Marks on Your Thermometer

measure these high and low temperatures. Obviously,
any property of matter that varies in a regular manner
with temperature may be made the basis of a tem-
perature scale.

Early experiments by Boyle showed that if a definite
mass of gas be compressed, doubling the pressure on
it reduces the volume of the gas to half. Four times
the pressure reduces the volume to one-fourth. In
other words, multiplying the pressure and volume
together always gives the same value for the product.
Actually, exact experiments with different gases later
showed that all known gases deviate from this law,
particularly at low temperatures and at high pres-
sures. But the relation was so useful that, for con-
venience, a perfect gas was imagined which obeyed
Boyle's Law completely.

Now, when a mass of gas, held at a constant pres-
sure, is cooled, the volume of the gas decreases.
This can be demonstrated by blowing up a balloon
with air and then pouring liquid air over it. As
the gas inside is cooled, it shrinks in volume and the
balloon becomes smaller. In this experiment the
pressure outside is held approximately the same,
because it is the pressure of the atmosphere.

The expansion and contraction of a perfect, ideal
gas, then, may be made the basis of temperature

[47]

Excursions in Science

measurement. Let's take a known volume of some
real gas, at centigrade, and measure the volume
changes as we change its temperature. Such experi-
ments show us that the volume of the gas increases
J^73 of its centigrade volume for each degree
centigrade rise in temperature. And going the other
way, the volume of the gas decreases ^73 of its
original volume for each degree centigrade drop in
temperature. If this is true, and experiment shows
that it is, we can cool the gas only 273 degrees below
zero centigrade. At that temperature the gas will
exert no pressure; the gas atoms or molecules will be
packed tightly together, with no voids or spaces
between them. We cannot imagine any lower tem-
perature. Therefore 273 degrees below zero centi-
grade is called the absolute zero of temperature.
And the temperature scale based on these experi-
mental results is called the absolute centigrade, or
the Kelvin scale. On this scale, is the absolute zero
of temperature; the freezing point of water is 273
absolute; the boiling point of water is 373 absolute.
Each degree of this scale represents the same tem-
perature change as does each degree on the centigrade
scale the difference between the two scales is merely
that of locating the scale zero.

[48]

The Marks on Your Thermometer

You understand that no real gas actually behaves
as does Lord Kelvin's ideal or perfect gas. All gases
have ceased to be gases at absolute zero. They turn
to liquids and then to solids before they reach the
zero of the Kelvin scale. Hence, gas thermometers
cannot be used to measure such low temperatures,
and other methods must be devised.

There are such other methods. Changes in electrical
resistance are used to measure both very low and
reasonably high temperatures. Optical methods,
depending on the light from incandescent bodies, are
used for very high temperatures. But the instruments
using these principles are all calibrated in terms of
one or the other of the conventional temperature
scales that we have been discussing.

[49]

METEORITES

by EDWARD S. C. SMITH

TJROFESSOR SMITH was born in Biddeford, Maine, and was
*" graduated from Bowdoin College, going to Harvard University
for his graduate study. He joined the faculty of Union College in
1923, where he is Professor of Geology and head of the Depart-
ment of Geology. He has contributed many articles to scientific
journals, has been President of the New York State Geological
Association, and is an authority on the geology of the State of
Maine, where much of his research has been carried on.

IF YOU look up into the heavens on any clear moon-
less night you may see a point of light flash through
the sky and disappear. It is as though one of the stars
had fallen from its position and been blotted out in
the depths of space. Such a phenomenon is commonly
called a "shooting star"; but it is not a star, but a
relatively small chunk of matter that has entered our
atmosphere at a speed of anywhere from 10 to 50
miles a second. This velocity produces enough friction
to raise such bodies to incandescence, so that most of
them are burned up completely at heights of about
75 miles. Some of them, however, survive this passage
through the atmosphere and reach the surface of the

[50]

Meteorites

earth. Those that are consumed before reaching the
earth's surface are called meteors; those that arrive
at the earth's surface are called meteorites.

All meteorites may be placed in three classes
those that are chiefly an iron and nickel alloy, those
that carry metallic and stony material in about equal
proportions, and those that are chiefly stony. The
metallic meteorites often contain cobalt; some contain
platinum. Of the total number of meteorites known,
the stony are in the majority.

No new elements have been discovered in meteor-
ites, but many compounds have been found that do
not occur naturally on the earth. Such a one is lawren-
ceite chemically a chloride of iron. The presence of
this substance in a meteorite is proof that it came from
a place devoid of oxygen, for in contact with oxygen
this chloride turns very readily into an oxide. Hence,
lawrenceite will cause the discoloration or even the
disintegration of a meteorite containing it, when
exposed to our atmosphere.

On the other hand, there are many minerals
present in meteorites that are familiar ones, such as
apatite, the feldspars, olivine, pyroxene, quartz, and
even diamonds. The metallic meteorites often show
a curious crystallization of their constituents that is
quite unknown terrestrially.

[51]

Excursions in Science

We are interested in these objects that fall from the
sky chiefly because they are the only tangible clues
to the kind of matter which makes up the universe
beyond our own little chunk of matter, the earth.

By means of the spectroscope, astronomers can tell
us what elements occur in the outer layers of the stars,
but meteorites 'can be handled, examined, and tested
in various ways; their messages are not transmitted
through millions of millions of miles of space by light
waves, but are, so to speak, delivered in person..
Some of these messengers come from our own solar
system, for revolving around the sun are unnumbered
bits of matter, from the size of dust to bodies weighing
many tons. We are, therefore, constantly being bom-
barded with extraterrestrial matter.

But the high velocity of many meteors is proof that
they do not originate in the solar system. They come
from the depths of interstellar space. It has been
estimated that several million meteors enter our
atmosphere each day a stupendous heavenly bar-
rage, of which we are scarcely aware. Meteors usually
become luminous at altitudes of about 60 to 100 miles
above the earth. Rarely do they become so highly
incandescent as to be visible in the daytime. One of
these daylight meteors passed over New England
several years ago, but it appeared to fall in the ocean.

[52]

Meteorites

The question is often raised: "If the earth is being
struck by so many of these missiles, has anyone ever
been killed or injured by them?" So far as is positively
known, no one has either been killed or injured. A
40-pound meteorite crashed through a house in
Bohemia in 1847, showering the residents with plaster
and other debris but injuring no one. In the Field
Museum at Chicago there is a small meteorite that
plunged through the roof of a barn and embedded
itself in the floor. Such examples of buildings being
struck are exceedingly rare.

The time before sunrise is, in general, the most
favorable for the observation of meteors. Then we
are in the position of being "head on" in our passage
through space, and the earth is catching up with the
slower meteors that may be moving in the same direc-
tion as the earth and in its path, or it is meeting those
moving in the opposite direction.

The favorable time for the arrival of meteorites
seems to be late in the afternoon and early in the
evening. The earth has then turned 180 degrees on
its axis, and any meteors that enter the earth's atmos-
phere are those that are catching up from behind.
Their velocities may be little greater than that of
the earth itself, so they are less liable to be consumed
in their earthward flight. Their speeds have been esti-

[53]

Excursions in Science

mated to be as low as 2 or 3 miles a second. In contrast,
morning meteors may travel as fast as 50 miles a
second.

While it is true that most of the "shooting stars"
are burned up, yet their substance in the form of
oxide is added to the atmosphere and gradually
settles to the surface of the earth. In this way thousands
of tons of matter in the form of meteoric dust are
added to our planet daily. Yet this amount, great as
it may seem, is really almost negligible when the
tremendous surface of the earth is considered.

Probably the largest known meteorite lies embedded
in the ground in southwest Africa. This is the recently
discovered Hoba iron, whose weight is approximately
60 tons. There are, however, in three widely separated
regions, evidences of catastrophic impacts of much
larger meteorites. The best known is probably the
famous Meteor Crater near Winslow, Arizona. Here,
on the flat desert lands, is a depression 3 miles in
circumference and nearly 600 feet deep, around which
have been recovered about 16 tons of metallic meteor-
ites. The crater is formed in a great thickness of sedi-
mentary rocks, principally sandstones and limestones,
some of which have been rendered highly porous
presumably as the result of a terrifio explosion.

[54]

Meteorites

At Henbury, central Australia, is a group of much
smaller meteor craters, the largest of which is about
220 yards across and about 60 feet deep. Many
meteorite fragments have been recovered from that
locality.

A third group of craters, as yet inadequately
described, lies in north-central Siberia. Doubtless
these also were caused by the fall of a swarm of
meteorites rather than by a single large one. It is
not pleasant to contemplate the damage and loss of
life that would be incident to such a swarm of meteor-
ites striking a large city. But the odds against such an
occurrence are very great indeed.

While meteors are likely to be seen almost any time,
there are periodic recurrences of so-called meteor
"showers," during which the number of meteors seen
in a given unit of time is much greater than usual.
In fact, it is probable that the awakening of the
modern interest in meteors and meteorites began with
the great meteor shower that occurred early in the
morning of November 12, 1833, when, according to
all accounts of it, the "sky presented a remarkable
exhibition of fireballs, commonly called shooting
stars."

The phenomenon was further described as "striking
and splendid," and the "flashes of light were so bright

[55]

Excursions in Science

as to awaken people in their beds." These meteors
seemed to radiate from a point in the direction of the
constellation Leo, and have been called the Leonids.
This shower was widely observed and recalled a
similar one on November 11, 1799. This led to the
belief that the swarms of meteors moved in a definite
orbit such that they would reappear every 33 years.
They did come again in 1867 according to schedule,
and should have appeared in 1899 or 1900, and again
in 1933 or 1934, but on both of the later occasions the
meteoric displays were highly disappointing. It seems
more than likely that the attraction of the great
planet Jupiter has disturbed the normal paths of
these swarms of meteorites, so that for some years at
least the earth will not pass through the main body
of them.

The study of meteors and meteorites is a fascinating
one, but quite aside from their mere spectacular
phases we may hope to gain from them valuable
information concerning not only the solar system but
the universe itself.

ANIMAL LIGHT

by DR. LEWIS R. KOLLER

R- KOLLER, born in New York City, studied at Cornell Univer-
sity, where he received his Doctor of Philosophy degree.
From 1917 to 1919 he was a Civilian Radio Engineer of the U. S.
Army Signal Corps. Later he taught physics at Cornell, joining the
General Electric Company, as physicist, in 1922. Since 1925 he has
been a member of the Research Laboratory staff. His Physics of
Electron Tubes was published by the McGraw-Hill Book Company
in 1934.

-< <+*-*> > >

ON SUMMER evenings the glow of the firefly is a
common sight. Few persons can observe it with-
out wanting to know more about it. Sunlight and
firelight, incandescent and arc light are taken for
granted. But there is something different about the
glow of the firefly. Perhaps it is because it lacks the
accompaniments that we usually associate with light.
There is no heat, no noise, no wiring, no switch.
Yet if we study the light of the firefly, we find that,
essentially, it is very much the same as other kinds of
light. It can be reflected, refracted, polarized, and it
has all the other attributes of ordinary light. Its chief

[57]

Excursions in Science

distinguishing characteristic is that very little heat is
produced with it. This kind of light production with-
out heat, sometimes known as "cold light," is called
luminescence.

The firefly and by the way, it is not a fly but a
beetle is by no means the only living source of light,
although perhaps it is the most familiar one. There
are altogether about 40 different orders (as the
zoologist calls them) of living things that produce
light. They include members of both the animal and
vegetable kingdoms, but strangely enough, they are
all either terrestrial or marine forms of life. No fresh-
water forms are luminous.

The only light-producing plants are two groups
that many of us perhaps do not think of as plants
the fungi and the bacteria. The part of a fungus that
we ordinarily see is the "fruit body, 55 but the fungi
possess also a network of threads called the mycelium.
It is, for the most part, the mycelium rather than the
fruit bodies that shows luminosity. The mycelium is
usually underground or concealed in decaying wood
or under the bark of a rotting tree stump. For this
reason luminosity is often observed when the bark
is removed from a decaying log or when the log itself
is shattered. This is sometimes called "fox fire. 55

[58]

Animal Light

Many kinds of bacteria give off light, particularly
those that are found on decaying meat or decaying
fish along the seashore.

The light-producing power is more widely dis-
tributed among animals than among plants. The
so-called phosphorescence of sea water is caused by
several forms of protozoa. These tiny single-celled
organisms are often present in numbers sufficient to
color the sea pink by day.

Many forms of jellyfish show luminosity. So do the
echinoderms, which include the brittle sea stars; the
cephalopods, which include the squids and many
marine worms; the crustaceans, the insects, and at the
top of the scale, the fishes. Several kinds of sharks are
luminous. All of these are inhabitants of salt water.
But luminosity is by no means confined to creatures
living in the depths of the sea, for many of them live
in shallow water or at the surface or near the shore.

Many insects are luminous and so, often, are their
larval forms and even their eggs. The best known of
these is the firefly or lightning bug, and its larval
form, the glowworm. Reports have been received of
luminosity in higher animals, but these have always
been found to be due to fungi or bacteria which have
been taken as food or which have in some way estab-
lished themselves in or on the body.

[59]

Excursions in Science

The production of light by living organisms is not
really a vital process. The plant or animal simply
manufactures a chemical that is capable of producing
light. This substance can be extracted and made to
produce light apart from the body of the living crea-
ture that manufactured it. So far, however, it has not
been possible to make these chemicals synthetically;
the secret belongs only to the animal.

The light-producing substance is called luciferin.
Luciferin produces light only when it combines with
oxygen and forms a new compound, called oxiluci-
ferin. Hence, without air or oxygen, no luminescence
can take place. The luciferin cannot combine with
oxygen, however, unless there is present another
chemical, called luciferase, which also is manufactured
by the animal. This substance acts as an enzyme or
catalyst which encourages the oxidation reaction.
Both of these substances can be extracted from the
luminous organs and be made to produce light when
mixed in a test tube. Thd" combination of oxygen and
luciferin produces a disturbance of the electrons of the
molecules that results in light. The color of the light
produced depends upon the lucif erase, while its
brightness depends upon the speed with which the
reaction takes place. A remarkable feature of the
chemistry of light-producing animals is that the luci-

[60]

Animal Light

ferin, after being oxidized, is reduced again by the
animal and thus is used repeatedly.

In some animals the light-producing materials, that
is, the luciferin and luciferase, are secreted in a slime
on the body or are ejected into the surrounding water.
Thus they give rise to luminosity outside the animal.
More often, however, as in the case of the firefly,
the light is produced in highly specialized light
organs or lamps within the body. These have some
remarkable engineering features. The light organs
are usually symmetrically placed on either side and
underneath the animal and throw the light down. In
general, they consist of a transparent layer of skin
under which is a layer of cells containing the light-
producing matter. Behind these is a layer of reflector
cells, which project the light outward. In some fishes
there is even a layer of cells serving as lenses. Since
oxygen is necessary for the production of the light,
the cells have a highly developed system of tubes for
supplying it.

Some forms, such as the bacteria and fungi, glow
continuously. Others emit light only when stimulated
from outside, as for instance when a boat sends a wave
through sea water. Some of the fishes have a screen,
similar to an eyelid, by means of which the light can
be shut off, while still other forms can control the

[61]

Excursions in Science

light-producing mechanism itself. Just how this is
accomplished is not yet understood.

The spectrum of animal light is neither a line nor a
continuous spectrum. It consists of a broad band of
blue-green or yellow-green light with practically no
measurable ultraviolet or infrared radiation. The
term "cold light" which has been applied to it has
given rise to the belief that the animal's way of pro-
ducing light is unusually efficient. This is not really
the case. The production of animal light is a by.-
product of the chemical reaction that takes place
when luciferin is oxidized. Some work done by
Professor E. N. Harvey, of Princeton University,
makes it possible to estimate the efficiency of this
reaction. His results show that luminous bacteria are
just about as efficient in converting energy into light
as are ordinary incandescent lamps. It is true that the
radiation produced by these organisms is all in the
region of the spectrum to which the human eye is
most sensitive, but only a small part of the energy
of the chemical reaction goes into light production.
It would take about 1500 fireflies to produce a one-
candlepower light.

The light production for a given weight of luciferin
is relatively small about Ms as much as we could get
by burning the same weight of a paraffin candle, or

[62]

Animal Light

as much as we would get from the same weight
of acetylene.

Just what purpose luminosity serves in nature is not
definitely known. In a few instances it is associated
with mating; in some cases it may aid the animal in
procuring food or it may be a means of protection.
But for the most part, its purpose is obscure.

[63]

EARS, HUMAN AND ELECTRIC

by ALBERT J. MUGHOW

R. MUCHOW is a native of Hartford, South Dakota. After
graduating in Electrical Engineering from the University
of South Dakota, he joined the General Electric Company and
was from 1929 to 1937 a member of the staff of the General Engi-
neering Laboratory, studying problems of sound measurement.
Since 1 937 he has been with the Warren Telechron Company. "

T A THAT we mean by "sound 55 depends upon the
* definition we choose. We may define sound as
the sensation perceived when the auditory nerves are
stimulated. Or, like most scientists, we may use the
word to designate the external physical disturbances
that are capable of affecting the ear, even though
there is no ear to hear. Thus the old dispute about the
bell ringing in the desert boils down to a matter of
definition of terms.

Man's first experiments with sound are hidden far
back in human history. Some of the most primitive
races have left records to show that they used musical
instruments. The art of producing pleasant sounds
called music developed to a high degree without

[64]

Ears, Human and Electric

much aid from the physical sciences. Aristotle, several
centuries before the Christian Era, used vibrating
strings to investigate the simple mathematical relations
that exist between harmonious sounds.

Galileo, during the sixteenth century, rediscovered
Aristotle's theories and reached the conclusion that
sound is associated with minute vibrations in air. In
1705 an English physicist demonstrated the correct-
ness of Galileo's concept by showing that sound could
not be transmitted through a vacuum where air does
not exist to serve as a medium of transmission. At
about the same time, a French mathematician demon-
strated the relationship between the pitch and the
rapidity of vibration of a sounding body. After this,
the discovery of the fundamental principles of sound
came thick and fast.

Even superficial observation will discover that
sound is closely connected with the vibration of a
sounding body. A bell is struck. You hear the sound,
and at the same time, by touching the bell, you can
feel the vibration. As the bell vibrates, it imparts a
similar vibratory motion to the air particles close to
the bell. The motion of these air particles is rapidly
passed on to those a little farther off. By a continua-
tion and extension of this process, the vibrating motion
of the bell sets all the surrounding air into vibration.

[65]

Excursions in Science

If we were able to see the particles of air in action
while excited by sound, we would notice that while
each particle makes only a very short excursion to
and fro, yet the disturbance moves outward from
the source at a speed of about 1100 feet a second.
(This corresponds to about 750 miles an hour.) The
distance any individual air particle travels to and fro
depends upon the intensity of the sound. In a moder-
ately loud sound, this distance may be only one and
one-half millionth* of an inch !

With even the loudest common sounds, the acoustic
power generated by the source is usually very small.
It has been estimated that if the entire population
of the United States were to talk in a normal con-
versational tone, the total power converted into sound
would be only about equal to that required to operate
a 100-watt incandescent lamp. Electrically, we can
get the equivalent power in our homes at a cost of
less than a cent an hour!

The quality of a sound depends upon the number,
the relative intensity, and the pitches of the various
tones present. Most sounds contain a variety of tones.
You may have noticed how the echo of a shout
directed at a cluster of trees sometimes returns to you
with a characteristic pitch higher than that of the
shout. The phenomenon may be explained by

[66]

Ears, Human and Electric

selective reflection of the sound, and is known as a
harmonic echo. The lower pitched components of
the shout may pass through the grove without being
appreciably reflected; the higher pitched components
are quite readily reflected and return to the listener
to produce an altered quality.

Many interesting phenomena associated with sound
such as reverberation in rooms, the roll of thunder,
the passage of sound through speaking tubes, echoes,
whispering galleries, harmonic echoes are the result
of the reflection of sound waves. Even the mythical
"ocean's roar" that one hears in a sea shell or a glass
tumbler can be explained by sound reflection. The
transmission of sound for long distances through
speaking tubes, railroad rails, and metal rods is made
possible by internal reflections at the boundaries, so
that the sound is confined.

This spreading of sound by internal reflections
through connecting metallic parts of a machine or
through the steel and concrete portions of a building
leads often to difficulties in locating a disturbance.
What sounds like a rattle in an automobile steering
wheel may be a loose connection near the front wheel.
And a hum or rumble audible on the top floor of an
apartment building may originate in machinery in
the cellar.

[67]

Excursions in Science

Having considered a few of the properties of sound,
let us turn our attention to the method by which we
hear. When sound waves in air strike the ear, they are
conducted into the external auditory canal and strike
upon the tympanic membrane, or eardrum, which
seals the inner end of the canal. The eardrum is set
in vibration by the impinging sound waves. These
vibrations are in turn transmitted with decreased
amplitude but increased pressure by a group of three
small bones the so-called hammer, anvil, and stirrup
which act like a chain of levers to vibrate the fluid
contained in the canal of the inner ear. This canal, or
labyrinth, is coiled into a small spiral of 2% turns
and contains a central membrane, in which the
auditory nerves terminate.

The vibrations excited in the fluid of the inner ear
stimulate nerves in various regions of the membrane.
The length of the central, or basilar membrane is
about 1J6 inches, and its greatest cross-sectional area
is less than five ten- thousandths of a square inch.
These dimensions are startling when we consider that
sounds ranging a thousandfold in frequency and
1000 billionfold in intensity are heard and differenti-
ated by this small but important part of the ear.

The human ear is capable of hearing only those
sounds that fall within certain pitch and intensity

[68]

Ears, Human and Electric

limits. Tests have shown that the lowest pitch that
the average ear can hear is about 16 vibrations a
second, and the highest 16,000 a second. This range
corresponds to that from the deepest note on a pipe
organ to a note about six octaves above middle C.
We are probably very fortunate to have our hearing
limited in this way. Microphones coupled to suitable
amplifiers indicate that many sounds exist in nature
that we can never hear directly because of their high
pitch. It is said that during the World War police
dogs were often secretly called by means of high-
pitched whistles that humans could not hear. It has
been demonstrated that many insects produce intense
sounds at high frequencies beyond our hearing range.
If our ears were as sensitive to sounds up to 25,000
vibrations a second as they are to tones an octave
above middle C, we should undoubtedly consider the
sound produced by a dog walking through grass very
intense. A cricket's chirp would sound quite different,
because we should be able to hear overtones or har-
monics that our ears now fail to catch.

In order for sound to be audible, it must possess
enough power to stimulate the auditory nerves. The
amount of power required depends somewhat upon
the pitch of the sound. The ear is most sensitive to

[69]

Excursions in Science

sounds having a frequency between one and four
octaves above middle C.

The very properties of the ear which enable it to
hear feeble sounds and yet avoid damage when listen-
ing to very loud sounds render it unreliable as a
measuring device. Its memory regarding the intensity
is very poor, and it is quite unable to determine the
pitch of the various tones present in sound. Moreover,
individuals differ greatly among themselves in their
judgment of loudness and in their reactions to various*
types of sound. TThese shortcomings of the human ear
have created a demand among investigators for
instruments that would measure sound and give
results commensurate with, or related to, the sensa-
tions of loudness perceived by the ear.

Within recent years the development of sensitive
microphones and vacuum-tube amplifiers has made
possible devices that are particularly adapted to
serve as "electric ears" for noise-measurement pur-
poses. The essential parts of an "electric ear," or a
sound meter, are a microphone to convert the sound
vibration into electric voltage variations, an ear-
weighting network to provide a response similar to
that of the human ear, and an amplifier fitted with
an indicating instrument to measure the intensity of
the sound.

[70]

Ears, Human and Electric

Such sound-measuring instruments are generally
portable and provide a means whereby a large number
of measurements may be taken in a short time with
the assurance that the readings may be accurately
repeated whenever desired. The results are given in
units called decibels, which are a measure of sound in
much the same way that degrees Fahrenheit are a
measure of temperature.

The feeblest sound that we can hear has a value of
about zero decibels; the loudest about 120 decibels.
The noise in a quiet country residence* averages about
30 decibels, in a quiet street 50 decibels, in an auto-
mobile at 40 miles an hour 70 decibels, and in a sub-
way car about 90 decibels. The scale chosen is such
that each increase of 10 decibels corresponds to a
1000 per cent increase in the intensity of the sound.
A sound of 120 decibels has an intensity one million
million times as great as a sound of zero decibels.
Expressing this tremendous range in another way,
we can say that the intensity of the feeblest sound we
can hear is to the loudest as one second of time is to
a million years !

These new instruments and standards for measuring
noise are being employed to determine what levels of
noise the public regards as acceptable, or comfortable,
for all sorts of living conditions in homes, offices,

[71]

Excursions in Science

workshops, and streets. They enable equipment
manufacturers and others concerned with promoting
quiet living conditions to specify by one system the
noise levels produced by apparatus. They have been
of great value in making possible a scientific approach
to the many problems encountered in locating and
controlling unpleasant noises that emanate from
various types of machinery. While this so-called
"electric ear" in no way enhances our hearing or
appreciation of a symphony or a bird song, it is help--
ing us to obtain a more complete understanding of the
nature of noise, and to achieve the desirable goal of
comfortable quietness.

[72]

VACUUM

by EDWARD F. HENNELLY

R. HENNELLY, a native of Johnstown, New York, is a graduate
of Union College. During the World War he was engaged in
submarine-detection work. Since 1912 he has been a member of the
staff of the General Electric Research Laboratory, where his
investigations of chemical and physical problems have often in-
volved the use of special high-vacuum techniques.

AN ABSOLUTE vacuum is or would be a portion
of space entirely free from matter. Man, how-
ever, has been unable, with the most refined chemical
and physical means of exhaust, to remove every trace
of matter from any portion of space, even the smallest.
For example, when a glass bulb, 5 inches in diameter,
has been made as empty as possible, it still contains
several million million gas molecules, although the
pressure within it has been reduced to less than one
thousand-millionth of an atmosphere.

The word "atmosphere 55 suggests the envelope of
gas which surrounds the earth, and if we review some
of the facts that are known about the earth's atmos-
phere, we shall be in a position to compare what

[73]

Excursions in Science

man has been able to accomplish in producing a
vacuum with the vacuum which may be found in
nature.

The earth's atmosphere is, in the main, a mixture
of two gases, nitrogen and oxygen. At the earth's
surface a cubic centimeter of space which is the
volume of an ordinary marble contains about a
million million million gas molecules. As we go to
higher levels of the atmosphere, we find the molecular
crowding less as the distance from the earth increases.
At a height variously estimated at 100 to 500 miles,
the atmosphere would be practically nonexistent;
that is, the condition would be found which corre-
sponds to our original definition of a vacuum empty
space.

These 500 miles, taking the maximum estimate,
are, of course, insignificant compared with the dis-
tances used to measure the spaces between the stars,
or even those in our own solar system. To avoid the
use of the tremendously large numbers that measure
these great spaces, let us consider a smaller physical
scale.

Imagine you have before you a small table-size
globe representing the earth one about 8 inches in
diameter. This would make a convenient reference
scale, since 1 inch would be about 1000 miles. The

[74]

Vacuum

earth's atmosphere, using our estimate of 500 miles,
could now be imagined as a gaseous envelope J-^ inch
thick surrounding the surface of the 8-inch globe.
The moon, on this scale, would be a sphere about
like a tennis ball at a distance of 20 feet. Except for
the thin layer of gas surrounding the earth, all the
space between the two spheres would be empty.

If we wished to add the sun to this scale, it would
be a sphere between 70 and 75 feet in diameter and
about a mile and a half away, and again, except for
the sun's atmosphere, all the space between earth
and sun would be empty. Finally, beyond our solar
system, the regions between the stars add to the
immensity of this empty space, leading to the esti-
mate that, if all the matter in the universe were evenly
distributed throughout space, there probably would
not be a molecule of gas in 10 cubic centimeters.

It might be thought, then, that a nearly perfect
vacuum could be obtained by enclosing some portion
of this empty space within a glass bulb. If such a
fanciful operation were possible, we should be defeated
in our attempt. All samples of matter that we can
obtain on earth have, since the beginning of time,
been saturated with volatile gases, and these gases
would continue to evolve indefinitely. So in our
experiment, the very walls of glass intended to exclude

[75]

Excursions in Science

stray molecules of gas would themselves be sources
of other gas, spoiling our sample of interstellar
vacuum.

Now to come back to earth. The history of science
records that more than 2500 years ago the Greek
philosophers discussed the nature of a perfect vacuum,
but they, like their followers and successors for
hundreds of years, were satisfied with discussions and
very little concerned with tests and experiments.

The name of Torricelli is associated with the early
experimental period of physical science. He filled a
glass tube, closed at one end, with mercury, and then
arranged that the open end was beneath the surface
of more mercury in a dish. He showed that when the
glass tube was longer than 30 inches, the mercury
column in the tube always sank until its top surface
was 30 inches above the surface of the mercury in the
dish. The space in the upper end of the tube above
the 30-inch level was called the Torricellian vacuum,
and for a long time it was considered to be the most
perfect vacuum possible. We know now, however,
that in such a space there still remained mercury
vapor, some traces of air, and probably, as was pointed
out previously, some gases given off by the glass tube.

Before turning to modern vacuum methods, let us
consider one more early experimenter, Otto von

[76]

Vacuum

Guerickc, who lived in Magdeburg in the middle
seventeenth century. He took two copper hemispheres,
about 22 inches in diameter, and fitted them together
as tightly as possible with a gasket soaked in wax
and oil to make an airtight joint. The air in the result-
ing sphere was pumped out through a small opening,
which was then closed with a tap. He then demon-
strated that two teams, each of eight horses, when
pulling in opposite directions, were unable to pull the
hemispheres apart. Von Guericke knew the explana-
tion of this phenomenon that, as a result of the
vacuum inside them, the hemispheres were held
together by the external pressure of the atmosphere.
Although the great physicist of Magdeburg carried
out this experiment close to three centuries ago, his
memory is honored with pageants in his native town
even to this day, and the experiment is repeated at
each one.

The last 50 years have seen great developments in
vacuum technique. Better pumps have been made.
More delicate and accurate methods of measuring
the degree of vacuum have been discovered, which,
if less spectacular, are certainly less cumbersome than
the 16-horse method of 200 years ago. These methods
have taught us many important things about common
materials.

[77]

Excursions in Science

For example, we now know that glass, as well as
other solid materials, is covered with a thin coating
of condensed air or of other gases like water vapor,
which adheres to the surface like a film of varnish.
This film of molecules is so stable at ordinary tem-
peratures that it will not come away rapidly, even in
the best vacuum. Yet if the film is not removed during
exhaust, it will later leave the surface gradually and
spoil the vacuum conditions. So, good modern vacuum
technique demands that a glass bulb, for an incandes-
cent lamp or X-ray tube or radio tube, be heated to
as high a temperature as possible while being pumped,
in order to remove this film.

We have learned, too, that both metal and glass
have dissolved in them large amounts of gas which
can be removed only by heating in vacuum.

Even after prolonged pumping and heating, how-
ever, there may still remain in an evacuated space
small amounts of what are called residual gases.
Purified charcoal, cooled by liquid air, is sometimes
used as a sponge to soak up these residual gas mole-
cules and remove them from the space.

Then there are chemical methods for reducing the
residual gas pressure in a vacuum tube. These are
represented by the practice of evaporating small
amounts of special metals, such as calcium and mag-

[78]

Vacuum

nesium. These metals condense on the glass wall to
give the familiar silver appearance of radio-tube bulbs.
Such metals are particularly active in combining with
oxygen and with gases containing oxygen, such as
water vapor, to form permanent solid compounds.

It is in no sense an admission of failure to note that
after these special operations, together with others
of a like nature, have been carefully carried out to
produce the highest degree of vacuum, there still
remain in the best exhausted device as many mole-
cules in a cubic centimeter as there are people on the
earth. Instead, it would be more nearly correct to
point out that vacuum equipment and technique have
developed fast enough to keep well ahead of the
requirements of those sciences for which they are, in
fact, the tools.

[79]

THE RED PLANET MARS

by DR. FREDERICK W. GROVER

TPVR. GROVER, born in Lynn, Massachusetts, received the degree
^^ of S.B. from the Massachusetts Institute of Technology and
of M.S. from Wesleyan University. He earned the degree of Doctor
of Philosophy at George Washington University and at Ludwig-
Maximilian University, Munich, Germany. He has taught physics
and astronomy at Wesleyan, has been a volunteer observer of the
Harvard Observatory, has been a member of the staff of the U. S.
Bureau of Standards, and has taught at Lafayette College and
Colby College. Since 1920 he has been a member of the faculty of
Union College, where he is Professor of Electrical Engineering. A
recognized authority on electrical measurements and inductance,
he is the author of some 30 monographs on these subjects. His book
on astronomy, The Pageant of the Heavens, was published by Long-
mans, Green & Company in 1937.

*- <>

To THE possessor of a small telescope. Mars,
although it is the nearest of all the planets except
Venus, is a disappointing object. Little more than a
tiny orange-red disk can be made out. With a large
telescope, permanent darker spots can be seen, and
their shapes were long ago mapped. A few hours
watching makes it evident that these dark areas drift

[80]

The Red Planet Mars

across the disk, and it is possible to determine that
Mars makes one complete revolution on its axis in
24 hours, 37 minutes, and 22 seconds. Therefore, the
Martian day is only about half an hour longer than
our own. Furthermore, the axis of Mars is inclined
to the plane of its orbit by an angle of 23^ degrees,
which is the same as the inclination of the earth.
This proves that Mars, too, has seasons, although each
season is twice as long as ours, because the Martian
year is about twice the earth's year.

Anyone who has watched the planets knows that
Mars is conspicuously bright for only a few months
every other year. This is because the distance between
Mars and the earth varies widely. Mars revolves
about the sun in an orbit which is, on the average,
about half again as far from the sun as is the earth's
orbit. It takes almost two of our years for the circuit.
Thus, at intervals of two years and two months, the
planet approaches as close as about half the distance
between the earth and the sun. At times halfway
between the dates of closest approach, the distance
of the planet reaches a maximum value of about two
and one-half times the distance of the earth from the
sun. Such wide variations in distance necessarily
bring about wide changes in apparent brightness.
When Mars is nearest, it approaches Jupiter in bright-

[81]

Excursions in Science

ness; at its farthest, it is no brighter than the stars
in the Big Dipper.

Although Mars has a day about the length of ours
and has seasons, there the similarity to conditions on
the earth ends. If we could view our earth from Mars,
it would appear like a bright star, probably brighter
than Jupiter appears to us. Looking at the earth
through a telescope, we would probably see the conti-
nental outlines, so familiar from our study of geog-
raphy, but blurred by haze, and extensive areas
would always be overlaid by clouds. By contrast, our
telescopic views of Mars are usually strikingly free
from obscuration or blurring. Sometimes, it is true,
small areas of Mars are dimmed by a thin haze, and
at times dusky moving spots are seen, which may be
dust storms on the planet. These facts suggest that
Mars has, at best, a very thin atmosphere and cast
doubt on the existence of any considerable water
supply.

Mars is a small planet, with only half the diameter
of the earth and with only one-tenth its mass. A man
weighing 150 pounds on the earth would weigh only
57 pounds on Mars, but any chance of making a
record high jump as a result of this favoring circum-
stance would be offset by the difficulty of breathing
in the Martian atmosphere. Our moon, whose diame-

[82]

The Red Planet Mars

ter is only one-half that of Mars, has lost all her
atmosphere and water vapor because of the weakness
of her gravitational pull. With Mars the same tend-
ency has been operative, but affairs are not so bad as
on the moon. Mars has an atmosphere, although it is
probably more tenuous than the atmosphere found
at the summits of our highest terrestrial mountains.
The spectroscope shows that there is, also, water on
Mars. Furthermore, we can see what appear to be
polar ice caps on Mars, which melt as the summer
advances and form again in the Martian winter. The
water available on the planet must, nevertheless, be
limited in amount.

Careful measurements of the tiny amounts of heat
radiated from different parts of the surface of Mars
have been made by Lampland and Coblentz in
Arizona and by Pettit and Nicholson at Mount
Wilson. These observers find that, in the regions near
the center of Mars, the summer day temperatures
can reach values as high as 50 or 60 Fahrenheit.
The worst feature is that, during the nights, the heat
accumulated during the day is radiated away so
rapidly that before sunrise the temperature may
drop lower than 100 below zero.

Thus the two commodities, air and water, which
we take for granted, are scarce on Mars, and the

[83]

Excursions in Science

Martians, supposing that any exist, must have diffi-
culty in keeping from freezing during the night.
And that brings us to the intriguing question whether
any evidence exists to indicate that Mars is inhabited.

In 1877, Schiaparelli published observations and
drawings of narrow, remarkably straight markings
running for hundreds of miles over the planet. As
the Martian summer advanced, these were seen to
grow more pronounced. Schiaparelli explained these
markings as due to vegetation bordering irrigation
channels. The straightness of the markings suggests
that they are artificial, and if this is so, the further
inference that they have been constructed by beings
possessed of extraordinary engineering ability.

These observations have been confirmed by certain
other astronomers, notably those at the Lowell
Observatory, in Arizona. However, other observers
studying Mars have seen only ill-defined markings.
It has been objected also that such markings are so
narrow and so near the limits of visibility, it is not
possible to be certain that they are continuous.

The whole subject is very puzzling, and it is diffi-
cult to see how certainty can ever be reached. Further,
all suggested schemes for signaling Mars with elaborate
and extensive arrangements of lights, or by radio
waves, assume the possibility that we could make our-

[84]

The Red Planet Mars

selves understood. To carry on an interchange of
ideas with a race of beings so organized physically
as to endure lack of air and water, and the extremes
of a perfectly terrible climate a race, moreover,
whose civilization may easily be either vastly more
advanced than our own or entirely rudimentary
would seem to be a hopeless undertaking.

However, nothing prevents each one of us from
constructing our own mental pictures of conditions
on Mars, the while we congratulate ourselves that our
lot has been cast on the earth. Distracted though it
may be with floods, dust storms, wars, and various
forms of human cruelty and strife, our earth offers
much better living conditions than does the red planet,
Mars.

[85]

CHEMICAL REACTIONS IN THE
HUMAN BODY

by DR. MURRAY M. SPRUNG

R. SPRUNG was born in Wahpeton, North Dakota, and studied
at the University of Minnesota, where he received his Doctor
of Philosophy degree in chemistry. He has held a National Research
Fellowship at Harvard, has taught at the University of Minnesota,
and has been a Research Associate at Princeton. In 1933 he joined
the General Electric Research Laboratory, where much of his
work has been in the field of organic chemistry.

THE human body, endowed as it may be with a
mysterious and wonderful vital force, still obeys
the same physical and chemical laws as does ordinary
inanimate matter. The changes that occur in the body,
most of which are chemical in nature, are thus funda-
mentally the same as reactions that are conducted
(with the aid of human intelligence) in beakers,
flasks, or similar chemical apparatus. In fact, many
reactions of physiological significance can be dupli-
cated in the laboratory merely by bringing together
the proper substances under conditions which approxi-
mate the normal environment of the body.

[86]

Chemical Reactions in the Human Body

The body itself participates in many of the trans-
formations which occur within its walls. Other
chemical changes that occur, however, primarily
concern substances added to the body for the purpose
of sustaining life. Such substances are, of course,
called foods. To understand the chemistry of many
of the vital processes, it is necessary to have some
knowledge of the chemical nature of foods.

The basic foods are usually classified as proteins,
carbohydrates, and fats. However, these basic foods
alone will not support life for any length of time.
One's diet must contain, in addition, water, essential
mineral elements, and certain other substances,
which are present in ordinary foodstuffs in relatively
minute amounts, known as vitamins.

The human body, in common with most forms of
living matter, is largely composed of but four chemical
elements oxygen, carbon, hydrogen, and nitrogen.
It is not surprising, therefore, that ordinary foods also
consist largely of these four elements. Individual
foods, however, differ appreciably in their composition
and chemical character.

The proteins, which are present in foods such as
eggs, meat, fish, and certain legumes, have been found
to contain carbon, hydrogen, nitrogen, and, in some
cases, sulphur. They consist of enormously large

[87]

Excursions in Science

molecules anywhere from 1000 to 100,000 times as
large as simple organic molecules like those of grain
alcohol, ether, or chloroform. By experiments carried
out in the ordinary manner, in glass or other inert
vessels, it is possible to break down protein molecules
into consecutively smaller and smaller products.
The end products of these transformations are simple
nitrogen-containing substances called amino acids,
which may be considered the fundamental building
blocks of protein molecules. About 20 of these build-
ing blocks are known. In the gigantic protein mole-
cules large numbers of individual amino acids are
strung together in some complex but regular pattern.
The exact nature of this pattern is the basis of numer-
ous researches now being carried on throughout the
world.

The carbohydrates include the principal energy-
producing nutrients, such as those contained in cereals,
potatoes, and other starchy vegetables. Sugars are
also included in this class. Carbohydrates are made up
of three elements only carbon, hydrogen, and
oxygen. Like the proteins, the complex carbohydrates
consist of very large molecules at least 1000 to 10,000
times as large as the molecules of simple organic
substances. They also may be broken down into unit
building blocks, and when this is done, a single carbo-

[88]

Chemical Reactions in the Human Body

hydrate molecule gives just one simple unit a sugar.
Thus, many starches, as well as cellulose, may be con-
verted completely to the simple sugar, glucose. Other
carbohydrates give simple sugars that are similar to,
but not identical with, glucose.

The third basic food group is very different from the
other two. The fats, of which butter and lard are
typical examples, consist of relatively small mole-
cules only about 10 times as large as those of
substances like alcohol and acetic acid. Like the carbo-
hydrates, the fats contain only carbon, hydrogen, and
oxygen. When broken down, outside the body, each
molecule of fat gives one molecule of glycerine and three
molecules of a fat acid. The complete chemical pattern
of the fats is, therefore, quite easily identified, and is
much simpler than that of either the carbohydrates
or the proteins.

Mineral elements are found in many different kinds
of foodstuffs. It is now recognized that at least 11
mineral elements are vital to normal physical health.
These are calcium, phosphorus, potassium, sulphur,
sodium, chlorine, magnesium, iron, manganese, cop-
per, and iodine. With the exception of calcium and
phosphorus, which are major constituents of the bones
and the teeth, these elements are present in the body
in very small concentrations as little as one part in

[89]

Excursions in Science

2000 in the case of magnesium, and one part in
2,000,000 in the case of iodine.

The vitamins also are found in a great variety of
different foodstuffs. It is impossible to discuss here the
best sources of the common vitamins or their chemical
natures, for they are a complex and heterogeneous
lot. At least seven vitamins are recognized as definite
chemical individuals, and several other substances
that are suspected of exercising vitamin functions are
now being investigated.

Let us now consider some of the chemical changes
that constitute the digestive processes.

Chewing causes food to come in contact with saliva,
which contains a substance known as ptyalin. Ptyalin
is a representative of an important group of substances
known as enzymes, which function in the body as
catalysts that is, they facilitate many of the chemical
reactions that occur. Specifically, in the presence of
ptyalin, starches are broken down into less complex
substances. The proteins and fats, however, are rela-
tively unaffected by this enzyme.

In the stomach, the food enters a region that is
acid because of the presence of hydrochloric acid.
Here it is brought into intimate contact with the
digestive juices, which contain a second enzyme,
pepsin. In an acid environment, pepsin is able to

[90]

Chemical Reactions in the Human Body

break down proteins into less complex bodies, just
as ptyalin is able to split carbohydrates. This action
requires a few hours, after which the partially digested
food passes on into the small intestine.

Here a mildly alkaline condition normally prevails.
As the food is received from the stomach, it encounters
more enzymes in the intestinal juices. The pancreas
and bile are also stimulated and begin to pump into
the intestine secretions bearing still other digestive
enzymes. All these secretions act together upon the
partially digested food. As a result, the splitting of
carbohydrates into simple sugars is completed. The
sugars thus formed are identical with those formed
from starches outside the body by the action of
appropriate chemicals. Proteins are also broken down
further in the intestine to simple amino acids again,
the same ones that are obtained from protein matter
in controlled laboratory experiments. And finally, the
fats are split into their simple components fat acids
and glycerin. All of these substances are readily
absorbed through the intestine walls.

At the same time that the basic food materials are
converted to useful products, the mineral elements and
vitamins also undergo chemical alterations. The
mineral elements are broken away from the organic
nutrients to which they are usually attached, and are

r 01 i

Excursions in Science

converted into substances that are readily assimilated.
The fate of the vitamins is still somewhat uncertain. It
is probable that some vitamins reach the circulatory
system and the vital organs essentially unchanged,
while others undergo deep-seated chemical transforma-
tions en route.

Let us assume then that all the foodstuffs, both basic
and auxiliary, have been modified in the ways peculiar
to the digestive processes, and that the absorbable
products have passed through the walls of the ali-
mentary canal. As far as our story is concerned, diges-
tion is now complete. But the processes of assimilation
have yet to occur. From the simple sugars, amino
acids, fat acids, glycerin, and water must be con-
structed tissues, bone, blood, muscles, and cell walls.

Let us therefore go one step further into some
phases of the phenomenon of metabolism, the term
used to designate the complex interconversions of
dead food and living plasma. Let us begin with the
glucose that has been formed within the alimentary
canal and absorbed into the blood stream and dis-
tributed throughout various parts of the system.
New organic catalysts now begin to act upon it. From
some of it the body reconstructs carbohydrate not
starch, which can't be utilized at this stage, but a
similar material called glycogen which is then

[92]

Chemical Reactions in the Human Body

stored in the liver and in certain muscles. From these
organs the glycogen can be withdrawn when it is
needed, and converted once again into glucose, and
finally burned to produce energy.

A similar fate awaits the fat acids and glycerin.
After passing through the intestinal walls, they are
recombined into fats that are essentially similar to
those originally present in the food. The regenerated
fats are taken up by the lymph vessels and sent into the
blood. When they finally reach the tissue walls, they
are burned, as in the case of the sugars, or stored in the
tissues as body fat to be burned when more urgently
needed.

The amino acids also pass into the blood stream and
are carried thence to all parts of the body. At the vari-
ous tissue walls, reactions occur which result in the
rebuilding of protein matter. However, all of the amino
acids formed in the system are not utilized in tissue
building; some of them are oxidized or otherwise
further disintegrated into simple waste materials,
which can be eliminated.

Finally, the human body utilizes the mineral ele-
ments in an amazingly efficient manner, for each ele-
ment is sent to that particular region where it is most
needed. Calcium and phosphorus go to the teeth and
bones; iron becomes part of the red blood corpuscles

[93]

Excursions in Science

or of the chromatin substances which preside over
vital cell activities; sodium, potassium, and chlorine
enter the body fluids, where they perform essential
and specific biochemical functions; the very minute
amount of iodine essential to normal health finds
its way, for the most part, into the thyroid gland.
Without this very small amount of iodine, the processes
of metabolism, over which the thyroid gland exercises
a delicate and subtle control, would be radically
upset.

It will not be possible to consider innumerable other
astonishing reactions that occur in the human body,
many of which are just as essential to life as those few
already discussed. Among them are the modes of
building vitamins from certain related nutrients
present in foods; the roles played by the vitamins
themselves in metabolism and bodily health; the
formation in the body of various hormones, those
physiologically essential factors among which are
thyroxine, adrenaline, insulin, and various reproduc-
tive factors; the complex interrelations of enzymes,
proteins, and hormones; the interconversions of differ-
ent food types within the system; the fascinating reac-
tions that lead to the formation of hemoglobin, the
substance that makes blood red, and its equally
fascinating role in the processes of oxidation.

[94]

Chemical Reactions in the Human Body

Thousands of scientists throughout the world
chemists, physicists, biologists, physicians are actively
engaged in studies that are extending the frontiers of
knowledge of these vital phenomena, yet an almost
infinite amount still remains to be done. Out of such
work will some day come an answer to the eternal quest
for a better physical life.

[95]

POWER FROM THE SUN

by DR. CLARENCE W. HEWLETT

R. HEWLETT is a native of Louisburg, North Carolina. He was
graduated from North Carolina A. and M. College, and
received his degree of Doctor of Philosophy from the Johns Hop-
kins University. He has been a physicist on the staff of the
Carnegie Institution of Washington, and has taught at North
Carolina A. and M. College, Johns Hopkins University, North
Carolina College for Women, and the State University of Iowa.
Since 1922 he has been a member of the staff of the General
Electric Research Laboratory.

POWER from the sun is nothing new. Practically all
the power that the world now uses comes directly
or indirectly from the sun's radiation.

Take coal, for instance. The energy contained in
coal was stored up by the conversion of solar energy
into the energy of chemical combination in the plant
life of the far-off carboniferous age. Water power, too,
gains its energy from the sun. We harness the fall of
rivers on their way from continental watersheds to the
ocean. But it is energy from the sun that evaporates
the water from the ocean and deposits it at the higher
levels of the watersheds.

[96]

Power from the Sun

There is another possible source of world power
one that has received much attention during the last 20
years. I refer to the ocean tides. But unlike the others
mentioned, power from the tides does not come from
the heat of the sun. It comes instead from the energy
of rotation of the earth about its axis, and from the
rotation of the earth and moon about each other and
about the sun. Projects to harness the tides have been
contemplated only in certain localities where the tidal
water rises and falls through heights of from 20 to 50
feet. Most of these projects have never progressed
much beyond the planning stage, because, in the
majority of cases, the cost of the necessary power
plant would be much greater than the cost of a steam
power plant to produce the same amount of electric
energy.

Ever since the invention of the steam engine,
dreamers have speculated on the possibility of gener-
ating power by using the sun's heat to vaporize water.
Time and again, experimental plants of this kind have
been built. Appreciable amounts of power have been
drawn from them. But all these attempts have run up
against the same insuperable difficulty. The cost of
the equipment for each unit of power produced cannot
compete with water power or with steam plants fired
with coal.

[97]

Excursions in Science

There are other serious obstacles to solar steam
engines, or in fact to any projects for the direct utiliza-
tion of the solar radiation. Sunlight is intermittent.
The regular alternation of day and night and the
unpredictable occurrence of storms and cloudy days
would interrupt the solar power plant. In order to
meet this situation, various forms of power storage
have been suggested to bridge over periods of darkness
and clouds.

Despite the discouraging obstacles to the direct use
of solar radiation, inventors and engineers are still
attacking the problem from many angles. They are
spurred by the thought that at some time in the future
the world's coal supply will become exhausted. Hope
springs eternal in the breast of the true scientist-
inventor; he has faith that at any time his experiments
and observations may reveal to him some new process
which will free him from the usual restrictions.

The idea of directly utilizing the sun's radiant
energy becomes more fascinating and attractive if we
realize the immense amounts of energy that are avail-
able. Suppose we take for our unit of comparison the
amount of heat that we obtain by burning a ton of coal.
Then let us calculate the amount of heat that the sun
radiates during one year. If we should attempt to
produce that heat by burning coal, we should require

[98]

Power from the Sun

4 X 10 28 tons of coal. To express this immense amount
in another way, write down the figure 4. Then write
23 zeros after it. That gives the number of tons.

But this is the total that the sun produces; the earth
intercepts only a small part of it. Again assuming that
we tried to reproduce, by burning coal, the heat that
the sun sends to the earth during one year. This time
we get 2 X 10 14 tons or 2 with 14 zeros after it.

How does this compare with the amount of coal we
now burn? The population of the earth consumes for
all purposes light, heat, and power only about half
a billion tons of coal a year. Therefore the energy that
comes from the sun is 400,000 times the energy we are
producing with coal. So, you see, there is a tremendous
amount of solar energy available. If the sun's radiant
energy could be fully utilized, the amount falling on a
single square yard would produce one horsepower.
But the methods available at the present time entail
unavoidable losses, and the best we can do now is to
produce one horsepower from 4 to 10 square yards.

Dr. C. G. Abbot, of the Smithsonian Institution, has
built a solar engine that has an efficiency of about 15
per cent. This compares favorably with the best
modern coal-fired steam power plants, which have
efficiencies ranging from 30 to 50 per cent. But despite
encouraging efficiency, there is still the cost of the solar

[99]

Excursions in Science

power plant, which would be several times greater
than for a coal-fired steam plant. So it seems that we
have a long way to go before steam plants operated
by the sun's heat will be commercially utilized.

From time to time it has been proposed that we use
the thermoelectric effect to harness the sun's energy.
When two wires of different metals are joined together
at their ends, thus making a closed circuit, and one
junction is heated while the other remains cold, an
electric current is set up in the circuit. This current
flows for as long as the two junctions are maintained
at different temperatures. Many experimental gen-
erators have been built on elaborations of this principle.
But the best efficiencies have been 1 or 2 per cent, and
the cost of equipment per unit of power is so great that
at present it is entirely out of the question to commer-
cialize this method of power generation.

During recent years a new type of photoelectric cell
has been developed. It is called a "blocking-layer"
cell, and it has led to some speculation as to its possi-
bilities for converting sunlight directly into electrical
energy. One form of blocking-layer cell consists of a
thin layer of the element selenium mounted on in
iron plate. On the free surface of the selenium there is
laid down a semi-transparent layer of an electrical
conductor, such as platinum or gold. When light falls

[100]

Power from the Sun

on the layer of selenium, electrons are liberated, and
these electrons are conducted away by the semi-
transparent layer of metal. If the iron plate is con-
nected to one terminal of a current-measuring
instrument, and the platinum or gold layer is con-
nected to the other terminal, an electric current of
from 15 to 20 milliamperes per square inch of cell
surface is produced when the cell is exposed to sun-
light. The power output is about one Kooo watt per
square inch of cell surface. In fact, it has been found
possible to construct a small and delicate electric
motor that runs very nicely when connected to a cell
so illuminated. But an output of 1 milliwatt per
square inch means only \% watts per square yard of
sunshine, whereas the actual power in that much
sunshine is roughly 746 watts. The efficiency is a little
less than one-fifth of 1 per cent. And here again the cost
of equipment is so tremendous that power generation
on a commercial scale is entirely out of the question.
To generate one horsepower with these blocking-layer
photocells, 570 square yards of photoelectric surface
would be required.

One of the reasons for the low efficiency is that only
a very small part of the radiation from the sun is
effective in generating electric energy. Roughly
speaking, only the visible light from the sunlight is

[101]

Excursions in Science

transformed into electric energy, while the longer
wave lengths the heat radiation serve only to raise
the temperature of the photoelectric cell. But even if
we consider only the sun's visible radiation, still the
efficiency is but 2 per cent.

While the efficient generation of power from sun-
light with these new photoelectric cells may not be
impossible, yet considerable improvements must be
made before it is practical. We must first find ways of
increasing the efficiency of transformation of solar
radiation into electric energy, and we must also find
ways of utilizing the heat radiation which now serves
no useful purpose in the photoelectric transformation.

And what is said about the method of photoelectric
cells applies almost equally well to the other methods
for utilizing the sun's radiation. The power is there
power greater than we can ever hope to utilize. It
remains for science to find ways of economically
transforming that power into forms that we can use.
And it explains why, in laboratories all over the world,
engineers and physicists are at least thinking about
new ways of putting to work the tremendous flood of
energy that comes from the sun. This energy is free;
it makes possible life on our planet; but we are power-
less to control or alter the rate of its arrival.

[102]

ODORS AND THEIR DETECTION

by DR. NEWELL T. GORDON

R. GORDON, born in Boonton, New Jersey, attended Princeton
University, and there received his Doctor of Philosophy de-
gree in the field of chemistry. After one year with the Bureau of
Explosives, Department of Labor of the State of New Jersey, he
joined the Chemical Warfare Service of the A.E.F. Joining the
General Electric Company in 1919, he went to the General Electric
Research Laboratory, in Schenectady, in 1926.

T A THENEVER a search for some lost article seems all
* but hopeless, we say, "It's like looking for a nee-
dle in a haystack." Yet, that is just about the problem
that your nose solves with astonishingly little effort; in
fact, your nose not only finds the needle but also
distinguishes it from a pin in that same haystack. For
the normal human nose can detect and identify one
part of odor in more than a billion parts of air
equivalent to finding a needle of medium size in a
haystack 25 feet square and 25 feet high.

Of course, the threshold values, or lowest concentra-
tions we are able to detect by the sense of smell, vary
widely for the different odors, and sometimes strong
odors have relatively high threshold values. For exam-

[103]

Excursions in Science

pie, camphor, ether, and oil of peppermint all have
high threshold values, while vanillin and musk have
the lowest threshold values recorded. Vanillin and
musk may be detected in concentrations 1000 times
less than that for oil of peppermint. A dog, whose
ability to follow a scent is so well known, can, undoubt-
edly, detect odors in much lower concentrations than
have been measured experimentally, and the fact that
this ability is influenced by the direction of the wind is
one indication of the nature of odors.

It is generally accepted that odors are molecules of
volatile substances that pass into the air in the same
manner as water evaporates. If odors, like light, were
due to radiation, they should spread equally in all
directions and should not be affected by wind or con-
vection currents in the air. However, we all know that
drafts are of prime importance in the spreading of
odors, and therefore odors cannot be due to radiation.

An interesting experiment carried out in the Re-
search Laboratory some time ago demonstrated that
odors are caused by molecules and not by solid par-
ticles. In the first part of this experiment, air containing
tobacco smoke was passed through an electrical
precipitator; in the second part, through a filter of
activated charcoal; and in the third part, through an

[104]

Odors and Their Detection

apparatus containing both the electrical precipitator
and the charcoal filter.

Perhaps I should explain that the electrical pre-
cipitator is a device, originally invented by Gottrell,
which in the simplest form consists of a metal tube with
a wire stretched along the axis. When a high voltage is
applied between the wire and the wall of the tube, any
solid particles contained in the gas or vapor passing
through the tube are eliminated by precipitation on the
walls. Activated charcoal, used in the second ap-
paratus, is a specially selected charcoal so treated
with steam at high temperature as to make it especially
efficient or active, as the name implies, in the absorp-
tion of gases. In other words, this treatment makes
charcoal a good sponge for gases.

Continuing now with the first part of our experi-
ment, the solid particles of tobacco smoke were
eliminated by the electrical precipitator, but the odor
passed through practically undiminished. In the
second part of the experiment, the smoke-laden air was
passed through a filter packed with activated charcoal.
This time the odor was greatly diminished, but the
smoke came through in clouds. Activated charcoal
absorbs organic odors, but solid particles of smoke
bounce along from one particle of charcoal to another,

[105]

Excursions in Science

rendering the filter ineffective for the elimination of
smoke.

Finally, both the particles of tobacco smoke and the
odor were eliminated when the smoke-laden air was
passed through the electrical precipitator and the
charcoal filter in series.

Since the evidence is conclusive that odors are
molecules of readily vaporized substances, we may
next ask by what process our sense of smell functions.
The olfactory mucous membrane, or organ for detect-
ing odors, is located in the upper part of the nasal
cavity and has a yellowish color which contrasts with
the rest of the chamber. Its area is approximately 1
square inch on each side of the nose. From this mem-
brane nerve fibers gather together, forming the olfac-
tory nerve, which leads directly to the brain. Each
nerve fiber comes from a sense cell that forms a part of
the olfactory organ, and all such cells reach through
this organ to the exposed surface. Here each cell
terminates in six to eight relatively long filaments, or
hairs, which float in the thin layer of mucous that
covers the olfactory surface. Molecules of an odor
strike this surface, dissolve in the fluid, and undergo
chemical reaction. For this reason the sense of smell
and the sense of taste, as well, are known as chemical
senses.

[106]

Odors and Their Detection

In ordinary respiration the passage of air through
the nose excites the sense of smell to only a limited
extent. This is accounted for by the fact that the air
follows a curved path and does not reach a point as
high as the olfactory area except by diffusion. If we
sniff, however, a turbulence is caused in the air flow,
and greatly increased numbers of molecules are
brought into direct contact with the sensitive area,
producing a wide variety of sensations depending
upon the chemical reactions involved.

The quality of an odor is usually named by associa-
tion with the object from which it emanates as the
odor of moth balls, of rubber, of paint, kerosene, shoe
polish, roses, violets. Attempts have been made to
classify odors, and Henning, one of the world's great
authorities on this subject has arranged them in six
groups:

1. Spicy odors, such as cloves and sassafras oil.

2. Flowery odors, such as heliotrope and geranium.

3. Fruity odors, such as orange and banana.

4. Resinous odors, such as turpentine and Canada
balsam.

5. Burnt odors, such as tar and pyridine.

6. Foul odors, such as carbon bisulphide and hydro-
gen sulphide.

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Excursions in Science

But many odors cannot be accommodated even by
this classification, and it becomes necessary to describe
some odors as belonging to two groups. A classification
on the basis of chemical structure also encounters
many difficulties and inconsistencies, so that no single
system is satisfactory for all purposes.

By comparison with this situation for odors, the
classification of tastes is simple and quite definite.
There are really only four well-defined kinds of taste
sour, salty, sweet, and bitter each one associated with
a particular area of the tongue. The wide variety of
so-called tastes is really due to our sense of smell, and
we all know how a cold in the head detracts from our
enjoyment of even the most savory foods. Some people
even claim that apples and onions taste almost alike if
eaten while the nose is held tightly closed.

Recent years have made us all familiar with the
photoelectric tube, which acts as an electric eye, and
with the microphone, which acts like an electric ear.
Is there, or can there be devised, an "electric nose"?

It is evident that any electrical device to detect and
measure odors must be not only exceedingly sensitive
but also very selective. Gases and vapors have one
property which can, perhaps, be made to serve this
purpose. They are able to absorb radiation of char-
acteristic bands or wave lengths particularly in the

[108]

Odors and Their Detection

infrared region beyond the red or long-wave-length
limit of the visible spectrum. This property of gases to
absorb heat rays was demonstrated as long ago as
1865 by the famous physicist John Tyndall, who suc-
ceeded Faraday at the Royal Institution. He found
that the amount of heat rays absorbed by different
gases and perfumes varied widely. If we were to draw
an analogy with his experiment, we might represent
his source of heat as the sun, the perfumes as clouds of
different densities, and his measuring instrument as a
thermometer. The thermometer reaches the highest
temperature in the direct rays of the sun, decreases
slightly when a light cloud obscures the sun, and falls
markedly when a dark cloud passes over. Tyndall
used a radiant heater as his sun or source of heat
waves, a tube containing perfume-laden air as the
clouds, and a sensitive electrical device, a thermo-
electric pile, as his thermometer.

He found that if he used the amount of heat ab-
sorbed by air as a standard, calling it unity, the per-
fume of sandalwood absorbed 32 units, oil of cloves 34
units, and aniseed 372 units. Here is an example of an
electric nose that can be made quite sensitive. It can
find the needle in the haystack, but it cannot distin-
guish it from the pin. It cannot distinguish between
sandalwood and cloves, or between a high concentra-

[109]

Excursions in Science

tion of sandalwood and a low concentration of aniseed.
If, however, an odor has the property of absorbing rays
of a particular or characteristic wave length, the
method might be used as a means of identification.

A somewhat similar method has been developed for
the detection of mercury vapor, and it has been in
successful operation for several years. In this device a
characteristic wave length in the invisible ultraviolet
region is absorbed by mercury, and the amount of
absorption is a measure of the concentration of mer-
cury present. A photoelectric tube is used in place of
the thermopile; and by simply reading the variations
in current through the photoelectric tube, it is possible
to measure the amount of mercury in the air. Five
atoms of mercury in a billion molecules of oxygen and
nitrogen of the air can thus be detected.

Of course, mercury has no odor, but it is well to have
a good electrical nose for mercury because, in high
concentrations, mercury vapor causes certain toxic
symptoms. A concentration of one part in 10 million
by volume is considered safe, and since this device is
able to sound an alarm when the concentration of
mercury is only one-twentieth of this amount, it
affords ample protection for situations in which the
nose fails to warn us. This means, using the analogy of
the haystack again, that the mercury detector could

[110]

Odors and Their Detection

find a needle and also distinguish it from a pin in a
haystack 10 feet square and 10 feet high a stack not
quite so large as the 25 foot example illustrating the
sensitivity of the nose, but still large enough to empha-
size the extreme sensitivity of the mercury detector.

The complexity of the factors involved in the sense of
smell has thus far retarded the development of an
electrical device for detecting odors, but the success of
the mercury detector encourages further work. Also,
recent improvements in instruments for the detection
of infrared rays illustrate the advances that may
eventually lead to the successful development of the
electric nose.

[nil

LILLIPUTIAN CHEMISTRY

by DR. HERMAN A. LEEBHAFSKY

R. LIEBHAFSKY was born in Zwittau, Austria-Hungary. After
studying at the A. and M. College of Texas and the Univer-
sity of Nebraska, he received his degree of Doctor of Philosophy
from the University of California, where he was an instructor
in chemistry for five years. Since 1934 he has been a physical
chemist in the General Electric Research Laboratory.

THE range of the quantities used in chemistry is very
wide. The foreman of a mine smelter deals with
tons of material; the laboratory chemist usually works
with a millionth of a ton, or a gram; the microchemist
works with a millionth of a gram, or a gamma. This
term, the Greek equivalent for the letter , has been
coined to describe this minute unit of mass, which
characterizes the scale of operations of microchemistry .
When I was much younger, I remember how im-
pressed I was with the delicacy of an ordinary chemical
balance. "This balance is so delicate," I was told,
"that it will weigh your signature." A piece of paper
was weighed; I wrote my full name (which fortu-
nately is fairly long) upon it, and the paper was

[112]

Lilliputian Chemistry

weighed again. Sure enough, the difference was
detected by the balance.

Recently I performed a similar experiment on the
microbalance in our laboratory but this time I
used, instead of my full name, only a period made
with a sharp-pointed pencil. Yet that period weighed
10 gammas, or enough to be very noticeable on the
balance. Each time you dot an i, your pencil becomes
several gammas lighter. Each time a raindrop falls,
from 50,000 to 100,000 gammas strike. One cent will
buy nearly 10,000 gammas of gold.

From another point of view, however, the gamma is
immense. A gamma of gasoline, for example, contains
enough molecules so that they might, if they could be
laid end to end, reach well across the Atlantic Ocean.
This point is important, for atoms or molecules in
such large crowds arc good, law-abiding citizens; they
behave, on the average, in a reproducible manner.
Catch them alone, however, and their behavior is not
always predictable. Because the gamma contains so
many molecules, the microchemist knows that the
laws that are valid for grams or pounds of matter
hold also in the realms of microchemistry. He is sure
that the relationships governing the reactions of a
speck of material almost invisible to the naked eye are
the same relationships that govern its reactions in bulk.

[113]

Excursions in Science

But why work with such small amounts? Well, some-
times larger amounts are not available, as when it is
necessary to examine the debris that surrounds a
pinhole leak in some sealed vessel. Or the substance
may be so precious that the amount consumed in
analysis must be kept at the minimum. Cases like this
are numerous; the less important involve substances
like gold, which everyone knows is precious, while
the more important involve substances like vitamins
and hormones, whose initial preparation or isolation
often requires almost unbelievable amounts of time
and labor.

Again, it may be necessary to establish the composi-
tion of an heirloom or antique smashing this in a
mortar to obtain a large sample is scarcely advisable,
and it is entirely unnecessary if microchemical methods
are employed. Valuable paintings by old masters have
been identified by removing and analyzing amounts
of pigment so small as to escape any but the most
minute scrutiny.

There are still other reasons for working with small
quantities. Many substances, like explosives and poi-
sons, which are dangerous or obnoxious to handle in
gram amounts, can be studied conveniently in amounts
much smaller. Time, too, can often be saved by micro-
chemical methods with no loss of accuracy a few

[114]

Lilliputian Chemistry

drops of solution can be evaporated much more
rapidly than a cupful, and a precipitate the size of a
pinhead dries more rapidly than one a hundred times
as large. And finally, since small platinum crucibles
and similar expensive pieces of equipment cost less
than large ones, the same amount of money will buy
more microchemical apparatus.

Naturally, the microchemist cannot carry out his
work according to traditional laboratory methods.
For the conventional beakers and test tubes must be
substituted vessels in the form of tiny capillary tubes.
Solutions cannot be poured out of these any more
than water can be poured out of a sponge, and for
much the same reason. So the microchemist transfers
his solutions by small loops at the end of a wire, or by
employing tubes small enough to fill themselves when
they are inserted beneath the surface of a liquid.
The behavior of liquids in small glass vessels is governed
by surface-tension forces the same forces that help
water to enter the roots of a plant.

Heating is often carried out on the steam bath,
because heating with any sort of a flame is liable to
blow the sample right out of the tube. When flames
must be used, they are so small that a lighted match is a
roaring inferno by comparison. Separation of solid
from liquid is usually accomplished, not by filtering,

[115]

Excursions in Science

but by centrifuging or "spinning down," using the
principle by which clothes are dried in the "spinner"
type of washing machine.

In many of his tests, a chemist observes how a pre-
cipitate forms in a test tube; the microchemist obtains
the same information by observing his much smaller
sample under a microscope. The microscopic evidence
is the more convincing because it magnifies each
crystal so that its characteristic form can be observed.
For the observer with a microscope, each substance
writes its own signature.

Microchemical analysis often develops into a kind of
detective work. Where the ordinary chemist has evi-
dence, the microchemist has only clues. Smudges,
smears, almost microscopic spots of corrosion these,
many times, are important bits of evidence in tracking
down and eliminating troubles in the design of
machinery.

Everyone is familiar with the vacuum tubes that
operate our radios. In many of these tubes there are
reactions occurring during operation which even yet
are not well understood. Sometimes the glass walls
become discolored but so slightly as to remain
transparent. By microchemical methods it is possible
to show that the discoloration is due to mixtures of
several metals that evaporate from the filament.
And it is possible, even with films so thin as scarcely to

[116]

Lilliputian Chemistry

be visible, to determine quite accurately the amounts
of each metal. Evidence of this kind helps us to under-
stand the reactions occurring on the filament, and
guides us in the building of better tubes.

The presence or absence of alcohol in blood and
living tissues is an important question, quite apart
from its bearing on the consumption of alcoholic
beverages. By a series of microchemical procedures,
almost unrivaled for elegant conception and execution,
three New York City chemists were able to prove that
ethyl alcohol in minute amounts is present in the
brain, liver, and blood of abstinent human beings and
of certain animals. The amount of alcohol in pigs'
brains is such that about 100 pounds of brains are
required to yield one drop of alcohol. Yet the presence
of this small amount of alcohol is an important clue in
establishing what chemical reactions keep animal life
going.

Microchemistry is a comparatively new field. Much
of the early work was done by men working in the so-
called life sciences biology and medicine. But today
few sciences have available such a variety of methods
as does microchemistry, and the success of chemistry on
a Lilliputian scale will, in time, undoubtedly modify
all laboratory procedures that can be done more
economically or more conveniently with amounts of
material smaller than those now customary.

[117]

HOW EARTHQUAKES GIVE US
THE INSIDE FACTS

by EDWARD S. C. SMITH

nriHE SURFACE of the earth is well known, but how
-* much do we know of the structure and the mate-
rials of the earth itself? The deeper mines, such as the
gold mines of South Africa, are about 8000 feet in
vertical depth, and in California oil is being obtained
from drillings reaching to 10,000 feet. Therefore, in
round numbers, 2 miles is about the present limit to
which man has penetrated into our planet. The earth's
radius is approximately 4000 miles; therefore, actual
experience goes but five-hundredths of 1 per cent of the
distance from surface to center. The observed increase
of pressure and temperature with depth is such that
little hope is held out that man will ever be able
physically to penetrate to levels thousands of feet
beyond those now attained.

There are many questions we would like to have
answered concerning the earth's real interior. If the
ordinary rocks at the earth's surface are of a density of
about two and a half to three times that of water, why
is it that the earth as a whole is about 5.6 times as
heavy as water? Is the center of the earth metallic?

[118]

How Earthquakes Give Us the Inside Facts

Is it solid? Is it liquid? Is it gaseous? For answers to
these and like questions we turn for assistance to
seismology, that branch of earth science which deals
with earthquakes and their related phenomena.

An earthquake is the trembling or, more strictly
speaking, the vibrating of the earth as a result of
energy suddenly released by adjustments that are
taking place within the earth itself. The earth's crust is
continuously being subjected to strains of various
kinds the causes of which are not fully understood.
As these strains accumulate, they finally become
greater than even the strongest rocks can withstand.
Fracturing on a grand scale then occurs. These earth
fractures are called, by geologists, faults. The vibra-
tions, resulting from the realignment of the broken
crustal blocks, pass through and around the earth;
they may be intense enough to damage or destroy
buildings and other structures, or they may be so
slight as to be detected only by delicate instruments
called seismographs devices for recording earth-
quake vibrations at great distances from their origin.
Many such instruments are in operation in all parts
of the world, and from them valuable data are con-
stantly being obtained.

Earthquakes caused by adjustments along faults are
called tectonic quakes (from the Greek, tektonikos,

[119]

Excursions in Science

meaning that which is concerned with building),
because faulting is closely associated with mountain
building and similar crusta movements. A few quakes
are associated with volcanic disturbances, but these
are usually local in character. Still fewer are the so-
called deep-focus earthquakes, which seem to be con-
nected with adjustments at depths of 200 miles below
the surface. Most tectonic quakes appear to originate
relatively near the surface, at depths of 25 miles or less,
and are referred to as shallow-focus earthquakes.

The crustal displacements along faults may fre-
quently be seen at the surface after earthquakes have
taken place. After the great San Francisco quake of
April 18, 1906, horizontal shifts of the ground, up to a
maximum of 21 feet, were to be observed along the
San Andreas fault. In 1891, a disastrous quake in
Japan produced horizontal displacements up to 12
feet, combined with vertical displacements up to 20
feet, along the fault responsible for that earthquake.
The faults themselves may often be traced for many
miles on the earth's surface; thus we are able to obtain
visible evidence of large-scale faulting associated with
many of the great earthquakes of recent times.

The origin of the earth vibrations resulting from
faulting may be illustrated by a simple experiment. If a
small piece of wood about the size of a common desk

[120]

How Earthquakes Give Us the Inside Facts

ruler be bent in the hands until it breaks, the ends will
vibrate very rapidly at the moment of fracture, some-
times with sufficient energy to cause a sharp, stinging
sensation in the palms. The elastic rebound of the
wood after fracture causes the vibration. The belief
that the earth's crust acts in a similar way when
fractured has led to the general acceptance of what is
called the elastic-rebound theory to explain the origin
of earthquake vibrations.

Studies of earthquakes, which may be said to have
been begun in 1846 by that pioneer in seismology,
Robert Mallet, show that when faulting takes place
vibrations of three different sorts are set up. The first
vibrations are analogous to sound waves; that is, they
are longitudinal or compressional waves which vibrate
back and forth in the direction of their propagation
and which alternately put earth particles under com-
pression and then under tension. As these are the first
waves to appear, they are called the primary or, for
short, the P waves. Their average velocity is 3.4 miles
per second.

Following immediately upon the heels of the com-
pressional primary waves comes a second group of
vibrations which are transverse or distortional waves
that cause the earth particles to swing back and forth
at right angles to the direction of propagation. These

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Excursions in Science

transverse waves have the somewhat lower velocity
of about 1.8 miles per second and are called the second-
ary or, for short, the S waves. Both the compressional
and the distortional waves spread out in all directions
from their source with approximately spherical wave
fronts.

The third and last set of waves to be generated are
those which travel along the surface of the earth. They
are of greater length and amplitude than the P or the
S waves, and they are of longer duration than either-
of the others. These waves have been called the main
waves or long waves and are technically referred to as
the L waves. They appear to have been seen sweeping
over the surface by numerous observers, in spite of their
speed of 2.3 miles per second. These L waves become
very important when considering surface effects of
earthquakes, but as we are now concerned with what
is happening underground, we shall confine our atten-
tion to the P and S phases. Three things ought to be
remembered about them. First, their velocities are
dependent upon the elasticity of the matter through
which they pass; second, their velocities depend also
upon the density of that matter, the denser it is the
slower the wave will travel; and finally a very impor-
tant point the S or transverse waves will not pass
through a substance having the properties of a liquid.

[122]

How Earthquakes Give Us the Inside Facts

Let us now digress for a moment to consider the
seismograph, the instrument which records these
several types of earth vibrations. In principle the
ordinary seismograph is a delicately balanced hori-
zontal pendulum, in some types an inverted pendulum,
which carries a very heavy bob, called the steady mass.
The pendulum is attached to a strong upright support,
which, in turn, is fastened to a massive pier. A light
boom coupled to the pendulum serves to record the
earth movements, considerably magnified, either
mechanically or photographically. When in operation,
the steady mass tends to remain quiet, acting as the
fulcrum of a lever, while the rest of the machine
partakes of the earth motion, recording it as a com-
plex sinuous curve, the seismogram, which it is the
task of the seismologist to analyze.

Various damping devices are necessary to prevent
the pendulum from swinging in its own natural period
and thus superimposing its own vibrations upon those
of the earth. A complete seismograph should consist
of two pendulums set at right angles to each other in
order to record all possible horizontal vibrations, and
if possible, a third instrument to respond to vertical
wave motion. A necessary adjunct to the seismograph is,
of course, a timing device for obtaining the accurate

[123]

Excursions in Science

times of reception, at the station, of the various phases
of any earthquakes being recorded.

It was early discovered that, knowing the time of
arrival of the several phases of earthquake vibrations
and their velocities, time-distance curves could be con-
structed from which the distance of seismograph sta-
tions from the origin of the earthquake could be
deduced. With the modern time-distance tables, data
from three stations only are needed to permit the very
exact location of an earthquake. And it is in the studies
of wave velocities originally begun for the purpose of
finding where earthquakes occur that much light has
been shed on the nature of the earth's interior.

It has been found that the velocity of the P waves
increases with depth until they reach a point about
1 800 miles below the surface very nearly half way to
the center of the earth where their speed, which has
increased now to about 8 miles a second, suddenly
drops off to about 5 miles a second, indicating an
abrupt and doubtless a very fundamental change
either in the material of which the inner earth is com-
posed or in its physical condition. The S waves behave
essentially like the P waves, gradually increasing their
velocity with depth until this 1800-mile region is
encountered, where they apparently disappear. When
we remember that the S waves are of the transverse

[124]

How Earthquakes Give Us the Inside Facts

sort, which cannot pass through a liquid, this appears
as a rather startling fact.

The earth's core, somewhat over 4000 miles in
diameter and including about one-sixth of its volume,
must then be of the physical nature of a liquid or gas,
yet one of high density, say around nine or ten times as
heavy as water, or just a little greater than the density
of metallic iron. Here is a clue to the density of the
earth as a whole, to which I have referred.

It should be noticed that both P and S waves in-
crease their velocity with increasing density until the
core is reached, which can only mean that the elastic-
ity of the outer shell increases enough to neutralize
any density increase. Doubtless the temperature
increase, and perhaps the physical condition as well,
in the outer shell accounts for this situation.

The transition from the outer shell to the inner core
is abrupt, indicating a sudden change in the nature of
the materials there or their physical condition, and the
bounding surface between the shell and core is called a
discontinuity. Earthquake waves reaching such a
surface of discontinuity may be variously reflected or
refracted, or may even follow the surface of discon-
tinuity itself, and our seismograms show that this is
exactly what happens.

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Excursions in Science

In addition to this major discontinuity when the core
of the earth is reached, other lesser discontinuities have
been found to exist at depths of 7>, 23, 37, and 750
miles, as indicated by the behavior of the P and S
phases of earthquake waves.

We may sum up as follows the deductions that have
been made from seismic studies concerning the interior
of the earth. The earth is made up of concentric shells
of different thicknesses whose densities increase with
depth, the central core being perhaps made up of
metallic iron with some nickel. This metallic core has
a radius of about 2100 miles and an average density
of about 9. Next come several transitional shells with a
total thickness of about 1100 miles and average density
of about 53^3 to 6, made up perhaps of a mixture of
metallic iron and silicates. Then comes a shell about
700 miles thick, of average density of 3.4, made up of
matter of the general nature of heavy silicates of iron
and magnesium. Finally, a 50-mile-thick shell of light
silicate matter, on the outside of which man has found
his home.

Is this the whole of the story? By no means; there is
still much to be done with the information which every
earthquake traces for itself by means of the seismo-
graph. Earthquakes give us the inside facts, and it is
the job of the scientist to interpret them correctly.

[126]

OZONE

by DR. FRANCIS J. NORTON

R. NORTON was born in Fort Plain, New York, and did his
undergraduate and graduate work at Yale University.
He was for six years a research chemist for the Solvay Process
Company, at Syracuse. Since 1930 he has been a member of the
General Electric Research Laboratory.

<-<-* >

THE air we breathe is made up, mainly, of two gases
nitrogen and oxygen. The chemical shorthand
symbol for oxygen is the letter O, and it stands for a
single atom. But ordinary oxygen, as it occurs in the
air or in tanks of compressed oxygen, consists of two
oxygen atoms closely linked together. We write this as
O2. Two atoms of oxygen thus joined are called an
oxygen molecule, and may be thought of as having a
dumbbell shape.

But single atoms of oxygen do exist in a few places.
One such place is 100 miles up in the atmosphere,
where they give color to the Northern Lights and add
to the very faint greenish hue of the night sky. Another
place where single oxygen atoms are found is in elec-
tric discharge tubes in the laboratory.

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Excursions in Science

When dry air or oxygen is passed through a high-
voltage electric discharge, a smooth blue- or purple-
colored glow is seen, and some of the oxygen molecules
are torn apart by the intense electrical forces in the
discharge. This produces single atoms of oxygen, but
these single atoms do not like to exist alone, and in a
small fraction of a second they combine again. Some
of them go back to ordinary molecules of C>2, but a
certain fraction link up to make a new kind of molecule
with three atoms of oxygen Os- This new molecule is
ozone. x

The new form of oxygen is a colorless gas. It has a
distinct and very powerful odor the characteristic
odor we notice when electric sparks or lightning dis-
charges have passed. In ancient times, the poet Homer
mentioned the characteristic odor that accompanied
the thunderbolts of Zeus. As Lawrence of Arabia has
translated it:

"Then Zeus thundered and at the same instant
struck the ship with his lightning. She reeled from stem
to stern at the divine stroke, and was filled with
brimstone fumes."

The fumes Homer described were not from brim-
stone that is, from burning sulphur they were ozone
and the oxides of nitrogen. But when occurring in very
dilute form, so that they can just be smelled, the odors

[128]

Ozone

of ozone, sulphur dioxide, nitrogen oxides, ammonia,
and chlorine are so nearly the same that they are diffi-
cult to distinguish. Homer can, therefore, be forgiven
for confusing ozone and sulphur dioxide.

A small amount of ozone may have a refreshing
odor, and the pure air of mountain tops sometimes
has in it a little ozone that can be smelled. However,
breathing ozone is not a pastime to be recommended.
Not long ago, experiments were reported on the effect
of ozone on guinea pigs. Over a period of weeks, the
animals breathing such low concentrations as one part
of ozone in a million parts of air had shorter lives than
animals breathing normal air, which ordinarily con-
tains a thousandth of this amount, or one part in a
billion. The ozone irritated the lungs and bronchial
tubes of the experimental animals, and pneumonia was
frequent. These experiments indicated that it might be
highly dangerous to inhale, for an hour, air contain-
ing 50 parts of ozone per million, and many chemists
can testify that a single breath of air containing 1 per
cent of ozone produces extremely uncomfortable
results.

Various gases differ in their activity, or readiness
to combine chemically with other molecules. Helium
and argon, for instance, are almost totally inactive, and
are called "inert 53 gases. Nitrogen is rather inert and

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Excursions in Science

will combine only under certain special conditions,
such as high temperatures and pressures in nitro-
gen-fixation factories, or in the soil with the aid of
nitrifying bacteria. Ordinary oxygen is much more
active. It combines with the blood in every breath we
take, and it warms our homes by uniting vigorously
with coal or oil to give flame.

In bleaching leather and linens, we may use the
oxygen of the air, working with the sunlight and the
dew, to remove the yellow color. Ordinary oxygen does
this by uniting with or oxidizing the yellow constituent
of the material, but the process may take days or weeks.
Ozone can bleach in a few seconds or minutes.

Ozone oxidizes and kills the bacteria in water, just
as chlorine does. It is widely used in France for this
purpose. It is also of use in controlling mold growth on
meats in cold-storage warehouses, and it can be used to
accelerate the drying of linseed-oil types of paint.

Thus ozone has its uses, and that is one reason why,
in laboratories all over the world, scientists have spent
much time studying it. Most of its uses derive from its
most characteristic property, its instability. In the
course of a few hours or days, depending on conditions,
it breaks down to form ordinary molecular oxygen
2 .

[130]

Ozone

Some very interesting experiments are possible with
ozone. Take a rubber band. Hang a weight on it to
stretch it to three times its length. Suspend it in a box
with glass sides, where it can be watched. In the nor-
mal course of events, it would stay like this for weeks or
months. But run a stream of ozone through the box;
while you watch, in just a few seconds, the rubber
shreds, cracks, breaks, and down comes the weight
with a bang. Ozone is very destructive to rubber.

This reaction of ozone with rubber raises a most
interesting point. Ozone exists in the upper atmos-
phere, at levels 20 to 40 miles above the earth, in
considerable quantity. As attempts are made to reach
higher and yet higher levels with sounding balloons
and stratosphere balloons, this ozone must be taken
into consideration. It is likely that the contact of
stretched rubber balloons with ozone would prove
disastrous in a short time.

In the visible region of the spectrum, ozone is
practically colorless and readily allows light to pene-
trate it. But in certain portions of the ultraviolet
spectrum, ozone possesses an intense band of "invisible
color," an absorption band. Weight for weight, in this
region ozone is as opaque to ultraviolet light as a sheet
of metal is to visible light.

[131]

Excursions in Science

This absorption of ultraviolet by ozone can be strik-
ingly demonstrated in the laboratory. A mercury arc
lamp produces large quantities of ultraviolet radiation.
If the envelope of the lamp is of quartz, the ultraviolet
can pass out through it. And if the lamp is surrounded
by a jacket that transmits ultraviolet, but is opaque
to visible light, then the lamp becomes an intense
source of invisible radiation not apparent to the eye,
but able to produce some interesting effects.

Among them, it is able to excite fluorescence in
many materials that is, to cause these materials to
glow with bright, visible colors. Therefore, if a screen
coated with a fluorescent paint is placed in the range
of the invisible radiation of the ultraviolet lamp, it will
glow with a brilliant light all its own. Suppose, now,
one holds his hand between the lamp and the screen.
The shadow of the fingers is thrown on the screen, as
would be expected; the hand, obviously opaque, is
cutting off the radiation from the lamp.

But connect an ozone generator to a glass tube, and
place the open end of the tube halfway between the
lamp and the screen. The ozone is colorless and invisi-
ble at least, it is by daylight. But with ultraviolet
there is a different story. The ozone escaping from the
tube will throw a shadow on the screen, a shadow
which curls and billows like black smoke. The ozone,

[132]

Ozone

escaping from the glass tube, is as opaque to ultra-
violet as was the intercepting hand. No one who has
seen this experiment can doubt the absorbing power of
ozone for ultraviolet.

The amount of ozone in the atmosphere above us is
measured by studying the absorption of ultraviolet
light from the sun. These measurements are made
photographically or with a quartz photoelectric tube,
for both these devices can see the regions in the spec-
trum invisible to our eyes. In this way ozone in high
levels of the atmosphere, through which sunlight or
moonlight has passed, can be determined.

If all the air in the atmosphere were compressed to
uniform sea-level pressure, there would be a layer 5
miles deep, of which 1 mile would be oxygen. Com-
pressed to the same extent, all the ozone in the atmos-
phere would form a layer only % inch deep. Yet this
J^-inch layer of unstable gas is what acts as a valve, so
to speak, for the ultraviolet radiation from the sun to
the earth. If there were no ozone in the atmosphere, it
is probable that the intense ultraviolet light from the
sun would be fatal to nearly all forms of life as we
know them. With more ozone, so much ultraviolet
would be cut out that the natural development of
vitamin D, so essential to animal well-being, would be
seriously curtailed.

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Excursions in Science

This, then, is the picture of ozone unstable tri-
atomic oxygen, O 3 ; formed electrically and having a
characteristic odor; very active, and a harmful or a
useful agent, according to the application we make of
it; forming and disappearing in the atmosphere high
above us, where it is a barrier to the intense ultra-
violet light of the sun, making life possible on the
earth.

[134]

THE EARTH AS A DIARY

by KARL A. PAULY

TVTR- PAULY is a native of Somervillc, Massachusetts. He was
graduated from the Massachusetts Institute of Technology,
was employed with the New England Telephone Company, and
joined the General Electric Company in 1899. Until his retirement,
in 1937, he was Engineer of the Company's Industrial Depart-
ment, and was the designer of many important installations of
electric apparatus. The study of geology and paleontology has
occupied his leisure time for many years.

T A THERE did the earth come from? How long has it
* V been here? What is its past history, and where is
it going from here? We may ask these questions, and
not realize that answers to some of them are to be
found in a diary in which our good earth has recorded
many important events of its past. And at this very
moment, the rivers and lakes are engaged in writing a
story of today for the benefit of those who will be here
to read it millions of years hence.

Even the dreaded earthquakes are but vibrations
caused by Nature's pen as it records aii important
event in earth history. The rocks, which we frequently
admire, are but the pages of this diary that our earth

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Excursions in Science

has kept so faithfully through millions of years that we
may satisfy our curiosity by prying into its past.

What do we find as we read the dusty and ofttimes
badly worn pages of this diary? Well, we learn that the
earth is probably billions of years old; that it has had
a very interesting career; that it was once molten and
that for a long time after the crust had covered the
molten interior there were tremendous volcanic
disturbances; that the crust has been and still is being
bent and folded by the enormous strain caused by
contraction as it cools down. We learn that nearly
all, if not all, parts of our present dry land have been
under the ocean at least once, and most of them many
times. So complete is the record that we can often
trace the progress of these oceans as they have worked
their way inland, and we can discriminate between the
shallow seas and the deeper oceans, the sandy beaches,
the mud flats, and the coral reefs. Sometimes the rip-
ples in the sand on the ancient beaches and the rain-
drops on the ages-old mud flats are clearly visible.

We also learn that great mountain ranges have
existed where none are found today these earlier
mountains having been worn away by the destructive
action of the weather and carried by the winds, the
brooks, and the rivers to the valleys, the lakes, and the
oceans below. So vast were some of these mountains

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The Earth as a Diary

that sedimentary rocks miles in depth and thousands
of square miles in area have been formed from the
sands of which their rocks were once composed.

We find scattered here and there throughout our
diary interesting stories of glacial periods that have
occurred many times in the past, during which vast
areas that now enjoy temperate climate were covered
with ice thousands of feet thick during perhaps hun-
dreds of thousands or even millions of years. We learn
that our earth has been inhabited for millions of years
by highly organized life, the very beginnings of which
are still unknown, because the early pages of earth's
diary either have been destroyed or still remain
hidden away in some undiscovered place under great
depths of overlying rock. Although there is no definite
proof of it, the evidence indicates that the development
of life on a large scale began in the sea, for there is
no record of land life found in the rocks until after
very great progress had been made in marine life.
Although definite knowledge of the earliest life is still
lacking, some clue to its character in some cases can
perhaps be gained from a careful study of the very
beginnings of the life cycle of some of our present-day
animals. But until discovered, these early pages of our
earth's history will remain a powerful stimulant, urg-

[137]

Excursions in Science

ing us on in our search for the beginnings of life on our
planet.

We find in studying our record that the early life has
been affected by its environment that the animals of
the mud flats and quiet shallow seas differ from those
of the sand beaches and deeper and more open waters.
We find recorded the complete life histories of many
animals that have come into existence in one locality,
spread to a greater or less extent throughout the waters
of the earth, and then passed completely out of
existence never to appear again, leaving only their
skeletons behind to assist our imaginations in picturing
them in actual life. On the other hand, the very begin-
nings of others, which have carried on through
hundreds of millions of years and are now common-
place in our waters today, are recorded in this rock
diary.

But in all of this we note progress. We find that the
development of life has been orderly. In it we find our
clues to biological evolution and our basis for the law
of the survival of the fittest. The gradual growth in
size of most animals with the progress of time is very
striking. Full-grown starfish, when they first made
their appearance in the early Ordovician period, were
about the size of a 25-cent piece, and I have a perfect

[138]

The Earth as a Diary

young specimen, which I found attached to a piece of
coral, that is no larger than a pinhead. Shellfish
resembling our modern clams and scallops were at
that time, for the most part, no larger than small
peas or lima beans.

Now that I have stated in a very general way what
our diary contains, you are perhaps wondering how
we that is, you and I who are not geologists or
paleontologists or some other "-gists" can enjoy the
thrill that comes from reading firsthand from this
diary. First we must learn the language in which this
diary is written. Immense pleasure may be derived
from nature, but studying nature is like putting money
in the bank. It pays excellent returns on what we put
into it, but we must make the deposit before we can
collect the interest. I fear the trouble with most of us
is a desire to collect our interest before we earn our
principal. If we want to cash in on nature, we must
be willing to devote a little time to the study of some
of the fundamentals involved. And if we do, with that
knowledge as a deposit in the bank, we will derive
an immense amount of pleasure in return for our
efforts. Learning enough to begin reading the simpler
stories of our earth's history is not a difficult task, and
I assure you that the interest of these first stories will
provide the urge to continue the study further.

[139]

Excursions in Science

The first step is to learn the characteristic rocks of
our district and the major subdivisions of our earth's
history to which they belong. This, as I have said, is
not a laborious job if we do not go too much into
detail. Then we should become interested in the record
of animal life to be found in these rocks. This is a very
natural sequence, because it is through the animal
life that they contain that many of the rocks are
known. Inexpensive elementary books are published,
which are ample for the beginner. Some states have
published most excellent pamphlets dealing with the
local rocks and fossils.

There seems to be inborn in most of us a desire to
make a collection of something at some period of our
lives. Collecting stamps is probably the most common
expression of this desire. As a side issue, we may add
greatly to our interest in our hobby by making a
collection of the minerals or fossils of our particular
locality, and if we choose, we may exchange dupli-
cates with collectors of other districts.

Collecting minerals or fossils has several real
advantages over collecting stamps. The size of our
stamp collection is determined largely by the size of
our pocketbook, while the size of our collection of
minerals or fossils depends upon the number of hours
we spend out in the sunshine, in the open country

[140]

The Earth as a Diary

poking around the rocks. Remember, we have access
to just as much material and we can make just as good
a collection of the material in our community as
anyone if we will put the necessary effort into it.
Also, nature does not discourage us by issuing a
new series of fossils or minerals every two or three
months.

Add to these the advantage that this book, our
earth's diary, has not yet been completely read.
There is a vast stretch of time hundreds of millions
of years perhaps between the time when animal life
first appeared on the earth and the time of the
oldest fossils that have been found. And there are
probably many species or varieties whose beginnings
are recorded in the rocks that are now exposed and
available for study, but whose beginnings have not
yet been discovered because these early specimens are
obviously rare and no one has yet had the good
fortune to find one. There are, no doubt, many other
species whose life cycles were short, or which were
very restricted in the areas that they occupied, which
are still unknown and which someone some day will
discover.

The thrill alone that comes from merely finding a
rare specimen amply repays your effort, and there is
always the possibility that by such a find you may

[141]

Excursions in Science

establish the birth of a species many millions of years
earlier or its continuance many millions of years later
than it was supposed to have existed. Who knows but
that it will be your good fortune to find the clue,
which, followed up, will ultimately unfold that great
unknown past of which nothing is known today.

[142]

ADVENTURES WITHIN THE ATOMS

by DR. Louis N. RIDENOUR

R. RIDENOUR was born in Montclair, New Jersey, and at-
tended the University of Chicago. He received his Doctor
of Philosophy degree from the California Institute of Technology.
After six months at the Institute for Advanced Study in Princeton,
he was, for two and one-half years, Instructor in Physics at
Princeton University. In 1938 he became Assistant Professor of
Physics at the University of Pennsylvania.

I. What Atoms Are

tremendous variety of form and structure and
-* property found in the world in which we live has
been shown by three centuries of chemical research
to be due to the combination, in various proportions
and under various conditions, of only about 90 differ-
ent substances. These apparently primary substances,
which long defied the most vigorous efforts of the
chemists to break them down into simpler substances,
are called the chemical elements. Familiar examples
are oxygen, gold, iron, copper, nitrogen, hydrogen,
carbon, and tin.

There are two possibilities regarding the ultimate
structure of the elements: either each is continuous, in

[143]

Excursions in Science

the sense that if one divided a bar of gold in two as
many times as he pleased, the successively tinier
and tinier parts would still show all the properties
of gold, ad infinitum; or, on the other hand, an ele-
ment is discrete, so that the imaginary dividing
process just mentioned, if carried far enough, would
finally reach the point where the last piece of gold
would contain just one of the particles from which the
gold was built, so that a further division would destroy
the goldlike properties of the particle. By a long series
of investigations, it was shown that the discrete view
of the structure of matter is the correct one, and the
tiny particles of which each element is built were
named atoms, from the Greek for "uncuttable."

It proved to be possible for nineteenth century
chemistry to measure a quantity which, for each
element, was proportional to the weight of the atoms
of that element, and when the elements were arranged
in a table in the order of increasing atomic weight,
periodic variations in their chemical properties were
observed. This, coupled with the fact that the atomic
weights of many elements seemed to be integral
multiples of the atomic weight of the lightest and
presumably simplest hydrogen led to the proposal,
made in 1815 by Prout, that all of the atoms heavier
than hydrogen were, in reality, built from hydrogen,

[144]

Adventures Within the Atoms

and that careful measurements of atomic weights
would disclose that the weights of all atoms were
integral multiples of that of hydrogen.

Careful measurements of atomic weights subse-
quently showed that nothing of the sort was true, and
the hypothesis of Prout fell into disrepute. At this
stage, the physicists took up the problem of the
structure of the atom, and it is largely their work
which has led to our present view of the way in which
atoms are built.

The daring hypothesis of Prout has been vindicated
in the sense that all atoms are now known to be built
of the same fundamental building stones, which are
three in number. They are named the proton, the
neutron, and the electron. The proton and the electron
are electrically charged; they have charges equal in
magnitude, but opposite in sign. The neutron, as its
name implies, is electrically neutral. In the sense in
which charges have been designated since the time of
Franklin, the charge of the proton is positive and
that of the electron is negative. All of these sub-
atomic entities are astronomically tiny; the mass of
a proton is roughly equal to that of a neutron, and
each has a mass of about a millionth of a millionth of
a millionth of a gram. (A 5-cent piece weighs five

[145]

Excursions in Science

grams.) The electron is still lighter about 2000 times
less massive than the proton or the neutron.

By years of painstaking investigation it has been
found that the atom of any chemical element is a
structure somewhat resembling an incredibly minute
sun and planetary system. At the center is a very
tiny, positively charged nucleus, which corresponds
to the sun in our solar system, and whirling about it,
as the planets revolve about the sun, are one or more
electrons. Now the protons and the neutrons that
enter into the structure of an atom are all concen-
trated in the nucleus of that atom, and it is clear that
the magnitude of the positive charge on a nucleus will
be determined by the number of protons in the
nucleus. In order that atoms be electrically neutral,
as it is a fact of experience that they are, there must
be as many planetary electrons outside the nucleus
as there are protons in the nucleus. Since the electrical
charges of proton and electron are equal and opposite,
if this condition is satisfied, the atom as a whole will
be neutral.

Now, it has been shown by experiment that the
chemical properties of an element are determined
wholly and solely by the number of planetary electrons
the atom of that element possesses. Since this is so,
and since the number of electrons the atom has is

[146]

Adventures Within the Atoms

dependent on the number of protons in the nucleus
of the atom, the problem of transmutation of the
chemical elements has now been defined, if not
solved. What is necessary is to add to or subtract
from the number of protons in the atomic nucleus;
the new nucleus thus formed will then gather around
itself a number of planetary electrons equal to the
number of protons to be found in its nucleus, and will
have chemical properties entirely characteristic of
this new number of electrons.

Gold, for example, consists of atoms of atomic
weight 197. These atoms have nuclei possessing a
positive charge equal to that of 79 protons, and there-
fore there are 79 orbital electrons whirling about the
nucleus of the ordinary electrically neutral gold atom.
Mercury, the next heavier element in the table of
elements, has a nuclear charge of 80, and 80 extra-
nuclear electrons. A mercury atom of charge 80 units
and mass 198 units then differs from a gold atom of
charge 79 and mass 197 only in that the mercury
nucleus possesses one more proton. Any operation
that would result in the removal of a proton from the
nucleus of a mercury atom of mass 198 would change
that mercury atom into an atom of gold.

So far we have not mentioned the neutron as an
atomic building stone; but it is found that, in every

[147]

Excursions in Science

case but one, the weight of an atom is greater than it
would be if the atom were built only of protons and
electrons. The additional weight is contributed by
neutrons, which are packed in the nucleus together
with the protons. In the nuclei of the light elements
there are roughly equal numbers of neutrons and
protons. You will see at once that, since the chemical
properties of an atom are determined by the number
of its orbital electrons, and since this number is
determined only by the number of protons in the'
nucleus, the possibility exists that there may be atoms
having the same chemical properties but different
atomic weights, corresponding to different numbers
of neutrons in the nucleus. It is, in fact, true that most
chemical elements are built of mixtures of such atoms,
which differ in weight, but not in chemical properties.
This is the reason that most atomic weights are not
integral multiples of the atomic weights of hydrogen.
The problem of transmutation of the atom, then, is
that of producing a permanent change in the atomic
nucleus; for, if an orbital electron simply be removed,
the atom as a whole is left positively charged and will
soon pick up an unclaimed electron from those drift-
ing about in its neighborhood. This alteration of the
nucleus is made difficult chiefly by two circumstances:
the extreme smallness of the nucleus of an atom, and

[148]

Adventures Within the Atoms

the intensity of the electrical forces that it exerts in
its immediate neighborhood. While one expects
tininess in atomic magnitudes, it is perhaps surprising
that the nucleus of an atom is so small that a million
million nuclei laid beside one another would extend
less than a quarter of an inch. The atom as a whole,
including its orbital electrons, is about 50,000 times
larger.

Now, the way in which transmutations are effected
in the laboratory is to hurl a stream of atomic pro-
jectiles moving with tremendous speeds up to about
a fifth the speed of light at a target of the material
in which the transmutation is to take place. Since
the nucleus of an atom, as just indicated, is so very
small an object in comparison with the structure of
the atom as a whole, by far the greater number of
the atomic projectiles spend their energy in collision
with the extranuclear electrons. Only one in a million
or one in ten million of the bombarding particles
comes close to the nucleus of one of the target atoms.
And here the second difficulty standing in the way of
producing transmutation begins to be felt the diffi-
culty connected with the electrical forces in the
neighborhood of an atomic nucleus.

You will remember that the nuclei of all atoms are
positively charged; this is true also of the nuclei of the

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atoms used as projectiles to produce the transmuta-
tions. Usually, atoms of ordinary hydrogen, of heavy
hydrogen, or of helium are used as bombarding
particles, for the reason that these atoms, being the
lightest of all, are most easily accelerated to the high
speeds necessary for this work. When the positively
charged bombarding nucleus comes into the neighbor-
hood of the positively charged target nucleus, they
repel each other strongly, owing to the electric re-
pulsion exerted by like electrical charges on one
another. Only if the bombarding nucleus has a great
deal of energy that is, if it is moving with a very high
speed will it be possible for it to overcome this
repulsion and penetrate to the heart of the target
nucleus. Therefore, since the positive charge on the
target nucleus depends on the number of protons
there present, and since the number of protons in a
nucleus increases with increasing atomic weight of
the chemical elements, it will be more difficult to
produce a transmutation in a heavy atom, like gold
or lead, than it is to produce one in a light atom, like
carbon or aluminum. This proves to be true experi-
mentally, and higher and higher energy particles are
required to produce transmutations as one progresses
from the lightest and simplest elements in the periodic
table to the heavier and more complex.

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Adventures Within the Atoms

But should not the neutron, having no electrical
charge, be able to enter all nuclei with great ease?
It should and it does. But because of this very fact,
one does not find any free neutrons in nature; they
are always combined into atomic nuclei. If one wishes
to produce a stream of neutrons for use in transmuta-
tion experiments, he must produce the neutrons by
a nuclear disintegration caused by charged particle
bombardment, in which case the effects, just men-
tioned, of electrical repulsion by the target nucleus
must be considered.

We have then progressed so far: to produce an
atomic transmutation we must first shoot sufficiently
many particles at a target so that there is a good
chance of one of them making a close collision with
one of the atomic nuclei in the target; then, when
such a close collision occurs, the bombarding particle
must have sufficient speed to overcome the electrical
repulsion exerted on it by the charge on the target
nucleus, and to win its way to the heart of that nucleus.

II. How to Change Atoms into Other Atoms

The nucleus of an atom is built entirely of protons,
which have a positive electrical charge, and of neu-
trons, which are electrically neutral. Now everyone
knows that like electric charges repel one another;

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this principle is, in fact, at the very basis of the
phenomena of electricity. How is it possible, then, that
the nucleus of an atom can be such a stable structure
if it is built in this manner? The answer is, of course,
that in order for this suggested model of nuclear
structure to be a possible one, we shall have to postu-
late an attractive force of a very unusual character
to act between the particles composing an atomic
nucleus. This force must vanish at distances bigger
than about a millionth of a millionth of an inch, for
experiment has shown that at distances larger than
this the force between two nuclear particles obeys
the same well-known law as the force between two
electrically charged pith balls if the particles are of
like charge, they repel each other. At the same time,
the force which we are inventing to hold atomic
nuclei together must, at smaller distances, be power-
ful enough completely to outweigh and overcome the
electrical repulsion between two protons.

Now, it sounds as if this were a force entirely re-
moved from our experience; and so, in fact, it is. It
is only in the study of atomic nuclei that the scientist
has to deal with distances small enough so that the
existence of this force is required by theory or can be
inferred from experimental results. And there is the

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Adventures Within the Atoms

best experimental evidence for the existence of this
force that we have required for nuclear cement.

The way in which the scientist alters the electric
charge of an atomic nucleus, and thereby produces a
transmutation, is by hurling a stream of very rapidly
moving nuclei at a target of the material in which
the transmutation is desired. The smallness of an
atomic nucleus in comparison with the size of the atom
as a whole makes a close collision between the pro-
jectile and the target nucleus a rare event, and the
electrical repulsion between the projectile nucleus
and the target nucleus since both are positively
charged requires that the projectile have a great
deal of energy. Only if it be moving very fast will it
be able to overcome this repulsion and reach the heart
of the target nucleus, the region where the short-
range attractive force just mentioned begins to come
into play.

Suppose that a particle has sufficient speed to* win
its way through the electrical repulsion of the target
nucleus and reach the heart of that nucleus. Then
what happens? The answer is that any one of a num-
ber of things may happen. For a moment the target
nucleus and the bombarding nucleus are fused to-
gether, but only for a moment. In the next instant,
the compound nucleus formed by their coalition

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Excursions in Science

separates, usually into two fragments. One of these
fragments may, in some cases, be identical with the
bombarding particles, in which case we are not justi-
fied in saying that a transmutation has taken place.
Oftener, however, neither fragment is identical with
the bombarding nucleus, and, because the total num-
ber of particles in the two final fragments must be the
same as the sum of the particles in the target nucleus
plus projectile, if neither fragment is identical with
the projectile, neither will be identical with the
target nucleus.

Let us take an example. Suppose that we bombard
a sodium target with nuclei of helium. Now all sodium
nuclei found in nature are alike and have an atomic
weight of 23. This signifies that there is a total of 23
particles in the sodium nucleus, of which 11 are
protons and 12 are neutrons. The helium nucleus is
one of the simplest and most stable of all and consists
of two protons and two neutrons. In the favorable
event that a helium projectile has penetrated to the
heart of a sodium nucleus, the momentary compound
nucleus thus formed consists of 13 protons and 14
neutrons. One of the things that may happen to it in
the instant after it has been formed is that a proton
may be ejected from it. This leaves behind a nucleus
having 12 protons and 14 neutrons. The chemical

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Adventures Within the Atoms

properties of an atom having 12 protons in its nucleus
(and therefore 12 extranuclear electrons) are those of
magnesium, and our new magnesium nucleus has an
atomic weight of 26, this number being the sum of
protons plus neutrons in the nucleus. The proton that
was ejected from the momentary compound nucleus
is the nucleus of an atom of ordinary hydrogen. We
have transmuted sodium into magnesium; and,
incidentally, helium into hydrogen. This example is
typical of all the transmutations now being brought
about in the laboratory.

To produce an atomic transmutation, then, it is
necessary to provide a stream of very swift nuclear
projectiles, and several different means of providing
them are at present in use. The first and simplest
means is that of letting nature provide them. Certain
radioactive elements in their decay shoot out very
swiftly moving particles that are called alpha particles.
These are in all respects identical with the nuclei of
ordinary helium atoms, so that if an experimenter
has at his disposal a sufficient amount of radium or
other suitable radioactive element, he may use a
stream of these swift helium nuclei to bombard a
target and produce transmutations. It was in this
way, by using the alpha particles from a decay
product of radium to bombard nitrogen, that Lord

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Excursions in Science

Rutherford achieved the first genuine transmutation
recorded in the history of science.

But radium and other radioactive elements are
expensive, and the quantities available are small,
while even the most energetic alpha particles emitted
from a natural radioactive element are not swift
enough to overcome the electrical repulsion exerted
on them by nuclei of atoms heavier than those of
potassium. What is desired is a way of producing a
stream of nuclear projectiles at will, in the laboratory,
without depending on the beneficence of nature.

In principle, the way of achieving this is obvious
and simple. Like electrical charges repel one another,
but unlike charges attract; so that all we need to do
is to strip one or more of the orbital electrons away
from each of the atoms that we propose to use as
projectiles, leaving the remainder of the atom posi-
tively charged, and then attract these charged atom
fragments to a negatively charged electrode. If this
electrode has a hole in it, some of the particles will
pass through, and they will emerge on the other side
with a f velocity that depends on the voltage to which
we have raised the negatively charged electrode that
attracted them.

Now clearly there are manifold difficulties con-
nected with this scheme, or it would have been put

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Adventures Within the Atoms

into practice long ago. Rutherford produced the first
nuclear disintegration in 1919, but it was not until
1932 that the first completely man-made disintegra-
tion was achieved. The biggest difficulty simply
concerns the magnitude of the voltage that must be
put on the attracting electrode. (I should say in passing
that it is customary to accelerate the projectiles in
several stages, but the principle remains the same.
Several perforated electrodes replace the one men-
tioned above, and the total voltage is divided among
them.) But in the "brute-force" method of accelera-
tion we are discussing, the total voltage between the
place where the projectiles are started and the place
where the target is located must be at least 1 million
volts to produce any but the simplest transmutations
in the lightest elements, and the more millions of
volts the better, if one desires to disintegrate moder-
ately heavy elements.

There are several ways of producing such high
voltages. First, one may simply extend ordinary
electrical practice and build transformers that step
up ordinary industrial voltages say 15,000 volts
to several million volts, a potential that is then
applied to a gigantic vacuum tube in which the
particles are accelerated. This method has been used
to supply voltages up to about 1J million volts, but

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Excursions in Science

is enormously expensive if that limit is exceeded, so
far as present-day technique is concerned.

Second, one may employ what is known as a surge
generator, in which each one of a large number of
electric condensers is charged to a moderate voltage
perhaps a tenth of a million volts and then all the
condensers are connected together in series and
discharged through the vacuum tube used to acceler-
ate the particles. If there are 20 condensers, then
one has 2 million volts available at the moment of
discharge.

The third and last important method for "brute-
force" acceleration of nuclear projectiles is that of
building an immense electrostatic machine. A con-
ducting sphere is insulated from the earth, and
electric charge is continually carried up to it and
deposited on it by an insulating belt that is driven
by a motor. If the sphere is well insulated and proper
precautions are taken to keep the charge from leaking
off into the air by the purplish brush discharge called
corona, and known to mariners and mountaineers as
St. Elmo's fire, voltages of several million volts can be
attained in this way. The largest machine of this sort
that is now (1938) in operation works at 2.7 million
volts, but several others are under construction which

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Adventurer Within the Atoms

their designers hope will attain voltages of 5 to 7
million volts.

You will have inferred, from my reference to the
foregoing methods of accelerating nuclear particles
as "brute-force" methods, that some subtler means of
producing high-energy particles for nuclear disin-
tegrations exist. Of several schemes that have been
proposed for providing high-energy particles without
the necessity of actually producing and controlling
high voltages, the cyclotron is the only one that is at
present in use in nuclear disintegration work. When I
last heard, the cyclotron at the University of Cali-
fornia was producing nuclear projectiles whose speeds
could only have been attained, using the "brute-
force" methods of acceleration, by their fall through
a potential difference of 8 million volts. And these
particles were being produced by an apparatus in
which the highest voltage employed is about 50,000
volts.

The explanation is relatively simple in principle
but devilishly complicated to apply in practice. The
positively charged atom-fragments which are to be
accelerated in the cyclotron are drawn toward and
through a negatively charged hollow electrode,
exactly as in the other methods of acceleration; but
in the cyclotron they are caused to move in a curved

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Excursions in Science

path which returns upon itself, so that they are
accelerated by the same voltage on the same electrode
not once, but many times.

If an electrically charged particle moves in a mag-
netic field at a uniform speed, its path will be a circle,
and the faster the particle moves, the bigger the radius
of the circle. Yet the relation between the size of
circle and speed is such that the time required for a
particle of any speed to traverse a semicircle is always
the same. In other words, even if a particle's speed
increases, it will always cross a certain diameter at
certain, regular times.

This, is the reason that the cyclotron works. For the
voltage that accelerates the particles is not a steady
one; it is rapidly alternating. And it is applied in such
a way that it gives the particles a forward pull twice
in each circuit of the apparatus. Because the time
taken the particle to traverse a semicircle is the same
for each trip, the particle arrives at the point where
the acceleration is applied just in time to get another
forward pull that is, another increment in its speed.
So around and around it goes, keeping step with the
accelerating voltage, traveling in a sort of ever-
expanding path, being accelerated twice in each
complete revolution.

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Adventures Within the Atoms

The maximum voltage supplying the acceleration
may be only 50,000 volts, but if the particle makes
80 complete revolutions it will have been accelerated
by this voltage 160 times and will have an energy
equal to that it would have gained by falling once
through a potential difference of 8 million volts.
Getting this apparatus to work for the first time was
the neatest trick of the decade in experimental physics.

Powerful as these methods of bombarding atoms
are, we must not expect that gross amounts of material
are transmuted by them. As we have seen, the trans-
mutation has to be performed an atom at a time, and
there are many millions of millions of millions of
atoms in a teaspoonful of water. There is the best of
evidence that such nuclear transmutations may some
day have profound world consequence. Yet, what the
nuclear physicists are doing today is trying to find
out how the universe is put together in the realm of
the infinitely small.

[161J

PROBABILITIES AND
IMPROBABILITIES

by FRANK BENFORD

li .|"R. BENFORD, born in Johnstown, Pennsylvania, was graduated
in electrical engineering from the University of Michigan.
For 18 years he was a physicist in the Illuminating Engineering
Laboratory of the General Electric Company, and since 1928 has
held the same position in the Research Laboratory of that com-
pany. A specialist in the problems of light and optics and the
author of about 75 papers on engineering and scientific subjects, he
is interested also in unusual applications of mathematics.

ONE would hardly expect to find a lesson in morals
buried deep in the history of a branch of mathe-
matics, but the history of the Theory of Probability
contains such a lesson, although it has a slight left-
handed twist.

A gambler in France wanted to know what the
odds were in favor of a certain event he was betting
on, and he took the problem to a Professor of Mathe-
matics at the University of Paris. The mathematician
found the answer, and at the same time he founded
what is at once the most interesting and the most
deceptive of the mathematical sciences. A lily of truth

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Probabilities and Improbabilities

thus grew from the mire of professional gambling,
and perhaps the moral is that good may occasionally
come from evil.

After being conceived in a gambling house, it is
only natural that the next development should come
through another application to gambling. It seems
there was a heads-or-tails game played with a single
coin. If the patron of the gambling house won the
first toss, he collected two roubles and got a second
toss. If he won this toss he got four roubles and a third
toss. The process of doubling the prize went on until
the patron lost a toss and thus ended the game. At
each toss the probability of getting another toss was
just one-half, but to compensate for this the value
of the next prize was doubled. The potential value of
each toss was one rouble, and the potential value of
each game was an infinite series of ones. The theory
of probabilities therefore said that the patron should
pay an infinite number of roubles for the privilege of
starting a game.

Now, this demand for an infinite payment would
have been bad for business, and besides, it just didn't
make sense. Even the mathematicians balked at
believing it. After expending some thought and several
infinities of words, they arrived at an abstruse equation
that brought the situation within the bounds of belief.

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Excursions in Science

These two events, one showing that there were
simple ways of computing probabilities and the other
showing that there was a more profound side to the
subject, were the beginnings of a vast literature on
Permutations and Combinations, Choice and Chance,
and the Theory of Errors. One distinguishing feature
of these branches of mathematics is the lack of cer-
tainty, as contrasted with the absolute certainty of
other branches. The second feature is that proba-
bility deals properly only in large groups of similaf*
events, while the other branches deal with single
events or with small groups. As an example, if we were
given the two sides of a right triangle, we could
foretell the third side with accuracy and certainty.
But the theory of probability will not tell us how a
coin will fall on three successive tosses. The theory
tells us what the average result will be if we make a
large number of trials. There are eight combinations
that may occur on three successive tosses, and there
is no certainty that any one particular combination
will occur. If a large number of trials are made, then
the theory can predict with something approaching
certainty that any one particular combination will
occur in a certain percentage of the trials.

There is one popular view of the law of probabilities,
as the man on the street reads that law, that either

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Probabilities and Improbabilities

amuses or infuriates the mathematician. On a roulette
wheel there are red spots and black spots. One system
of gambling is to watch the wheel until red turns up
three times in succession and then bet on black for the
next turn. The idea here is that red having come up
more than its due share of times, black must now come
up in order to come out even according to the law of
probabilities. This assumes that the wheel has both a
memory and a conscience, and says to itself, "It is now
time to be black for a few turns in order to play fair
and fulfill the law."

This misuse of a perfectly good mathematical con-
ception makes the mathematician see red and tear his
hair, because he has written essays, treatises, papers,
and books to show that past history has no such
influence on future events. If the wheel is both accurate
and honest, then each turn is wholly independent of
preceding turns, and the chance for black remains
exactly the same each turn, regardless of the number
of successive appearances of red. Each turn is a com-
plete event in itself and, like the humble mule, has
neither pride of ancestry nor hope of posterity.

One of the most useful branches of probability is
the Theory of Errors. If you stopped a statistician on
the street and asked him, "How tall will be the next
man to come around the corner?" he would say

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Excursions in Science

something like, "Five feet 9 inches, plus or minus
1 inch." This answer is not intended to be mysterious
or evasive. It is a very definite answer that contains
two facts. First, he has evidence to show that the
average height of a man in that city will, according to
statistics, be 5 feet 9 inches. Second, just half the men
in that city will, according to statistics, be between
5 feet 8 inches and 5 feet 10 inches tall. The remaining
half will be either shorter or taller than his 5 feet
9 inches plus or minus 1 inch. He therefore has really
said, "It is an even chance that the next man to come
around that corner will be within 1 inch of the average
height, which is 5 feet 9 inches."

Only a few short years ago the theory of probability
was but little used outside college classrooms, but
today it has invaded nearly every science and every
branch of engineering. One of the most useful appli-
cations is in the sampling of manufactured articles.

Suppose that a certain steel bar is to be 1 inch in
diameter, but a variation of one-thousandth of an
inch either greater or less than the exact inch can be
tolerated. If 10,000 of these bars are made every day,
it would obviously be expensive to measure every one
of them in the routine of inspection. The theory of
sampling indicates that if only a few of the 10,000 are
selected at random and measured, the probability

[166]

Probabilities and Improbabilities

of, say, just one bar in the day's production being
defective can be computed. If this probability is
small, and only a few bars need be carefully measured,
then it is evident that the theory has graduated from
college and is in overalls in the factory, which is where
all good theories finally find permanent employment.
Anyone dealing in probabilities must remember
that the laws, derived for large numbers of events,
can be applied safely only to events in bulk. And most
important of all, probabilities are not certainties; they
are mixtures, in known parts, of probabilities and
improbabilities. Anyone thinking otherwise is due for
an expensive education if he backs his opinion with
money.

[167]

MEN AND METALS

by EARL R. PARKER

TV >T R - PARKER, a native of Denver, Colorado, is a graduate in
*" metallurgical engineering of the Colorado School of Mines.
Since 1935 he has been a member of the staff of the General
Electric Research Laboratory, as a research metallurgist.

IF, SUDDENLY, something should happen to destroy
all the iron on the earth, we'd be without auto-
mobiles and railroads. We'd lose our furnaces and
plumbing. Nails and bolts and jackknives and axes
would disappear. How would we manage to get along?

Would we all die? I think not. We'd be no worse off
than our ancestors were three or four thousand years
ago; for the history of our civilization and progress
has been the history of the search for better tools, and
it has gone hand in hand with the discovery of metals.

The first men of whom we have any trace knew
nothing about metals. They must have lived almost
half a million years ago, because the tools they used
are found buried underneath the gravels left behind
by the glacier that spread across much of our northern
hemisphere. These tools are pieces of flint. They

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Men and Metals

have been shaped for use, but so slightly and crudely
that it is hard to be sure that they were not broken
by frost, chipped by falling, or cracked by natural
rock pressure. They are our earliest records of the
Stone Age, which lasted in western Europe until
only four or five thousand years ago.

Why did the Stone Age come to an end? Because
our primitive ancestors discovered the use of metals.
And that's where the story of Men and Metals really
begins, as we try to trace the history of the growing
use of metals by mankind.

When primitive man was looking for stones to use
for knives and hammers, he, like a child, was attracted
by pretty colors and curious shapes. Any bright object
caught his eye as he wandered along the bank of the
stream, which was his natural highway. And so,
presumably, he found a glistening yellow stone. When
he tried to hammer it, he found that it was soft too
soft to serve as knife or ax. So our Stone Age friend
hammered his yellow stone into a ring or a bracelet,
and wore it proudly as a decoration. This yellow
stone was a nugget of gold. And because gold occurs
free and uncombined in nature, it was probably
the first metal discovered by man.

Now, silver and copper are two other metals that
are sometimes found in the native, or uncombined

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Excursions in Science

state. And whenever a people have discovered for
themselves the use of metal, the first metal tools have
been made, wholly or in part, of copper. Hammered
copper has been found among remains 6500 years old.
But it took time to learn how best to use copper.
Fully 2000 years passed before the early metal workers
graduated from pounding bits of metal they picked
up, and worked out a method of smelting copper from
its ores and casting it in the form for use.

Probably the first reduction from ore came as an
accident. We can imagine a campfire blazing on a
hearth built of rough stones. One of these stones
contains copper ore in the form of copper oxide or
copper carbonate. Copper ore, the glowing charcoal
of the fire, heat the ore is reduced to the metal. And
the fire tender finds among the ashes an irregular lump
of the precious red metal. It dawns upon him that he
is master of a great and valuable secret the secret of
making copper.

Now, this discovery, which was important to our
primitive savage friend, is equally important to us.
For he had found one of the basic procedures of metal-
lurgy, and from that simple discovery has come our
great metals industry, with the civilization which
rests upon it. The smelting of metal for the making of
better tools hastened the clearing of forests. Better

[170]

Men and Metals

tools made possible better crops, the building of better
houses, the construction of better boats. And, most
important of all, it led to the discovery that other
metals could be obtained by the same method.

But we are getting ahead of our story. After copper
had been smelted, someone tried making a hole to
collect the molten metal. Then this hole was lined with
clay; then the floor of the hearth was enclosed with
stones, arranged to form a wall. And that was the
evolution of the metallurgical furnace.

Our primitive metalworker, familiar with the camp-
fire, knew that a breeze made the fire burn brighter.
So he fanned the fire. The natives of western Africa,
today, use for this purpose fans made from tough
grass and rushes. And then some mechanical genius,
experimenting with a bag made from the hide of an
animal he had killed, found that he could get a
pulsating draft of air by squeezing the bag; and there
was the bellows for the furnace.

But copper was still being made in lumps and then
being hammered into shape. After a time which
may have been several centuries someone noticed
that, while the metal would soften and run, like fat
or wax, when placed in a hot fire, it always solidified
when it cooled; and that, also like fat or wax, it
retained the form of the surface on which it was

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Excursions in Science

allowed to cool. So from that it was only a step to
making molds and casting the metal into the finished
form of knife or ax. Some of the cast axes and swords
made in this way were very beautiful. They have
been dug out of old graves in many parts of Europe.
Preserved in museums, they compare, as works of
art, with some of the finest works of modern artists.
Because the copper commonly contained some tin,
we call these relics bronze, and the age in which they
were produced has been called the Bronze Age. But
another metal was coming into use a metal that
gave its name to yet another age, the Age of Iron.

Iron ores are abundant; next to aluminum, iron is
the most plentiful of the metallic elements in the crust
of the earth. As long ago as 3500 B.C. the Egyptians
had occasional bits of iron, which they used for orna-
ments. To them it was more precious than gold, and
these pieces of iron were either fragments of meteors
or the result of accidental smelting operations.

But the Iron Age did not really begin in earnest
until iron was plentiful enough to be put to industrial
use. This, in Europe, was about 700 B.C., when iron
tools and weapons began to replace bronze. The
primitive furnaces that had melted bronze were not
hot enough actually to melt iron; but a spongy mass
of metal was obtained that could be hammered or

[172]

Men and Metals

"wrought" into shape. And that, presumably, was
the origin of "wrought iron, 55 which is in use today.
Until the fourteenth century, wrought iron was the
only form available. Then a blowing engine was
invented that made possible enough heat to melt
iron so that it could be cast. Therefore, it took some
2000 years to progress from wrought iron to cast
iron.

Although, during the Middle Ages, steelmaking
improved rapidly, yet there was one great mystery.
Why did a piece of steel become hard and strong
when it was quenched that is, heated and then
plunged into cold water? It took the microscope,
almost in our own times, to fathom that mystery. Yet
we find the answer simple enough. When the iron is
hot, carbon is dissolved in the metal. When the metal
is suddenly cooled, the carbon precipitates as fine
particles of iron carbide. These particles act like
little hard blocks or keys in the grains of the steel,
holding the grains in position and preventing slipping
and yielding.

The process of discovering things by accident did
not end in savage, or even in medieval, times. Many
of our metallurgical processes were observed long
before science was far enough advanced to give an
explanation. For instance, it has long been known that

[173]

Excursions in Science

steel is brittle when certain structures are present.
Science has shown that these structures are produced
by the impurities, sulphur and phosphorus. It was
observed that some steels remained bright, while
others under identical conditions rusted badly. Again
metallurgical science demonstrated that the rust-
resisting steels contained impurities of nickel and
chromium; and in addition to resisting corrosion,
these steels were stronger and tougher than ordinary
steels.

With discoveries like this, the science of metallurgy
caught up with the metal industry and, instead of
following and explaining, went out ahead and charted
the progress of industry. Small amounts of different
elements were intentionally added, to determine their
effect on the properties of the steel. Nickel, chromium,
silicon, and manganese, in small percentages, increase
strength and toughness. Tungsten, vanadium, and
chromium greatly increase the hardness. Molybdenum
and tungsten give steel increased strength at red heat,
so that boilers, stills, and turbines can be operated at
very high temperatures. And the study and progress
of alloy steels is going forward at an ever-accelerating
rate.

If we look closely at our modern civilization, we see
that it is built on a foundation of steel. Steel makes

[174]

Men and Metals

possible our skyscrapers, our vast railroad systems, our
automobiles, all the electrical apparatus that gives us
electric light and power. If we try to picture what our
civilization would be like if iron were taken from us,
in order to get an adequate comparison we have to go
back to the days of the Stone Age and the Bronze Age.

[175]

THE USE OF LIGHT IN CHEMISTRY

by DR. GORTON R. FONDA

R. FONDA was born in New York City and was graduated from
New York University. Later he attended the Technische
Hochschule, Karlsruhe, Germany, where he received the degree
of Dr. Ing. Since joining the staff of the General Electric Research
Laboratory, in 1910, he has carried on investigations in chemistry
and physics, many of them dealing with the problems of light
production.

THE chemist's concern is with the elements, 92 in
number, which make up our world. We think of
him as dissolving a thing up, testing it with different
reagents, getting a precipitate so that we can finally
conclude that the substance is made up of such and
such elements. But frequently he finds that he can
to advantage depend more on physics than on
chemistry.

The first recorded case is of the Greek philosopher
who was asked to find out whether the king's crown
was or was not made of gold. Chemistry in those days
was so limited that this poor man could think of no
way to prove it. To cool his overheated brain, he

[176]

The Use of Light in Chemistry

tried a bath. When he slid down into the tub, which
he had absent-mindedly filled full to the brim, of
course an equal volume of water splashed over on the
floor. At once he saw the solution. He need only weigh
the crown, and get its volume by measuring the water
that it displaced. The ratio would give the density.
Then he could answer the king, for gold is twice as
heavy as brass. Density measurements have been used
ever since by the chemist in his analytical work.

An even more useful way in which physics aids the
chemist is by means of the character of the light given
off by substances when they are heated. Suppose a
little table salt is sprinkled into a colorless flame. The
flame turns a brilliant yellow identical, in fact, with
the color given off by the sodium lamps used to light
highways. The cause of the color is in each case the
same, for table salt is a compound of sodium, and in
the heat of the flame it breaks up and the element
sodium forms a vapor that becomes luminescent.
Suppose that one used, instead of sodium, a salt of
potassium a very similar element. Then the flame
would be colored violet. That distinction was dis-
covered in 1760, and it has been made use of ever
since in separating these two elements. But it was not
until 100 years later that the next step forward was
taken.

[177]

Excursions in Science

Since Newton's day it has been known that, when
sunlight is passed through a prism, it is broken up
into the spectral colors. Around 1800 there lived in
Bavaria a man named Joseph Fraunhofer. His father's
trade of glazier led him to be interested in applica-
tions of glass other than simply for use in window-
panes, and he found how to make better lenses. Then
he turned his attention to prisms. He combined both
prisms and lenses in an improved form of instrument,
which gave an enlarged image of the spectrum. This
was the origin of the spectroscope. It was so superior
to Newton's simple prism that it stimulated the
examination of spectra from all kinds of substances.

It was a German chemist, Bunsen, who finally
developed a new use for the spectroscope. His name is
familiar from association with the burner that he
designed, still used in all laboratories and its principle
applied to our gas ranges the Bunsen burner.
Bunsen was interested in the analysis of the famous
cure waters from natural mineral springs. He realized
that, coming from the earth's interior, they might
very well hold in solution some new types of salts or
even some new elements from minerals with which
they had come in contact. These minerals had long
troubled the chemist, for their analysis never added
up to 100 per cent; something was evidently missing.

[178]

The Use of Light in Chemistry

It was in 1860 that Bunsen found what it was. Not
content with examining the colors of flames into which
these waters were sprayed, he turned the spectroscope
on the flame. The spectrum produced was not the
continuous bands of differing color that are formed
by sunlight, but was made up of a succession of sharp
lines. Sodium, for instance, gave a strong yellow line.
Bunsen saw this through his spectroscope, and he
saw the lines of other elements that he recognized.
But, in addition, he saw two blue lines that were new.
This gave him the clue to the presence in the waters of
a new element. By chemical means he separated its
salt and named the new element caesium, from the
Latin word describing the blue of the heavens. This
work of his in 1860 began the branch of science which
in recent years has developed into that valuable
tool spectral analysis.

In fact, its usefulness began at once. It was found
that the luminosity of a substance could be excited in
ways other than by heating in a flame. An electric
discharge through a gas was one way. At present, we
have round about us many examples of gas discharges
mercury lamps, sodium lamps, and neon lamps.
Neon, a gas, is one of a group of elements that we
call the rare gases. Neon occurs in air, but only to the
extent of about 1/10,000 of 1 per cent. Most of the

[179]

Excursions in Science

other rare gases are even less plentiful in the atmos-
phere. Their separation was long and tedious, but its
guide was the spectroscope, for it had by this time
become recognized that every element has a charac-
teristic pattern of lines scattered through its spectrum.

Light, like a radio signal, is transmitted through
space as waves. Each color has a different wave length.
Radio waves run in length from 600 to 1800 feet in
the broadcast range, and down to 30 feet in the short-
wave bands. But light waves are much shorter still-^-
less than 1/30,000 inch in length. The spectroscope
is so sensitive that differences in wave length less than
1/1000 of this amount can be measured.

This extreme sensitivity has made possible the
discovery of new elements. Helium, another of the
rare gases, is an example. It was first discovered by
the Englishman, Lockyer, in 1868. He took advantage
of an eclipse of the sun to examine with a spectroscope
the characteristics of the glowing gases in the outer
atmosphere of the sun. He discovered an orange-
yellow line in its spectrum, and he was able to measure
its wave length so accurately as to prove that it could
come from no previously known element. Conse-
quently, he concluded that it occurred only in the
sun, and he named it helium, from the Greek word for
sun. In the course of time, however, it was found also

[180]

The Use of Light in Chemistry

on the earth first, in the gaseous volcanic eruptions
of Mt. Vesuvius, then in radioactive minerals, and
finally in air itself, but so extremely dilute that it
could be detected only with a spectroscope.

There are other rare elements besides the rare
gases. One group of them is known as the rare earths.
Their separation is even more involved, and in this,
too, the spectroscope proved its value. In order to
vaporize them, it was necessary to introduce them
into an electric arc. The discharge became colored,
and its spectrum showed again characteristic lines of
differing wave length. This not only guided their
separation, but it led to the discovery of several new
elements. Notable for his work in this field was the
Austrian, Auer von Welsbach. He put his discoveries
to use by devising a new type of light from illuminat-
ing gas that of the gas mantle. We call it by his name,
the Welsbach burner. It employs a finely woven
netting of rare-earth oxides.

Further studies in recent years have shown the
spectroscope so important for all analytical work that
it has become a regular part of the chemist's equip-
ment. It is quick, and it can detect an element in
quantities as low as 1/10,000 of 1 per cent. Its
use is, however, limited to amounts of 3 per cent
or less.

[181]

Excursions in Science

An alternative method, which has yet to come into
general use, can detect any amount. Instead of deal-
ing with the visible or ultraviolet light given off by
substances, it examines their X rays. X rays are
formed when a substance is bombarded with electrons
whose velocities are thousands of times greater than
those in the arc discharges used to excite visible light.
In contrast to the visible spectrum of an element, the
X-ray spectrum has in it only a few lines, so that
there is less chance for confusion. The substance to
be tested can be smeared over the target of an X-ray
tube. A simpler method is furnished by the Coolidge
cathode-ray tube, from which high-voltage electrons
are shot out into the open air through an extremely
thin window of metal foil. In this case one need only
place the substance to be tested in front of the window,
with an X-ray spectroscope pointed at it.

X rays are light, just as are radio waves, only they
are at the other extreme of the spectrum. They are
several thousandfold shorter in wave length even than
visible light. The spectroscope necessary for recording
them has, therefore, to be of a different type. Visible
light is broken up into its spectrum, not only by a
prism, but also by what is called a diffraction grating
a succession of parallel lines ruled on a piece of
glass or metal. The condition for its operation is that

[182]

The Use of Light in Chemistry

the distance between the lines must be comparable
with the wave length of the light. How to get a satis-
factory grating for X rays was a problem until it was
solved by the German, von Laue, and the English-
man, Sir William Bragg. They found that a crystal
could be used as a grating. Just as a pile of bricks is
made up of layers, one on top of another, so a crystal
is built up of layers of atoms. The distance between
them turns out to be of the same order of size as the
wave length of X rays. In this way a crystal of our
common table salt became a refined scientific tool.

Perhaps this account of spectral analysis has served
to emphasize how far the chemist has gone afield in
the pursuit of his calling. It is no longer sufficient that
he confine his attention to test tubes and reagent
bottles. He has been obliged to apply himself to
physics as well. He has had to broaden his outlook.
He comes to realize that the domain of science is not
fixed, but is always moving and finding new direc-
tions in which to move. This is a healthy attitude for
anyone to acquire in facing a world that is changing
as rapidly as our present one.

[183]

THE TIDES

by DR. FREDERICK W. GROVER

A i OLD proverb reads, "Time and tide wait for no
man." Those of you who spend your vacations
on the seacoast know that bathing and boating en-
gagements have to be arranged to suit the tide. Those
whose activities lie upon the coastal waters have to
take the rise of the tide into account in navigating
shoal waters, steering their course to avoid or make
use of the tidal currents. Year in and year out, the
water recedes, uncovering rocks and shoals, only
inexorably to return to cover them again and to creep
up the posts of the dock or to hurl itself against the
sea wall. Ceaselessly the cycle of ebb and flow repeats
itself, neither hastening nor resting, while one genera-
tion of mankind follows another.

Even a short sojourn on the seashore teaches a few
fundamental facts about the tide. On our Atlantic
coast, high tide and low tide follow one another at
regular intervals of a little more than 6 hours. If the
time of one tide be noted, the next may be expected
about 12^ hours later. About the same interval
separates the times of two low waters. Thus, there

[184]

The Tides

are two periods of high water each 24 hours, with
two periods of low water equally spaced between
them. The water level changes most rapidly and the
water currents are most rapid halfway between high
water and low water, while, for an appreciable interval
around high water and low water, the current ceases
and there is slack water in preparation for the reversal
of the direction of the tidal current.

Furthermore, regular observations continued
throughout a few weeks will show that, at times,
the water level rises higher than normal only to
recede to a lower point than normal. Those who know
will tell you that these spring tides, as they are called,
occur at the times of full moon and new moon, and
they will be followed a week later, at the quarter of
the moon, by high tides lower than the average
accompanied by low tides where the water does not
recede so far as usual.

It has been recognized for centuries, in fact ever
since the centers of civilization began to press on from
the nearly tideless Mediterranean to the shores of the
Atlantic where the tides are well developed, that the
changes that have just been outlined are connected
in some way with the moon.

Perhaps the earliest existing account of the tides is
that of Pliny, A.D. 77. Seven hundred years later the

[185]

Excursions in Science

Venerable Bede, writing in northern England, records
that the times of high tide may vary considerably
between places separated by only moderate distances.
But not until the discovery of the law of gravitation
by Newton, in 1687, was a scientific explanation of
the tides proposed. In his great work, the Principia,
Newton proved mathematically that the attractive
force of the moon and, to a less extent, the attractive
force of the sun should suffice to explain the produc-
tion of the tides.

The tide-producing forces, in fact, follow accurate
astronomical laws. The moon exerts on the earth an
attractive force that varies in magnitude from point
to point. Since, however, the earth is a rigid body,
the net effect is a pull equal to the average value, that
is, the value that exists at the center of the earth.
The pull of the moon on the portions of the ocean
that lie, at the moment, nearest the moon is greater
than this value, while the force on the water on the
opposite side of the earth from the moon is less than
the value at the center of the earth. These differences
of force are only about one ten-millionth of the
weight of the water that is, the force by which the
earth attracts the water to itself so that the water
is not lifted bodily away from the earth.

[186]

The Tides

However, only at points directly under the moon
and those exactly opposite the moon, on the other
side of the earth, is the moon's pull on the water
exactly vertical. Everywhere else it is inclined to the
vertical, so that it tends to move the water hori-
zontally. Now, a very small force acting horizontally
on a fluid is able to give it a motion along the surface,
so that the water is raised above the general level under
the moon and on the opposite side of the earth.

As the earth rotates on its axis, those regions where
the water is heaped up maintain their positions with
respect to the moon, and consequently there are two
tidal waves moving around the earth. If the earth
were completely covered with water, every point
on the earth would be passed over by one or the other
of these tidal waves every 12 hours and 25 minutes.
The retardation of 25 minutes is explained by the
motion of the moon around the earth, which takes
27^ days and which causes the moon to come to the
meridian of any place on the average 50 minutes
later every day.

The attraction of the sun also gives rise to tidal
forces. Although the sun is vastly greater in size than
the moon, its distance from the earth is also so much
greater that the solar tidal force is only four-ninths
that of the moon. If it were acting alone, the sun

[187]

Excursions in Science

would give rise to high tide at midnight and noon
every day, with low tides at six o'clock in the morning
and evening.

Since the tide-producing forces of the moon and
the sun have different periods, they sometimes act in
conjunction and sometimes subtract from each other.
The former state of affairs occurs at new moon and
at full moon, and gives rise to the spring tides; the latter
occurs at the quarters of the moon, and the neap tides
result. The tidal forces in these cases are, respectively,"
20 per cent greater and 20 per cent less than the
average. Also, the moon's tidal effect is greater when
it is in perigee (that is, nearest the earth) and least
when it is most distant (apogee). In this case also the
range is some 20 per cent greater and less than the
average. Spring tides that occur when the moon is
in perigee and neap tides occurring at apogee repre-
sent the greatest possible extremes that can occur. A
further modifying factor is the movement of the moon
north and south of the equator during the month.
This has the effect of giving rise to inequality of the
two high tides that occur any day.

The laws of variation of the tide-producing forces
are accurately known, and their values may be pre-
dicted at any desired time and for any place. The
tides actually produced by these forces are, however,

[188]

The Tides

profoundly modified by the existing distribution of
land and water on the earth. Consider, for example,
the tides of our Atlantic seaboard. On the progres-
sive wave theory above outlined, we should expect
a tide of only a foot or two in range, which would
occur later and later as the wave traveled westward.
Actually, tidal ranges of 5 to 10 feet are common,
and high water occurs practically at the same time all
along the coast.

At the beginning of the present century, Dr. Harris,
of the U. S. Coast and Geodetic Survey, pointed out
that the tidal phenomena observed could be ex-
plained as manifestations of stationary wave systems
set up by the tide-producing forces. As a simple
example of what is meant by stationary waves, sup-
pose one end of a rectangular trough containing water
to be raised and then lowered again into its original
position. A water wave will travel down the tray,
will be reflected, and will return, continuing thus to
move back and forth until it dies out. If, however, the
end of the tray be lifted and lowered regularly at
just the proper frequency, the water surface may be
made to move rhythmically as a whole in such a way
that when the level at one end is high, the other end
is low, and vice versa, while the level of the water
along a line across the middle of the tray neither rises

[189]

Excursions in Science

nor falls. This line of stationary level is called a nodal
line.

The same result may be obtained if pressure be
applied to the water surface at one end at just those
moments when the water level is starting to lower.
Under these circumstances, a very small force, regu-
larly supplied at just the right frequency, will sustain
a large oscillation of the water surface. The period of
the oscillation that is, the requisite interval between
impulses is greater, the greater the length of the
tray and the smaller the square root of the depth of
the water.

Dr. Harris has mapped a number of regions of the
ocean basins whose length and depth bear such
relations as to make them responsive to the 12-hour-
and-25-minute period of the semidaily cycle of lunar
tide-producing forces. One of these regions abuts on
the Atlantic coast line of the United States, while
the nodal line runs northeast from the islands that
form the eastern boundary of the Caribbean Sea.
Tidal measurements taken on some of these islands
show a very small range of tidal motion. A further
confirmation of the stationary-wave theory lies in
the fact that high tide occurs at practically the same
time all along the coast. A still more crucial test of
the theory is given by the fact that the tidal currents

[190]

The Tides

are zero at the times of high tide and low tide and
greatest halfway between. If it were instead a progres-
sive wave phenomenon, the tidal currents should be
greatest at the crest and trough of the wave, and zero
halfway between.

The stationary-wave hypothesis gives also an ex-
planation of the tides of the Bay of Fundy, the highest
tides in the world. The length and depth of the bay
are such that its waters will respond most strongly
to impulses having a period of about 12 hours, with
a nodal line across the entrance of the bay. The forces
of the rather large tidal oscillations outside the bay
serve as the sustaining forces for the still larger oscil-
lations of water level in the bay itself. Along its inner
reaches, a tidal range of from 40 to 50 feet is common.
Those of you who have visited Eastport, Maine, or
Saint John, New Brunswick, will remember the great
height of the piles of the docks. Most impressive
of all are the vessels stranded on the mud flats at low
tide in the Basin of Minas, Nova Scotia, and the amaz-
ing swiftness of the returning waters when the tide
comes in.

Still another example of an unusual tide, although
one of small range in this case, is furnished by the
Marquesas Islands, in the Pacific, where high tides
occur at about noon and midnight every day, and low

[191]

Excursions in Science

tides at 6 A.M. and 6 P.M. Evidently, these are solar
tides, and the lunar influence is negligible. These
islands lie near a nodal line of one of the ocean basins
whose period agrees with the 12^-hour period of the
semidaily lunar attractive force a striking confirma-
tion of theory.

Accurate predictions of the times and heights of
future tides, at the different ports, are of importance
to mariners and pilots. These may be made by
mathematical analysis of long-continued records
obtained by tidal gauges. From these may be calcu-
lated numerically the effectiveness of the various tide-
producing forces already discussed, and from these
components may be computed the tidal movements
to be expected in the future. Labor is saved and
accuracy assured by performing this synthesis with
a machine that automatically plots and combines all
these component contributing influences. The U. S.
Coast Survey has designed and has used for many
years a machine that predicts and draws curves that
take into account more than 20 separate influences
entering into the existing tides. Almanacs giving the
times of high tides and low tides and their heights for
every day of the year are published, two or three
years in advance, for all the principal ports of the
country.

[ 192 ]

The Tides

Such data are accurate and dependable under all
ordinary conditions of weather. In general, the effects
of the winds are not important in their influence on
the tidal heights. However, with winds of hurricane
force blowing toward the land, the tide may reach
heights entirely abnormal and unpredictable, as a
number of tragic incidents have clearly proved. In
such cases there are acting tide-producing forces
quite unusual in magnitude and lying outside of the
list of those orderly forces whose action we have been
considering.

[193]

WHAT HAFFENS IN A
GAS-DISCHARGE LAMP?

by CLIFTON G. FOUND

iy >TR. FOUND was born in Claremont, Ontario, and was graduated
-*" from the University of Toronto, where he carried on gradu-
ate study. He came to the General Electric Research Laboratory in
1916. During the World War he was engaged in research on sub-
marine detection. Since 1 925 his work in the Laboratory has been
mainly in the field of electric discharges in gases.

IN THESE days, with neon and mercury lamps
glowing red and green and blue in advertising
signs, and with sodium lamps casting their yellow
light over many highways, there is no need to explain
what a gas-discharge lamp is. But many a person,
looking at such a lamp, has asked, "How does it
work?" So let us see if we can answer that question.
As an example to study, let's pick a sodium lamp,
which delivers light of a golden yellow color.

The lamp itself is a glass tube containing metallic
sodium a tube into the ends of which are sealed two
metal electrodes. One electrode, called the cathode,
conducts the electric current into the lamp. The other
electrode, called the anode, carries the current away

[194]

What Happens in a Gas-discharge Lamp?

after it has passed through the space. The air, of
course, has been pumped out of the tube.

What carries the electric current across the space
between cathode and anode? The same carriers that
perform that task in a radio tube electrons; for radio
tubes, photoelectric tubes, and neon and mercury
and sodium lamps are all electron tubes. They all
depend for their operation on tiny elementary
particles which have an electric charge.

The electrons may be produced in various ways.
The electrons in our sodium lamp come from the
cathode. When the metal of the cathode is heated to
a comparatively high temperature, electrons are
boiled off from the metal. When a positive voltage
is applied to the opposite electrode the anode
the electrons, which carry a negative electric charge,
are pulled across the space and are collected on the
anode. By this process, the space is made a conductor
of electricity.

Although we have pumped the air out of the space,
it is far from empty; for the metallic sodium that was
placed in the tube evaporates under the influence of
the heat that is applied to it sends out, to fill that
space, a seething mass of sodium atoms. In every
cubic inch there are 60,000 billion atoms, all moving
about madly, colliding with one another, and getting

[195]

Excursions in Science

in the way of the electrons. And it is the interaction
of the electrons with these sodium atoms that produces
the light.

None of us can imagine even a million, let alone
60,000 billion. So, for a moment, let us try to visualize
what happens when just one electron and one sodium
atom collide.

An electron passing across the space from the
cathode to the anode may be compared to a small
boy running through a crowd. As the boy progresses,
he is certain to collide with one or more persons. Now
when he collides with a man, one of several things
may happen. If the boy is moving rather slowly, he
may merely bounce away from the man without
doing more than change his own direction of motion.

However, if the boy is traveling faster, the force
of the collision may be enough to disturb the man. For
example, it may knock the man's hat off. If the hat is
attached to the man's coat lapel by an elastic band, the
hat will still remain in the man's possession, and in due
course it will be returned to its original position on
the man's head.

If, however, the boy is traveling at a still higher
speed, the collision may be so violent that not only is
the man's hat dislodged from his head, but the
elastic band is broken. Then the hat and the man are

[ 196 ]

What Happens in a Gas-discharge Lamp?

completely separated, and the identity of the owner
of the hat is entirely lost.

Before applying our analogy to the lamp, let me
explain that an atom such as a sodium atom con-
sists of a nucleus surrounded by several electrons,
which are held to it by forces that may be likened to
the elastic band on the man's hat. The magnitude of
the force holding an electron to a nucleus differs for
different substances, and the energy required to sepa-
rate them is determined by the structure of the atom
and is characteristic of that particular type of atom.

Now let's see how the electron resembles the small
boy. When an electron, on its way between the
cathode and the anode, collides with a sodium atom,
one of several things may happen. If the speed of the
electron is low, the sodium atom may be unaffected
by the collision. Only the path of the electron is
changed. A collision of this character is known as an
elastic collision, and is of only minor importance in
the production of light.

If the speed of the moving electron is sufficiently
great, the collision may be so violent that the sodium
atom is disrupted, or ionized. This term is used to
describe the condition of an atom that has been
disturbed to such an extent that one of the electrons
composing the atom has been completely separated

[197]

Excursions in Science

from its parent -just as the hat was knocked off and
lost. In other words, the atom has been split up into
an electron and a positively charged part, called a
positive ion. We now have an extra electron that is
free to collide with other sodium atoms. The function
of the positive ion is to make the space between the
electrodes a better conductor of the electric current.
It behaves like a traffic policeman and permits high
currents to flow at comparatively low voltages.

In our analogy we had a third case, in which the
man's hat was dislodged but not lost. This too has its
counterpart in the lamp. It takes place when the speed
of the electron is higher than a certain critical value,
but is still too low to cause ionization. When this type
of collision occurs, the structure of the sodium atom
is altered. One of the electrons of the atom is dis-
lodged from its normal position. But it does not get
far enough away from its normal position to become
an independent electron. In this state, the atom is
said to be excited. The displaced electron later returns
to its normal position, and when this takes place
that is, when the hat is returned to the man's head
the energy that the atom received from the colliding
electron is given out again in the form of radiation
in the form of light. In the case of sodium, this radia-
tion is the characteristic yellow sodium light. Thus,

[198]

What Happens in a Gas-discharge Lamp?

an exciting collision puts the sodium atom into a
state from which it is able to produce light. Therefore
this third type of collision is the most important kind
of collision in a lamp.

Now to return to our sodium lamp. It is not, as was
pointed out earlier, merely an inert glass tube con-
taining metallic sodium. It is a tube in which, every
second, millions of electrons are leaving the heated
cathode. These electrons are being speeded up by
the applied voltage. They are colliding with many
of the billions of sodium atoms in the space. Some of
the collisions produce positive ions which aid in the
conduction of the electric current across the space.
Others produce excited atoms which are responsible
for the production of light.

Of course, no one has ever seen a single atom.
Probably no one will ever see an atom or an electron
or a molecule. These particles of electricity and matter
are far too small to be directly visible. But although
the scientists who work with them do not strain their
eyes and their tempers looking for them, they have
plenty of evidence of their existence and of their
complex interactions. And not the least of this evi-
dence is the light emitted when millions of electrons
encounter, every second, billions of atoms in gas-
discharge lamps.

[199]

SCIENCE AND SUPERSTITION

by NEIL B. REYNOLDS
<<<<<>

"|l JTR. REYNOLDS, a native of Scotia, New York, was graduated
-***-* in chemistry from Union College, and did graduate work
in physics at Princeton University. He was for six years a research
physicist in the General Electric Research Laboratory, was from
1933 to 1935 a member of the physics staff of the Massachusetts
Institute of Technology, and since 1935 has been a special writer
for the General Electric Company.

<-<-< >

PHYSICISTS and chemists are fortunate. In their
laboratories they deal with things that can be
counted and weighed and measured, and they can
repeat their experiments over and over to verify their
results. But there are other scientists who are not so
fortunate. Because exact, formulated knowledge is
scarce, they have at times to fall back on such dubious
information as is contained in superstitions and old
wives' tales.

Chief among these scientists are the archeologists.
Their laboratories are, literally, heaps of ruins. The
experiments they study were performed centuries ago,
and the records have been ravaged by war and earth-
quake, fire and plough. Yet the archeologists must

[200]

Science and Superstition

gather up what poor, miserable fragments have
survived, and from them reconstruct the whole history
of the original experiments. It sounds utterly hopeless,
doesn't it?

But the archeologists 5 success is a matter of record.
From hut circles, broken pottery, a few badly pre-
served skeletons, a little jewelry, a lot of stone arrow-
heads, bronze and iron axes and knives from such
rubbish they have rebuilt the history of civilization.
They have told us what we know of the people of the
Stone Age; then, of races that had, somehow, learned
to smelt the metal copper, and to alloy it with tin to
make bronze; then, later still, of the same or other
peoples who learned to smelt and forge iron which
brings us down to historic times and the Age of Iron, in
which we are now living.

But let us see how superstition and folklore can aid
in this scientific exploration of prehistory, and how
science can help to explain superstition.

We speak of the four seasons: spring, summer,
autumn, winter. Spring begins with the vernal equi-
nox, about March 21; summer at the solstice,
June 22; autumn at the fall equinox, late in Septem-
ber; and winter at the shortest day, or winter solstice,
December 22. There's a good astronomical reason

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for choosing these dates, and they divide the year into
four equal quarters.

But people didn't always use these days to mark the
seasons a fact demonstrated by Sir Norman Lockyer,
the British scientist who discovered helium in the
spectrum of the sun. Lockyer made a study of the
alignment of Stonehenge, in England that mysterious
circle of towering great gray stones. He found that if
he stood at the center of the circle and watched the sun
rise on the longest day of the year, it rose almost but
not quite exactly on the center line of a long avenue
that leads up to the circle. It looked as though the
people who built Stonehenge, very many centuries
ago, had used the circle to keep their calendar correct,
to mark the celebration of the official beginning of
summer.

Lockyer, an astronomer, knew that the position of
the rising sun at the longest day has been gradually
shifting, because of a phenomenon known as the
Precession of the Equinoxes. What was a perfect
alignment a few thousand years ago would be out of
line at the present time by a small but measurable
amount. Actually, at Stonehenge, there was an error
in alignment. So, assuming that the primitive astrono-
mers who built Stonehenge had done a good job of

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observing the rising sun, Lockyer measured the
existing error, made some calculations, and came out
with the approximate date at which Stonehenge was
erected about 1860 B.C., or 3800 years ago.

But Lockyer found evidence also confirmed at
other prehistoric monuments that people earlier still
had used another calendar. By sighting over other,
older stones, it was possible to determine the rising
sun on the morning of the first of May. And here's
where superstition comes in.

Divide the year into equal quarters, starting at May
1. You get, approximately, August 1, November 1,
and February 1 as the other quarter days. The old
pagan holiday, Lammas, used to be celebrated early
in August. Hallowe'en falls close to November 1.
Candlemas Day is February 2. And May Day is, of
course, the first of May. In the celebration of each of
these, there are customs that betray an ancient, pagan
origin. And the evidence of stone alignment, supple-
mented by scraps of tradition, indicates that long
ago these holidays marked the beginnings of the
seasons: spring, summer, autumn, winter.

Baskets of flowers, on May Day, are certainly ap-
propriate to the onset of summer. In parts of Scotland
and Ireland, leases and contracts are renewed on

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Martinmas, early in November, an indication that
the official year once began then. In Scotland, some
local elections are still held on that day. Indeed, here
in the United States, Election Day is "the first Tues-
day after the first Monday in November," which may
or may not be a coincidence.

And then Candlemas Day. If, on that day, the
ground hog comes from his hibernation and does not
see his shadow, spring is supposed to begin. Note
that this takes place on February 2, which, according
to the old May-November calendar, was officially
the beginning of spring.

But if the ground hog does see his shadow on Candle-
mas Day, what then? According to superstition, the
beginning of spring is delayed six weeks. And that six
weeks brings it within a few days of March 21, the
vernal equinox, the beginning of spring in our more
modern reckoning. In other words, the superstition
about the ground hog makes that animal decide, each
year, between a calendar in use today and a calendar
which has been abandoned at least 5000 years!

This may not be science, in the accepted sense. No
scientist would credit that a woodchuck, by turning
his back on the February sun, decides the seasons.
We have lost our belief in all these superstitions

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that is, many of us have. But, as a race, we have not
forgotten them. And scientists, trying to piece together
the history of mankind, trying to account for our
psychology and some of the peculiarities of our
behavior, find in such remembered superstitions clues
that exist nowhere else.

[205]

STONES PRECIOUS AND
OTHERWISE

by DR. E. G. ROCHOW

IT'S the little things that count in our modern lives.
A tiny trace of a thing called a vitamin can prevent
a disease; a few hundred ths of a per cent of lead com-
pound in gasoline can prevent its knocking in a motor;
a small amount of a chemical compound in rubber
keeps tires from cracking before they wear out.
Science pays a great deal of attention to details, in
order that our lives may run more smoothly, and many
of us think of this as a strictly modern trend. It isn't.
When we consider precious stones, for example, we
find that the ancients set up some very fine distinctions
between what was precious and what was not. They
pointed out small differences on nonscientific grounds,
and thereby started a long tradition in gems. It is
interesting to apply some modern chemistry to the
subject to find out what there is in a gem that makes it
so valuable.

A gem is primarily a mineral. And since there is
some latitude in the definition of minerals, let us limit
ours to those inanimate substances that have a char-
acteristic form and chemical composition that allow

[206]

Stones Precious and Otherwise

us to tag them with a name. Quartz is a very common
mineral; every region has some local name for it. In
the neighborhood of Schenectady it is found in the
form of small, shapely crystals called Lake George
diamonds, or Glens Falls diamonds, or Herkimer
diamonds, or simply rhinestones. These crystals of
quartz have considerable appeal and, therefore, have
some value above that of the ordinary rocklike varieties.
However, these quartz crystals sometimes have a rose
color because they contain a small amount of manga-
nese oxide, and we then speak of them as rose quartz
and raise the price. If the mineral is colored yellow by
iron, it is citrine, or false topaz; if it is colored purple,
it becomes amethyst and the value goes up again.
Obviously, these semiprecious stones are all alike
except for small differences in chemical composition,
and we must conclude that their appeal and their
value lie in these traces of coloring compounds.

Why isn't quartz a precious stone? Well, for one
thing it isn't rare. Quartz is in almost every igneous,
sedimentary, or metamorphic rock; it forms the sand
on our beaches and much of the dust in our atmos-
phere. It's too plentiful to be expensive. Furthermore,
a gem material should be harder than quartz, so that
it will not be scratched by dust. A gem must have also
some fire or brilliance, and except in the case of

[207]

Excursions in Science

the diamond, we usually demand some color also.
Fashion may dictate the color, and it sometimes
dictates the gem as well.

Color in precious and ornamental stones may be
of two kinds inherent or due to impurities. If the
color is due to the main constituent and is therefore
inherent in the composition, we call the stone idio-
chromatic. Azurite and malachite have their char-
acteristic blue and green colors because they are basic
carbonates of copper; turquoise is a lovely blue because
it is a double phosphate of copper and aluminum.
Many ornamental stones are idiochromatic minerals,
but few gems are.

The local quartz that we mentioned was colorless in
the pure form, and sometimes derived some color from
small amounts of impurities. Minerals that are colored
this way we call allochromatic, meaning colored by
foreign substances. Obviously, the color is of little aid
in identifying an allochromatic stone, and we must rely
on other properties, such as density, hardness, index of
refraction, and dispersion.

Among the really precious stones, the ruby and the
sapphire are known to everyone. These are allochro-
matic variations of the mineral corundum, which is
crystalline aluminum oxide. Most natural corundum
is opaque and dingy, and while it finds use as an

[208]

Stones Precious and Otherwise

abrasive, called emery, no one values it for its appear-
ance. If the corundum is a clear, flawless crystal, how-
ever, we call it a sapphire. White sapphire has a value
of $5 or more per carat. (The carat, you will remember,
is two-tenths of a gram, and there are 2270 carats to
the pound.)

Corundum makes a good gem mineral because it is
very hard and has considerable brilliance. Therefore,
sapphires have always been highly esteemed. If the
stone happens to be colored blue by a trace of titanium,
it is more valuable. Yellow sapphires are worth as
much as $125 a carat for the fine Ceylon stones, and
yet these differ from the white sapphire only in that
they contain approximately 0.92 per cent of plain iron
oxide. The value of the iron as a coloring agent is,
therefore,

120
00092 X 2270 = $29,600,000, per pound

The iron actually contributes this much to the value of
the gem, and I think that you will agree that it is worth
it. You will also agree that this is perhaps the most
expensive iron in the world.

One never hears of red sapphires, because we call
them rubies. The ruby is this same mineral, corundum,
containing a small amount of chromium in such form

[209]

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as to color it red. A stone exactly similar in color and
properties is made in some quantity by fusing alumi-
num and chromium oxides in such a way as to form a
single crystal. Such synthetic rubies bring lower prices
than the natural gems solely because they are not so
rare. The coloring agent, chromium, is a common
element, widely used at present in stainless steel and as
chrome plate. As a metal it is worth about 80 cents a
pound. As a coloring agent in natural ruby (which
contains about 3 per cent chromium and is worth as
much as $1500 a carat) its value is

1500

QQJ- X 2270 = $113,000,000 per pound

This is about as high as we can go in the price of color-
ing agents.

What about emeralds, which have long been favorite
gems? The emerald is a variety of the mineral beryl,
which is a beryllium aluminum silicate. The colorless
mineral itself is not particularly attractive, because its
index of refraction and its dispersion are so low that it
has little sparkle or fire, and it is only moderately
hard. When it is colored a light blue-green it is called
aquamarine, and in some other colors it is called
heliodor. The deep-green variety that we call emerald
is very rare and expensive, and the appealing color is

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Stones Precious and Otherwise

caused by a small percentage of chromium in the form
of a lower oxide.

The mineral chrysoberyl is a beryllium aluminate
and is therefore chemically related to the beryls. An
interesting and popular variety is known as alexan-
drite, and this gem has the striking property of being
an emerald-green color in daylight and a columbine
red in artificial light. The marked change is due to
strong absorption of yellow light, and to the fact that
the stone is pleochroic, meaning that the absorption
varies in the different directions in the crystal. A
synthetic sapphire designed to imitate the play of
colors in alexandrite is now being sold, and is made by
fusing aluminum oxide with 3 per cent of vanadic
oxide.

From a purely scientific standpoint it is difficult
to understand why the mineral zircon is not used more
as a gem material. In the colorless form it is next to the
diamond in sparkle and play of colors, for it has an
index of refraction and dispersion second only to that
gem. It is not nearly so hard as diamond, however.
There are some very attractive colors, including
yellow, green, and blue. Uranium is one of the coloring
agents. "Hyacinth" is the name applied to the yellow
and orange varieties, but for the most part zircon has

[211]

Excursions in Science

not been popular enough even to warrant a distinctive
name.

It would scarcely be fair to talk about gems with-
out mentioning the diamond, even though it is less
interesting chemically than many of the other stones.
As you know, diamond is a dense, isotropic, crystalline
variety of carbon, capable of great brilliance and fire
when properly cut. It occurs in many colored forms,
but in contrast to most gem minerals it reaches its
highest value when colorless. The sparkle and play of
colors in a clear diamond are so marked that a per-
manent color detracts from its appeal rather than add-
ing to it. Those stones that are absolutely colorless are
called "first water," and bring the highest prices;
good green, blue, and red tints are next in value, and
the so-called blue-white stones are quite popular. The
more plentiful yellow and brown stones are worth
much less.

The diamond is outstanding in hardness as well as
in brilliance, with the practical result that diamonds
may be worn in rings for many years without per-
ceptible scratching of the polished surfaces. The old
Mohs scale of hardness used by mineralogists placed
diamond at the top of the list with a hardness of 10,
corundum next with an arbitrary value of 9, topaz
next at 8, quartz at 7, and so on down to the very soft

[212]

Stones Precious and Otherwise

talc at 1. The intervals in this scale are unequal, and
it is recognized that the step from corundum at 9
to diamond at 10 is greater than the entire scale from
1 to 9. It is now possible to measure the actual hard-
ness of gems by an objective method, and the results
are surprising to one used to the old hardness scale.
If we establish a standard interval based on quartz
at 7 and corundum at 9 and use this for our true
scale, the hardest diamonds have a hardness of 42!
There are some diamonds that will rate as low as 36
on our new scale, and then there is an impressive
blank space until we come to boron carbide at 19.
Carborundum will have the value of 14.

As some of you may know, all diamonds do not
glitter. There are dark varieties, known as bort or
bortz, which are crushed and used to polish other
gems. Recently bort and poor gem stones have been
adapted to cutting tools and drills, but the best
diamond for such uses has long been the carbonado, a
tough gray or black variety that does not fracture
readily. A good black carbonado is worth more
per carat than a poor gem stone, for it is better suited
to do hard work, and a lovely appearance is of no
use whatever. The demands for precision machining
in the manufacture of automobiles and other products
of our age have increased the demand for industrial

[213]

Excursions in Science

diamonds enormously since 1920. In 1936 we im-
ported 1,166,000 carats of industrial diamonds, and
only 445,000 carats of cut gems, so that the industrial
need now exceeds the aesthetic. Of course the value
of the industrial stones is lower, despite the greater
volume, for the workaday world has no need for the
large, clear gems that are prized as jewels. It is inter-
esting, however, that the great majority of diamonds
entering this country now have laboring jobs to do,
and the king of gems is no longer just an ornament.

[214]

CHASING THE MOON'S SHADOW

by DOROTHY A. BENNETT

-iss BENNETT, a native of Minneapolis, was graduated from the
University of Minnesota. From 1930 to 1939 she was with
the American Museum of Natural History, in New York, where
she was Assistant Curator of the Hayden Planetarium. She was
Associate Editor of the magazine The Sky, coauthor of Handbook of
the Heavens, published by Whittlesey House, and designer of the
Star Explorer, a revolving star map. She organized and went as
a member of the Hayden Planetarium Grace Eclipse Expedition
to Peru in 1937. In 1939 she returned to the University of Minne-
sota to be associated with the University Press.

ALONG ago as August 31, 1932 (the day of the last
total eclipse visible in eastern North America)
a group ot us planned to be in Peru in 1937. And these
plans began to be realized when, in April, 1937, the
Hayden Planetarium-Grace Eclipse Expedition set
sail for the south. Of course, it wasn't quite so easy as
that. There were a good many hours spent in getting
information about the eclipse, studying its path,
learning the weather conditions, and trying to choose
a suitable place from which to observe it.

[215]

Excursions in Science

Strangely enough, finding any land at all was a real
problem. There were only a few places along the
shadow's path where there was land. The eclipse
began at sunrise, way over near Australia, with just a
few little islands in its path, and then it jumped nearly
6000 miles over empty ocean before it reached Peru.

Different observers chose different vantage points.
The National Geographic-U. S. Navy Expedition
selected Canton Island, near the sunrise end. Shortly
after 9 A.M. the shadow of the moon carried the eclipse
into the eyes of the instruments on Canton Island, re-
mained for about four minutes, and then rushed on
across the ocean to keep its appointment with Dr.
Stokely and Dr. Stewart.

These scientists were in a boat cruising along the
eclipse path, out where the sun was almost overhead.
Theirs was the thrill of a hundred lifetimes, for they
saw the sun completely disappear for 7 minutes and 6
seconds almost the longest time possible for an
eclipse. There had not been an eclipse like this one in
1200 years.

Why was this eclipse so different? Because the
various factors which always produce an eclipse were
especially favorable. For example, not only was the
moon directly between us and the sun, but it was also
very close to us. When it came between us and the

[216]

Chasing the Moon's Shadow

sun, and out behind it stretched a long, dark cone of
shadow, that umbra or shadow more than reached the
earth. It was, in addition, unusually wide in cross
section.

I have said that the moon was near the earth. The
distance varies because the moon does not move in a
perfect circle around the earth. It can come as close as
222,000 miles, or be as far away as 253,000 miles.
We usually say 240,000 miles as an average. In the
same fashion, the earth doesn't move in a perfect
circle around the sun, but is nearly 3,000,000 miles
closer to the sun in January than it is in June. And
that's another favorable factor that made this par-
ticular eclipse last so long. The moon was closest to us,
and the sun was farthest away. Both conditions com-
bined to lengthen the shadow and therefore the time of
the eclipse.

The eclipse occurred near the equator another
favorable condition. You see, the time of totality at
any one spot depends upon how long it takes the
shadow of the moon to pass over. Only as long as the
observer stands within the umbra does the sun appear
totally hidden. The shadow moves very swiftly,
actually about 2000 miles an hour. This motion comes
from the motion of the moon in space, but it is neces-
sary also to take into consideration the turning of the

[217]

Excursions in Science

earth upon its axis, for this moves the observer under
the moon's shadow. At the equator, the earth is
turning fastest close to 1000 miles an hour. And it
turns in the direction in which the shadow moves. This
means, you see, that a person at the equator will stay
with the eclipse longer because he will ride along with
it as the earth turns.

All these things, and many others, had to be known
before we set off for Peru. We knew, for instance, that
at Huanchaco, on the coast, the sun would be high,
that the moon's shadow would strike there first, and
that the sun should be hidden for 2 minutes and 33
seconds. (It was only out in the Pacific, near noon, that
the eclipse time was unusually long.)

Therefore Dr. Fisher, of the Planetarium, with Mrs.
Isabel M. Lewis, of the Naval Observatory, estab-
lished themselves at Haunchaco to photograph the
shadow of the moon as it first came in sight of land.
But at this place there was likely to be coastal fog, so it
seemed safer to scatter the members of the party.
Therefore, a little farther south, nearer the center line
of the eclipse and over 2000 feet in the mountains
above the coastal fog, there were other members of
our expedition: Dana K. Bailey, of Steward Observa-
tory, and Dr. Serge Korff, of the Carnegie Institute of
Terrestrial Magnetism. They had two telescopic

[218]

Chasing the Moon's Shadow

cameras and a polar axis. The axis, with the aid of a
driving clock, could turn the cameras backward as
fast as the earth moved forward. This made it possible
to keep the sun always in the telescope's view during
these 3 % minutes of totality. Such a pair of cameras,
too, was at another mountain station farther to the
south, under the direction of Mr. William H. Barton,
Associate Curator of the Planetarium. There, at Cerro
de Pasco, we were stationed 14,600 feet above the sea.
At this location the sun was hidden for 143 seconds
less than 2^ minutes. In Dr. KorfPs station, near the
center of the path and many miles closer to the noon
position, the eclipse's shadow took longer to pass than
at our station longer too than for Dr. Fisher, for he
was toward the north edge of the path of totality, where
the diameter of the shadow was very small and its
movement swift. Our station at Cerro was south of the
central line and near the other edge of the shadow. It
was moving rapidly here too, at sundown, almost
ready to taper off the curved surface of the earth into
empty space.

Somewhere between the Bailey-Korff station and
Cerro was the broadcasting location, where Raymond
Newby, of Columbia Broadcasting, had set up his
equipment in the mountains. And then, 25,000 feet
above the sea was Major Albert W. Stevens, of the

[219]

Excursions in Science

U. S. Army Air Corps, in a Pan-American plane, to
guarantee success in case of the failure of weather
conditions at all the land stations.

To all these stations equipment had to be carried. It
made a formidable list:

4 telescopic cameras
2 polar axes

2 driving clocks

2 small telescopes

3 chronometers

1 Fairchild air camera
7 motion-picture cameras

5 still cameras

Then there were two portable dark rooms, surveyor's
transits, artist's canvas, observers' binoculars, and the
complete broadcasting equipment. So, by four o'clock
on the afternoon of June 8, the eclipse just didn't have
a chance to escape us! There were 12 official watchers
and an equal number of eager assistants.

At the Bailey-Korff station, five exposures were
made with the 90-inch telescope, and six exposures
with the 72-inch camera. One picture of totality on
Kodachrome was made in the 72-inch camera, and an
unusual color photograph of the scene of totality by
Mr. Bailey with his small camera.

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Chasing the Moon's Shadow

Off at the seacoast, Dr. Fisher made continuous
motion pictures, showing not only the total eclipse
and the corona around the sun, but also the beautiful
"diamond-ring" effect at beginning and end. And up
in the mountains at Cerro de Pasco, eight exposures
were made in each of the two big cameras. One of the
long-exposure photographs at Cerro made by Mr.
Barton shows tremendous extension of the coronal
streamers and excellent detail in the inner corona.
Motion pictures by Charles Coles show the progress of
the eclipse, and a series of paintings by the artist D.
Owen Stephens depicts the marvelous beauty of the
scene with unusual accuracy.

From his 5-mile-high station in the plane, Major
Stevens made pictures of the eclipse which have
proved of great interest. In the clear air of the upper
atmosphere it was possible to get unusual definition of
the corona. On his pictures appears a uniform sphere
of light about the sun that seems independent of the
streamers that we have always associated with the
sun's upper atmosphere. Investigation has verified, to
the satisfaction of many, that this so-called Globular
Corona is a real and definite characteristic form of the
corona that had not been successfully photographed or
investigated before. There are others, however, who
feel that more eclipses must be studied before the

[221]

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globular sphere can be recognized as a physical entity.

And so, as you can see, everyone had plenty to do
and had to work fast when the actual time for the
eclipse arrived. And although, as Dr. Fisher often
says, we didn't put all our eggs in one basket,
but carried on various activities in five different loca-
tions, the remarkable thing was that every station
had a perfect view of the eclipse !

Exciting as it is to prepare for an eclipse, to get
the equipment ready, and to make the observations,
there's really nothing that I can think of that is quite
as remarkable as actually watching a total eclipse.

There you stand, with no sign that anything unusual
is going to happen. The sun rises as on any other day.
It climbs the sky from east to west; clouds may scud
across the heavens; life goes on as usual. Then, all of a
sudden, at the very second that the astronomers
predicted, a black spot appears on the edge of the sun.
As you watch, it creeps over the face of the sun and
you realize that the invisible moon is becoming visible
as it hides the sun.

Overhead the sky grows a bit darker; the landscape
takes on a leaden hue; a breeze springs up from no-
where; the temperature drops, and you draw your
coat about you. Off around the horizon the colors of
sunset climb into the sky yellow and rose and salmon

[222]

Chasing the Moon's Shadow

pink. Overhead darkness seems to be falling, and out
there the sun has almost disappeared. Finally, but a
thin crescent remains.

Then, as the last bit of sunlight disappears, there is
a brilliant flash. One small point of sunlight swells to a
great brilliant spot, and all around the dark edge of
the moon flashes forth a ring of light. It looks like a
golden circlet set with a giant diamond solitaire. Then
the diamond breaks into tiny chips and disappears,
while out beyond the golden ring delicate streamers
flash a million and a half miles into space.

Totality is here; the moon has completely hidden the
everyday sun. But visible now is that wonderful,
mysterious, unknown sun that is usually hidden in the
brightness of day. It is actually the sun's upper atmos-
phere thin gases that extend millions of miles, un-
known gases that are seen so seldom, studied at such
infrequent intervals, that they still puzzle modern
scientists. Some would call them "coronium" and
admit them to be unknown materials in the sun's
corona. Others would label them "known gases
existing under unknown conditions," and say they are
oxygen and nitrogen and familiar terrestrial materials
that exist on the sun under entirely different conditions.

We at Cerro had 143 seconds in which to watch this
gorgeous sight. Into the pearly streamers of the corona

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licked rose-red flames of the prominences 50,000
miles. Really these were jets of hydrogen, helium, and
calcium gases thrown off from the spots upon the sun's
face. Appearing first on the eastern edge of the moon's
disk, they blinked from view as the moon passed on,
and then emerged upon the western rim and seemed to
climb high into the corona as the passing moon left
more and more of them in view.

And it was like night. Out in the dark sky Mars
could be seen, and some of the fainter stars. All over
the land darkness seemed to have fallen. The green
hills had become purple, the sparkling lake dun-
colored, the distant snowcapped peaks violet, and all
about the horizon were the colors of the sunset or the
dawn. It actually was both, for night had fallen in the
midst of day.

But with the passing of the moon, a~"diamond ring"
flashed forth; shadow bands scudded through the air;
crescent images appeared on the ground; and the
whole landscape seemed bathed in the golden light of a
mysterious and sudden day. Off in the distance the
dark shadow of the moon retreated, sloping now at
sundown, soon to slant off into the emptiness of space
and leave no record of its passing except in the mind's
eye of the fortunate observer, and on the silver coating
of the photographic plate.

[224]

HOW YOUR RADIO TUBES WORK

by ELMER D. MCARTHUR

R. MCARTHUR, a native of Salamanca, New York, took his
degree in Electrical Engineering at Union College. In 1925
he entered the Research Laboratory of the General Electric Com-
pany, and since 1 930 he has been a member of the Vacuum Tube
Engineering Department of that Company. He is the author of
Electronics and Electron Tubes, published by John Wiley & Sons in
1936.

THE high- vacuum tube's sole object in life is to con-
trol the flow of electricity through other pieces of
electrical apparatus. That sounds simpler than it really
is. It must be able to vary the flow of electricity in the
circuit to which it is connected, smoothly, from zero to
a fairly large value. The changes may be very small or
very large, but in any event the tube must be capable
of causing these variations almost instantly, with a
minimum loss of power, and it must perform in exactly
the same way every time it is used. In addition, the
tube must perform its job under the guiding influence
of another electrical circuit; that is, it must be an
electrical device which, itself, is controlled electrically.

[225]

Excursions in Science

When we speak of a current of electricity in a wire
we actually mean the flow of electrons through the
wire. Now, we know something about the behavior and
properties of electrons, but we know nothing about the
material from which they are made. We call it elec-
tricity. The flow of huge numbers of electrons, each
carrying the same small quantity of electricity, makes
up the electric current. Such a current will flow in a
continuous metal wire connected to the poles of a
battery. As long as the circuit is closed and the
battery supplies pressure (which in electrical terms is
called voltage or potential), the current will flow. It
may be stopped by cutting the wire, just as you turn off
your electric lights or your radio by opening the
switch, and this leads us to the fundamental discovery
from which grew the high-vacuum tube.

Why does opening the metallic circuit stop the flow
of current? Is it because the intervening air is imper-
vious to electricity? No, it is because the electrons can-
not leave the metal to jump the open gap except under
special conditions. One of these conditions was dis-
covered by Edison while he was experimenting with
an electric lamp having the ordinary hot filament and
an additional metal plate near the filament. He found
that when the filament was cold he could connect a
battery between the filament and the cold plate and

[226]

How Your Radio Tubes Work

have no current flow. This result was expected. How-
ever, he discovered that current did flow around the
circuit and through the more-or-less empty space
between the filament and the plate as long as the fila-
ment was heated to a high temperature. Furthermore,
he found that the current flow took place only when
the cold plate was connected to the positive pole of the
battery.

This phenomenon, which was called the "Edison
effect," long lacked both explanation and applica-
tion. It did show clearly that vacuum lamps, or bulbs,
could be made to conduct electricity in one direction
only could be made one-way traffic highways for
electrons.

In the years that followed, a number of distinguished
scientists men like Richardson, Dushman, Langmuir,
Reimann, and Becker studied this effect and explained
it. Today a good deal is known about the emission of
electrons from hot metal surfaces, although the studies
still continue in many laboratories to discover better
materials as sources of electrons.

In the huge high-vacuum tubes that supply the
power for a broadcast transmitter, the cathode which
is the name given to the electrode from which the
electrons leave is made of strands of pure tungsten
wire heated to a temperature of about 4000 Fahren-

[227]

Excursions in Science

heit. Look at one of the tubes in your radio set. The
glowing rod in the center is the cathode. It is a thin
nickel cylinder coated on the outside with oxides of
barium and strontium, and heated from within
by a tiny heater. In addition to these two types of
cathodes, there are several others better suited for other
special types of tubes.

One of the first applications of the Edison effect was
made by Fleming, who built small tubes each con-
taining a hot filament and a nearby cold plate or
anode. This early vacuum tube, called the "Fleming
valve," was used by Fleming to receive radio signals.
The radio signals brought to your receiver from your
antenna are minute high-frequency alternating cur-
rents. We call such a current alternating because it
first flows in one direction through the circuit and then
reverses and flows the other way. This high-frequency
alternating current makes the transmission of messages
without wires possible, but it cannot be used without
modification to operate a telephone receiver or a
loud-speaker. It must first be changed into a pulsating
direct current or, as we say, it must be rectified.
Fleming recognized in the Edison effect the ideal
rectifier for high-frequency currents.

This becomes clearer when we remember that the
electrons can leave the hot filament and flow to the

[228]

How Your Radio Tubes Work

plate, but current flow in the reverse direction cannot
occur; that is, electrons cannot leave the plate and
flow to the filament.

Fleming's valves therefore produced just the right
effect. The alternating-current radio signal flowing
into the tube was changed to a current flowing in only
one direction because the tube offered a closed circuit
to current in one direction and an open circuit to
current in the other direction. The ability of vacuum
tubes to rectify an alternating current is not confined
to radio signals. It can be used with very low-frequency
alternating currents. In your radio receiver one of the
vacuum tubes converts alternating current from your
home power lines into the direct current needed by the
set. In many of the receivers there is another small two-
electrode high-vacuum tube performing essentially
the same function as did the original Fleming valve.

So far we have seen how the electron current can be
made to leave the hot filament. The question naturally
arises as to what happens to the electrons, once they
are free of the metal boundary. As I have pointed out,
they flow across the empty space to the plate or anode
and continue their journey around the circuit. They
must have a reason for going to the anode, and this
reason was supplied by the battery which Edison

[ 229 ]

Excursions in Science

connected between the plate and the filament in his
lamp.

When two separate pieces of metal are connected to
the poles of a battery, electrons are pushed into one
plate by the battery and drawn out of the other plate.
Therefore, one plate has an excess number of electrons
and the other plate a deficit. The plate having an
excess of electrons is therefore charged to a negative
potential, and the other plate carries an equal positive
charge. That is the condition which exists at every
open circuit as long as none of the excess electrons can
escape. There is no steady current flow in the system
merely a static unbalance of the total number of
electrons.

But there is a field of force between the two plates,
called the electric field. It is the result of the attrac-
tive force between the two plates carrying charges of
opposite polarity. If electrons were liberated from the
plate having an excess, they would fall to the other
plate through this electric field in much the same way
that a released object falls to earth through the
gravitational field of the earth. We have no control
over the gravitational field, but the electric field be-
tween the two plates can be changed at will. It depends
primarily upon the distance between the plates and
upon the battery voltage. Higher battery voltages pack

[230]

How Your Radio Tubes Work

more electrons into one plate at the expense of the
other and so cause a larger attractive force between
the two plates.

Suppose, now, a battery is connected to the filament
and the plate in such a way that it charges the plate
positive by driving excess electrons into the filament.
When the filament is hot, many of these electrons leave
the filament and fall through the electric field to the
plate. Ordinarily, not all of the electrons can leave.
Only as many leave as can be drawn across by the
electric field. This observation continued to be a puzzle
until Langmuir pointed out that the electrons flowing
through the empty space partially destroy the electric
field, and that the flow of electrons away from the
filament always adjusts itself to the amount required
to reduce the field near the surface of the filament to
zero. With this concept, it was but a short step to the
formal statement of the law that governs the current
flow between two electrodes. This law, called the
space-charge law, states that for every value of electric
field applied between the filament and the plate there
will be a definite current of electricity.

This work also pointed out one of the needs for the
high vacuum. The air, as we know, is made up of tiny
molecules of several gases. These gas molecules and
atoms, although they are very small, are huge com-

[231]

Excursions in Science

pared with the much smaller electrons. If this gas were
allowed to remain in the space between filament and
plate, the electrons would have no chance of following
a direct path to the plate. It would be like a hunter
trying to shoot through a dense forest without hitting
the trees. To provide an uninterrupted path, the air
must be pumped out. Not all the air is removed, but
enough to reduce the air pressure within the tube to
about one-billionth of atmospheric pressure.

The other reason for the high vacuum is of course
that, like a lamp, the hot filament would burn out in a
few seconds if the oxygen were not removed.

Now we have seen that the electric field can be
varied either by changing the distance between the
electrodes or by changing the applied voltage. The
greatest improvement in the old Fleming valve came
from the realization that the electric field, and there-
fore the current flow, can be controlled also by voltage
applied to other electrodes either in or near the space
between the filament and the plate.

This idea gave birth to the modern high-vacuum
amplifier tube. The additional electrode is a mesh of
fine wires which completely surrounds the filament.
Thifc electrode is called the grid. In your receiving
tubes the voltage applied between this grid and the

[232]

How Your Radio Tubes Work

filament controls the attractive force exerted by the
anode.

Because it can modify the electric field, the grid can
control the electron current that flows from the fila-
ment through the open spaces in the grid to the anode.
Furthermore, the voltage on the grid has a much larger
effect on the amount of current flow than an equal
voltage on the plate. In other words, a small voltage
applied between the filament and the grid will produce
the same effect on the plate current as a much larger
voltage applied between the filament and the plate.
It is this property that permits the use of the tube as an
amplifier.

In your radio set, the tiny alternating current picked
up from the broadcast station is applied between the
grid and the filament of one of the tubes. It causes a
much larger variation in the current flow from the
filament to the plate, and a correspondingly larger
voltage in the electrical circuit connected to the plate.
We say the signal has been amplified. Perhaps it is still
too small. If so, it may be amplified again and again
until finally, modified and amplified, it is fed to the
loud-speaker and brings you your radio program.

[233]

THE MACHINERY OF HEREDITY

by DR. CARYL P. RASKINS

R. HASKINS, a native of Schenectady, did his undergraduate
work at Yale University and received his Doctor of Philos-
ophy degree from Harvard University. He has been a member of
the General Electric Research Laboratory staff, and a Research
Associate at both Harvard and Massachusetts Institute of Tech-
nology. He now holds the post of Research Professor at Union
College, and he is Director of the Haskins Laboratories, established
in 1936. He is the author of the book Of Ants and Men,
published by Prentice-Hall, Inc., in 1939.

THE phenomenon of inheritance is one which, from
very ancient times, has captivated the imagination
of men. Both because of its important practical applica-
tions to the welfare of the human race and its more
fascinating theoretical implications, it has received a
vast amount of reasonably disorganized investigative
effort over a very long period of time. Very primitive
man may ruin his potential crop wealth by selecting
for generations from his poorest available stock, as
does the Indian of the inter-Andean valleys when he
habitually eats his best potato tubers, year after

[234]

The Machinery of Heredity

year, and reserves for planting only those not fit for
consumption.

But man needs only to have reached a very low
stage of civilization to realize what the principles of
heredity, in general, mean to him. He needs but to be
an Arab of an ancient nomadic group to preserve the
pedigrees of his horses with meticulous care, or to be an
Egyptian to guard jealously his best strains of wheat.
At a more primitive stage than this he will preserve his
own lineage with care if it be of the stock of leadership,
fully convinced that, if his parents were of the caliber
of kings, he too should qualify.

Vaguely and dimly, then, over an immense period of
time, mankind has recognized and crudely used some
principles of heredity. But progress in unfolding the
details of the picture has been tremendously slow, for
the problems involved are difficult ones, and their
solution, or even the recognition of their existence, had
to wait upon the development of suitable concepts and
suitable tools. It seems possible that we stand today
upon, or near, the threshold of a fuller knowledge of the
processes of heredity than we have ever before.

Human characteristics, mental as well as physical,
follow very definite courses in their transmission from
one generation to another. Some of these courses are
very simple, and are empirically, although not analyt-

[235]

Excursions in Science

ically, well understood. Such things as color blindness,
hemophilia, blondness, eye color, and hereditary
feeble-mindedness follow simple and well-defined
channels of inheritance, while stature and various
other physical features and a number of mental talents
are blended in a fashion not wholly understood.

Again, the manner of inheritance of physical features
of size, weight, and configuration in animals and plants
is vitally important to the stockbreeder or the agri-
culturist, and through him to the public at large. The
breeder's ability to eliminate undesirable character-
istics and to encourage desirable ones in the plants and
animals with which he deals will be entirely dependent
upon his knowledge of heredity in them. Other vital
questions, of broader scope but less direct practical
application, can be answered only out of a fuller
knowledge of the nature of inheritance, of the chro-
mosome, which apparently carries the hereditary
material, and of the gene, which is thought to be the
underlying unit of a single inherited character. The
entire picture of the processes of organic evolution,
with the resulting splendor and variety of the life of
our earth, and of the fundamental nature of living
matter itself, can never be achieved without a knowl-
edge of the structure of the gene. And it is entirely
possible that in the constitution of the gene, if it ever

[236]

The Machinery of Heredity

be thoroughly known, may be found the make-up of
living matter.

For many years inheritance was thought of as a very
stable thing. Characters might assort in different ways
from parent to offspring, but they reappeared in
essentially unchanged form, even if in different com-
binations. It was known that very rarely so-called
mutations appeared individuals that differed strik-
ingly, and in no accountable fashion, from their
predecessors, and whose own unusual features were
transmitted to succeeding generations, thus setting
up a new race. Discoveries of such mutations were
attended with the greatest interest. Occasionally they
were useful, but they were uncontrollable and un-
predictable, and in number far too few to constitute
other than scientific curiosities.

It was therefore of the highest importance for genetic
theory when it was found, very shortly after the dis-
covery of X rays by Roentgen in 1895, that, by ir-
radiating the cells of plants and animals, such changes
could be brought about within them that mutations,
long regarded as rare and isolated phenomena, could
be artificially produced in a number and variety
previously undreamed of. After considerable pre-
liminary work, which occupied the opening years of
the present century, the new power has been put to

[237]

Excursions in Science

good and striking use. Experiments with X-rayed
tobacco seedlings, undertaken by Goodspeed and
others in 1928, disclosed in a total population of 168
plants, 136 to be of wholly new types, with inheritable
characteristics. Dwarf, low, and tall varieties appeared;
varieties with large leaves or small leaves; those with
dark bottle-green leaves or light gray-green leaves,
with tough leaves or tender leaves, with light-pink,
pink, or purple-red flowers. The variations in the
flavor of the leaves must have been similarly wide, but
it was too soon to test for this. Mosaic corn, white
barley plants, barley "vines," tobaccos nine times the
height of the normals, a cotton in which the seed is free
of the lint, and potato tubers in which the normal
period of dormancy has been broken, modifications in
color and form of lilies, petunias, delphiniums, and
many other flowers have all resulted from the numer-
ous experiments in which X-ray genetics have been
applied to agronomy. This, however, is but a beginning.
In the X-ray tube we have a single agent which,
used in apparently the same way, or with only small
perceptible differences of operation in different cases,
can profoundly modify the course of life treated with it,
stimulating it to increased productivity, deforming it,
destroying it after a delayed interval, or blasting it
instantly to death. How is it that such opposite results

[238]

The Machinery of Heredity

can be produced under similar conditions? Is there any
way of segregating the good results from the bad and
applying them in the service of humanity? What
would be the financial benefits accruing from such a
development?

The first two of these questions are extraordinarily
difficult ones and have not been answered satis-
factorily today, but the understanding of the remark-
able phenomena involved has become far more
complete of recent years, and the near future may
possibly witness much further progress. To appreciate
and evaluate the phenomena involved, it is necessary
to consider what happens when a single cell, and
especially the chromosomes and genes within it,
encounters the shattering force of the X-ray beam and
the electrons that it releases.

There is much evidence to indicate that, when the
cells of an organism have been caused to mutate by an
X-ray beam, or by other electromagnetic radiation of
high quantum energy, the actual genetic changes have
been brought about by the absorption in, or passage
through, a genie locus of one or more electrons of the
photo or recoil types. Very similar genetic changes can
be induced by direct beams of electrons, or by particu-
late emanations from radioactive materials. Very
recently it has been found that showers of neutrons

[239]

Excursions in Science

apparently chargeless particles of enormous penetrat-
ing power in most materials can bring about similar
effects. But beyond this strong suspicion, our knowl-
edge completely ends, and the questions that crowd
upon one another from the darkness are almost endless
and nearly all vitally important.

What is the size of a gene? What sort of change is
represented when a gene is mutated? Do all mutations
require the same amount of energy, or can we select
among them by the quantity of energy we apply, or' in
the way in which we apply it? What is the highest
frequency with which we can cause a single gene to
mutate, and why? Why have the genes heretofore been
so enormously stable in the face of most modifying
agents outside of radiations? Are natural mutations,
which occur far too numerously, relatively, to be
accounted for by natural ionizing radiation entirely,
different from those that we produce in the laboratory?
If we could alter the rate or character of mutational
response in large groups of organisms, would we not
modify in large measure the course of life on our
earth? And then come the finer questions of detail
and procedure, pressing on the heels of the more gen-
eral ones. The list of things we want to know is ap-
parently endless.

[240]

The Machinery of Heredity

These are all questions of grave difficulty, yet they
are those which the biophysicist of today and tomorrow
must solve; and great power over forces of nature
forces that at present are but haphazard and uncon-
trolled phenomena awaits their correct solution.
Slowly and painfully, yet steadily, a beginning is
being made.

We have been engaged, for instance, in an at-
tempted determination of the physical size of a given
gene the gene for the well-known character for white
eyes in the fruit fly using a method first fully evolved
at the Institut Curie several years ago. It postulates
that, if one shoots at the bull's-eye of a target with a
machine gun and knows the distribution of his hits and
the number of bullets that he fires on the target for
each time that he reaches the center, then the size of
that center can be calculated. Such a method tells us
that this gene is about the size of a molecule of insulin
specifically, that it has a radius, if we wish to con-
sider it a sphere, of four ten-millionths of a centimeter.
This is not an unreasonable answer, and may be a
useful one. We have gone on, in the same manner, to
attempt to determine whether this gene is modified in
the same fashion under the same conditions at widely
separated temperatures.

[241]

Excursions in Science

In another series of experiments we are using neu-
trons in place of X rays to check the effect of varying
distribution of ions; and, in still another, streams of
cathode rays to obtain a wide range of electron densi-
ties at dosages where time may be varied so as to
maintain the total energy input constant. With the
same tool, intracellular volumes other than genes can
be investigated, and we have become interested in
probing the molecular complex that gives to the
nitrogen-fixing bacterium its marvelous power to
obtain from the air, at room temperatures and pres-
sures, the gas that man can fix in available form only at
the expense of tremendous energy. Here, too, belong
investigations of the nature of the complex of chloro-
phyll molecules that operate in manufacturing, from
carbon dioxide and water and with sunlight for
energy source, the sugars upon which we as a race
wholly depend, by processes which at present we can-
not satisfactorily duplicate.

Endless problems await the hand of the well-
trained biophysicist and, especially, the X-ray gene-
ticist. We have spoken of the practical work that he can
do in the induction of new varieties of plants, and
possibly of animals, in agriculture and stockbreeding
work. We have touched on the powerful tools that he
may evolve for the solution of such important theore-

[242]

The Machinery of Heredity

tical questions as the nature of heredity in man, the
nature of organic evolution, and possibly the structure
of life itself.

Succeeding years may well see us more and more
dependent upon the minute forms of plant life upon
the yeasts for our nourishment, upon certain bacteria
as aids to us in the manufacture of such chemicals as
organic acids, alcohols, esters, celluloses, sugars, and
resins. It will see us waging an ever-increasingly bitter
attack upon the bacteria and protozoa that threaten
our lives the tubercle bacillus in its coating of lipoid
material, the hemolytic typhus organism with its
resistance to antitoxin, the conjugated diphtheria
bacterium, the hosts of obscure protozoan fevers
that contest the advance of the white man into the
tropics. Little is known of mutation or heredity in the
bacteria, but some very amazing phenomena ap-
parently stand half revealed. Essentially, nothing is
known of mutation in them under ionizing radiations.
And herein lies a field, ready at hand for exploitation,
which is filled with the richest rewards for the first
comer, which is new enough so that the veriest layman
may feel that his chance of contribution is nearly as
great as that of the veteran in the field, and the scope
of which is wide enough so that, in our present
ignorance, we cannot delimit its boundaries.

[243]

FLUORESCENCE AND
PHOSPHORESCENCE

by DR. GORTON R. FONDA

the close of the sixteenth century, in Bologna
that ancient city in northern Italy famous for
its sausage there lived a certain shoemaker. He made
money at his trade, and then spent it in the study and
practice of alchemy. Nowadays we look rather patron-
izingly on the alchemists as deluded souls, forever
trying to convert common metals into gold. But we
tend to forget that alchemy was an important stage in
the growth of chemistry, and that the alchemists did
much to advance the knowledge and practice of that
science.

Even this humble shoemaker alchemist made a
notable discovery. In the course of his laboratory
experiments he found that a certain mineral, which he
had picked up on the hills nearby, continued to shine
brightly in the dark after previous exposure to light.
Actually, this mineral was heavy spar, a barium
sulphide. This was the first time that the phenomenon
we now call fluorescence had come to anyone's attention.
Other scientists of the age were greatly excited by the
discovery, and called the mineral Bologna stone.

[244]

Fluorescence and Phosphorescence

Its fame started further studies. It was soon found
that the fluorescent light excited from this stone had
always the same color, regardless of the color of light
used for its illumination a notable observation that
has since been found to hold fairly well for all classes
of fluorescence. Then other substances were found that
behaved similarly, not only minerals but also organic
materials, such as the tincture of certain woods and
leaves, and finally, solutions of the artificial dyes.
Nevertheless, the accumulation of a definite and com-
plete knowledge of the formation and behavior of
fluorescence was slow.

For instance, it was not until about 1840 that Sir
John Herschel noted the shimmer of blue fluorescence
from a solution of quinine sulphate when it was held in
the path of a strong beam of light, and then observed
that the beam of light, after passage through the solu-
tion, was unable to provoke the blue light in a second
solution held in its path. This was a clear demonstra-
tion that fluorescence is produced by light of one
definite color, or, as we say, wave length. When that
constituent color is removed from a beam of light, as
was done by absorbing it in the first solution of quinine
sulphate, then that which remains is unable to bring
about any further fluorescence, although we still
perceive it as a beam of light. It was not until 1852,

[245]

Excursions in Science

however, that this was fully appreciated, and a com-
plete statement was given of the nature of fluorescence
by the English scientist. Stokes. It was he, by the way,
who gave the phenomenon its present name of
fluorescence, in honor of fluorspar, a mineral which
had been found to exhibit it.

When a beam of light is passed through a prism, it
is broken up into the spectral colors, ranging from red
to violet. Extending down into wave lengths shorter
than the violet there is radiation, invisible to the eye,
but nevertheless very real. It is this that gives us sun-
burn and germicidal action radiation appropriately
called the ultraviolet, because it lies beyond the violet.

Now the color of a substance is due to the fact that
it absorbs certain of these spectral colors. The portion
that it does not absorb is passed on to the eye and per-
ceived as the color by which we call it. Stokes found
that fluorescence could be excited only by light whose
color, or wave length, was such that it might be
absorbed by the fluorescent substance. He found also,
and it has become known as Stokes' Law, that the
color of the fluorescent light given off is, in general,
of longer wave length than the color of the light that
excites the fluorescence. Take as an example the dye,
rhodamine. Its solution exhibits a brilliant red color,
and it has a strong absorption for green and yellow

[246]

Fluorescence and Phosphorescence

light. Now, examine a solution of rhodamine under
green light; the solution appears a more brilliant red
than ever. Experience will tell you that not every red
solution does this. Try a bottle of red ink, which like-
wise absorbs the green and yellow. Placed under green
light, it appears black. All of the green is absorbed by
it, and since it does not fluoresce, no light whatever
can be given off from it.

Not all fluorescent substances are excited by light
whose wave length is so close to their fluorescent color.
Take, for instance, the natural minerals willemitc,
which is a zinc silicate, and calcite, a calcium car-
bonate. Both are white in color. That means that they
absorb no light in the visible range of the spectrum.
Will they, therefore, show no fluorescence? Well, it is
true that they will show none under any of the spectral
colors ranging from red to violet. But we must not
overlook the ultraviolet. And they do have an absorp-
tion for radiation in the ultraviolet. When exposed,
therefore, to light from a quartz mercury lamp, their
fluorescence flashes out in colors of startling brilliance
green for willemite and red for calcite. Not all
samples of willemite and calcite are fluorescent, nor
are they the only minerals that fluoresce. There are
many others, each yielding fluorescence of a different
color. It makes a fascinating chase, getting out into the

[247]

Excursions in Science

hills, searching out minerals, identifying them, and
then trying them out to see if they develop fluorescence.

Before we describe any further experiments, some-
thing should be said about how fluorescence occurs.
Why is it that a substance should give off a colored
light when illumined with light of a different color?
An explanation is at hand the moment one considers
what can be called the atomic structure of the sub-
stance, and then goes even deeper and examines the
structure of the atom itself.

Suppose we are examining an office building. Seeing
it first from a distance, our earliest impression is of its
over-all shape, which was determined by the design of
the architect. Similarly, a mineral sample at first glance
is nothing but an object with a shape determined by
the hammer blows that chipped it out. Closer examina-
tion brings out details in both cases. When we enter
the building, we find it divided into square rooms
about the same shape and size as those in every other
office building, regardless of the exterior shape of the
building, whether narrow and high or broad and long.
Just so with the mineral. The X ray allows us to inspect
its interior, and it reveals a regular pattern of com-
partments, just as regularly laid out as the rooms in
a building. Each one of these compartments con-
stitutes an atom.

[248]

Fluorescence and Phosphorescence

But the analogy goes even further. Each room of the
building has people moving about in it, all actively
engaged under the direction of an individual who
remains always comfortably disposed in a large chair,
quiet and dignified the boss. Each of these people has
a desk, which represents his headquarters; but occa-
sionally the orders that he receives require him to get
up and move somewhere else, perhaps to go to one of
the wall cases to file a letter. An identical situation
holds within the compartment occupied by the atom;
for still closer scrutiny shows that the atom is made up
of many individual units. Some of them, called
electrons, are very active, constantly in motion. Like
the workers in the office, they seem to be arranged in
some orderly style about another unit, just as quiet and
reposeful as the boss, called the nucleus. In addition to
the normal activity of the electrons, as they arc engaged
at their desks, so to speak, some one of them will
occasionally receive a message and, in response to it,
move away that is, go off to the walls.

Now it is this movement that is important for the
development of fluorescence. It denotes what is known
as excitation of the atom. It occurs in one of two ways:
either in an electric discharge, where the atom receives
an impulse from a free electron carrying an electric
current and passes it on to one of its constituent

[249]

Excursions in Science

electrons; or else by absorption of an appropriate beam
of light, which can convey a similar impulse. In each
of these ways the atom can be excited and an electron
ejected. In each of these ways external energy is
brought to bear on the atom the force of a blow from
an electron or the force of a blow from a beam of
light. And in each case enough of this energy is trans-
ferred to an electron to hurl it out from its normal
position to an outer one.

The next step is readily anticipated. When the
electron bounces back to its normal position, like a
ball on a rubber string, the energy received from the
blow is given up. When this energy is thus released, it
can reappear in two ways, as heat or as light.

If the substance is a gas, virtually all of the energy
reappears as light, and in the simplest case this fluo-
rescent light is of the same wave length or color as that
of the exciting light. But in a solid the case is different.
There are thousands of times as many atoms in any
given volume of a solid as in the same volume of a gas.
As a consequence of this crowded condition, there are
thousands of times as many collisions or bumps be-
tween atoms in any given period of time. Collisions be-
tween excited atoms lead to a loss of their stored-up
energy, so that some of it is converted into heat before
it can be reemitted as light. Because of this loss, the

[250]

Fluorescence and Phosphorescence

fluorescent light is of lower energy content, so that it
reappears in longer wave lengths than characterized
the exciting light. In other words, it is displaced toward
the red end of the spectrum.

Now we can come back to our organic dye, rhoda*
mine. If a solution is made of it and exposed to green or
yellow light, a strong red fluorescence appears. There
is just one requirement that the solution be extremely
dilute. As it becomes more concentrated, the intensity
of fluorescence falls off, finally decreasing to a mere
trace in a concentrated solution. Solid rhodamine
itself shows no fluorescence whatever. Why? Because
under increasing concentration, molecules of rhoda-
mine are thrown closer and closer together until finally
an excited molecule loses all of its energy by bumps
with its neighbors and has none left to emit as light.

A similar behavior is shown by the minerals. Some
outstanding examples are zinc silicate and the sulphides
of calcium, barium, and strontium, as well as of zinc.
The common feature in all of these is the absence of
fluorescence in the pure salt. They become luminescent
only after fusion with some other metal, called an
activator. The amount of this activator must be
extremely small. Above 2 per cent, the fluorescence is
lowered, and when the concentration becomes too

[251]

Excursions in Science

high, the fluorescence no longer appears at all. An-
other case of too great concentration.

With some fluorescent salts, particularly the sul-
phides, luminescence continues after the exciting light
has been removed. To this phenomenon is given the
name phosphorescence. The electrons, which had been
thrown out from their normal paths during excitation,
give rise to fluorescence, as we have seen, when they
return to their normal positions. In this case, however,
their return has very evidently been delayed. There is
such complexity within the molecule that the return
of the electron becomes a highly involved process.

One can make these fluorescent minerals artificially.
Silicates are the easiest, and anyone with a little
laboratory equipment can try it. Take about equal
parts of pure zinc oxide and silica, add about 1 per
cent of manganese oxide, mix thoroughly by grinding,
and then fire in a porcelain crucible at 1000 centi-
grade or higher for an hour or longer. Put a cover on
the crucible and wrap some asbestos around it to
retain the heat better. Then hunt up a friend who has
a quartz mercury lamp and find out how strong
luminescence you have been able to produce. Compare
your sample with natural willemite. You may have
improved on nature.

[252]

Fluorescence and Phosphorescence

So far, mention has been made only of the fluorescent
minerals and the fluorescent dyes. But fluorescence
is by no means confined to these. It is of frequent
occurrence among the products of nature. As a conse-
quence, it can be used as a means of analysis, in testing
for purity or for adulterants. Butter shows a color
different from that of margarine. Milk fluoresces, but
only while fresh. Cheese shows a range of colors that
vary as the ripening progresses. Lubricating oils
fluoresce, and the color is different for those that tend
to gum. Flour from different grains fluoresces differ-
ently. And here is an interesting test to distinguish
between false and true perennials of rye. Plant the
seed between moist filter papers so that it will ger-
minate. In a few days rootlets form, and the paper
absorbs from them some of their sap and acquires a
stain. Test this stain for fluorescence. All the false
perennials give a fluorescent stain, but the true do not.

Bacteria and fungi fluoresce, all of them differently.
But the mere fluorescence from them is sufficient
evidence of the extent of aging in meat and fish.

There is an interesting application of fluorescence
that has a romantic tinge, and at the same time it
opens possibilities for detecting alterations in legal
documents and bank checks. It has to do with
parchment.

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Excursions in Science

In Europe many centuries ago, parchment was
treasured as the only available medium on which
books could be written. A monk would do beautiful
work copying out a book carefully, word by word, on
parchment. But the next generation would consider his
product not so worthy of immortality as some new
book, freshly composed. So, because parchment was
scarce and expensive, the carefully written words of the
old book would be erased and a new book would be
written on the old parchment. Was the original book
then totally lost? Apparently, for no trace of it could be
seen by the unaided eye. But fortunately the ink had
left a colorless but fluorescent dye within the parch-
ment, and when photographs are taken under ultra-
violet, the film will often disclose the original as well as
the later writing.

[254]

A GAUGE THAT MEASURES
MILLIONTHS OF AN INCH

by DR. KATHARINE B. BLODGETT

T"\R. BLODGETT, a native of Schencctady, attended Bryn Mawr
and the University of Chicago. After some years as physicist
on the staff of the General Electric Research Laboratory, she
continued her studies in the Cavendish Laboratories of Cambridge
University, England, where she received the degree of Doctor of
Philosophy. She is now associated with Dr. Irving Langmuir, in
the General Electric Research Laboratory, studying the properties
of thin films.

THE scientist in a laboratory is always measuring
something. With his centimeter scale, his ther-
mometer, his stop watch, and his chemical balance he
is constantly measuring the quantities that control
the progress of his experiment. Often there arc a
dozen different quantities that must be measured in a
single experiment quantities such as weight, volume,
length, thickness, current, voltage, pressure, tempera-
ture, time, and many others. These measurements are
the set of keys by which the work of one scientist
becomes available to all scientists, for by means of
these measurements the experiments that are per-

[255]

Excursions in Science

formed in one laboratory can be reproduced accurately
by workers in other laboratories. Thus, new experi-
mental methods that are developed in Sweden, for
example, are promptly reproduced, tested, and utilized
by investigators in the laboratories of the United States,
Holland, Japan, and many other countries.

I want to describe a method that is used for measur-
ing thicknesses of a few millionths of an inch. Scientists
need to measure very thin films of various substances,
in order to understand the workings of many impor-
tant processes. For example, when oil is used to lubri-
cate two bearing surfaces, the question arises as to how
thick the coating of oil must be to prevent the surfaces
from seizing. Science has found that in the case of
bearings that are operated at low speed, the lubricant
need have a thickness of only one ten-millionth of an
inch in order to lubricate the surfaces perfectly. The
study of insulating materials, of photoelectric cells, of
films of oxide on metal surfaces, and of many other
problems is concerned with films that are too thin to
measure by means of ordinary instruments.

A good micrometer gauge measures accurately a
thickness of one one-thousandth of an inch. A very
good gauge can measure pne ten-thousandth of an
inch. But the problem of measuring one millionth of an
inch is entirely outside the range of micrometers.

[256]

A Gauge that Measures Millionths of an Inch

Fortunately, nature has provided an admirable
solution. Everyone knows that when a soap bubble is
blown until the wall of the bubble becomes very thin,
the bubble reflects light of many colors. These colors
are a special property of thin films. The colors seen in
the films of oil that cover the puddles in the street
after a rain are due to precisely the same optical prop-
erty of thin films as the colors of the soap bubble. If
you examine a film of oil spread on water, such as one
of the oil films spread on a wet pavement, you see that
the oil appears to be vividly colored in streaks and
circles of yellow, red, blue, and green, although you
know that before the oil spread out into a thin film it
was certainly not bright-colored. Probably, it was
crankcase oil that dripped from an automobile and its
color was brown or black.

The variety of colors reflected by the oil when it is
spread in a thin film is due to the fact that thin films
sort out colors in the sunlight in such a way that a film
of one thickness reflects yellow light, a greater thick-
ness red light, a still greater thickness blue light. That
is to say, the color is determined by the thickness of the
film. Therefore, the rings and streaks of color exhibited
by oil films on the pavement are in fact accurate con-
tour lines, and their pattern constitutes an exact con-
tour map of the film. The scale to which nature has

[257]

Excursions in Science

drawn this map for our observation is amazingly small.
For example, the thickness marked out by a red ring
differs from the thickness of the adjoining yellow ring
by only one millionth of an inch, yet an observer,
unless he is color blind, has not the slightest difficulty
in distinguishing the regions of different thickness.

The colors that are seen in thin films of oil and
other substances are called interference colors. They occur
for the following reason. When sunlight shines on the
oil, two rays of light are reflected by the oil film; one
ray is reflected from the upper surface of the film, and
the other ray penetrates the film and is reflected from
the under surface. The ray that travels the longer
distance that is, down through the oil and up again
therefore has to lag behind the ray reflected from the
upper surface, which travels the shorter distance.
When the thickness of the oil film is one-half wave
length of light, the amount of lag that occurs causes
the two rays to interfere with each other and produce
no light.

Rays of light are waves similar to radio waves. They
have many different wave lengths, and each color cor-
responds to a separate wave length. Therefore, when
the optical thickness of the film is one-half wave
length of blue light, the two blue rays reflected by the
film interfere with each other and the film reflects no

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A Gauge that Measures Millionths of an Inch

blue light at all. The action reminds one of the Ging-
ham Dog and the Calico Cat that ate each other up.
When all the blue light is removed from sunlight, the
remaining light is yellow, so a film that has an optical
thickness that is one-half wave length of blue light
appears yellow. By the same token, a film that has an
optical thickness that is one-half wave length of green
light appears red. And so on.

Violet and blue light have the shortest wave lengths
of all light that is visible to the human eye; therefore,
the thinnest films in which interference colors can be
seen have a yellow color. If you will examine the oil
films in the street, to which we have already referred,
you will find that the outermost ring is commonly a
faint straw yellow, the color sometimes fading out at
the edge to a region which has no color at all. In this
region the thickness of the film is much less than a half
wave length of any visible light.

The lengths of waves of light of different colors
have been carefully measured by scientists and are
known with very great accuracy. Light of the various
shades we call blue has wave lengths ranging from 17
to 19 millionths of an inch; green light, from 19 to 22
millionths of an inch; yellow light, from 22 to 24;
and red light, from 24 to 27 millionths of an inch.
Using these values of the wave length, you can know

[259]

Excursions in Science

the optical thickness of any region of a thin film by its
color.

The most fascinating entertainment can be had with
all sorts of colored oil films by a simple method. A tray
or a large pan is needed which can be filled with water
to the very brim. The rim of the pan should be waxed
with paraffin wax so that the water can stand in the
pan a little higher than the rim without running over
the edge. Two or three flat bars of metal or glass,
about half an inch wide and more than long enough to
reach across the pan, should also be coated with
paraffin. Place the pan on a table indoors, in front of a
window, and in a position in which the water in the
pan will reflect the sky but will not receive direct
sunlight. (The glare from direct sunlight reflected from
the water surface makes it almost impossible for anyone
to see the oil films. Also the colors of the oil will appear
far more vivid if the inside of the pan is black.) One of
the best types of oil to use for the films is old oil taken
from the crankcase of an automobile. New lubricating
oil commonly does not spread on water, but old oil
spreads very rapidly because of the oxidized substances
it contains.

After the pan has been filled with water to the brim,
scrape the surface of the water clean by placing one of
the waxed metal bars across the top of the pan from

[260]

A Gauge that Measures Millionths of an Inch

edge to edge and sliding the bar along from one end of
the pan to the other. Then place a very tiny drop of oil
on the water from the tip of a fine wire. The oil will
cover the surface with a film that is yellow, red, blue,
or green, depending on the thickness of the film. Alter
the thickness by sliding the bar along the pan and
watch the colors change. If the film is initially red and
you move the bar so as to allow the film to expand to a
larger area, the film becomes thinner and instantly
changes to yellow. If you compress the film, it changes
to blue. If you compress it still further, it turns to green
and then to yellow again. This second yellow film
has about the same appearance as the first yellow film
you obtained by expanding the film, but obviously it
has not the same thickness. It occurs for the reason that
the interference colors seen when the film thickness is
one-half wave length of light are repeated when the
thickness is increased to one wave length, and are
repeated again at three-halves wave length. They are
called the first-order, second-order, and third-order
interference colors.

One of the uses that science has for interference
colors is for the measurement of the thickness of films
of oxide on metals. When a bar of steel or copper is
heated in a flame, the surface of the metal turns to a
straw-yellow color, then purple, then a deep blue.

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Excursions in Science

These are interference colors, and by comparing these
colors with a standard color gauge one can know the
depth of the oxide film.

Science has a color gauge to use for this purpose. The
method of building the gauge was developed as a by-
product of a study of the structure and behavior of
certain types of molecules. When a small amount of
stearic acid is placed on water, the individual molecules
of which the stearic acid is composed endeavor to
attach themselves to the water surface, with the result
that the stearic acid spreads out over the water until
each molecule has a place on the surface. Stearic acid
in bulk is a white wax that looks rather like paraffin
wax, but when it spreads on water in a layer one
molecule deep the layer is so extremely thin that it is
entirely invisible. The stearic acid molecule is shaped
like a chain. It is made up of 18 carbon atoms forming
the links of the chain, plus 36 hydrogen atoms and 2
oxygen atoms attached to the links. The entire length
of this collection of 56 atoms is one ten-millionth
of an inch. When the molecules spread on water, only
one end of the chain attaches itself to the water, so that
as the molecules crowd together the chains are forced
into an upright position on the water surface. The
molecules thus form a layer that has a thickness of one
ten-millionth of an inch. By a dipping process the

[262]

A Gauge that Measures Millionths of an Inch

stearic acid can be transferred to a metal or glass sur-
face, one layer at a time, and the successive layers are
deposited on top of each other in such a way that a
film can be built having any desired number of layers.
This is the method that is used for building the color
gauge. On a piece of polished metal 3 inches long and
1 inch wide, films are built in a series of steps having
thicknesses of 21 layers, 41, 61, 81 layers, on up to 201
layers. Therefore, the steps have thicknesses of 2, 4, 6, 8
millionths of an inch, up to 20 millionths of an inch.
These steps appear as bands of bright interference
colors. Films of iron oxide or of other substances are
then matched in color to one of the steps of the gauge,
and by this means the thickness of the oxide film is
determined.

[263]

AN AMATEUR LOOKS AT
ARCHEOLOGY

by P. SCHUYLER MILLER

TV yf"R. MILLER was born in Troy, New York, and was graduated
from Union College, where he later took a graduate degree
in chemistry. He has been Laboratory Assistant in the Department
of Psychology of Union College and, since 1934, has been con-
nected with public education activities in Schenectady, where he. is
now Adult Education Secretary, Schenectady Department of
Public Instruction. He is an Affiliate of the Society for American
Archeology and is Secretary-treasurer of the Van Epps-Hartley
Chapter, New York State Archeological Association.

A SHORT time ago I had the doubtful pleasure of see-
ing Harold Lloyd, in a moving picture, give a
hilarious impersonation of an archeologist in full cry
after an ancient inscription. Let me say at once that I
am not finding fault with Mr. Lloyd's acting. It is
just that for the first time I saw myself as others must
see me.

A man who persists in digging in the city dump for
scraps of broken crockery, old shoes, and worn-out
turkey wings is likely to be netted by the dogcatcher
and locked up in the booby hatch. I know of no better

[264]

An Amateur Looks at Archeology

way to lose my friends than to start looking under their
rugs and behind their doors for bent pins and lost
collar buttons. But as an archeologist, those are just
the places where I would be happiest. The innumer-
able little things that we use in our everyday life
sooner or later wear out, or go out of style, or are lost,
and they all turn up in the city dump, piled with old
soupbones and broken bricks and sodden ashes, over
similar mementoes that our parents and their parents
before them left behind. Taken all together, layer after
layer, they tell the story of our civilization during a
period of a century or more they do to an archeologist,
at any rate. The Indian woman who swept the remains
of her evening meal into a dark corner of the lodge
frequently swept with them a bone needle, or a broken
comb, or one of her husband's best fishhooks. Looking
in places like these for the relics that will tell the story
of an ancient people is plain common sense, and to my
way of thinking common sense is the foundation of all
science.

We Americans have a well-established tradition of
relic hunting. The first settlers found themselves hob-
nobbing with a race without a history, whose only
knowledge of their past was handed down from father
to son in myths and tribal legends. Plowing the fields,
the pioneers found relics of that forgotten past and,

[265]

Excursions in Science

being even then born souvenir hunters, they began to
collect them. What farm boy doesn't have a cigar box
full of Indian arrowheads tucked away somewhere, or
maybe even a few polished stone pieces set out on the
mantel shelf to make other collectors' eyes glitter?
For three centuries we have collected Indian relics as
curios, without any thought for the story they could
tell. Mounds have been blown open and village sites
dug over, until they look like the aftermath of the
Spanish war. Skillful forgers found that they could sell
homemade arrowheads and axes to people who hadn't
the time or the ambition to pick them up, and even
today they are doing a rousing business in fake Indian
relics. But in the meantime, a few exceptional men
here and there throughout the growing nation were
trying to puzzle out the meaning of the things that were
being found. To them we owe the beginning of
scientific archeology in this country.

Most people are thrilled by a good detective story.
That is the thrill that archeology can give you. Every
flint arrow, every broken potsherd, every buried
hearth is a clue to the life story of the men and women
who used and lost them hundreds or even thousands of
years ago. By using the sense he was born with and
whatever scientific ingenuity he can muster, our
archeological detective can reconstruct the story that

[266]

An Amateur Looks at Archeology

those relics tell, as Sherlock Holmes or Philo Vance
reconstructs a crime. By carefully excavating a village
site, he unearths evidence that helps him to form a
picture of the daily life of the people who lived there
what they ate, what tools they used, even something
of what they believed. A cemetery near the village
may show him what the people looked like. Other
similar villages come to light, and he gradually builds
up the history of their relations with each other and
with other hostile and friendly tribes. In the end, when
all the clues have been found and all the deductions
made, there emerges a grand, moving panorama
of ancient races trekking across the face of the earth,
struggling against hostile men and still more hostile
nature, and gradually developing the characteristic
way of life that is their culture, setting them apart
from all other peoples.

The archeologist of today, whether he is studying the
wonderful stone cities of the Mayas in Yucatan or the
no less puzzling remains of the Laurentian culture in
New York State, finds a use for every tool of modern
science. A radio detector of the latest type will help him
locate the iron traders' axes that were buried in the
graves of the Iroquois clans during the colonial period.
A new plastic compound developed for use in police
work enables him to make molds of decayed fabrics too

[267]

Excursions in Science

delicate to be taken out of the ground. His knowledge
of geology and physical geography permits him to
trace the ancient trade routes over which copper was
brought from Lake Superior, shell from the Atlantic
coast or the Gulf of Mexico, soapstone from Connecti-
cut, and fine flint from Ohio, Pennsylvania, or the
great prehistoric quarry at Coxsackie on the lower
Hudson River. If there is no tool to suit his needs, he
invents one. Unlike scientists in other fields, he can
never repeat an experiment. History happens only
once.

The story of American archeology today is the story
of increasing cooperation between the professional
students in the museums and universities and the
amateurs who have only their leisure time to devote to
their hobby. The museum men develop new tech-
niques of excavation and restoration, uncover new
problems, and ferret out the answers to old ones. But
we amateurs know every square yard of the country-
side where we live. We have surface-hunted every
plowed field and dug into every refuse heap and corn
pit for miles around. We know where to look for the
threads of evidence that the professional needs to
complete his tapestry of ancient times. And as our
scientific curiosity is stirred up, we find that we are

[268]

An Amateur Looks at Archeology

contributing something of real worth to the story of
the American Indian.

Let me tell about a puzzle which has been tantaliz-
ing our own local chapter of the New York State
Archeological Association. A few miles north of
Schenectady is a large swamp known as the Consalus
Vlaie. Old-timers can remember when there was a
considerable area of open water at its center, but today
it is fast filling up with sphagnum moss, tamaracks,
dwarf spruce, and other bog vegetation. Recently, a
group of local naturalists has been studying this swamp.
They tell us that the plants they have found there
normally grow only at much higher altitudes, or in a
subarctic climate. This news revives the old theory that
the Vlaie was originally a glacial lake, formed when
the great ice sheet was retreating from eastern New
York, and now transformed by the mosses that have
crept out from its ancient shore line into a quaking
morass that is a haven for wild life of all kinds.

It is only natural that primitive hunters would find
such a place a happy hunting ground. There is ample
evidence that ancient men once camped along its
margin. Buried fire-places, masses of broken flint, and
fire-cracked stone are easily found. Unusual types of
implements have been turned up by the plow, some of

[269]

Excursions in Science

them crude and some of them beautifully made. But
who were the men that made them?

We know, from finds in other parts of the United
States, that man did inhabit this continent at the close
of the glacial period, 10,000 or 20,000 years ago. Were
the men whose traces we have found at the Consalus
Vlaie related to these first Americans, living here when
the mastodon and the giant beaver still ranged through
New York State? Were they the forerunners of the
Eskimo, wandering down out of the North at some
much later date? Were they the ancestors of the
Mohicans and other Algonquian tribes found here
by the first explorers? Or were they an unknown peo-
ple whose existence we have never before suspected?

We hope that the naturalists can settle the question
of how old the Vlaie really is. I have said that they
find plants of a type that bears out the idea that the bog
had its origin at a time when the climate was colder. A
study of the shell deposits along the old shore line,
such as has been made in Canada, may give us another
clue to the age of the place. There are many such in-
direct avenues of approach, all of them worth trying.

But who were the people themselves? They left very
little behind them, and that long ago. A layer of
several inches of soil covers their hearths in some
places. We must first discover what they did leave, and

[270]

An Amateur Looks at Archeology

find out whether it fits into our scheme of ancient
Indian cultures, as it has been worked out for this
region. Even if their culture was not identical with
any that is known, there may be indications that they
were influenced or replaced by some known people.
We have found no pottery; it may be that they had
not discovered the art of agriculture. The flint they
used was of poor quality; perhaps they had not lived
here long enough to find the ledges that would yield
the best material. Until we have excavated their camp
sites beside the Vlaie and made every possible clue tell
its story, we shall not know whether we are reading an
uncut chapter in the history of man in America, or
whether, as is probably the case, we are merely adding
new information to the story of a people already known
from other excavations.

Not everyone finds the science of archeology as
absorbing as I do. Unfortunately, the magpie spirit is
still with us. People ask, "What do you pay for arrow-
heads? What is my collection worth?" The answer is,
"Nothing unless every piece is documented."

An uncatalogued collection of Indian relics is like
a collection of paintings by unidentified artists. They
may be beautiful, but who made them? You may be
sure that you own a Titian, or a Rembrandt, or a

[271]

Excursions in Science

Gainsborough. But do you? Can you prove it? The
archeological value of any specimen is in the story it
tells. The relics themselves are just so many pieces of
cleverly shaped stone and bone.

The least that any serious collector can do, in his
own interests as well as those of archeology, is to keep a
catalogue of his collection and a map of the sites he has
explored. Each specimen should be numbered and
listed in a record book or on file cards, together with
the place where it was found and any other informa-
tion about it. For example, the fact that certain pieces
were found together in a pit or grave would be very
important, as would a note to the effect that you
found potsherds only above the plowline on a certain
site. Such information may give a clue to the relations
between a whole series of ancient cultures. Thus, an
Indian relic is like a dog; the longer its pedigree, the
more it is worth.

Abroad, in England, France, Germany in fact,
throughout all of Europe the amateur archeologist
has long had a recognized standing. Many of the most
outstanding contributions to our knowledge of ancient
men have been made by doctors, lawyers, clergymen,
or businessmen who have turned the casual curiosity
of the hobbyist into the intelligent inquisitiveness of

[272]

An Amateur Looks at Archeology

the true archeologist. Here in America there are
opportunities, too opportunities to contribute to
our all-too-meager knowledge of prehistoric man on
this continent. And the way to do it is to set out to be
a real archeologist, instead of just another relic
hunter.

[273]

IDENTIFYING MOLECULES

by DR. MURRAY M. SPRUNG

MANY persons are attracted to scientific study by the
desire to understand, to imitate, and ultimately
to improve on nature. The opportunity to better
nature's handiwork is perhaps nowhere greater than
in chemistry particularly in that branch known as
organic chemistry, where an understanding of certain
of the principles upon which nature builds has made
it possible to produce, synthetically, many substances
that were once obtainable only from natural sources.
The purple dye, indigo, is an example. This valu-
able colored substance has, for centuries, been
gathered painstakingly from plants by native workers
in the Orient. Yet today almost all the indigo used
is synthetic. Similarly, one of the most common of
perfume essences, oil of wintergreen, was previously
obtained only from the creeping plant whose name it
bears. Today synthetic oil of wintergreen, known to
chemists as methyl salicylate, is produced cheaply
and in large quantities. And one might go on through
a whole list of other substances of commercial impor-
tance wood alcohol, carbolic acid, camphor, musk,
alizarin, adrenalin, vanillin, and many more.

[274]

Identifying Molecules

The chemist is able to produce, seemingly almost at
will, these and a host of other materials once obtain-
able only through the working of complex life proces-
ses. To be able to do so, however, presumes an
abundance of previous experience and knowledge of
the laws of molecular architecture; for certainly he
cannot build anything without a key to the structure
of the substance to be built. With this guide, however,
he can proceed, on the basis of known principles, to
put together the building blocks, or atoms, in the
correct arrangement. His first job, then, is to establish
the identity of the molecule he wishes to build to
know what atoms this molecule contains and how
these atoms are linked together.

The branch of chemistry most closely concerned
with the identification and building of molecules is
organic chemistry the chemistry of the compounds
of carbon. And a broad field it is, for there are several
hundred thousand known compounds that contain
carbon, and each one is in some way different from
all the others.

The study of organic chemistry received its first
great impetus around 1828, when the first compound
containing carbon was prepared artificially in a
laboratory. It was a comparatively simple compound,
called urea. Urea has the chemical formula CH 4 ON 2 ,

[275]

Excursions in Science

which means that it contains one carbon atom, four
hydrogen atoms, one oxygen atom, and two nitrogen
atoms, all bound together.

With this pioneering experiment as a pattern, more
and more organic compounds were synthesized until,
today, tens of thousands have been prepared. In this
period, too, thousands of substances that occur in
nature, but that have not yet been fabricated by
man, have been studied sufficiently so that their
identity by which we mean their internal molecular
architecture is known beyond a reasonable doubt.

After obtaining a pure specimen of a substance to
be identified, one sets about determining what differ-
ent kinds of atoms are present in the molecule, and
how many of each one. To answer the first question,
a qualitative analysis must be carried out, making use
of reactions that are characteristic of each chemical
element whose presence is suspected. Then, to answer
the second question, a quantitative analysis is made.
This consists, almost literally, of tearing the separate
elements out of the compound, one by one, and con-
verting them into relatively simple substances that
can be weighed or otherwise measured.

The next step is a little more difficult to follow, so
let us tackle it with the aid of an example a com-
pound that is found in nature, and that may also be

[276]

Identifying Molecules

produced by a number of synthetic processes. The
substance is a liquid and may be obtained in a high
state of purity.

A qualitative analysis shows that it contains only
three kinds of atoms: those of carbon, hydrogen, and
oxygen.

A quantitative analysis shows that it is made up of
about 48 parts of carbon, 12 parts of hydrogen, and 32
parts of oxygen, all in combination, of course. (As a
matter of convenience we have expressed the com-
position of the substance in somewhat odd numbers
rather than in the more usual parts per hundred.
The reason for this will appear a little later.)

Now, before we can go any further, we must stop
for a moment to consider one or two entirely funda-
mental chemical relationships. We encounter, first,
Dalton's hypothesis, which underlies the whole of
chemistry, and which we can accept without hesita-
tion. It states that atoms exist, and that they cannot
be altered by ordinary chemical means.

Our second rule and it has been amply demon-
strated is that atoms combine to form molecules.
When they do so, it is found that the ratio in which
they combine by volume, if they are gases may
be expressed by simple numbers, such integers as
1, 2, 3, 4, and so on. That is, one cubic foot of one gas

[277]

Excursions in Science

may combine with two cubic feet of another, or two
cubic feet of one with three of another.

If the elements that react are not gases, but liquids
or solids, another simple rule is observed. The weights
of elements that combine, whether solid, liquid, or
gaseous, are perfectly definite and reproducible.
Furthermore, the weights of an element which com-
bine with two or more different elements are again
related to one another as simple numbers. This rule
is called the law of combining proportions.

Now, to show that it's not so complicated as it
sounds, we'll take another example. Experiment
shows that 16 weight units of oxygen combine with
a certain weight of mercury, but that 32 weight units
of oxygen combine in the case of tin, 48 weight units
in the case of aluminum, and 64 units in the case of
iron. Divide each of these numbers by 16, and you
will get the simple numbers 1, 2, 3, 4. All the combin-
ing units of oxygen are simple multiples of 16.

The lowest weight of an element which enters into
chemical combination is called its atomic weight.
Applying this to oxygen, as we have just done, we
find that the atomic weight of oxygen is 16.

This is the way all this applies to our problem of
identifying molecules. Since compounds are made up
of atoms, it follows that the weight of any given com-

[278]

Identifying Molecules

pound must be made up of the sum of the weights of
all its constituent atoms. Therefore, if we know what
atoms are present in the compound, and what per-
centage of each, we should be able to tell bearing
in mind the principles just discussed exactly how
many atoms of each kind are combined together in the
compound.

So now let's return to our original compound, with
its 48 parts of carbon, 12 parts of hydrogen, and 32
parts of oxygen. The unit or atomic weight of carbon
is 12, of hydrogen 1, and of oxygen 16. Put these two
sets of figures down together, as follows: 48:12:32
12:1:16. Inspection readily shows that if we divide
the first set (the actual compositions) by the corre-
sponding members of the second set (the atomic
weights) we get the numbers 4:12:2. Since we have
divided total weight by unit weight, we must have
arrived at the number of atoms of each kind that are
combined together in our compound. That means
four carbons, twelve hydrogens, and two oxygens. Or
simpler still, dividing by two, in our unknown com-
pound every oxygen atom is associated with two
carbon atoms and with six hydrogen atoms. Therefore,
following the usual chemical notation, we may repre-
sent it as G2H 6 O, which is the simplest possible formula.

[279]

Excursions in Science

It is the simplest possible formula for this reason.
We have determined the ratio of the atoms, but we are
not yet sure of the actual molecule. There might be
twice as many, or three times as many, of each of the
atoms that is, it might possibly be C^Hi^O^ or
C 6 Hi 8 O3, instead of the simple C2H 6 O.

To decide between these possibilities, we must now
determine the molecular weight, which is the weight of
a single molecular unit. One possible way to determine
the molecular weight of our liquid is to vaporize, it
and find out how much heavier it is than a substance
of known molecular weight. In the present case, the
vapor turns out to be 1.438 times as heavy as oxygen
gas. (An oxygen molecule is made up of two oxygen
atoms and so its molecular weight is twice 16, or 32.)
Therefore, the molecular weight of the unknown
compound is 1.438 times 32, or very nearly 46.

The sum of the weights of the atoms represented in
the formula C2H 6 O namely, the sum of 2 times 12,
6 time 1, and 1 times 16 is also 46. And so we have
made sure that the simplest possible formula, C2H 6 O,
is, in this case, the actual molecular formula.

So, by the use of ordinary arithmetic and a few
fundamental chemical laws, we have tracked down
the formula of our unknown compound. But we are
not at the end of the trail yet. Before we can claim

[280]

Identifying Molecules

that we have actually identified it, we must discover
how the atoms in the compound C 2 H 6 O are linked
together. This part of the problem is not unlike trying
to ascertain, without being able to see into the room
itself, how a number of people are seated in a room.
The chemical mystery can be solved only by studying
the reactions of the compound often a long and
tedious process, but necessary in many chemical
investigations. The experimental results can be
summarized as follows:

1. Of the six hydrogen atoms present, one is differ-
ent from the other five.

2. This hydrogen is associated in some manner with
the single oxygen atom, since in various reactions they
v are removed together.

3. To determine how the remaining two carbon
atoms and five hydrogen atoms are put together, we
must use the so-called "rule of valence," which states
that each carbon atom always has four other atoms,
or groups of atoms, tied to it.

These are the clues from which we are able to piece
together the solution of the mystery of our unknown
compound. (Actually, the reasoning in such chemical
problems is not much different from that used by the
master detectives of fiction.) We can now sketch a
rough diagram to show how the atoms are arranged.

[281]

Excursions in Science

Imagine that the two carbon atoms and the single
oxygen atom are attached together in a straight line,
like three apples pierced by a stick. The first carbon
atom has three hydrogen atoms attached to it per-
haps like three cherries attached by individual tooth-
picks to the first apple. The second apple (or carbon
atom) has two cherries (or hydrogen atoms) attached
to it. The lone oxygen atom, which is the third apple
on the stick, has the sixth and different hydrogen
atom attached to it.

There, completely pictured, is our up-to-now
unknoWn compound. In a few minutes we have
indicated the steps which, in actual performance,
might take many days of experiment and calculation.
But what is the molecule that we have tracked down
by so much effort? It is ordinary grain alcohol!

In a similar fashion we could build up, on paper, as
many as we pleased of the several hundred thousand
known organic compounds. We could describe the
molecular structure of drugs, of dyes, of perfumes,
of the natural or derived constituents of coal tar and
petroleum, of the many important commercial
chemicals that can be synthesized using lime and coke
as the starting materials. If we were sufficiently
skilled and sufficiently ambitious, we might attempt
to identify the molecule of chlorophyll, the green

[282]

Identifying Molecules

coloring matter of plants, or of hemoglobin, the red
coloring matter of the blood. Through just such efforts,
the vexing problem of the nature of the vitamins has
been partially solved. Progress is now being made in
the study of hormones. We now know also a great
deal about the chemical identity of rubber, cellulose,
starch, and the protein substances all of which are
examples of the "giant molecules" of nature. A single
one of these molecules may contain tens of thousands
of individual atoms linked together.

When the enormously difficult problem of one of
these giant molecules, or of the vitamins or hormones,
is attacked, the method is fundamentally similar to
the one we have outlined in studying alcohol. Whether
the compound to be identified is found in nature or
in a laboratory beaker, it must first be isolated, it
must be carefully purified, it must undergo qualitative
and quantitative analyses, its molecular weight must
be determined, experimental studies of its reactions
must be made. All these facts, when put together
properly, will disclose the particular pattern in which
the atoms are arranged. And all these facts, properly
verified and correctly interpreted, can lead to only
one complete picture of the molecule.

[283]

ELECTRON OPTICS

by DR. RALPH P. JOHNSON

TP\R. JOHNSON was born in St. Pauls, North Carolina, attended the
University of Richmond and the University of Virginia, and
received his degree of Doctor of Philosophy from the Massachusetts
Institute of Technology. He has held the position of physicist with
the Geophysical Research Corporation, has taught mathematics
at the University of Richmond, and since 1936 has been a physicist
on the staff of the General Electric Research Laboratory.

MOST of us, whether we realize it or not, are fairly
well acquainted with electrons, the tiny ulti-
mate particles of negative electricity. When we turn
on an ordinary incandescent lamp, it is a current of
electrons running through the tungsten filament that
heats it white-hot. In the tubes of our radio, electrons
evaporate out of a heated piece of metal, the cathode,
and travel through the various grids to the collector.
In the photoelectric tube, which opens doors, starts
drinking fountains, sorts black beans from white
ones, makes talking moving pictures possible, and
does a multitude of other tasks great and small there
again is a current of electrons, set free by light

[284]

Electron Optics

millions of electrons flying through a vacuum or
through an atmosphere of argon, from one piece of
metal to another.

"Optics," the science of light, is also a familiar
word, and the underlying principles of optics are
matters of common experience. In free space, light
travels in straight lines. But when a ray of light
passes, at some angle other than a right angle, from
one medium to another from air to glass, for ex-
ample the ray is bent. Therefore, lenses can be
made that will divert light rays as we wish, and tele-
scopes, microscopes, cameras, and eyeglasses are
possible.

The electron was discovered about 40 years ago,
and the principles of optics have been known for more
than two centuries. The phrase "electron optics" is,
however, a comparatively new one. At first sight it is
an odd combination. What connection is there between
particles of negative electricity and rays of light?

Actually, the connection is a close one and a useful
one. It has long been known that the paths of electrons
traveling through space can be bent by electric and
magnetic fields. Since electrons are negatively charged,
they are attracted to a piece of metal that is positively
charged, and they are repelled by a negatively
charged piece of metal. This accounts for the bending

[285]

Excursions in Science

that electrons experience when they travel through
electric fields. And, since a flow of electrons is an
electric current, electrons may be pushed sideways
that is, their path may be bent in a magnetic field,
just as the armature windings in an operating electric
motor are pushed sideways by the magnetic field
of the pole pieces.

A few years ago it was discovered that the bending
of the path of an electron as it goes through electric
and magnetic fields is exactly like the bending of a
light ray as it passes through a system of lenses the
same mathematical equations describe both. Since
this similarity exists, it is possible to make use immedi-
ately of all the knowledge, accumulated during two
centuries, about the behavior of light rays, and to
apply this knowledge to the behavior of the paths
followed by streams of electrons. Such terms as "elec-
tron lens," "electron image," "electron microscope,"
and "electron optics" become justifiable and useful.

We want now to look at two or three of the recent
electron devices which have optical counterparts.
First, we consider the "electron spotlight." In an
ordinary spotlight the rays that leave the lamp, in all
directions, are collected and concentrated in a single
direction. Analogously, the electrons emitted in all
directions from a cathode, such as a heated piece of

[286]

Electron Optics

metal, can be focused into an intense narrow beam
or pencil. When this beam strikes a screen of fluores-
cent material, a spot of light is formed. The electron
spotlight tube becomes very useful when the beam, on
its way from the focusing "lens" to the fluorescent
screen, passes between a pair of metal plates or
between the poles of an electromagnet. The beam
may then be deflected up and down, or sideways,
as the voltage on the plates or the current in the
electromagnet is varied. The spot of light on the
screen can thus trace out a graph of the varying volt-
age or current. The beam of electrons acts like the
pointer of an ordinary meter, but with this difference:
the beam can easily trace out variations that are
much too rapid for any other kind of meter to follow.

This electron spotlight, which is usually called a
cathode-ray tube, is one of the most useful tools of
modern research. It may eventually become a very
familiar, everyday object; for a cathode-ray tube, with
an electron beam of varying intensity sweeping back
and forth over a fluorescent screen, is one of the final
image-forming devices in television receivers.

Electron beams are finding wide use also in the
study of metal surfaces. If a narrow beam of electrons
is directed obliquely against a solid surface, some of
the electrons will strike the surface and then will be

[287]

Excursions in Science

reflected away again. The direction in which these
reflected electrons leave the metal is determined by
the arrangement of the atoms at the surface. If the
surface atoms are piled up regularly, like bricks in a
building, the electrons bounce away only in a few
definite directions. But if the surface atoms are piled
up in hodgepodge fashion, the electrons are scattered
away in many directions. Down below the surface
the metal atoms are arranged in order this is known
from studies with X rays which, unlike the electrons,
go so deep into the sample that the surface conditions
make little difference. The experiments with electron
beams, however, show that on some metals the surface
itself can be changed from a regular array of atoms
to an irregular array by the right kind of polishing
operations. The hodgepodge surface is tougher and
smoother than the orderly surface, and so is more
desirable where two metals have to rub against each
other. These studies of surfaces with electron beams
are revealing how automobile cylinders, for example,
can be made more resistant to wear.

The electron microscope is an important new device
which involves electron optics. In one form, electron
lenses are so arranged that an enlarged image of the
cathode is formed on a fluorescent screen. By simply
looking at the electron image on the screen, one can

[288]

Electron Optics

tell immediately which parts of the cathode are
sending out the most electrons these are the brightest
parts of the image.

Later and more versatile types of the electron
microscope do more. A beam of electrons is concen-
trated on the specimen to be studied, which is pre-
pared as a thin film through which electrons can pass.
Since different thicknesses and densities within the
specimen transmit different proportions of the beam,
the emerging electrons form a kind of shadow pattern
of the specimen's structure. This emerging beam,
by means of electron lenses, is magnified and made
to focus on a fluorescent screen, producing an enlarged
picture which can either be observed directly or photo-
graphed and then further enlarged photographically.

One limitation to the magnification of optical
microscopes has been the wavelength of light; it is
impossible to distinguish clearly objects much smaller
than the light waves by which they are viewed.
Because electrons behave like light waves of very
much shorter wavelengths, the "resolving power" of
an electron microscope can be made very much
greater. Already many objects that were too small
ever to be clearly seen with light-optical instruments
have been photographed, in considerable detail, by
this most promising application of electron optics.

[289]

Excursions in Science

Strictly speaking, there is no electron telescope.
There is, however, an electron-operated tube which
behaves very much like a camera and which promises
to have some applications in telescopic work. This
tube has a photoelectric surface at one end and a
fluorescent screen at the other, and between the two
is an electron lens. When a light image falls on the
photoelectric surface, the emitted electrons are
focused by the electron lens onto the fluorescent screen,
and the image is reproduced there. The photoelectric
surface can be made sensitive to infrared light, which
is invisible to the human eye. This tube, in effect,
changes the invisible infrared image on the photo-
surface into a visible image on the fluorescent screen.

And this is an unusual and a valuable accomplish-
ment. It is not possible to allow the long-wave invisible
infrared rays to fall directly on the fluorescent screen
and to produce visible light on the screen. Converting
infrared radiation into visible light, directly by a
fluorescent screen, would be somewhat like stepping
up to a change booth in a subway, presenting a nickel
to the cashier, and getting a quarter in return.

Of course, the reverse exchange is quite possible.
Thousands of people daily exchange quarters for
nickels. Similarly, it is quite possible to let short-wave
ultraviolet rays fall on a screen and there produce

[290]

Electron Optics

visible light. That is done often. The unusual behavior
of this recent electron-optical tube is that, by means
of a sort of "double play" infrared to electron
beam to visible light we can, in effect, get quarters
in exchange for nickels. At least we can, in this fashion,
convert invisible infrared energy into visible light
images. Infrared rays can penetrate through haze
more easily than can visible light, so the use of this
tube along with an ordinary telescope may extend the
range of clear vision in hazy weather.

It is not to be thought that these developments of
electron optics have all happened solely as the result
of the discovery that light rays and electron beams
follow the same mathematical equations. The dis-
covery of this analogy has, however, pointed the way
to new research in several directions, and has simplified
the problem of nomenclature in a new, rapidly grow-
ing, and important branch of physics.

[291]

THE LIMITATIONS OF SCIENCE

by LAURENCE A. HAWKINS

IV yf"R- HAWKINS, born in Pittsficld, Massachusetts, holds degrees
"* from Williams College and Massachusetts Institute of
Technology. In 1903 he went from the Stanley Electrical Manu-
facturing Company to the General Electric Company, where he
was in turn a member of the Patent Department and the Railway
Signal Department. In 1912 he joined the Research Laboratory,
where he holds the position of Executive Engineer.

MARVELOUS indeed are the advances of the physical
sciences. Nothing seems beyond their ultimate
grasp. We see the physicist reaching into the infinitesi-
mal heart of the atom, transmuting one element into
another at will. We see the astronomer reaching out
into unimaginable space, measuring the distances to,
and the motions of, nebulae a billion billion miles
away. Chemistry is producing thousands of new
materials for the service of man, while preventive
and curative medicine and surgery are conquering
one dread disease after another, and have lengthened
the average span of human life by decades.

Applied science, by radio, flashes the spoken word
half-way around the earth in a fifteenth of a second, or

[292]

The Limitations of Science

broadcasts it to a million listeners, or, by television,
brings before our eyes events far removed from normal
vision. Through electrical appliances, it has given
us in the home, at the touch of a button, more com-
forts and conveniences than Aladdin ever dreamed
of, and, through electric motors, has given industry
the power of hundreds of millions of tireless slaves.

While no one man may know all that modern
science has accomplished, yet there are widespread
recognition and acclaim for the wonders it has
wrought. Scientific achievement is generally esteemed
as the highest manifestation of the human intellect.

But this generous esteem in which science is held
carries a latent danger to science itself. Of late years
the question has been asked, with growing frequency,
why the aggregate brain power of our scientists is
not applied to righting the grievous wrongs with
which we are beset on every hand.

We have seen millions unemployed, dependent on
relief, and thousands of factories operating on part
time, while, even if they had been working overtime,
they could not have produced enough to provide a
comfortable living standard for all our people. We
have seen farmers ruined by a glut of foodstuffs, while
multitudes in our cities were going hungry. Looking
abroad we have seen the horizon growing dark with

[293]

Excursions in Science

storm clouds, conflicting political systems confronting
each other threateningly, national antagonisms grow-
ing more acute, treaties no longer binding their
signatories, and international law forgotten. Racial
intolerances were adding fuel to the flames of passion.
One ferocious war after another was breaking out,
until now we face the threat of another world
war, even more terrible and devastating than the
last.

In such a crisis, when disturbances at home
threatened our economic system and war abroad
threatened civilization itself, why did not the army
of science, comprising as it did so much of the brain
power of the world, see its duty and come to the
rescue? Why waste precious time in studies of ultra-
macroscopic nebulae millions of light-years away,
or of ultramicroscopic atomic nuclei, when there were
acute problems pressing on every side, involving the
happiness and lives of millions of fellow men? Why
fiddle when Rome was burning?

The increasingly general belief that the scientist
may be the savior of our distressed world, while
flattering to him, can lead only to disappointment,
and disappointment may change into hostility. Soon
the public may be asking, "If science cannot solve
our most direful problems, what good is it? Why

[294]

The Limitations of Science

spend millions of dollars on such futile institutions
as scientific laboratories? Why not close them, divert
the money to social relief, and let the scientist seek
more useful employment?"

But reflection should show that the hopes that
science may solve our domestic problems, social and
economic, and may free us from the threat and
horrors of war, arise from a faulty understanding of
the scope and limitations of science.

The scientist is an explorer in the field of nature.
He seeks new facts and new principles, which others,
such as the engineer, the industrialist, the physician,
or the educator may use for the good of mankind.
He supplies, as it were, the raw materials for tech-
nological progress and for elevating our standards of
living. He is like a mineralogist exploring for new
mineral deposits. From the ores he discovers, metal-
lurgists may produce better or less costly alloys, and
automotive engineers may use these alloys to build
improved motorcars for the public use. But the in-
crease in the number of cars may give rise to new
problems in traffic congestion; some may be driven
carelessly or recklessly, with a steadily rising total of
casualties; some may even be used by criminals for
escaping from the scene of a crime, or taking a victim
"for a ride." Acute problems may arise, but why look

[295]

Excursions in Science

to the mineralogist to solve them? He has his own
field of useful work, and, however able he may be, his
special training fits him in no way for dealing with
traffic problems or crime waves.

So too a physicist or a chemist may discover an
important new fact which gives rise to a new industry,
but which produces a temporary dislocation of older
industries and increases unemployment for the time
being. His discovery may even be used to produce a
new and terrible weapon that further enhances the
horrors of modern warfare. As an individual, he would
doubtless deplore such unfortunate consequences of
his labors, but as a chemist he can no more be held
responsible for the misapplication of his discovery
than could a manufacturer of surgical implements if
one of his knives were used to commit murder.

Nor, as a chemist, can he reasonably be expected to
solve the economic or military problems that arise,
even if his own discovery has made them more diffi-
cult. As a chemist, he is not trained or qualified to be
an economist or a statesman. We may need more and
abler economists. If so, our only recourse is to train
them. We do need more and abler statesmen. Our
only recourse is in better selection and training. It is
foolish to turn to the natural sciences to seek leader-
ship in wholly different fields. To look to natural

[2961

The Limitations of Science

science for a cure for our economic and international
ills is as unreasonable as to look to our economists or
statesmen for a cure for cancer.

In one way, and in one way only, can the scientist
help us in our economic, social, and international
problems. His special knowledge qualifies him no
better than the rest of us to set the world to rights.
But if, by precept and example, he can teach us to
adopt the scientific attitude, we shall be enormously
advanced toward the solution of our problems.
The scientist has learned that he must base his opinions
solely on verifiable fact. No preconceptions, no
emotional bias, no traditional or authoritarian dogma
may be permitted to deflect his thinking. The clear
light of established truth is his only guide.

Imagine what it would mean if we could approach
our economic, social, and international problems with
that attitude! Neither class prejudice, nor racial
antagonisms, nor national hatreds could longer sway
us. The emotional demagogue would be out of a job.
Loyalty to true principle would survive, but loyalty
to catchwords would disappear. Even selfish interest
would be laid aside, while policies for the general good
were being studied for their wisdom. Differences of
opinion would be debated, without bitterness, not
for the sake of victory, but solely to elicit the truth.

[297]

Excursions in Science

Before such an approach, how many of our danger-
ous problems would solve themselves! How relatively
easy would the solution of the rest become!

Not in our generation nor in the next can we hope
for such a change in the mental attitude of the mass of
men. But in time it may come. Not scientific knowl-
edge, but the scientific approach, may in the end
prove to be the savior of democracy and civilization.

[298]

INDEX

A

Abbot, C. G., solar engine, 99
Absolute temperature scale, 48
Alcohol, in blood, 117

molecular structure of, 277-

282

Alexandrite, color of, 211
Alpha particle, for nuclear bom-
bardment, 155
Amethyst, 207
Amino acid, product of digestion,

23, 88, 91, 93

Amplifier, vacuum tube, 233
Anode, of electron tube, 194, 228
Apogee, cause of neap tides, 1 88
Aquamarine, 210
Archeology, of American Indian,

264-273

Archimedes' Principle, 176, 177
Aristotle, sound, 65
Astronomical year, beginning of,

28
Atom, definition of, 13

excited, cause of fluorescence,

249-252

source of light, 198
nucleus of, 146-161, 249

forces within, 152
structure of, 143-151, 248-250
weight of, 14

Atomic weight, 14, 278, 279
Azurite, color of, 208

B

Bailey, Dana K., eclipse expedi-
tion, 218, 220

Barton, William H., eclipse ex-
pedition, 219, 221

Becker, Joseph A., thermionic
emission, 227

Bede, Venerable, tides, 186

Benford, Frank, "Probabilities
and Improbabilities," 162

Bennett, Dorothy A., "Chasing
the Moon's Shadow," 215

Beryl, composition of, 210

Blodgett, Katharine B., " A Gauge
That Measures Millionths of
an Inch," 255
surface films, 9

Bologna stone, fluorescence of,
244

Bortz, form of diamond, 213

Boyle's law, 47

Bragg, Sir William, X-ray dif-
fraction, 183

Bronze Age, tools of, 172, 201

Bunsen, Robert W., spectrum
analysis, 178

Byrd, Richard E., antarctic, 27

Caesium, discovery of, 179
Calorie, definition of, 21

[299]

Excursions in Science

Calories, average human require-
ments, 22
in various foods, 24

Candlemas Day, quarter day of
old calendar, 203, 204

Canton Island, eclipse expedi-
tion to, 216

Carat, weight of, 209

Carbohydrate, basic element of

food, 23, 87
chemical composition of, 88, 89

Carbonado, form of diamond,
213

Cathode, of electron tube, 194,
227

Cathode-ray tube, used in tele-
vision, 287

Centrifuge, use in microchemis-
try, 116

Cerro de Pasco, Peru, eclipse
expedition to, 219, 221

Charcoal, absorption of gas in,
78, 105

Chemical elements, periodic sys-
tem of, 16-19

Chemicals, organic, synthetic,
274

Chromosome, carrier of heredi-
tary units, 236

Chrysoberyl, 211

Citrine, form of quartz, 207

Coal, annual world consumption
of, 99

Coast and Geodetic Survey, tide
predictions, 189, 192

Coles, Charles, eclipse expedi-
tion, 221

Collision, elastic, in gas dis-
charge, 197

Color, interference, 8, 257-263
thickness gauge for films, 8, 263

Combining proportions, law of,
277, 278

Consalus Vlaie, Indian remains
found at, 269-271

Coolidge cathode-ray tube, 182

Corona, electrical, 158
solar, globular, 221

nature of, 221, 223, 224

"Coronium," in sun's corona, 223

Corundum, varieties of, 208, 209

Cottrell, F. G., smoke precipita-
tor, 105

Coxsackie, N.Y., prehistoric flint
quarry, 268

Crystal as diffraction grating, 183

Curie Institute, radioactivity, 241

Current, electric, electronic na-
ture of, 226

Cyclotron, principle of, 159-161

D

Dalton's hypothesis, 277
Decibel, values for common

sounds, 71

Detector, mercury vapor, 110
Diamond, hardness of, 212, 213
industrial (bortz, carbonado),

213

Dushman, Saul, thermionic emis-
sion, 227

E

Ear, "electric," 70

human, frequency response of,

69,70
structure of, 68

[300]

Index

Earth, atmosphere of, 74, 75

density of, 118

inner constitution of, 126

orbit around sun, 217

speed at equator, 218
Earthquakes, causes of, 119-121

displacements produced by,
120

tectonic, 119

waves produced by, 121-125
Eastport, Maine, tides at, 191
Eclipse, solar, 215-224
Edison effect, 226-228
Elder, Frank R., "The Marks on

Your Thermometer," 43
Election Day, connection with

old calendar, 204
Electricity, frictional, 35

static, 35
Electromagnetic waves, wave

lengths of, 180, 259
Electron, atomic particle, 145

mass of, 146

Electrostatic generator, for nu-
clear bombardment, 158
Emerald, color of, 210
Emery, form of corundum, 209
Energy, from coal, annual world

consumption, 99
Enzymes, in digestion, 90, 91
Equinox, fall, 201

vernal, 28, 201, 204
Errors, theory of, 165

F

Fahrenheit temperature scale,
45,46

Fat, basic element of food, 23, 87

chemical composition of, 89
Films, lubricating oil, thickness

of, 256

soap bubble, 8, 257
Firefly, luminescence of, 57-63
Fisher, Clyde, eclipse expedition,

221, 222

Fleming valve, 228, 229, 232
Fluorescence, of common mate-
rials, 253

mechanism of, 248-252
of quinine sulphate, 245
of rhodamine, 246, 247
used in deciphering manu-

scrips, 254

of willemite and calcite, 247
Fonda, Gorton R., "Fluores-
cence and Phosphorescence,"
244

"The Use of Light in Chemis-
try," 176

Food, basic elements of, 87
mineral elements in, 89, 90
minimum human require-
ments, 24

Found, Clifton G., "What Hap-
pens in a Gas-discharge
Lamp?" 194
Fox fire, luminescence of fungus,

58
Fraunhofer, Joseph, spectroscope,

178
Fundy, Bay of, tides in, 191

Galileo, pendulum, 29
sound vibrations, 65

[301]

Excursions in Science

Gamma, unit of mass, 112, 113

Gas, perfect, 49

Gems, 206-214 .

Gene, carrier of inheritance, 236

size of, 240, 241

Germanium, properties of pre-
dicted, 19
Glens Falls diamond, form of

quartz, 207

Glucose, product of digestion, 89
Glycerin, product of digestion,

23,89

Glycogen, stored in liver, 92, 93
Goodspeed, T. H., mutations by

X rays, 238
Gordon, Newell T., "Odors and

Their Detection," 103
Ground hog, Candlemas Day

superstition, 204
Grover, Frederick W., "The

Red Planet Mars," 80
"The Tides," 184
Guericke, Otto von, vacuum, 76,

77

H

Hallowe'en, quarter day of old
calendar, 203

Hardness scales, 212, 213

Harmonic echo, 67

Harris, R. A., theory of tides,
189, 190

Harvey, E. N., animal lumines-
cence, 62

Haskins, Caryl P., "The Ma-
chinery of Heredity," 234

Hawkins, Laurence A., "The
Limitations of Science," 292

Hayden Planetarium Grace
Eclipse Expedition, 215

Heavy spar, fluorescence of, 244

Heliodor, 210

Helium, discovery of, 180

Hcnnelly, Edward F., "Vac-
uum," 73

Heredity, 234-243

Herkimer diamond, form of
quartz, 207

Herschel, Sir John, fluorescence,
245

Hewlett, Clarence W., "Power
from the Sun," 96

Homer, ozone produced by
lightning, 128

Huanchaco, Peru, eclipse expedi-
tion to, 218

I

Indigo, produced synthetically,

274
Infrared radiation, absorption

by perfumes, 109
penetration of haze by, 290
Interference, colors produced by,

8, 257-263

Iodine, in thyroid gland, 94
lonization, of sodium atom, 197

Johnson, Ralph P., "Electron
Optics," 284

Kelvin temperature scale, 48
Roller, Lewis R., "Animal
Light," 57

[302]

Index

Korff, Serge, eclipse expedition,
218, 219

Lake George diamond, form of
quartz, 207

Lammas, quarter day of old
calendar, 203

Langmuir, Irving, "Simple Ex-
periments in Science," 3
space-charge law, 231
thermionic emission, 227

Laue, Max von, X-ray diffrac-
tion, 183

Leonids, recurrence of, 56

Lewis, Isabel M., eclipse expedi-
tion, 218

Licbhafsky, Herman A., "Lilli-
putian Chemistry," 112

Lightning, artificial, 39
natural, 35-42

current, voltage, and power

in, 38, 39

fatal accidents from, 42
speed of, 36
streamer preceding, 36

Lightning rods, 41

Lockycr, Sir Norman, discovery

of helium, 180
study of Stonchenge, 202, 203

Luciferase, catalyst in lumines-
cence, 60

Luciferin, luminescence due to,
60

Luminescence, animal, efficiency

of, 62, 63
method of production, 60

M

McArthur, Elmer D., "How
Your Radio Tubes Work,"
225

McEachron, Karl B., "The Na-
ture of Lightning," 35

Magdeburg hemispheres, 77

Malachite, color of, 208

Mallet, Robert, earthquakes, 121

Marquesas Islands, solar tides at,
191

Mars, atmosphere of, 83
canals on, 84
distance from earth, 81
gravity on, 82

length of day and year on, 81
temperatures on, 83

Martinmas, relic of old calendar,
204

Mavor, James W., "Where Hu-
man Energy Comes From,"
20

May Day, quarter day of old
calendar, 203

May-November calendar, evi-
dence for former use of,
203, 204

Mendelyeev, Dmitri, periodic
system of elements, 1 51 9

Mercury, transmutation to gold,
147

Mercury arc, source of ultra-
violet, 247

Metabolism, basal, 22

Metals, discovery of, 168175

Meteorites, largest known speci-
mens, 54, 55

[303]

Excursions in Science

Meteorites, minerals found in, 51

velocity of, 53, 54
Meteors, consumed in atmos-
phere, 51
recurring showers, Leonids, 55,

56
Microchemistry, techniques of,

115, 116

Microscope, electron, 286, 288
Miller, P. Schuyler, "An Ama-
teur Looks at Archeology,"
264

Minas, Basin of, tides in, 191
Minerals, allochromatic, 208

idiochromatic, 208
Mohs scale of hardness, 212, 213
Molecular weight, method of

determining, 280
Moon, orbit around earth, 217
Muchow, Albert J., "Ears, Hu-
man and Electric," 64
Mutations, produced by neu-
trons, 242
produced by X rays, 237-240

N

National Geographic U. S.
Navy Expedition, solar
eclipse, 216

Neon, discovery of, 179
Neutron, atomic particle, 145
mass of, 145

mutations produced by, 242
Newby, Raymond, eclipse ex-
pedition, 219
Newton, Sir Isaac, dispersion of

light, 178
law of gravitation, 186

Norton, Francis J., "Ozone," 127
Nose, human, sensitivity of, 103

Odors, absorption spectra of, 109
classification of, 107
threshold values for, 103, 104
Optics, electron, 284-291
Ozone, absorbed by ultraviolet,

131, 132

bleaching action of, 130
destructive to rubber, 131
effect of breathing, 129
in upper atmosphere, 133

Paleontology, 135-142

Parker, Earl A., "Men and

Metals," 168
Pauly, Karl A., "The Earth as a

Diary," 135

Pepsin, agent in digestion, 90
Perigee, cause of spring tides, 188
Periodic system of elements,

16-19

Phosphorescence, cause of, 252
Photoelectric cell, blocking layer,

100, 101
Photoelectric surface, sensitive

to infrared, 290
Photosynthesis, efficiency of, 25,

26
Pittsfield, Mass., high- voltage

research at, 39
Pliny, tides, 185
Polar axis, 219, 220

[304]

Index

Precession of the equinoxes,

Stonehenge dated by, 202
Principia, Newton, 186
Probability, theory of, 162-167
Protein, basic element of food,
23,87

chemical composition of, 87

molecular weight of, 9
Proton, atomic particle, 145
Prout's hypothesis, 144, 145
Ptyalin, agent in digestion, 90

Quartz, common names for, 207
distribution of, 207
rose, 207
transparent to ultraviolet, 132

R

Radio tubes, operation of, 225-

233

Reaumur temperature scale, 46
Rectifier, vacuum-tube, 229
Reimann, A. L., thermionic

emission, 227
Reynolds, Neil B., "Science and

Superstition," 200
Rhinestone, form of quartz, 207
Richardson, O. W., thermionic

emission, 227

Ridenour, Louis N., "Adven-
tures Within the Atoms,"

143
Rochow, E. G., "Atoms and

Their Family Relations," 11
"Stones Precious and Other-
wise," 206

Roentgen, Wilhelm K., X rays,

237

Rose quartz, 207
Ruby, chemical composition of,

208-210
Rutherford, Sir Ernest, nuclear

disintegration, 156, 157

St. Elmo's fire, electrical corona,

158

Saint John, N. B., tides at, 191
Sapphire, chemical composition

of, 208, 209
Schiaparelli, Giovanni, canals on

Mars, 84

Seismograph, principle of, 123
Selenium, photoelectric property

of, 101

Smell, human organ of, 106
Smith, Edward S. G., "How

Earthquakes Give Us the

Inside Facts," 118
"Meteorites," 50
Smoke prccipitator, electrical,

105

Solar energy, efficiency of con-
version of, 26, 99-102
intercepted by earth, 24, 25, 99
Solstice, used to date Stonehenge,

202
Sound, energy equivalent of, 66

speed of, 66
Space-charge law, vacuum tubes,

231

Spectroscope, invention of, 178
X-ray, 182

[305]

Excursions in Science

Spectrum analysis, developed

by Bunsen, 179

discovery of elements by, 179-
181

"Spotlight," electron, 286, 287

Sprung, Murray M., "Chemical
Reactions in the Human
Body," 86
"Identifying Molecules," 274

Stearic acid, size of molecule, 262

Steel, rust resisting, 174
tempering of, 173

Stephens, IX Owen, eclipse ex-
pedition, 221

Stevens, Albert W., eclipse ex-
pedition, 219, 221

Stewart, John Q., eclipse expedi-
tion, 216

Stokely, James, eclipse expedi-
tion, 216

Stokes' law, of fluorescence, 246

Stone Age, tools of, 169, 201

Stonehcnge, date of erection of,
202, 203

Superstitions, 200-205

Surge generator, for nuclear
bombardment, 158

Thermometer, gas, 47, 48

liquid, 44
Tide, energy from, 97

neap, 188

nodal line, 190

origin of, 186, 187

solar, 187, 192

spring, 185, 188

stationai y-wave theory, 189,

190
Time, mean solar, 30

sidereal, 30

Tonks, Lewi, "Time," 27
Topaz, false, 207
Torricellian vacuum, 76
Transmutation of elements, 147-

161
Turquoise, color of, 208

U

Ultraviolet radiation, absorbed

by ozone, 131-133
excites fluorescence, 247
Urea, synthesis of, 275

Taste, classification of, 108
Temperature, absolute zero of, 48

blood, 45, 46
Temperature scale, Celsius, 46

centigrade, 46

Fahrenheit, 45, 46

Kelvin or absolute, 48

R6aumur, 46
Thermoelectric effect, 100

Vacuum, highest obtainable, 73

residual gases in, 78

Torricellian, 76

Vacuum tube, amplification by,
233

function of grid, 232

rectification by, 229
Vitamins, basic element of food.
87

number identified, 90

[306]

Index
w x

Wave lengths, of electromagnetic x ' ra V spectroscope, 182, 183

waves, 180, 259 2C rays, mutations produced by,

Welsbach, Auer von, rare earth 237-241

elements, 181 production of, 182

Wintergreen, oil of, synthetic, z

274

Wrought iron, origin of, 173 Zircon, 211

[307]