Our world; a sketch of origins according to science

Front matter

Class.

Book.

CopyrightN°.__

Preface

SOUND ideas relating to the public welfare are not effective until so generally shared as to guide public opinion. The essentials of physical science are the basis of all sound thinking. The more thoroughly and generally they are understood, therefore, the better for social, political and economic conditions. The sole purpose of this book is to present in as brief compass and plain terms as practicable the principal data of general science as now accepted, without exploiting special theories. If evolution appears to be the key to explanation of our world in all its phases it is because the evidence now admits of no other.

The chief difficulty in preparing such a book is the choice of materials from a vast and various mass from many sources. Yet this difficulty is somewhat lessened by the consideration that most of the details of science have been developed in the search for principles and in the application of those principles to practical uses. The arrangement follows the natural sequence, except that, for clearness, some general causes are stated in connection with specific phenomena; for the main divisions of science overlap and are governed alike by the laws of matter.

C H. P.

Contents

Chapter Page

I Cosmic Phases . . . . 1 1

II In the Beginning 36

Chapter I Cosmic Phases The Spectrum

THE spectroscope, devised by Kirchhoff and Bunsen in 1859, shows the elements of any object that emits light, whether a distant orb or a filmy nebula. It has solved the mystery of certain of the variable stars, made the sun a field of intimate research, and shown the direction in which the solar system is traveling. These and similar results have revolutionized astronomy and projected the theory of evolution through the vast of starlit space. The nature and functions of this instrument must be understood before the facts it has demonstrated can be fully appraised.

Light is a result of motion of or within the atoms of the matter affected and communicated by the ether supposed to pervade all matter and all known space. The presence of this ether cannot be proven by any method yet known. It exists in theory to account for the waves of energy — heat, light, and electricity — which are known and determined with extreme accuracy.

For many years dark lines across the various colors of the solar spectrum had attracted attention. They are called the Fraunhofer lines, from the name of the investigator who first made them the subject of serious investigation; but it was not until after the spectroscope came into use and the wave theory of light was generally accepted that the results were explained and applied to the solution of many problems of astro-physics. Spectrum analysis has thus become a leading factor in the modern science of astronomy and a powerful aid in physics and chemistry.

It has led td several improvements in the instrument which have added greatly to its value in the many uses to which it is put. The most important of these is in substituting a so-called grating in lieu of prisms. This grating is a plate of glass or speculum metal ruled with accurately spaced and parallel lines, in some cases with 60,000 or more to the inch — in itself an extraordinary mechanical achievement. The main purpose of these appliances is to lengthen the spectrum by diffraction in order to show all the lines, which number many thousands, but with as little loss of brilliancy as possible, since the difficulties of observation increase with the distance from the source of the light. The grating also permits an accurate count of the frequency of the waves — the number per second, which is of vital moment in many investigations ; and considering the fact that the sensation of sight is produced by waves ranging from 400 million million to 800 million million, in round numbers, per second, the measurement and analysis of these waves rank among the greatest technical attainments of science.

The rays are admitted through a minute slit, say one-tenth of an inch long and one-thousandth of an inch wide, to pass through a lens making them parallel; thence to a series of prisms, an echelon of thin glass plates, or a grating, which transmits or reflects them through another lens by which they are focused a short distance in front of the eye or a photographic plate for permanent record and comparison with the results of laboratory investigation, so far as that is possible. The prisms, owing to lesser loss of light, are most used in astronomical work, in connection of course with the telescope.

Every element, when heated to the point of incandescence can thus be identified, under suitable conditions, as infallibly as a person by his fingerprints, for the spectrum of one element is never duplicated by that of another. When, therefore, it is found that a given element — iron or hydrogen, for example — shows certain characteristics by examination in the laboratory, its presence in a distant star or nebula will likewise be indicated. Investigations so conducted have established several results of decisive import in studying the constitution, evolution and motion of the stars and other astronomic objects.

The spectrum of an incandescent solid body, a liquid or a condensed gas is continuous, that is to say, the normal colors are not crossed by lines of any kind. The spectrum of an incandescent gas or vapor consists of bright lines arranged according to the different elements, or bright lines upon a faint continuous spectrum. If the light is from a source that would otherwise yield a continuous spectrum, but passing through gases or vapors less heated, dark lines are produced by absorption. When such a body is moving toward the earth or the earth toward it, the lines shift slightly toward the violet; and when the body is receding from the earth or the earth from it, the shift is toward the red. The rate of this change, as found by comparison with a similaf spectrum of a stationary light, affords data from which the speed may be calculated. By this method the velocity with which stars and comets are moving, the orbits of the variable stars, the path of the solar system and many other motions involved in the problems of celestial mechanics are determined. And be it understood that these conclusions are not theories, but facts as provable as any in physical science. They are the effects of the laws of light, which inevitably follow from the nature of light itself.

Light radiates through free space — as from a star to the earth at the rate of 299,800 kilometers (186,330 miles) per second, the velocity being calculated with a precision correct within 30 kilometers. This amounts to about 6 million million miles per year. The stars are all at such great distances from us that the unit of measurement is called a "light-year," the distance that light travels in a year. The nearest lucid star, Alpha Centauri, 1 in the southern hemisphere, is about 4^ light-years from the sun; the next nearest, a catalogue star (21,185 Lalande), in a different direction, is 7 ; and Sirius, the brightest of all the stars, in a yet different direction, is 9. The average distance between neighboring stars, so far as their distances have been calculated, is from 6 to 8 light-years ; and probably the remote stars are similarly spaced, except where there are groups or clusters of stars comprising systems. This average, of course, is only a rude generalization, for the variations are many and enormous.

To ascertain the distance of a star is one of the most delicate and difficult measurements in astronomy. The method thus far employed is that of triangulation, the same as that used by surveyors in topographical work. The conditions create the difficulty. The angles can be determined only by the parallax — the apparent change in the position of a star produced by the change in the position of the earth in its orbit around the sun. The base line of this measurement is the diameter of the orbit, about 186 million miles. Yet this is too short to afford a basis for calculating the distance of only a very small proportion of the stars. Even some of the brighter ones are so far away that an appreciable angle cannot be defined. Recently such progress has been made in estimating stellar distances by means of the characteristics and degrees of light from variable stars in clusters so far distant as to show no parallax that there is some prospect of perfecting methods that will also determine the distances and dimensions of stars that are not variable. These methods are a development of spectrum analysis.

A FINITE UNIVERSE

The total number of stars visible through the greatest telescopes is somewhat less than 200 million, though the number that can be photographed is much greater. It is mathematically certain that if the brilliant stars were infinite in number, and light suffers absolutely no diminution in passing through space, the entire sky would be suffused

COSMIC PHASES IS

with a glow. There is no evidence as yet that light is so diminished; and there are substantial reasons for thinking that the number of stars is limited. Astronomers are almost unanimously of opinion that the stellar system which constitutes our universe is not infinite, but is limited in all directions. The evidence indicates a spheroid formation, much flattened, the northern hemisphere of which i§ not coincident with the vista presented by the skies of the earth's northern hemisphere, the plane of the equator forming an angle of about 62 degrees with the plane of the Milky Way.

This conception is founded upon the most thorough observations possible to make. The total number of stars shown by photographs of all the stellar regions reveals a progressive decrease away from the Galaxy, while through the Galaxy the distance is so great that the stars more remote cannot be resolved by the most efficient instruments; yet the spectroscope shows unerringly that the glow in the outlying and impenetrable regions is light from condensed bodies. In other words, if the average number of stars per unit of space is the same in the Galaxy as it is toward the poles, the effect we behold would be produced by the greater distance through it — the greater extension of the equatorial plane of the spheroid.

No other theory accounts for the phenomena; and it is aided by the present position of the solar system. The fact has been established that the sun and its retinue are moving in the general direction of the constellation of Lyra, near the present position of the magnificent Vega, a star of the northern hemisphere. The speed of this motion is about 19 kilometers per second. A simple calculation will therefore show that the early history of the earth, even of the human race, was passed in a vastly different region of the universe from that through which it is now voyaging.

Yet the velocity of the sun is very much less than that of most of the stars, so far as their motion is known. The average speed has been estimated at 26 kilometers per second ; but such an average has small significance because of the enormous variations from it. Some of the stars are moving at such a rapid rate as to forbid any idea of relation, except in those cases where similarity of speed and direction among a group of neighboring stars indicates a separate system. The beautiful Arcturus was long supposed to have the greatest velocity of any star — between 200 and 300 miles per second. Even in ancient times its change of position was noted by the diligent students of the heavens. Modern astronomy, however, has found that this speed is exceeded by several other stars of telescopic order. It has often been remarked, as illustrating the vastness of stellar distances, that notwithstanding the movement of all the stars if the astrologers of antiquity could now survey them they would detect no considerable changes in the constellations with which they were so familiar.

In studying the possibilities of the celestial mechanism, the diversity of direction in stellar motion is a fact of much importance. Efforts have been made to find evidence that the movements of the stars are governed by some sort of universal concert; but they have thus far been unavailing on anything like a general scale. Two great streams in opposite directions, but parallel with the galactic plane and perhaps other streams, are thought by some observers to be shown by transverse motions ; but these conclusions embrace but a small proportion of all the stars. In any event, there remains a diversity of movements that cannot now be brought into any semblance of system or coordination.

It would seem remarkable if there were no star streams. If the spheroid conception of the universe be true, whatever may be irregularities of the exterior, there must be a cause or combination of causes, and the only causes now conceivable are gravitation and momentum. If the solar system be near or within easy view of the central region, the conclusion is obvious that the planetary type of motion does not propel the stars around a central body. In fact neither the sun nor any of the stars, the proper motion of which has been determined, reveals an orbit. Measurements have not been conducted long enough; and it may require many centuries of observation before sufficient data can be accumulated to determine with any assurance whether stellar movements have an orbital character.

There are, of course, many stars very much larger than the sun; but this difference is more of extension than of mass. The largest known stars are greater than the sun, in most cases, mainly because they are in a more diffused or gaseous condition, which contracts with age. Again assuming our universe to be finite in extent, it may be readily imagined that the ether or other medium of radiation does not extend indefinitely beyond the outer stars ; hence there would be no ultimate loss of potential energy by dissipation into space. Inasmuch as the universe shows no signs of condensation after the lapse of inconceivable time, the problem is narrowed to the principle of perpetual motion, which appears to actuate the material universe in the atom and at large ; and this problem may lie in the realm of the unknowable.

EVOLUTION OF STARS

Armed with the spectroscope, astronomers were not slow to apply the theory of evolution to the stars. The evidence was so suggestive that the principle gained general recognition. The universality of the laws of gravitation and radiation was supplemented by the discovery that the elements and properties of matter are the same wherever matter exists in the universe. These elements do not always exist in the same combinations, and it is not apparent that all of them are in every astronomic body. Thus certain elements exist on the earth that are not known to be in the sun; and certain other elements are in some of the stars and nebulae that are not known to be in others. These facts are shown by the spectroscope ; indeed, there are many lines in some of the spectra that are not yet identified. These discrepancies are the subject of unremitting research and will doubtless eventually be accounted for. Without pursuing this highly technical branch of science further, it suffices to say that the unusual and unknown elements form but a small proportion of the masses of matter scattered through the cosmos ; hence the assumption is entirely safe that the material universe is as homogeneous in its constituents as it is in its laws. This leads to the conclusion that the evolutionary processes of the stars are general, the results varying with the conditions. If, therefore, it can be determined what the several stages are, we may form a definite conception as to the origin of the solar system and of the earth itself. This has naturally become the paramount object of astronomical theory and research. That great progress has been made will be manifest by an untechnical recital of the leading facts which the telescope, the spectroscope and the camera have demonstrated. Any theory of stellar evolution is confronted at the outset with two formidable obstacles : the remoteness of the stars and the duration of time required for their successive periods of development. As the former has, in some degree, been surmounted by optical aid, so has the latter by the great number of stellar objects representing all the stages through which matter passes in being organized into stars and systems, excepting the lesser features of planetary character, which probably exist in immense numbers, though invisible. Within the entire range of the intellectual faculties there is nothing approaching in sublimity the ideas evoked by this wondrous panorama, viewed as stages in the evolution of worlds.

MULTIPLE STARS

There are now known about 150 stars that are variable in brightness because of partial eclipse. In each case an obscure companion passes at regular intervals between the star and the line of sight. Of this class, Algol is usually taken as the type of a very significant phenomenon; hence some details concerning it will be illustrative. It has long been known as the demon star (that being its name in

Arabic), owing to its plainly visible wink, during which it changes from about the second to nearly the fourth magnitude for a short time during every period of 2 days, 20 hours, 48 minutes and 55 seconds. The star is somewhat more than 1,000,000 miles in diameter, and the companion about 800,000, a little less than that of the sun. The distance between the two is somewhat more than 3,000,000 miles, and their combined mass about two-thirds that of the sun. At long intervals occur slight irregularities in the rhythm of the variations, which have been ascribed either to the revolution of both bodies around a third invisible one, or, more probably, to perturbations caused by the attraction of other members of an invisible system.

In all instances of the Algol type the essential features are similar — a light and a dark or less brilliant body producing a periodical eclipse because the plane of the mutual revolution happens to lie in the line of sight. As this phenomenon is possible only because of the accident of position and the fact that the two bodies are relatively near together, there are undoubtedly great numbers of unknown binaries of the same type which cannot be detected. Moreover, the presumption arises that the visible stars form but a comparatively small part of the entire number of stellar bodies comprising the universe. There is, of course, no way to reach even an approximately reliable estimate as to the proportion; yet some eminent authorities have expressed the opinion, based upon the motion of the visible stars impelled by universal gravitation, that they number at least four or five dark bodies to every one that is luminous. The proportion, however, is not very important to the general theory of evolution. It is enough to know that dark bodies are numerous and that in earlier stages they were incandescent, having lost their light through radiation ; and unless the universe is slowly running down — a rather irrational thought, in view of the great number of nascent stars — they are awaiting the action of conditions and forces that may sooner or later revive their dormant energies.

Another type of binaries which perfectly illustrates a stage through which Algol's companion has passed is the star known as Beta Lyrse, in the same constellation as Vega and at intervals nearly as brilliant. This also is composed of two stars revolving around a common center of gravity in an orbit directly in the plane of vision. Both are still in a highly gaseous state, the mean density of the system being a little less than that of our atmosphere. The larger of the two is about twice the mass of the smaller, and, as might be expected, is only about one-half as bright, doubtless owing to the greater rapidity that marks the evolution of the smaller bodies ; yet the mass of the main star is nearly ten times that of the sun. The centers of the two bodies are about 30,000,000 miles apart. As these figures are based solely on results of the spectroscope, they are only approximate, but no doubt are accurate enough to afford a fair idea of the material facts. Both bodies being bright, they are more brilliant when seen side by side than when one is behind the other, and therefore present the appearance of a variable star at regular intervals. The number of binaries of this type is very large.

A still earlier phase of stellar development is clearly shown by a large number of stars of the U Pegasi type. Here are two bright gaseous bodies either in contact or nearly so. This condition is more difficult to observe, particularly in remote stars, because when the lines of the spectra are not sharply defined precise calculations cannot be made; yet it may be a common process by which binaries are formed, resulting from the rapid rotation of a huge body in a rarified state. It first becomes a pear-shaped mass, which then divides into two separate bodies of unequal size. These tend through tidal movements and condensation to draw farther apart until a stable distance is reached according to the law of gravitation. And here would seem to be the mainspring of the mechanism that prevents the consolidation of nebulous matter beyond the limits fixed by its physical constitution. Evidently, matter can combine only so long as the power of gravitation is greater than the momentum of revolution — centrifugal force; and that gaseous bodies revolve at higher rates of speed after consolidation sets in, and because of it, is^apparent from the fact that all the stars, like the sun, in their gaseous stages are spheroids through physical necessity. If two or more bodies collide the heat generated resolves their masses into a gaseous condition in which the former processes are renewed. This may be so or not ; but the hypothesis is as reasonable as any that can be formulated in the absence of positive knowledge. "The system," says Campbell, "would not run down until all the kinetic energy had been converted into heat, and all the heat generated had been dissipated. This would not occur until all material in the universe had been combined into one body, or into two bodies in mutual revolution. However, if there are those who say that the universe in action is eternal, through the operation of compensating principles as yet undiscovered, no man of science is at present equipped to prove the contrary."

These three types of binary stars, variable because of the character and motion of their components, exist in all manner of gradation, as might be supposed from their number and apparent differences in age and composition. Besides these types, tens of thousands of other double stars are disclosed by the telescope. With these, the orbits are not in line of sight, hence they appear merely as double, where both are luminous. In many cases one or both of the components are also double. In addition to the vast number of stars known to be binaries, it is thought by competent authorities that nearly one-half of all the other stars that appear single are really double. In any event, the phenomenon is so common in all quarters of the universe that it must indicate the normal course of evolution in conditions that are very general.

That such conditions have existed on an immense scale in diverse regions is shown by the fact that, besides the pairs of stars, there are very numerous systems composed of from three stars to clusters containing many thousands. For example, Mizar and Polaris are triple. Castor and many others are quadruple. Theta Orionis is one of a system of six, and Epsilon Lyrae, of seven. The Pleiades, whose six most visible stars are known to every one who has the slightest acquaintance with the northern skies, have also several thousand telescopic members all moving together in the same general direction accompanied by a more or less nebular environment visible by reflection and possibly in the way of being gradually absorbed, or, as some observers maintain, the product of stellar dissolution.

These systems exist in every variety ; stars of every order of brightness are combined in every way ; and in many clusters the proportion of variable stars is large. Even the larger clusters are varied in form and constitution. Some are small and irregular both in outline and in the distribution of the stars, like Pleiades, while others are enormous, like the Magellanic clouds in the southern skies, resembling in their general appearance the character of the Milky Way. Other clusters, to the number of several scores, are globular, and their components are arranged with considerable regularity, like the aggregation in Hercules, which to the naked eye is a luminous cloud, but is resolved by the telescope into thousands of stars, each one a sun. How all these clusters assumed and maintain their present character are secrets for the future to solve.

Recent investigation of star clusters, however, has already greatly advanced the state of knowledge concerning them. One important result has been to confirm the probability that all the known clusters belong to the sidereal system of which the Milky Way is the principal evidence. But this result has also greatly enlarged prior conceptions of the size of that system. The dimensions of the greater clusters are so vast that the stars composing them are scarcely nearer to one another than those of our own region of the skies. The relatively slight attraction of bodies so far separated is evidently balanced by their motion, and this, in general, prevents any group or cluster from coalescing through gravitation.

STAGES OF STELLAR EVOLUTION

Important as are the results so far attained through the study of the variable stars, similar investigations of the physical nature and stages of stellar evolution have been even more fruitful of definite knowledge. So many stars of every variety are within reach of optical examination that the study has been conducted by many astronomers and physicists with unflagging zeal and brilliant achievement. These cosmic phases are rapidly assuming the aspect of an exact science ; but they are so diversified, so complex and so technical that in a general sketch only the more salient features may be presented.

The red stars are at the extremes of the scale of classification. They are the youngest or the oldest, not necessarily in time, but in the stages through which they have passed; for obviously the stages of evolution of a small star would be shorter than those of a large one — the heat would sooner be dissipated. Yet the red stars, to be visible for the immense distance their light must travel, must have gained or retained a considerable degree of brightness. If a star is not in a brighter stage than Jupiter, of the solar system, it is totally invisible ; not even the dark companions of the double stars can be seen by reflected light. At best, therefore, in studying the evolution of stars, direct knowledge cannot extend much beyond the point w r here consolidation has reached the state of incandescent gas. But fortunately from this point the members of our own system unquestionably illustrate aptly enough the later phases of all stars that have lapsed into invisibility.

In recent years the spectroscopic study of the stars has developed a generally recognized gradation into- classes ranging from blue to dark red. This is the usual way of arranging them in the order of the successive phases through which they pass from youth to old age. This classification, however, is not sharply defined, since the various types shade insensibly into one another. Thus between the dark red and the reddish yellow and the yellow and the light blue stars the tints are very numerous. The spectra of the great majority of stars are continuous, except for dark or absorption lines, which increase steadily from a few for the blue stars to many for the red, of the old or dwarf stars. In their early stages, whatever the degree of brightness, the stars are so diffuse and therefore of so much greater size that they are called "giants." This condition distinguishes them from the older "dwarfs" which have shrunk through condensation. It is supposed that the length of time required for a star to gain its maximum brightness is much less than for it to expire. This subject is yet a difficult problem, but it is of profound interest, as the existence of life on the earth depends upon the continuation of the sun's heat at not very much less than the present degree.

The changes in the spectra of the stars as they pass through successive stages suggests the inquiry, Why do not the elements shown in the older stars appear also in the younger if they are present, as they must be potentially at least? The answer invades the most obscure province of physical chemistry. "The conditions," says Campbell, "in the nebulae and in the youngest stars are such that only the simplest elements like hydrogen and helium, and in the nebulae nebulium, which we think are nearest to the elemental state of matter, seem to be able to form or exist in them; and the temperature must lower, or other conditions change to the conditions existing in the older stars, before what we may call the more complicated elements can construct themselves out of the more elemental forms of matter. The oxides of titanium and of carbon found in the red stars, where the surface temperatures must be relatively low, would dissociate themselves into more elemental components and lose their identity if the temperature and other conditions were changed back to those of the early helium stars. There is no evidence, to the best of my knowledge, that the elements known on our earth are not essentially universal in distribution, either in the form which the elements have in the earth, or dissociated into simpler forms whenever the temperatures or other conditions make dissociations possible or unavoidable."