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IBRARY

D UNIVERSITY OF CALIFORNIA. is. BERKELEY, CALIFORNIA ane

THE LIBRARY OF THE UNIVERSITY

OF CALIFORNIA

PRESENTED BY A PROF. CHARLES A. KOFOID AND : MRS. PRUDENCE W. KOFOID EARTH

SCIENCES LIBRARY

BOHN’S SCIENTIFIC LIBRARY.

—_————

HUMBOLDT’S COSMOS.

+

et Ree ay x: J > + ae 2 s

COSMOS: A SKETCH

PITYSICAL DESCRIPTION OF THE UNIVERSE.

BY

ALEXANDER VON HUMBOLDT.

TRANSLATED FROM THE GERMAN,

BY E: C. OTTE AND B. H. PAUL, Ph. D., F.C.S.

Nature vero rerum vis atque majestas in omnibus momentis fide caret, si quis modo partes ejus ac non totam complectatur animo.—Plin., Hist. Nat., lib. vii. c. 1.

FOL, fV,

LONDON: GEORGE BELL & SONS, YORK ST., COVENT GARDEN, AND NEW YORK,

1892.

4

Go Sith RE Be

OISS8 HER /EF2

Vv, 4

EARTH SCIENCES LIBRARY

GENERAL SUMMARY OF CONTENTS

OF

VOLS. III. AND IV. OF COSMOS.

Special results of Observation in the domain of Cosmical Phenomena.— Introduction.

Retrospect of the subject. Nature considerea under a two-fold aspect: in the pure objectivity of external phenomena, and in their inner reflection in the mind.—A significant classification of phenomena leads of itself to their casual connection.—Completeness in the enumeration of details is not intended, at least in the representation of the reflected picture of nature under the influence of the creative power of imagination.— Besides an actual or external world, there is produced an ideal or an inner world: filled with physical symbolic myths, different according to race and cli- mate, bequeathed for centuries to subsequent generations, and clouding a clear view of nature.—Fundamental imperfectibility of the knowledge of cosmical phenomena. The discovery of empirical laws, the insight into the causal connection of phenomena, description of the universe, and theory of the universe. How, by means of existing things, a small part of their genetic history is laid open.—Different phases of the theory of the uni- verse, attempts to comprehend the order of nature.—Most ancient fun- damental conception of the Hellenic mind: physiologic phantasies of the Tonian school, germs of the scientific contemplation of nature. Double direction of the explanation of natural phenomena, by the assumption of ma- terial principles (elements), and by processes of rarefaction and condensa- tion. Centrifugal revolution. Theories of vortices. The Pythagoreans; philosophy of measure and harmony, commencement of a mathematical treatment of physical phenomena.—The order and government of the universe according to the physical works of Aristotle. ‘The communication of motion considered as the cause of all phenomena; the tendency of the Aristotelean school but little directed to the opinion of the heterogeneity of matter,—This species of natural philosophy bequeathed in fundamental ideas and form to the Middle Ages. Roger Bacon, the Mirror of Waiure of Vincentz of Beauvais, Liber Cosmographicus of Albertus

RAS Saad

vi GENERAL SUMMARY

Magnus, Imago Mundi of the Cardinal Pierre d’ Ailly.—Progress through Giordano Bruno and Telesio.—Clearness in the conceptions of gravitation as mass attraction, by Copernicus.—First attempt at a mathematical appli- cation of the doctrine of gravitation, bv Kepler.—The work on the Cosmos by Descartes (Traité du Monde) nobly undertaken, did not appear until long after his death, and only in fragments; the Cosmotheoros of Huygens, unworthy of the great name.—Newton, and his work Philosophie Natu- ralis Principia Mathematica.—Endeavour towards a knowledge of the universe as a Whole. Is the problem solvable of tracing back to one principle all physical knowledge, from the law of gravitation to the for- mative activities in the organic and animated bodies? What has been discovered does not by a long way exhaust the discoverable. The imper- fectibility of empiric investigation makes the problem of explaining the changeability of matter from the forces of matter an indefinite one.

A. UranotoeicaL Portion of the Physical Description of the Universe, pp. 29—32. Two sections, one of which comprises the heaven of fixed stars ; the other, our solar system, p. 29.

a. AsTRoGNosy ; Heaven of the fixed stars,

I. The realms of space, and conjectures regarding that which appears to occupy the space intervening between the heavenly bodies, pp. 29—-50.

II. Natural and telescopic vision, pp. 51—96; Scintillation of the stars, 99—111; Velocity of light, pp. 111—119; Results of photometry, pp. 119—137.—Order of the fixed stars according to their luminous intensity.

III. Number, distribution, and colour of the fixed stars, pp. 138— 188; Stellar clusters (stellar swarms), pp. 188—193; The Milky Way interspersed with a few nelulous spots, pp. 193—203,

IV. New stars, and stars that have vanished, pp. 204—217; Va- riable stars, whose recurring periods have been determined, pp. 217—240; Variations in the intensity of the light of stars whose periodicity is as yet uninvestigated, pp. 240—247.

V. Proper motion of the fixed stars, pp. 248—252; Problematical existence of dark cosmical bodies, pp. 252—255; Parallax— measured distances of some of the fixed stars, pp. 255—264 ; Doubts as to the assumption of a central body for the whole sidereal heavens, pp. 264—270.

VI. Multiple, or double stars—Their number and ocusiii dis. tances.—Period of revolution of two stars round a common centre of gravity, pp. 271—289.

VII. Nebulous spots.—Are these only remote and very dense clusters of stars ?—The two Magellanic Clouds, in which crowded

OF CONTENTS. vu

nebulous spots are interspersed with numerous steffar swarms: The so-called black spots (Coal-sacks) of the Southern hemi- sphere, pp. 291—350.

B. Sorar REGton, pp. 351—466. I. The Sun considered as the central body, pp. 359—401. IJ. The Planets, pp. 402—466. A. General consideration of the planetary world, pp. 402—466, a. Principal Planets, pp. 403—462. b. Secondary Planets, pp. 462—466.

B. Special enumeration of the planets and their moons as parts of the solar system, p. 467.

Sun, pp. 467—470.

Mercury, pp. 470—473.

Venus, pp. 473—476.

Earth, pp. 476, 477.

Moon of the Earth. pp. 477—502.

Mars, p. 502—504.

The small planets, p. 505; Flora, Victoria, Vesta, Iris, Metis, Hebe, Parthenope, Astra, Egeria, Irene, Euno- mia, Juno, Ceres, Pallas, Hygeia;

Jupiter, pp. 511—515.

Satellites of Jupiter, pp. 515—517.

Saturn, pp. 517—522. Satellites of Saturn, pp. 523, 524.

Uranus, pp. 524—520.

Satellites of Uranus, pp. 526, 527.

Neptune, pp. 527-—530.

Satellites of Neptune, pp. 531, 532.

III. The comets, pp. 553—560. IV. Ring of the zodiacal light, pp. 561—565. _V. Shooting stars, fire-balls, meteoric stones, pp. 566-—596. Conclusion, pp. 597—601. Corrections and additions to vol. iii. p. xiii, Index. Special analysis of the individual sections of the astronomical part of the Cosmos. a. ASTROGNOSY.

1. Cosmical space :—Only isolated portions are measurable, p. 34. -—Resisting medium, celestial atmosphere, cosmical ether, p. 36, notes

vill GENERAL SUMMARY

15—18.—Radiation of heat by the stars, p. 42, note 26.—Temperature of space, pp. 44—47.—Limited transparency? p. 46.—Regularly de- creased period of revolution of the Comet of Encke, p. 47.—Limitation of the atmosphere? p. 49.

Il. Natural and telescopic visions—Very different sources of light present similar relations of refraction, p. 54.—Different velocities of the light of ignited solid bodies and that of frictional electricity, p. 56.— Position of the Wollastonian lines, p. 56.—Influence of tubes, p. 53.— Optical means of distinguishing between direct and reflected light, and the importance of the means to physical astronomy, p. 56.—Limits of ordinary vision, p. 60.—Imperfection of the organ of vision; false diameter of the stars, p. 66.—Influence of the form of an object upon the minimum visual angle in experiments as to visibility; necessity of a difference of luminous intensity of ,;; visibility of distant objects, positively and negatively, pp. 61—72.—On the visibility of stars by day with the naked eye from wells or upon lofty mountains, p. 72.—A feeble light by the side of a stronger, p. 61, note 15,—Extending ray and star tails, p- 65.—On the visibility of the satellites of Jupiter by the naked eye, p- 64.—Undulation of the stars, p. 77.—Commencement of telescopic vision; application to measurement, pp. 78—81.—Refractors of great length, p. 81.—Reflectors, p. 82.—Day observations ; how strong mag- nifying powers facilitate the finding of the stars by day, p. 87.—Ex- planation of the sparkling and scintillation of the stars, p. 96.—Velocity of light, pp. 105—118.—Order of magnitude of the stars; photometric relations and methods of measurement, pp. 119—132.—Cyanometer, p- 129.—Photometric order of the fixed stars, pp. 132—137.

III. Number, distribution, and colour of the fixed stars; Stellar clusters and the Milky Way:—States of the sky which hinder or favour the detection of stars, p. 138.—Number of the stars; how many may be seen with the naked eye, p. 140.—How many have been inserted in stellar charts with determinations of position, p. 145.— Conjectural estimation of the number of stars which can be visible in the entire heavens with our present powers of penetrating space, p. 141.—Con- templative astrognosy of uncivilized people, p. 147.—-The Grecian sphere, p. 159.—The crystal sky, p. 164.—False diameter of the fixed stars in telescopes, p. 174.—Smallest objects in the heavens which have yet been seen, p. 175.—Difference of colours in the stars, and the changes which have taken place in the colours since antiquity, p. 175.—Sirius (Sothis), p- 178.—The four royal stars, p. 184.—Gradual acquaintance with the Southern heaven, p. 185.—Distribution of the fixed stars, laws of relative accumulation, gauging, p. 187.—Clusters and swarms of stars, p. 189. The Milky Way, p. 193.

IV. Stars that have newly appeared and disappeared ; variable stars and changes in the intensity of their light whose periodicity has not been investigated :—New stars in the last 2,000 years, p. 204—Periodically changeable stars: Historical particulars, p. 203.— Colour, p. 24.—

OF CONTENTS. ix

»

Number, p. 222.—Order recognizable in apparent irregularity; great differences of brightness; periods within periods, p. 226.—Argelander’s table of the variable stars with commentary, p. 232.—Variable stars in undetermined periods (m Argfs, Capella, stars of the Urse Major and Minor), p. 246.—Reference to the possible changes of temperature on the Earth’s surface, p. 246.

V. Proper motion of the fixed stars, dark cosmical bodies, parallax ; doubts as to the assumption of a central body for the entire heaven of fixed stars :—Change of the physiognomy of the sky, p. 248.—Amount of the proper motion, p. 251.—Evidence in favour of the probable existence of non-luminous podies, p. 253.—Parallax and measurement of ‘the distance of some fixed stars from our solar system, p. 255.— The aberration of light may be applied to the determination of the paral- lax of double stars, p. 264. The discovery of the proper motion of the fixed stars has led to the knowledge of the motion of our own solar system, and even to the knowledge of the direction of this motion, pp- 251 and 264.—Problem of the situation of the centre of gravity of the whole heaven of fixed stars and central suns? p. 267, and note 38 and 39.)

VI. Double stars, period of revolution of two suns round a common centre of gravity :—Optical and physical double stars, p. 272; number, p- 273.—-Uniformity and difference of colour; the latter not the conse- quence of optical deception, of the contrast of complementary colours, p- 282, notes 15—21.—Change of brightness, p. 285.—Multiple com- binations (three to six fold), p. 285.—Calculated orbitual elements, half major axis and period of rotation in years, p. 289.

VII. Nebulae, Magellanic Clouds, and Coal-sacks:—Resolvability of the nebulz; questions as to whether they are all remote and crowded clusters of stars? p. 291 (note 25 and 26).—Historical particulars, p. 293 (note 44).—Number of nebule whose positions are determined, p. 309 (notes 35 and 36).—Distribution of nebule and clusters of stars in the northern and southern hemispheres, p. 311; spaces poor in nebule, and the maxima of accumulation, p. 312, and note 41.—Configuration of nebule: spherical, annular, spiral, and planetary nebule, p. 317.— Nebula (cluster of stars) in Andromeda, pp. 295—318 (note 46); nebula in Orion’s sword, pp. 297—329 (notes 12, 27, 61, 63, 67, and 68); large nebula round 7 Argis, p. 531; nebula in Sagittarius, p. 333; nebula in Cygnus and Vulpes; spiral nebula in the northern Canes Venatici, p. 323.—The two Magellanic Clouds, p. 335, (note 88).—Black spots or Coal-sacks, p- 347.

$8. The Solar region; planets and their moons, ring of the zodiacal light, and swarms of meteor-asteroids, p. 351—401.

I. The Sun considered as a central body:—Numerical data, p. 361 (note 4—6).— Physical constitution of the surface; envelopes of the dark solar globe; Sun-spots, facule, p. 362,—Diminutions in the daylight

x GENERAL SUMMARY

recorded by the annalists; problematic obscurations, p. 379 (note 22).— Intensity of the light in the centre and at the edge of the Sun’s dise p. 387 (note 24, 25).—Correlation of light, heat, electricity, and mag- netism ; Seebeck, Ampére, Faraday, p. 395.—Influence of the Sun’s spots upon the temperature of our atmosphere, p. 390.

Il. The Planets:

A. General comparative considerations: a. Principal Planets: 1, Number and epoch of discovery, p. 403.—Names, planetary

days (week), and planetary hours, p. 408 (notes 13 and 14).

2. Classification of the planets in two groups, p. 422.

3. Absolute and apparent magnitudes ; configuration, p. 426.

4. Order of the planets and their distances from the Sun; the so-called law of Titius; old belief that the cosmical bodies which we now see were not all visible from the beginning ;

Proselenes, p. 429, and notes 18—34,

5. Masses of the planets, p. 445.

6. Densities of the planets, p. 446.

7. Periods of sidereal revolution and axial rotation, p. 448.

8. Inclination of the planetary orbits and axes of rotation ; their

influence upon climate, p. 449 (note 42).

b. Secondary planets, p. 457. B. Special consideration; enumeration of the individual planets and their relation to the Sun as central body. The Sun, pp. 467—70. Mercury, pp. 470—473. Venus ; spots, pp. 473—476. The Earth; numerical relations, pp, 476—477.

The Moon of the Earth; produces light and heat ; ash-grey or earth-light in the Moon; spots; nature of the Moon’s surface, mountains and plains, measured elevations; pre- vailing type of circular configuration; craters of elevation without continuing eruptive phenomena ; old traces of the reaction of the interior upon the exterior (the surface) ; absence of Sun and Earth tides, as well of currents as transportive forces, on account of the want of a liquid element ; probable geognostic consequences of these rela- tions, pp. 477—502. :

Mars; ellipticity; appearances of surface altered by change of the seasons, pp. 502—504.

The small planets, pp. 505—510.

Jupiter : periods of rotation; spots and belts, pp. 511—515.

Satellites of Jupiter, pp. 515—d17.

OF CONTENTS. Xi

»

Saturn; bands, rings, eccentric position, pp. 517—522. Satellites of Saturn, pp, 523—524.

Uranus, pp. 524—526. Satellites of Uranus, pp. 526—527:

Neptune: discovery and elements, pp. 527—530. Satellites of Neptune, pp. 531—532.

Ill. The Comets: with the smallest masses occupying immense spaces ; configuration ; periods of revolution ; separation ; elements of the interior comets, pp. 533—560.

IV. The ring of the zodiacal light: Historical particulars.—Intermit- tence two-fold; hourly and annual ?—Distinction to be made between the cosmical luminous process which belongs to the zodiacal light itself and the variable transparency of our atmosphere.—Importance of a long series of corresponding observations under the tropics at different eleva- tions above the sea from 9 to 12,000 feet.—Refiection like that at sunset. —Comparison in the same night with certain parts of the Milky Way.—- Question as to whether the zodiacal light coinc eg with the plane of the Sun’s equator, pp. 561—565.

V. Shooting stars, fire-balls, meteoric-stones :—Qldest positively deter- mined fall of aérolites, and the influence which the fall at AZgos Potamos and its cosmical explanations exercised upon the theories of the universe of Anaxagoras and Diogenes of Apollonia (of the later Ionic school) ; force of revolution which counteracts the power of the fall (centrifugal force and gravitation), pp. 566—572 (notes 5-9).— Geometric and physical relations of meteors in sporadic and periodic falls; divergence of the shooting-stars; definite points of departure; mean number of sporadic and periodic shooting: stars in an hour in different months, pp. 572—579, notes 13—14.—Besides the stream of St. Laurentius, and the now more feeble November phenomenon, four or five other falls of shooting-stars have been discovered which very probably occur periodicaily during the year, p. 579, notes 20—21.—Height and velocity of the meteors, p. 583. —Physical relations, colour and tails, process of combination, magnitudes ; instances of the firing of buildings, p. 583.—Meteoric stones; falls of aérolites when the sky is clear, or after the formation of a small dark meteoric cloud, p. 587, notes 25 end 26.—Problematical abundance of the shooting-stars between midnight and the early hours of morning (hourly variations), p. 590.—Chemical relations of the aérolites; analogies with the constituents of telluric rock, pp. 592—596.

Conclusion:—Retrospect of the undertaking.—Limitation consistent with the nature of a physical description of the universe.—Representation of the actual relations of cosmical bodies to each other.—Kepler’s laws of planetary motion. —Simplicity of the Uranological problem in opposi- tion to the telluric, on account of the exclusion of material heterogeneity and change.—Elements of the stability of the planetary system, pp. 597 —601.

HUMBOLDT’S CORRECTIONS AND ADDITIONS

TO VOL. III.

Page 40, line 20.

Since the printing of that part of the Cosmos, where a doubt is expressed as to whether it has been ‘‘ shown with certainty that the positions of the Sun influence the terrestrial magnetism,’’ the new and excellent inves- tigations of Faraday have proved the reality of such an influence. Long series of magnetic observations in opposite hemispheres (e. g., Toronto in Canada, and Hobart Town in Van Diemen’s Land), show that the terrestrial magnetism is subject to an annual variation, which depends upon the relative position of the Sun and Earth.

Page 75, line 29.

The remarkable phenomenon of the undulation of stars has very recently been observed at Trier by very, trustworthy witnessses, in Sirius, between 7 and 8 o’clock, while near the horizon. See the letter of Herrn Flesch, in Jahn’s Unterhaltungen fiir Freunde der Astronomie.

Page 178, line 17, note 50.

The wish which I strongly expressed that the historical epoch in which the disappearance of the red colour of Sirius falls should be more positively determined, has been partially fulfilled by the laudable industry of Dr. Wépcke, a young scholar, who combines an excellent acquaintance with Oriental languages with distinguished mathematical knowledge. The translator and commentator of the important Algebra of Omar Alkhayyami, writing to me from Paris, in August, 1851, says, ‘‘ I have examined the four manuscripts in this place of the Uranography of Abdurrahman Al-Sufi, in reference to your suggestion contained in the astronomical volume of the Cosmos, and found that a Bootis, a Tauri, a Scorpii, and a Orionis, are all expressly called red; Sirius, on the contrary, is not. Moreover, the passages referring to it are uniformly as follows in atl the four manuscripts :—‘‘ The first among its (Great Dog) stars is the large, brilliant one in his mouth, which is represented on the Astrolabium, and is called Al-jemaanijah.’’ Is it not probable from this investigation, and from what I quoted from Alfragani, that the epoch of the change of colour falls between the time of Ptolemseus and the Arabs.

xiv HUMBOLDT S CORRECTIONS

Page 264, line 13.

In the condensed statement of the method by which the parallax of the double stars is found by means of the velocity of light, it should be said: The time which elapses between the moment in which the planetary secondary star is nearest to the Earth, and that in which itis most distant from it is always longer when the star passes from the point of greatest proximity to that of greatest elongation, than in the converse, when it returns from the point of greatest elongation to that of greatest proximity.

Page 289, line 1.

In the French translation of the astronomical volume of the Cosmos, which, to my great gratification, M. H. Faye has again undertaken, this learned astronomer has much enriched the section upon double stars, I had myself neglected to make use of the important treatises of M. Yvon Villarceau, which were read av the Institute in the course of the year 1849. (See Connaissance des Temps pour l’an 1832, pp. 3—128). I quote here from the table by M. Faye, of the orbital elements of eight double stars, the first four stars, which he considers to be the most certainly determined :—

Elements of the Orbits of Double Stars.

Semi Period of N f Name Eccen- | revolu- aed ¥ and Magnitude, sie tricity. | tion in mes axis. Calculator,

Years.

3/857 | 0°4164 | 58°262 | Savary ... 1830

E Urse Majoris, 3/278 | 0°3777 | 60°720 | J. Herschel 1849 (4th and 5th Mag.) | 2295 | 0°4037 | 61°300 | Miidler ... 1847 27-439 | 0°4315 | 61°576 | Y. Villarceau 1849

Ochi bi 4-328 | 0°4300 | 73°862 | Encke ... 1832 ean 4 eek 'M ) 4”-966 | 0°4445 | 92°338 | Y. Villarceau 1849 (4th an 48*) | 4-800 | 0°4781 | 92°000 | Madler ... 1849

£ Herculis; 1”-208 | 0°4320 | 30°220 | Midler ... 1847 (3rd and 65th Mag.)| 1/254 | 0°4482 | 36°357 | Y. Villarceau 1847

0”-902 | 0°2891 | 42°500 | Madler ... 1847 , n Corone, 17-012 |.0°4744 | 42°501 | Y. Villarceau 1847 (55th and 6th Mag.) 1111 | 0°4695 | 66°257 peysete 2nd

AND ADDITIONS. XV

»

The problem of the period of revolution of 7 Corone admits of two solutions: of 42°5 and 66°3 years; but the late observations of Otto Struve give the preference to the second. M. Yvon Villarceau finds the semi-major axis, eccentricity, and period of revolution, in years :

Virginis 3446 0°8699 153°787 Cancri 07-934 0°3662 58°590 a Centauri 12”:128 0°7187 78°486

The occultation of one fixed star by another, as was presented by Z Her- culis, I have called apparent (p. 287). M. Faye shows that it is a con- sequence of the spurious diameter of the stars (Cosmos, vol. iii. pp. 66 and 170,) seen in our telescopes. The parallax of 1830, Groombridge, which I gave (p. 27) as 0%°226, is fowmd by Schlttter and Wichmann, 0*°182, and by Otto Struve, 0°034

VII.

NEBULOUS SPOTS.—-ARE THESE ONLY REMOTE AND VFRY DENSE CLUSTERS OF /STARS?—THE TWO MAGELLANIC CLOUDS, IN WHICH CROWDED NEBULOUS SPOTS ARE INTERSPERSED WITH NUMEROUS STELLAR SWARMS.— THE SO-CALLED COAL-SACKS OF THE SOUTHERN HEMI- SPHERE.

Amone the visible cosmical bodies occupying the regions of space, besides those which shine with stellar light (whether self-luminous, or illumined like planets, stars isolated or in multiple groups, and revolving round a common centre of gravity), there are also masses which present a faint and milder nebulous light.' These bodies, which appear at one time as sharply defined, disc-formed, luminous clouds, at another as irregularly and variously shaped masses, widely diffused over large spaces, seem to the naked eye, at first sight, to be wholly different from those cosmical bodies of which we treated fully in the last four sections of the Astrog- nosy. In the same way that there is an inclination to infer from the observed and as yet unexplained motion of the visible cosmical bodies* the existence of others hitherto zn- visible, so the knowledge gained as to the resolvability of a considerable number of nebulous spots has recently led to

? Cosmos, vol. i. pp. 69-73, 75 and 131; vol. ii. p. 710; vol. iii. pp. 44-49, 189, 208 and 220. ® (osmos, Vol. iii. pp. 252-254.

VOL. Iv. B

292 COSMOS

conclusions regarding the non-existence of all nebule, and indeed of all cosmical vapour generally. But whether these well-defined nebulous spots be a self-luminous vapoury matter, or remote, closely-thronged globular clusters of stars, they must ever remain objects of vast importance in the knowledge of the structure of the universe and of the contents of space. The number whose positions have been determined by right ascension and declination, exceeds 3,600. Some of the more irregularly diffused, measure eight lunar diame- ters. According to William Herschel’s earlier estimate, made in 1811, these nebulous spots cover at least 335th part of the whole visible firmament. As seen through colossal telescopes, the contemplation of these nebulous masses leads us into regions from whence a ray of light, according to an assumption not wholly improbable, requires millions of years to reach our earth, to distances for whose measurement the dimensions (the distances of Sirius, or the calculated distances of the binary stars in Cygnus and the Centaur) of our nearest stratum of fixed stars scarcely suffice. If these nebulous spots be elliptical or spherical sidereal groups, their very conglomeration calls to mind the idea of a mysterious play of gravitating forces by which they are governed, If they be vapoury masses, having one or more nebulous nuclei, the various degrees of their conden- sation suggest the possibility of a process of gradual star- formation from inglobate matter. No other cosmical structure —no other subject of this branch of astronomy more contem- plative than measuring—is, in like degree, adapted to excite the imagination, not merely as a symbolic image of the infi- nitude of space, but because the investigations of the different conditions of existing things, and of their presumed connection

? Cosmos, vol. i. p. 68.

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of sequence, promises to afford us an insight into the laws of genetic development.

The historical development of our knowledge of nebulous bodies teaches us that here, as in the progress of almost every other branch of physical science, the same opposite opinions, which still have numerous adherents, were maintained long since, although on weaker grounds. Since the general use of the telescope, we find that Galileo, Dominique Cassini, and the sagacious John Michell, regarded all nebule as remote clusters of stars; whilst Halley, Derham, Lacaille, Kant, and Lambert, maintained the existence of starless nebulous masses. Kepler (like Tycho Brahe before the invention of the tele- scope) was a zealous adherent of the theory of star-formation from cosmical vapour—from condensed conglobate celestial nebulous matter. He believed “‘ cal: materiam tenuissimam (the vapour which shines with a mild stellar light in the Milky Way,) ex unum globum condensatam, stellam effingere,” and grounded his opinion, not on the process of condensation operating in defined roundish nebulous spots, (for these were unknown to him,) but on the sudden appearance of new stars on the margin of the Galaxy.

If we take into account the number of objects discovered, the accuracy of their telescopic investigation, and the gene- ralization of views, the history of nebulous spots, like that of double stars, may be said to begin with William Herschei, Until his time there were not more than 120 unresolved nebuke in both hemispheres, whose positions were deter- mined, including even the results of Messier’s meritorious labours; and in 1786 the great astronomer of Slough pub- lished the first catalogue, containing 1000. I have already fully pointed out in an earlier portion of this work that the bodies named nebulous stars (vededoedets) by Hipparchus and Geminus in the Cafasterisms of the pseudo-Eratosthenes

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and in the Almagest of Ptolemy, are stellar clusters which ap- pear to the naked eye with a nebulous lustre. This designa- tion, latinized nebulose, passed in the middle of the thirteenth century into the Alphonsine Tables, probably through the pre- ponderating influence of the Jewish astronomer, Isaac Aben Sid Hassan, Chief Rabbi of the wealthy synagogue at Toledo. The Alphonsine Tables first appeared in print in 1483 at Venice.

The first notice of a remarkable aggregation of innumerable true nebulous spots, blended with stellar swarms, dating from the middle of thetenth century, is in the writings of an Ara- bian astronomer, Abdurahman Sufi, a native of the Persian Trak, The White Ox, which he saw shining with a milky light far below Canopus, was undoubtedly the larger Magel- lanic cloud, which with an apparent breadth of nearly twelve lunar diameters, extends over a portion of the heavens mea~ suring forty-two square degrees. No mention is made by European travellers of this phenomenon until the beginning of the sixteenth century, although, 200 years earlier, the Normans had advanced as far along the Western coasts of Africa as Sierra Leone (8° 30’ N. Lat.) It might have been expected that a nebulous mass of such vast extent,

* Cosmos, vol. iii. pp. 121 and note, and 190 and note.

6 Prior to the expedition of Alvaro Becerra. The Por- tuguese advanced beyond the equator in 1471. See Hum- boldt’s' Examen critique de UV Hist. de la Géographie du Nouveau Continent, tom. i. pp. 290-292. In eastern Africa the Lagides had availed themselves, for purposes of commerce, of the passage along the Indian Ocean, and, favoured by the south-west monsoon (Hippalus), had passed from Ocelis in the Straits of Bab-el-Mandeb to the Malabar emporium of Muziris and to Ceylon (Cosmos, vol. ii. p. 539, and note), Althougn the Magellanic Clouds must have been seen in all these voyages, we incet with no record of their appearance.

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which was distinctly visible to the naked eye, would have attracted attention sooner.®

The first ¢solated nebula which was observed and recognized by the telescope as wholly starless and as an object of special nature was the nebula near »v Andromedsz, which, like that last mentioned, is also visible to the naked eye. Simon Marius (Mayer of Gunzenhausen, in Franconia), originally a musician, and subsequently Court mathematician of one of the Mar- graves of Colmbach, the same person who saw the satellites of Jupiter nine days earlier than Galileo,’ has also the merit

* Sir John Herschel, Observations at the Cape, § 132.

7 Op. cit. pp. 357, 509 (note 43). Galileo, who endea- voured to refer the difference in the days of discovery (29th of December, 1609, and 7th of January, 1610,) to a differ- ence in the calendar, maintained that he had seen the satel- lites of Jupiter one day éarlier than Marius, and even allowed himself to be so far carried away by his indignation at ‘“ the falsehood of the heretical impostor of Gutzenhausen”’ (“bugia del impostore eretico Guntzenhusano,”) as to declare his belief ** that very probably the heretic, Simon Marius, never observed the Medicean planets,” (‘‘ che molto probabilmente tl eretico, Simon Mario, non ha osservato giammat i Pianeti Medicet.”’\— See Opere di Galileo Galilei, Padova, 1744, tom. ii. pp. 235- 237; and Nelli, Vita e Commercio letterario di Galilei, 1793, vol. i. pp. 240-246. The “heretic” had nevertheless expressed himself very pacifically and modestly in reference to the extent of merit due to his discovery. ‘I simply affirm,’ says Simon Marius, in the preface to the Mundus Jovialis, “hee sidera (Brandenburgica) a nullo mortalium mihi ulla ratione commonstrata, sed. propria indagine sub ipsissimum fere tempus, vel aliquanto citius quo Galilzus in Italia ea primum yidit, a me in Germania adinventa et obser- vata fuisse. Merito igitur Galileo tribuitur et mane laus prime inventionis horum siderum apud Italos. An autem inter meos Germanos quispiam ante me ea invencrit et viderit, hactenus intelligere non potui.” ‘I simply affirm that I was

296 COSMOS.

of having given the first, and indeed a very accurate descrip- tion ofa nebula. In the preface to his Mundus Jovialis,® he relates, that “‘on the 15th of December, 1612, he observed a fixed object differing in appearance from any he had ever seen. It was situated near the 3rd and northern star of Andromeda’s girdle; seen with the naked eye, it appeared to him to be a a mere cloud, and by the aid of the telescope he could not discover any signs of a stellar nature, a circumstance which distinguished it from the nebulous stars in Cancer, and from other nebulous clusters. All that could be recognized was a whitish glimmering appearance, brighter in the centre, and fainter towards the margins. With a diameter of 4 of a degree, the whole resembled a light seen from a great dis- tance through half-transparent horn plates: (s¢milis fere splendor apparet, si a longinguo candela ardens per cornu pel= lucidum de noctu cernatur).” Simon Marius hazards a con- jecture whether this singular star be not of recent formation, but will not give a decided opinion, although it strikes him as singular that Tycho Brahe, who had enumerated all the stars in the girdle of Andromeda, should have said nothing of this nebulosa. The Mundus Jovialis, which first appeared in 1614, indicates, therefore, as I have already observed elsewhere,* the

led to the discovery of these stars not by any reasonings of uthers, but by the result of my own investigations, and that they were observed by me in Germany, about the very same time or a little sooner than Galileo first saw them in Italy. To Galileo, among the Italians, is therefore due the merit of having first discovered these stars. But whether, among my own countrymen in Germany, any person before me has dis- covered and seen them, I have not as yet been able to ascer- tain.”

8 Mundus Jovialis. anno 1609, detectus ope perspicilli Bel- gict. (Noribergz, 1614.)

* Cosmos, vol. ii. p. 702.

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difference between a nebulous spot unresolvable by the telese copic powers of that age, and a cluster of stars,* to which the - mutual proximity of its numerous small stars, not visible to the naked eye, imparts a nebulous lustre. Notwithstanding the great improvements made in optical instruments, the nebula in Andromeda was considered for nearly two centuries . and a half—as at its discovery—to be wholly devoid of stars, until two years since, the transatlantic observer, George Bond, of Cambridge in Massachusetts, discovered 1,500 small stars within the limits of the nebula. I have not hesitated to class it amongst the stellar clusters, although the nucleus has not hitherto been resolved.”

It is probably only to be ascribed to some singular accident that Galileo, who, when the Sidereus Nuntius appeared in 1610, had already made frequent observations of the constellation of Orion, should have subsequently mentioned, in his Saggiatore, no other nebule in the firmament but those which his own weak optical instruments had resolved into stellar clusters, although he might long before have learnt, through the Mundus Jovialis of the discovery of the starless nebula in Andro- meda. When