How Electrons Produce X-Ray ImagesThe 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.
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 forexamining 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 objectsplaced 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 wewere 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.
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.
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.
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 theconstruction 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, orvibrating, and it is this motion which constitutes thetemperatureof 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 aspositive 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 inthe 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, ormolecules, of matter in such a variety of forms. First of all, we play the most important part within the atoms. We haveformed 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 anelement. 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 ofchlorineto an atom ofsodiumand thereby produce a molecule of common salt. In another case we unite an atom ofoxygento two atoms ofhydrogen, 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 thiscohesive forcein 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 callsalum, and we require to unite about a thousand atoms together to make one molecule ofalbumen(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.
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.
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.
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 formedheliumatoms, 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 methat 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 æther, 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 themgamma 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 usbeta rays. These fast-flying electrons have had experiences which never fall to electrons except when escaping from an atom. Their velocity is so great thatthey 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 themalpharays, 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 wordgradualseems 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 itas 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?
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.
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.
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 bodyis 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 æther.
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.
As explained by the author inChapter 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]
As explained by the author inChapter 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]
[1]"Scientific Ideas of To-day." By Chas. R. Gibson, F.R.S.E. (London: Seeley & Co., Ltd. Five shillings net.)
[1]"Scientific Ideas of To-day." By Chas. R. Gibson, F.R.S.E. (London: Seeley & Co., Ltd. Five shillings net.)
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 namepositive electricity, and to the othernegative 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 calledLeyden 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 certainparts 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 ofmagnetismwere 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, HansChristian 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 insulatedwire wound around a piece of soft iron, the iron became a magnet; when the current was stopped the magnetism disappeared. Such magnets are calledelectro-magnets. If a piece of hard steel is treated in the same way it becomes apermanent 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 ofbarium platinocyanide. These screens were in use for another purpose previous to the discovery of X-rays.
We know now thatchemical affinityis 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 æther 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.
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