the sun produced waves in the aether, and that when these aether waves
fell upon other atoms on this planet, these were set into a state of
vibration, thus producing heat and light. Now if man had only stopped to
think, he would have seen how ridiculous it was to speak of atoms of
matter producing waves in the aether. He ought to have known that atoms
of matter cannot affect the aether, for it offers no resistance to
matter moving through it.
Man might have pictured himself riding on the back of this great planet,
flying through space at a speed very similar to that of a rifle bullet,
and yet even the flimsy blanket of air surrounding the planet is not
disturbed by the aether through which it is rushing.
It is true that the atoms of matter play an important part in the origin
of heat, but the atoms in the sun could no more affect the atoms on the
earth than could a man on the earth push the moon about. It is the very
intimate connection between us electrons and the all-pervading aether
which enables our fellows in the sun to communicate with those of us
upon this planet. Where would man be without us?
[Illustration: PROTECTION AGAINST A DISCHARGE OF ELECTRONS
_By permission of Siemens Schuckert Werke_
_Berlin_
When a man is encased completely in an over-all made of flexible
metallic gauze he is proof against shock due to a discharge of
high-tension electricity. The part played by electrons in the case of
electric shock is explained in Chapter IV.]
I cannot understand wherein man should find any mystery in connection
with this very simple action of ours. You will picture our distant
fellow-electrons making very rapid revolutions around the atoms of
matter to which they are attached as satellites. Just as the moon
circles around the earth, so do we circle around our atoms, but at an
enormously greater speed. Of course the whole length of our orbit is
inconceivably small, and the speed of our revolutions is inconceivably
great. It is our rapid motion through the aether which produces those
waves known to man as radiant heat and light. Some one may ask how it is
that we electrons can disturb the aether while the giant atoms cannot.
The obvious answer is that we are not matter, but electricity; we are
not in the same category as atoms of matter.
To complete the picture which I was drawing, you have only to think of
the aether waves arriving upon this planet and disturbing sympathetic
electrons, causing them to revolve around their atoms in similar fashion
to our distant fellows who are producing the aether waves.
It may be that some people get confused between this action and that of
those electrons who are shot off bodily from the sun towards the earth.
Believe me, there is no connection between the two things. The stream of
electrons shot off from the sun is deflected towards the magnetic poles
of the earth, and as the electrons enter the upper layers of the
atmosphere they produce that beautiful luminous effect which man
describes as an _Aurora_.
I have never taken part in one of these great displays, for, as far as
my recollection goes, I have never been in the sun, although some
fellow-electrons declare that at one time we were all in the same great
glowing mass of which the sun, and every member of the solar system,
formed a part. However that may be, I certainly have no experience of
aurorae, but I have assisted in producing the very same effect upon a
small scale within a vacuum tube. The air remaining in these so-called
vacuum tubes is just as rarified as the air in the upper layers of the
atmosphere, and when we are shot across the tube we act in the same way
as those electrons arriving upon this planet from the sun.
You will observe that as a surplus of electrons arrives upon the earth
from the sun, the earth is naturally a negatively electrified body, but
I need hardly say that the earth does not keep all the electrons which
arrive upon it.
My scribe points out that I am wandering from the story which I set out
to tell in this chapter, so I shall try and please him.
The direct cause of light, whether it be natural or artificial, is the
rapid motion of electrons around atoms of matter. If they revolve at a
comparatively slow speed they produce those aether waves which man calls
_radiant heat_. If these satellite electrons, however, desire to affect
the eye of man, they have to move around at a very much greater speed.
If we travel at too fast a speed, then we cease to cause the sensation
of light. But, believe me, all the waves we make are of the same nature,
no matter what names man has given them. The only difference we can make
in the waves is the rate at which they follow one another. Of course we
can also make them larger or smaller in height, or, in other words, of
greater or less amplitude, but that does not affect their properties.
In the following chapter I shall tell you of some remarkable phenomena
which our different aether waves produce in the brain of man.
CHAPTER XIV
HOW WE PRODUCE COLOUR
_THE SCRIBE'S NOTE ON CHAPTER FOURTEEN_
Colour is merely a sensation in the brain.
What the electrons really produce are aether waves, and these
give rise to the sensations of colour.
However, the electrons may claim to produce colour in the same
sense as we savages produce pain in fellow-men by firing
rifle-bullets at them.
The electron explains how some objects appear white, while
others are red, and so forth.
It explains also how electrons produce artificial light.
The electron twits man upon his ridiculously wasteful processes
of obtaining artificial light.
CHAPTER XIV
HOW WE PRODUCE COLOUR
In the preceding chapter I have been telling you how we electrons
produce waves in the aether ocean. I pointed out that if we make the
waves follow each other at too slow or too fast a rate they fail to
affect man's eyes.
It may seem strange to you that only a very small range of our aether
waves should affect man's visionary apparatus. Of course this limitation
lies beyond our province; we can produce endless variety of aether
waves--it is man's organs which fail to appreciate the bulk of these.
However, there is plenty of variety in the sensations which we can
produce in man. If we make the waves follow each other at a certain
speed, man says he has the sensation of _red_. If we move faster, he
speaks of _orange-colour_, and as we increase our speed he names his
further sensations as _yellow_, _green_, _blue_, and _violet_. Then if
we combine all these waves--that is, if we produce them all at one
time--he says he has the sensation of _white_. If we produce none of
these waves, he calls the result _black_.
While we electrons are very versatile, our actions are dependent in a
great measure upon circumstances. For instance, if an electron is acting
as a satellite to one particular kind of atom, its rate of revolution
around that atom may be very different from that of an electron
similarly attached to another kind of atom. We electrons are all
identical, but the speed of revolution is determined by the kind of
atom. The reason is very simple; electrons revolve around some atoms at
a much greater distance than they would around other atoms. Those making
only the smaller orbits not only get around their atoms in less time,
but they are also travelling at a greater pace. It is this fact which
enables the electrons to produce the various wave-lengths which
stimulate the different colour sensations in the brain of man.
I think you will have no difficulty in seeing how it is that we come to
produce such a variety of wave-lengths--in other words, how we are able
to make the waves follow each other more or less rapidly. You will
understand that we do not produce colours; we merely make various waves
in the aether, and these waves excite the colour sensations in man. I
mention this simple fact, because I hear many people speaking of our
aether waves as "coloured rays," which, of course, is quite a ridiculous
description.
Suppose some of those waves which give rise to the red sensation happen
to fall upon a lump of matter which contains only electrons capable of
producing waves that affect the green sensation. What will happen? There
will be no response, and the object, although viewed by "red light,"
will appear black.
If an object, such as the white paper upon which my scribe is recording
my story, contains a variety of atoms with electrons capable of
revolving at all the different rates which produce colour sensations,
then when "white light" falls upon the object it appears white (all the
colour sensations combined). If, on the other hand, a "red light" only
falls upon it, then only the electrons capable of responding to that
rate of wave will be set in motion, and the object will appear red, and
so on with the other rates of aether waves.
So far I have been telling you what happens when different waves of
light fall upon us. Now I shall endeavour to explain how man has caused
us to produce artificial light. At present all man's methods in this
direction are dependent upon making some substance so hot that it
becomes incandescent. Even his most modern methods seem to us to be
ridiculously wasteful and most roundabout. I shall speak only of the
electric glow lamp, as I have had some experience in connection with
this.
On one occasion I had been taking part in a regular forward march from
copper atom to copper atom in a conducting wire. I had no idea of the
purpose of our march till I suddenly found myself handed over to some
carbon atoms, who were in a very lively state of vibration. We had much
more difficulty in making our way through this substance, and it was the
passive resistance offered to the advance of the electrons who had
preceded me that had driven the carbon atoms into this state of great
excitement. In our march through the copper conductor we had been
offered very little resistance, so that we had left the copper atoms in
peace--at least man could not detect easily any excitement (heat). But
so long as our forced march was maintained among the carbon atoms, so
long did the high temperature exist.
You will understand I and the other marching electrons did not produce
the waves of light sent out by the glow lamp. What we did was to set the
atoms of carbon into a rapid vibratory state, and they in turn caused
their satellite electrons to hasten their pace. Some electrons produced
one rate of waves, and some another rate, but by the time the carbon was
incandescent there were electrons sending out all the variety of
wave-lengths, the combination of which produces the sensation of white.
I have accused man of adopting very wasteful processes, so I had better
explain the matter. In the preceding description of what is occurring in
an electric glow lamp, I have spoken only of those aether waves which
constitute light. But there are myriads of electrons in the carbon of
the glow lamp that never attain the requisite speed to produce those
waves; they revolve around their atoms at too slow a rate. They
certainly disturb the aether, but the crests of the waves are so far
apart that they do not affect the eyes of man. The business of these
waves is to set up heat in the bodies upon which they fall. You may be
surprised to know that in this contrivance of man, called an electric
glow lamp, and, indeed, in all his other artificial light-producers, he
causes far more electrons to produce radiant heat than the desired light
waves. A most wasteful process!
Man has a long way to travel yet before he succeeds in producing
artificial light by a reasonable process. Indeed I doubt if any of you
can realise, as we do, how exceedingly stupid the existing methods are.
Think for a moment of the glow-worm, in which we electrons produce light
without setting up any wasteful heat waves. There is a strong contrast
between this peaceful plan and that of the excited carbon atoms. When
will man succeed in discovering this secret of ours?
CHAPTER XV
WE SEND MESSAGES FROM THE STARS
_THE SCRIBE'S NOTE ON CHAPTER FIFTEEN_
It is remarkable that man has been able to discover what the
distant stars are made of.
Our knowledge concerning the chemistry of the stars has been
obtained by means of the spectroscope, in which a beam of light
from the star is passed through a glass prism.
The result is the well-known image of the coloured spectrum, in
which certain well-defined lines appear, according to the
distant elements originating the aether waves.
The electron explains the whole subject from its own point of
view.
CHAPTER XV
WE SEND MESSAGES FROM THE STARS
It is only within recent times that man has observed that we send
messages from the distant stars to this planet. But there is nothing new
to us in this proceeding; we have been busy sending these messages ever
since the solar system was formed. Through all those ages we have kept
on sending these messages, knowing that in time man must come to take
notice of them.
If the subject should happen to be new to you, you will be anxious to
know to what kind of messages I refer. Needless to say, they are
wireless messages--waves in the great aether ocean. The waves, to which I
refer specially, fall within that small range of which I told you
something in the preceding chapter. In other words, they are those waves
to which man has given the name _light_. But what special information
do these waves, coming from the stars, convey to man? They tell him of
what materials these distant stars are made. Needless to say, it is we
electrons who produce those informative waves.
You are familiar with our method of producing waves. You know that we
whirl around the atoms of matter at prodigious speeds, and that
according to the number of revolutions we make per second, we produce
waves of corresponding frequencies.
In an earlier chapter I have hinted that the speed of the revolving
electron is determined by the kind of atom to which it acts as a
satellite. For instance, when electrons revolve around iron atoms they
produce certain wave-lengths, while those moving around hydrogen atoms
produce an entirely different series of waves. But how is man to
recognise these?
It is quite evident that man may gaze at a distant star and be little
the wiser concerning the different lengths of the waves which impinge
upon his eyes. He may observe that the sensation is inclined to red,
from which he may infer that the waves are long ones--that they are
farther apart than some of the waves produced by a white-hot body. But
had man been content to try and decipher our wireless messages in this
rough-and-ready manner, he would never have gained the interesting
information which we have now placed in his hands. How, then, did we
enable man to read our messages?
Our plan may seem to be somewhat mysterious, but I assure you that it is
really very simple. When these aether waves of light fall upon a
triangular prism of glass, the waves are bent out of their normally
straight path. But the point that may seem strange to you, is that those
waves which produce the sensation of red are not bent so much as the
others. The more rapidly the waves follow one another, the greater is
the bending of such a ray from its original direction. In this way the
various wave-lengths are all spread out, so that they form an image like
a coloured ribbon, red at one end, being followed by orange, yellow,
green, blue, and violet. Every man must be familiar with this coloured
spectrum. When some of my fellows are enclosed in drops of water in the
air they produce a great rainbow spectrum across the heavens. But I
must tell you how we electrons succeed in bending these rays of light.
I have told you already how we either absorb or reflect the aether waves
which happen to fall upon us. In most substances it is only those
electrons very near the surface that are disturbed. They succeed in
stopping the waves. They may do this in either of two different ways. If
the satellite electrons are attracted strongly by their atoms, the
electrons will spin around the atoms keeping time to the movements of
the incoming waves, and in this way the electrons take up the energy of
the waves. In doing this, the electrons send out fresh waves in the
aether. This is the real explanation of what man calls _reflection_ of
light.
[Illustration: THE SPECTROSCOPE AND THE ELECTRONS' WIRELESS MESSAGES
The spectroscope is seen in the extreme left of No. 1 photograph. The
instrument is explained at page 207.
The operator is passing an electric current through a glass tube
containing a rarefied gas, causing the gas to become luminous. When he
examines its light through the spectroscope he sees bright lines as
shown in photograph No. 2, and from the position of these lines he can
tell what substance is producing the light. No. 2 is the spectrum of
mercury vapour. No. 3 is part of the spectrum of the sun. Note the dark
lines, as explained in the text.]
In the second case, the electrons are not so firmly attached to their
atoms, so that the incoming waves dislodge them, and they are knocked
about from atom to atom, and in this way the energy of the waves is
frittered away. Man speaks of the light having been _absorbed_ by the
substance upon which it fell. In both cases the only electrons which
take part in these actions are those electrons who can move in
sympathy with the incoming waves.
It will be clear to you that only those of us who are near the surface
of a substance know anything about these incoming waves. The electrons
attached to atoms in the interior of the substance are left in peace,
owing to the defensive actions of our fellows on the outside. But this
is not the case with all substances. There are some congregations of
atoms through which the aether waves can make their way. Man calls such
materials _transparent_; for example, glass and water are transparent
substances. The fact of the matter is that in such substances none of us
are able to respond to the incoming waves, and so we cannot stop them. I
should say almost none of us, for there are always a few electrons
present who happen to be in sympathy with the incoming waves. That is
why no substance is perfectly transparent.
The point concerning which I wish to speak in particular is this.
Although we allow the aether waves to pass through such substances, we do
offer some slight resistance to the passage of the waves; the faster the
to-and-fro motion of the waves, the more resistance do we offer. That
is why the waves of highest frequency are bent farthest from the
straight line when passed through a glass prism. We actually force the
aether waves to travel slower through a piece of glass than through the
air.
Now there should be no mystery concerning our action in a triangular
piece of glass. Whatever combination of aether waves falls upon it, the
different trains of waves are sorted out according to their frequencies.
Suppose, for instance, that aether waves emitted from some incandescent
sodium are passed through a glass prism. The bulk of the electrons
attached to the sodium atoms are capable of revolving at speeds which
produce waves causing the sensation of yellow. Hence there will appear a
very distinct line of yellow light in the spectrum. But why should the
light be in the form of a line? Simply because our aether waves are
passed through a narrow slit in a shutter. But I need not trouble you
with further details of our actions, which, although very simple to us,
may seem somewhat strange to you.
You will understand, however, that we form bright lines in different
parts of the spectrum, according to the kinds of atoms to which we are
attached. It was this fact which attracted man's attention to our
wireless messages. He soon discovered the meaning of these lines, for he
commenced to take exact notes of the different positions in which we
placed these lines. He saw that when we were attached to hydrogen atoms
we always produced three prominent lines; a very distinct line in the
red section, another in the blue part, and a third one somewhat fainter
and farther along in the blue. On the other hand, when attached to
sodium atoms, we produced two very distinct lines in the yellow. When
attached to iron atoms we produced a great variety of lines in the
spectrum. Of course these substances have to be incandescent to enable
us to produce the aether waves.
Now it will be clear to you how we send wireless messages from the
distant stars. These stars are great masses of flaming gases, so that
the satellite electrons are kept busy dancing attendance to excited
atoms. The electrons are constantly sending out aether waves, which reach
this planet. We sort out these waves when man passes them through a
glass prism, mounted in a telescope arrangement which he calls a
_spectroscope_. He then examines the positions of the lines we produce
in the resulting spectrum, and from these he knows what kinds of atoms
are present in the distant star. It is we who have informed man that
there are forty different materials in the sun, the most common of which
are hydrogen, sodium, iron, copper, nickel, and zinc. Of course these
all exist in a gaseous form.
There is one point about which I need hardly trouble you, although it is
worth mentioning in passing. While we produce bright lines in the
spectrum of any incandescent substance on this planet, our messages from
the stars appear as dark lines. The reason for this is that there are
cooler masses of the gases surrounding the incandescent masses forming
the stars, and these cooler gases completely absorb the waves we
produce. So completely are these waves absorbed that blank spaces are
left in the spectrum, and these are the dark lines to which I refer. As
they are in the same positions that the bright lines would have occupied
had the waves reached the earth, it makes no difference to the reading
of our messages.
Curiously enough, some of our actions in forming lines in the spectrum
led to our actual discovery by man; but I shall tell you of this in the
following chapter.
CHAPTER XVI
HOW MAN PROVED OUR EXISTENCE
_THE SCRIBE'S NOTE ON CHAPTER SIXTEEN_
Several men of note declared that "little particles" revolved
around the atoms of matter, and that it was the motion of these
particles which produced the well-known aether waves of light.
This idea was suggested by the result of certain mathematical
calculations.
It was some time before real experimental proof was obtained.
The electron tells its own tale of this great discovery.
When the electron speaks of a spectrum line being shifted up or
down the scale, it means towards the violet or the red end
respectively.
We may picture the spectrum as analogous to the keyboard of a
piano.
In the second part of this chapter, the electron explains how it
has enabled man to discover that certain stars are approaching
the earth, while others are receding from it.
CHAPTER XVI
HOW MAN PROVED OUR EXISTENCE
We electrons had waited long ages for man to acknowledge our services,
but we did not despise the acknowledgment which a few men accorded us
upon the basis of their mathematical calculations. It was natural,
however, that we should want something more definite than this.
You can imagine our joy when real experimental proof of our existence
was established. Perhaps you think that we should have been satisfied
with this. But even this did not bring acknowledgment from many outside
scientific circles, and not even from all within those circles. As our
services to man are universal, we feel that all men should become
acquainted with our doings. Indeed that was the chief argument used by
my fellow-electrons, who urged me to write this autobiography. The
story of our actual discovery by man is an interesting one.
It all came about in a very simple manner, but in quite a different way
from what most electrons expected. Man reasoned within himself that if
we electrons really did revolve around atoms and thus produce waves in
the aether, as had been suggested, he ought to be able to affect our
movements by disturbing the aether in which we were revolving. Of course
man cannot disturb the aether directly; he must employ some of us to do
this for him. He caused us to produce a very powerful magnetic field,
which, as you know, is a disturbance of the aether. Man did not bother
thinking about _us_ in this connection; he simply sent an electric
current around an electro-magnet, but I have explained to you the very
active part we play in electric and magnetic actions.
From my story in the preceding chapter, you are aware that man had
observed the meaning of the bright lines in the spectrum of any
incandescent body. When he examined the aether waves we send out from
sodium atoms, he found two very distinct lines in the yellow. Because of
the brightness of these lines, man selected a sodium flame to
experiment with in the present case.
You will picture a great host of my fellow-electrons revolving around
the atoms in a sodium flame. The flame was placed between the poles of a
very powerful electro-magnet, and a beam of aether waves (light) produced
by us was directed into the spectroscope. The experimenter focussed all
his attention upon one of the bright yellow lines. He noted very
carefully the exact position in which we placed it. He then produced the
magnetic field around the flame, in which my fellow-electrons were
revolving at a steady pace, and, behold, the line which he was watching
split up into two lines, one taking up a position a little higher up the
spectrum scale, and the other going a little lower down towards the red
end. What could this mean?
Man had no difficulty in knowing the cause of this alteration; indeed,
it was exactly what he had hoped would take place. Of the two new lines,
one represented waves a little shorter, while the other line indicated
waves a little longer or farther apart, than the original waves forming
the single line. This could only come about by some of the electrons
having had their rate of revolution increased, while that of others had
been reduced. These alterations were due to the aether disturbance (the
magnetic field). Those electrons whose orbits happened to lie in one
position had their rate of revolution increased, while those whose
orbits lay in another position had their speed reduced. Man was
convinced at last that we "particles" were real existing things.
Whenever man withdrew the aether disturbance, the electrons fell back
into their natural rate of revolution, and the original single line
appeared in the spectrum.
I took no part in the original experiment which gave absolute proof of
our existence, but since then I have been present in a laboratory when
the same experiment has been repeated.
This is not the only case in which we alter the positions of definite
lines in the spectrum. Indeed, we have given man some interesting
information about the motions of distant stars--information which he
could not have obtained in any other way. We have sent wireless messages
from distant stars, indicating that they were approaching the earth,
while electrons aboard other stars have signalled that they are receding
from the earth. All this may seem mysterious to you, and yet our actions
in the matter are very simple. Indeed, we do nothing but what I have
told you of in the preceding chapters. We send out definite wave-lengths
in the manner described already. But if we are on board a star which is
travelling towards the earth, our waves will naturally follow a little
closer at each other's heels. On the other hand, if the star is receding
from the earth, the waves must be a little farther apart than they would
be if the star were at rest.
You will understand that the electrons are revolving at the same speeds
in both cases, but the forward movement of the star crowds the waves
together, while a receding star stretches them out a little farther
apart. The result at the receiving end is that the crowded waves are
just as though they had come from electrons revolving at a greater speed
than is actually the case. Hence the line appears farther along the
spectrum, up the scale of frequencies, than would have been the case
had the star not been moving forward in the line of sight. Thus if the
hydrogen lines, of which I have spoken elsewhere, should appear higher
up the spectrum than usual, then man knows that the star from which
these waves are coming is approaching the earth.
It will be evident that when known lines in the spectrum are shifted
down the scale (towards the red end of the spectrum), then the rate of
the waves has been decreased, and man knows that the star carrying these
stimulating electrons is receding from him.
You will observe that we electrons perform no new duty in connection
with this matter; it is entirely the motion of the body carrying us that
alters the positions of the lines. But I must hasten on to tell you of
some personal experiences.
CHAPTER XVII
MY X-RAY EXPERIENCES
_THE SCRIBE'S NOTE ON CHAPTER SEVENTEEN_
The present generation were all very much interested in the
discovery of X-rays.
With the aid of a battery and an induction coil, man causes an
energetic electrical discharge to pass through a vacuum tube.
When the flying electrons strike upon a little metal target
placed in their path, they produce the well-known Roentgen rays.
We have all become familiar with the great penetrating powers of
these rays.
The electron may be left to tell its own story.
CHAPTER XVII
MY X-RAY EXPERIENCES
It was no surprise to us that we could produce what man calls X-rays,
but we were very much surprised at the use to which man put these
splashes which we made in the aether. A limited number of us had been
producing X-rays on our own account for many ages, but I shall tell you
of that in a later chapter, when you will hear how we made the world
talk.
I must tell you of my own experiences in connection with these X-rays,
which I hear some men describe also as _Roentgen rays_. I found myself
once more within a large vacuum tube, and as soon as I felt a crowd of
my fellows pushing me forward, I was quite prepared to be shot across
the tube, as on previous occasions. Personally, I was not prepared for
what was to come. Just as we reached the centre of the tube we collided
with a metal plate or target. It was no joke to be pulled up so suddenly
when travelling at a terrific speed. I noticed at the time that our very
sudden stoppage had a peculiar effect upon the aether. Of course we never
bothered about a name for this disturbance; it is man who requires to
have names for everything. He was quite right to call this aether
disturbance "X-rays," for even now he does not know the real nature of
these. I have heard him describe them as thin pulses in the aether, but
there is something more.
I may as well confess that although we observed this aether disturbance
arising from our sudden stoppage, we paid little attention to it, until
it became apparent that man was continuing to produce these rays for
some special purpose. He had discovered that we could shoot these rays
right through many solid substances which were not transparent to light.
But I have not told you how man came to know that we could produce these
penetrating rays.
On one occasion we were sending out these rays, which, by the way, do
not cause any sensation in man's visionary apparatus. The room was in
darkness. Some of the invisible rays fell upon a collection of small
chemical crystals which were fixed on the surface of a screen. Our
fellow-electrons, who were attached to the atoms of the crystals, were
bestirred into action. They could not reflect the X-rays, but they set
up regular trains of waves in the aether, some of which came within the
range that affects man's vision. Man knew that this chemical screen
could not produce light on its own account, and it became apparent that
the vacuum tube must be sending some aether waves towards the chemical
screen.
As the electrons on the screen produced an aether disturbance different
from that which fell upon it, man called this a _fluorescent screen_.
At first we took merely a passing interest in the experiments which man
made with these X-rays of ours, for it seemed to us as though man
thought them only good enough for amusing his friends. Indeed, we paid
little heed to what he was doing, until we observed that the rays were
being used by surgeons. We were interested at once, for here we could
serve man.
My first experience in this connection was quite interesting. A young
girl had got a needle into her hand while she was playing about, and the
surgeons were at a loss to know where the needle had lodged. We lost no
time in producing X-rays which could penetrate the flesh of the hand,
and reach the fluorescent screen on the other side. The bones of the
hand blocked the way of our rays, but not so completely as the needle
did. Hence we produced upon the screen a faint shadow of the flesh of
the hand, a much deeper image of the bones, and a black shadow of the
needle. This enabled the surgeon to see where the needle was hiding.
Sometimes we were called upon to produce rays for detecting bullets in
the flesh, or for showing the nature of a fractured bone. We were never
surprised to find that our call was to detect a coin in the throat of a
child, but in this connection a big surprise awaited some of us. I was
not one of the party, but I have the information from some
fellow-electrons.
[Illustration: HOW ELECTRONS PRODUCE X-RAY IMAGES
The upper photograph shows the X-ray apparatus in use. The operator is
examining the bones of the lady's hand, which she places between the
X-ray tube and the fluorescent screen. The rays pass through the flesh,
but are obstructed by the bones, the rings, and the bangle, so that a
shadowgraph or image is formed upon the screen, which becomes luminous
where the rays succeed in reaching it. The actual examination is made in
a dark room. Owing to the way X-ray photos are taken (by contact) the
image is reversed in a photograph, so that a left looks like a right
hand.]
A party of electrons were present within an X-ray tube at a large
hospital, when they were called upon to produce rays for examining
the throat of a little girl. They had become so used to this call that
they did not doubt there would be a coin in the child's throat. However,
they lost no time in producing the penetrating rays, and you can imagine
their surprise when they produced the image of a toy bicycle upon the
screen. It seemed ridiculous that such a toy could have entered a
child's throat.
When we had shown the surgeons exactly where the toy was, they set to
work to remove it. The electrons heard later that the operation was
successful in every way. Every one was interested, and we were proud. I
do not wish to appear boastful, but I wonder how many operations owe
their success to these rays which we produce for man.
It was natural that man should try if these searching rays could affect
the chemicals upon a photographic plate, and we soon proved that they
could. It made no difference to us whether man kept the plate sealed up
in its light-proof envelope, or whether he placed the plate within a
wooden box. These protecting covers offered no barrier to our rays. We
produced shadowgraphs of any objects placed between our tube and the
photographic plate.
Two of my early experiences may be of interest to you. The first of
these seemed to me a rather tame affair. Our X-ray tube appeared to be
arranged for the amusement of fashionable folk. One grand lady placed
her hand behind the fluorescent screen, whereupon we produced an image
of the bones of her hand and very dark images of all the many rings upon
her fingers. Several of the rings had enormous diamonds, but it was
after she had gone away that I overheard two gentlemen speaking about
the rings. One asked the other if he had observed the beautiful
diamonds, whereupon the other roared with laughter. It seems that we
proved them to be imitation diamonds, for our rays could not penetrate
them, whereas they have no difficulty in passing through real diamonds.
We therefore produced black shadows of the imitation diamonds. Little
did the grand lady know how we had exposed her sham jewels.
My second experience was a very curious one. I learned that our tube was
being carried to some distance. After a while we were placed beside a
peculiar-looking object, which the men referred to as the "mummy." One
of the men suggested that they should photograph its feet, but before
doing so they darkened the room and set us to work upon the fluorescent
screen. The owner of the mummy got rather nervous as to what we might
disclose, and as the force urging us into action was somewhat erratic at
first, we produced only a very indistinct image. We were greatly amused
at the nervous excitement of the owner; he seemed to think our verdict
was that there were no bones. However, the man with the apparatus soon
got things into better condition, and this enabled us to produce X-rays
satisfactorily. The result was that they secured some excellent
photographs of the hidden bones of the mummy.
Before telling you how we made the world talk, I should like to give you
a clear idea of our relationship to the atoms of matter.
CHAPTER XVIII
OUR RELATIONSHIP TO THE ATOMS
_THE SCRIBE'S NOTE ON CHAPTER EIGHTEEN_
We have no doubt that an atom of matter is a miniature solar
system of revolving electrons.
These electrons, being negative particles of electricity, would
repel each other just as any two similarly electrified bodies
do.
There must therefore be some equivalent of positive electricity,
but whether this exists in the form of a sphere or in separate
particles we have no definite knowledge.
One atom differs from another in the number of electrons which
go to make up the atom.
The electron explains how the atoms of matter are united to one
another, how different compound substances are formed, and how
chemical changes take place.
CHAPTER XVIII
OUR RELATIONSHIP TO THE ATOMS
I am sorry that this part of my story must remain incomplete for the
present. I am not free to tell you all I know; you must try and get
behind the scenes on your own account.
One thing I am at liberty to tell you is that my fellow-electrons who
are locked up within the atoms are not without hope that they may gain
their freedom once more at some future time. I know this first-hand, for
I have met some fellow-electrons who have escaped from within an atom,
but I shall delay telling you about these fellows till the succeeding
chapter. My object in mentioning this fact now is to give you confidence
in what I am about to say regarding the nature of the atom.
On one occasion I overheard a conversation between two men who were
discussing the construction of matter. One remarked that the atoms were
the bricks of the universe, whereupon the other asked how the little
bricks were cemented together. I wish that man could have seen a lump of
matter as we see it. He would have been surprised to learn that the
atoms never really touch each other. They are always surging to and fro,
or _vibrating_, and it is this motion which constitutes the
_temperature_ of the body which they compose.
It must be clear, however, that in a solid body one atom attracts
another atom across the intervening atomic spaces. This is another duty
devolving upon us; what we do, really, is to upset the electric balance
between the different atoms, and thus produce electrical attraction.
First of all, perhaps, I should explain that the different kinds of
atoms are simply congregations of different numbers of electrons. Of
course there is the other part, of which I am forbidden to speak--the
part which man vaguely describes as _positive electricity_. However, you
may take it from me that while it is true that the main difference
between an atom of gold and an atom of iron, or of oxygen, is in the
number of electrons it contains, there is a very important difference in
the arrangement of the electrons. You know that they form rings outside
one another, all of which revolve at enormous speeds. The number of
electrons in the different rings varies according to the kind of atom.
It is quite correct for man to speak of the atoms containing certain
definite numbers of electrons, but I should like you to understand
clearly that the exact number of electrons is not permanently fixed; one
or more electrons can slip off one atom and become attached to a
neighbouring atom which happens to be capable of accepting it or them.
It is the interchange of these few detachable electrons that causes one
atom to attract another. In other words, it is the differently charged
atoms which attract each other, just as man crowds a surplus of
electrons on to one object and finds it attracted bodily towards another
object having a deficiency of electrons.
It is this electrical attraction between the atoms which enables us to
build up the particles, or _molecules_, of matter in such a variety of
forms. First of all, we play the most important part within the atoms.
We have formed only a limited number of such atoms. I am not free to
tell you exactly how many, for man has discovered only about eighty of
these different congregations of electrons, each kind of which he calls
an _element_. The way in which we have coupled these different
elementary atoms together must appear remarkable to all thinking men;
there seems to be no end to the possible variety of combinations.
In one case we unite an atom of _chlorine_ to an atom of _sodium_ and
thereby produce a molecule of common salt. In another case we unite an
atom of _oxygen_ to two atoms of _hydrogen_, and the resulting
combination is an invisible molecule of ordinary water.
It has always seemed to me very strange how some men have difficulty in
regard to these combinations. I have heard a man ask how two different
gases, hydrogen and oxygen, when united, should form a liquid, and not a
gas. I wish you could see things as we see them. The atoms are neither
gaseous, liquid, nor solid; they are little worlds of revolving
electrons.
I have spoken of the attraction between atoms, and again between
molecules, in forming a solid body. It will be clear that there is less
of this _cohesive force_ in the case of a liquid, whereas it is absent
entirely in the case of a gas. In this case the molecules have become so
far separated from one another that they cease to attract each other,
and if left free they will soon part company, and spread themselves
broadcast over the face of the earth.
Whether a substance passes into a solid, a liquid, or a gaseous state,
the atoms remain constant, but their vibratory motion is altered very
considerably. However, I was about to tell you that we electrons can
make some very interesting combinations of atoms. Those I have mentioned
so far are of a very simple nature, but we have built up individual
molecules containing hundreds of atoms. We link about a hundred atoms
together and produce a molecule of what man calls _alum_, and we require
to unite about a thousand atoms together to make one molecule of
_albumen_ (the white of an egg).
When man speaks of a chemical change having taken place in a substance,
it is simply the electrons who have made a friendly interchange of
detachable electrons, thereby causing a different assemblage of the same
atoms. During these changes we never alter the nature of the atom. That
little world of revolving electrons known as an atom of gold, remains
always an atom of gold. But you must not run away with the idea that the
atoms will never change. Indeed, man has discovered that the atoms are
not eternal, as I shall explain in the following chapter.
CHAPTER XIX
HOW WE MADE THE WORLD TALK
_THE SCRIBE'S NOTE ON CHAPTER NINETEEN_
The discovery of radium is within the memory of all.
Many exaggerated statements went abroad at the outset, but the
real facts are full of interest, and they have shed much new
light on many subjects.
Three different kinds of radiation were found to be emitted by
radium.
At first man could not tell what these were, so he named them
after the first three letters of the Greek alphabet--Alpha,
Beta, and Gamma, rays.
The electron tells the interesting story of these rays, and
relates the experiences of some fellow-electrons who escaped
from within a radium atom.
CHAPTER XIX
HOW WE MADE THE WORLD TALK
We electrons were amused at the stir which we unconsciously caused
throughout the civilised world. We had done nothing different from what
we had been doing for ages, but a few men had been taking note of what
we were about, and when the phenomena to which I refer became known to
the world, many wild rumours were circulated.
One of these rumours was to the effect that steam-engines and their
expensive furnaces were to disappear very quickly. If the two last words
had been omitted--I should not say that the prophecy is untrue, but man
has a long way to travel yet before reaching that goal. My fellows
within the atoms have sufficient energy to supply all mankind with power
if he could but unlock even a small fraction of it.
Another statement was that this newly discovered substance, _radium_,
could cure some diseases which man had believed to be incurable. All I
shall say about this is that the statement was an exaggerated one.
Then it was said that radium disproved much of man's scientific
knowledge, but instead of that being so, we electrons have greatly
extended man's knowledge by our radio-active actions. If any man
believed the atoms of matter to be eternal, we certainly disproved that.
Here, in radium, man could see atoms going to pieces.
I have questioned a fellow-electron who escaped from a radium atom as to
what upset their equilibrium, but I find that he does not know, or he
pretends not to know. All he has told me is that he was flung off
suddenly from within the atom with great energy, for he had been
revolving at a tremendous speed. In his sudden flight he passed some
newly formed _helium_ atoms, which contained many of those electrons who
had been his co-partners in the former radium atom. Being an electron,
he was travelling at a far greater speed than these flying atoms of
matter, but he assures me that these helium atoms were going faster
than atoms can travel under any other circumstances.
Another thing that this escaped electron told me was that when he and
his fellow-electrons made a sudden start on leaving the atom of radium
they caused a proper splash in the surrounding aether, just such as we
electrons produce when we are suddenly stopped in an X-ray tube. Man
observed these rays proceeding from radium, but, not knowing the cause
of them, he called them _gamma rays_. We can, of course, produce
radiographs when these rays fall upon photographic plates. Indeed, some
of my fellow-electrons, when escaping from radium, have produced rays
sufficient to penetrate a six-inch boulder and affect a photographic
plate lying beneath the boulder. In time man recognised these rays as
X-rays.
Man did not find only these rays--he discovered that electrons were
escaping, but before he had recognised what we were, he had named us
_beta rays_. These fast-flying electrons have had experiences which
never fall to electrons except when escaping from an atom. Their
velocity is so great that they can be shot right through a sheet of
aluminium foil. If these escaped electrons are allowed to settle on any
object, they will necessarily cause an overcrowding, or, in other words,
the object will become negatively electrified.
The one thing that puzzled man most was to find out what the helium
atoms were. He had named them _alpha_ rays, but as he found he could not
get them to penetrate even a thin sheet of paper, he was confident that
they must be atoms of matter. It was only when he had gathered
sufficient to examine the spectrum that he found these to be helium
atoms.
I think what really made the world talk was the fact that electrons were
escaping from what had been supposed to be an eternal habitation. In
other words, this material radium was actually going to pieces. That is
to say, _gradually_, as far as man is concerned, for, looking at it from
our point of view, the word _gradual_ seems out of place entirely. The
breaking up of an atom is really of the nature of an explosion. It is a
continual bombardment that is proceeding in radium. Why man is apt to
think of it as a gradual effect is that there is such an enormous
number of atoms in a tiny speck of radium, that even the incessant
series of explosions will take a very long time to break down the whole
of the small particle.
Electrons differ in their opinions as to whether man will succeed in
drawing upon this internal energy of the atom. My own difficulty is
that, having been a roaming electron at all times, I have no idea
regarding the cause of the atomic explosions. I have remarked already
that the electrons locked up within the atoms possess more energy than
man could ever use. If all these electrons were deprived of their
energy, the atoms of matter would cease to exist, and man, where would
he be?
CHAPTER XX
CONCLUSION
_THE SCRIBE'S NOTE ON CHAPTER TWENTY_
Not many of us have realised the true importance of electrons in
the Creator's plans.
In the following short chapter the electron is made to sum up a
few of the wonders which it has related, in order to focus our
attention upon the grand place which the electrons occupy in the
universe.
CHAPTER XX
CONCLUSION
From what I have told you of myself and my fellow-electrons, it must be
apparent that we are of tremendous importance to man. I have told you
something of the part we played in building up this world--how we not
only form the atoms of matter, but also hold these bricks of the
universe together. I have given you a rough sketch of the composition of
these bricks.
You must have realised also that without us the whole universe would be
in darkness. There would be no light, no heat, and consequently no life.
Indeed, there could be no material existence without us.
Where would man be if we failed to perform our mission? He could not
exist if we even neglected a few of our duties. Not only do we form the
atoms of which his body is composed, also holding these together, but
we produce all those chemical changes within his body which are
absolutely necessary to maintain life. His very thoughts are dependent
upon our activities.
I have told you how we send man's messages across the earth, and how we
transmit power from place to place. Also how we have enabled man to gain
knowledge of the distant stars, and to examine the bones of his living
body.
If man could cross-examine me or any of my fellows, I expect the first
question would be--What are you electrons made of? But man must find
this out for himself. The Creator has placed man in a world full of
activity, and it is of intense interest to man to discover the meaning
of all that lies around him. That is why I have been bound over by my
fellows to tell you only so much of our history as man has discovered.
But I am disclosing no secret when I admit that our very existence as
electrons is dependent upon the aether.
If I can find another scribe to write a revised biography for me a few
hundred years hence, I shall have a much more interesting tale to tell,
for many of our doings, of which man knows nothing at present, will be
secrets no longer by that time.
APPENDIX
_THE SCRIBE'S NOTE ON APPENDIX_
As explained by the author in Chapter I., this appendix has been
added for the sake of those readers who may wish further details
than have been given in the electron's story.
It is only necessary to give a brief notice of the more
important particulars, as the author has written recently upon
this subject in a popular form.[1]
[Footnote 1: "Scientific Ideas of To-day." By Chas. R. Gibson, F.R.S.E.
(London: Seeley & Co., Ltd. Five shillings net.)]
APPENDIX
It was known two thousand years ago that when a piece of amber was
rubbed with a woollen cloth, the amber would attract light objects
towards it. Amber was considered to be unique in this respect.
About the year 1600, one of Queen Elizabeth's physicians, Dr. William
Gilbert, inquired into this attractive property of amber. He found that
many other substances possessed the same property. Indeed it is common
to all substances in some degree. We say the amber or other object is
"electrified."
It was observed by the early experimenters that there were two kinds of
electrification. To one of these they gave the name _positive
electricity_, and to the other _negative electricity_.
Every electrified object will attract an object which is not
electrified, and two objects which are oppositely electrified will
attract one another also. But two objects which are similarly
electrified will repel each other.
Man got tired of rubbing objects by hand, so he fitted up simple
machines in which glass cylinders or plates were rubbed against leather
cushions. The electricity was then collected by little metal points
supported on an insulated metal sphere.
The experiment of attempting to store electricity in a glass vessel
filled with water was made at the University of Leyden (Netherlands).
The water was replaced later by a coating of tin-foil on the inner
surface, while a similar metallic coating on the outside took the place
of the experimenter's hand. These jars are called _Leyden jars_, after
the place in which the discovery was made.
About 1790, Professor Galvani, of Italy, observed that the legs of a
freshly killed frog twitched at each discharge of an electrical machine.
Later he found that the same twitching occurred when he connected
certain parts with a piece of copper and zinc. He believed this to be
due to "animal electricity" secreted within the frog.
Professor Volta, also of Italy, proved that Galvani's idea was wrong,
and that the electricity resided in the metals rather than in the frog.
He showed that when two pieces of dissimilar metal were put in contact
with one another, there was a slight transference of electricity between
them. He constructed a pile of copper and zinc discs, with a moist cloth
between each pair or couple, and by connecting wires from the top copper
disc to the lowest zinc disc he was able to show that an appreciable
current of electricity was produced. Later he placed a piece of copper
and a piece of zinc in a vessel containing acidulated water, whereupon
he found that a steady current of electricity was obtained. This was the
invention of electric batteries.
The phenomena of _magnetism_ were known to the ancients, but it was not
until the nineteenth century that we found any real connection between
electricity and magnetism. In 1819, a Danish philosopher, Hans
Christian Oersted, discovered that an electric current passing in a wire
affected a magnet in its neighbourhood. If the magnet was supported on a
pivot, after the manner of a compass needle, it would turn round and
take up a position at right angles to the wire carrying the electric
current.
The molecular theory of magnetism presumes that every molecule of iron
is a tiny magnet, having a north and south pole. In a piece of
unmagnetised iron, these tiny magnets are all lying so that they
neutralise one another. When they are turned round so that their north
poles are all lying in one direction, then the iron is said to be
magnetised.
The electron theory of magnetism does not do away with the older
molecular theory just referred to. The electron theory goes a step
farther, and tells us that these molecules are magnets because of a
steady motion of electrons around the atoms of iron.
It was discovered in 1825 that when an electric current was sent through
an insulated wire wound around a piece of soft iron, the iron became a
magnet; when the current was stopped the magnetism disappeared. Such
magnets are called _electro-magnets_. If a piece of hard steel is
treated in the same way it becomes a _permanent magnet_. It was this
intimate connection between electricity and magnetism, or, in other
words, the invention of these electro-magnets, which brought us electric
bells, telegraphs, telephones, dynamos, and electric motors.
It should be noted that while iron is attracted by either pole of a
magnet, there is such a thing as magnetic repulsion. This, however,
takes place only between two magnets, and then only between like poles.
* * * * *
Some German physicists made a number of electrical experiments with
vacuum tubes. When Sir William Crookes (England) was experimenting with
similar vacuum tubes he suggested that matter was in a "radiant" state
during the electric discharge within the tubes.
In 1880, H. A. Lorentz, of Amsterdam, declared that light was due to the
motion of small particles revolving around the atoms of matter.
Professor Zeeman, of Holland, produced experimental proof of Lorentz's
theory. He showed that the revolving "particles" were influenced by a
powerful magnetic field, in the manner explained in the electron's
story. This discovery was made in 1896, or sixteen years after Lorentz's
declaration. It was Dr. Johnstone Stoney, of Dublin University
(Ireland), who christened these particles "electrons."
The X-rays were observed for the first time by Professor Roentgen, of
Germany, in 1895. The screens used for viewing the luminous effects
produced by the X-rays are coated with very fine crystals of _barium
platinocyanide_. These screens were in use for another purpose previous
to the discovery of X-rays.
We know now that _chemical affinity_ is merely electrical attraction
between the atoms of matter.
The spectroscope consists of a glass prism, or series of prisms, mounted
between two metal tubes. One tube is provided at one end with a vertical
slit, through which the light that is to be examined is passed. At the
other end of the tube is a lens, so that the beam of light from the slit
emerges through the lens as a pencil of parallel rays. The pencil of
light then falls upon the glass prism, striking it at an angle. In
passing through the prism, the light is bent round so that it enters the
second tube, which is simply a small telescope. The prism separates the
aether waves according to their wave-lengths, and produces the well-known
coloured spectrum, which is magnified by the telescope. The reason for
the bending of the different waves is explained in the electron's
story.
INDEX
Absorption of light, 148
Aether, the, 24
Aether waves, 96, 131, 133, 137, 146, 148, 163
Alpha rays from radium, 190
Alternating electric current, 121
Amber electrified, 32, 34 to 37, 201
Artificial light, 140, 142
Atoms breaking up, 188, 190
Atoms co-operating with electrons, 108, 123
Atom's internal energy, 187, 191
Atoms of matter, 52, 54, 78, 128, 180, 184
Attraction between atoms, 180
Attraction, electrical, 35, 202
Attraction, magnetic, 78, 205
Aurora, 132
Automatic telegraph transmitter, 91
Battery, electric, 70, 203
Beginning of the world, 53
Beta rays from radium, 189
Birth of the moon, 52, 54
Bricks of the universe, 180, 195
Chemical affinity, 206
Chemical combinations, 56, 182
Chemistry of the stars, 52, 55, 144, 153
Chlorine atoms, 56, 182
Cloud formation, 56
Circuit, earth, 72
Coherer, tube, 98
Cohesive force, 183
Colour, 136
Compass needle, 77
Complete electric circuit, 71
Conductors, 37, 68
Connecting link between aether and matter, 118, 127
Corpuscles, 66
Crookes, Sir William, 205
Current of electricity, 68
Dark lines in spectrum, 154
Detachable electrons, 78, 181
Detecting imitation diamonds, 174
Direct electric current, 121
Discharge of electricity, 42
Discharge through a vacuum, 60
Discovery of electrons, 160, 206
Discovery of X-rays, 169
Dynamo, 116, 118
Earth circuit, 72
Electrical discharge, 42
Electricity, positive, 23, 32, 39, 52, 180
Electricity, negative, 23, 32, 39
Electric battery, 70
Electric current, 68, 70
Electric motor, 116, 122
Electric shock, 47
Electrified objects, 37, 38, 201
Electro-magnets, 76, 81, 83, 118, 205
Electrodes, 61
Electrocution, 49
Electron as a go-between, 118
Electron, derivation of the word, 23
Electron, discovery of, 160, 206
Electrons, 25, 32, 66, 78, 138, 162, 195
Energy transmission through the aether, 73, 121
Energy within the atom, 187, 191
Field, magnetic, 68, 76, 118
Fluorescent screen, 169, 206
Galvani's discovery, 202
Gamma rays from radium, 189
Gilbert's discovery, 201
Glass, electrified, 37, 38
Glass prism, 147, 152
Glow-lamp, electric, 140, 141
Glow-worm, 142
Heat, radiant, 126, 131, 133, 142
Helium atoms, 188, 190
Hydrogen atoms, 55, 182
Insulators (non-conductors), 37, 47
Iron atoms, 77
Iron wires discarded, 88
Lamp, electric, 140
Leyden jar, 42, 202
Light, 23, 60, 64, 133
Light absorbed, 148
Light, artificial, 140, 142
Light, reflected, 148
Lightning, 42, 48
Lines in the spectrum, 152, 154, 160, 162
Lorentz's declaration, 206
Magnetic attraction, 78, 205
Magnetic field, 68, 76, 118
Magnetic repulsion, 205
Magnetism, 73, 76, 203, 204
Magnetism and electricity, 73
Magnets, electro-, 76, 81, 83, 205
Magnets, permanent, 83
Mariner's compass, 77
Matter, 52, 54
Metal electrified, 37, 38
Molecules of matter, 181, 183
Moon's birth, 52, 54
Morse telegraph, 88
Motion in line of sight, 162
Motor, electric, 116, 122
Negative electricity, 23, 32, 39
Oersted's discovery, 204
Oxygen atoms, 182
Permanent magnets, 82
Positive electricity, 23, 32, 39, 52, 180
Prism of glass, 147, 152
Radiant heat, 131, 133, 142
Radiant matter, 63, 205
Radium, 188
Rainbow, 147
Rays from radium, 189, 190
Reflection of light, 148
Repulsion, electrical, 202
Repulsion, magnetic, 205
Roentgen rays, 167
Roentgen's discovery, 168, 206
Sea, cause of saltness, 56
Shock, electric, 47
Silk, electrified, 38
Sodium atoms, 56, 182
Spark, electric, 44
Spectroscope, 152, 154, 207
Spectrum, 144, 147, 152, 154
Speed of electrons in conductor, 70
Stars approaching the earth, 162
Stars, constituents of the, 52, 55, 146
Stoney, Dr. Johnstone, 206
Sun, constituents of the, 154
Sun's heat, 128, 131
Telegraph signals, 90
Telegraphy, wireless, 95
Telephone, 109
Telephony, wireless, 110
Temperature, 180
Tramway, electric, 117, 118, 122
Transparent substances, 149
Vacuum tubes, 60, 61, 132, 205
Velocity of electrons, 70
Volta's discovery, 203
Waves in the aether, 96, 133, 137, 146, 148, 163
Wireless messages from the stars, 162
Wireless telegraphy, 95
Wireless telephony, 110
X-rays, 166, 206
X-rays from radium, 189
X-ray photography, 173
Zeeman proves existence of electrons, 161, 206
Printed by BALLANTYNE, HANSON & CO.
Edinburgh & London
* * * * *
Transcriber's Note
The following changes have been made to the original text:
Page xi: "always necessary, How" changed to "always necessary. How"
Page 205: "vacuum tubes, When" changed to "vacuum tubes. When"
Page 214: "Negative electricity, 23, 32, 9" changed to "Negative
electricity, 23, 32, 39"