The Outline of Science, Vol. 1 (of 4)

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Sec. 2

The Wonder-World of Atoms

The exploration of this wonder-world of atoms and molecules by the
physicists and chemists of to-day is one of the most impressive triumphs
of modern science. Quite apart from radium and electrons and other
sensational discoveries of recent years, the study of ordinary matter is
hardly inferior, either in interest or audacity, to the work of the
astronomer. And there is the same foundation in both cases--marvellous
apparatus, and trains of mathematical reasoning that would have
astonished Euclid or Archimedes. Extraordinary, therefore, as are some
of the facts and figures we are now going to give in connection with the
minuteness of atoms and molecules, let us bear in mind that we owe them
to the most solid and severe processes of human thought.

Yet the principle can in most cases be made so clear that the reader
will not be asked to take much on trust. It is, for instance, a matter
of common knowledge that gold is soft enough to be beaten into gold
leaf. It is a matter of common sense, one hopes, that if you beat a
measured cube of gold into a leaf six inches square, the mathematician
can tell the thickness of that leaf without measuring it. As a matter of
fact, a single grain of gold has been beaten into a leaf seventy-five
inches square. Now the mathematician can easily find that when a single
grain of gold is beaten out to that size, the leaf must be 1/367,000 of
an inch thick, or about a thousand times thinner than the paper on
which these words are printed; yet the leaf must be several molecules
thick.

The finest gold leaf is, in fact, too thick for our purpose, and we turn
with a new interest to that toy of our boyhood the soap-bubble. If you
carefully examine one of these delicate films of soapy water, you notice
certain dark spots or patches on them. These are their thinnest parts,
and by two quite independent methods--one using electricity and the
other light--we have found that at these spots the bubble is less than
the three-millionth of an inch thick! But the molecules in the film
cling together so firmly that they must be at least twenty or thirty
deep in the thinnest part. A molecule, therefore, must be far less than
the three-millionth of an inch thick.

We found next that a film of oil on the surface of water may be even
thinner than a soap-bubble. Professor Perrin, the great French authority
on atoms, got films of oil down to the fifty-millionth of an inch in
thickness! He poured a measured drop of oil upon water. Then he found
the exact limits of the area of the oil-sheet by blowing upon the water
a fine powder which spread to the edge of the film and clearly outlined
it. The rest is safe and simple calculation, as in the case of the
beaten grain of gold. Now this film of oil must have been at least two
molecules deep, so a single molecule of oil is considerably less than a
hundred-millionth of an inch in diameter.

Innumerable methods have been tried, and the result is always the same.
A single grain of indigo, for instance, will colour a ton of water. This
obviously means that the grain contains billions of molecules which
spread through the water. A grain of musk will scent a room--pour
molecules into every part of it--for several years, yet not lose
one-millionth of its mass in a year. There are a hundred ways of showing
the minuteness of the ultimate particles of matter, and some of these
enable us to give definite figures. On a careful comparison of the best
methods we can say that the average molecule of matter is less than
the 1/125,000,000 of an inch in diameter. In a single cubic centimetre
of air--a globule about the size of a small marble--there are thirty
million trillion molecules. And since the molecule is, as we saw, a
group or cluster of atoms, the atom itself is smaller. Atoms, for
reasons which we shall see later, differ very greatly from each other in
size and weight. It is enough to say that some of them are so small that
it would take 400,000,000 of them, in a line, to cover an inch of space;
and that it takes at least a quintillion atoms of gold to weigh a single
gramme. Five million atoms of helium could be placed in a line across
the diameter of a full stop.

[Illustration: An atom is the smallest particle of a chemical element.
Two or more atoms come together to form a molecule: thus molecules form
the mass of matter. A molecule of water is made up of two atoms of
hydrogen and one atom of oxygen. Molecules of different substances,
therefore, are of different sizes according to the number and kind of
the particular atoms of which they are composed. A starch molecule
contains no less than 25,000 atoms.

Molecules, of course, are invisible. The above diagram illustrates the
_comparative_ sizes of molecules.]

[Illustration: INCONCEIVABLE NUMBERS AND INCONCEIVABLY SMALL PARTICLES

The molecules, which are inconceivably small, are, on the other hand, so
numerous that if one was able to place, end to end, all those contained
in, for example, a cubic centimetre of gas (less than a fifteenth of a
cubic inch), one would obtain a line capable of passing two hundred
times round the earth.]

[Illustration: WHAT IS A MILLION?

In dealing with the infinitely small, it is difficult to apprehend the
vast figures with which scientists confront us. A million is one
thousand thousand. We may realise what this implies if we consider that
a clock, beating seconds, takes approximately 278 hours (i.e. one week
four days fourteen hours) to tick one million times. A billion is one
million million. To tick a billion the clock would tick for over 31,735
years.

(In France and America a thousand millions is called a billion.)]

[Illustration: THE BROWNIAN MOVEMENT

A diagram, constructed from actual observations, showing the erratic
paths pursued by very fine particles suspended in a liquid, when
bombarded by the molecules of the liquid. This movement is called the
Brownian movement, and it furnishes a striking illustration of the truth
of the theory that the molecules of a body are in a state of continual
motion.]

The Energy of Atoms

And this is only the beginning of the wonders that were done with
"ordinary matter," quite apart from radium and its revelations, to which
we will come presently. Most people have heard of "atomic energy," and
the extraordinary things that might be accomplished if we could harness
this energy and turn it to human use. A deeper and more wonderful source
of this energy has been discovered in the last twenty years, but it is
well to realise that the atoms themselves have stupendous energy. The
atoms of matter are vibrating or gyrating with extraordinary vigour. The
piece of cold iron you hold in your hand, the bit of brick you pick up,
or the penny you take from your pocket is a colossal reservoir of
energy, since it consists of trillions of moving atoms. To realise the
total energy, of course, we should have to witness a transformation such
as we do in atoms of radio-active elements, about which we shall have
something to say presently.

If we put a grain of indigo in a glass of water, or a grain of musk in a
perfectly still room, we soon realise that molecules travel. Similarly,
the fact that gases spread until they fill every "empty" available space
shows definitely that they consist of small particles travelling at
great speed. The physicist brings his refined methods to bear on these
things, and he measures the energy and velocity of these infinitely
minute molecules. He tells us that molecules of oxygen, at the
temperature of melting ice, travel at the rate of about 500 yards a
second--more than a quarter of a mile a second. Molecules of hydrogen
travel at four times that speed, or three times the speed with which a
bullet leaves a rifle. Each molecule of the air, which seems so still in
the house on a summer's day, is really travelling faster than a rifle
bullet does at the beginning of its journey. It collides with another
molecule every twenty-thousandth of an inch of its journey. It is turned
from its course 5,000,000,000 times in every second by collisions. If we
could stop the molecules of hydrogen gas, and utilise their energy, as
we utilise the energy of steam or the energy of the water at Niagara, we
should find enough in every gramme of gas (about two-thousandths of a
pound) to raise a third of a ton to a height of forty inches.

I have used for comparison the speed of a rifle bullet, and in an
earlier generation people would have thought it impossible even to
estimate this. It is, of course, easy. We put two screens in the path of
the bullet, one near the rifle and the other some distance away. We
connect them electrically and use a fine time-recording machine, and the
bullet itself registers the time it takes to travel from the first to
the second screen.

Now this is very simple and superficial work in comparison with the
system of exact and minute measurements which the physicist and chemist
use. In one of his interesting works Mr. Charles R. Gibson gives a
photograph of two exactly equal pieces of paper in the opposite pans of
a fine balance. A single word has been written in pencil on one of these
papers, and that little scraping of lead has been enough to bring down
the scale! The spectroscope will detect a quantity of matter four
million times smaller even than this; and the electroscope is a million
times still more sensitive than the spectroscope. We have a
heat-measuring instrument, the bolometer, which makes the best
thermometer seem Early Victorian. It records the millionth of a degree
of temperature. It is such instruments, multiplied by the score,
which enable us to do the fine work recorded in these pages.

[Illustration: _Reproduced from "The Forces of Nature" (Messrs.
Macmillan)._

A SOAP BUBBLE

The iridescent colours sometimes seen on a soap bubble, as in the
illustration, may also be seen in very fine sections of crystals, in
glass blown into extremely fine bulbs, on the wings of dragon-flies and
the surface of oily water. The different colours correspond to different
thicknesses of the surface. Part of the light which strikes these thin
coatings is reflected from the upper surface, but another part of the
light penetrates the transparent coating and is reflected from the lower
surface. It is the mixture of these two reflected rays, their
"interference" as it is called, which produces the colours observed. The
"black spots" on a soap bubble are the places where the soapy film is
thinnest. At the black spots the thickness of the bubble is about the
three-millionth part of an inch. If the whole bubble were as thin as
this it would be completely invisible.]

Sec. 3

THE DISCOVERY OF X-RAYS AND RADIUM

The Discovery of Sir Wm. Crookes

But these wonders of the atom are only a prelude to the more romantic
and far-reaching discoveries of the new physics--the wonders of the
electron. Another and the most important phase of our exploration of the
material universe opened with the discovery of radium in 1898.

In the discovery of radio-active elements, a new property of matter was
discovered. What followed on the discovery of radium and of the X-rays
we shall see.

As Sir Ernest Rutherford, one of our greatest authorities, recently
said, the new physics has dissipated the last doubt about the reality of
atoms and molecules. The closer examination of matter which we have been
able to make shows positively that it is composed of atoms. But we must
not take the word now in its original Greek meaning (an "indivisible"
thing). The atoms are not indivisible. They can be broken up. They are
composed of still smaller particles.

The discovery that the atom was composed of smaller particles was the
welcome realisation of a dream that had haunted the imagination of the
nineteenth century. Chemists said that there were about eighty different
kinds of atoms--different kinds of matter--but no one was satisfied with
the multiplicity. Science is always aiming at simplicity and unity. It
may be that science has now taken a long step in the direction of
explaining the fundamental unity of all the matter. The chemist was
unable to break up these "elements" into something simpler, so he called
their atoms "indivisible" in that sense. But one man of science after
another expressed the hope that we would yet discover some fundamental
matter of which the various atoms were composed--_one primordial
substance from which all the varying forms of matter have been evolved
or built up_. Prout suggested this at the very beginning of the century,
when atoms were rediscovered by Dalton. Father Secchi, the famous Jesuit
astronomer said that all the atoms were probably evolved from ether; and
this was a very favoured speculation. Sir William Crookes talked of
"prothyl" as the fundamental substance. Others thought hydrogen was the
stuff out of which all the other atoms were composed.

The work which finally resulted in the discovery of radium began with
some beautiful experiments of Professor (later Sir William) Crookes in
the eighties.

It had been noticed in 1869 that a strange colouring was caused when an
electric charge was sent through a vacuum tube--the walls of the glass
tube began to glow with a greenish phosphorescence. A vacuum tube is one
from which nearly all the air has been pumped, although we can never
completely empty the tube. Crookes used such ingenious methods that he
reduced the gas in his tubes until it was twenty million times thinner
than the atmosphere. He then sent an electric discharge through, and got
very remarkable results. The negative pole of the electric current (the
"cathode") _gave off rays which faintly lit the molecules of the thin
gas in the tube_, and caused a pretty fluorescence on the glass walls of
the tube. What were these Rays? Crookes at first thought they
corresponded to a "new or fourth state of matter." Hitherto we had only
been familiar with matter in the three conditions of solid, liquid, and
gaseous.

Now Crookes really had the great secret under his eyes. But about twenty
years elapsed before the true nature of these rays was finally and
independently established by various experiments. The experiments proved
"that the rays consisted of a stream of negatively charged particles
travelling with enormous velocities from 10,000 to 100,000 miles a
second. In addition, it was found that the mass of each particle was
exceedingly small, about 1/1800 of the mass of a hydrogen atom, the
lightest atom known to science." _These particles or electrons, as they
are now called, were being liberated from the atom._ The atoms of matter
were breaking down in Crookes tubes. At that time, however, it was
premature to think of such a thing, and Crookes preferred to say that
the particles of the gas were electrified and hurled against the walls
of the tube. He said that it was ordinary matter in a new
state--"radiant matter." Another distinguished man of science, Lenard,
found that, when he fitted a little plate of aluminum in the glass wall
of the tube, the mysterious rays passed through this as if it were a
window. They must be waves in the ether, he said.

[Illustration: _From "Scientific Ideas of To-day_."

DETECTING A SMALL QUANTITY OF MATTER

In the left-hand photograph the two pieces of paper exactly balance. The
balance used is very sensitive, and when the single word "atoms" has
been written with a lead pencil upon one of the papers the additional
weight is sufficient to depress one of the pans as shown in the second
photograph. The spectroscope will detect less than one-millionth of the
matter contained in the word pencilled above.]

[Illustration: _Reproduced by permission of X-Rays Ltd._

THIS X-RAY PHOTOGRAPH IS THAT OF A HAND OF A SOLDIER WOUNDED IN THE
GREAT WAR

Note the pieces of shrapnel which are revealed.]

[Illustration: _Photo: National Physical Laboratory._

AN X-RAY PHOTOGRAPH OF A GOLF BALL, REVEALING AN IMPERFECT CORE]

[Illustration: _Reproduced by permission of X-Rays Ltd._

A WONDERFUL X-RAY PHOTOGRAPH

Note the fine details revealed, down to the metal tags of the bootlace
and the nails in the heel of the boot.]

Sec. 4

The Discovery of X-rays

So the story went on from year to year. We shall see in a moment to what
it led. Meanwhile the next great step was when, in 1895, Roentgen
discovered the X-rays, which are now known to everybody. He was
following up the work of Lenard, and he one day covered a "Crookes tube"
with some black stuff. To his astonishment a prepared chemical screen
which was near the tube began to glow. _The rays had gone through the
black stuff; and on further experiment he found that they would go
through stone, living flesh, and all sorts of "opaque" substances._ In a
short time the world was astonished to learn that we could photograph
the skeleton in a living man's body, locate a penny in the interior of a
child that had swallowed one, or take an impression of a coin through a
slab of stone.

And what are these X-rays? They are not a form of matter; they are not
material particles. X-rays were found to be a new variety of _light_
with a remarkable power of penetration. We have seen what the
spectroscope reveals about the varying nature of light wave-lengths.
Light-waves are set up by vibrations in ether,[2] and, as we shall see,
these ether disturbances are all of the same kind; they only differ as
regards wave-lengths. The X-rays which Roentgen discovered, then, are
light, but a variety of light previously unknown to us; they are ether
waves of very short length. X-rays have proved of great value in many
directions, as all the world knows, but that we need not discuss at this
point. Let us see what followed Roentgen's discovery.

[2] We refer throughout to the "ether" because, although modern
theories dispense largely with this conception, the theories of
physics are so inextricably interwoven with it that it is necessary,
in an elementary exposition, to assume its existence. The modern
view will be explained later in the article on Einstein's Theory.

While the world wondered at these marvels, the men of science were
eagerly following up the new clue to the mystery of matter which was
exercising the mind of Crookes and other investigators. In 1896
Becquerel brought us to the threshold of the great discovery.

Certain substances are phosphorescent--they become luminous after they
have been exposed to sunlight for some time, and Becquerel was trying to
find if any of these substances give rise to X-rays. One day he chose a
salt of the metal uranium. He was going to see if, after exposing it to
sunlight, he could photograph a cross with it through an opaque
substance. He wrapped it up and laid it aside, to wait for the sun, but
he found the uranium salt did not wait for the sun. Some strong
radiation from it went through the opaque covering and made an
impression of the cross upon the plate underneath. Light or darkness was
immaterial. The mysterious rays streamed night and day from the salt.
This was something new. Here was a substance which appeared to be
producing X-rays; the rays emitted by uranium would penetrate the same
opaque substances as the X-rays discovered by Roentgen.

Discovery of Radium

Now, at the same time as many other investigators, Professor Curie and
his Polish wife took up the search. They decided to find out whether
the emission came from the uranium itself or _from something associated
with it_, and for this purpose they made a chemical analysis of great
quantities of minerals. They found a certain kind of pitchblende which
was very active, and they analysed tons of it, concentrating always on
the radiant element in it. After a time, as they successively worked out
the non-radiant matter, the stuff began to glow. In the end they
extracted from eight tons of pitchblende about half a teaspoonful of
something _that was a million times more radiant than uranium_. There
was only one name for it--Radium.

That was the starting-point of the new development of physics and
chemistry. From every laboratory in the world came a cry for radium
salts (as pure radium was too precious), and hundreds of brilliant
workers fastened on the new element. The inquiry was broadened, and, as
year followed year, one substance after another was found to possess the
power of emitting rays, that is, to be radio-active. We know to-day that
nearly every form of matter can be stimulated to radio-activity; which,
as we shall see, means that _its atoms break up into smaller and
wonderfully energetic particles which we call "electrons."_ This
discovery of electrons has brought about a complete change in our ideas
in many directions.

So, instead of atoms being indivisible, they are actually dividing
themselves, spontaneously, and giving off throughout the universe tiny
fragments of their substance. We shall explain presently what was later
discovered about the electron; meanwhile we can say that every glowing
metal is pouring out a stream of these electrons. Every arc-lamp is
discharging them. Every clap of thunder means a shower of them. Every
star is flooding space with them. We are witnessing the spontaneous
breaking up of atoms, atoms which had been thought to be indivisible.
The sun not only pours out streams of electrons from its own atoms, but
the ultra-violet light which it sends to the earth is one of the most
powerful agencies for releasing electrons from the surface-atoms of
matter on the earth. It is fortunate for us that our atmosphere absorbs
most of this ultra-violet or invisible light of the sun--a kind of light
which will be explained presently. It has been suggested that, if we
received the full flood of it from the sun, our metals would
disintegrate under its influence and this "steel civilisation" of ours
would be impossible!

But we are here anticipating, we are going beyond radium to the
wonderful discoveries which were made by the chemists and physicists of
the world who concentrated upon it. The work of Professor and Mme. Curie
was merely the final clue to guide the great search. How it was followed
up, how we penetrated into the very heart of the minute atom and
discovered new and portentous mines of energy, and how we were able to
understand, not only matter, but electricity and light, will be told in
the next chapter.

THE DISCOVERY OF THE ELECTRON AND HOW IT EFFECTED A REVOLUTION IN IDEAS

What the discovery of radium implied was only gradually realised. Radium
captivated the imagination of the world; it was a boon to medicine, but
to the man of science it was at first a most puzzling and most
attractive phenomenon. It was felt that some great secret of nature was
dimly unveiled in its wonderful manifestations, and there now
concentrated upon it as gifted a body of men--conspicuous amongst them
Sir J. J. Thomson, Sir Ernest Rutherford, Sir W. Ramsay, and Professor
Soddy--as any age could boast, with an apparatus of research as far
beyond that of any other age as the _Aquitania_ is beyond a Roman
galley. Within five years the secret was fairly mastered. Not only were
all kinds of matter reduced to a common basis, but the forces of the
universe were brought into a unity and understood as they had never been
understood before.

[Illustration: ELECTRIC DISCHARGE IN A VACUUM TUBE

The two ends, marked + and -, of a tube from which nearly all air has
been exhausted are connected to electric terminals, thus producing an
electric discharge in the vacuum tube. This discharge travels straight
along the tube, as in the upper diagram. When a magnetic field is
applied, however, the rays are deflected, as shown in the lower diagram.
The similarity of the behaviour of the electric discharge with the
radium rays (see diagram of deflection of radium rays, _post_) shows
that the two phenomena may be identified. It was by this means that the
characteristics of electrons were first discovered.]

[Illustration: THE RELATIVE SIZES OF ATOMS AND ELECTRONS

An atom is far too small to be seen. In a bubble of hydrogen gas no
larger than the letter "O" there are billions of atoms, whilst an
electron is more than a thousand times smaller than the smallest atom.
How their size is ascertained is described in the text. In this diagram
a bubble of gas is magnified to the size of the world. Adopting this
scale, _each atom_ in the bubble would then be as large as a tennis
ball.]

[Illustration: IF AN ATOM WERE MAGNIFIED TO THE SIZE OF ST. PAUL'S
CATHEDRAL, EACH ELECTRON IN THE ATOM (AS REPRESENTED BY THE CATHEDRAL)
WOULD THEN BE ABOUT THE SIZE OF A SMALL BULLET]

[Illustration: ELECTRONS STREAMING FROM THE SUN TO THE EARTH

There are strong reasons for supposing that sun-spots are huge
electronic cyclones. The sun is constantly pouring out vast streams of
electrons into space. Many of these streams encounter the earth, giving
rise to various electrical phenomena.]

Sec. 5

The Discovery of the Electron

Physicists did not take long to discover that the radiation from radium
was very like the radiation in a "Crookes tube." It was quickly
recognised, moreover, that both in the tube and in radium (and other
metals) the atoms of matter were somehow breaking down.

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