The Outline of Science.
by J. Arthur Thomson.
INTRODUCTION.
There is abundant evidence of a widened and deepened interest in modern science. How could it be otherwise when we think of the magnitude and the eventfulness of recent advances?
But the interest of the general public would be even greater than it is if the makers of new knowledge were more willing to expound their discoveries in ways that could be "understanded of the people." No one objects very much to technicalities in a game or on board a yacht, and they are clearly necessary for terse and precise scientific description. It is certain, however, that they can be reduced to a minimum without sacrificing accuracy, when the object in view is to explain "the gist of the matter." So this OUTLINE OF SCIENCE is meant for the general reader, who lacks both time and opportunity for special study, and yet would take an intelligent interest in the progress of science which is making the world always new.
The story of the triumphs of modern science is one of which Man may well be proud. Science reads the secret of the distant star and anatomises the atom; foretells the date of the comet"s return and predicts the kinds of chickens that will hatch from a dozen eggs; discovers the laws of the wind that bloweth where it listeth and reduces to order the disorder of disease. Science is always setting forth on Columbus voyages, discovering new worlds and conquering them by understanding. For Knowledge means Foresight and Foresight means Power.
The idea of Evolution has influenced all the sciences, forcing us to think of everything as with a history behind it, for we have travelled far since Darwin"s day. The solar system, the earth, the mountain ranges, and the great deeps, the rocks and crystals, the plants and animals, man himself and his social inst.i.tutions--all must be seen as the outcome of a long process of Becoming. There are some eighty-odd chemical elements on the earth to-day, and it is now much more than a suggestion that these are the outcome of an inorganic evolution, element giving rise to element, going back and back to some primeval stuff, from which they were all originally derived, infinitely long ago. No idea has been so powerful a tool in the fashioning of New Knowledge as this simple but profound idea of Evolution, that the present is the child of the past and the parent of the future. And with the picture of a continuity of evolution from nebula to social systems comes a promise of an increasing control--a promise that Man will become not only a more accurate student, but a more complete master of his world.
It is characteristic of modern science that the whole world is seen to be more vital than before. Everywhere there has been a pa.s.sage from the static to the dynamic. Thus the new revelations of the const.i.tution of matter, which we owe to the discoveries of men like Professor Sir J. J. Thomson, Professor Sir Ernest Rutherford, and Professor Frederick Soddy, have shown the very dust to have a complexity and an activity heretofore unimagined. Such phrases as "dead" matter and "inert" matter have gone by the board.
The new theory of the atom amounts almost to a new conception of the universe. It bids fair to reveal to us many of nature"s hidden secrets. The atom is no longer the indivisible particle of matter it was once understood to be. We know now that there is an atom within the atom--that what we thought was elementary can be dissociated and broken up. The present-day theories of the atom and the const.i.tution of matter are the outcome of the comparatively recent discovery of such things as radium, the X-rays, and the wonderful revelations of such instruments as the spectroscope and other highly perfected scientific instruments.
The advent of the electron theory has thrown a flood of light on what before was hidden or only dimly guessed at. It has given us a new conception of the framework of the universe. We are beginning to know and realise of what matter is made and what electric phenomena mean. We can glimpse the vast stores of energy locked up in matter. The new knowledge has much to tell us about the origin and phenomena, not only of our own planet, but other planets, of the stars, and the sun. New light is thrown on the source of the sun"s heat; we can make more than guesses as to its probable age. The great question to-day is: is there one primordial substance from which all the varying forms of matter have been evolved?
But the discovery of electrons is only one of the revolutionary changes which give modern science an entrancing interest.
As in chemistry and physics, so in the science of living creatures there have been recent advances that have changed the whole prospect. A good instance is afforded by the discovery of the "hormones," or chemical messengers, which are produced by ductless glands, such as the thyroid, the supra-renal, and the pituitary, and are distributed throughout the body by the blood. The work of physiologists like Professor Starling and Professor Bayliss has shown that these chemical messengers regulate what may be called the "pace" of the body, and bring about that regulated harmony and smoothness of working which we know as health. It is not too much to say that the discovery of hormones has changed the whole of physiology. Our knowledge of the human body far surpa.s.ses that of the past generation.
The persistent patience of microscopists and technical improvements like the "ultramicroscope" have greatly increased our knowledge of the invisible world of life. To the bacteria of a past generation have been added a mult.i.tude of microscopic animal microbes, such as that which causes Sleeping Sickness. The life-histories and the weird ways of many important parasites have been unravelled; and here again knowledge means mastery. To a degree which has almost surpa.s.sed expectations there has been a revelation of the intricacy of the stones and mortar of the house of life, and the microscopic study of germ-cells has wonderfully supplemented the epoch-making experimental study of heredity which began with Mendel. It goes without saying that no one can call himself educated who does not understand the central and simple ideas of Mendelism and other new departures in biology.
The procession of life through the ages and the factors in the sublime movement; the peopling of the earth by plants and animals and the linking of life to life in subtle inter-relations, such as those between flowers and their insect-visitors; the life-histories of individual types and the extraordinary results of the new inquiry called "experimental embryology"--these also are among the subjects with which this OUTLINE will deal.
The behaviour of animals is another fascinating study, leading to a provisional picture of the dawn of mind. Indeed, no branch of science surpa.s.ses in interest that which deals with the ways and habits--the truly wonderful devices, adaptations, and instincts--of insects, birds, and mammals. We no longer deny a degree of intelligence to some members of the animal world--even the line between intelligence and reason is sometimes difficult to find.
Fresh contacts between physiology and the study of man"s mental life; precise studies of the ways of children and wild peoples; and new methods like those of the psycho-a.n.a.lyst must also receive the attention they deserve, for they are giving us a "New Psychology" and the claims of psychical research must also be recognised by the open-minded.
The general aim of the OUTLINE is to give the reader a clear and concise view of the essentials of present-day science, so that he may follow with intelligence the modern advance and share appreciatively in man"s continued conquest of his kingdom.
J. ARTHUR THOMSON.
I.
THE ROMANCE OF THE HEAVENS.
THE SCALE OF THE UNIVERSE--THE SOLAR SYSTEM.
-- 1.
The story of the triumphs of modern science naturally opens with Astronomy. The picture of the Universe which the astronomer offers to us is imperfect; the lines he traces are often faint and uncertain. There are many problems which have been solved, there are just as many about which there is doubt, and notwithstanding our great increase in knowledge, there remain just as many which are entirely unsolved.
The problem of the structure and duration of the universe [said the great astronomer Simon Newcomb] is the most far-reaching with which the mind has to deal. Its solution may be regarded as the ultimate object of stellar astronomy, the possibility of reaching which has occupied the minds of thinkers since the beginning of civilisation. Before our time the problem could be considered only from the imaginative or the speculative point of view. Although we can to-day attack it to a limited extent by scientific methods, it must be admitted that we have scarcely taken more than the first step toward the actual solution.... What is the duration of the universe in time? Is it fitted to last for ever in its present form, or does it contain within itself the seeds of dissolution? Must it, in the course of time, in we know not how many millions of ages, be transformed into something very different from what it now is? This question is intimately a.s.sociated with the question whether the stars form a system. If they do, we may suppose that system to be permanent in its general features; if not, we must look further for our conclusions.
The Heavenly Bodies.
The heavenly bodies fall into two very distinct cla.s.ses so far as their relation to our Earth is concerned; the one cla.s.s, a very small one, comprises a sort of colony of which the Earth is a member. These bodies are called planets, or wanderers. There are eight of them, including the Earth, and they all circle round the sun. Their names, in the order of their distance from the sun, are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Ura.n.u.s, Neptune, and of these Mercury, the nearest to the sun, is rarely seen by the naked eye. Ura.n.u.s is practically invisible, and Neptune quite so. These eight planets, together with the sun, const.i.tute, as we have said, a sort of little colony; this colony is called the Solar System.
The second cla.s.s of heavenly bodies are those which lie outside the solar system. Every one of those glittering points we see on a starlit night is at an immensely greater distance from us than is any member of the Solar System. Yet the members of this little colony of ours, judged by terrestrial standards, are at enormous distances from one another. If a sh.e.l.l were shot in a straight line from one side of Neptune"s...o...b..t to the other it would take five hundred years to complete its journey. Yet this distance, the greatest in the Solar System as now known (excepting the far swing of some of the comets), is insignificant compared to the distances of the stars. One of the nearest stars to the earth that we know of is Alpha Centauri, estimated to be some twenty-five million millions of miles away. Sirius, the brightest star in the firmament, is double this distance from the earth.
We must imagine the colony of planets to which we belong as a compact little family swimming in an immense void. At distances which would take our sh.e.l.l, not hundreds, but millions of years to traverse, we reach the stars--or rather, a star, for the distances between stars are as great as the distance between the nearest of them and our Sun. The Earth, the planet on which we live, is a mighty globe bounded by a crust of rock many miles in thickness; the great volumes of water which we call our oceans lie in the deeper hollows of the crust. Above the surface an ocean of invisible gas, the atmosphere, rises to a height of about three hundred miles, getting thinner and thinner as it ascends.
[Ill.u.s.tration: LAPLACE.
One of the greatest mathematical astronomers of all time and the originator of the nebular theory.]
[Ill.u.s.tration: Photo: Royal Astronomical Society.
PROFESSOR J. C. ADAMS.
who, antic.i.p.ating the great French mathematician, Le Verrier, discovered the planet Neptune by calculations based on the irregularities of the orbit of Ura.n.u.s. One of the most dramatic discoveries in the history of Science.]
[Ill.u.s.tration: Photo: Elliott & Fry, Ltd.
PROFESSOR EDDINGTON.
Professor of Astronomy at Cambridge. The most famous of the English disciples of Einstein.]
[Ill.u.s.tration: FIG. 1.--DIAGRAMS OF THE SOLAR SYSTEM.
THE COMPARATIVE DISTANCES OF THE PLANETS.
(Drawn approximately to scale).
The isolation of the Solar System is very great. On the above scale the nearest star (at a distance of 25 trillions of miles) would be over one half mile away. The hours, days, and years are the measures of time as we use them; that is: Jupiter"s "Day" (one rotation of the planet) is made in ten of our hours; Mercury"s "Year" (one revolution of the planet around the Sun) is eighty-eight of our days. Mercury"s "Day" and "Year" are the same. This planet turns always the same side to the Sun.]
[Ill.u.s.tration: THE COMPARATIVE SIZES OF THE SUN AND THE PLANETS (Drawn approximately to scale) On this scale the Sun would be 17-1/2 inches in diameter; it is far greater than all the planets put together. Jupiter, in turn, is greater than all the other planets put together.]
Except when the winds rise to a high speed, we seem to live in a very tranquil world. At night, when the glare of the sun pa.s.ses out of our atmosphere, the stars and planets seem to move across the heavens with a stately and solemn slowness. It was one of the first discoveries of modern astronomy that this movement is only apparent. The apparent creeping of the stars across the heavens at night is accounted for by the fact that the earth turns upon its axis once in every twenty-four hours. When we remember the size of the earth we see that this implies a prodigious speed.
In addition to this the earth revolves round the sun at a speed of more than a thousand miles a minute. Its path round the sun, year in year out, measures about 580,000,000 miles. The earth is held closely to this path by the gravitational pull of the sun, which has a ma.s.s 333,432 times that of the earth. If at any moment the sun ceased to exert this pull the earth would instantly fly off into s.p.a.ce straight in the direction in which it was moving at the time, that is to say, at a tangent. This tendency to fly off at a tangent is continuous. It is the balance between it and the sun"s pull which keeps the earth to her almost circular orbit. In the same way the seven other planets are held to their orbits.
Circling round the earth, in the same way as the earth circles round the sun, is our moon. Sometimes the moon pa.s.ses directly between us and the sun, and cuts off the light from us. We then have a total or partial eclipse of the sun. At other times the earth pa.s.ses directly between the sun and the moon, and causes an eclipse of the moon. The great ball of the earth naturally trails a mighty shadow across s.p.a.ce, and the moon is "eclipsed" when it pa.s.ses into this.
The other seven planets, five of which have moons of their own, circle round the sun as the earth does. The sun"s ma.s.s is immensely larger than that of all the planets put together, and all of them would be drawn into it and perish if they did not travel rapidly round it in gigantic orbits. So the eight planets, spinning round on their axes, follow their fixed paths round the sun. The planets are secondary bodies, but they are most important, because they are the only globes in which there can be life, as we know life.
If we could be transported in some magical way to an immense distance in s.p.a.ce above the sun, we should see our Solar System as it is drawn in the accompanying diagram (Fig. 1), except that the planets would be mere specks, faintly visible in the light which they receive from the sun. (This diagram is drawn approximately to scale.) If we moved still farther away, trillions of miles away, the planets would fade entirely out of view, and the sun would shrink into a point of fire, a star. And here you begin to realize the nature of the universe. The sun is a star. The stars are suns. Our sun looks big simply because of its comparative nearness to us. The universe is a stupendous collection of millions of stars or suns, many of which may have planetary families like ours.
-- 2.
The Scale of the Universe.
How many stars are there? A glance at a photograph of star-clouds will tell at once that it is quite impossible to count them. The fine photograph reproduced in Figure 2 represents a very small patch of that pale-white belt, the Milky Way, which spans the sky at night. It is true that this is a particularly rich area of the Milky Way, but the entire belt of light has been resolved in this way into ma.s.ses or clouds of stars. Astronomers have counted the stars in typical districts here and there, and from these partial counts we get some idea of the total number of stars. There are estimated to be between two and three thousand million stars.
Yet these stars are separated by inconceivable distances from each other, and it is one of the greatest triumphs of modern astronomy to have mastered, so far, the scale of the universe. For several centuries astronomers have known the relative distances from each other of the sun and the planets. If they could discover the actual distance of any one planet from any other, they could at once tell all the distances within the Solar System.
The sun is, on the latest measurements, at an average distance of 92,830,000 miles from the earth, for as the orbit of the earth is not a true circle, this distance varies. This means that in six months from now the earth will be right at the opposite side of its path round the sun, or 185,000,000 miles away from where it is now. Viewed or photographed from two positions so wide apart, the nearest stars show a tiny "shift" against the background of the most distant stars, and that is enough for the mathematician. He can calculate the distance of any star near enough to show this "shift." We have found that the nearest star to the earth, a recently discovered star, is twenty-five trillion miles away. Only thirty stars are known to be within a hundred trillion miles of us.
This way of measuring does not, however, take us very far away in the heavens. There are only a few hundred stars within five hundred trillion miles of the earth, and at that distance the "shift" of a star against the background (parallax, the astronomer calls it) is so minute that figures are very uncertain. At this point the astronomer takes up a new method. He learns the different types of stars, and then he is able to deduce more or less accurately the distance of a star of a known type from its faintness. He, of course, has instruments for gauging their light. As a result of twenty years work in this field, it is now known that the more distant stars of the Milky Way are at least a hundred thousand trillion (100,000,000,000,000,000) miles away from the sun.
Our sun is in a more or less central region of the universe, or a few hundred trillion miles from the actual centre. The remainder of the stars, which are all outside our Solar System, are spread out, apparently, in an enormous disc-like collection, so vast that even a ray of light, which travels at the rate of 186,000 miles a second, would take 50,000 years to travel from one end of it to the other. This, then is what we call our universe.
Are there other Universes?
Why do we say "our universe"? Why not the universe? It is now believed by many of our most distinguished astronomers that our colossal family of stars is only one of many universes. By a universe an astronomer means any collection of stars which are close enough to control each other"s movements by gravitation; and it is clear that there might be many universes, in this sense, separated from each other by profound abysses of s.p.a.ce. Probably there are.
For a long time we have been familiar with certain strange objects in the heavens which are called "spiral nebul-" (Fig 4). We shall see at a later stage what a nebula is, and we shall see that some astronomers regard these spiral nebul- as worlds "in the making." But some of the most eminent astronomers believe that they are separate universes--"island-universes" they call them--or great collections of millions of stars like our universe. There are certain peculiarities in the structure of the Milky Way which lead these astronomers to think that our universe may be a spiral nebula, and that the other spiral nebul- are "other universes."
[Ill.u.s.tration: Photo: Harvard College Observatory.
FIG. 2.--THE MILKY WAY.
Note the cloud-like effect.]
[Ill.u.s.tration: FIG. 3--THE MOON ENTERING THE SHADOW CAST BY THE EARTH.
The diagram shows the Moon partially eclipsed.]
[Ill.u.s.tration: From a photograph taken at the Yerkes Observatory.
FIG. 4.--THE GREAT NEBULA IN ANDROMEDA, MESSIER 31]
Vast as is the Solar System, then, it is excessively minute in comparison with the Stellar System, the universe of the Stars, which is on a scale far transcending anything the human mind can apprehend.
THE SOLAR SYSTEM.
THE SUN.
-- 1.
But now let us turn to the Solar System, and consider the members of our own little colony.
Within the Solar System there are a large number of problems that interest us. What is the size, ma.s.s, and distance of each of the planets? What satellites, like our Moon, do they possess? What are their temperatures? And those other, sporadic members of our system, comets and meteors, what are they? What are their movements? How do they originate? And the Sun itself, what is its composition, what is the source of its heat, how did it originate? Is it running down?
These last questions introduce us to a branch of astronomy which is concerned with the physical const.i.tution of the stars, a study which, not so very many years ago, may well have appeared inconceivable. But the spectroscope enables us to answer even these questions, and the answer opens up questions of yet greater interest. We find that the stars can be arranged in an order of development--that there are stars at all stages of their life-history. The main lines of the evolution of the stellar universe can be worked out. In the sun and stars we have furnaces with temperatures enormously high; it is in such conditions that substances are resolved into their simplest forms, and it is thus we are enabled to obtain a knowledge of the most primitive forms of matter. It is in this direction that the spectroscope (which we shall refer to immediately) has helped us so much. It is to this wonderful instrument that we owe our knowledge of the composition of the sun and stars, as we shall see.
"That the spectroscope will detect the millionth of a milligram of matter, and on that account has discovered new elements, commands our admiration; but when we find in addition that it will detect the nature of forms of matter trillions of miles away, and moreover, that it will measure the velocities with which these forms of matter are moving with an absurdly small per cent. of possible error, we can easily acquiesce in the statement that it is the greatest instrument ever devised by the brain and hand of man."
Such are some of the questions with which modern astronomy deals. To answer them requires the employment of instruments of almost incredible refinement and exact.i.tude and also the full resources of mathematical genius. Whether astronomy be judged from the point of view of the phenomena studied, the vast ma.s.ses, the immense distances, the -ons of time, or whether it be judged as a monument of human ingenuity, patience, and the rarest type of genius, it is certainly one of the grandest, as it is also one of the oldest, of the sciences.
The Solar System.
In the Solar System we include all those bodies dependent on the sun which circulate round it at various distances, deriving their light and heat from the sun--the planets and their moons, certain comets and a mult.i.tude of meteors: in other words, all bodies whose movements in s.p.a.ce are determined by the gravitational pull of the sun.
The Sun.
Thanks to our wonderful modern instruments and the ingenious methods used by astronomers, we have to-day a remarkable knowledge of the sun.
Look at the figure of the sun in the frontispiece. The picture represents an eclipse of the sun; the dark body of the moon has screened the sun"s shining disc and taken the glare out of our eyes; we see a silvery halo surrounding the great orb on every side. It is the sun"s atmosphere, or "crown" (corona), stretching for millions of miles into s.p.a.ce in the form of a soft silvery-looking light; probably much of its light is sunlight reflected from particles of dust, although the spectroscope shows an element in the corona that has not so far been detected anywhere else in the universe and which in consequence has been named Coronium.
We next notice in the ill.u.s.tration that at the base of the halo there are red flames peeping out from the edges of the hidden disc. When one remembers that the sun is 866,000 miles in diameter, one hardly needs to be told that these flames are really gigantic. We shall see what they are presently.
Regions of the Sun.
The astronomer has divided the sun into definite concentric regions or layers. These layers envelop the nucleus or central body of the sun somewhat as the atmosphere envelops our earth. It is through these vapour layers that the bright white body of the sun is seen. Of the innermost region, the heart or nucleus of the sun, we know almost nothing. The central body or nucleus is surrounded by a brilliantly luminous envelope or layer of vaporous matter which is what we see when we look at the sun and which the astronomer calls the photosphere.
Above--that is, overlying--the photosphere there is a second layer of glowing gases, which is known as the reversing layer. This layer is cooler than the underlying photosphere; it forms a veil of smoke-like haze and is of from 500 to 1,000 miles in thickness.
A third layer or envelope immediately lying over the last one is the region known as the chromosphere. The chromosphere extends from 5,000 to 10,000 miles in thickness--a "sea" of red tumultuous surging fire. Chief among the glowing gases is the vapour of hydrogen. The intense white heat of the photosphere beneath shines through this layer, overpowering its brilliant redness. From the uppermost portion of the chromosphere great fiery tongues of glowing hydrogen and calcium vapour shoot out for many thousands of miles, driven outward by some prodigious expulsive force. It is these red "prominences" which are such a notable feature in the picture of the eclipse of the sun already referred to.
During the solar eclipse of 1919 one of these red flames rose in less than seven hours from a height of 130,000 miles to more than 500,000 miles above the sun"s surface. This immense column of red-hot gas, four or five times the thickness of the earth, was soaring upward at the rate of 60,000 miles an hour.
These flaming jets or prominences shooting out from the chromosphere are not to be seen every day by the naked eye; the dazzling light of the sun obscures them, gigantic as they are. They can be observed, however, by the spectroscope any day, and they are visible to us for a very short time during an eclipse of the sun. Some extraordinary outbursts have been witnessed. Thus the late Professor Young described one on September 7, 1871, when he had been examining a prominence by the spectroscope: It had remained unchanged since noon of the previous day--a long, low, quiet-looking cloud, not very dense, or brilliant, or in any way remarkable except for its size. At 12:30 p.m. the Professor left the spectroscope for a short time, and on returning half an hour later to his observations, he was astonished to find the gigantic Sun flame shattered to pieces. The solar atmosphere was filled with flying debris, and some of these portions reached a height of 100,000 miles above the solar surface. Moving with a velocity which, even at the distance of 93,000,000 miles, was almost perceptible to the eye, these fragments doubled their height in ten minutes. On January 30, 1885, another distinguished solar observer, the late Professor Tacchini of Rome, observed one of the greatest prominences ever seen by man. Its height was no less than 142,000 miles--eighteen times the diameter of the earth. Another mighty flame was so vast that supposing the eight large planets of the solar system ranged one on top of the other, the prominence would still tower above them.[1]
[1] The Romance of Astronomy, by H. Macpherson.
[Ill.u.s.tration: FIG. 5.--DIAGRAM SHOWING THE MAIN LAYERS OF THE SUN.
Compare with frontispiece.]
[Ill.u.s.tration: Photo: Royal Observatory, Greenwich.
FIG. 6.--SOLAR PROMINENCES SEEN AT TOTAL SOLAR ECLIPSE, May 29, 1919. TAKEN AT SOBRAL, BRAZIL.
The small Corona is also visible.]
[Ill.u.s.tration: FIG. 7.--THE VISIBLE SURFACE OF THE SUN.
A photograph taken at the Mount Wilson Observatory of the Carnegie Inst.i.tution at Washington.]
[Ill.u.s.tration: FIG. 8.--THE SUN.
Photographed in the light of glowing hydrogen, at the Mount Wilson Observatory of the Carnegie Inst.i.tution of Washington: vortex phenomena near the spots are especially prominent.]