The Mystery and Power of Light
ALONG in the early seventies of the last century there was a boy who herded oxen through the long summer nights on the plains of Serbia, and all unconsciously he put himself through as severe an intelligence test as we can well imagine. Having the gift of vision, he looked at the stars, and he saw something. Bearing in his mind the ringing poetry about the firmament, which his mother repeated from the Psalms of David,—the Psalms of Saint David I believe they say in the Eastern Rite, — his proper and wholesome youthful curiosity was aroused, and he asked himself the question, What is Light? He then set himself the most far-reaching problem in physical science, one that still remains unsolved; and to this day he and many others who live in enlightenment are diligent in the great quest. Incidentally he has given us such discoveries as long-distance telephony, important features in radio-transmission, and other inventions, besides a life of inspired teaching. I refer to Professor Michael Pupin, now of Columbia University.
That is the way of Nature. She is not at all interested in us, but she is amazingly rich and lavish in her gifts. Whoever is able to keep his precious endowment of curiosity, — which most of us lose at school or in college, or allow through weakness of will to become strangled by the stupidities of our daily toil, — who has a mathematical sense of proportion, and enjoys diligence in research, is almost certain of a reward. He is sure to find something worth while in response fo his inquiries of Nature, even though the most cherished goal remains hidden from him.
I
Light, as Sir Evelyn de la Rue has said, is our nearest visible approach to infinity. Its velocity is the greatest known. It dashes through space at the rate of over 186,000 miles a second, and it seems to be ‘beyond numbers,’ for it remains constant from an approaching or a retreating body. That is, if we add to it, it does not increase, and if we subtract from it, it does not grow less. Does not this partake of the nature of infinity? We shall soon reach another instance in which arithmetic at first glance seems to be wrong, but not in so confusing or bewildering a measure as this curiosity in regard to the velocity of light.
Experiments in physical science point to the conclusion that all matter, whether in the heavens above, the earth beneath, the waters under the earth, or anywhere else — in the substance of all the stars and planets and moons and satellites and meteorites throughout the universe, is composed of positive and negative charges of electricity — and of nothing else. The ninety-two chemical elements, of which we know all but four, differ from each other only in the number and arrangement of the positive and negative charges in their atoms or smallest particles.
Toward the end of the last century it was found that every atom of hydrogen gives up on electrolysis a single negative charge of electricity; one single negative charge and no more; we call it an electron, or the unit of electricity. Electric currents consist in a drive or push of electrons. When this negative charge or electron is given up, the hydrogen atom becomes a hydrogen ion; and the hydrogen ion is a single positive charge of electricity, which is also called a proton. The atom of hydrogen is the lightest and smallest of all the atoms, and consists of one positive and one negative charge of electricity and nothing else.
If we arrange all the elements in a row according to the comparative weights of the atoms, beginning with hydrogen — which is the lightest of all — as No. 1, setting down helium, which is next in order of comparative weight, as 2, and so on, with lithium 3, beryllium 4, boron 5, carbon 6, nitrogen 7, oxygen 8, and right on substantially as the atomic weights increase, until we come to uranium, which is the heaviest of all and therefore 92, we have them numbered from 1 to 92, and these numbers we call the atomic numbers of the elements.
Shortly before the Great War it was discovered by a student at Cambridge University that the atomic number tells us how many free protons or positive charges there are at the centre of the atom, and also the number of electrons that surround it. Every atom is neutral: that is, it has the same number of positive as it has negative charges; the same number each of protons and electrons.
This discovery demonstrates, for instance, that the atom of nitrogen — which is No. 7, as we have just observed — has seven free protons or positive charges concentrated in the nucleus, and seven electrons whirling about it. Carbon has six of each, oxygen eight, and so on.
The name of the gifted young discoverer was Mosely. He was killed at Gallipoli. His loss is, for science, one of the tragedies of the war.
II
There being 92 different elements, there are 92 different varieties of atoms, and much attention has been paid of late to their respective structures. The more generally accepted theory is that they resemble very minute solar systems, in which the electrons follow their orbits as planets revolve around the sun. These systems become exceedingly complex as the higher numbers are reached, much as a solar system with ninety-two planets would be very complex.
Atoms are small, remarkably small. If on a winter’s day at sea level we were to change all the atoms in a cubic foot of air, in which the atoms are bound mostly in pairs and bobbing about free, like so many balloons— if we were to change every atom into a grain of fine sand that would pass through a sieve of 100 mesh to the square inch, how much sand should we have? We should have enough and to spare to fill a trench three feet deep and a mile wide from New York to San Francisco. Four fifths of these atoms in the air are nitrogen, element No. 7. Hydrogen atoms are much smaller. And of course there are atoms which are much larger, although the volume of an atom does not necessarily increase with its mass.
The mass or weight of the atom is due principally to the proton, the electron being only 1/1850 of the positive charge, whereas the volume of the electron is much larger.
Another point to bear in mind is that even this almost infinitely minute mass of the electron, this 1/1850 part of the lightest atom there is, is due principally to its velocity in circling about the proton.
A commonplace — but fortunately not an everyday — example may add emphasis to this observation. I have the misfortune to weigh about 225 pounds. If I were to stand on a high table and to step from it to your shoulders and balance myself as you walked about, you would be carrying a mass of 225 pounds.
But suppose I were to ascend to the roof of a six-story house and were to jump down, landing on your shoulders as you stood on the ground. Then the impact would be much more, and this distressing jolt of my mass on your suffering shoulders would be due in part to the velocity of my fall. But this is misleading, because at such a velocity I should still retain a mass of 225 pounds; whereas, if I were to fall upon you at infinite velocity, we should enter into a new system of weights and measures, and we may at least be certain that neither of us would be in a condition to discuss the matter. Perhaps we had better drop the subject now.
We do not know of such a thing as an electron at rest. If such a condition exists, has the electron any substance — as we understand substance? Is an electron a whirl of energy and nothing more? I do not know.
Excepting hydrogen, the atoms of all the elements have, in addition to free protons in the nucleus of each and free electrons whirling about it, hydrogen and helium atoms packed in the nucleus, packed in very tight and staying there. But this does not alter the fact that all atoms of all elements are composed of positive and negative charges of electricity and nothing else, for that is the substance of the atoms of hydrogen and helium, as well as of the others.
III
Let us consider these electrons in the atoms as revolving about, each one in its orbit and at great velocity. True, the orbits are small, but the velocities are such that it takes fifteen figures to record the number of revolutions per second. Fifteen figures is at least 100 trillions, and it takes about 3,000,000 years to tick off 100 trillion seconds.
We cannot always see, to believe.
The electrons on the outside of atoms arc, like all inanimate nature, constantly striving, as it were, to reach what is called maximum entropy, or run-down-ness; to arrive at the most permanent available condition which requires the least energy to maintain it; to find, so to speak, the easiest available job. Thus water tends to run down hill; metals tend to combine with oxygen or sulphur and to reach the more permanent form of ores. And if an electron on the outside of an atom is brought into contact with another atom in which there is an easier orbit available, an orbit in which less energy is required to maintain the electron in its giddy whirl, it will jump from the one to the other, from the higher to the lower, from the harder to the easier.
These jumps of electrons from one atom or group of atoms to another constitute the whole of all the chemical phenomena found in Nature. They do not always jump from the higher to the lower. We can sometimes force them from lower to higher if we supply the energy, as we often do, in the form of heat. Sometimes we inject a little energy to start the reaction from higher to lower, and then the process goes on of itself, as when we light a fire on the hearth. There are certain set ways of electrons in the presence of positive charges, as, for instance, their tendency to form pairs or groups of eight — octets — so that the wanderings of electrons become a study of great complexity. But that need not worry us here. Suffice it to say that whenever we see any change going on in the nature of a substance, any chemical change, it is due entirely to a shiftingabout among the outside electrons of the atoms which compose it.
The presence of currents of electricity indicates a swarm or drive of free electrons, and since all electrons are alike in force, it stands to reason that atoms give them up and take on others; that there is a great deal of this changing of electrons going on all the time; and that every electron is, so to speak, trying to find the easiest available job within reach — the orbit that requires the least measure of energy to maintain it. When, then, an electron jumps within an atom from one orbit to another, from one that requires more energy to one that requires less, the difference in energy required to maintain it in its first orbit over that required to maintain it in its second, is given off. Now this difference is always the same. It is called a quantum of energy, and it is the basis of the Quantum Theory. The quantum of energy is also proposed as the unit of light. Light is a manifestation of energy, and — evidently — of electrical energy.
IV
Some time back we referred to a second apparent irregularity of arithmetic which we were to meet. It takes the substance of 16 hydrogen atoms to make one of oxygen: 8 free protons in the nucleus, and 8 electrons in the space outside, and there are either 8 more hydrogen atoms or 2 helium atoms packed into the nucleus. It requires the substance of 4 hydrogen atoms to make one atom of helium: 2 free protons in the nucleus, 2 electrons outside, and 2 more hydrogen atoms in the packing. Now the weights of these atoms are comparative, oxygen being 16, helium 4, but hydrogen, instead of being 1, is 1.008. Why, then, is the mass of the helium atom, which is 4 times 1.008, not 4.032? Why is not oxygen 16.128? But they are not. Helium is 4 and oxygen is 16. Is arithmetic wrong? No; it appears that when hydrogen is consolidated into helium the fractional mass — the eight one-thousandths of each hydrogen atom — is transformed from matter into energy! We are no longer definite and cocksure as we used to be, about the distinction between matter and energy. When we thought atoms were solid granules we had everything down pat, and could be very much more glib about it. We had a working hypothesis which was the result of observation, and we mistook it for a fact.
Einstein has opened this great gate for our study and consideration: energy and matter are interchangeable. And these changes from one to the other are constantly taking place. Matter is a manifestation of energy.
Spectroscopic analysis shows us all the elements contained in the sun, and we know that it contains vast quantities of hydrogen and helium. If, then, one tenth of the hydrogen which we know to be contained in the sun were resolved into helium, this fractional mass, the eight one-thousandths of the hydrogen atoms, would, by such a transformation, yield solar energy to last for a thousand million years! Please consider the significance of this: the sun no more a ball of fire as we know fire, but rather a vast synthesis of matter: creation going on to-day even as it was going on when this earth was hurled forth as a gigantic clod into space.
And let us carry this farther: in the earth and in planets and moons and meteorites are the heavy radioactive elements, too complex to be permanent, and giving off constantly out of their atoms — what? They give off alpha and beta and gamma ‘rays’ the while they degenerate into lighter elements, as radium, thorium, and uranium degenerate into lead. Now alpha rays are protons in pairs: the nuclei of helium atoms. Beta rays are electrons. And gamma rays are of the nature of X-rays, only much shorter than those ordinarily produced, and these partake of the nature of light. In other words, as these heavy elements degenerate to those which are lighter, from uranium back in the scale toward hydrogen, they give off into space positive and negative charges of electricity, while the energy required to maintain the protons in the nuclei and the electrons in their orbits is set free as gamma rays, which are of the nature of light.
Thus we have what seems to be an endless cycle of creation and disintegration of matter. The protons and electrons shot forth by radioactivity are too light to be held by gravity — and so from every planet and moon throughout the universe they fly away and away — whither? After æons of time to organize themselves again to hydrogen atoms and so on, from hydrogen to helium, and then to lithium and beryllium and carbon and nitrogen and oxygen, down the list of elements to make a new sun ? Or to feed an old one? Who knows?
V
We cannot tell yet what light is, but it is evident that it partakes of the nature of electrical energy. Sir Isaac Newton proposed that light was due to the drive of infinitely minute particles through space, and he called those particles corpuscles. Then followed the wave theory, which has led the fashion for many years. We can measure the length of the impulses of light, or the waves, as we like to call them. And since we like to call them waves we naturally ask the question, Waves of what? We can’t have waves of nothing. So we postulate the ether of space, which must be infinitely elastic and have other properties equally remarkable.
To be the medium in which waves are propelled at the rate of 186,000 miles a second, the ether of space must be dense, very dense. It has been calculated that it must be 800 times as dense as lead. Then when we sit opposite one another at table and engage in discourse we are surrounded by something 800 times as heavy as lead. We, the table, everything we regard as matter, must consist principally of holes in the ether. Of course it is n’t impossible, but it is disturbing. And it is the best we can do if we insist on light as waves.
We need the ether of space as a working hypothesis, and at times we don’t know what to do without it; but it always is, in a way, puzzling. Sir Oliver Lodge declares this ether to be the abode of departed spirits. But if spirits can do all the things that are attributed to them, one wonders why they need the ether. Perhaps we need it more than they do.
We have spoken of the disposition of all things inanimate to run down, to get into the most permanent condition possible, to get along with the least measure of energy. In life the tendency is the opposite. We pump water uphill, we separate metals from their ores, we are in constant opposition to inanimate nature. The presence of life reverses the rules. Instead of running down and giving off energy in the process, we living things must take on constantly a supply of energy from the outside. We starve to death without fuel — that is, food. And we get substantially all our energy from the sun. Every green leaf of every tree and plant contains great numbers of cells. In every cell is a minute quantity of an enzyme or organic catalyst called chlorophyll, which is produced by the plant. Into these cells drift carbon dioxide and the vapor of water, and the rays of the sun coming through space for 90,000,000 miles strike that leaf, and there they develop the energy they carry: develop it as heat. Under heat the cell closes, the chlorophyll changes the water vapor and carbon dioxide to formaldehyde, giving some oxygen back to the air, and the formaldehyde to sugar, to starch, to gums, to lignin and cellulose, which — with a few minerals drawn from the earth — make up the tree.
When we cut a tree down and burn it in the fireplace, we use as much oxygen from the air as was given off when the wood grew, and this combines with the substances of the wood to form water vapor and carbon dioxide again — for white smoke is usually steam. And the heat which was developed from the rays of the sun when the wood grew we get back again as we warm our fingers and toes by the open fireplace — another great cycle of nature! The steer cats the grass that grew by the power of the sun, and we eat the beef, whereby we too live by the power of the sun. The same power that produces our coal raises water for the waterfall; in short, it is from the sun that we derive substantially all the energy required for life and work.
There is a record of early Persian kings who flourished before the days of the Chaldeans from whom Abraham sprang, and of these ancient wise men it is written that they said: ‘We worship God and God only. We regard the sun as his symbol, because from it come both light and heat. Moreover, in it are contained all the elements of the earth!’ We children of men have been neglectful of the precious fruits of knowledge passed on to us in the course of our long, unwritten history.
VI
All the energy we get from the sun is of the nature of light. We stand, as it were, on our tiptoes, trying to peer over the outer rim of knowledge of this very thing, and seeing as yet very little. The firefly develops great luminosity but little heat, and here is another secret. As light passes undisturbed through space it leaves space dark. It develops only on contact; develops as energy, whether as light or heat or both. And of the vast measure which it develops, only a minute fraction is used to maintain life. Nature is not interested in life, and is not economical in conserving it.
Now let us be very practical and say that, since the price of gasoline has gone up, we are resolved to use the energy of the sun, which shines free for all, to propel our motor cars. We can do it, provided the prohibition enforcement officer does not forbid us. We plant corn, cultivate it intensively, harvest it, change the starch to sugar by means of a diastase, and then ferment it into beer. From the beer we distill alcohol, and we have an excellent fuel, a cleaner fuel than gasoline. We have used the light of the sun for about ninety days to grow our corn, and we have developed from each acre of our land the equivalent of about two fifths of a ton of coal. This we achieve with good weather-conditions and the best practice of husbandry.
But suppose, instead of the comfortable slow method of Nature, we were to discover more than we now know in regard to the nature of light. Suppose we learn more about the quanta of energy, demonstrate them to be units of light, and go as far ahead as we have gone with the chemical elements. Or learn to control them and resolve them into foot-pounds, as we do with currents of electricity. Suppose someone like Sir J. J. Thomson or Einstein or Planck or our own Michelson of Chicago or Millikan of Pasadena or Wood of Baltimore—or who shall it be? — were to devise an apparatus to intercept the blast of energy we get from the sun and to transform it into the equivalent of heat or electrical currents or foot-pounds? It would make us look rather small with our little crop of corn!
The while we have been planting and hoeing and harvesting and finally getting the equivalent in alcohol of two fifths of a ton of coal to the acre, there has been delivered to that very acre of land by the sun, during the same ninety days, the equivalent of about 1500 tons of coal. By means of agriculture we have been able to use no more than 1/2000 of the energy delivered to us. The rest, so far as our specific purpose of getting fuel for our motor cars is concerned, has been wasted.
It is not irreverent to try to beat Nature. That is our business. We should still be wild people in the woods if we did not try constantly to do this very thing. If we could get the equivalent of 1500 tons of coal from one acre in three months, we should get four times that measure in a year, for already we have made allowance for rainy and short days. We should then have from that same acre of land the equivalent of 6000 tons of coal instead of two thirds of one. With such an invention, fifty plots of land of two square miles each would furnish all the power we need in the United States, without the need of any coal or falling water.
Now look at the picture. Our foolish and wasteful way of mining and transporting and burning coal would be a thing of the past, for, of course, we should cook and heat by electricity. There would be no more chimneys or ugly smokestacks. No soot in cities or smoke anywhere. No quarrels between nations about resources of coal and oil, which would become chemical raw materials with plenty and to spare. No more trouble about fuel for our ships. Nobody would need to be hungry or in physical want of any sort, provided always we had the understanding and the intelligence — and, above all, the character — to meet such a day of light.
Perhaps it will be better if several generations go the way of all flesh before this great discovery is made, because we are hardly worthy, in this present year of grace, to wield such power. It might spoil us. We are still little children compared with what we may become— if we try!