History of the Intellectual Development of Europe, Volume II (of 2)

Extension of attraction or gravity. Up to the time of Newton there were only very vague ideas that the earth's attraction extended to any considerable distance. Newton was led to his discovery by reflecting that at all altitudes accessible to man, gravity appears to be undiminished, and that, therefore, it may possibly extend as far as the moon, and actually be the force which deflects her from a rectilinear path, and makes her revolve in an orbit round the earth. Admitting the truth of the law of the inverse squares, it is easy to compute whether the moon falls from the tangent she would describe if the earth ceased to act upon her by a quantity proportional to that observed in the case of bodies falling near the surface. In the first calculations made by Newton, he found that the moon is deflected from the tangent thirteen feet every minute; but, if the hypothesis of gravitation were true, her deflection should be fifteen feet. It is no trifling evidence of the scrupulous science of this great philosopher that hereupon he put aside the subject for several years, without, however, abandoning it. At length, in 1682, learning the result of the measures of a degree which Picard had executed in France, and which affected the estimate of the magnitude of the earth he had used, and therefore the distance of the moon, he repeated the calculations with these improved data. It is related that "he went home, took out his old papers, and resumed his calculations. As they drew to a close, he became so much agitated that he was obliged to desire a friend to finish them." The expected coincidence was verified. And thus it appeared that the moon is retained in her orbit and made to revolve round the earth by the force of terrestrial gravity.

The cause of Kepler's laws. These calculations were founded upon the hypothesis that the moon moves in a circular orbit with a uniform velocity. But in the "Principia" it was demonstrated that when a body moves under the influence of an attractive force, varying as the inverse square of the distances, it must describe a conic section, with a focus at the centre of force, and under the circumstances designated by Kepler's laws. Newton, therefore, did far more than furnish the expected solution of the problem of elliptical motion, and it was now apparent that the existence of those laws might have been foreseen, since they arise in the very necessities of the case.

Resistless spread of the heliocentric theory. This point gained, it is obvious that the evidence was becoming unquestionable, that as the moon is made to revolve round the earth through the influence of an attractive force exercised by the earth, so likewise each of the planets is compelled to move in an elliptical orbit round the sun by his attractive force. The heliocentric theory, at this stage, was presenting physical evidence of its truth. It was also becoming plain that the force we call gravitation must be imputed to the sun, and to all the planetary bodies as well as to the earth. Accordingly, this was what Newton asserted in respect to all material substance.

Perturbations accounted for. But it is a necessary consequence of this theory that many apparent irregularities and perturbations of the bodies of the solar system must take place by reason of the attraction of each upon all the others. If there were but one planet revolving round the sun, its orbit might be a mathematically perfect ellipse; but the moment a second is introduced, perturbation takes place in a variable manner as the bodies change their positions or distances. An excessive complication must therefore be the consequence when the number of bodies is great. Indeed, so insurmountable would these difficulties be, that the mathematical solution of the general problem of the solar system would be hopeless were it not for the fact that the planetary bodies are at very great distances from one another, and their masses, compared with the mass of the sun, very small.

Results of the theory of gravitation. Taking the theory of gravitation in its universal acceptation, Newton, in a manner that looks as if he were divinely inspired, succeeded in demonstrating the chief inequalities of the moon and planetary bodies; in determining the figure of the earth – that it is not a perfect sphere, but an oblate spheroid; in explaining the precession of the equinoxes and the tides of the ocean. To such perfection have succeeding mathematicians brought his theory, that the most complicated movements and irregularities of the solar system have been satisfactorily accounted for and reduced to computation. Trusting to these principles, not only has it been found possible, knowing the mass of a given planet, to determine the perturbations it may produce in adjacent ones, but even the inverse problem has been successfully attacked, and from the perturbations the place and mass of a hitherto unknown planet determined. It was thus that, from the deviations of Uranus from his theoretical place, the necessary existence of an exterior disturbing planet was foreseen, and our times have witnessed the intellectual triumph of mathematicians directing where the telescope should point in order to find a new planet. The discovery of Neptune was thus accomplished.

It adds to our admiration of the wonderful intellectual powers of Newton to know that the mathematical instrument he used was the ancient geometry. Not until subsequently was the analytical method resorted to and cultivated. This method possesses the inappreciable advantage of relieving us from the mental strain which would otherwise oppress us. It has been truly said that the symbols think for us. The "Principia;" its incomparable merit. Mr. Whewell observes: "No one for sixty years after the publication of the 'Principia,' and, with Newton's methods, no one up to the present day, has added any thing of value to his deductions. We know that he calculated all the principal lunar inequalities; in many of the cases he has given us his processes, in others only his results. But who has presented in his beautiful geometry or deduced from his simple principles any of the inequalities which he left untouched? The ponderous instrument of synthesis, so effective in his hands, has never since been grasped by any one who could use it for such purposes; and we gaze at it with admiring curiosity, as on some gigantic implement of war which stands idle among the memorials of ancient days, and makes us wonder what manner of man he was who could wield as a weapon what we can hardly lift as a burden."

Philosophical import of Newton's discoveries. Such was the physical meaning of Newton's discoveries; their philosophical meaning was of even greater importance. The paramount truth was resistlessly coming into prominence – that the government of the solar system is under necessity, and that it is mathematically impossible for the laws presiding over it to be other than they are.

Thus it appears that the law of gravitation holds good throughout our solar system. But the heliocentric theory, in its most general acceptation, considers every fixed star as being, like the sun, a planetary centre. Unity of idea in the construction of the universe. Hence, before it can be asserted that the theory of gravitation is truly universal, it must be shown that it holds good in the case of all other such systems. The evidence offered in proof of this is altogether based upon the observations of the two Herschels on the motions of the double stars. Among the stars there are some in such close proximity to each other that Sir W. Herschel was led to suppose it would be possible, from observations upon them, to ascertain the stellar parallax. While engaged in these inquiries, which occupied him for many years, he discovered that many of these stars are not merely optically in proximity, as being accidentally in the same line of view, but are actually connected physically, revolving round each other in regular orbits. The motion of these double suns is, however, in many instances so slow as to require many years for a satisfactory determination. Gravitation of double stars. Sir J. Herschel therefore continued the observations of his father, and with other mathematicians, investigated the characteristics of these motions. The first instance in which the true elliptic elements of the orbit of a binary star were determined was given by M. Savary in the case of chi Ursæ Majoris, indicating an elliptic orbit of 58 ¼ years. But the period of others, since determined, is very much longer; thus, in sigma Coronæ, it is, according to Mr. Hind, more than 736 years. From the fact that the orbits in which these stars move round each other are elliptical, it necessarily follows that the law of gravitation, according to the inverse square, holds good in them. Considering the prodigious distances of these bodies, and the departure, as regards structure of the systems to which they belong, from the conditions obtaining in our unisolar system, we may perhaps assert the prevalence of the law of gravitation throughout the universe.

Coloured light of double stars. If, in association with these double suns – sometimes, indeed, they are triple, and occasionally, as in the case of epsilon Lyræ, quadruple – there are opaque planetary globes, such solar systems differ from ours not only in having several suns instead of a single one, but, since the light emitted is often of different tints, one star shining with a crimson and another with a blue light, the colours not always complementary to one another, a wonderful variety of phenomena must be the result, especially in their organic creations; for organic forms, both vegetable and animal, primarily depend on the relations of coloured light. How varied the effects where there are double, triple, or even quadruple sunrises, and sunsets, and noons; and the hours marked off by red, or purple, or blue tints.

Grandeur of Newton's discoveries. It is impossible to look back on the history of the theory of gravitation without sentiments of admiration and, indeed, of pride. How felicitous has been the manner in which have been explained the inequalities of a satellite like the moon under the disturbing influence of the sun; the correspondence between the calculated and observed quantities of these inequalities; the extension of the doctrine to satellites of other planets, as those of Jupiter; the determination of the earth's figure; the causes of the tides; the different force of gravity in different latitudes, and a multitude of other phenomena. The theory asserted for itself that authority which belongs to intrinsic truth. It enabled mathematicians to point out facts not yet observed, and to foretell future events.

And yet how hard it is for truth to force its way when bigotry resists. In 1771, the University of Salamanca, being urged to teach physical science, refused, and this was its answer; "Newton teaches nothing that would make a good logician or metaphysician; and Gassendi and Descartes do not agree so well with revealed truth as Aristotle does."

The earth in time. Among the interesting results of Newton's theory may be mentioned its application to secular inequalities, such as the acceleration of the moon's mean motion, that satellite moving somewhat quicker now than she did ages ago. Laplace detected the cause of this phenomenon in the influence of the sun upon the moon, combined with the secular variation of the eccentricity of the earth's orbit. Moreover, he showed that this secular inequality of the motion of the moon is periodical, that it requires millions of years to re-establish itself, and that, after an almost inconceivable time, the acceleration becomes a retardation. In like manner, the same mathematician explained the observed acceleration in the mean motion of Jupiter, and retardation of that of Saturn, as arising from the mutual attraction of the two planets, and showed that this secular inequality has a period of 929 ½ years. With such slow movements may be mentioned the diminution of the obliquity of the ecliptic, which has been proceeding for ages, but which will reach a limit and then commence to increase. These secular motions ought not to be without interest to those who suffer themselves to adopt the patristic chronology of the world, who suppose that the earth is only six thousand years old, and that it will come to an end in about one thousand years more. They must accept, along with that preposterous delusion, its necessary consequences, that the universe has been so badly constructed, and is such a rickety machine, that it can not hold together long enough for some of its wheels to begin to revolve. Astronomy offers us many illustrations of the scale upon which the world is constructed as to time, as well as that upon which it is constructed as to space.

Dominion of law in the universe. From what has been said, the conclusion forces itself upon us that the general laws obtaining as respects the earth, hold good likewise for all other parts of the universe; a conclusion sustained not only by the mechanism of such motions as we have been considering, but also by all evidence of a physical kind accessible to us. The circumstances under which our sun emits light and heat, and thereby vivifies his attendant planets, are indisputably the same as those obtaining in the case of every fixed star, each of which is a self-luminous sun. There is thus an aspect of homogeneousness in the structure of all systems in the universe, which, though some have spoken of it as if it were the indication of a uniformity of plan, and therefore the evidence of a primordial idea, is rather to be looked upon as the proof of unchangeable and resistless law.

Ruin of anthropocentric ideas. What, therefore, now becomes of the doctrine authoritatively put forth, and made to hold its sway for so many centuries, that the earth is not only the central-body of the universe, but in reality, the most noble body in it; that the sun and other stars are mere ministers or attendants for human use? In the place of these utterly erroneous and unworthy views, far different conceptions must be substituted. Man, when he looks upon the countless multitude of stars – when he reflects that all he sees is only a little portion of those which exist, yet that each is a light and life-giving sun to multitudes of opaque, and therefore, invisible worlds – when he considers the enormous size of these various bodies and their immeasurable distance from one another, may form an estimate of the scale on which the world is constructed, and learn therefrom his own unspeakable insignificance.

Aids for measurements in the universe. In one beat of a pendulum a ray of light would pass eight times round the circumference of the earth. Thus we may take the sunbeam as a carpenter does his measuring-rule; it serves as a gauge in our measurements of the universe. A sunbeam would require more than three years to reach us from alpha Centauri; nine and a quarter years from 61 Cygni; from alpha Lyræ twelve years. These are stars whose parallax has been determined, and which are therefore nearest to us.

Clusters of stars. Of suns visible to the naked eye there are about 8000, but the telescope can discern in the Milky Way more than eighteen millions, the number visible increasing as more powerful instruments are used. Our cluster of stars is a disc divided into two branches at about one-third of its length. In the midst of innumerable compeers and superiors, the sun is not far from the place of bifurcation, and at about the middle of the thickness. Outside the plane of the Milky Way the appearance would be like a ring, and, still farther off, a nebulous disc.

Distribution of matter and force in space. From the contemplation of isolated suns and congregated clusters we are led to the stupendous problem of the distribution of matter and force in space, and to the interpretation of those apparent phantoms of self-luminous vapour, circular and elliptic discs, spiral wreaths, rings and fans, whose edges fade doubtfully away, twins and triplets of phosphorescent haze connected together by threads of light and grotesque forms of indescribable complexity. Perhaps in some of these gleaming apparitions we see the genesis, in some the melting away of universes. There is nothing motionless in the sky. In every direction vast transformations are occurring, yet all things proclaim the eternity of matter and the undiminished perpetuity of force.

Limit of the theory of gravitation. The theory of gravitation, as delivered by Newton, thus leads us to a knowledge of the mathematical construction of the solar system, and inferentially likewise to that of other systems; but it leaves without explanation a large number of singular facts. It explains the existing conditions of equilibrium of the heavenly bodies, but it tells us nothing of their genesis; or, at the best, in that particular it falls back on the simple fiat of God.

Phenomena of the solar system. The facts here referred to conduct us, however, to another and far higher point of view. Some of them, as enumerated by Laplace, are the following: – 1. All the planets and their satellites move in ellipses of such small eccentricity that they are nearly circles; 2. The movements of the planets are in the same direction and nearly in the same plane; 3. The movements of the satellites are in the same direction as those of the planets; 4. The movements of rotation of these various bodies and of the sun are in the same direction as their orbitual motions, and in planes little different.

The nebular hypothesis. The nebular hypothesis requires us to admit that all the ponderable material now constituting the various bodies of the solar system once extended in a rarefied or nebulous and rotating condition, beyond the confines of the most distant planet. That postulate granted; the structure and present condition of the system may be mathematically deduced.

For, as the vast rotating spheroid lost its heat by radiation, it contracted, and its velocity of rotation was necessarily increased; and thus were left behind from its equatorial zone, by reason of the centrifugal force, rotating rings, the same result occurring periodically again and again. These rings must lie all in one plane. They might break, collapsing into one rotating spheroid, a planet; or into many, asteroids; or maintain the ring-like form. From the larger of these secondary rotating spheroids other rings might be thrown off, as from the parent mass; these, in their turn breaking and becoming spheroids, constitute satellites, whose movements correspond to those of their primaries.

We might, indeed, advance a step farther, and show how, by the radiation of heat from a motionless nebula, a movement of rotation in a determinate direction could be engendered, and that upon these principles, the existence of a nebulous matter admitted, and the present laws and forces of nature regarded as having been unchanged, the manner of origin of the solar system might be deduced, and all those singular facts previously alluded to explained; and not only so, but there is spontaneously suggested the cause of many minor peculiarities not yet mentioned.

Facts accounted for by it. For it follows from the nebular hypothesis that the large planets should rotate rapidly, and the small ones more slowly; that the outer planets and satellites should be larger than the inner ones. Of the satellites of Saturn, the largest is the outermost; of those of Jupiter, the largest is the outermost save one. Of the planets themselves, Jupiter is the largest, and outermost save three. These cannot be coincidences, but must be due to law. The number of satellites of each planet, with the doubtful exception of Venus, might be foreseen, the presence of satellites and their number being determined by the centrifugal force of their primary. The hypothesis also points out the time of revolution of the planets in their orbits, and of the satellites in theirs; it furnishes a reason for the genesis and existence of Saturn's rings, which are indeed its remaining witnesses – their position and movements answering to its requirements. It accounts for the physical state of the sun, and also for the physical state of the earth and moon as indicated by their geology. It is also not without furnishing reasons for the existence of comets as integrant members of our system; for their singular physical state; for the eccentric, almost parabolic orbits of so many of them; for the fact that there are as many of them with a retrograde as with a direct motion; for their more frequent occurrence about the axis of the solar system than in its plane; and for their general antithetical relations to planets.

Whether nebulæ actually exist. If these and very many other apparently disconnected facts follow as the mechanical necessities of the admission of a gravitating nebula – a very simple postulate – it becomes important to ascertain whether, by actual observation, the existence of such material forms may be demonstrated in any part of the universe. It was the actual telescopic observation of such objects that led Herschel to the nebular hypothesis. He concluded that there are two distinct kinds of nebulæ, one consisting of clusters of stars so remote that they could not be discerned individually, but that these may be discerned by sufficient telescopic power; the other being of a hazy nature, and incapable of resolution. Nebulæ do not occur at random in the heavens: the regions poorest in stars are richest in them; they are few in the plane of our sidereal system, but numerous about its poles, in that respect answering to the occurrence of comets in the solar system. The resolution of many of these hazy patches of light into stars by no means disproves the truly nebulous condition of many others.

Fortunately, however, other means than telescopic observation for the settlement of this question are available. In 1846, it was discovered by the author of this book that the spectrum of an ignited solid is continuous, that is, has neither dark nor bright fixed lines. Fraunhofer had previously made known that the spectrum of ignited gases is discontinuous. Here, then, is the means of determining whether the light emitted by a given nebula comes from an incandescent gas, or from a congeries of ignited solids, stars, or suns. If its spectrum be discontinuous, it is a true nebula or gas; if continuous, a congeries of stars.

In 1864, Mr. Huggins made this examination in the case of a nebula in the constellation Draco. It proved to be gaseous.

Subsequent observations have shown that of sixty nebulæ examined, nineteen give discontinuous or gaseous spectra; the remainder continuous ones.

It may, therefore, be admitted that physical evidence has at length been obtained, demonstrating the existence of vast masses of matter in a gaseous condition, and at a temperature of incandescence. The hypothesis of Laplace has thus a firm basis.

Opposition to the nebular hypothesis. Notwithstanding the great authority of the astronomers who introduced it, the nebular hypothesis has encountered much adverse criticism; not so much, however, from its obvious scientific defects, such as its inability to deal with the cases of Uranus and Neptune, as from moral and extraneous considerations. There is a line in Aristophanes which points out precisely the difficulty:

Ὁ Ζεὺς οὐκ ὤν, ἀλλ' ἀντ' αὐτοῦ Δῖνος νυνὶ βασιλεύων.

A reluctance to acknowledge the presidency of law in the existing constitution and movements of the solar system has been yielded only to be succeeded by a reluctance to acknowledge the presidency of law in its genesis. And yet whoever will reflect on the subject will be drawn to the conclusion that the principle involved was really settled by Newton in his "Principia" – that is to say, when it became geometrically certain that Kepler's laws originate in a mathematical necessity.

As matters now stand, the nebular hypothesis may be regarded as the first superficial, and therefore imperfect, glimpse of a series of the grandest problems soon to present themselves for solution – the mathematical distribution of matter and force in space, and the variations of that distribution in time.

The intellectual ruin of ecclesiasticism. Such is the history of the dispute respecting the position of the earth in the universe. Not without reason, therefore, have I assigned the pontificate of Nicolas V. as the true close of the intellectual dominion of the Church. From that time the sceptre had passed into another hand. In all directions Nature was investigated, in all directions new methods of examination were yielding unexpected and beautiful results. On the ruins of its ivy-grown cathedrals, Ecclesiasticism, surprised and blinded by the breaking day, sat solemnly blinking at the light and life about it, absorbed in the recollection of the night that had passed, dreaming of new phantoms and delusions in its wished-for return, and vindictively striking its talons at any derisive assailant who incautiously approached too near. I have not space to describe the scientific activity displayed in all directions; to do it justice would demand volumes. Mathematics, physics, chemistry, anatomy, medicine, and all the many branches of human knowledge received an impulse. Wonderful development of scientific activity. Simultaneously with the great events I have been relating, every one of these branches was advancing. Vieta made the capital improvement of using letters as general symbols in algebra, and applied that science to geometry. Tycho, emulating Hipparchus of old, made a new catalogue of the stars; he determined that comets are beyond the moon, and that they cut the crystalline firmament of theology in all directions. Gilbert wrote his admirable book on the magnet; Gesner led the way to zoology, taking it up at the point to which the Saracens had continued Aristotle, by the publication of his work on the history of animals; Belon at the same time, 1540, was occupied with fishes and birds. Fallopius and Eustachius, Arantius and Varolius, were immortalizing themselves by their dissections: the former reminding us of the times of Ptolemy Philadelphus, when he naïvely confesses "the Duke of Tuscany was obliging enough to send living criminals to us, whom we killed and then dissected." Piccolomini laid the foundations of general anatomy by his description of cellular tissue. Coiter created pathological anatomy, Prosper Alpinus diagnosis, Plater the classification of disease, and Ambrose Paré modern surgery. Such were the occupations and prospect of science at the close of the sixteenth century.

The movement becomes still more vigorous. Scarcely had the seventeenth opened when it became obvious that the movement, far from slackening, was gathering force. It was the age of Galileo. Descartes introduced the theory of an ether and vortices; but, hearing of the troubles that had befallen Galileo, was on the point of burning his papers. Several years later, he was restrained from publishing his "Cosmos" "from a pious desire not to treat irreverently the decrees of the holy chair against the planetary movement of the earth." This was in 1633, when the report of the sentence of the Inquisition was made known. He also developed Vieta's idea of the application of algebra to geometry, and brought into prominence the mechanical fact, destined to an important application in physical astronomy, that every curvilinear deflection is due to a controlling force. To him, among Europeans, also is to be attributed the true explanation of the rise of water in an exhausted space – "the weight of the water counter-balances that of the air." Napier perfected his great and useful invention of logarithms. Hydraulics was created by Castelli; hydrostatics by Torricelli, who also discovered barometric variations: both were pupils of Galileo. Fabricius ab Aquapendente discovered the valves in the veins; Servetus almost detected the course of the circulation. Harvey completed what Servetus had left unfinished, and described the entire course of the blood; Asellius discovered the lacteals; Van Helmont introduced the theory of vitality into medicine, and made the practice or art thereof consist in regulating by diet the Archeus, whose seat he affirmed to be in the stomach. In strong contrast with this phantasy, Sanctorio laid the foundation of modern physiology by introducing the balance into its inquiries. Pascal, by a decisive experiment, established the doctrines of the weight and pressure of the air, and published some of the most philosophical treatises of the age: "his Provincial Letters did more than any thing to ruin the name of the Jesuits." The contagion spread to the lawyers: in 1672 appeared Puffendorf's work on the "Law of Nature and Nations." The phlogistic theory, introduced by Beccher and perfected by Stahl, created chemistry, in contradistinction to the Arabian alchemy. Otto Guericke invented the air-pump, Boyle improved it. Hooke, among many other discoveries, determined the essential conditions of combustion. Far above all contemporaries in mathematical learning and experimental skill, Newton was already turning his attention to the "reflexions, refractions, inflexions and colours of light," and introducing the idea of attractions into physics. Ray led the way to comparative anatomy in his synopsis of quadrupeds; Swammerdam improved the art of dissection, applying it to the general history of insects; Lister published his synopsis of shells; Tournefort and Malpighi devoted themselves to botany; Grew discovered the sexes of plants; Brown the quinary arrangement of flowers. Geology began to break loose from the trammels of theology, and Burnet's Sacred theory of the Earth could not maintain its ground against more critical investigations. The Arabian doctrine of the movement of the crust of the earth began to find supporters. Lister ascertained the continuity of strata over great distances; Woodward improved mineralogy; the great mathematician, Leibnitz, the rival of Newton, propounded the doctrine of the gradual cooling of the globe, the descent of its strata by fracture, the deposit of sedimentary rocks, and their induration. Among physicians, Willis devoted himself to the study of the brain, traced the course of the nerves and classified them, and introduced the doctrine of the localization of functions in the brain. Malpighi and Lewenhœck applied the microscope as an aid to anatomy; the latter discovered spermatozoa. Graaf studied the function of the generative organs; Borelli attempted the application of mathematics to muscular movement; Duverney wrote on the sense of hearing, Mayow on respiration; Ruysch perfected the art of injection, and improved minute anatomy.

But it is in vain to go on. The remainder of these pages would be consumed in an attempt to record the names of the cultivators of science, every year increasing in number, and to do justice to their works. From the darkness that had for so many ages enveloped it, the human mind at last emerged into light. The intellectual motes were dancing in the sunbeam, and making it visible in every direction.

Institution of scientific societies. Despairing thus to do justice to individual philosophers and individual discoveries, there is, however, one most important event to which I must prominently allude. It is the foundation of learned societies. Imitating the examples of the Academia Secretorum Naturæ, instituted at Naples, 1560, by Baptista Porta, and of the Lyncean Academy, founded 1603 by Prince Frederic Cesi at Rome for the promotion of natural philosophy, the Accademia del Cimento was established at Florence, 1637; the Royal Society of London, 1645; and the Royal Academy of Sciences in Paris, 1666.

Review of anthropocentric philosophy. Arrived at the close of the description of this first great victory of scientific truth over authority and tradition, it is well for us to pause and look back on the progress of man from the erroneous inferences of his social infancy to the true conclusions of his maturity – from anthropocentric ideas, which in all nations and parts of the world have ever been the same, to the discovery of his true position and insignificance in the universe.

The sky, apparent nature of. We are placed in a world surrounded with illusions. The daily events of our life and the objects before us tend equally to deceive us. If we cast our eyes on the earth, it seems to be made only to minister to our pleasures or our wants. If we direct our attention to the sky, that blue and crystalline dome, the edges of which rest on the flat land or the sea – a glacial vault, which Empedocles thought was frozen air, and the fathers of the Church the lowest of the seven concentric strata of heavens – we find a thousand reasons for believing that whatever it covers was intended by some Good Being for our use. Of the various living things placed with us beneath it, all are of an inferior grade when compared with ourselves, and all seem intended for us. The conclusions at which we thus arrive are strengthened by a principle of vanity implanted in our hearts, unceasingly suggesting to us that this pleasant abode must have been prepared for our reception, and furnished and ornamented expressly for our use.

Anthropocentric ideas of God. But reflexion teaches us that we came not hither of ourselves, and that doubtless the same Good Being who prepared this delightful abode brought us as tenants into it. From the fact of our own existence, we are insensibly and inevitably led to infer the existence of God; from the favourable circumstances in which our lot is cast, we gather evidences of His goodness; and in the energy which natural phenomena often display, we see the tokens of His power. What other explanation can we give of tempests in the sea or lightning in the heavens? Moreover, it is only during a part of our time – our waking hours – that we are brought into relation with these material things; for the rest, when we are asleep, a state in which we spend more than a third part of our life, we are introduced to other scenery, other beings, another world. Of the world and heaven. From these we gather that there are agents of an intangible and more ethereal mould, perhaps of the nature of Him who brought us here, perhaps His subordinates and messengers. Whence do they issue and whither do they go? Is there not beyond the sky above us a region to which our imperfect vision cannot penetrate, but which may be accessible to them from the peaks of elevated mountains, or to be reached only with wings? And thus we picture to ourselves a heaven shut off from earth, with all its sins and cares, by the untroubled and impenetrable sky – a place of light and repose, its pavement illuminated by the sun and countless other shining bodies – a place of peace, but also a place of power.

Of evil beings and hell. Still more, a thousand facts of our life teach us that we are exposed to influences of an evil nature as well as to those that are good. How often, in our dreams, does it happen that we are terror-stricken by the approach of hideous forms, faces of fearful appearance, from which we vainly struggle to escape. Is it not natural for us to attribute the evil we see in the world to these as the good to those? and, since we can not conceive of the existence of beings without assigning them a place, where shall we find for these malignant spirits a habitation? Is it not in the dark region beneath the ground, far away from the realms of light – a region from which, through the volcano, smoke and burning sulphur are cast into this upper world – a place of everlasting fire and darkness, whose portals are in caves and solitudes of unutterable gloom?

Of man, the supernatural. Placed thus on the boundary between such opposing powers, man is the sport of circumstances, sustained by beings who seek his happiness, and tempted by those who desire his destruction. Is it at all surprising that, guided by such obvious thoughts and simple reasonings, he becomes superstitious? that he sees in every shadow a spirit, and peoples every solitary place with invisibles? that he casts a longing look to the good beings who can protect him, seeking to invoke their aid by entreaties, and to propitiate their help by free-will sacrifices of things that are pleasant and valuable? Open to such influences himself, why should he not believe in the efficacy of prayer? His conscious superiority lends force to his suspicion that he is a worthy object for the opposing powers to contend for, a conclusion verified by the inward strifes he feels, as well as by the trials of life to which he is exposed.

His immortality and future life. But dreams at night, and sometimes visions by day, serve to enforce the conclusion that life is not limited to our transitory continuance here, but endures hereafter. How often at night do we see the well-known forms of those who have been dead a long time appearing before us with surprising vividness, and hear their almost forgotten voices? These are admonitions full of the most solemn suggestions, profoundly indicating to us that the dead still continue to exist, and that what has happened to them must also happen to us, and we too are destined for immortality. Perhaps involuntarily we associate these conclusions with others, expecting that in a future life good men will enjoy the society of good beings like themselves, the evil being dismissed to the realms of darkness and despair. And, as human experience teaches us that a final allotment can only be made by some superior power, we expect that He who was our Creator shall also be our Judge; that there is an appointed time and a bar at which the final destination of all who have lived shall be ascertained, and eternal justice measure out its punishments and rewards.

Inducements to morality. From these considerations there arises an inducement for us to lead a virtuous life, abstaining from wickedness and wrong; to set apart a body of men who may mediate for us, and teach us by precept and example the course it is best for us to pursue; to consecrate places, such as groves or temples, as the more immediate habitations of the Deity to which we may resort.

Such are the leading doctrines of Natural Theology of primitive man both in the old and new continent. They arise from the operations of the human mind considering the fitness of things.

Just as we have in Comparative Anatomy the structure of different animals examined, and their identities and differences set forth, thereby establishing their true relations; just as we have in Comparative Physiology the functions of one organic being compared with those of another, to the end that we may therefrom deduce their proper connexions, so, from the mythologies of various races of men, a Comparative Theology may be constructed. Course of Comparative Theology. Through such a science alone can correct conclusions be arrived at respecting this, the most important of the intellectual operations of man – the definite process of his religious opinions. But it must be borne in mind that Comparative Theology illustrates the result or effect of the phase of life, and is not its cause.

Corrections of anthropocentric ideas. As man advances in knowledge he discovers that of his primitive conclusions some are doubtless erroneous, and many require better evidence to establish their truth incontestably. A more prolonged and attentive examination gives him reason, in some of the most important particulars, to change his mind. He finds that the earth on which he lives is not a floor covered over with a starry dome, as he once supposed, but a globe self-balanced in space. The crystalline vault, or sky, is recognized to be an optical deception. It rests upon the earth nowhere, and is no boundary at all; there is no kingdom of happiness above it, but a limitless space, adorned with planets and suns. Instead of a realm of darkness and woe in the depths on the other side of the earth, men like ourselves are found there, pursuing, in Australia and New Zealand, the innocent pleasures and encountering the ordinary labours of life. By the aid of such lights as knowledge gradually supplies, he comes at last to discover that this, our terrestrial habitation, instead of being a chosen, a sacred spot, is only one of similar myriads, more numerous than the sands of the sea, and prodigally scattered through space.

Consequence of discovering the form of the earth. Never, perhaps, was a more important truth discovered. All the visible evidence was in direct opposition to it. Detection of its insignificance. The earth, which had hitherto seemed to be the very emblem of immobility, was demonstrated to be carried with a double motion, with prodigious velocity, through the heavens; the rising and setting of the stars were proved to be an illusion; and, as respects the size of the globe, it was shown to be altogether insignificant when compared with multitudes of other neighbouring ones – insignificant doubly by reason of its actual dimensions, and by the countless numbers of others like it in form, and doubtless, like it, the abodes of many orders of life.

And so it turns out that our earth is a globe of about twenty-five thousand miles in circumference. The voyager who circumnavigates it spends no inconsiderable portion of his life in accomplishing his task. It moves round the sun in a year, but at so great a distance from that luminary that, if seen from him, it would look like a little spark traversing the sky. It is thus recognized as one of the members of the solar system. Other solar bodies. Other similar bodies, some of which are of larger, some of smaller dimensions, perform similar revolutions round the sun in appropriate periods of time.

Magnitude of the universe. If the magnitude of the earth be too great for us to attach to it any definite conception, what shall we say of the compass of the solar system? There is a defect in the human intellect which incapacitates us for comprehending distances and periods that are either too colossal or too minute. We gain no clearer insight into the matter when we are told that a comet which does not pass beyond the bounds of the system, may perhaps be absent on its journey for more than a thousand years. Distances and periods such as these are beyond our grasp. They prove to us how far human reason excels imagination, the one measuring and comparing things of which the other can form no conception, but in the attempt is utterly bewildered and lost.

The infinity of worlds. But as there are other globes like our earth, so too there are other worlds like our solar system. There are self-luminous suns exceeding in number all computation. The dimensions of this earth pass into nothingness in comparison with the dimensions of the solar system, and that system, in its turn, is only an invisible point if placed in relation with the countless hosts of other systems which form, with it, clusters of stars. Our solar system, far from being alone in the universe, is only one of an extensive brotherhood, bound by common laws and subject to like influences. Even on the very verge of creation, where imagination might lay the beginning of the realms of chaos, we see unbounded proofs of order, a regularity in the arrangement of inanimate things, suggesting to us that there are other intellectual creatures like us, the tenants of those islands in the abysses of space.