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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 

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 

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 

" 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 

330 West 42nd Street, New York 


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

W. R. W. 




General Electric Company 


Supervisor of Science , New Fork State Department of Education 


A division of the McGraw-Hill Book Company, Inc. 

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







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 

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 

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. 



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 ] 


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. 










by DR. E. G. ROCHOW 



TIME 27 



























OZONE 127 





by DR. Louis N. RIDENOUR 

I. What Atoms Are 143 

II. How to Change Atoms into Other Atoms 151 

















by DR. E. G. ROCHOW 








INCH 255 










INDEX 299 

[ i 



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. 


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 

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, 


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. 


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 


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 


Excursions in Science 

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

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. 


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. 


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. 



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. 


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. 


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 


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 

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 


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 

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. 


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 

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 


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 

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 

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 


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 


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. 




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 


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 


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 


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 


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 


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 


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 




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- 


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- 



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- 


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 



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 

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 


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 

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 



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 


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 

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. 




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 


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 


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 


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 

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 


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 

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 


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 


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. 


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. 




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 


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. 


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 


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 


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 


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. 


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. 




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 



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. 


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. 



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- 


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 

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. 



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 

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 

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


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. 



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 


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 

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 


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. 


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- 


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 


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 


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. 




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 


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. 


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 


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. 


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 


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 


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. 


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, 


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. 




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 


Excursions in Science 

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

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 

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 

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 



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 


Excursions in Science 

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

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 



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 


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- 



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. 




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 


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- 


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 

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- 


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 


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- 


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, 




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. 


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 


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 

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- 


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 


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 


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 


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 

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 


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 

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. 


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. 




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. 


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 

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. 


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 


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 


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 


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 


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. 




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- 


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 


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, 


Excursions in Science 

rendering the filter ineffective for the elimination of 

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 


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 

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 

5. Burnt odors, such as tar and pyridine. 

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


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 


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- 


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 


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. 




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 


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. 


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 


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, 


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 

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 


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 

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. 




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? 


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, 


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 


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 


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 

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. 


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 


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 


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. 


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. 




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. 


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 



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 

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 


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 . 



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. 


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, 



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. 


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 




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 


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 


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- 


Excursions in Science 

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

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 

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 


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. 


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 


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 

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 

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 


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. 



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 


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, 


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 


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 


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 


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 


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 

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 


Excursions in Science 

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. 


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; 


Excursions in Science 

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 


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 


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 


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 


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 


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 


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 

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 


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 

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 


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. 


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. 




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 


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. 

[ 163 ] 

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 


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 


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 


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 




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 

[ 168 ] 

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 


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 


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 


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 


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 

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 


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 

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 

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


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. 




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 

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 

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 


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 


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. 


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 


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 


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. 


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 


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. 




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 


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 


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. 


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 


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, 


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 


Excursions in Science 

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

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 


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 


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 

[ 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 




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 


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 


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 


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, 


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. 




"|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 


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 


Excursions in Science 

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 

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 


Science and Superstition 

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 


Excursions in Science 

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 


Science and Superstition 

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. 



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 


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 


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 


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, 

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 


Excursions in Science 

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 


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 


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 

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 


Excursions in Science 

not been popular enough even to warrant a distinctive 

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 


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 


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. 




-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. 


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 


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 

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 


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 


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 


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. 


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 


Excursions in Science 

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 


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 


Excursions in Science 

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. 




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 

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. 


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 


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 

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 

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- 


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 


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 

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 

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 


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- 


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 


How Your Radio Tubes Work 

filament controls the attractive force exerted by the 

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 

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. 




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 


The Machinery of Heredity 

year, and reserves for planting only those not fit for 

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- 


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 


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 


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 


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 

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 


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. 


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. 


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- 


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. 




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 

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. 


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, 


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 


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 


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. 


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 


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 


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 


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. 


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 


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. 




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- 


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. 


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 


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 


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 


Excursions in Science 

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

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 


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. 


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 


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 




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 


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 

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, 


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 


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 


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 

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 


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 


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 


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 


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 


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 




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. 


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 , 


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 


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 

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 


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- 


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 

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. 


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 


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. 


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 


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. 




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 


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 

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 


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 


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 


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 


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. 


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 


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. 




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 


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 


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 

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 


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 


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 


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. 


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. 




Abbot, C. G., solar engine, 99 
Absolute temperature scale, 48 
Alcohol, in blood, 117 

molecular structure of, 277- 


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, 


Archimedes' Principle, 176, 177 
Aristotle, sound, 65 
Astronomical year, beginning of, 

Atom, definition of, 13 

excited, cause of fluorescence, 


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 


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, 

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 


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, 

Cathode, of electron tube, 194, 

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, 

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 


Dalton's hypothesis, 277 
Decibel, values for common 

sounds, 71 

Detector, mercury vapor, 110 
Diamond, hardness of, 212, 213 
industrial (bortz, carbonado), 


Dushman, Saul, thermionic emis- 
sion, 227 


Ear, "electric," 70 

human, frequency response of, 

structure of, 68 



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, 

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 


Fahrenheit temperature scale, 

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," 

"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, 

Fraunhofer, Joseph, spectroscope, 

Fundy, Bay of, tides in, 191 

Galileo, pendulum, 29 
sound vibrations, 65 


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, 


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, 



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, 

Hewlett, Clarence W., "Power 
from the Sun," 96 

Homer, ozone produced by 
lightning, 128 

Huanchaco, Peru, eclipse expedi- 
tion to, 218 


Indigo, produced synthetically, 

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 



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, 

Luminescence, animal, efficiency 

of, 62, 63 
method of production, 60 


McArthur, Elmer D., "How 
Your Radio Tubes Work," 

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, 

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, 

Mavor, James W., "Where Hu- 
man Energy Comes From," 

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, 

Mercury arc, source of ultra- 
violet, 247 

Metabolism, basal, 22 

Metals, discovery of, 168175 

Meteorites, largest known speci- 
mens, 54, 55 


Excursions in Science 

Meteorites, minerals found in, 51 

velocity of, 53, 54 
Meteors, consumed in atmos- 
phere, 51 
recurring showers, Leonids, 55, 

Microchemistry, techniques of, 

115, 116 

Microscope, electron, 286, 288 
Miller, P. Schuyler, "An Ama- 
teur Looks at Archeology," 

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 


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, 


Phosphorescence, cause of, 252 
Photoelectric cell, blocking layer, 

100, 101 
Photoelectric surface, sensitive 

to infrared, 290 
Photosynthesis, efficiency of, 25, 

Pittsfield, Mass., high- voltage 

research at, 39 
Pliny, tides, 185 
Polar axis, 219, 220 



Precession of the equinoxes, 

Stonehenge dated by, 202 
Principia, Newton, 186 
Probability, theory of, 162-167 
Protein, basic element of food, 

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 


Radio tubes, operation of, 225- 


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," 

Rochow, E. G., "Atoms and 

Their Family Relations," 11 
"Stones Precious and Other- 
wise," 206 

Roentgen, Wilhelm K., X rays, 


Rose quartz, 207 
Ruby, chemical composition of, 

Rutherford, Sir Ernest, nuclear 

disintegration, 156, 157 

St. Elmo's fire, electrical corona, 


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, 


Solar energy, efficiency of con- 
version of, 26, 99-102 
intercepted by earth, 24, 25, 99 
Solstice, used to date Stonehenge, 

Sound, energy equivalent of, 66 

speed of, 66 
Space-charge law, vacuum tubes, 


Spectroscope, invention of, 178 
X-ray, 182 


Excursions in Science 

Spectrum analysis, developed 

by Bunsen, 179 

discovery of elements by, 179- 

"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, 

Time, mean solar, 30 

sidereal, 30 

Tonks, Lewi, "Time," 27 
Topaz, false, 207 
Torricellian vacuum, 76 
Transmutation of elements, 147- 

Turquoise, color of, 208 


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, 

function of grid, 232 

rectification by, 229 
Vitamins, basic element of food. 

number identified, 90 


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 


Wrought iron, origin of, 173 Zircon, 211