Volume II Part 15 (1/2)
_Evidences of a slowly declining Temperature, and, therefore, of a long Time.--The Process of Events by Catastrophe and by Law.--a.n.a.logy of Individual and Race Development.--Both are determined by unchangeable Law._
_Conclusion that the Plan of the Universe indicates a Multiplicity of Worlds of infinite s.p.a.ce, and a Succession of Worlds in infinite Time._
[Sidenote: Age of the earth.] A victory could not be more complete nor a triumph more brilliant than that which had been gained by science in the contest concerning the position of the earth. Though there followed closely thereupon an investigation of scarcely inferior moment--that respecting the age of the earth--so thoroughly was the ancient authority intellectually crushed that it found itself incapable of a.s.serting by force the Patristic idea that our planet is less than six thousand years old.
[Sidenote: The question is impersonally solved.] Not but that a resistance was made. It was, however, of an indirect kind. The contest might be likened rather to a partisan warfare than to the deliberate movement of regular armies under recognized commanders. In its history there is no central figure like Galileo, no representative man, no brilliant and opportune event like the invention of the telescope. The question moves on to its solution impersonally. A little advance is made here by one, there by another. The war was finished, though no great battle was fought. In the chapter we are entering upon there is, therefore, none of that dramatic interest connected with the last.
Impersonally the question was decided, and, therefore, impersonally I must describe it.
[Sidenote: Oriental and Western doctrines of the age of the earth.] In Oriental countries, where the popular belief a.s.signs to the creation of man a very ancient date, and even a.s.serts for some empires a duration of hundreds of thousands of years, no difficulty as respects the age of the earth was felt, there seeming to have been time enough for every event that human researches have detected to transpire. But in the West, where the doctrine that not only the earth, but the universe itself, was intended for man, has been carried to its consequences with exacting rigour, circ.u.mstances forbid us to admit that there was any needless delay between the preparation of the habitation and the introduction of the tenant. They also force upon us the conclusion that a few centuries const.i.tute a very large portion of the time of human existence, since, if we adopt the doctrine of an almost limitless period, we should fall into a difficulty in explaining what has become of the countless myriads of generations in the long time so past, and, considering that we are taught that the end of the world is at hand, and must be expected in a few years at the most, we might seem to arraign the goodness of G.o.d in this, that He has left to their fate immeasurably the larger proportion of our race, and has restricted His mercy to us alone, who are living in the departing twilight of the evening of the world.
[Sidenote: Correction of the European doctrine.] But in this, as in the former case, a closer examination of the facts brings us to the indisputable conclusion that we have decided unworthily and untruly; that our guiding doctrine of the universe being intended for us is a miserable delusion; that the scale on which the world is constructed as to time answers to that on which it is constructed as to s.p.a.ce; that, as respects our planet, its origin dates from an epoch too remote for our mental apprehension; that myriads of centuries have been consumed in its coming to its present state; that, by a slow progression, it has pa.s.sed from stage to stage, uninhabited, and for a long time uninhabitable by any living thing; that in their proper order and in due lapse of time, the organic series have been its inhabitants, and of these a vast majority, whose numbers are so great that we cannot offer an intelligible estimate of them, have pa.s.sed away and become extinct, and that finally, for a brief period, we have been its possessors.
Of the intentions of G.o.d it becomes us, therefore, to speak with reverence and reserve. In those ages when there was not a man upon the earth, what was the object? Was the twilight only given that the wolf might follow his fleeing prey, and the stars made to s.h.i.+ne that the royal tiger might pursue his midnight maraudings? Where was the use of so much that was beautiful and orderly, when there was not a solitary intellectual being to understand and enjoy? Even now, when we are so much disposed to judge of other worlds from their apparent adaptedness to be the abodes of a thinking and responsible order like ourselves, it may be of service to remember that this earth itself was for countless ages a dungeon of pestiferous exhalations and a den of wild beasts.
[Sidenote: It elevates rather than degrades the position of man.] It might moreover appear that the conclusions to which we come, both as respects the position and age of the world, must necessarily have for their consequences the diminution and degradation of man, the rendering him too worthless an object for G.o.d's regard. But here again we fall into an error. True, we have debased his animal value, and taught him how little he is--how insignificant are the evils, how vain the pleasures of his life. But, as respects his intellectual principle, how does the matter stand? What is it that has thus been measuring the terrestrial world, and weighing it in a balance? What is it that has been standing on the sun, and marking out the orbits and boundaries of the solar system? What is it that has descended into the infinite abysses of s.p.a.ce, examined the countless worlds that they contain, and compared and contrasted them together? What is it that has shown itself capable of dealing with magnitudes that are infinite, even of comparing infinites together! What is it that has not hesitated to trace things in their history through a past eternity, and been found capable of regarding equally the transitory moment and endless duration? That which is competent to do all this, so far from being degraded, rises before us with an air of surpa.s.sing grandeur and inappreciable worth. It is the soul of man.
[Sidenote: Relations of the earth in time.] From the facts given in the last chapter respecting the relations of the earth in s.p.a.ce, we are next led to her relations in time.
So long as science was oppressed with the doctrine of the human destiny of the universe, which, as its consequence, made this earth the great central body, and elevated man to supreme importance, there was much difficulty in treating the problem of the age of the world. The history of the earth was at first a wild and fict.i.tious cosmogony. Scientific cosmogony arose, not from any theological considerations, but from the telescopic ascertainment of the polar compression of the planet Jupiter, and the consequent determination by Newton that the earth is a spheroid of revolution. With a true cosmogony came a better chronology.
[Sidenote: Anthropocentric ideas of the beginning and end of the world.]
The patristic doctrine had been that the earth came into existence but little more than five thousand years ago, and to this a popular opinion long current was added, that its end might be very shortly expected.
From time to time periods were set by various authorities determining the latter event, and, as true knowledge was extinguished, the year 1000 came to be the universally appointed date. In view of this, it was not an uncommon thing for persons to commence their testamentary bequests with the words, ”In expectation of the approaching end of the world.”
But the tremendous moment pa.s.sed by, and still the sun rose and set, still the seasons were punctual in their courses, and Nature wore her accustomed aspect. A later day was then predicted, and again and again disappointment ensued, until sober-minded men began to perceive that the Scriptures were never intended to give information on such subjects, and predictions of the end of the world fell into discredit, abandoned to the illiterate, whose morbid antic.i.p.ations they still amuse.
As it was thus with the end of our planet, so it was as regards her origin. By degrees evidence began to acc.u.mulate casting a doubt on her recent date, evidence continually becoming more and more cogent.
[Sidenote: Rise of the doctrine of illimitable age.] In no insignificant manner did the establishment of the heliocentric theory, aided by the discoveries of the telescope, a.s.sist in this result. As I have said, it utterly ruined past restoration the doctrine of the human destiny of the universe. With that went down all arguments which had depended on making man the measure of things. Ideas of unexpected sublimity as to the scale of magnitude on which the world is constructed soon enforced themselves, and proved to be the precursors of similar ideas as to time. At length it was perceived by those who were in the van of the movement that the Bible was never intended to deliver a chronological doctrine respecting the beginning any more than the end of things, and that those well-meaning men who were occupied in wresting it from its true purposes were engaged in an unhappy employment, for its tendency could be no other than to injure the cause they designed to promote. Nevertheless, so strong were the ancient persuasions, that it was not without a struggle that the doctrine of a long period forced its way--a struggle for the age of the earth, which, in its arguments, in its tendencies, and in its results, forcibly recalls the preceding one respecting the position of the earth; but, in the end, truth overrode all authority and all opposition, and the doctrine of an extremely remote origin of our planet ceased to be open to dispute.
In a scientific conception of the universe, illimitable s.p.a.ces are of necessity connected with limitless time.
[Sidenote: Indications depending on the progressive motion of light.]
The discovery of the progressive motion of light offered the means of an absolute demonstration of this connexion. Rays emitted by an object, and making us sensible of its presence by impinging on the eye, do not reach us instantaneously, but consume a certain period in their pa.s.sage.
If any sudden visible effect took place in the sun, we should not see it at the absolute moment of its occurrence, but about eight minutes and thirteen seconds later, this being the time required for light to cross the intervening distance. All phenomena take place in reality anterior to the moment at which we observe them by a time longer in proportion as the distance to be travelled is greater.
There are objects in the heavens so distant that it would take many hundreds of thousands of years for their light to reach us. Then it necessarily follows, since we can see them, that they must have been created and must have been s.h.i.+ning so long.
The velocity with which light moves was first determined by the Danish astronomer Romer from the eclipses of Jupiter's satellites, November, 1675. It was, therefore, a determination of the rate for reflected solar light in a vacuum, and gave 198,000 miles in a second. In 1727, Bradley determined it for direct stellar light by his great discovery of the aberration of the fixed stars. More recently, the experiments of M.
Foucault and those of M. Fizeau, by the aid of rotating mirrors or wheels, have confirmed these astronomical observations, Fizeau's determination of the velocity approaching that of Romer. Probably, however, the most correct is that of Struve, 191,515 miles per second.
[Sidenote: Investigation of the age of the earth through the phenomena of heat.] This astronomical argument, which serves as a general introduction, is strengthened by numerous physical and physiological facts. But of the different methods by which the age of the earth may be elucidated, I shall prefer that which approaches it through the phenomena of heat. Such a manner of viewing the problem has led to its determination in the minds of many thinking men.
[Sidenote: Astronomical heat alone on the earth's surface.] As correct astronomical ideas began to prevail, it was perceived that all the heat now on the surface of our planet is derived from the sun. Through the circ.u.mstance of the inclination of her axis of rotation to the plane of her annual motion, or through the fact of her globular form occasioning the presentation of different parts of her surface, according to their lat.i.tudes, with more or less obliquity, and hence the reception of less or more of the rays, there may be local and temporary variations. But these do not affect the general principle that the quant.i.ty of heat thus received must be the same from year to year.
[Sidenote: The equilibrium of interior heat.] This thermometric equilibrium not only holds good for the surface, it may also be demonstrated for the whole ma.s.s of the planet. The day has not shortened by the 1/200 of a second since the time of Hipparchus, and therefore the decrease of heat can not have been so much as the 1/300 of a Fahrenheit degree, on the hypothesis that the mean dilatation of all terrestrial substances is equal to that of gla.s.s, 1/180000 for one degree. If a decline had taken place in the intrinsic heat of the earth, there must have been a diminution in her size, and, as a necessary consequence, the length of the day must have become less. The earth has therefore reached a condition of equilibrium as respects temperature.
[Sidenote: Its ancient decline.] A vast body of evidence has, however, come into prominence, establis.h.i.+ng with equal certainty that there was in ancient times a far higher temperature in the planet; not a temperature concerned with a fraction of a degree, but ranging beyond the limits of our thermometric scale. The mathematical figure of the earth offers a resistless argument for its ancient liquefied condition--that is, for its originally high temperature. But how is this to be co-ordinated with the conclusion just mentioned? Simply by the admission that there have elapsed prodigious, it might almost be said limitless, periods. [Sidenote: Necessity for a long time.] As thus the true state of affairs began to take on shape, it was perceived that the age of the earth is not a question of authority, not a question of tradition, but a mathematical problem sharply defined: to determine the time of cooling of a globe of known diameter and of given conductibility by radiation in a vacuum.
In such a state of things, what could be more unwise than to attempt to force opinion by the exercise of authority? How unspeakably mischievous had proved to be a like course as respects the globular form of the earth, which did not long remain a mere mathematical abstraction, but was abruptly brought to a practical issue by the voyage of Magellan's s.h.i.+p. And on this question of the age of the earth it would have been equally unwise to become entangled with or committed to the errors of patristicism--errors arising from well-meant moral considerations, but which can never exert any influence on the solution of a scientific problem.
[Sidenote: Indications of the interior heat of the earth.] One fact after another bearing upon the question gradually emerged into view. It was shown that the diurnal variations of temperature--that is, those connected with night and day--extend but a few inches beneath the surface, the seasonal ones, connected with winter and summer, to many feet; but beyond this was discovered a stratum of invariable temperature, beneath which, if we descend, the heat increases at the rate of 1 Fahr. for every fifty or seventy feet. The uniformity of this rate seemed to imply that, at depths quite insignificant, a very high temperature must exist. This was ill.u.s.trated by such facts that the water which rushes up from a depth of 1794 feet in the Artesian well of Grenelle has a temperature of 82 Fahr. The mean temperature of Paris being about 51 Fahr., these numbers give a rate of 1 for every fifty-eight feet. If, then, the increase of heat is only 100 per mile, at a depth of less than ten miles every thing must be red hot, and at thirty or forty in a melted state. It was by all admitted that the rise of temperature with the depth is not at all local, but occurs in whatever part of the earth the observation may be made. The general conclusion thus furnished was re-enforced by the evidence of volcanoes, which could no longer be regarded as merely local, depending on restricted areas for the supply of melted material, since they are found all over the land and under the sea, in the interior of continents and near the sh.o.r.es, beneath the equator and in the polar regions. It had been estimated that there are probably two thousand aerial or subaqueous eruptions every century. Some volcanoes, as aetna, have for thousands of years poured forth their lavas, and still there is an unexhausted supply. Everywhere a common source is indicated by the rudely uniform materials ejected. The fact that the lines of volcanic activity s.h.i.+ft pointed to a deep source; the periodic increments and decrements of force bore the same interpretation. They far transcend the range of history. The volcanoes of central France date from the Eocene period; their power increased in the Miocene, and continued through the Pliocene; those of Catalonia belong to the Pliocene, probably. Coupled with volcanoes, earthquakes, with their vertical, horizontal, and rotary vibrations, having a linear velocity of from twenty to thirty miles per minute, indicated a profound focus of action. The great earthquake of Lisbon was felt from Norway to Morocco, from Algiers to the West Indies, from Thuringia to the Canadian lakes. It absolutely lifted the whole bed of the North Atlantic Ocean. Its origin was in no superficial point.