Volume II Part 14 (1/2)
[Sidenote: 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 G.o.d.
[Sidenote: 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.
[Sidenote: The nebular hypothesis.] The nebular hypothesis requires us to admit that all the ponderable material now const.i.tuting 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 ma.s.s; these, in their turn breaking and becoming spheroids, const.i.tute 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.
[Sidenote: 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 furnis.h.i.+ng 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 ant.i.thetical relations to planets.
[Sidenote: Whether nebulae 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 nebulae, one consisting of cl.u.s.ters 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. Nebulae 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 nebulae 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 ma.s.ses of matter in a gaseous condition, and at a temperature of incandescence. The hypothesis of Laplace has thus a firm basis.
[Sidenote: 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 Ura.n.u.s and Neptune, as from moral and extraneous considerations. There is a line in Aristophanes which points out precisely the difficulty:
Ho Zeus ouk on, all' ant' autou Dinos nuni basileuon.
A reluctance to acknowledge the presidency of law in the existing const.i.tution 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 s.p.a.ce, and the variations of that distribution in time.
[Sidenote: 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 a.s.signed the pontificate of Nicolas V. as the true close of the intellectual dominion of the Church. From that time the sceptre had pa.s.sed 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 pa.s.sed, dreaming of new phantoms and delusions in its wished-for return, and vindictively striking its talons at any derisive a.s.sailant who incautiously approached too near. I have not s.p.a.ce 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. [Sidenote: 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 navely 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 cla.s.sification of disease, and Ambrose Pare modern surgery. Such were the occupations and prospect of science at the close of the sixteenth century.
[Sidenote: 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 publis.h.i.+ng 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 s.p.a.ce--”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 sh.e.l.ls; Tournefort and Malpighi devoted themselves to botany; Grew discovered the s.e.xes 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 cla.s.sified them, and introduced the doctrine of the localization of functions in the brain. Malpighi and Lewenhoeck 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.
[Sidenote: Inst.i.tution 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 Naturae, inst.i.tuted 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.
[Sidenote: 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.
[Sidenote: 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.