UCrNRLF

UNIVERSITY OF CALIFORNIA.

FROM THE LIBRARY OF

DR. JOSEPH LECONTE.

GIFT OF MRS. LECONTE. No.

COSMOS:

SKETCH

OF A

PHYSICAL DESCRIPTION OF THE UNIVERSE.

BY

ALEXANDER VON HUMBOLDT.

VOL. Ill— PART I.

Natures vero rerum vts atqtie majestas in omnibus momentisfide caret, si quit modo partet </'«« ae non totam complectatur animo.— PLIN. H. N. lib. vii. c. 1.

TRANSLATED UNDER THE SUPERINTENDENCE OF

LIEUT.-COL. EDWARD SABINE, E.A., Y.P.&TRBAS. R.S.

LONDON:

PRINTED FOR

LONGMAN, BROWN, GREEN, AND LONGMANS,

PATERNOSTER ROW J AMI)

JOHN MURRAY. ALBEMARLE STREET.

. 1851. UNIVERSITY

QM

LONDOK :

VTitsoN AMD OOILTT, 57, SKIHNEB STKBBT, SNOWHIU..

CONTENTS.

Page INTKODTJCTION.

Historical Eeview of the attempts which had for their object the consideration of the phenomena of the Universe re- garded as a whole ..... 3—25

SPECIAL RESULTS OF OBSEKVATION IN COSMICAL PHENOMENA.

A. UEAFOLOGICAI POETION of the physical description of the universe. a. ASTEOGWOSY ....... 26—29

I. Cosmical space, and conjectures respecting what appears to occupy the intervals between the hea- venly bodies . . . . . . . 30 42

n. Natural and telescopic vision, p. 43 67 ; Scin- tillation of stars, p. 67—71 ; Velocity of light, p. 71—78 ; Photometric results, p. 78—85 . 42—85

HI. Number, distribution, and colour of the fixed stars, p. 86—118 ; Clusters of stars, p. 119—123 ; Milky way, p. 124—131 ..... 86—131

IV. Newly appeared and vanished stars, p. 132 147 ; Variable stars with recurring and mea- sured periods, p. 147 171 ; Variation of light in celestial bodies of which the periodicity has not yet been investigated, p. 171—177 . . 132— 177

98831

11

CONTENTS.

Page

V. Proper motion of the fixed stars, p. 178—182 ;

Problemetical existence of dark bodies, p. 182 185 ; Parallax and measured distances of some of the fixed stars, p. 185 192 ; Motion of the solar system, and doubts concerning the assump- tion of a central body for the whole sidereal heavens, p. 192—198 . . . . . 178—198

VI. Double or multiple stars ; their number and distances apart, and periods of revolution around

a common centre of gravity .... 199—214-

NOTES.

To Introduction . i ix

To special results of observation ix

To section I. x xiv

To section II. . xiv xlv

To section III. xlvi— kvi

To section IV ... kvi— kx

To section V. kx— kxiv

To section VI kxiv kxviii

TABLES.

Clusters of stars .... . 120—123

New stars . 138—147

Variable stars . . 163—171

Parallaxas ... 190

Elements of the orbits of double stars . . . 214

Photometric tables of stars . xlii xl

COSMOS,

VOL. III.

COSMOS:

A PHISICAL DESCRIPTION OF THE UNIVEBSE.

SPECIAL RESULTS OF OBSERVATION IN THE DOMAIN OF COSMICAL PHENOMENA.

INTRODUCTION.

IN pursuance of the aim which I had proposed to myself, as attainable in a degree commensurate with my own powers and with the present state of knowledge, I have consi- dered Nature, in the two volumes of the Cosmos which have already appeared, in a twofold point of view. I have sought to represent her, first, in the pure objectivity of external phsenomena, and, next, as the reflex of the image received through the senses on the mirror of man's inner being, his ideas and feelings.

The external world of phsenomena has been described under the scientific form of a general picture of Nature in her two great spheres, uranologic and telluric ; beginning with the stars which glimmer amidst nebulae in the most distant regions of space, and descending through our plane-

4 SPECIAL RESULTS OF OBSEIIVATION IN THE DOMAIN

tary system to the vegetable covering with which the earth is invested, and to the minutest organisms often floating in the air, which escape our unassisted vision. In order to allow us to contemplate with greater clearness the existence of a common bond comprehending the whole of the material universe, the government of never changing laws, and the causal connection of entire groups of phenomena so far as is yet known to us, it was necessary to avoid the accumula- tion of detached facts. Such care appeared more particu- larly requisite where, in the telluric sphere of the Cosmos, by the side of the dynamic actions of moving forces, we find manifested the powerful influence of the specific hetero- geneity of matter. In the sidereal or uranological part of the Cosmos, the problems, in all that can be reached by observation, are in their nature of admirable simplicity ; being by the theory of motion susceptible of rigid calcula- tion, according to the attracting force of matter and the quantity of its mass. If, as I believe, we are justified in regarding the aerolites, or meteoric asteroids, as parts of our planetary system, they, but they only, by falling upon our globe, enable us to recognise diversity of substance in bodies belonging to cosmical space external to our own planet. (l) We have here the reason why terrestrial phse- nomena have hitherto been less generally, and less success- fully, subjected to mathematical development and treatment, than have the movements of the heavenly bodies, with their mutual perturbations and periodical returns, governed, so far as our perceptions extend, only by the one fundamental force of homogeneous matter.

My endeavours in the telluric portion of the description of Nature were directed to the arrangement of the phseno-

OF THE COSMOS. INTRODUCTION. 5

mena in significant order, suggestive of their causal connec- tion. The terrestrial globe was described in its form, its mean density, the gradations of its temperature increasing with increasing depth, its electro-magnetic currents and evolution of polar light. On the reaction of the interior of the planet upon its external crust depend all the phsenomena of volcanic activity ; comprising those of earthquakes in more or less complete circles of waves, as well as their simply dynamic effects, eruptions of gas, hot springs, and mud. The most powerful manifestation of internal terres- trial activity is the elevation of fire-emitting mountains. We have described volcanoes, both central and forming chains, not only as destructive agents, but also as producing or emitting various substances, and still forming under our eyes, for the most part periodically, those classes of rock which we term eruptive rocks ; while, in contrast with this forma- tion, we have also shewn the precipitation, likewise still going on, of sedimentary rocks from fluids containing their minute constituent particles in solution or suspension. Such a comparison of that which is still in process of elab6- ration, with those strata of the crust of the globe which have long since been solidified, conducts to the distinction of geological epochs, and to a secure determination of the successive age of formations, in which lie enveloped, in successive series chronologically recognisable, the remains of extinct races of plants and animals, forming the Moras and Eaunas of an earlier world. The modes of formation, altera- tion, and upheaving of the strata, varying at different geo- logical epochs, are conditions on which all the particular features of the surface of the globe depend : on them depend the distribution of land and water, and the configuration and

6 SPECIAL RESULTS OF OBSERVATION IN THE DOMAIN

extent of the continental masses in the vertical as well as in the horizontal direction. These features of the earth's surface constitute, in their turn, conditions on which depend the thermic state of oceanic currents, the meteorological

J O

processes of the aerial covering of our planet, and the geo- graphical and typical distribution and extension of animal and vegetable forms. This brief allusion to the order and manner in which the various telluric phenomena are pre- sented, in the view or picture of Nature in the first volume of my work, is, I think, sufficient to shew that the mere bringing together of great and apparently complicated results of observation, may promote insight into their causal connection. On the other hand, the interpretation of Nature is obscured when the description languishes under too great an accumulation of insulated facts.

If, in a carefully designed objective representation of the world of phsenomena, completeness in the enumeration of par- ticulars ought not to be desired, neither should it be sought for in the description of the reflex of external nature on the human mind. Here it was needful to draw the limits still closer. The measureless domain of human thought, fer- tilised for thousands of years by the impulses and powers of mental activity, presents in different races, and at dif- ferent stages of civilisation, at one time a cheerful, and at another a melancholy, aspect ; (2) a delicate appreciation of the beautiful in nature, or a dull insensibility to all that she can display. At an early period we see the human mind directed to the deification of natural forces or powers, and of certain objects of the material universe ; at a later period it followed religious impulses of a higher and more purely spiritual character. (3) The internal reflex of external

OF THE COSMOS. INTRODUCTION. 7

phenomena influences in a variety of ways the mysterious process of the formation of language, (4) a process in which original physical temperament, and the impressions received from surrounding nature, both act as powerful concurrent elements. Man elaborates within himself the rough mate- rials supplied through the senses ; and the results or pro- ducts of such mental processes belong as essentially to the domain of the Cosmos, as do the external phenomena which are reflected in the internal mirror of the mind.

As the image of nature reflected under the influence of excited creative imagination cannot be preserved pure and true, there arises, by the side of what we call the actual or external world, an ideal or internal world, tilled with fantastic and partly symbolical myths, and animated by creatures of fabulous shape, whose different parts are borrowed either from various animals of the present crea- tion, or even from the remains of extinct species. (5) Mar- vellous and fabulous flowers and trees spring from the mythical soil, as in the songs of the Edda, the giant ash, the world-tree, Ygdrasil, whose branches rise above the heavens, while one of its triple roots reaches down to the raging fountains of the lower world. (6) Thus the cloud-land of physical myths is filled, according to the particular cha- racter of the race and climate, either with pleasing images or shapes of terror, and these enter into the circles of ideas of later generations, to whom they are bequeathed.

If my published work does not correspond sufficiently to the title, of which I have often acknowledged the imprudent boldness, the reproach of incompleteness must especially attach to that portion which touches on the spiritual life in the Cosmos, or the reflex image of external nature in the

8 SPECIAL RESULTS OF OBSERVATION Iff THE DOMAIN

domain of human thought and feeling. In this part of my undertaking I have more particularly contented myself with dwelling on the subjects which lay most in the direction of my previously long-cherished studies : on the manifestations of the more or less vivid feeling of nature in classical antiquity, and in modern times; on the fragments of poetic description of nature, whose tone of colouring has been so materially influenced by individuality of national character, and by the religious monotheistic view of crea- tion ; on the pleasing magic of landscape painting ; and on the history of the physical contemplation of the Uni- verse ; i. e. the history of the gradual development, in the course of two thousand years, of the recognition of the unity of phsenomena, and of the Universe as a Whole.

In a work so comprehensive, and at once scientific and literary in its aim, all that a first and imperfect attempt can aspire to accomplish is, to influence rather by what it may call forth than by what it can itself supply. A book of Nature, which may be worthy of so exalted a title, can only be looked for when the natural sciences, notwithstanding their inherent incapability of absolute completion, shall yet, by continued progress and extension, have reached a higher standing point ; and when thus a new and clearer light shall have been thrown alike on the two spheres of the one Cosmos, the external world perceived by the senses, and its internal reflection in the mind.

I think I have sufficiently indicated the reasons which have determined me not to give to the general picture of Nature a wider extension. It remains for the third and last volume of my work to supply some of the deficiencies of the earlier ones, and to put forward those results of

OF THE COSMOS. INTRODUCTION. 9

observation which form the principal basis of present scientific opinion. The order of succession in which these results are presented will again be that which, in confor- mity with previously enounced principles, was followed by me in the general view of Nature. Before, however, pro- ceeding to particular results in the several sciences, I desire still to add a few more general elucidatory considerations. The unexpected favour with which my undertaking has been received, both in my own and in other countries, makes me doubly feel the need of expressing myself once more as distinctly as possible in reference to the fundamen- tal idea of the entire work ; and respecting -requirements which I have never even attempted to fulfil, because, accord- ing to my individual view of our experimental knowledge, their fulfilment could not be contemplated by me. With these considerations, to which I am led by the desire of justifying my manner of proceeding, there are naturally associated historical reminiscences of earlier attempts to discover the idea of the Universe, which should so compre- hend its structure as to reduce all phsenomena, in their causal connection, to a single principle.

The fundamental principle (7) of my work on the Cosmos, as developed by me more than twenty years ago in lectures delivered in the French and German languages, at Paris and at Berlin, consists in the constant tendency or endea- vour to embrace the phsenomena of the universe as a natural Whole ; to shew how, in particular groups of the phsenomena, those conditions which are common to the entire group, i. e. the government of great and comprehensive laws, have been discovered and recognised, and by what means we ascend from the knowledge of these laws to that of their

10 SPECIAL RESULTS OF OBSERVATION IN THE DOMAIN

causal connection. Such a tendency to advance continu- ally towards the comprehension of the plan of the Universe, or the order of Nature, commences with the combination and generalisation of particular facts ; with the recognition of the conditions under which phenomena, i. e. the mani- festations of physical alterations, are always reproduced in a similar manner : it conducts to the thoughtful consideration of the materials supplied by observation and experiment ; but it does not conduct to a " view of the Universe derived from speculation and the development of thought alone, or to a science or doctrine of the unity of Nature apart from experience." We are, I here repeat it, still far from the time, when it may be thought possible to concen- trate all the perceptions of our senses into the unity of one comprehensive idea embracing the whole of Nature. The safe path was perceived a full century before "Francis Bacon, by Leonardo da Yinci, and indicated by him in a few words : " Comminciare dalF esperienza, e per mezzo di questa, scoprirne la ragione." (8) In many groups of phse- nomeria we must, indeed, still content ourselves with a deduction of empirical laws ; but the highest object of all investigation into nature, though seldom attained, is the discovery of physical causes. (9) This is most satisfac- torily and conclusively accomplished, when it is possible to connect the laws of phenomena with the causes which explain them, by the intervention of mathematical rea- soning. It is, however, only in some particularly fa- voured parts of natural science that the "physical descrip- tion" coincides with the "physical explanation of the universe." The two expressions cannot yet be regarded as identical. The inherent grandeur and solemnity of that

OF THE COSMOS. INTRODUCTION. 11

mental labour, the boundaries of which are hereby marked, consist in the elevating consciousness of the infinite nature of the object of its efforts, the comprehension of the unknown and inexhaustible fulness of creation, whether formed or in process of formation, whether existing or to be hereafter developed.

Such efforts, acting throughout all ages, must have led often, and under many various forms, to the illusory hope of having attained the goal, and found the prin- ciple by which all that is variable in the material universe, the totality of all the phsenomena which are cog- nizable by the senses, might be explained. After a long period in which, in conformity with the early fundamental mode of contemplation of the Hellenic national mind, the forming, transforming, and destroying forces of nature had been honoured as divine or spiritual powers, clothed in human forms, (10) there became developed amidst the phy- siological fancies of the Ionic school the germ of a scientific contemplation of Nature. The first cause of all phenomena was explained in two different directions (n), sometimes ac- cording to mechanical, and sometimes according to dynamic views, from the assumption of concrete corporeal princi- ples called " elements of nature," or from processes of rarefaction and condensation. The hypothesis, primarily perhaps of Indian origin, of four or five substantially dif- ferent elements, has continued, from the didactic poem of Empedocles to the most recent times, to mingle itself with all systems of natural philosophy, forming an evidence and monument of high antiquity of man's desire to seek for the generalisation and simplification of ideas, not only in forces, but also in the qualitative essences of substances.

In the later development of the Ionic physiology, An ax-

12 SPECIAL RESULTS OP OBSERVATION IN THE DOMAIN

agoras of Clazomene passed from the assumption of ma- terial forces to the idea of a Spirit, distinct from all matter but intermixed with all its homogeneous ultimate particles. He spoke of the world-regulating Mind (vovg) governing the continually progressive formation of the Universe, and being the original cause of all motion, and thus of all physical phenomena. It is by the assumption of a centrifugal re- volving movement (12), by whose intermission, previously noticed, he accounts for the fall of meteoric stones, that Anaxagoras explains the apparent motion of the celestial sphere from East to West. This hypothesis indicates the commencement of vortex- theories, which more than two thousand years afterwards became of much cosmical im- portance by the writings of Descartes, Huygens, and Hooke. This work is not the place in winch to enquire whether Anaxagoras means by the " world-regulating Mind" the Godhead itself, or whether he only means to speak pan- theistically of a spiritual principle in the general life of Nature. (13)

In marked contrast with the two divisions of the Ionic School, though likewise embracing the whole Universe, is the mathematical symbolism of the Pythagoreans. In the phenomena of the Universe, their regards were fixed ex- clusively on the dominion of law in the determination of form (the five fundamental forms) ; and on the ideas of number, measure, harmony, and antithesis. To them, things were mirrored in numbers, which are as it were an " imitative representation"" (/u/^o-tc) thereof. They saw in the illimitability of numbers, inasmuch as they can be endlessly repeated and increased, the character of eternity, and of the infinitude of Nature. They considered that the

OF THE COSMOS. INTRODUCTION. 13

essence of things may be known by ratios of numbers, and their alterations and transformations by combinations of numbers. Plato's Physics also contain attempts to reduce all the essences of substances in the universe, and their gradations of changes, to corporeal forms ; and these to the simplest (triangular) plane figures. (14) But what the ulti- mate principles (as it were the elements of the elements), may be, "this," said Plato, with modest diffidence, "is known to God alone, and to whomso is beloved by Him among men." This mathematical treatment of physical phenomena, the formation of atomic doctrines, the philosophy of measure and of harmony, have continued to a late period to influ- ence the development of the natural sciences : they have also contributed to lead fanciful discoverers astray from the true road, into by-paths which it may be requisite to notice in the history of the physical contemplation of the Universe. " There dwells a peculiar and fascinating charm recognised by all antiquity in the simple relations of time and space as manifested in tones, numbers, and lines."" (15)

The idea of the order and government of the Universe shines forth pure and exalted in the writings of Aristotle. All the phenomena of Nature are described in the "Auscultationes Physicse" as moving vital activities of a Universal Power. On the " unmoved Motor of the World depend Heaven and Nature," (16) Nature being the terrestrial sphere of phse- nomena. The " Orderer," and the final cause of all alte- rations which can be perceived, must be regarded as imper- ceptible to sense, as distinct from all matter. (17) Unity in the different manifestations of force in substances is raised by Aristotle to the rank of a leading principle, and these manifestations of force are themselves always reduced to

14 SPECIAL RESULTS OF OBSERVATION IN THE DOMAIN

motions. Thus we even findin»the book "De Anima" (18) the germ of the undulatory theory of light. The sensation of seeing follows from a movement or vibration of the medium between the sight and the object seen, not from effluxes either from the object or from the eye. Hearing is compared with seeing, as sound is also a consequence of concussion of the air.

In inculcating the exercise of thoughtful reason in the search after that which is general or universal amidst the particular facts perceived by the senses, Aristotle always com- prehends the whole of Nature, and the internal connection not only of forces but also of organic forms. In the book which treats of the parts (organs,) of animals, he clearly enounces his belief in the gradual chain of beings ascending from lower to higher forms. Nature proceeds in uninter- rupted progressive development from the inanimate (ele- mentary,) through plants to animals : advancing first to " what indeed is not properly an animal, but so nearly allied thereto that it is on the whole but little distinguished from one."" (19) In the transition of forms " the intermediate steps are almost insensible/'' (20) The unity of Nature is to the Stagirite the great problem of the Cosmos. He says, with singular vivacity of expression, "In Nature nothing is isolated; there is no want of connection as in a bad tragedy." (21)

In all the physical writings of this profound, sage, and accurate observer of nature, we cannot fail to recognise the philosophical tendency to subordinate all the pheno- mena of the one Cosmos to a single principle of expla- nation ; but the defective state of knowledge, and ignorance of the method of experimenting, (i. e.} of calling forth phenomena under definite conditions), prevented even small

OP THE COSMOS. INTRODUCTION. 15

groups of physical processes from being comprehended in their causal connection. All was reduced to ever recurring antitheses of cold and heat, moisture and drought, primitive density and rarity ; and even to the effecting of alterations in the material world by means of a kind of internal antago- nism (antiperistasis), which reminds us of our present hypotheses of opposite polarities and the contrasts of -f and . (22) Aristotle's supposed solutions of problems do but reproduce the facts themselves in disguise; and in explaining meteorological and optical processes, his elsewhere ever powerful and concise style often passes into self com- placent diffuseness or Hellenic verbal redundancy. As the mind of Aristotle was but little directed to diversity of sub- stances, but chiefly to the consideration of motion, we see the fundamenal idea of ascribing all telluric natural phse- nomena to the impulse of the motion of the heavens, (i. e. the revolution of the celestial sphere), recurring continually, always indicated and cherished with special partiality, but not presented with definiteness or precision. (23) The impulse here spoken of imports only the communication of motion as the ground of all terrestrial phaenomena. Pan- theistic views are excluded : the Godhead is the highest " presiding Unity, regulating all things, revealing Himself in all spheres of the entire Universe, giving to each creature its destination, and hoi ding all together by His absolute power ,"(24) The ideas of purpose and adaptation are not so much ap- plied to the subordinate processes of nature, (those of in- organic elementary nature), as by preference to the higher organisations (25) of the animal and vegetable worlds. It is remarkably striking that in the teaching of Aristotle, as if he had been aware of the distribution of masses and the

16 SPECIAL RESULTS OF OBSEKVATION IX THE DOMAIN

existence of perturbations, the Deity employs a number of astral Spirits to maintain the planets in their eternal ap- pointed courses. (26) The stars display the image of the Divinity in the visible world. The small pseudo- Aristotelian book of the Cosmos, which is certainly of Stoic origin, is not mentioned here, notwithstanding its name. It presents, it is true, in a descriptive manner, and often with animated rhetoric and vivacity of colouring, both the heavens and the earth, mid the currents of the ocean and of the atmosphere ; but it manifests no tendency to reduce the phenomena of the Cosmos to general physical principles, i. e., to principles founded in the properties of matter.

I have dwelt the longer on the most brilliant epoch of antiquity, as respects views of Nature, in order to place in opposition the earliest and the more recent attempts at generalisation. In the intellectual movement which has taken place in the course of centuries, and which in reference to the enlargement of the domain of cosmical contemplation was described in another portion (27) of the present work, the end of the 13th and beginning of the 14th centuries were particularly distinguished; but the Opus Majus of Eoger Bacon, the Mirror of Nature of Vincentius of Beau- vais, the Physical Geography (Liber Cosmographicus) of Albertus Magnus, the Picture of the World (Imago Muiidi) of Cardinal Petrus de Alliaco, (Pierre d'Ailly), are works which, however powerfully they may have influenced their cotemporaries, do not correspond in their contents to the titles which they bear. Among the Italian opposers of Aristotle's Physics, Bernardino Telesio of Cosenza was the founder of a "Rational" system of natural science, in which he regarded all the phaenomena of matter, itself passive, as

OF THE COSMOS. INTRODUCTION. 17

the effects of two incorporeal principles, (activities, forces, or powers,) heat and cold. Even the whole of organic life, ("animated" plants and animals) is the production of these two eternally-divided forces, one of which, heat, belongs to the celestial, and the other, cold, to the terrestrial sphere.

With fancy still more unregulated, but gifted with a pro- found spirit of research, Giordano Bruno of Nola attempts in three works entitled " De la Causa Principio e Uno," " Con- templationi circa lo Infinito, Universe e Moudi innumerabili," and " De Minirno et Maximo," to embrace the entire Uni- verse. (2S) In the " Natural Philosophy'' of Telesio, a cotem- porary of Copernicus, we perceive at least the endeavour to reduce the variations of matterto two of its fundamental forces, " which are indeed imagined as acting from without," yet are similar to the fundamental forces of attraction and repulsion in the dynamic doctrines of Boscovich and Kant. The cosmi- cal views of Giordano Bruno are purely metaphysical; they do not seek the causes of sensible phenomena in matter itself, but touch on ee the infinity of space filled with self luminous worlds, the animation of these worlds by souls, and the relations of the highest Intelligence, God, to the universe." Although himself but scantily furnished with mathematical knowledge, Giordano Bruno was, nevertheless, up to the time of his dreadful martyrdom, (29) an enthusiastic admirer of Copernicus, Tycho Brahe, and Kepler. Although a co- temporary of Galileo, he died before the invention of the telescope by Hans Lippershey and Zacharias Jansen, and could not therefore witness the discovery of Jupiter's satel- lites, the phases of Yenus, and the nebulse. With daring confidence in what he termed "lume interno, ragione natn- rale, altezza dell' intelleto," he gave himself up to happy

vor.. m. C

18 SPECIAL RESULTS OF OBSERVATION IN THE DOMAIN

conjectures respecting the movement of the fixed stars, the planetary nature of comets, and the deviation of the figure of the Earth from that of a perfect sphere. (30) Gre- cian antiquity is also full of such uranological divinations, which have been subsequently realised.

In the development of thought respecting cosmical relations of which the leading forms and epochs have been here enume- rated, it was Kepler who, fully 78 years before the publication of Newton's immortal work of the " Principia Philosophise naturalis," came nearest to a mathematical application of the doctrine of gravitation. Although the Eclectic Sim- plicius expressed in a general manner that " the non-falling of the heavenly bodies was caused by the centrifugal force having the upper hand of the proper falling force, the down- ward traction;" although John Philoponus, a disciple of Ammonius, the son of Hermeas, ascribed the movements of the heavenly bodies " to a primitive impetus and to the con- tinued tendency to fall •" and although Copernicus, as was noticed in an earlier part of the present work, describes the merely general idea of gravitation, as it acts in the Sun as the centre of the planetary world, and in the Earth and Moon, in these remarkable words : " Gravitatem non aliud esse quam appetentiam quandam naturalem partibus inditam a divina providentia opificis universorum, ut in unitatem integritatemque suam sese conferant, in formam globi co- euntes ;" yet it is ' in Kepler, in the Introduction to the book "De Stella Martis," (31) that we first find numerical quantities assigned to the attracting forces which the Earth and the Moon exercise upon each other in the ratio of their masses. It distinctly adduces the ebb and flow of the sea (32) as a proof that the attracting power of the Moon, (virtus

OF THE COSMOS. INTRODUCTION. 19

tractoria) extends as far as the Earth ; and he even says that this force, " similar to that which the magnet exercises upon iron/' would deprive the Earth of water, if the Earth itself ceased to attract the water. Unfortunately, ten years later, in 1619, this great man, perhaps out of deference to Galileo, who ascribed the ebb and flow to the rotation of the Earth, gave up the true explanation, and in the Harmonice Mundi described the Earth as a living animal whose whale- like respirations, in periodical alternations of sleeping and waking dependent on the solar time, cause the swelling and sinking of the ocean. The profound mathematical genius, recognised by IJaplace, which shiiies forth in one of Kepler's writings (33), makes us regret that the discoverer of the three great laws of all planetary movement did not persevere in the path, in which his views respecting the attraction of masses had led him to enter.

Descartes, furnished with a greater variety of knowledge in the natural sciences than Kepler, and himself the founder of several parts of a mathematical system of physics, under- took to embrace the whole world of phsenomena, the ce- lestial sphere, and all that he knew of animate and inanimate terrestrial Nature, in a work to which he gave the names of "Traite du Monde" and "Summa Philosophise." The organization of animals, and particularly that of man, for the understanding of which he pursued for eleven years a systematic course of anatomical study, (34) was to form the concluding portion of the work. In his correspondence with Father Mersenne, we find many complaints of the slow progress of the undertaking, and of the difficulty of arranging and combining such numerous materials. This Cosmos, which. Descartes always called his World (son.

20 SPECIAL RESULTS OF OBSERVATION IN THE DOMAIN

Monde), was finally to have been sent to press at the con- clusion of 1633 ; but the report of the sentence passed upon Galileo in the Inquisition at Rome (which was only made known four months later, in October, 1633, by Gassendi and Bouillaud), arrested its progress, and deprived the world of a great work, executed with so much labour and care. The motives for its non-publication were the love of a quiet and peaceful life in his retirement at Dev enter, and a pious anxiety not to shew himself disrespectful to the Pope's decree against the Earth's planetary motion. (35) It was not until 1664, fourteen years after the philosopher's death, that some fragments of the work were printed under the strange title of " Le Monde, ou Traite de la Lu- miere." (36) The three chapters which treat of Light hardly form a fourth part of the whole. On the other hand the sections which belonged originally to Descartes' Cosmos, and contained considerations on the motion and.solar distance of the planets, on terrestrial magnetism, on tides, and on earthquakes and volcanoes, were transferred to the third and fourth parts of the celebrated work entitled " Principes de la Philosophic."

The " Kosmotheoros" of Huygens, which was not pub- lished until after his death, notwithstanding its high-sound- ing and significant name, hardly deserves to be mentioned in this enumeration of cosmical essays. It contains the dreams and conjectures of a great man on the vegetable and animal worlds of distant heavenly bodies, and especially on the altered forms under which mankind may appear there. One seems to be reading Kepler's " Somnium Astronomi- cum/' or Kircher's " Ecstatic Journey." As Huygens al- ready, like the astronomers of the present day, allowed to

OF THE COSMOS. INTRODUCTION. 21

the Moon neither air nor water, (37) he finds the supposed existence of lunar men present to him still greater diffi- culties than that of the inhabitants of the remoter planets " rich in clouds and vapour."

The immortal author of the Philosophise Naturalis Prin- cipia Mathernatica, succeeded, by the assumption of a single all- governing fundamental moving force, in embracing the whole uranological portion of the Cosmos in the causal connection of its phenomena. Newton first raised physical astronomy to a mathematical science, and made it the solu- tion of a great problem of mechanics. The quantity of matter in each heavenly body gives the measure of its at- tracting force, a force which acts in the inverse ratio of the square of the distance, and determines the magnitude of the perturbing actions which not only the planets, but all the heavenly bodies in space, exert upon each other. But the Newtonian theorem of gravitation, so admirable for simpli- city and generality, is not limited in its cosmical application to the sphere of uranology ; it governs also terrestrial phse- nomena in directions still partly uninvestigated ; it gives the key to periodic movements in the ocean and in the atmosphere, (3S) to the solution of problems of capillarity, endosmose, and many chemical electro -magnetic and organic processes. Newton himself (39) already distinguished the " attraction of mass," as it manifests itself in all celestial bodies and in the phaenomena of the tides, from " molecular attraction," which acts at infinitely small distances and in the closest contact.

Thus among all human efforts to reduce all variations taking place in the world known to us through our senses to a single fundamental principle, the doctrine of gravita-

Z'Z SPECIAL RESULTS OF OBSERVATION IN THE DOMAIN

tioii shews itself the most comprehensive and the most rich in cosmical promise. It is indeed true, notwithstanding the brilliant progress made in modern times in Stoechiornetry (calculation of chemical elements and of the ratios of volume in compound gases), we are not yet able to reduce all theories of substances to a mathematical explanation. Em- pirical laws have been discovered, and in following the widely extended views of the atomic or of the corpuscular philosophy, many things have been rendered more accessible to mathematical treatment ; but from the boundless hetero- geneity of matter, and the multifarious conditions of aggre- gation of what are called the particles of mass, the demon- strations of these empirical laws can as yet by no means be derived from the theory of " contact attraction," with the same certainty as is effected by the establishment of Kepler's three great laws on the basis of the theory of " mass attraction" or gravitation.

Yet, after Newton had recognised all the motions of the heavenly bodies as consequences of one single force, he did not, with Kant, regard gravitation itself as an essential pro- perty of matter, (40) but as either derived from a higher force still unknown to him, or as the result of a "revolving of the Ether which fills all space, and is more rare in the intervals between the particles of mass, and increases in density outwards." The latter view is developed in detail in a letter to Robert Boyle, (41) dated 28th February, 1678, which ends with the words, " I seek in the Ether the cause of gravitation." Eight years later, as may be seen from a letter to Halley, Newton gave up this hypothesis of denser and rarer Ether altogether. (42) It is a striking circumstance that, in 1717, nine years before his death, in the extremely

OF THE COSMOS. INTRODUCTION. 23

short preface to the second edition of his Optics, he thought it necessary to declare explicitly that he by no means re- garded gravitation as an " essential property of bodies" : (43) while more than a century before, in 1600, Gilbert had viewed magnetism as a force inherent in all matter. So much did the most profound of thinkers, Newton himself, who ever leaned so strongly to experience, hesitate in respect to the " ultimate mechanical cause" of motion.

The establishment of a science of Nature, from the laws of gravity up to the formative impulse in animated bodies, as one organic Whole, is no doubt a brilliant problem, and one worthy of the human intellect ; but the imperfect state of so many parts of our knowledge places insuperable diffi- culties in the way of its solution. The impossibility of complete experimental knowledge, in a boundless sphere of observation, renders the problem of explaining all the changes of matter from the powers of matter itself an " in- determinate problem.'" What is perceived is far from exhausting what is perceivable. If, to recall only the pro- gress of the time nearest to our own, we compare the imperfect knowledge of nature possessed by Gilbert, Eobert Boyle, and Hales with the present, and if we remember that the rate of progress is a rapidly increasing one, we may have some idea of the periodical endless transformations which still await all the physical sciences. New substances and new powers will be discovered. Even though many natural processes, as those of light, heat, and electro-mag- netism, being reduced to movement (undulations), have become accessible to mathematical treatment, yet there remain the often referred to, and perhaps unconquerable, problems of the cause of chemical diversity of substance,

24 SPECIAL RESULTS OF OBSERVATION IN THE DOMAIN

and of the order and proportion s, seemingly not reducible to any laws, of the magnitudes, densities, inclinations of axis, and eccentricities of orbit of the planets, the numbers and distances of their satellites, the form of continents, and the position of their loftiest mountain chains. All these cir- cumstances (having reference to space geographical or celes- tial), which are here instanced merely as examples, can as yet only be regarded as natural facts, of which we know the existence but not the explanation. But although neither the causes nor the connection of these facts are yet known to us, I (Jo not therefore term them in any sense accidental. They are doubtless the results of events or occurrences in space at the time of the formation of our planetary system, and of geological phenomena which accompanied or pre- ceded the elevation of the outermost strata of our globe into continents and mountain chains. Our knowledge of the early period of the physical history of the Universe does not reach back far enough to enable us to describe that which exists in its process of formation. (44)

But although it has not yet been possible in all cases fully to recognise the causal connection between phenomena, no part of the domain of the natural sciences can be ex- cluded from the study of the Cosmos, or the physical de- scription of the Universe. Bather that study comprehends the whole of such domain, the phenomena of both spheres, celestial and telluric ; but it does so only under the single point of view of the tendency towards the recognition of the Universe as a Whole. (45) As, in the description of what has taken place in the moral and political sphere, the historian (46) cannot directly discern, accord- ing to man's view, the plan of the government of the world,

OF THE COSMOS. INTRODUCTION. 25

but can only divine it through the ideas by which it manifests itself; so the investigator of nature, in seeking to present cosmical relations, is penetrated by the convic- tion that the number of impelling, forming, and producing powers or forces of the material universe, is far indeed from having been exhausted by the results hitherto ob- tained, either by immediate observation, or by the analysis of phenomena.

SPECIAL RESULTS IN THE URANOLOGICAL

A.

RESULTS OF OBSERVATION IN THE URANOLOGICAL PORTION OF THE PHYSICAL DESCRIPTION OF THE UNIVERSE.

WE commence afresh with the depths of space and with the remote sporadically-scattered clusters of stars which present themselves to telescopic vision as faintly shining nebulae. We descend step by step to the double stars, often of two different colours, which revolve around a common centre of gravity ; to the nearer strata of stars, one of which appears to, include our planetary system ; and lastly, through this planetary system to the air- and sea-surrounded spheroid which we inhabit. I have noticed in an earlier volume, in the introduction to the general picture of Nature, (47) that this