. i i It tsumurJaa ,Iami:s Dickson Clark W. C. I B -4- S -j&HlBlttil >"' ^^ ^ GEOL. LIS. COSMOS: A SKETCH OP A PHYSICAL 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. Naturae 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. VOL. IV. NEW YORK: HARPER & BROTHERS, PUBLISHERS, 329 & 331 PEARL STREET, FRANKLIN SQUARE. 185 6. SUMMARY. Vols. III. and IV. GENERAL SUMMARY OF THE CONTENTS. Special Results of Observation in the Domain of Cosmical Phenomena.- Introduction. Retrospect of the subject. Nature considered under a two-fold as pect : 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 imagina- tion. Besides an actual or external woi'ld, there is produced an ideal or an inner world ; filled with physical symbolic myths, different ac- cording to race and climate, bequeathed for centuries to subsequent generations, and clouding a clear view of nature. Fundamental im- perfectibility 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. Dif- ferent phases of the theory of the universe, attempts to comprehend the order of nature. Most ancient fundamental conception of the Hellenic mind: physiologic phantasies of the Ionian school, germs of the scien- tific contemplation of nature. Double direction of the explanation of natural phenomena, by the assumption of material principles (elements), and by processes of rarefaction and condensation. Centrifugal revolu- tion. Theories of vortices. The Pythagoreans ; philosophy of meas- ure and harmony, commencement of a mathematical treatment of phys- ical phenomena. The order and government of the universe according to the physical works of Aristotle. The communication of motion con- sidered 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 Nature of Vincentz of Beauvais, Liber Cosmographicus of Albertus Magnus, Imago Mundi of the Cardinal Pierre d'Ailly. Progress through Giordano Bru- no and Telesio. Clearness in the conceptions of gravitation as mass at- traction, by Copernicus. First attempt at a mathematical application of the doctrine of gravitation, by Kepler. The work on the Cosmos by Descartes (Traits du Monde) nobly undertaken, did not appear until long after his death, and only in fragments; the Cosmotheoros of Huy- gens, unworthy of the great name. Newton, and his work Philosophic Naturalis Principia Mathematica. Endeavor toward 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 IV GENERAL SUMMARY formative activities in the organic and animated bodies? What has been discovered does not by a long way exhaust the discoverable. The imperfectibility of empiric investigation makes the problem of ex- plaining the changeability of matter from the forces of matter an indef- inite one. A. Uranological Portion of the Physical Description of the Uni- verse— p. 26-28. Two sections, one of which comprises the heaven of fixed stars; the other, our solar system — p. 26. a. Astrognosy ; Heaven of the fixed stars. I. The realms of space, and conjectivres regarding that which appears to occupy the space intervening between the heaven- ly bodies — p. 29-41. II. Natural and telescopic vision— p. 49-72 ; Scintillation of the stars — 73-83 ; Velocity of light — p. 84-88 ; Results of photom- etry— p. 89-102. Order of the fixed stars according to their luminous intensity. III. Number, distribution, and color of the fixed stars — p. 103- 139 ; Stellar clusters (stellar swarms) — p. 140-143 ; The Milky Way interspersed with afeto nebulous spots — p. 144-151. IV. New stars, and stars that have vanished — p. 151-160; Va- riable stars, whose recurring periods have been determined — p. 160-177 ; Variations in the intensity of the light of stars whose periodicity is as yet uninvestigated — p. 177-182. V. Proper motion of the fixed stars — p. 182-185 ; Problematical existence of dark cosmical bodies — p. 185-187; Parallax — measured distances of some of the fixed stars — p. 187-194; Doubts as to the assumption of a central body for the whole sidereal heavens — p. 195-199. VI. Multiple, or double stars — Their number and reciprocal dis tances. Period of revolution of two stars round a common center of gravity — p. 199-213. VII. Nebulous spots. Are these only remote and very dense clusters of stars? The two Magellanic Clouds, in which crowded nebulous spots are interspersed with numerous stel- lar swarms. The so-called black spots (Coal-sacks) of the Southern hemisphere — p. 13-53 0. Solar Region — p. 53-134. I. The Sun considered as the central body — p. 59-88. II. The Planets— p. 88-134. A. General consideration of the planetary world — p. 88-134. a. Principal Planets — p. 89-131. b. Secondary Planets — p. 131-134. B. Special enumeration of the planets and their moons as parts of the solar system — p. 134. Sun— p. 135-137. OF CONTENTS. V Mercury — p. 137, 138. Venus— p. 138-141. Earth— p. 141. Moon of the Earth — p. 141-159. Mars— p. 159, 160. The small planets — p. 1G1; Flora, Victoria, Vesta, Iris, Metis, Hebe, Parthenope, Astraea, Egeria, Irene, Euno- mia, Juno, Ceres, Pallas, Hygeia ; Jupiter— p. 165-168. Satellites of Jupiter— p. 169, 170. Saturn— p. 170-174. Satellites of Saturn— p. 174, 175. (Jranus— p. 175, 176. Satellites of Uranus — p. 176, 177. Neptune— p. 177-180. Satellites of Neptune — p. 180, 181. III. The comets— p. 181-201. IV. Ring of the zodiacal light— p. 201-204. V. Shooting stars, fire-balls, meteoric stones — p. 204-226 Conclusion— p. 227-230. Corrections and additions to vol. hi., p. xi., xii. Index, p. 231-234. Special analysis of the individual sections of the astronomical part of the Cosmos. a. ASTKOGNOSY. I. Cosmical space' Only isolated portions are measurable — p. 30. Resisting medium, celestial atmosphere, cosmical ether — p. 31, note t, and p. 33, note *. Radiation of heat by the stars — p. 35, note %. Tem- perature of space — p. 37-39. Limited transparency? — p. 48. Regu- larly decreased period of revolution of the Comet of Encke — p. 39. Limitation of the atmosphere? — p. 40. II. Natural and telescopic vision : Very different sources of light pre- sent similar relations of refraction — p. 44. Different velocities of the light of ignited solid bodies and that of frictional electricity — p. 45. Position of the Wollastonian lines — p. 45. Influence of tubes — p. 43. Optical means of distinguishing between direct and reflected light, and the importance of the means to physical astronomy — p. 45. Limits of ordinary vision — p. 48. Imperfection of the organ of vision ; false di- ameter of the stars — p. 52. Influence of the form of an object upon the minimum visual angle in experiments as to visibility; necessity of a dif- ference of luminous intensity of J^ ; visibility of distant objects, posi- tively and negatively — p. 48-56. On the visibility of stars by day with the naked eye from wells or upon lofty mountains — p. 56. A feeble light by the side of a stronger — p. 49, note *. Extending ray and star tails — p. 52. On the visibility of the satellites of Jupiter by the naked eye — p. 50. Undulation of the stars — p. 59. Commencement of tel- escopic vision; application to measurement — p. 60-62. Refractors of great length — p. 63. Reflectors — p. 63. Day observations; how strong magnifying powers facilitate the finding of the stars by day — p. 66. VI GENERAL SUMMARY Explanation of the sparkling and scintillation of the 6tars — p. 73. Ve- locity of light — p. 79-88. Order of magnitude of the stars; photomet- ric relations and methods of measurement — p. 89-98. Cyanometer — p. 97. Photometric order of the fixed stars — p. 99-102. III. Number, distribution, and color of the fixed stars ; Stellar clusters and the Milky Way : States of the sky which hinder or favor the de- tection of stars — p. 103. Number of the stars ; how many may be seen with the naked eye — p. 104. How many have been inserted in stellar charts with determinations of position — p. 108. Conjectural estimation of the number of stars which can be visible in the entire heavens with our present powers of penetrating space — p. 105. Contemplative as- trognosy of uncivilized people — p. 109. The Grecian sphere — p. 118. The crystal sky — p. 123. False diameter of the fixed stars in telescopes — p. 129. Smallest objects in the heavens which have yet been seen — p. 130. Difference of colors in the stars, and the changes which have taken place in the colors since antiquity — p. 130. Sirius (Sothis) — p. 132. The four royal stars — p. 136. Gradual acquaintance with the Southern heaven — p. 137. Distribution of the fixed stars, laws of rela- tive accumulation, gauging — p. 138. Clusters and swarms of stars — p. 140. The Milky Way— p. 143. IV. Stars that have neicly appeared and disappeared ; variable stars and changes in the intensity of their light tohose periodicity has not been investigated : New stars in the last 2000 years — p. 151. Periodically changeable stars: Historical particulars — p. 151. Color — p. 165. Num- ber— p. 164. Order recognizable in apparent irregularity; great dif- ferences of brightness ; periods within periods — p. 167. Argelander's table of the variable stars with commentary — p. 172. Variable stars in undetermined periods (rj Argus, Capella, stars of the Ursa? Major and Minor) — p. 181. Reference to the possible changes of temperature on the Earth's surface — p. 181. 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. 182. Amount of the proper motion — p. 184. Evidence in favor of the probable existence of non-luminous bodies — p. 186. Parallax and measurement of the dis- tance of some fixed stars from our solar system — p. 187. The aberra- tion of light may be applied to the determination of the parallax of double stars — p. 194. 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 — p. 184 and 194. Problem of the situation of the center of gravity of the whole heaven of fixed stars and central suns? — p. 196, and note \, p. 198, and p. 199, note *. VI. Double stars, period, of revolution of two suns round a common center of gravity : Optical and physical double stars — p. 200; number — p. 201. Uniformity and difference of color ; the latter not the conse- quence of optical deception, of the contrast of complementary colors — p. 207, note *, p. 206, and p. 209, note *. Change of brightness— p. 209. Multiple combinations (three to six fold) — p. 209. Calculated orbitual elements, half major axis and period of rotation in years — p. 213. VII. Nebulce, Magellanic Clouds, and Coal-sacks : Resolvability of tho nebula?; questions as to whether they are all remote and crowded OF CONTENTS. Vll clusters of stars ? — p. 13 (note §, p. 22, and p. 23, note *"). Historical particulars — p. 14 (note *, p. 28). Number of nebulae whose positions are determined — p. 26 (notes * and +). Distribution of nebula; and clusters of stars in the northern and southern hemispheres — p. 27 ; spaces poor in nebulae, and the maxima of accumulation — p. 28, and note *. Configuration of nebulae: spherical, annular, spiral, and plan- etary nebula; — p. 31. Nebula (cluster of stars) in Andromeda — p. 16- 31 (note t, p. 31); nebula in Orion's sword — p. 17-39 (notes *, p. 18, t, p. 23, §, p. 36, *, p. 38, §, p. 39, and *, p. 40) ; large nebula round 7/ Argus — p. 40 ; nebula in Sagittarius — p. 41 ; nebula in Cygnus and Vul- pes ; spiral nebula in the northern Canes Venatici — p. 41. The two Ma- gellanic Clouds — p. 43 (note *, p. 48). Black spots or Coal-sacks — p. 5 1 . (3. The Solar region ; planets and their moons, ring of the zodiacal light, and swarms of meteor-asteroids — p. 53-88. I. The Sun considered as a central body : Numerical data — p. 59 (note *, p. 59, and p. 62, note *). Physical constitution of the surface; en- velopes of the dark solar globe ; Sun-spots, faculae — p. 61. Diminutions in the daylight recorded by the annalists ; problematic obscurations — p. 73, and note. Intensity of the light in the center and at the edge of the Sun's disk — p. 79, and note; also p. 81, note *. Correlation of light, heat, electricity, and magnetism ; Seebeck, Ampere, Faraday — p. 84. Influence of the Sun's spots upon the temperature of our at- mosphere— p. 80. II. The Planets : A. General comparative considerations : a. Principal Planets : 1. Number and epoch of discovery — p. 89. Names, planetary days (week), and planetary hours — p. 92, and note t; also p. 94, note *. 2. Classification of the planets in two groups — p. 102. 3. Absolute and apparent magnitudes; configuration — p. 105. 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. 106, note *, p. 108, and p. 120, note *. 5. Masses of the planets — p. 118. 6. Densities of the planets — p. 119. 7. Periods of sidereal revolution and axial rotation — p. 120. 8. Inclination of the planetary orbits and axes of rotation ; their influence upon climate — p. 121, and note t, p. 126. b. Secondary planets — p. 127. B. Special consideration ; enumex-ation of the individual planets and their relation to the Sun as central body. The Sun—]). 135-137. Mercury— p. 137, 138. Venus; spots — p. 138-141. Tks Earth; numerical relations — p. 141. Vlll GENERAL SUMMARY The Moon of the Earth ; produces light and heat ; ash-gray 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 sur- face) ; absence of Sun and Earth tides, as well of current* as transportive forces, on account of the want of a liquid element ; probable geognostic consequences of these re- lations— p. 141-159. Mars ; ellipticity ; appearances of surface altered by change of the seasons — p. 159, 160. The small planets — p. 161, 162. Jupiter : periods of rotation ; spots and belts — p. 165-168. Satellites of Jupiter — p. 169, 170. Saturn : bands, rings, eccentric position — p. 170-174. Satellites of Saturn — p. 174, 175. Uranus — p. 175, 176. Satellites of Uranus — p. 176, 177. Neptune: discovery and elements — p. 177-181. Satellites of Neptune — p. 181-201. III. The Comets : with the smallest masses occupying immense spaces ; configuration ; periods of revolution ; separation ; elements of the interior comets — p. 181-201. 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 it- self and the variable transparency of our atmosphere. Importance of a long series of corresponding observations under the tropics at different elevations above the sea from 9 to 12,000 feet. Reflection like that at sunset. Comparison in the same night with certain partsrf>f the Milky Way. Question as to whether the zodiacal light coincides with the plane of the Sun's equator — p. 201-204. V. Shooting stars, fire-balls, meteoric stones : Oldest positively determ- ined fall of aerolites, and the influence which the fall of /Egos Potamos and its cosmical explanations exercised upon the theories of the uni- verse 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) — p. 204-209, note ], p. 207, and p. 209, note *. 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 — p. 209-214, note \, p. 210, and p. 211, note *. Besides the stream of St. Laurentius, and the now more feeble Novem- ber phenomenon, four or five other falls of shooting stars have been discovered which very probably occur periodically during the year — p. 214, note *, p. 215, and p. 216, note *. Height and velocity of the meteors — p. 217. Physical relations, color and tails, process of com- bination, magnitudes; instances of the firing of buildings — p. 217. Me- teoric stones; falls of aerolites when the sky is clear, or after the for- mation of a small dark meteoric cloud — p. 220, note +, and p. 221. note *. OF CONTENTS. IX Problematical abundance of the shooting stars between midnight and the early hours of morning (hourly variations) — p. 222. Chemical re- lations of the aerolites ; analogies with the constituents of telluric rock —p. 223-226. Conclusion : Retrospect of the undertaking. Limitation consistent with the nature of a physical description of the universe. Representa- tion of the actual relations of cosmical bodies to each other. Kepler's laws of planetary motion. Simplicity of the uranological problem in opposition to the telluric, on account of the exclusion of material hete- rogeneity and change. Elements of the stability of the planetary sys* tern— p. 227-230. A 2 HUMBOLDT'S CORRECTIONS AND ADDITIONS TO VOL. III. Page 34, line 22. Since the printing of that part of the Cosmos where a doubt is ex- pressed as to whether it has been " shown with certainty that the posi- tions of the Sun influence the terrestrial magnetism," the new and ex- cellent investigations of Faraday have proved the reality of such an in- fluence. Long series of magnetic observations in opposite hemispheres (c. 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 59, line 2. The remarkable phenomenon of the undulation of stars has veiy re cently been observed at Trier by very trustworthy witnesses, in Sirius, between 7 and 8 o'clock, while near the horizon. See the letter of Herrn Flesch, in Jahn's Unterhaltungen fur Freunde der Astronomic Page 132, line 21, note *. The wish which I strongly expressed that the historical epoch in which the disappearance of the red color of Sirius falls should be more positively determined, has been partially fulfilled by the laudable in- dustry of Dr. Wopcke, a young scholar, who combines an excellent ac- quaintance with Oriental lauguages 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 all 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-jemaanijak." Is it not probable from this investigation, and from what I quoted from Alfragani, that the epoch of the change of color falls between the time of Ptolemfeus and the Arabs. Page 194, line 21. 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 b» Xll HUMBOLDT S CORRECTIONS AND ADDITIONS. said, The time which elapses between the moment in which the plane- tary secondary star is nearest to the Earth, and that in which it is 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 213, 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 at the Institute in the course of the year 1849. (See Connaissance des Temps pour Van 1832, p. 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 cer- tainly determined : Elements of the Orbits of Double Stars. Name and Magnitude. Semi- major axis. „ Period of £?c.?n- 'revolution t™1^'- in Years. Name of the Calcu- lator. f Ursse Majoris, (4th and 5th Mag.) 3"-857 3"-278 2"-295 2"-439 0-4164 0-3777 0-4037 0-4315 58-262 60-720 61-300 61-576 Savaiy 1830. J. Herschel..l849. Madler 1847. Y. Villarceau 1849. p Ophiuchi, (4th and 6th Mag.) 4"-328 4"-966 4"-800 0-4300! 73-862 0-4445 92-338 0-4781 92-000 Encke 1832. Y. Villarceau 1849. Madler 1849. £ Herculis, (3d and 6 -5th Mag.) l"-208 l"-254 0-4320 0-4482 30-220 36-357 Madler 1847. Y. Villarceau 1847. 7] Coronae, (5-5thand6thMag.) 0"-902 1"-012 1"-111 0-2891 0-4744 0-4695 42-500 42-501 66-257 Madler 1847. Y. Villarceau 1847. The same, 2d result. The problem of the period of revolution of -n Coronas 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 periods of revolution in years. yVirginis 3"-446 0-8699 153-787 \ Cancri 0"-934 0-3662 58-590 a Centauri 12"-128 0-7187 78-486 The occupation of one fixed star by another, as was presented by £ 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. hi., p. 66 and 170) seen in our telescopes. The parallax of 1830, Groombridge, which I gave (p. 27) as 0"-226, is found by Schlliter and Wichmann, 0"182, and by Otto Struve, 0"-034. COSMOS. VII. NEBULOUS SPOTS. ARE THESE ONLY REMOTE AND VERY DENSE CLUSTERS OF STARS ? THE TWO MAGELLANIC CLOUDS, IN WHICH CROWDED NEBULOUS SPOTS ARE IN- TERSPERSED WITH NUMEROUS STELLAR SWARMS. THE SO- CALLED COAL-SACKS OF THE SOUTHERN HEMISPHERE. Among the visible cosmical bodies occupying the regions of space, besides those which shine with stellar light (wheth- er self-luminous, or illumined like planets, stars isolated or in multiple groups, and revolving round a common center of gravity), there are also masses which present a faint a?id milder nebulous light* These bodies, which appear at one time as sharply defined, disk-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 vis- ible cosmical bodies,! the existence of others hitherto invisi- ble, so the knowledge gained as to the resolvability of a con- siderable number of nebulous spots has recently led to con- clusions regarding the non-existence of all nebulae, and, in- deed, of all cosmical vapor generally. But whether these well-defined nebulous spots be a self-luminous vapory mat- ter, or remote, closely-thronged globular clusters of stars, they must ever remain objects of vast importance in the knowl- edge of the structure of the universe and of the contents of space. The number whose positions have been determined by riffht ascension and declination exceeds 3600. Some of the it- Cosmos, vol. i., p. 85-89, 91, and 142; vol. ii., p. 328; vol. iii., p 37-41, 140, 154, and 162. r Cosmos, vol. hi., p. 185, 186 14 COSMOS. more irregularly diffused measure eight lunar diameters. Ac cording to William Herschel's earlier estimate, made in 1811, these nebulous spots cover at least g-y^th Pal't °f 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 bi- nary stars in Cygnus and the Centaur) of our nearest stra- tum of fixed stars scarcely suffice. If these nebulous spots be elliptical or spherical sidereal groups, their very conglom- eration calls to mind the idea of a mysterious play of gravi- tative forces by which they are governed. If they be vapory masses, having one or more nebulous nuclei, the various de- grees of their condensation suggest the possibility of a process of gradual star-formation from inglobate matter. No other cosmical structure — no other subject of this branch of astron- omy more contemplative than measuring — is, in like degree, adapted to excite the imagination, not merely as a symbolic image of the infinitude of space, but because the investiga- tion of the different conditions of existing things, and of their presumed connection of sequences, promises to afford us an in- sight 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 acute John Michell regarded all nebulae as remote clusters of stars ; while Halley, Derham, Lacaille, Kant, and Lambert maintained the existence of starless nebulous mass- es. Kepler (like Tycho Brahe before the invention of the telescope) was a zealous adherent of the theory of star-forma- tion from cosmical vapor — from condensed conglobate celes- tial nebulous matter. He believed " cozli materiam tenuis- si?na?n (the vapor which shines with a mild stellar light in the Milky Way) in unum globum co?idensatam, stellam ef- fingered and grounded his opinion, not on the process of con- densation 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. * Cosmos, vol. i., p. 84. NEBULjE. 15 If we take into account the number of objects discovered, the accuracy of their telescopic investigation, and the gener alization of views, the history of nebulous spots, like that ot double stars, may be said to begin with William Herschel. Until his time there were not more than 120 unresolved neb- ulae in both hemispheres whose positions were determined, including even the results of Messier's meritorious labors ; and in 1786 the great astronomer of Slough published the first catalogue, containing 1000. I have already fully point ed out, in an earlier portion of this work, that the bodies named nebulous stars (vecpeXoeidelc) by Hipparchus and Geminus in the Catasterisms of the pseudo-Eratosthenes and in the Almagest of Ptolemy, are stellar clusters which appear to the naked eye with a nebulous luster.^ This des- ignation, Latinized nebulosce, passed in the middle of the thirteenth century into the Alphonsine Tables, probably through the preponderating influence of the Jewish astrono- mer, Isaac Aben Sid Hassan, chief Rabbi of the wealthy synagogue at Toledo. The Alphonsine Tables were first printed in 1483 at Venice. The first notice of a remarkable aggregation of innumer- able true nebulous spots, blended with stellar swarms, dating from the middle of the tenth century, is in the writings of an Arabian astronomer, Abdurrahman Sufi, a native of the Per- sian Irak. The White Ox, which he saw shining with a milky light far below Canopus, was undoubtedly the larger Magellanic Cloud, which, with an apparent breadth of nearly twelve lunar diameters, extends over a portion of the heav- ens measuring forty-two square degrees. No mention is made by European travelers of this phenomenon until the begin- ning of the sixteenth century, although, 200 years earlier, the Normans had advanced as far along the western coasts of Af- rica as Sierra Leone (8° 30' N. Lat.).f It might have been expected that a nebulous mass of such vast extent, which * Cosmos, vol. iii., p. 91, and note, and 140, and note. t Prior to the expedition of Alvaro Becerra. The Portuguese ad- vanced beyond the equator in 1471. — See Humboldt's Examen Critique de VHist. de la Ge"ographie dn Nouveau Continent, torn, i., p. 290-292 In Eastern Africa the Lagides had availed themselves, for purposes of commerce, of the passage along the Indian Ocean, and, favored by the southwest 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. 172, and note). Although the Magellanic Clouds must have been seen in all these voyages, we meet with no record of their appearance. 16 COSMOS. was distinctly visible to the naked eye, would have attracted attention sooner.* The first isolated nebula which was observed and recog- nized by the telescope as wholly starless and as an object of special nature was the nebula near v Andromeda^, 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 Margraves of Colmbach, the same person who saw the sat- ellites of Jupiter nine days earlier than Galileo,! has also the merit of having given the first, and, indeed, a very accurate description of a nebula. In the preface to his Mundus Jovi- alis,X 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 3d and northern star of Andromeda's girdle ; seen with the naked eye, it ap- peared to him to be a mere cloud, and by the aid of the tel- escope he could not discover any signs of a stellar nature, a * Sir John Herschel, Observations at the Cape, § 132. t Op. cit., p. 357, 509 (note 43). Galileo, who endeavored to refer the difference in the days of discovery (29th of December, 1609, and 7th of January, 1610) to a difference in the calendar, maintained that he had seen the satellites of Jupiter one day earlier 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 im- postore eretico Guntzenhusa?io") as to declare his belief " that very prob- ably the heretic, Simon Marius, never observed the Medicean planets" (" che molto probabilmente il eretico, Simon Mario, non ha osservato gi- ammai iPianeti Medicei"). — See Operedi Galileo Galilei, Padova, 1744, torn, ii., p. 235-237; and Nelli, Vita e Commercio letterario di Galilei, 1793, vol. i., p. 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, "haec sidera (Brandenburgica) a nullo mortalium mihi ulla ratione commonstrata, sed propria indagine sub ip- sissimum fere tempus, vel aliquanto citius quo Galilaeus in Italia ea pri- mum vidit, a me in Germania adinventa et observata fuisse. Merito igitur Galilgeo tribuitur et manet laus primae inventionis horum side- rum apud Italos. An autem inter meos Germanos quispiam ante me ea invenerit et viderit, hactenus intelligere non potui." " I simply af- firm that I was led to the discovery of these stars, not by any reason- ings of others, but by the result of my own investigations, and that they were observed by me in Germany about the very same time, or a lit- tle 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 be- fore me has discovered and seen them, I have not as yet been able to ascertain." X Mundus Jovialis, anno 1609, deteclus ope pertpicilli Belgici. (Nori bergae, 1614.) NEBULvE. 17 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, bright- er in the center, and fainter toward the margins. With a di- ameter of one fourth of a degree, the whole resembled a light seen from a great distance through half-transparent horn plates (similis fere splendor apparet, si a longinquo cande- la ardens per comic pellucidum de noctu cernatur)." Si- mon Marius hazards a conjecture whether this singular star be not of recent formation,#but will not give a decided opin- ion, 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 Jo- vialis, which first appeared in 1614, indicates, therefore, as I have already observed elsewhere,*1 the difference between a nebulous spot unresolvable by the telescopic 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 luster. Notwithstanding the great improvements made in optical instruments, the nebula in Andromeda was considered for nearly two centuries and a half — as at its dis- covery— to be wholly devoid of stars, until two years since, the transatlantic observer, George Bond, of Cambridge, in Massa- chusetts, discovered 1500 small stars within the limits of the nebula. I have not hesitated to class it among the stellar clusters, although the nucleus has not hitherto been resolved 4 It is probably only to be ascribed to some singular acci- dent that Galileo, who, when the Sidereus Nuntius appear- ed in 1610, had already made frequent observations of the con- stellation of Orion, should have subsequently mentioned, in his Saggiatore, no other nebulae in the firmament but those which his own weak optical instruments had resolved into stellar clusters, although he might long before have learned, through the Mundus Jovialis, of the discovery of the starless nebula in Andromeda. When he speaks of the nebulose del Orione e del Prescpe, he understands by the expression merely "aggregations (coacervazioni) of innumerable small stars. "$ He successively delineates, under the deceptive designations of nebidosce capitis, cinguli, et ensis Orionis, clusters of stars, * Cosmos, vol. ii., p. 320. t Germ., Sternhaufen ; French, amas d'etoiles. t Cosmos, vol. iii., p. 142. § Galilei notd che le Nebulose di Orione null1 altro erano die mucchi e coacervazioni (V innumerabili Stelley — Nelli, Vita di Galilei, i., p. 208- 18 COSMOS. in which he exults in having discovered 400 hitherto unob- served stars in a space of one or two degrees. He never makes any reference to unresolved nebulous matter. Yet how could the great nebulous spot in the sword of Orion have failed to rivet his attention ? But, although this great ob- server probably never saw the irregular nebula in Orion, or the roundish disk of a so-called irresolvable nebula, still his general views^ on the intrinsic nature of nebulous spots were very similar to those to which the greater number of our astronomers of the present day in-line. Like Galileo, Hevel of Dantzig, who, although a distinguished observer, was not much inclined to rely upon telescopic observation for aid in cataloguing the stars,! made no mention in his writings of the great nebula in Orion. His star catalogue, moreover, did not contain upward of 16 nebulous spots, of which the posi- tions were accurately determined. At length, in the year 1656, Huygens discovered the neb- * " In primo integram Ononis constellationem pingere decreveram ; vero, ab ingenti stellarum copia, temporis vero inopia obrutus, aggres- eionem hanc in aliam occasionem distuli. Cum non tan turn in Galaxia Lacteus ille candor veluti albicantis nubis spectetur, sed complures con- similis coloris areolee sparsim per cethera subfulgeant, si in illarum, quam- libet specillum convertas, stellarum constipatarum ccetum offendes. Amplius (quod magis mirabile) stellae, ab astronomis singulis in hanc usque diem nebulosce appellatae, stellarum minim in modum consitarum gregessuut : ex quarum radiorum commixtione, dum unaquaque ob ex- ilitatem, seu maximam a nobis remotionem, oculorum aciem lugit, can- dor ille consurgit, qui densior pars coeli, stellarum aut solis radios re- torquere valens, hucusque creditus est." — Opere di Galileo Galilei, Pa- dova, 1744, torn, ii., p. 14, 15. " At first I had resolved to describe the whole constellation of Orion ; but the multitude of the stars and the want of leisure compelled me to postpone the undertaking till another occasion. Since not only in the Milky Way may be observed that brill- iancy as of a whitish cloud, but several areoles of a similar color are scattered through the firmament ; if you direct the glass to any one of them, you will meet with a host of clustered stars. Moreover, the stars (still stranger to say) which, by every astronomer, are to this day call- ed nebulous, are clusters of stars lying close together in a wonderful manner, from the combination of whose rays (while they can not be separately distinguished by the eye on account of their minuteness, or their very great distance from us) arises that whiteness, which, from its capacity of reflecting the rays of the stars or of the sun, has been hith- erto supposed to belong to a denser part of the atmosphere." — Side reus Nimtius, p. 13, 15 (Nos. 19-21), and 35 (No. 56). t Compare Cosmos, vol. hi., p. 41. I also remember a vignette at the close of the introduction to Hevel's Firmamentum Sobescianum, 1687, in which three genii are represented, two of whom are making ob servations with Hevel's sextants. The third genius is carrying a tele- scope which he appears to be worshiping, while those observing ex- claim, Pro. stat nudo oculo .' nebulae. 19 ula in the sword of Orion, which is so important from its extent and form, and has become so famous from the num- ber and celebrity of its subsequent investigators.1* Huygens was the means of inducing Picard (in 1676) to devote himself diligently to the investigation of this nebulous body. Ed- mund Halley, during his sojourn in St. Helena in 1677, was the first to determine any of the nebulous spots belonging to portions of the southern heavens not visible in Europe, al- though his observations embraced only a very small number. The lively interest taken by the great Cassini (Jean Dom- inique) in all branches of contemplative astronomy, led him, toward the close of the seventeenth century, to a more care- ful exploration of the nebulae in Andromeda and Orion. He thought he could detect alterations in the latter since Huy- gens's observations, and that he " had recognized stars in the former which could not be seen with telescopes of low pow- ers." There are reasons for regarding the assertion of an alteration of figure as a delusion ; not entirely so the exist- ence of stars in the nebula in Andromeda since the remark- able observations of George Bond. Cassini, moreover, con- jectured, on theoretical grounds, the possibility of such a res- olution of the nebula ; since, in direct opposition to Halley and Derham, he considered all nebulous spots to be very re- mote stellar swarms. f The faint mild effulgence in Androm- eda was indeed, according to his opinion, analogous to the zodiacal light, which he also conjectured to be composed of a crowd of densely, thronged, small planetary bodies, t Lacaille's residence in the southern hemisphere (at the Cape of Good Hope, and in the Isle of France and Bourbon, between 1750- 1752), so considerably increased the number of known nebu- lous spots, that Struve has justly remarked, that from the ob- servations of this traveler more was known, at that time, of * Huygens, Systema Saturnium, in his Opera varia, Lugd. Bat., 1724, torn, ii., p. -\>23 and 593. t "Dans les deux n6buleuses d'Andromede et d'Orion, j'ai vu des etoiles qu'on n'apercoit pas avec des lunettes communes. Nous ne Sa- vons pas si Ton ne pourrait pas avoir des lunettes assez grandes pour que toutela nebulosite put se resoudreen de plus petites etoiles, comme il arrive a. celle du Cancer et du Sagittaire." 'i I have seen stars in the nebula of Andromeda and Orion," says Dominique Cassini, " which can not be recognized by ordinary instruments. We are ignorant whether telescopes may not be constructed of sufficient power to resolve the whole nebula into smaller stars, as has been done in the case of the nebulae in Cancer and Sagittarius." — Delambre, Hist, de V Astr. Mo- derne, torn, ii., p. 700 and 744. t Cosmos, vol. i., p. 141, note. 20 COSMOS. the nebulous bodies of the southern hemisphere, than of those which were visible in Europe. Lacaille, moreover, success- fully attempted to divide nebulse into classes according to their apparent configuration ; he also was the first to undertake, though with little result, the difficult task of analyzing the heterogeneous contents of the Magellanic Clouds {nubecula major et mi?ior). If we subtract the 14 nebulse, which, even with instruments of low powers, were perfectly resolved into true clusters of stars, from the other 42 isolated nebulous spots which Lacaille observed in the southern heavens, there re- main only 28, while Sir John Herschel, by the aid of more powerful instruments, as well as greater skill and superior powers of observation, succeeded in discovering under the same zone, and also independently of clusters, as many as 1500 nebulous spots. Devoid of personal knowledge or experience of the subject, and originally ignorant of each other's attempts, although both had very similar aims in view,* Lambert (from 1749) and Kant (from 1755) speculated with admirable sagacity on nebulous spots, detached galaxies, and sporadic nebulous and stellar islands scattered singly through the realms of space. Both inclined to the nebular hypothesis, and to the idea of a perpetual development in the regions of space, and even of a star-formation from cosmical vapor. The great traveler, Le Gentil (1760—1769), long before his voyages, and his unsuc- cessful observations of the transit of Venus, had imparted ani- mation to the study of nebulae by his observations on the con- stellations of Andromeda, Sagittarius, and Orion. He made use of an object-glass of Campani's, 37 feet in focal length, which was in the possession of the Paris Observatory. In entire opposition to the views of Halley, Lacaille, Kant, and Lambert, the intellectual John Michell declared (as Galileo and Dominique Cassini had done) that all nebulse were stel- lar clusters, aggregations of very minute or very remote tel- escopic stars, whose existence would undoubtedly be some day revealed by means of more perfect optical instruments.! * On the community and difference of ideas between Kant and Lambert, as well as- in reference to the period of their publications, see Struve, Etudes d'Astr. Stellaire, p. 11. 13, 21, notes 7, 15, and 33. Kant's Allgemeine Natur-Geschichte und Theoric des Himmels appear- ed anonymously, and was dedicated to Frederick the Great, 1755. Lambert's Photdmetria, as already remarked, appeared in 1760; and his Sammlung kosmologischer Brief e uber die Einrichtung dcs Welt- banes, in 1761. ) " Those nebulae," says John Michell in 1767 (Philos. Transact., vol. NEBULiE. 21 Compared with the slow progress we have hitherto depicted, the knowledge of nebulous spots received a rich accession of facts by the persevering industry of Messier. His catalogue of 1771 contains, after deducting the older nebula? discovered by Lacaille and Mechain, 66 which had not been previously observed. He had the merit of doubling the number of the nebulous spots hitherto enumerated in both hemispheres, al- though his labors were carried on in the ill-supplied Observa- toire de la Marine (Hotel de Clugny).* To these feeble beginnings succeeded the brilliant epochs of the discoveries of William Herschel and his son. The for- mer began, as early as 1779, a regular exploration of the nu- merous nebulous masses with which the heavens are studded. These observations were made with a seven-feet reflector. His colossal forty-feet telescope was completed in 1787; and in the three catalogues! which he published in 1786, 1789, and 1802, he indicated the positions of 2500 nebulae and clusters of stars. Until 1785, or almost as .late as 1791, this great observer appears to have been more disposed, like Michell, Cassini, and the present Lord Rosse, to regard the nebulous spots which he was unable to resolve as very remote clusters of stars ; but a prolonged consideration of the subject between 1799 and 1802 led him to adopt the nebular theory, as Halley and Lacaille had done, and even, with Tycho Brahe and Kepler, the theory of a star-formation through the grad- ual condensation of cosmical vapor. The two hypotheses, however, are not necessarily connected. $ The nebulous and stellar clusters observed by Sir William Herschel were sub- jected by his son to a renewed investigation from 1825 to 1833 ; he also enriched the older catalogues with 500 new objects, and published in the Philosophical Transactions for 1833 (p. 365-481) a complete catalogue of 2307 nebula? and clusters of stars. This great work contains all that had been discovered in the heavens of Central Europe ; and in the five succeeding years (from 1834—1838) we find Sir John Her- lvii., for 1767, p. 251), "in which we can discover either none, or only a few stars, even with the assistance of the best telescopes, are probably systems that are still more distant than the rest." * Messier, in the Mim. de V Acadimie des Sciences, 1771, p. 435, and in the Connaissance des Temps pour 1783 et 1784. The whole catalogue contains 103 objects. t Philos. Transact., vols, lxxvi., lxxix., and xcii. X " The nebular hypothesis, as it has been termed, and the theory of sidereal aggregation, stand, in fact, quite independent of each other. "— Sir John Herschel, Outlines of Astronomy, § 872, p. 599. 22 cosmos. schel engaged at the Cape of Good Hope in exploring the whole of the visible firmament with a colossal twenty-feet reflector, and adding 1708 determinations of position to his previous catalogue of 2307 nebulas and clusters of stars !* Only one third of the southern nebulas and clusters of stars in Dunlop's catalogue (containing 629 nebulous bodies, ob- served from 1825—1827, at Paramatta, with a nine-feet re- flector, having a nine-inch speculum!) were inserted in Sir John Herschel's work. A third great epoch in our knowledge of these mysterious cosmical bodies commenced with the construction of the mar- velous fifty-three feet telescope! of the Earl of Rosse, at Par- sonstown. All that had ever been advanced on either side of the question, during the long fluctuation of opinions in the different stages of the development of cosmical contemplation, was now made the subject of keen discussion in the contest regarding the nebular hypothesis and its asserted untenabil- ity. It appears, from all the notices I have been able to col- lect from the works of distinguished astronomers long accus- tomed to the observation of nebulous spots, that out of a large number of nebulas indiscriminately taken from among all the classes contained in the catalogue of 1833, and regarded as irresolvable, almost all (Dr. Robinson, the Director of the Ar- magh Observatory, enumerates more than 40 such) have been perfectly resolved. § Sir John Herschei maintains the same * The numbers which I here give include the objects enumerated from Nos. 1 to 2307 in the European, Northern Catalogue of 1833, and those from Nos. 2308 to 4015 in the African, Southern Catalogue. — Ob- servations at the Cape, p. 51-128. t James Dunlop, in the Philos. Transact, for 1828, p. 113-151. t Compare Cosmos, vol. iii., p. 65, and note. § See An Account of the Earl of Rosse' s great Telescope, p. 14-17, which gives a list of the nebulae resolved by Dr. Robinson and Sir James South in March, 1845. " Dr. Robinson could not leave this part of his subject without calling attention to the fact that no real nebula seemed to exist among so many of these objects chosen without any bias : all appeared to be clusters of stars, and every additional one which shall be resolved will be an additional argument against the existence of any such." — Schumacher, Astr. Nachr., No. 536. In the Notice sur les gra?ids Telescopes de Lord Oxmantown, aujourd'hui Earl of Rosse (Bib- liotheque Universelle de Geneve, torn, lvii., 1845, p. 342-357), we find the following passage: " Sir James South rappelle que jamais il n'a vu de representations sideriales aussi magnifiques que celles que lui oftrait l'instrument de Parsonstown; qu'une bonne partie des nebuleuses se presentaient comme des amas ou groupes d'etoiles, tandis que quelques auti-es, a ses yeux du moins, n'offraient aucune apparence de resolution en etoiles." "Sir James South remarks that he never beheld more mag- nificent representations of the stars than those he saw in the Parsons- NEBULyE. 23 view, as well in his opening address before the British Asso- ciation at Cambridge in 1845, as in the Outlines of Astron- omy, 1849, where he expresses himself as follows : "The magnificent reflecting telescope constructed by Lord Rosse, six feet in aperture, has resolved or rendered resolvable mul- titudes of nebulae which had resisted all inferior powers. . . . Although, therefore, nebulae do exist which, even in this pow- erful telescope, appear as nebulae, without any sign of resolu- tion, it may very reasonably be doubted whether there be really any essential physical distinction between nebula? and clusters of stars."* The constructor of the powerful optical apparatus at Par- sonstown, who always discriminates between the result of act- ual observation and the promises of a knowledge to which we hope to attain, expresses himself with much caution re- garding the nebula in Orion, in a letter to Professor Nichol, of Glasgow,! dated Parsonstown, 19th of March, 1846 : "In accordance with my promise of communicating to you the result of our examination of Orion, I think I may safely say, that there can be little, if any, doubt of the resolvability of the nebula. Since you left us, there was not a single night when, in absence of the moon, the air was fine enough to ad- mit of our using more than half the magnifying power the speculum bears ; still we could plainly see that all about the town telescope, and that a great number of nebulae appeai-ed like clus- ters or groups of stars, while others, at least to his sight, presented no appearance of resolution." * See Outlines, p. 597, 598 ; also the Report of the Fifteenth Meeting of the British Association held at Cambridge in June, 1845, p. xxxvi. : " By far the major part," says Sir John Herschel, " probably, at least, nine tenths of the nebulous contents of the heavens, consist of nebula? of spherical or elliptical forms, presenting every variety of elongation and central condensation. Of these a great number have been resolved into distant stars (by the reflector of the Earl of Rosse), and a vast mul- titude more have been found to present that mottled appearance which renders it almost a matter of certainty that an increase of optical pow- er would show them to be similarly composed. A not unnatural or un- fair induction would therefore seem to be, that those which resist such resolution do so only in consequence of the smallness and closeness of the stars of which they consist; that, in short, they are only optically, and not physically nebulous. Although nebula? do exist which, even in this powerful telescope (of Lord Rosse), appear as nebuhe, without any sign of resolution, it may very reasonably be doubted whether there be really any essential physical distinction between nebuhe and clus- ters of stars." t Dr. Nichol, Professor of Astronomy at Glasgow, published the let- ter above referred to in his Thoughts of some Important Points relating to the System of the World, 184G, p. 55. 24 cosmos. trapezium is a mass of stars, the rest of the nebulae also abounding with stars, and exhibiting the characteristics of re- solvability strongly marked." At a subsequent period (1848) Lord Rosse had not announced that his expectations had as yet been fulfilled, although he cherished the hope of being able to resolve the remaining portion of the nebula into stars. When we separate the results of actual observation from those of mere inductive conclusions in this much-disputed question of the existence or non-existence of a self-luminous, vaporous matter in the universe, we find that although the increasing improvements in telescopic vision may indeed con- siderably diminish the number of nebulae, they can not by any means wholly exhaust them. By the application of increas- ing powers, each new instrument may resolve what the pre- ceding ones had left unresolved, but it must, at the same time, in consequence of its greater powers of penetrating space, re- place (at least partially) the resolved nebulas by others not previously reached.^ A resolution of the older, and the dis- covery of new nebulae, would therefore follow one another in endless succession, as the fruit of increased optical power. For if we suppose a different result, we must either, accord- ing to my view, assume the occupied regions of space to be limited, or that the world-islands, to one of which our system belongs, are so remote from each other that no telescopic in- strument can ever be invented of sufficient power to penetrate to the confines of any other of these worlds, and that our last or extremest nebulae may resolve themselves into clusters of stars, which, like the stars in the Milky "Way, " are projected on a black ground entirely free from vapor."f But can we believe in the probability of a condition of the universe, and of a degree of perfection in optical instrumc its, in which the entire firmament will no longer exhibit any unresolved neb- ulous spots ? The hypothetical assumption of a self-luminous fluid, ap- pearing, when sharply defined, in round or oval nebulous spots, must not be confounded with the equally hypothetical as- sumption of a non-luminous ether pervading the universe, and generating by its unduJatory motion the phenomena of light, radiant heat, and electro-magnetism.J The emanations from cometary nuclei, which, in the form of tails, frequently extend over enormous tracts of space, disperse the substance of which they are composed — and with which we are unacquainted — * Compare Edinburgh Review, vol. lxxxvii., 1848, p. 186. t Cosmos, vol. iii., p. 144, and note. t Ibid., p. 34. NEBULiE. 25 among the planetary orbits of our solar system, which they intersect. But when separated from the controlling nucleus, this substance ceases to be perceptibly luminous. Newton even considered it possible that vapores ex sole et stellisjizis et caudis comet arum, " vapors from the sun, the stars, and the tails of comets," might blend with our terrestrial atmos- phere.* No telescope has as yet indicated any sidereal char- acter in the vaporous, rotating, and flattened ring of the zodi- acal light. Whether the particles of which this ring consists, and which, according to some, are conceived to rotate upon themselves in obedience to dynamic conditions, and, accord- ing to others, merely to revolve round the Sun, are illumined or self-luminous, like many kinds of terrestrial vapors,! is a question as yet undecided. Dominique Cassini believed them to be small planetary bodies. % It seems as if it were a re- quirement of the human intellect to seek in all fluid bodies for discrete molecular particles, § similar to the full or hollow vesicles of which clouds are formed ; while the gradations in the decrease of density in our planetary system, from Mercury to Saturn and Neptune (from 1*12 to 0*14; the Earth being ^=1), leads the mind to the consideration of comets, through the external layers of whose nuclei even a faint star contin- ues visible, and finally to that of discrete particles, so deficient in density that their solidity, either within large or small di- mensions, can scarcely be characterized, except by the limits which bound them. It was by such considerations as to the constitution of the apparently vaporous zodiacal light that Cassini, long before the discovery of the so-called smaller plan- ets between Mars and Jupiter, and prior to all conjectures re- garding meteor-asteroids, was led to the idea that there exist cosmical bodies of all dimensions and all degrees of density. We here almost involuntarily touch upon the old metaphys- ical controversy regarding 'matter of primitive fluidity and that composed of discrete molecular particles, and therefore more amenable to mathematical treatment. From hence we turn the more readily to our former consideration of the pure- ly objective part of the phenomenon. In the 3926 (2451 + 1475) positions which belong, a. to the portion of the firmament visible at Slough, and which we shall here, for the sake of brevity, term the northern heav- ens, according to the three catalogues of Sir William Herschel * Newton, Philos. Nat. Principia Mathematica, 1760, torn, iii., p. 671 1 Cosmos, vol. i., p. 141. \ Ibid., p. 140 $ Observations at the Cave, 0 109-111. Vol. IV.— B 26 cosmos. from 1786 to 1802, and the above-named great exploration of the heavens published by his son in the JPhilos. Transact. of 1833 ; and b. to the portion of the southern heavens visi- ble at the Cape of Good Hope, according' to Sir John Her- schel's African Catalogues, nebulae and clusters of stars are set down indiscriminately together. I have, however, deemed it best, notwithstanding the natural affinity of these objects, to enumerate them separately, in order to indicate a definite epoch in the history of their discovery. I find that the North- ern Catalogue^ contains 2299 nebulee and 152 clusters of stars ; the Southern or Cape Catalogue, 1239 nebulee and 236 clusters of stars. We have, therefore, 3538 for the num- ber of the nebulae throughout the firmament which were given in these catalogues as not yet resolved into clusters. This number may, perhaps, be increased to 4000, if we take into account 300 or 400 seen by Sir William Herschel, f but not again determined, and the 629 observed by Dunlop at Para- * The data on which these numbers are based require some expla- nation. The three catalogues of the elder Herschel contain 2500 objects, viz., 2303 nebulae and 197 clusters of stars. (Madler, Astr., p. 448.) These numbers were altered in the subsequent and far more exact ex- ploration made by Sir John Herschel (Observations of Nebulas and Clus- ters of Stars made at Slough with a twenty-feet reflector, between the years 1825 and 1833, in the Philosophical Transactions of the Royal Society of London for the year 1833, p. 3G5-481). About 1800 objects were identical with those of the three earlier catalogues ; but 300 or 400 were temporarily excluded, and more than 500 newly discovered were determined according to Right Ascension and Declination. (Struve, Astr. Stellaire, p. 48.) The Northern Catalogue contains 152 clusters of stars, consequently 2307 — 152=2155 nebulae; but, in reference to the Southern Catalogue {Observations at the Cape, p. 3, § 6, 7), we have to subtract from the 4015 — 2307 = 1708 objects, among which there are 236 clusters of stars (see Op. cit., p. 3, § 6, 7, p. 128), 233, viz., 89-}- 135-f-9, as belonging to the Northern Catalogue, and observed by Sir William and Sir John Herschel at Slough, and by Messier in Paris. There remain, therefore, for the Cape* observations, 1708 — 233=1475 nebula? and clusters of stars, or 1239 nebulas alone. We have, how- ever, to add 135-f-9=144 to the 2307 objects of the Northern Slough Catalogue, which increase its numbers to 2451 objects, in which, after subtracting 152 clusters, there remain 2299 nebulas, a number which is not, however, very strictly limited to the latitude of Slough. When numerical relations are to be given in the topogi'aphy of the firmament of both hemispheres, the author feels that although such data are from their nature variable, owing to the differences in the epochs and the advances of observation, he is bound to have regard to their accuracy. In a sketch of the Cosmos, it must be endeavored to delineate the con- dition of science appertaining to a definite epoch. t Sir John Herschel says, in his Observations at the Cape, p. 134, " There are between 300 and 400 nebulas of Sir William Herscbel's Cat- alogue still Unobserved by me ; for the most part, very faint objects." NEBULAE. 27 matta, with a nine-inch Newtonian reflector, of which Sir John Herschel included only 206 in his catalogue.*" Simi- lar results have recently been published by Bond and Miid- ler. The number of nebulae, compared with that of double stars, appears, therefore, according to the present condition of science, to be in the ratio of 2 : 3 ; although it must not be forgotten that under the designation of double stars are included those which are merely optically double, and that hitherto alterations of position have only been observed in a ninth, or perhaps but an eighth portion of the whole number. f The above numbers — 2299 nebula?, with 152 clusters of stars, in the Northern, and only 1239 nebulae, with 236 clus- ters of stars, in the Southern Catalogue — show that the south- ern hemisphere, with a smaller number of nebulae, possesses a preponderance of clusters of stars. If we assume that all nebulae are, from their probable constitution, resolvable, as merely more remote clusters of stars or stellar groups, com- posed of smaller and less thronged, self-luminous celestial bod- ies, this apparent contrast (whose importance has been the more noticed by Sir John Herschel$ in consequence of his having employed reflectors of equal powers in both hemi- spheres) indicates, at least, a striking difference in the nature and cosmical position of nebulae, that is to say, in reference to the directions in which they present themselves to the ob- servation of the inhabitants of the earth in the northern or southern firmament. We owe to the same great observer our first accurate knowl- edge of, and cosmical survey of, the distribution of nebulae and groups of stars throughout the entire heavens. With a view of investigating their position, relative local accumulation, and the probability or improbability of their being arranged in accordance with certain characteristic features, he classi- fied between three and four thousand objects graphically, in divisions, each embracing a space measuring 3° Declination and 15m. Right Ascension. The greatest accumulation of nebulous spots occurs in the northern hemisphere, where they are distributed through Leo Major and Leo Minor ; the body, tail, and hind feet of the Great Bear ; the nose of Camelo- pardalus ; the tail of the Dragon ; Canes Venatici ; Coma Berenices (where the north pole of the galaxy is situated); k * Op. cil., § 7. Compare Dunlop's Cat. of Nebula: and Clusters of the Southern Hemisphere, in the Philos. Transact, for 1828. p. 1 14—146 t Cosmos, vol. iii., p. 200. t Observations at the Cape, § 105-107. $ In the Cosmos, vol. iii., p. 144, lines 5 and 6 from the top, by an 28 cosmos. the right foot of Bootes ; and more especially through the head, wings, and shoulder of Virgo. This zone, which has been termed the nebulous region of Virgo, contains, as al- ready stated,^ one third of all the nebulous bodies in a space embracing the eighth part of the surface of the celestial hem- isphere. It does not stretch far beyond the ecliptic, extend- ing only from the southern wing of Virgo to the extremity of Hydra and to the head of the Centaur, without reaching its feet or the Southern Cross. A less dense accumulation of nebulae in the northern hemisphere, which extends further south than the former, has been named by Sir John Herschel the nebulous region of Pisces. It forms a zone, beginning with Andromeda, which it almost entirely incloses, stretch- ing beyond the breast and wings of Pegasus, and the band uniting the Fishes, and extending toward the southern galac- tic pole and Fomalhaut. A striking contrast to these accu- mulations presents itself in the barren region lying near Per- seus, Aries, Taurus, the head and chest of Orion, around Au- riga, Hercules, Aquila, and the whole constellation of Lyra.f If we divide all the nebulas and clusters of stars contained in the Northern Catalogue (of Slough), and classified accord- ing to Right Ascension (as given in Sir John Herschel's Ob- servations at the Cape), into six groups of four hours each, we obtain the following result : R. Asc. Oh. 4h 311 4 8 .... 179 8 12 .... 606 R.Asc.l2h. 16h 850 16 20 121 20 0 239. By a more careful separation, according to Northern and Southern Declination, we find that in the six hours' Right Ascension from 9h. — 15h., there are accumulated 1111 neb- ulae and clusters of stars in the northern hemisphere alone, viz. \% From 9h. lOh... . . 90 From 12h. 13h.... . . 309 10 11 ... . . 150 13 14 ... . . 181 11 12 ... . . 251 14 15 .. . .. 130. error of the press, the words south pole and north pole have been con- founded. * " In this region of Virgo, occupying about one eighth of the whole surface of the sphere, one third of the entire nebulous contents of the heavens are congregated." — Outlines, p. 596. t In reference to this barren region, see Observations at the Cape, $ 101, p. 135. X I have based these numerical data on a computation of the numbers yielded by the projection of the northern heavens as given in Observa- tions at the Cape, pi. xi. NEBULA. 29 The actual northern maximum lies, therefore, between 12h. and 13h., very near the north galactic pole. Beyond that point, between 15h. and 16h. toward Hercules, the dim- inution is so rapid that the number 130 is followed directly by 40. The southern hemisphere presents not only a smaller num- ber, but a far more regular distribution of nebulae. Regions destitute of nebulae here frequently alternate with sporadic nebulae. An actual local accumulation, more dense, indeed, than the nebulous region of Virgo in the northern heavens, occurs only in the Great Magellanic Cloud, which alone con- tains as many as 300 nebulae. The immediate polar regions of both hemispheres are poor in nebulae, and to a distance of 15° the Southern Pole is still more so than the Northern, in the ratio of 4 to 7. The present North Pole exhibits a small nebula, only 5 minutes' distance from it, while a similar neb- ulous body, which Sir John Herschel has aptly named Nebula polarissima Australis (No. 3176 of his Cape Catalogue, R. A. 9h. 27m. 56s. ; N. P. D. 179° 34' 14"), is situated at a dis- tance of 25 minutes from the South Pole. This paucity of stars in the south polar region, and the absence of any pole- star visible to the naked eye, were made the subject of bitter lamentation by Amerigo Vespucci and Vicente Yanez Pinzon, when, at the close of the fifteenth century, they penetrated far beyond the equator to Cape San Augustin, and when the former even expressed the erroneous opinion that the fine passage of Dante, " Io mi volsi a man destra, e posi mente " and the four stars described as " non viste mai fuorcK alia prima gente" referred to antarctic polar stars. ^ * Humboldt, Examen Critique de VHist. de la Gdographie, torn, iv., p. 319. The Venetian Cadamosto (more properly called Alvise da Ca da Mosto) first turned his attention to the discovery of the position of a south polar star when in company with Antoniotto Usodimare, at the mouth of the Senegal, in 1454, in the course of one of the many voy- ages in which the Portuguese engaged, under the auspices of the In- fante Don Henrique, for the purpose of advancing along the western 6hores of Africa, beyond the equator. " While I still see the north polar star," he writes, being then in about 13° north latitude, " I can not see the south polar star itself, but the constellation which T perceive toward the south is the Carro del ostro (wagon of the south). ( Aloysh Cadam. Navig., cap. 43, p. 32 ; Ramusio, Delle Navigationi et Viaggi, vol. i., p. 107.) Could he have traced the figure of a wagon among some of the larger stars of the constellation Argo ? The idea that both poles had a constellation of the " Wain" or wagon appears to have been so universal in that age, that there is a drawing of a constellation per- fectly similar to Ursa Minor, supposed to have been seen by Cadamosto, both in the Itinerarium Portugallense, 1508, fob 23, b, and in Grynams 30 COSMOS. We have hitherto considered nebulae in reference to their number and their distribution in what we call the firmament (Novus Orbis, 1532, p. 58) ; while Ratnusio (Navigationi, vol. i., p. 107), and the new Colleccao de Nolicias para a Hist, e Geog. das Nacoes Ultra- marinas (torn, ii., Lisboa, 1812, p. 57, cap. 39), in the place of the for- mer, give an equally arbitrary drawing of the Southern Cross. (Hum- boldt, Examen Crit. de VHist. de la Geogr., torn, v., p. 236.) Since, in the Middle Ages, and probably for the sake of replacing the two Dau- cers, xopevrai, of Hyginus (Poet.Astron., iii., l),i. e., the Ludenles of the Scholiast of Germanicus, or the Custodes of Vegetius in the Lesser Wain, the stars (3 and y of Ursa Minor had been denominated the Guards, le due guardie, of the neighboring north pole, on account of their rotation round that point, and as this designation, as well as the habit of determ- ining polar altitudes by these Guards (Pedro de Medina, Arte de Nave- gar, 1545, lib. v., caps. 4-7, p. 183-195), was familiar to the European pilots of all nations in the northern seas, so erroneous conclusions led men to believe from analogy that they could recognize in the southern horizon the polar star which had so long been sought for. It was not until Amerigo Vespucci's second voyage (from May, 1499, to Septem- ber, 1500), when he and Vicente Yanez Pinzon (both voyages are per- haps one and the same) advanced as far in the southern hemisphere as Cape San Augustin, that they devoted themselves diligently, but to no purpose, to the search for a visible star in the immediate vicinity of the South Pole. (Bandini, Vita e Lettere di Amerigo Vespucci, 1745, p. 70; Anghiera, Oceanica, 1510, dec. i., lib. ix., p. 96; Humboldt, Exa- men. Crit., torn, iv., p. 205, 319, 325.) The South Pole was then situ- ated within the constellation Octans, so that (3 of Hydrus, if we follow the reduction of Brisbane's" Catalogue, had still a southern declination of fully 80° 5'. " While I was engaged in observing the wonders of the southern heavens, and in vaiuly seeking for a pole-star, I was remind- ed," says Vespucci, in his letter to Pietro Francesco de' Medici, " of an expression made use of by our Dante, when, in the first chapter of the Purgatorio, he depicts a presumed passage from one hemisphere to the other, and in describing the Antarctic Pole, says, Io mi volsi a man des- tra In my opinion, the author intended in these verses to in- dicate the pole of the other firmament by his four stars (non viste mai fuorcli1 alia prima gente). I am the more certain of this, because I act- ually saw four stars, which together formed a lozenge, and had a slight (?) movement." Vespucci refers to the Southern Cross, la croce mara- vigliosa of Andrea Corsali (Letter from Cochin, dated January 6, 1515, in Ramusio, vol. i., p. 177), whose name he did not then know; but which subsequently served to mark to all pilots the position of the South Pole (as/3 and y Urs. Min. indicated the North Pole. (Mim. de V Acad, des Scieyices, 1666-1699. torn, vii., part 2. Paris, 1729, p. 58.) This constellation also served for determinations of latitude. (Pedro de Me- dina, Arte de Navegar, 1545, lib. v., cap. xi., p. 204.) Compare my in- vestigation of the celebrated passage of Dante in the Examen Crit. de VHist. de la Geogr., torn, iv., p. 319-334. I there drew attention to the fact that a of the Southern Cross, which was carefully observed in modern times by Dunlop (1826), and by Rumker (1836) at Paramatta, is one of those stars whose multiple nature was first recognized in 1681 and 1687 by the Jesuits Fontaney, Noel, and Richaud. (Hist, de V Acad, dep. 1686-1699, torn, ii., Par., 1733, p. 19; M6m de V Acad, dep. 1666- 1699, torn, vii., 2, Par., 1729, p. 206 ; Lettres 6difiantes, recueil vii., 1703, — an apparent distribution which must not, however, be con founded with their actual distribution through the regions of space. We now, therefore, proceed to the consideration of the remarkable differences presented by their individual forms, which are either regular (globular, more or less elliptical, an- nular, planetary, or resembling the photosphere surrounding a star) or irregular, and almost as difficult to classify as those of the aggregated aqueous vapor of our atmosphere — the clouds. The elliptical (spheroidal) form* has been regarded as the normal type of nebula; ; this form is most readily re- solved into clusters of stars when it assumes a globular shape in the telescope ; but when, on the other hand, with instru- ments of equal powers, it appears much flattened, elongated in one dimension, and discoidal, it is less easy of resolution.! Gradual transitions of form from the round to the elonsrated, elliptical, or awl-shaped form, are of frequent occurrence in the heavens. (Philos. Transact., 1833, p. 494, pi. ix., figs. 19-24.) The nebula is always condensed around one or more central points (nuclei). It is only by a discrimination between round and oval nebula that we recognize double nebidce ; for as no relative motion is perceptible among the individual neb- ulous bodies, either in consequence of its absence or its ex- treme slowness, we are deficient in a criterion by which to p. 79.) This early recognition of binary systems, long before that of £ Ursaa Maj. {Cosmos, vol. iii., p. 185), is the more remarkable, as Lacaille, seventy years later, did not describe a Crucis as a double star; perhaps (as Riimker conjectures), because the main star and the companion were then not sufficiently distant from each other. (Compare Sir John Her- 6chel, Observations at the Cape, § 183-185.) Richaud also discovered the binary character of a Centauri almost simultaneously with that of a Crucis, and fully nineteen years before the voyage of Feuillee, to whom Henderson erroneously attributed the discovery. Richaud remarks " that, at the time of the comet of 1G89, the two stars which form the double star a Crucis were at a considerable distance from each other; but that in a twelve-feet refractor both parts of a Centauri could be dis- tinctly recognized, and appeared to be nearly in contact. * Observations at the Cape, § 44, 104. t Cosmos, vol. iii., p. 140, and note. As we have already remarked in reference to clusters of stars (Ibid., p. 143), Mr. Bond, of the United States, succeeded, by means of the great space-penetrating power of his refractor, in completely resolving the very elongated, elliptical neb- ula of Andromeda, which, according to Bouillaud, had been already described before the time of Simon Marius in 985 and 1428. It has a reddish light. Near this celebrated nebula lies the still unresolved, but very similarly shaped nebula, discovered on the 27th of August, 1783, by my honored friend, Miss Caroline Herschel, who died at au advanced age, universally esteemed. (Philos. Transact., 1833. No. 61 of the Catalogue of Nebula;, fig. 52.) 32 cosmos. prove the existence of a mutual relation between the two, as in distinguishing between physically and merely optically double stars. Figures of double nebulae are given in the Philos. Transact, for the year 1833, figs. 68-71. Compare also Herschel, Outlines of Astr., k 878 ; Observ. at the Cape of Good Hope, §120. Annular nebulae are of the rarest occurrence. According to Lord Rosse, we are acquainted with seven of these bodies in the northern hemisphere ; the most celebrated of these is situated between (3 and y Lyrae (No. 57, Messier ; No. 3023 of Sir John Herschel's Catalogue), and was discovered in 1779 by Darquier at Toulouse, when Bode's Comet passed near it. Its apparent size is nearly equal to that of Jupiter's disk, and its form is an ellipse, whose greater and lesser axes are in the ratio of 5 to 4. The interior of the ring is not black, but somewhat illumined. Sir William Herschel dis- covered some stars in the ring, which has since been entirely resolved by Lord Rosse and Mr. Bond.^ The splendid an- nular nebulae of the southern hemisphere, numbered 3680 and 3686, appear, on the contrary, perfectly black in the interior of the rings. The last-named of the two is not elliptical, but perfectly round ;f all are probably annular clusters of stars. The increasing power of optical instruments appears, more- over, generally to render the contour of both elliptical and annular nebulae less defined ; thus, for instance, Lord Rosse's colossal telescope exhibits the annular nebula of Lyra in the form of a simple ellipse, with remarkable divergent, thread- like nebulous appendages. The transformation effected in a nebulous spot — Lord Rosse's Crab nebula — which appears in instruments of inferior power to be a simple elliptical body, is particularly striking. The so-called planetary nebulae, which were first observed by the elder Herschel, and which rank among the most re- markable phenomena of the heavens, although of less rare occurrence than annular nebulae, do not number, according to Sir John Herschel, more than 25, of which nearly three fourths lie within the southern hemisphere. These bodies present the most striking resemblance to planetary disks ; the * " Annular Nebula." — Observations at the Cape, p. 53 ; Outlines of Astr., p. 602. " Nebulcuse perfor£e.'n — Arago, in the Annuaire for 1842, p. 423; Bond, in Schum., Aslron. Nachr., No. 611. t Observations at the Cape, p. 114, pi. vi., figs. 3 and 4. Compare also No. 2072 in the Philos. Transact, for 1833, p. 466. See Nichol, Thoughts on the System of the World, p. 21, pi. iv., and p. 22, pi. i. fig. 5. NEBULA. 33 greater number are round, or somewhat oval, and either sharply defined, or indistinct and vaporous at the margins. The disks of many of these nebulae present a very uniform light, while others appear mottled, or of a peculiar texture as if curdled. No trace of condensation round a central point has ever been observed. Lord Rosse has recognized five plan- etary nebulous spots to be annular nebulae, having one or two central stars. The largest of these planetary nebulae is sit- uated in the Great Bear (near /3 Ursae Maj.), and was discov- ered by Mechain in 1781. The diameter of the disk* is 2' 40". The planetary nebula in the Southern Cross (No. 3365, Observations at the Cape, p. 100), with a disk having a di- ameter scarcely equal to 12", exhibits the brightness of a star of the 6 -7th magnitude. Its light is indigo-blue, and the same color, which is very remarkable in nebulae, is observed in three other objects of the same form, although in the lat- ter the blue is less intense.! The blue color of some plan- etary nebulae does not militate against the possibility of their being composed of small stars ; for we find blue stars not only as the individual members of a pair of double stars, but even stellar clusters composed entirely of blue stars, or of the lat- ter interspersed with small red and yellow stars. $ The question whether planetary nebulae are very remote nebulous stars, in which our telescopic vision is unable to rec- ognize the difference between a luminous central star and the vaporous envelope surrounding it, has already been considered in the beginning of my Delineation of Nature. k Would that Lord Rosse's colossal telescope might finally be the means of * If we consider the planetary nebula in the Great Bear to be a sphere having an apparent diameter of 2' 40", " and assume its distance to be equal to the known distance of 61 Cygni, we shall obtain an act- ual diameter for the sphere, which is seven times greater than the orbit described by Neptune." — Outlines, § 876. t Outlines, p. 603; Observations at the Cape, § 47. There is an or- ange-red star of the eighth magnitude in the vicinity of No. 3365 ; but the planetary nebula retains its deep indigo-blue color when the red star is not in the field of the telescope. The color is, therefore, not the effect of contrast. X Cosmos, vol. hi., p. 136, 208, and note. The companion and the main star are blue, or bluish, in more than 63 double stars. Indigo- blue stars are intermixed in the splendid, many-colored clusters of stars, No. 3435 of the Cape Catalogue (Dunlop's Catalogue, No. 301). An en- tirely uniform blue cluster of stars is observed in the southern heavens (No. 573 of Dunlop ; No. 3770 of Sir John Herschel). This cluster has a diameter of 3£', with prolongations measuring 8' in length; the stars are of the 14th and 16th magnitude. (Observations at the Cape, p. 119.) § Cosmos, vol. i., p. 85, and note. Compare Outlines, § 877. B 2 34 cosmos. elucidating the nature of these remarkable planetary vapor ous disks ! Although there is considerable difficulty in ac- quiring a clear conception of the complicated dynamic condi- tions under which, in a globular or spheroidally flattened stel- lar cluster, the rotating crowded suns, whose specific density, is greater toward the center, constitute a system of equilibri- um ;* this difficulty increases still more in those circular, well-defined, planetary nebulous disks which exhibit a per- fectly uniform brightness, without any increase of intensity to- ward the center. Such a condition seems to depend less upon sphericity of form (the state of aggregation of many thousand small stars) than on the existence of a gaseous photosphere, which is supposed, as in our Sun, to be covered with a thin, untransparent, or very faintly illuminated stratum of vapor. Does the light in the planetary nebulous disk appear to be thus uniformly diffused simply in consequence of the great distance, which causes the difference between the center and the margins to disappear ? The fourth and last order of regular nebulae comprises Sir William Herschel's nebulous stars, i. e., true stars surround- ed by a milky nebula, which is very probably connected with, and dependent upon, the central star. Yery different opin- ions exist as to whether the nebula, which, according to Lord Rosse and Mr. Stoney, appears to be perfectly annular in some of these groups (Philos. Transact, for 1850, pi. xxxviii., figs. 15 and 16), is self-luminous, forming a photosphere like our Sun, or whether (which, however, is less probable) it is sim- ply illumined by the central Sun. It was the opinion of Der- ham, and to $ some extent also of Lacaille, who discovered many nebulous stars at the Cape of Good Hope, that the stars were situated far from the nebulas on which they were pro- jected. Mairan appears (1731) first to have expressed the view that nebulous stars are surrounded by an atmosphere of light appertaining to them.f We even find that some of the larger stars (of the 7th magnitude, for instance, as No. 675 * On the development of the dynamic relations manifested in the partial attractions in the interior of a globular cluster of stars, which ap- pears in a telescope of weak power as a round nebula increasing in density toward the center, see Sir John Herschel, in Outlines of As- tronomy, § 8G6 and 872: Observations at the Cape, § 44, 111 to 113; Philos. Transact, for 1833, p. 501; Address of the President in the Report of the Fifteenth Meeting of the British Association, 1845, p. xxxvii. t Mairan, Traitt de I'Aurore Boriale, p. 263 ; Arago, in the Annuaire for 1842, p. 403-413. VEBUL E. :{f) of the Catalogue oi' lb33) have a photosphere, whose diam eter measures from 2' to 3'.* The large nebulous masses of irregular configuration com- pose a class of nebulae differing entirely from those we have described as regular, and which are, at all events, faintly de- fined. They are-characterized by the most variously un sym- metrical forms, having indefinite and confused outlines. These bodies, which constitute mysterious phenomena sui generis, have mainly given occasion to the opinions advanced in ref erence to the existence of cosmical clouds and self-luminous ncbuhc, supposed to be distributed through the regions of space, and to resemble the substratum of the zodiacal light. These irregular nebulae, which cover a portion of the firma- ment several square degrees in extent, present a striking con- trast with the smallest of all the regular isolated and oval nebulous disks, which is equal in luminous intensity to a tel- escopic star of the 14th magnitude, and is situated between the constellations Ara and Apus, in the southern hemisphere.! No two of the unsymmetrical, diffused nebulous masses re- semble one another ;$ but, adds Sir John Herschel, from the experience of many years' observation, one thing observed in reference to them, and which gives them a peculiar charac- ter, is, that all are situated within or very near to the mar- gins of the Milky Way, and may be regarded as offshoots from it. On the contrary, the regularly shaped and well-defined small nebulous spots are partly scattered over the whole heav- ens, and partly compressed together in special regions, far from the Milky Way, as, for instance, in the northern hemi- sphere, in the regions of Virgo and Pisces. Although the large irregular nebulous mass in the sword of Orion is certainly sit- uated at a considerable distance from the visible margin of * In other instances these nebulous stars are only of the eighth to the ninth magnitude; as Nos. 311 and 450 of the Catalogue of 1833, fig. 31 having photospheres of 1/ 30". (Outlines, § 879.) t Observations at the Cafe, p. 117, No. 3727, pi. vi., fig. 16. % We meet with remarkable forms of irregular nebulae, as, for in- stance, the omega-shaped (Observations at the Cape, pi. ii., fig. 1, No. 2008), which has been investigated and described by Lament, and by a meritorious North American astronomer. Mr. Mason, whose early loss is much to be lamented (Mem. of the Amer. Pkitos. Society, vol. vii.. p 117) ; a nebula having from 6 to 8 nuclei (Observations at the Cape, p 19, pi. hi., fig. 4); the cometary tuft-like form in which the nebulous rays seem occasionally to expand, as from a star of the ninth magni- tude (pi. vi., fig. 18, Nos. 2534 and 3688); a silhouette profile, or bust- like outline (pi. iv., fig. 4, No. 3075); a fissure-like opening, inclosing a filiform nebula (No. 3501, pi. iv., fig. 2 ; Outlines. ft 883 ; Observations at the Cape, § 121). 36 cosmos. the Galaxy (fully 15°), still even it may perhaps belong to that prolongation of its branch which appears to lose itself from a and e Persei toward Aldebaran and the Hyades, and to which we have already referred at p. 147. The brilliant stars which gave early celebrity to the constellation of Orion, are, moreover, reckoned to belong to that zone of very large and probably less remote stars, whose prolonged direction in- dicates the vast circle of the Southern Galaxy, passing through e Orionis and a Crucis.* The opinion which at one time prevailed so extensively! of the existence of a galaxy of nebulce intersecting the stellar Milky Way almost at right angles, has not been confirmed by more recent and accurate observations in reference to the dis- tribution of symmetrical nebulee in the firmament.! There certainly are, as has already been observed, very great accu- mulations at the northern pole of the Galaxy, while a very considerable abundance of nebulous matter is also observed at the south galactic pole near Pisces ; but in consequence of the many interruptions which break the zone, we are unable to indicate any large circle connecting these poles together, and formed by a continued line of nebulae. William Her- schel, in advancing this view in 1784, at the close of his first treatise on the structure of the heavens, developed it with a caution worthy of such an observer, and from which doubt was not entirely excluded. Some of the irregular, or, rather, unsymmetrical nebulae (as those in the sword of Orion, near rj Argus in Sagittarius and in Cygnus), are remarkable for their extraordinary size ; others (as Nos. 27 and 51 of Messier's Catalogue) for their singular forms. It has already been noticed in reference to the large nebula in the sword of Orion, that Galileo never mentioned it, al- though he devoted so much attention to the stars between the girdle and the sword, k and even sketched a map of this re- * Cosmos, vol. iii., p. 147. Outlines, § 785. t Cosmos, vol. i., p. 150, and note ; Sir John Herschel's first edition of his Treatise on Astronomy, 1833, in Lardner's Cabinet Cyclopccdia, § 616; Littrow, Tkeoretische Astronomie, 1834, th. ii.. $ 234. % See Edinburgh Review, January, 1848, p. 187, and Observations at the Cape, § 96, 107. " The distribution of the nebula? is not like that of the Milky Way," says Sir John Herschel, " in a zone or band en- circling the heavens ; or if such a zone can be at all traced out, it is with so many interruptions, and so faintly marked out through by far the greater part of its circumference, that its existence as such can be hardly more than suspected." § " There can be no doubt," writes Dr. Galle, " that the drawing" NEBULJE. St gion of the heavens. That which he names Ncbulosa Ori onis, and delineates in the vicinity of Ncbulosa Prcesejie, ht expressly declares to be an accumulation of small stars (stcl latum cotistipatarum) in the head of Orion. In the draw- ing which he gives in the Siderius Nuncius, § 20, extend- ing from the girdle to the beginning of the right leg (a On- onis), I recognize the multiple star 6 above the star t. The instruments employed by Galileo did not magnify more than from eight to thirty times. It is probable that as the nebula in the sword is not isolated, but appears, when seen through imperfect instruments or a hazy atmosphere, like a halo round the star 6, its individual existence and configuration may have escaped the notice of the great Florentine observer. He was, moreover, little inclined to assume the existence of nebulae.* It was not until fourteen years after Galileo's death, in the year 1656, that Huygens first observed the great nebula of Orion, of which he gave a rough sketch in the Systema Satur- nium, which appeared in 1659. "While," says this great man, " I was observing, with a refractor of twenty-five feet focal length, the variable belts of Jupiter, a dark central belt in Mars, and some faint phases of this planet, my attention was attracted by an appearance among the fixed stars, which, as far as I know, has not been observed by any one else, and which, indeed, could not be recognized, except by such pow- erful instruments as I employ. Astronomers enumerate three stars in the sword of Orion, lying very near one another. On one occasion, when, in 1656, I was accidentally observing the middle one of these stars through my telescope, I saw twelve stars instead of a single one, which, indeed, not unfrequently (Opere di Galilei, Padova, 1744, torn, ii., p. 14, No. 20) ''which you gave me includes the girdle and sword of Orion, and consequently also the star 6; but it is difficult, owing to the striking inaccuracy of the drawing, to recognize the three small stars in the sword (the middle one of which is 6), and which appear to the unaided eye to be placed in a straight line. I conjecture that you have correctly designated the star c, and that the bright star to the right and below, or the one imme- diately above it, is 6." Galileo expressly says, " In primo integram Orionis Constellationem pingere decreveram : verum, ab ingenti stel- larum copia, temporis vero inopia obrutus, aggressionem hanc in aliam occasionem distuli." Considering Galileo's observation of the constel- lation of Orion, we are the more struck by the circumstance that the 400 stars which he thought he had counted between the girdle and the sword of Orion in a space often square degrees (Nelli, Vita di Galilei, vol. i., p. 208), should subsequently (according to Lambert, Cosmolog. Briefe, 1760, p. 155) have led him to the erroneous estimate of 1,050,000 stars for the whole firmament. (Struve, Astr. Stellaire, p. 14, and note 16.) * Cosmos, vol. ii., p. 331. 38 cosmos. happens in using the telescope. Three of this number were almost in contact with one another, and four of them shone as if through a mist, so that the space around them, having the form drawn in the appended figure, appeared much bright- er than the rest of the sky, which was perfectly clear, and looked almost black. This appearance looked, therefoie, al- most as if there were a hiatus or interruption. I have fre- quently observed this phenomenon, and up to the present time as always unchanged in form ; whence it would appear that this marvelous object, be its nature what it may, is very probably permanently situated at this spot. I never observed any thing similar to this appearance in the other fixed stars." (The nebulous spot in Andromeda, described fifty-four years earlier by Simon Marius, must therefore either have been un- known to him, or did not attract his attention.) That which has usually been regarded as nebulous matter, adds Huygens, " even the Milky Way, when seen through telescopes, exhib- its nothing nebulous, and is nothing more than a multitude of stars, thronged together in clusters. "# The animation of * " Ex his autem tres illae pene inter se contiguae stellse, cumque his aliae quatuor, velut trans nebulam lucebant : ita ut spatium circa ip- sas, qua forma hie couspicitur, multo illustrius appareret reliquo ornni coelo ; quod cum apprime serenum esset ac cerneretur nigerrimum, ve- lut hiatu quodam interruptum videbatur, per quem in plagam magis lu- cidam esset prospectus. Idem vero in hanc usque diem nihil immutata facie sa?pius atque eodem loco conspexi ; adeo ut perpetuam illic sedem habere credibile sit hoc quidquid est portenti : cui certe simile aliud nusquam apud reliquas fixas potui animadvertere. Nam creterse nebu- losae olim existimata?, atque ipsa via lactea, perspicillo inspects, nullas nebulas habere comperiuntur, neque aliud esse quam plurium stellarum congeries et frequentia." — Christiani Hugenii, Opera varia, Lugd. Bat., 1724, p. 540-541. " Of these, however, those three almost contiguous stars, and, with these, four others, shone, as it were, through a nebula, so that the space around them, as is shown in this figure, is much more brilliant than all the rest of the sky ; and when this is very serene and appears quite dark, it seemed broken by a sort of gap, through which one looked upon a brighter region behind. The same thing I have since beheld over and over again, without any change in its appearance and in the same position, so that one might almost believe that this marvelous object, whatever it is, is permanently fixed there ; it is cer- tain I have nowhere else noticed any thing similar to this in the other fixed stars ; for those which have generally been considered as nebula?, and even the Milky Way itself, when seen through a telescope, are found to have nothing nebulous about them, but are nothing mote than a mul- titude of several stars clustered together." Huygens himself estimated the powers he employed in his twenty-five feet refractor as equal to a hundred diameters (p. 538). Are the "quatuor stelhe trans nebulam lucentes" the stars of the trapezium ? The small and very rough sketch (Tab. xlvii., fig. 4, Phenomenon in Orione. Novum) represents only a group NEBULiE. 39 Jiis first description testifies the freshness and depth oi* the impressions produced on his mind ; but how great is the dis- tance from this first sketch, made in the middle of the sev- enteenth century, and the somewhat less imperfect descrip- tions of Picard, Le Gentil, and Messier, to the admirable de- lineations of Sir John Herschel (1837), and of William C. Bond (1848), the Director of the Observatory at Cambridge, U. S. !* The former of these two astronomers had the great ad- vantage! of observing the nebula in Orion since 183 1, at the Cape of Good Hope, at an altitude of 60°, and with a twen- ty-feet reflector, by which means he was enabled to render his earlier delineations of 1824-1826 more perfect. $ The positions of 150 stars, mostly of from the fifteenth to the eighteenth magnitudes, in the vicinity of 6 Orionis, were de- termined. The celebrated trapezium, which is not surround- ed by a nebula, is formed of four stars of the fourth, sixth, seventh, and eighth magnitudes. The fourth star was dis- covered (in 1666 ?) by Dominique Cassini, at Bologna ;§ the fifth (y') in 1826, by Struve ; and the sixth (a), which is of the thirteenth magnitude, in the year 1832, by Sir John Herschel. De Yico, the Director of the Observatory at the Collegio Romano, announced in the beginning of the year 1839 that he had discovered three other stars in the trapezi- um with his great Cauchoix refractor. These have not been observed either bv Sir John Herschel or Mr. Bond. That portion of the nebula nearest the almost unnebulous trapezi- um, and forming, as it were, the anterior part of the head above the throat, the regio liuygeniana, is speckled, and of a granular texture, and has been resolved into clusters of stars both by Lord Rosse's colossal telescope and by the large of three stars, near an indentation which one might certainly regard as the Si?ius Magnus. Perhaps the drawing gives only the three stars in the trapezium, which range from the fourth to the seventh magnitude. Dominique Cassini, moreover, boasts that he was the first who observed the fourth star. * William Cranch Bond, in the Transactions of the American Academy of Arts and Sciences, New Series, vol. iii., p. 87-96. t Observations at the Cape, § 54-69, pi. viii. ; Outlines, $ 837 and 885, pi. iv., fig. 1. X Sir John Herschel, in the Memoirs of the Astronomical Society, vol. ii., 1824, p. 487-495, pi. vii., viii. The latter of these gives the nomen- clature of the separate regions of the nebula in Orion, which have been explored by so many astronomers. § Delambre, Hist, de I'Astron. Moderne, torn, ii., p. 700. Cassini reckoned the appearance of this fourth star ("aggiunta della quarta Stella alle tre contigue") among the changes which had taken place in the nebula of Orion in his time. 40 COSMOS. Cambridge (XJ. S.) refractor.* Many positions of the smaller stars have been determined by accurate observers of the pres- ent day ; as, for instance, Lamont at Munich, and Cooper and Lassell in England. The first named of these employed a 1200-fold magnifying power. Sir William Herschel was of opinion, from a comparison of his own observations made with the same instruments, from 1783 to 1811, that altera- tions had taken place in the relative brilliancy and in the outlines of the great nebula of Orion. f Bouilland and Le Gentil had maintained the same opinion in reference to the nebula in Andromeda ; but the thorough investigations of Sir John Herschel have rendered the occurrence of any such cos- mical changes, although formerly considered to be well estab- lished, exceedingly doubtful, to say the least. The large nebula round t] Argils is situated in that por- tion of the Milky Way which extends from the feet of the Centaur, through the Southern Cross, toward the middle part of Argo, and is so distinguished by the intensity of its mag- nificent effulgence. The light emanating from this region is so extraordinary, that Captain Jacob, an accurate observer, and a resident in the tropical parts of India, remarks, entirely in harmony with my prolonged experience, " Such is the gen- eral blaze from that part of the sky, that a person is imme- diately made aware of its having risen above the horizon, though he should not be at the time looking at the heavens, by the increase of general illumination of the atmosphere, re- sembling the effect of the young Moon."$ * " It is remarkable, however, that within the area of the trapezium no nebula exists. The general aspect of the less luminous and cirrous portion is simply nebulous and irresolvable, but the brighter portion, immediately adjacent to the trapezium, forming the square front of the head, is shown with the eighteen-inch reflector broken up into masses (very imperfectly represented in the figure), whose mottled and cur- dling light evidently indicates, by a sort of granular texture, its consist- ing of stars, and when examined under the great light of Lord Rosse's reflector, or the exquisite defining power of the great achromatic at Cambridge, U. S., is evidently perceived to consist of clustering stars. There can, therefore, be little doubt as to the whole consisting of stars, too minute to be discerned individually even with these powerful aids, but which become visible as points of light when closely adjacent in the more crowded parts." — Outlines, p. 609. William C. Bond, who nrnde use of a twenty-five feet refractor, having a fourteen-inch object-gl iss, says, " There is a great diminution of light in the interior of the trapezi- um, but no suspicion of a star." {Memoirs of the American Acade. ■'//s- triacarum, Lips., 1721, torn, i., p. 458. 1547 A.D. The 23d, 24th, and 25th of April, consequently the days preceding and immediately succeeding the battle of Miihlbach, in which the Elector John Frederick wras taken prisoner. Kepler says in Paralipom. ad Vitellium, quibus Astronomia: pars Optica traditur, 1604, p. 259, " The elder and younger Gemma record that in the year THE SUn's SPOTS. 77 As, according to Du Sejour's calculation, the longest possi- ble duration of a total eclipse of the Sun can not be more than 7m. 58s. at the equator, nor more than 6m. 10s. for the lati- tude of Paris, the decrease of daylight which is recorded by the annalists may, on account of its duration for many hours, possibly be referred to one or other of the three following and very different causes : 1 . A disturbance in the process of the evolution of light, as it were a diminution of intensity in the photosphere ; 2. Obstructions (such as a greater and denser formation of clouds) in the outermost opaque vaporous en- velope investing the photosphere, by which the radiation of solar light and heat is impeded ; 3. The impure condition of our atmosphere, arising, for instance, from the obscuring (most- ly organic) meteoric dust, rain, or sand-rain, such as is de- scribed by Macgowan to have continued for several days to- gether in China. The second and third of these causes do not require the occurrence of a diminution of the electro-mag- netic light process, perhaps (of the perpetual polar light*), in the solar atmosphere, but the last-named cause excludes the visibility of stars at noon, of which such frequent mention is made in these mysterious and vaguely-described obscurations. Arago's discovery of chromatic 'polarization has not only confirmed the existence of the third and outermost envelope 1547, before the battle between Charles V. and the Duke of Saxony, the Sun appeared for three days as if it were suffused by blood, while at the same time many stars were visible at noon." " Refert Gemma, pater et filius, anno 1547, ante conflictum Caroli V. cum Saxon ia; Duce, Solem per tres dies ceu sanguine perfusum comparuisse, ut etiam Stellas plereque in meridie conspicerentur." Kepler (in Stella Nova in Serpentario, p. 113) further expresses his uncertainty as to the cause of the phenomenon ; he asks whether the diminution of the Sun's light be owing to some celestial causes: " Solis lumen ob can- i • • sas quasdam sublimes hebetari " whether it be owing to tht> wide diffusion of some cometary substance, " materia cometica latius sparsa," for the cause can not have originated in our atmosphere, since the stars were visible at noon. Schnurrer (Chronik der Seu- chen, th. ii., p. 93) thinks, notwithstanding the visibility of the stars, that the phenomenon must have been the same as the so-called " Hohenrauch," for Charles V. complained before the battle " that the Sun was always obscured when he was about to engage with the enemy." "Semper se nebulae densitate infestari, quo ties sibi cum hoste pugnanduui sit." (Lambert, Hortens. de hello German., lib. vi., p. 182.) * Horrebow {Basis Astronomic, 1735, § 226) makes use of the same expression. Solar light, according to him, is "a perpetual Northern light within the Sun's atmosphere, produced by the agency of powerful magnetic forces." (See Hanow, in Joh. Dan. Titius's Gemoinnutzige Abhandlungcn uber natilrliche Dinge, 17G8, p. 102.) 78 cosmos. of the Sun, but has likewise added considerable weight to the conjectures advanced in reference to the whole physical con- stitution of the central body of our planetary system. " A ray of light which reaches our eyes, after traversing many millions of miles, from the remotest regions of heaven, an- nounces, as it were of itself, in the polariscope, whether it is reflected or refracted, whether it emanates from a solid, or fluid, or gaseous body, it announces even the degree of its in- tensity. {Cosmos, vol. i., p. 52, and vol. ii., p. 332.) It is essential to distinguish between natural light, as it emanates directly from the Sun, the fixed stars, or flames of gas, and is polarized by reflection from a glass plate at an angle of 35° 25', and that polarized light which is radiated as such from certain substances (as ignited bodies, whether of a solid or liquid nature). The polarized light which emanates from the above-named class of bodies very probably proceeds from their interior. As the light thus emanates from a denser body into the surrounding attenuated atmospheric strata, it is re- fracted on the surface, and in this process a part of the re- fracted ray is reflected back to the interior, and is converted by reflection into polarized light, while the other portion ex- hibits the properties of light polarized by refraction. The chromatic polariscope distinguishes the two by the opposite position of the colored complementary images. Arago has shown, by careful experiments extending beyond the year 1820, that an ignited solid body (for instance, a red-hot iron ball), or a luminous, fused metal, yield only ordinary light, in rays issuing in a perpendicular direction, while the rays which reach our eyes from the margins, under very small angles, are polarized. When this optical instrument, by which the two kinds of light could be distinguished, was applied to gas flames, there was no indication of polarization, however small were the angles at which the rays emanated. If even the light be generated in the interior of gaseous bodies, the length of way does not appear to lessen the number and intensity of the very oblique rays in their passage through the rare media of the gas, nor does their emergence at the surface and their transi- tion into a different medium cause polarization by refraction. Now, since the Sun does not either exhibit any trace of polar- ization when the light is suffered to reach the polariscope in a very oblique direction, and at small angles from the margin, it follows from this important comparison that the light shin- ing in the Sun can not emanate from the solid solar body, nor from any liquid substance, but must be derived from a gase- riir. si\ g spots. 79 ous, self-luminous envelope. We thus possess a material phys- ical analysis of the photosphere. The same instrument has, however, also led to the conclu- sion that the intensity of the light of the Sun is not greater in the center of the disk than at its margins. When the two complementary colored images of the Sun — the red and blue — are so arranged that the margin of the one image falls on the center of the other, perfect white will be produced. If the intensity of the light were not the same in the different parts of the Sun's disk — if, for example, the center were more luminous than the margin, then the partial covering of the images in the common segments of the blue and red disk would not exhibit a pure white, but a pale red, because the blue rays would only be able to neutralize a portion of the more numerous red rays. If, moreover, we remember that in the gaseous photosphere of the Sun, in opposition to that which occurs in solid or liquid bodies, the smallness of the angle at which the rays of light emanate does not cause their number to diminish at the margins, and as the same angle of vision embraces a larger number of luminous points at the margins than in the center of the disk, we could not here reckon upon that compensation which, were the Sun a lu- minous iron globe, and consequently a solid body, would take place between the opposite effects of the smallness of the an- gle of radiation and the comprehension of a larger number of luminous points at the same visual angle. The self-lumin- ous gaseous envelope, i. e., the solar disk visible to us, must therefore (in opposition to the indications of the polariscope, which shows the margin and the center to be of equal intens- ity) appear more luminous in the center than at the margin. The cause of this discrepancy has been ascribed to the outer- most and less transparent vaporous envelope surrounding the photosphere, which diminishes the light from the center less than that of the marginal rays on its long passage through the vaporous envelope.* Bouguer, Laplace, Airy, and Sir * Arago, in the M&moires des Sciences Matkdm. et Phys. de V Imtilut de France, annee 1811, partie i., p. 118; Matthieu, in Delambre, Hist, de V Astr. au dix-huitieme siccle, p. 351, 652 ; Fourrier, Eloge de William Herschel, in the Mim. de V Institut, torn, vi., annee 1823 (Par., 1827), p. lxxii. It is alike remarkable and corroborative of the great uniform- ity of character in the light of the Sun, whether emanating from its cen- ter or its margins, that, according to an ingenious experiment made by Forbes, during a solar eclipse in 1836, a spectrum formed from the cir- cumferential rays alone was identical both in reference to the number and position of the dark lines or stripes intersecting it, with the spec- 80 COSMOS. John Herschel, are all opposed to these views of my friend, and consider the intensity of the light weaker at the margin trum arising from the entire solar light. When, therefore, rays of cer- tain refrangibility are wanting in solar light, they have probably not passed into the Sun's atmosphere, as Sir David Brewster conjectures, since the circumferential rays produce the same dark lines when they shine through a much thicker medium. — Forbes, in the Comptes Rendus, torn, ii., 1836, p. 576. I will append to this note all the facts that I col- lected in the year 1847, from Arago's MSS. : " Des phenomenes de la polarisation colore e donnent la certitude que !e bord du Soleil a la meme intensity de lumiere que le centre; car en pla^ant dans la polariscope un segment du bord sur un segment du cen- tre, j'obtiens (comme effet complementaire du rouge et du bleu) un blanc pur. Dans un corps solide (dans une boule de fer chauffee au rouge) le meme angle de vision embrasse une plus grande etendue au bord qu'au centre, selon la proportion du cosinus de Tangle : mais dans la meme proportion aussi, le plus grand nombre de points materiels emettent une lumiere plus faible, en raison de leur obliquiti. Le rap- port de Tangle est naturellemeut le meme pour une sphere gazeuse, rnais l'obliquite ne produisant pas dans les gazes le meme effet de dimi- nution que dans les corps solides, le bord de la sphere gazeuse serait plus lumiueux que le centre. Ce que nous appelons le disque lumi- aeux du Soleil, est la photosphere gazeuse, comme je Tai prouve par le manque absolu de traces de polarisation sur le bord du disque. Pour expliquer done Vegalite d'intensite du bord et du centre indiquee par le polariscope, il faut admettre une enveloppe exterieure, qui diminue (eteint) moins la lumiere qui vient du centre que les rayons qui vien- nent sur le long trajet du bord a Tceil. Cette enveloppe exterieure forme le couronne blanchatre dans les eclipses totales du Soleil. La lumiere qui emane des corps solides et liquides incandescens, est par- tiellement polarisee quand les rayons observes forment, avec la surface de sortie, un angle d'un petit nombre de degres ; mais il u'y a aucune trace sensible de polarisation lorsqu'on regarde de la meme mariiere dans le polariscope des gazes enflammes. Cette experience demontre que la lumiere solaire ne sort pas d'une masse solide ou liquide incan- descente. La lumiere ne s'engendre pas uniquement a la surface des .orps ; une portion nait dans leur substance meme, cette substance fut- elle du platine. Ce n'est done pas la decomposition de Toxygene am- biant qui donne la lumiere. L'emission de lumiere polarisee par le fer iiquide est un effet de refraction au passage vers un moyen d'une moindre densite. Partout ou il y a refraction, il y a production d'un peu de lu- miere polarisee. Les gazes n'en donnent pas, parceque leurs couches ti'ont pas assez de densite. La Lune, suivie pendant le cours d'une lu- naison entiere, offre des effets de polarisation, excepte a Tepoque de la pleine Lune et des jours qui en approchent beaucoup. La lumiere sol- aire trouve, surtout dans les premiers et derniers quartiers, a la surface, hiegale (montagneuse) de notre satellite, des inclinaisons, de plans con- venables pour produire la polarisation par reflexion." " The phenomena of chromatic polarization afford evidence that the margin of the Sun has the same intensity of light as the center; for by placing in the polariscope a segment of the margin upon a central seg- ment, I obtain a pure white as the complementary effect of* red and blue. In a solid body (as in an iron ball heated red-hot), the same visual angle embraces a larger extent of the margin than of the center the sun's sfots. 81 than in the center. The last named of these distinguished physicists and astronomers expresses himself as follows, in reference to this question.^' " Now, granting the existence of such an atmosphere, its form, in obedience to the laws of equilibrium, must be that of an oblate spheroid, the elliptic- ities of whose strata differ from each other and from that of the nucleus. Consequently, the equatorial portions of this according to the ratio of the cosine of the angle ; but in the same ratio, the greater number of the material points emit a feehler light, in con- sequence of their obliquity. The ratio of the angles is naturally the same for a gaseous sphere ; but since the obliquity does not produce the same amount of diminution in gases as in solid bodies, the margin of the gas- eous sphere would be more luminous than its center. That which we tenn the luminous disk of the Sun is the gaseous photosphere, as I have proved by the entire absence of every trace of polarization on the mar- gin of the disk. To explain the equality of intensity indicated by the polariscope for the margin and the center, we must admit the existence of an outer envelope, which diminishes (extinguishes) less of the light which comes from the center than from the marginal rays having a longer way to traverse before they reach the eye. This outer envel- ope forms the whitish corona of light observed in total eclipses of the Sun. The light which emanates from solid and liquid incandescent bodies is partially polarized when the rays observed form an angle of a few degrees with the surface from whence they emerge ; but there is no sensible evidence of polarization when incandescent gases are seen in the polariscope. This experiment proves, therefore, that solar light does not emanate from a solid mass or an incandescent liquid. Light is not engendered solely on the surface of bodies ; but a portion originates within the substance itself, even when the experiment is made with platinum. Light, therefore, is not produced by the decom- position of the ambient oxygen. The emission of polarized light from liquid iron is an effect of refraction during its passage toward a medium of lesser density. Wherever there is refraction, a small amount of po- larized light must be produced : gases do not emit polarized light, be- cause their strata do not possess the requisite amount of density. When the Moon is followed through all its phases, it will be found to afford evidences of polarization, excepting at the full moon, and the days im- mediately preceding and following it. It is more especially during the first and last quarters that the unequal (mountainous) surface of our satellite presents suitable inclinations for the polarization of solar light by reflection." * Sir John H e rsch el, A stron. Observ. made at the Cape of Good Hope, § 425, p. 434; Outlines of Astr., § 395, p. 234. Compare Fizeau and Foucault, in the Comptes Rendus de V Acad, des Sciences, t. xviii., 1844, p. 860. It is remarkable enough that Giordano Bruno, who was burned eight years before the invention of the telescope, and eleven years be- fore the discovery of the spots of the Sun, should have believed in the rotation of the Sun upon its axis. He considered, on the other hand, that the center of the Sun was less luminous than the edges. Owing to an optical deception, he believed that he saw the disk turn round, and the whirling edges expand and contract. (Jordano Bruno, par Christian Bartholmess, torn, ii., 1847, p. 367.) D 2 82 cosmos. envelope must be of a thickness different from that of the polar, density for density, so that a different obstacle must be thereby opposed to the escape of heat from the equatorial and the polar regions of the Sun." Arago is engaged at the present moment in a series of experiments, by which he pur- poses to test not only his own views, but also to reduce the results of observation to accurate numerical relations. A comparison between solar light and the two most intense kinds of artificial light which man has hitherto been able to produce, yields, according to the present imperfect condition of photometry, the following numerical results : Fizeau and Foucault found, by their ingenious experiments, that Drum- mond's light (produced by the flame of the oxyhydrogen lamp directed against a surface of chalk) was to the light of the Sun's disk as 1 to 146. The luminous current, which in Da- vy's experiment was generated between two charcoal points by means of a Bunsen's battery, having forty-six small plates, was to the light of the Sun as 1 to 42 ; but when very large plates were used, the ratio was as 1 to 2 -5, and this light was, therefore, not quite three times less intense than solar light. ^ When we consider the surprise still experienced at the cir- cumstance of Drummond's dazzling light forming a black spot when projected on the Sun's disk, we are doubly struck by the felicity with which Galileo, by a series of conclusions as early as 1612, f on the smallness of the distance from the Sun at which the disk of Yenus was no longer visible to the naked eye, arrived at the result that the blackest nucleus of the Sun's spots was more luminous than the brightest portions of the full Moon. William Herschel, assuming the intensity of the whole light of the Sun at 1000, estimated the average light of the penumbrse at 469, and the black nuclei at 7. According to this estimate, which is certainly very conjectural, a black nu- cleus would yet possess 2000 times more light than the full * Fizeau and Foucault, Recherches sur V Intensity de la Lumiere 6mise par le Charbon dans V Experience de Davy, in the Compfes Rendu s, torn, xviii., 1844, p. 753. " The most intensely ignited solid (ignited quick- lime in Lieutenant Drummond's oxyhydrogen lamp) appear only as black spots on the disk of the Sun when held between it and the eye." — Outlines, p. 36 ( Cosmos, vol. ii., p. 325-326}. t Compare Arago's commentary on Galileo's letter to Marcus Welser, as well as his optical explanation of the influence of the diffuse reflected solar light of the atmospheric strata which covers the object seen in the sky upon the field of a telescope, as it were, with a luminous vail,\n the Annuaire du Bureau des Long, for 1842, p. 482-487. BOLAK LIGHT. s'i Moon, since the latter, according to Bouguer, is 300,000 less bright than the Sun. The degree of illumination of the nu- clei visible to us, i. c, of the dark'body of the Sun illumined by reflection from the walls of the opened photosphere, the interior atmosphere from which the penumbrse are generated, arid by the light of the strata of our terrestrial atmosphere through which we see it, has been strikingly manifested on the occasion of several transits of Mercury. When compared with the planet, whose dark side was turned toward us, the near and darkest nuclei presented a light brownish-gray ap- pearance.* The admirable observer, Counselor Schwabe, of Dessau, was particularly struck by this difference of blackness between the planet and the nuclei, in the transit of Mercury on the 5th of May, 1832. On the occasion of my observing the transit of this planet in Peru, on the 9th of November, 1802, in consequence of being engaged in measuring the dis- tances from the threads, I was unfortunately unable to make any comparison between the different intensities of the light, although Mercury's disk almost touched the nearest dark spot. Professor Henry, of Princeton, North America, had al- ready shown, by his experiments in 1815, that the Sun's spots radiate a perceptibly less heat than those portions on which there were no spots. The images of the Sun and of a large spot were projected on a screen, and the differences of heat- measured by means of a thermo-electrical apparatus.! Whether rays of heat differ from rays of light by a differ- ence in the lengths of the transversal vibrations of ether, or whether they are identical with rays of light, but that a cer- tain velocity in the vibrations which generates very high tem- peratures is requisite to excite the impression of light in our organs, the Sun, as the main source of light and heat, must nevertheless be able to call forth and animate magnetic forces on our planet, and more especially in the gaseous strata of our atmosphere. The early knowledge of thermo-electrical phenomena in crystallized bodies (such as tourmaline, bora- cite, and topaz), and Oersted's great discovery (1820) that every conducting body charged with electricity exerts a defin- ite action on the magnetic needle during the continuation of the electrical current, afforded practical evidence of the cor- relation of heat, electricity, and magnetism. Basing his de- ductions on the idea of such an affinity, Ampere, who ascribed * Midler, Astr., p. 81. t Philos. Mag., ser. iii., vol. xxviii., p. 230; and Poggend., Annalen, bd. lxviii., p. 101. 84 cosmos. all magnetism to electrical currents which lie in a plane at right angles to the axes of the magnet, advanced the in- genious hypothesis that terrestrial magnetism (the magnetic charge of the Earth) was generated by electrical currents, circulating round the planet from east to west ; and that the horary variations of the magnetic declination are on this ac- count consequences of the fluctuations of heat, varying with the position of the Sun, by whose action these currents are excited. These views of Ampere have been confirmed by Seebeck's thermo-magnetic experiments, in which differences of temperature of the points of contact of a circle composed of bismuth and copper, or other heterogeneous metals, affect the magnetic needle. Another recent and brilliant discovery of Faraday's, the notice of which has been of almost simultaneous occurrence with the printing of these pages, throws an unexpected light on the same important subject. While the earlier researches of this great physicist showed that all gases are diamagnetic, i. e., assume a direction from east to west, as bismuth and phosphorus, but that this property is most feebly exhibited in oxygen, it has been shown by his latest researches, which were begun in 1847, that oxygen alone, of all gases, like iron, assumes a position from north to south, and that oxygen gas loses a portion of its paramagnetic force by expansion and by elevation of the temperature. Since the diamagnetic activity of the other constituents of the atmosphere, such as the nitro- gen and carbonic acid, are not modified by expansion or by an elevation of temperature, it only remains for us to consid- er the oxygen, " which surrounds the whole Earth, as it were, like a large sphere of sheet tin, and receives magnetism from it." The half of this sphere which is turned toward the Sun is less paramagnetic than the opposite half; and as the bound- aries of these halves are constantly altered by their rotation and revolution round the Sun, Faraday is inclined to refer a portion of the variations of terrestrial magnetism on the Earth's surface to these thermic relations. The assimilation thus shown by experiment to exist between a single gas (oxy- gen) and iron, is an important discovery of our own age,* which derives additional value from the fact that oxygen probably constitutes the half of all the ponderable matters * Faraday upon atmospheric magnetism, in the Exper. Researches on Electricity, series xxv. and xxvi. (Philos. Transact, for 1851, part i.) § 2774, 2780, 2881, 2892, 2968, and for the history of the investigation, $ 2847. THE sun's spots. 85 that occur in accessible portions of our Earth. Without as- suming magnetic poles in the Sun's body, or any special mag- netic forces in the solar rays, the central body may, as a pow- erful source of heat, excite magnetic activity on our planet. The attempts that have been made to prove, by means of meteorological observations prosecuted for many years at in- dividual spots, that one side of the Sun (for instance, the side which was turned toward the Earth on the 1st of January, 184G) possesses a more intense heating power than the oppo- site one,* have not led to more reliable results than the older Greenwich observations of Maskeleyne, which were supposed to prove that the Sun had decreased in diameter. The observations made by Counselor Schwabe, of Dessau, for reducing the periodicity of the Sun's spots to definite nu- merical relations, appear to have a surer foundation. No as- tronomer of the present day, however admirable may have been his instruments, could have devoted his attention more continuously to this subject than Schwabe, who, during the long period of twenty-four years, frequently examined the Sun's disk upward of 300 days in the year. As his observa- tions of the Sun's spots from 1844 to 1850 have not yet been published, I have presumed so far on our friendship as to re- quest that he would communicate them to me, and at the same time answer a number of questions which I proposed to him. I will close this section of the Physical Constitu- tion of our Central Body with the observations with which this observer has allowed me to enrich the astronomical por- tion of my work. " The numbers contained in the following table leave no doubt that, at least from the year 1826 to 1850, the occur- rence of spots has been so far characterized by periods of ten years, that its maxima have fallen in the years 1828, 1837, and 1848, and its minima in the years 1833 and 1843. I have had no opportunity," says Schwabe, " of acquainting myself with the older observations in a continued series, but I willingly concur in the opinion that this period may itself be further characterized by variability."! * Compare Nervander of Helsingfors, in the Bulletin de la Classe Physico-Mathim. de V Acad, de St. Pttersbourg, torn, iii., 1845, p. 30-32; and Buys-Ballot, of Utrecht, in Poggend., Annalen der Physilc, vol. lxviii., 1846, p. 205-213. t I have distinguished by inverted commas the quotations from Schwabe's manuscript communications from p. 85-87. Only tho ob- servations of the years 1826 to 1843 have already been puhlished in Schumacher's Astron. Nackr., No. 495 (btl. xxi., 1844), p. 235. 86 COSMOS. Year. Groups. Days showing no Spots. Days of Ob- servation. 1826 118 22 277 1827 161 2 273 1828 225 0 282 1829 199 0 244 1830 190 1 217 1831 149 3 239 1832 84 49 270 1833 33 139 267 1834 51 120 273 1835 173 18 244 1836 272 0 200 1837 333 0 168 1838 282 0 202 1839 162 0 205 1840 152 3 263 1841 102 15 283 1842 68 64 307 1843 34 149 312 1844 52 111 321 1845 114 29 332 1846 157 1 314 1847 257 0 276 1848 330 0 278 1849 238 0 285 1850 186 2 308 " I observed large spots visible to the naked eye in almost all the years not characterized by the minimum ; the largest appeared in 1828, 1829, 1831, 1836, 1837, 1838, 1839, 1847, 1848. I regard all spots whose diameter exceeds 50" as large, and it is only when of such a size that they begin to be visible to even the keenest unaided sight. " The spots are undoubtedly closely connected with the formation of faculse, for I have often observed faculse or shal- lows formed at the same points from whence the spots had disappeared, while new solar spots were also developed with- in the faculse. Every spot is surrounded with a more or less bright luminous cloud. I do not think that the spots exert any influence on the annual temperature. I register the height of the barometer and thermometer three times in the course of each day, but the annual mean numbers deduced from these observations have not hitherto indicated any ap- preciable connection between the temperature and the num- ber of the spots. Nor, indeed, would any importance be due to the apparent indication of such a connection in individual cases, unless the results were found to correspond with others derived from many different parts of the Earth. If the solar THE SUN S SPOTS. 87 spots exert any slight miluence on our atmosphere, my tables would, perhaps, rather tend to show that the years which exhibit a larger number of spots had a smaller number of fine days than those exhibiting few spots." (Schum., Astron. Nachr. ,^o. 638, § 221.) " William Herschel named the brighter streaks of light which are seen only toward the Sun's circumference, facidce, and the vein-like streaks visible only toward the center of the Sun's disk, shallows (Astr. Nachr., No. 350, p. 243). I am of opinion that the faculce and shallows are both derived from the same conglobate luminous clouds, which appear more intensely bright at the circumference, but, being less luminous in the center of the Sun's disk than the surface, exhibit the appearance of shallows. I think it preferable to designate all the brighter portions of the Sun as luminous clouds, dividing them, according to their form, into globate and vein-like. These luminous clouds are irregularly dis- tributed over the Sun, and when more strongly manifested occasionally impart a mottled or marbled appearance to the disk. This is often distinctly visible over the entire circum- ference of the Sun, and sometimes even to its poles, but yet always most decidedly manifested in the two proper zones of the spots, even when no spots are visible in those regions. At such times these bright zones of Sun-spots vividly remind one of Jupiter's belts. " The fainter portions lying between the vein-like lumin- ous clouds on the general surface of the Sun are deeper in- dentations, and always present a shagreen-like gray, sand- like appearance, reminding the observer of a mass of uni- formly-sized grains of sand. On this shagreen-like surface we may occasionally notice exceedingly small faint gray (not black) pores, which are further intersected by very delicate dark veins. (Astr. Nachr., No. 473, p. 28G.) These pores, when present in large masses, form gray nebulous groups, constituting the penumbrsB of the Sun-spots. Here the pores and black points may be seen spreading from the nucleus to the circumference of the penumbra, generally in a radiating form, which occasions the identity of configuration so frequently ob- served to exist between the penumbra and the nucleus." The signification and connection of these varying phenom- ena can never be manifested in their entire importance to the inquiring physicist until an uninterrupted series of repre- sentations of the Sun's spots* can be obtained by the aid of * Sir John Herschel, Observations at the Cape, p. 434. 88 cosmos. mechanical clock-work and photographic apparatus, as the result of prolonged observations during the many months of serene weather enjoyed in a tropical climate. The meteor- ological processes at work in the gaseous envelopes of the dark body of the Sun are the causes which produce the phe- nomena termed Sun-spots and conglobate luminous clouds. It is probable that there, as in the meteorology of our own planet, the disturbances of very multifarious and complicated character depend upon such general and local causes, that it can only be by means of prolonged observations, character- ized by completeness, that we can hope to solve even a por- tion of this still obscure problem. II. THE PLANETS. General comparative considerations of a whole class of cosmical bodies must here precede their individual descrip- tion. These considerations refer to the 22 principal planets and 21 moons {satellites, or secondary planets'] which have been discovered up to the present time, not to the planetary bodies in general, among which the comets whose orbits have been calculated are alone ten-fold more numerous. The planets possess, upon the whole, a feeble scintillation, inas- much as they shine by the reflected light of the Sun, and their planetary light emanates from disks. (Cosmos, vol. hi., p. 76.) In the ash-colored light of the Moon, as well as in the red light of its obscured disk, which is seen with great in- tensity between the tropics, the Sun's light undergoes, in reference to the observer upon the Earth, a twice repeated change in its direction. Attention has been already directed elsewhere* to the fact that the Earth and other planets pos- sess in themselves a feeble power of emitting light, as is specially proved by some remarkable phenomena upon that portion of Venus which is turned away from the Sun. "We shall consider the planets according to their number, the sequence of their discovery, their volumes compared either with each other or with their distances from the sun ; ac- cording to their relative densities, masses, periods of rotation, degrees of eccentricity, the inclinations of their axes, and characteristic differences within and beyond the zone of the * Cosmos, vol. i., p. 201, and note p. 202. THE 1'LANETS. 89 small planets. In the comparative contemplation of these subjects, it is consistent with the nature of this work to be- stow especial attention upon the selection of the numerical relations, which, at the period in which these pages appear, are considered to be the most accurate, i. e., the results of the most recent and reliable investigations. a. PRINCIPAL PLANETS. 1. Number and Epoch of Discovery. — Of the seven cos* mical bodies which, from the most remote antiquity, have been distinguished by their constantly varying relative po- sition toward each other from those which apparently main- tain the same positions and distances — the scintillating stars of the region of fixed stars [orbis inerrans] — there are only five which appear star-like, " quinque stellce errantes ;" they are Mercury, Venus, Mars, Jupiter, and Saturn. The Sun and the Moon remained almost separated from the others, since they form large disks, and also on account of the greater importance attached to them in accordance with religious myths.*1 Thus, according to Diodorus (ii., 30), the Chaldeans were acquainted with only five planets. Plato also says distinctly in the Timaius, where he only once mentions the planets, "Hound the Earth, fixed in the center of the Cosmos, move the Moon, the Sun, and five other stars, which have received the name of planets ; the whole, therefore, in seven revolutions."! In the old Pythagorean representation of the celestial system, according to Philolaus, the five planets were mentioned in a similar manner among the ten deified bod- ies which revolve round the central fire (the focus of the universe, tor la) " immediately beneath the region of fixed stars ;"$ these were succeeded by the Sun, Moon, Earth, and the avrixQuv (the anti-Earth). Even Ptolemy always speaks of only five planets. The enumeration of the planets in sys- tems of seven, as Julius Firmicus distributed them among the decani, k as they are represented in the zodiacal circle of Bi- * Gesenius, in the Hallischen Litteratur-Zeitung, 1822, Nos. 101 and 102 (Supplement, p. 801-812). Among the Chaldeans, the Sun aud Moon were held to be the two principal deities ; the five planets mere- ly represented genii. t Plato, in the TimcEiis, p. 38, Steph. ; Davis's translation, ed. Bohn, p. 342. X Bockh, De Platonico systemate Coslestium globorum et de vera in- dole astronomies Philolaicce, p. xvii., and the same in Philolaus, 1819, p. 99. § Jul. Firmicus Materuus, Astron., libri viii. (ed. Pruckner, Basil 1551), lib. ii., cap. 4, of the time of Constantine the Great. 90 COSMOS. anchini (probably of the third century after Christ), exam- ined by myself elsewhere,* and as they are met with in the Egyptian monuments of the time of the Caesars, does not be- long to the ancient astronomy, but to the subsequent epochs, in which astrological chimeras had become universally dif- fused.! We must not be surprised that the Moon was in- cluded in the series of the seven planets, since, with the ex- ception of a memorable theory of attraction put forward by Anaxagoras {Cosmos, vol. ii., p. 309, and note), its more intimate connection with the Earth was scarcely ever sus- pected by the ancients. On the contrary, according to an opinion respecting the system of the world which VitruviusJ and Martianus Capella§ quote, without stating its originator, Mercury and Venus, which we call planets, are represented as satellites of the Sun, which itself revolves round the Earth. * Humboldt, Monumens des Peuples Indigenes de V Amirique, vol. ii., p. 42-49. I have already directed attention in 1812 to the analogy be- tween the zodiac of Bianchini and that of Dendera. Compare Letronne, Observations Critiques sur les Representations Zodiacales, p. 97 ; and Lepsius, Chronologie der JEgypter, 1849, p. 80. t Letronne, Sur VOrigine du Zodiaque Grec, p. 29. Lepsius, Chro nol. der yEgypt., p. 83. Letronne opposes the old Chaldean origin of the planetary week on account of the number seven. t Vitruv., De Arckit., ix., 4 (ed. Rode, 1800, p. 209). Neither Vitru- vius nor Martianus Capella mention the Egyptians as the originators of a system, according to which Mercury and Venus are considered as sat- ellites of the planetary Sun. The former says, " Mercurii autem et Ve- neris stelhe circum Solis radios, solem ipsum, uti centrum, itineribus coronantes, regressus retrorsum et retardationes faciunt." "But Mer- cury and Venus, which encircle in their orbits the Sun itself as a center, retrogress and proceed slowly round its rays." § Martianus Mineus Felix Capella, De Nuptiis Philos. et Mercurii, lib. viii. (ed. Grotii, 1599, p. 289) : " For though Venus and Mercury appear to rise and set daily, yet their orbits do not, however, go round the Earth, but revolve round the Sun in a wider orbit. In fact, the center of their orbits is in the Sun, so that they are sometimes above it . . . ." " Nam Venus Mercuriusque licet ortus occasusque quotidianos osten- dant, tamen eorum circuli Terras omnino non ambiunt, sed circa Solem laxiore ambitu circulantur. Denique circulorum suorum centrum in Sole constituunt, ita ut supra ipsum aliquando " As this place is written over, " Quod Tellus non sit centrum omnibus planetis," *' Be- cause the Earth is not the center of all the planets," it may certainly, as Gassendi asserts, have had an influence upon the first views of Coper- nicus, more than the passages attributed to the great geometer, Apol- lonius of Perga. However? Copernicus only says, " Minime contem- nendum arbitror, quod Martianus Capella scripsit, existimans quod Ve- nus et Mercurius circumerrant Solem in medio existentem." " 1 by no means think that we should despise what Martianus Capella has writ- ten, who supposes that Venus and Mercury revolve round the Sun, which is fixed in the center " Compare Cosmos, vol. ii., p. 312, and note. THE PLANETS. 01 There is as little foundation for considering such a system as this to be Egyptian,* as there is for confounding it with the Ptolemaic epicycles or the system of Tycho. The names by which the star-like planets of the ancients were represented are of two kinds : names of deities, and significantly descriptive names derived from physical char- acters. Which part of them originally belonged to the Chal- deans, and which to the Egyptians, is so much the more dif- ficult to determine from the sources which have hitherto been made use of, as the Greek writers present us, not with the original names employed by other nations, but only transla- tions of these into Greek equivalents, which were more or less modified by the individuality of those writers' opinions. What knowledge the Egyptians possessed anterior to the Chal- deans, whether these latter are to be considered merely as gift- ed disciples of the former,! is a question which infringes upon the important but obscure problem of primitive civilization of the human race, and the commencement of the develop- * Henry Martin, in his Commentary to the Timceus (Etudes sur le Timie de Platon, torn, ii., p. 129-133), appears to me to have explain- ed very happily the passage in Macrobius respecting the ratio Chaldao- rum, which led the praiseworthy Ideler into error (in Wolff's and Bntl matin's Museum der Alterthums-Wissenschaft, bd. ii., s. 443, and in his Treatise -upon Eudoxus, p. 48). Macrobius (in Somn. Scipionis, lib. i., cap. 19 ; lib. ii., cap. 3, ed. ]634, p. 64 and 90) says nothing of the sys- tem mentioned by Vitrnvius and Martianus Capella, according to which Mercury arid Venus are satellites of the Sun, which, however, itself re- volves with the other planets round the Earth, which is fixed in the center. He enumerates only the differences in the succession of the orbits of the Sun, Venus, Mercury, and the Moon, according to the views of Cicero. He says, '-Ciceroni, Archimedes et Chaldaeorum ra- tio consentit ; Plato /Egyptios secutus est." " Archimedes and the sys- tem of the Chaldseans agree; Plato followed that of the Egyptians." When Cicero exclaims, in the eloquent description of the whole plan- etary system (Somn. Scip., cap. 4, Edmond's translation, ed. Bohn, p. 294). " Hunc (Solem) ut comites consequuutur Veneris alter, alter Mer- curii cursus;" " The motions of Venus and Mercury follow it (the Sun) as companions," he refers only to the proximity of the Sun's orbit and those of the two inferior planets, after he had previously enumerated the three cursus of Saturn, Jupiter, and Mars, all revolving round the immovable Earth. The orbit of a secondary planet can not surround that of a principal planet, and yet Macrobius says distinctly, " /Egyp- tiorum ratio talis est: circulus, per quern Sol discurrit, a Mercurii cir- culo ut inferior ambitur, ilium quoque superior circulus Veneris inclu- dit " " The following is the system of the Egyptians : the circle in which the Sun moves is encompassed by the circle of Mercury, which in its turn is encircled by the larger one of Venus." The orbits are all permanently parallel to each other mutually surrounding. t Lepsius, Chronologie der JEgyptcr, th. i., p. 207. 92 cosmos. ment of scientific ideas upon the Nile or the Euphrates. The Egyptian names of the 36 Decans are known ; but the Egyp- tian names of the planets, with the exception of one or two, have not been transmitted to us.^ It is remarkable that Plato and Aristotle employed only the names of deities for the planets which Diodorus also mentions ; while at a later period, for example, in the book De Mundo, erroneously attributed to Aristotle, a combina- tion of both kinds of names are met with, those of deities, and the descriptive (expressive) names : (paivuv for Saturn. a~iX- 6cjv for Mercury, nvpoeig for Mars.f Although the name * The name of the planet Mars, mutilated by Vettius Valens and Cedrenus, must, in all probability, correspond to the name Her-tosch, as Seb does to Saturn. (Lepsius, Chronol. der JEgypt., p. 90 and 93.) t The most striking differences are met with on comparing Aristot., Metaph., xii., cap. 8, p. 1073, ed. Bekker, with-Pseudo-Aristot., De Mun- do, cap. 2, p. 392. The planet names Phaethou, Pyrois, Hercules, Stil- bon, and Juno, appear in the latter work, which points to the times of Apuleius and the Antonines, in which Chaldean astrology was already diffused over the whole Roman empire, and the terms of different na- tions mixed with each other. (Compare Cosmos, vol. ii., p. 29, and note). Diodorus Siculus says positively that the Chaldeans first named the planets after their Babylonian deities, and that these names were thus transferred to the Greeks. Ideler (Eudoxus, p. 48), on the cou- traiy, ascribes these names to the Egyptians, and grounds his ai'gument upon the old existence on the Nile of a seven-day planetary week ( Hand- buck der Chronologic, bd. i., p. 180): an hypothesis which Lepsius has completely disproved (Chronologie der JEg., th. i., p. 131). I will here collate from Eratosthenes, from the editor of Epinomis (Philippus Opuntius?), from Geminius, Pliny, Theou of Smyrna, Cleomedes, Achil- les Tatius, Julius Firmicus, and Simplicius, the synonyms of the five oldest planets, as they have been transmitted to us chiefly through pre- dilection for astrology : Saturn: (paivuv, Nemesis, also called a sun by five authors (Theon. Smyrna, p. 87 and 105, Martin) ; Jupiter : (paeOuv, Osiris ; Mars: Ttvpoeig, Hercules; Venus: euoQopog, quotiopog, Lucifer; eairepog, Vesper ; Juno, Isis; Mercury: ct'O&uv, Apollo. Achilles Tatius (Isag. in Phaen. Arati, cap. 17) considers it strange " that the Egyptians, as well as the Greeks, should call the least lumin- ous of the planets the shining" (perhaps only because it brought pros- perity). According to Diodorus, the name refers to the opinion " that Saturn was that planet which principally and most clearly foretold the future." — Letronne, Sur VOrig'me du Zodiaque Grec, p. 33, and in the Journal des Savarits, 1836, p. \7 . Compare also Carte ron, Analyse des Recherches Zodiacales, p. 97. Names which are transmitted as equiv- alents from one people to another, certainly depend in many cases, in addition to their origin, upon accidental circumstances, which can not be investigated ; however, it is necessary to remark here, that etymo- iogically, (ftaivetv expresses a mere shining, a fainter evolution of light, THE PLANETS. 93 of Sun was strangely enough applied to Saturn, the outer- most of the then known planets, as is proved by several pas- which is continuous or constant in intensity, while ori?i6eiv refers to an intermittent scintillating light of greater brilliancy. The descriptive names: a£duv) to the colored glowing Mars (ivvpdeic ), to Venus ((puoipdpoc), and to Mer- cury (oti?i6uv). My acquaintance with the Indian name of Saturn (' sanaistschara), the slowly wandering, induced me to ask my celebrated friend Bopp whether, upon the whole, a distinction between names of deities and descriptive names was also to be made in the Indian planetary names, as in those of the Greeks, and probably the Chaldeans. I here insert the opinion, for which I am indebted to this great philologist, arrang- ing the planets, however, according to their actual distances from the Sun, as in the above table (commencing with the greatest distance), not as they stand in Amarakoscha (by Colebrooke, p. 17 and 18). There are, in fact, among the five Sanscrit names three descriptive ones : Sat- urn, Mars, and Venus. " Saturn: 'sanaistschara, from 'sanais, slow, and tschara, going: also 'sauri, a name of Vishnu (derived as a patronymic from 'sura, Grand- father of Kii) and 'sani. The planet name 'sani-varafor, ' dies Saturni,' is radically related to the adverb 'sanais, slow. The names of the week- days derived from planets appears, however, not to have been known to Amarasinha. They are, indeed, of later introduction. " Jupiter : Vrihaspati ; or, according to an older Vedic mode of writ- ing which Lassen follows, Brihaspati : the Lord of increase, a Vedic deity: from vrih (brih), to grow, and pati, lord. "Mars: angaraka (from angara, burning coal); also lohitanga, the red body : from lohita, red, and anga, body. " Venus: a male planet, which is called sukra, i. e., the brilliant. An- other name of this planet is daitya-guru: Teacher, guru, the Titans, Daityas. " Mercury : Budha not to be confounded as a planet name with Buddha, the founder of the religious sect; also Rauhineya, the son of the nymph Rohinl, wife of the Moon (soma), on which account the plan- et is sometimes called saumya, a patronymic of the Sanscrit word mond. The etymological root of budha, the planet name, and buddha, the name of the saint, is budh, to know. It seems to me improbable that Wuotan (Wo tan, Odin) are connected with Budha. This conjecture is found- ed, indeed, principally upon the external similarity of form, and upon the correspondence of the name of the day of the week, ' dies Mercu- rii,' with the old Saxon Wodanes-dag, and the Indian Budha-vara, i. e., Budha's day. The primitive signification of vara is repetition, for ex- ample, in bahuvaran, many times, often ; it subsequently occurs at the end of a compound word with the signification day. Jacob Grimm derives the German Wuotan from the verb watan, vuot (the German waten), which signifies meare, transmeare, cum impetu ferri, and ortho- graphically corresponds to the Latin vadere. (Deutsche Mylhologie, p. 94 cosmos. sages in the Commentary of Simplicius (p. 122), to the eighth book of the De Codo of Aristotle, in Hyginus, Diodorus, and Theon of Smyrna, it certainly was only its position, and the length of its orbit, which raised it above the other planets. The descriptive names, however old and Chaldean they may be, were not very frequently employed by the Greek and Ro- man writers until the time of the Caesars. Their diffusion is connected with the influence of astrology. The planetary signs are, with the exception of the disk of the Sun and the Moon's crescent upon Egyptian monmnents, of very recent origin ; according to Letronne's researches,^ they would not 120.) Wuotan, Odinn, is, according to Jacob Grimm, the all-powerful, all-penetrating being : ' qui omnia permeat,' as Lucan says of Jupiter." — Compare, with reference to the Indian names of the days of the week, Budha and Buddha, and the week-days in general, the observations of my brother, in his work Ueber die Vcrbindungen zwischen Java und In- dien (Kawi Sprache, bd. i., p. 187-190). * Compare Letronne, Sur V Amulette de Jules Cesar et les Signes Plan- ctaires, in the Revue Arche'ologiqve, Annee III., 1846, p. 261. Salmasius considered the oldest planetary sign for Jupiter to be the initial letter of Zevc, that of Mars a contraction of the cognomen -&ovpiog. The sun- disk was rendered almost unrecognizable by an oblique and triangular bundle of rays issuing from it. As the Earth was not included among the planets in any of the ancient systems, except, perhaps, the Philo- Pythagorean, Letronne considers the planetary sign of the Earth " to have come into use after the time of Copernicus." The remarkable passage in Olympiodorus, on the consecration of the metals to individ- ual planets, is taken from Proclus, and was traced by Boekh (it is in p. 14 of the Basil edition, and at p. 30 of Schneider's edition). — Com- pare, for Olympiodorus, Aristot., Meteorol., ed. Ideler, torn, ii., p. 163. The scholium to Pindar (Isthm.), in which the metals are compared with the planets, also belongs to the new Platonic school. — Lobeck (Aglaophamus in Orph., torn, ii., p. 936). In accordance with the same connection of ideas, planetary signs by-and-by became signs of the met- als ; indeed, some (as Mercurius, for quicksilver, the argentum vivum and hydrargyrus of Pliny) became names of metals. In the valuable collection of Greek manuscripts of the Paris Library are two manu- scripts on the cabalistic, or so-called sacred art, of which one (No. 2250) mentions the metals consecrated to the planets without planetary signs; the other, however (No. 2329), which, according to the writing, is of the fifteenth century (a kind of chemical dictionary), combines the names of the metals with a small number of planetary signs. (Hofer, Histoire de la Chimie, torn, i., p. 250.) In the Paris manuscript No. 2250, quicksilver is attributed to Mercury, and silver to the Moon, while, on the contrary, in No. 2329, quicksilver belongs to the Moon, and tin to Jupiter. Olympiodorus has ascribed the latter metal to Mer- cury. Thus indefinite were the mystic relations of the cosmical bodies to the metallic powers. This is also the appropriate place to mention the planetary hours and the planetary days in the small seven-day period (the week), concern- ing the antiquity and diffusion of which among remote nations more THE PLANETS. 95 date further back than the tenth century. Even upon stones with Gnostic inscriptions they are not met with. Subsequent correct views have only recently been established. The Egyptians had originally no short periods of seven clays, but periods often days, simi- lar to the week, as has been proved by Lepsius (Chronologie der JEg., p. 132), and as is also testified by monuments which date back to the most remote times of the erection of the large pyramids. Three such decades formed one of the twelve months of the solar year. On read- ing the passage in Dio Cassius (lib. xxxvii., cap. 18), " That the custom of naming the days after the seven planets was first adopted by the Egyptians, and had, in no very long time, been communicated by them to all other nations, especially the Romans, with whom it was then al- ready quite familiarized," it must not be forgotten that this writer lived in the later period of Alexander Severus, and that, since the first irrup- tion of the Oriental astrology under the Caesars, and in consequence of the early and extensive commerce of so many races of people in Alex- andria, it was the fashion among Western nations to call every thing Egyptian which appeared ancient. The seven-day week was undoubt- edly the earliest and most diffused among the Semitic nations ; not only among the Hebrews, but even among the nomadic Arabians long be- fore the time of Mohammed. I have submitted to a learned investiga- tor of Semitic antiquities, the Oriental traveler Professor Tischendorf, at Leipsic, the question whether, besides the Sabbath, there occur in the Old Testament any names for the individual days of the week (other than the second and the third of the schebua) 1 Whether no planetary name for any one day of the seven-day period occurred any where in the New Testament at a period in which it was certain that the foreign inhabitants of Palestine already pursued planetary astrology ? The an- swer was, " There is an entire absence, not only in the Old and New Testameuts, but also in the Mischna and Talmud, of any traces of names of week-days taken from the planets. Neither is the expression the second or third day of the schebua employed ; and time is general- ly reckoned by the days of the month ; the day before the Sabbath is also called the sixth day, without any further addition. The word Sab- bath was also transferred to the week throughout (Ideler, Handbuch der Chronol., bd. i., p. 780); consequently, the first, second, and third day of the Sabbath stand for the days of the week in the Talmud as well. The word e66o/j.uc for schebua is not in the New Testament. The Talmud, which certainly extends from the second to the third cen- tury, has descriptive Hebrew names for a few planets, for the brilliant Venus and the red-colored Mars. Among these, the name of Sabbatai (literally Sabbath-star) for Saturn is especially remarkable, as among the Pharisaic names of the stars which Epiphanius enumerates, the name Hochab Sabbath is employed for Saturn." Has not this had an influ- ence upon the conversion of Sabbath day into Saturn day, the " Saturni sacra dies" of Tibullus (Eleg., i., 3, 18)? Another passage in Tacitus extends the range of these relations to Saturn as a planet and as a tra- ditional historical personage. (Compare also Fiirst, Kultur- vnd. Litle- raturgeschichte der Juden in Asien, 1849, p. 40.) The different luminous forms of the Moon certainly attracted the ob- servation of hunters and herdsmen earlier than astrological phantasms. It may therefore be assumed, with Ideler, that the week has origin- ated from the length of the synodic months, the fourth part of which amounts, on the average, to 7$ days; that, on the contrary, references 96 cosmos. transcribers have, however, added them to Gnostic and al- chemistic manuscripts ; scarcely, in any case, to the oldest to the planetary series (the sequence of their distances from each oth- er), together with the planetary hours and days, belongs to an entirely different period of advanced and speculative culture. With reference to the naming of the individual week-days after plan- ets, and the ammgement and succession of the planets — Saturn, Venus, Jupiter, Mercury, and Mars, Moon, Sun, situated, according to the most ancient and widely-diffused belief (Gem- inus, Element. Astr., p. 4; Cicero, Somn. Scip., cap. 4; Firmicus, ii., 4, Edmond?s translation, ed. Bohn, p, 294-298), between the sphere of fixed stars and the immovable earth as a central body, there have been three views put forward : one derived from musical intervals ; another from the astrological names of the planetary hours ; a third from the distribution of each three decans, or three planets, which are the rulers (domini) of these decans among the twelve signs of the zodiac. The first two hypotheses are met with in the remarkable passage of Dio Cassius, in which he endeavors to explain (lib. xxxvii., cap. 17) why the Jews, according to their laws, celebrated the day of Saturn (our Saturday). "If," says he, " the musical interval which is called did. reaadpov, the fourth, is applied to the seven planets according to their times of revolution, and Saturu, the outermost of all, taken as the start- ing-point, the next which occurs is the fourth (the Sun), then the sev- enth (the Moon), and in this way the planets are encountered in the same order of succession in which their names have been applied to the week-days." A commentary upon this passage is given by Vincent, Sur les Manuscrits Grecs relative a la Musique, 1847, p. 138. Compare also Lobeck, Aglaophamus, in Orph., p. 941-946. The second expla- nation of Dio Cassius is borrowed from the periodical series of the plan- etary hours. " If," he adds, "the hours of the day and the night are counted from the first (hour of the day), and this ascribed to Saturn, the following to Jupiter, the third to Mars, the fourth to the Sun, the fifth to Venus, the sixth to Mercury, the seventh to the Moon, always recommencing from the beginning, it will be found, if all the twenty- four hours are gone through, that the first hour of the following day coincides with the Sun, the first of the third with the Moon; in short, the first hour of any one day coincides with the planet after which the day is named." In the same way, Paulus Alexandrinus, an astronomic- al mathematician of the fourth century, calls the ruler of each week- day that planet whose name agrees with the first hour of the particular day. These modes of explaining the names of week-days have hitherto been very generally considered as the more correct ; but Letronne en- tertains a third explanation — the distribution of any three planets over a sign of the zodiac — which he considers to be the most adequate, upon the evidence of the long-neglected zodiacal circle of Bianchini, pre- served in the Louvre, to which I myself directed the attention of ar- chaeologists in 1812, on account of the remarkable combination of a Greek and Kirgisch-Tartar zodiac. (Letronne, OLserv. Crit. et Archtol. sur VObjet. des Representations Zodiacales, 1824, p. 97-99.) This dis- tribution of planets among the 36 decans of the Dodecatomerla is pre- THE TLA NETS 97 manuscripts of Greek astronomers ; of Ptolemy, of Theon, or of Cleomedes. The earliest planetary signs, some of which cisely that which Julius Firmicus Maternus (ii., 4) describes as " sig- norum decani eorumque domini." If those planets are separated which in each of the signs are the first of the three, the succession of the plan- etary days in the week is obtained (Virgo: Sun, Venus, Mercury; Libra: Moon, Saturn, Jupiter ; Scorpio: Mars, Sun, Venus; Sagittarius: Mercury which may here serve as an example for the first four days of the week : Dies Soils, Luna, Martis, Mercurii). As, according to Diodorus, among the Chaldeans, the number of the planets (star- like) originally amounted only to five, and not seven, all the here-men- tioned combinations in which more than five planets form periodical series appear to be not of old Chaldean origin, but much rather to date from a subsequent astrological period. (Letronne, Sur V Orlglne du Zodiaque Grec, 1840, p. 29.) With respect to the concordance of the arrangement of the planets as days of the week with their arrangement and distribution among the decans in the zodiacal circle of Bianchini, a brief explanation will, perhaps, be acceptable to some readers. If a letter is assigned to each cosmical body in the order of succession adopted in antiquity (Saturn a, Jupiter b, Mars c, Sun d, Venus e, Mercury /, Moon g), and with these seven members the following periodical series are formed— a b c d ef g, abed.... there is obtained, 1st, by passing over two members of the distribution among the decans, each of which comprises three planets (the zodiacal sign of the first one giving, in each case, its name to the week-day), the new periodical series adgefbe, adgc.... that is, Dies Saturni, Soils, Lunce, Martis, and so on; 2dly, the same new series, adgc.... obtaiued by the method of Dio Cassius, according to which the sue cessive week-days take their names from the planet which rules the first hour of the day, so that alternately a member of the periodical seveu-membered plauet-series is to be taken, and twenty-three mem- bers to be passed over. Now it is immaterial, in the case of a period- ical series, whether it is a certain number of members which is passed over, or whether it is this number increased by any multiple of the number of members (in this case seven) of the period. By passing over twenty-three (=3.7-|-2) members, according to the second meth- od, that of the planetary hours, the same result is obtained as when the first method, that of the decans, is adopted, in which only two members are to be passed over. Attention has already been directed (page 92, note t) to the remark- able resemblance between the fourth day of the week, dies Mercurii, of the Indian Budha-vara, and the old Saxon Wodanes-dag. (Jacob Grimm, Deutsche Mythologie, 1814, bd. i., p. 841.) The identity af- firmed by William Jones to exist between the founder of the Buddhist religion and the race of Odin or Wuotau, and Wotan, famous in North- ern heroic tales, as well as in the history of Northern civilization, will, perhaps, gain more interest when it is called to mind that the name of Wotan is met with in a part of the new continent as belonging to a half- mythical, half-historical personage concerning whom I have collected Vol. TV.— E OS COSMOS. (Jupiter and Mars) originated, as Salmasius has shown, with his ordinary acuteness, from letters, and were very different from ours ; the present form reaches scarcely beyond the fif- a great number of notes in my work on the monuments an il myths of the natives of America (Vues des Cordilleres et Monumens des Peuples Indigenes de V Ameriqite, torn, i., p. 208, and 382-384 ; torn, ii., p. 356). This American Wotan is, according to the traditions of the natives of Chiapa and Soconusco, the grandson of the man who saved his life in a boat during the great deluge, and renewed the human race ; he com- menced the erection of large buildings, during which time ensued a confusion of languages, war, and dispersion of races, as in the erection of the Mexican pyramids of Cholula. His name was also transferred to the calendar of the natives of Chiapa, as was the name of Odin in the north of Germany. One of the five-day periods — four of which formed the month of the people of Chiapa and the Aztecs — was named after him. While the names and signs of the days among the Aztecs were taken from animals and plants, the natives of Chiapa (properly Teochiapan) assigned to the days of the month the names of twenty chieftains who, coming from the north, had led them so far southward. The names of the four most heroic, Wotan or Wodan, Lambat, Been, and Chiuax, commenced the small periods of five-day weeks, as did the svmbols of the four elements among: the Aztecs. Wotan and the other chieftains indisputably belonged to the race of the Tolteks, who invaded the country in the seventh century. Ixtlilxochitl (his Christian name was Fernando de Alva), the first historian of his people (the Aztecs), says distinctly, in the manuscripts which he completed as early as the beginning of the sixteenth century, that the province of Teochiapan and the whole of Guatemala were peopled by Tolteks from one coast to the other; indeed, in the beginning of the conquest of the Spaniards, a family was still living in the village Teopixca who boasted of being descended from Wotan. The Bishop of Chiapa, Francisco Nunez de la Vega, who presided over a provincial council in Guatemala, has, in his Preambulo de las Constituciones Diocesanas, collected a great deal of information respecting the American tradition of Wotan. It is also still very undecided whether the tradition of the first Scandinavian Odin (Odinn, Othinus) or Wuotau, who is said to have emigrated from the banks of the Don, has an historical foundation. (Jacob Grimm, Deutsche Mythologie, bd. i., p. 120-150.) The identity of the Ameri- can and Scandinavian Wotan, certainly not founded on mere resem- blance of sound, is still quite as doubtful as the identity of Wuotan (Odinn) and Buddha, or that of the names of the founder of the Bud- dhist religion and the planet Budha. The assumption of the existence of a seven-day Peruvian week, which is so often brought forward as a Semitic resemblance in the division of time in both continents, is founded upon a mere error, as has been al- ready proved by Father Acosta (Hist. Natural y Moral de las Indias, 1591, lib. vi., cap. 3), who visited Fern soon after the Spanish conquest; and the Inca, Garcilaso de la Vega, himself corrects his previous state- ment (parte i., lib. ii., c. 35) by distinctly saying there were three fes- tivals in each of the months which were reckoned after the moon, and that the people should work eight days and rest upon the ninth (parte i., lib. vi., cap. 23). The so-called Peruvian weeks, therefore, con listed of nine days. (See my Vues des Cordillens. torn. i.. p. 311-3 13 THE PLANETS. 9'J teenth century. The symbolizing habit of consecrating cer- tain metals to the planets belongs, undoubtedly, to the new Platonic doctrines of the Alexandrian school in the fifth cen- tury, as is ascertained from passages in Proclus {ad Tim., ed. Basil, p. 14), from Olympiodorus, as well as by a late scholium to Pindar (Isthm., vol. ii.). (Compare Olympiod., Comment. in Arislot., Meteorol., cap. 7, 3 in Ideler's edition of the Me- teorol., torn, ii., p. 163 ; also torn, i., p. 199 and 251 .) Although the number of the visible planets amounted, ac- cording to the earliest limitation, to five, and subsequently, by the addition of the large disks of the Sun and Moon, in- creased to seven, conjectures were prevalent, even in antiqui- ty, that beyond these visible planets there were yet other less luminous, unseen planets. This opinion is stated by Simpli- cius to be Aristotelean. "It is probable that such dark cos- mical bodies which revolve round the common center some- times give rise to eclipses of the moon as well as the earth." Artemidorus of Ephesus, whom Strabo often mentions as a geographer, believed in the existence of an unlimited number of such dark, revolving cosmical bodies. The old ideal body, the anti-earth (dvrcxOcJv) of the Pythagoreans, does not be- long to this class of conjectures. The earth and the anti- earth have a parallel concentric motion ; and the anti-earth, conceived in order to avoid the assumption of the rotatory motion of the earth, moving in a planetary manner round the central fire in twenty-four hours, can scarcely be any thing else than the opposite hemisphere — the antipodean portion of our planet.* When from the 43 principal and secondary planets now known (a number six times greater than that of the planet- ary bodies known to the ancients), the 36 objects which have been discovered since the invention of the telescope are chro- nologically separated according to the succession of their dis- covery, there is obtained for the seventeenth century nine, for the eighteenth century also nine, and for the half of the nineteenth century eighteen newly-discovered planet*. * Bockh, Uebcr Philolaus, p. 102 aud 117. 100 . COSMOS. Sequence of the Planetary Discoveries (of principal and secondary planets) since the Invention of the Telescope in the Year 1608. (A.) The Seventeenth Century. Four satellites of Jupiter : Simon Marius, at Ansbach, De- cember 29, 1609 ; Galileo, January 7, 1610, at Padua. Triple configuration of Saturn : Galileo, November, 1610 ; Hevelius, hypothesis of two lateral bars, 1656 ; Huygens', final discovery of the true form of the ring, December 7, 1657. The sixth satellite of Saturn (Titan) : Huygens, March 25, 1655. The eighth satellite of Saturn (the outermost, Japetus) : Do- min. Cassini, October, 1671. The fifth satellite of Saturn (Rhea) : Cassini, December 23, 1672. The third and fourth satellites of Saturn (Tethys and Dione) : Cassini, end of March, 1684. (B.) The Eighteenth Century. Uranus : "William Herschel, May 13, 1781, at Bath. The second and fourth satellites of Uranus : William Her- schel, January 11, 1787. The first satellite of Saturn (Mimas) : William Herschel, August 28, 1789. The second satellite of Saturn (Enceladus) : William Her- schel, September 17, 1789. The first satellite of Uranus : William Herschel, January 18, 1790. The fifth satellite of Uranus : William Herschel, February 9, 1790. The sixth satellite of Uranus : William Herschel, February 28, 1794. The third satellite of Uranus : William Herschel, March 26, 1794. (C.) The Nineteenth Century. Ceres* : Piazzi, at Palermo, January 1, 1801. Pallas*: Olbers, at Bremen, March 28, 1802. Juno* : Harding, at Lilienthal, September 1, 1804. Vesta* : Olbers, at Bremen, March 29, 1807. (During 38 years no planetary discoveries were made). Astrea* : Hencke, at Dresden, December 8, 1845. THE TLANETS. 101 Neptune : Galle, at Berlin, September 23, 184G. The first satellite of Neptune : W. Lassell, at Starfield, near Liverpool, November, 184G ; Bond, at Cambridge (U. S.). Hebe*: Hencke, at Dresden, July 1, 1847. Iris* : Hind, in London, August 13, 1847. Flora* : Hind, in London, October 18, 1847. Metis* : Graham, at Markree Castle, April 25, 1848. The seventh satellite of Saturn (Hyperion) : Bond, at Cam bridge (U.S.), September, 16-19; Lassell, at Liverpool, September 19-20, 1848. Hvgeia* : De Gasparis, at Naples, April 12, 1849. Parthenope* : De Gasparis, at Naples, May 11, 1850. The second satellite of Neptune : Lassell, at Liverpool, Au- gust 14, 1850. Victoria*: Hind, in London, September 13, 1850. Egeria* : De Gasparis, at Naples, November 2, 1860. Irene* : Hind, in London, May 19, 1851 ; and De Gasparis, at Naples, May 23, 1851. In this chronological summary* the principal planets are distinguished from the secondary planets or satellites by a dif- ferent type. Some bodies are included in the class of princi- pal planets, which form a peculiar and very extended group, forming, as it were, a ring of 132 millions of geographical miles, situated between Mars and Jupiter, and are generally called small planets, as well as telescopic planets, co-planets, asteroids, or planetoids. Of these, four were discovered in the first seven years of this century, and ten during the last six years ; which latter circumstance is to be attributed less to the perfection of the telescopes, than the industry and dex- terity of the investigators, and especially the improved charts enlarged by additions of fixed stars of the ninth and tenth magnitudes. It is now more easy to distinguish between * In the history of the discoveries, it is necessary to distinguish be- tween the epoch at which the discovery was made, and the time of its first announcement. In consequence of a neglect of this distinction, dissimilar and erroneous dates have been introduced into astronomical manuals. So, for example, H ivy gens discovered the sixth satellite of Saturn (Titan) on March 25, 1655 (Huy genii Opera varia, 1724, p. 523), and did not announce it until March 5, 1656) Systema Saturnium, 1659, p. 2). Huygens, who devoted himself uninterruptedly from March, 1655, to the study of Saturn, had already obtained the full and indubi table view of the open ring on December 17, 1657 {Systema Saturnium, p. 21), but did not publish his scientific explanation of all the phenom- ena until the year 1659. (Galileo had thought that he saw, on each side of the planet, only two projecting circular disks.) 102 COSMOS. moving josmical bodies and fixed. See Cosmos, vol. iii., p. 115.) The number of the principal planets has been exactly doub- led since the first volume of Cosmos appeared,* so excessive- ly rapid is the succession of discoveries, the extension and per- fection of the topography of the planetary system. . 2. Classification of the Planets in two Groups. — If the region of small planets situated in the solar system betiveen the orbits of Mars and Jupiter, but, on the whole, nearer to the former, is considered as a separating zone — as it were, an intermediate group — then, as has already been remarked, those planets which are nearest to the sun, the interior (Mercury, Venus, the Earth, and Mars), present several resemblances among each other, and contrasts with the exterior planets (Jupiter, Saturn, Uranus, and Neptune), or those which are more remote from the sun, beyond this separating zone. Of these three groups, the intermediate one occupies a space scarcely equal to half the distance of the orbit of Mars from that of Jupiter. Of the space between the two great princi- pal planets, Mars and Jupiter, that part which is nearest to Mars is, as far as has hitherto been observed, the most close- ly filled ; for if, in the zone which the asteroids occupy, the two outermost, Flora and Hygeia, are examined, it will be found that Jupiter is more than three times further from Hy- geia than Flora is from Mars. The most distinctive features of this intermediate group of planets are the great inclination and eccentricity of their interlacing orbits, and the extreme smallness of the planets. The inclination of the orbits to- ward the ecliptic increases in that of Juno to 13° 3', in that of Hebe even to 14° 47', of Egeria to 16° 33', of Pallas even to 34° 37' ; while in the same intermediate group it falls as low, in the orbit of Astrea, as 5° 19', in that of Parthenope to 4° 37', and that of Hygeia to 3° 47'. The whole of the orbits of the small planets having inclinations smaller than 7° are, to go from the large to the small, those of Flora, Me- tis, Iris, Astrea, Parthenope, and Hygeia. Nevertheless, none of these orbits attain such a small degree of inclination as those of Venus, Saturn, Mars, Neptune, Jupiter, and Uranus. The eccentricities partly exceed even that of Mercury (0-206) ; for Juno, Pallas, Iris, and Victoria have 0-255, 0'239, 0232, and 0-218, while Ceres (0-076), Egeria (0-086), and Vesta (0-089) have orbits less eccentric than Mars (0*093), without, * Cosmos, vol. i., p. 92. Compare also Encke, in Schumacher' s Astron Nachr., vol. xxvi., 1848, No. G22, p. 347. THS PLANETS. 108 however, attaining to the approximative circular orbits of the other planets (Jupiter, Saturn, and Uranus). The diameter of the telescopic planets is immeasurably small ; and accord- ing to observations made by Lamont in Munich, and Miidler with the Dorpat refractor, it is probable that the largest of the small planets is at the utmost only 145 geographical miles in diameter ; that is, one fifth of that of Mercury, one twelfth of that of the Earth. If the four planets nearest to the Sun, situated between the ring of the asteroids (the small planets) and the central body, are called interior planets, they will all agree in presenting a moderate size, a greater density, less flattened at the poles, and, at the same time, rotating slowly round their axes (in periods of rotation of nearly 24 hours), and, with the excep- tion of one (the Earth), without moons. On the contrary, the four exterior planets, those which are more remote from the Sun, situated between the ring of asteroids, and the, to us, un- known limits of the solar system (Jupiter, Saturn, Uranus, and Neptune), are considerably larger, live times less dense, their axial rotation more than twice as rapid, and their num- ber of moons greater in the proportion of 20 to 1 . The in- terior planets are all smaller than the Earth (Mercury and Mars | and \ smaller in diameter) ; the exterior planets, on the contrary, are from 4*2 to 11 '2 larger than the Earth. The density of the Earth being taken as =1, the densities of Yenus and Mars are the same to within less than ^ ; the density of Mercury is also but very little more, according to Encke's determination of his mass. On the contrary, none of the exterior planets exceed in density \ ; Saturn, indeed, is only |, almost only half the density of the other exterior planets and the Sun. Tiie exterior planets present the soli- tary phenomenon of the whole solar system, the wonderful circumstance of one of its principal planets being surrounded by an unattached ring ; also atmospheres which, in conse- quence of the peculiarity of their condensation, appear to us variable ; in Saturn, indeed, sometimes as interrupted bands. Although in the important classification of the planets into two groups of interior and exterior planets, the general char- acters of absolute magnitude, density, flattening at the poles, velocity of rotation, absence of moons, present themselves as' dependent upon the distances, i. e., lrom their semi-orbital axes, this dependence can not be affirmed of each one of these groups. Up to the present time we are ignorant, as I have already remarked, of any internal necessity, any mechanical « 104 COSMOS. law of nature, which (like the beautiful law which connects the square of the periods of revolution with the cube of the major axes) represents the above-named elements of the order of succession of the individual planetary bodies of each group in their dependence upon the distances. Although the planet which is nearest to the Sun (Mercury) is the densest, even six or eight times denser than some of the exterior planets, Jupiter, Saturn, Uranus, and Neptune, the order" of succes- sion, in the case of Venus, the Earth, and Mars, or Jupiter, Saturn, and Uranus, is very irregular. The absolute mag- nitudes do generally, as Kepler has already observed (Har- monice Mundi, vol. iv., p. 194 ; Cosmos, vol. i., p. 93-97), increase with the distances ; but this does not hold good when the planets are considered individually. Mars is small- er than the Earth, Uranus smaller than Saturn, Saturn small- er than Jupiter, and succeeds immediately to a host of plan- ets, which, on account of their smallness, are almost im- measurable. It is true the period of rotation generally in- creases with the distance from the Sun ; but it is, in the case of Mars, slower than in that of the Earth, slower in Saturn than in Jupiter. The external world of forms, I again repeat it, can only be represented in the enumeration of relations of space, as something actually existing in nature, and not as the subject of intellectual deductions of previously known causal rela- tions. No universal law for the cosmical regions is here traced, any more than for terrestrial regions in the culmina- ting points of mountain chains, or in the configuration of con- tinents. These are natural facts which have resulted from the conflict of numerous attractive and repulsive forces, un- der conditions which are unknown to us. We here enter with eager and unsatisfied curiosity upon the obscure domain of incipient formation. It is to these phenomena that the so- frequently misused term of natural facts may be applied in its strictest sense, cosmical processes which have taken place during spaces of time of, to us, immeasurable extent. If the planets have been formed from revolving rings of nebulous matter, it must, after having commenced to aggregate into globes, according to the preponderating influence of individ- * ual centers of attraction, have passed through an intermina- ble series of conditions in order to have formed sometimes simple, sometimes interwoven orbits, planets of such different magnitudes, flattening, and density, with and without moons, and even, in one case, to blend the satellites into a solid ring. THE PLANETS. 105 The present form of things, and the exact numerical determ- inations of their relations, has not hitherto been able to lead us to a knowledge of the past states, or a clear insight into the conditions under which they originated. These condi- tions must not, however, on that account, be called accident- al, as men call every thing whose genetic organ they are not able to explain. 3. Absolute and apparent Magnitude ; Configuration. — The diameter of the largest of all the planets (Jupiter) is 30 times as great as the diameter of the smallest of those which have been determined with certainty (Mercury) ; near- ly 11 times as great as the diameter of the Earth. Yery nearly the same relations obtain between Jupiter and the Sun. Their diameters are nearly as 1 to 10. It has been asserted, perhaps erroneously, that the distance of the me- teoric stones, which there is a tendency to consider as small planetary bodies, from Vesta, which, according to a measure- ment by Madler, is 66 geographical miles in diameter, there- fore 80 miles less than the diameter of Pallas according to Lamont, is not greater than the distance of Vesta from the Sun. According to these relations, there must be meteoric stones of 517 feet in diameter. Fire-balls certainly have, while they retain a disk-like appearance, a diameter amount- ing to 2600 feet. The dependence of the flattening at the poles upon the ve- locity of rotation appears most strikingly in the comparison of the Earth as a planet of the interior group (Rot., 23'1, 56'; Flattening, -^\-^) with the exterior planet Jupiter (Rot., 91'- 55'; Flattening, according to Arago, TlT ; according to John Her- echel, TV), and Saturn (Rot., 10h- 29'; Flattening, j\). But Mars, whose rotation is still 41 minutes slower than the ro- tation of the Earth, has, even when a much smaller result is assumed than that of William Herschel, very probably a much greater flattening. Does the reason of this anomaly, inas- much as the figure of the surface of an elliptical spheroid ought to correspond with the velocity of rotation, consist in the difference of the law of the increasing density toward the center of the superincumbent strata? or in the circumstance that the liquid surface of some planets was solidified before they could assume the figure appertaining to their velocity of rotation ? The important phenomena of the backward motion of the equinoctial points or the apparent advance of the stars (precession), that of nutation (oscillation of the Earth's axis), and the variation of the inclination of the E 2 106 COSMOS. ecliptic, depeni, as theoretical astronomy proves, upon the configuration. The absolute magnitudes of the planets, and their distance from the Earth, determine their apparent diameter. We have, therefore, to arrange the planets according to their ab- solute (actual) magnitudes, proceeding from the larger to the smaller : The small planets with involved orbits, of which the larg- est appears to be Pallas and Vesta : Mercury, Neptune, Mars, Uranus, Venus, Saturn, Earth, Jupiter. The apparent equatorial diameter of Jupiter, at a mean distance from the Earth, is 38"-4, while that of Venus, which is nearly equal in magnitude to the Earth, is only 16*9"; that of Mars, 5"*8. But the apparent diameter of the disk of Venus increases in the inferior conjunction to 62", while that of Jupiter attains only an increase to 46". It is neces- sary to call to mind in this place that the point of the orbit of Venus at which it appears to us with the brightest light, falls between the inferior conjunction and her greatest digres- sion from the Sun, because in that position the small lumin- ous crescent gives the most intense light, on account of its greatest proximity to the Earth. Upon the average, Venus appears the most beautifully luminous, even casting shadows in the absence of the Sun, when at a distance of 40° east or west from the Sun ; the apparent diameter then amounts to only 40", and the greatest width of the illuminated phase is scarcely 10". Apparent Diameter of Seven Planets. Mercury at a mean distance 6"-7 (oscillates from 4""4 to 12") Venus a u 16" •9 ( " 9"-5to62") Mars a C( 5"-8 ( 3"-3 to 23") Jupiter a «( 38"-4 ( " 30" to 46") Saturn it (< 17"1 ( " 15" to 20") Uranus (1 i i 3"9 Neptune cc i 2"*7 The volumes of the planets in relation to the Earth are : Mercury as 1 16-7 Jupiter as 1414 : 1 Venus (< 1 1-05 Saturn " 735 : 1 Earth <( 1 1 Uranus " 82 : 1 Mars <( 1 7-14 Neptune " 108 : 1 THE PLANETS. 107 while the volume of'the Sun is to that of the Earths 1 107 124. Small alterations in the measurements of the diameters in- crease the data of volumes in the ratio of their cubes. The moving planets which agreeably enliven the aspect of the heavens, influence us simultaneously by the magnitudes of their disks and their proximity, by the color of their light, by scintillation — which is not entirely wanting to some plan- ets, in certain positions — and by the peculiarity with which their different surfaces reflect the Sun's light. Whether a feeble evolution of light from the planets themselves modifies the intensity and properties of their light, is a problem which still remains to be solved. 4. Arrangement of the Planets and their Distances from the Sun. — In order to form a general conception of the plan- etary system as a whole, so far as it is yet known, and to rep- resent it in its mean distances from the central body, the Sun, the following table is given, in which, as has always been the custom in astronomy, the mean distance of the Earth from the Sun (20,682,000 geographical miles) is taken as unity. The greatest and smallest distances of the individual planets from the Sun in aphelion and perihelion — according as the planet is situated in the ellipse whose focus is occupied by the Sun, at that point of the major axis (line of apsides) which is the farthest from or nearest to the focus — will be added afterward, when treating of the planets individually. By the mean distance from the Sun, of which alone mention will be made in this place, is to be understood, the mean of the great- est and smallest distance, or the half major axis of the plan- et's orbit. It must also be observed, that the numerical data employed, both previously and hereafter, are for the most part taken from Hausen's careful classification of the planetary elements in Schumacher's Jahrbuch for 1837. Where the data refer to time, they are, in the case of the older and larger planets, for the year 1800 ; but in the case of Neptune, for the year 1851, by the aid of the Berlin astronomisclien Jahr- buch of 1853. The comparison of the small planets occur- ring afterward, and for which I am indebted to Dr. Galle, refers exclusively to more recent epochs. Distances of the Planets from the Sun. Mercury 0*38709 I Earth 1-00000 Venus 0-72333 Mars 1 52369 108 COSMOS. Small Planets Flora 2-202 Victoria 2335 Vesta 2-362 Iris 2385 Metis 2-386 Egeria 2579 Juno 2-669 Ceres 2-768 Pallas 1773 Hygeia 3- 151 Hebe 2-425 Jupiter 5-20277 Parthenope 2.448 Saturn 9-53885 Irene 2553 Uranus 19-18239 Astrea 2-577 Neptune 30-03628 The simple observation of rapidly diminishing periods of revolution, from those of Saturn and Jupiter to Mars and Venus, led, at a very early time, under the assumption that the planets were attached to movable spheres, to conjectures as to the distances of these spheres from each other. As there are no traces of methodically-instituted observations and measurements to be found among the Greeks before the time of Aristarchus of Samos, and the establishment of the Alexandrinian Museum, a great difference arose in the hypoth- esis as to the arrangement of the planets and their relative distances ; whether according to the most prevailing system, with reference to their distances from the Earth as the fixed center, or, as among the Pythagoreans, with reference to the distances from the focus of the universe. The principal sub- ject on which there was a discrepancy of opinion was the position of the Sun, that is, its relative situation in reference to the inferior planets and the Moon.* The Pythagoreans, who considered number to be the source of all knowledge, the real essence of all existing things, applied their theory of num- bers, the all-blending doctrine of numerical relations, to the geometrical consideration of the five regular bodies, to the musical intervals of tone which determine, accord, and form different kinds of sound, and even to the system of the uni- verse itself, supposing that the moving, and, as it were, vi- brating planets, exciting sound-waves, must produce a spher- al music, according to the harmonic relations of their inter- vals of space. " This music," they add, " would be perceived * Bockh, De Platonico Syst., p. xxiv., and in Philolaos, p. 100. The succession of the planets, which, as we have just seen (page 94. note), gave rise to the naming of the week-days after the planetary deities, that of Geminus is distinctly called the oldest by Ftolema'us. (Almag.. xi., cap. i.) He blames the motives from which "the moderns hau placed Venus and Mercury beyond the Sun." THE PLANETS. 109 by the human car if it was rendered insensible by extreme familiarity, as it is perpetual, and men are accustomed to it from childhood."* The harmonic part of the Pythagorean doctrine of numbers thus became connected with the figura- tive representation of the Cosmos precisely in the Platonic Timajus ; for " cosmogony is to Plato the work of the union of opposite first causes, brought about by harmony. "f He attempted, moreover, to illustrate the tones of the universe in an agreeable picture, by attributing to each of the planetary spheres a syren, who, supported by the stern daughters of Ne- cessity, the three Fates, maintain the eternal revolution of the world's axis."$ Such a representation of the Syrens, in whose place the Muses are sometimes substituted as the choir of heaven, has been, in many cases, handed down to us in an- tique monuments, especially in carved stones. Mention is constantly made of the harmony of the spheres, although gen- erally reproachfully, throughout the writings of Christian an- tiquity, and all those of the Middle Ages, from Basil the Great to Thomas Aquinas and Petrus Alliacus.§ * The Pythagoreans affirm, in order to justify the reality of the tones produced by the revolution of the spheres, that hearing takes place only where there is an alternation of sound and silence. — Aristot., De Ccelo, ii., 9, p. 290, No. 24-30, Bekker. The inaudibility of the spheral music is also accounted for by its overpowering the senses. — Cicero, De Rep., vi., 18. Aristotle himself calls the Pythagorean tone-myth pleasing and ingenious (no/iipuc nai TrepirrcJc), but untrue (1. c, No. 12-15). t Bockh, in Philolaus, p. 90. \ Plato, De Republica, x., p. 617 {Davis's translation, Bohn's Class. Lib., p. 307). He estimates the planetary distances according to two entirely different progressions, one by doubling, the other by tripling, from which results the series 1. 2. 3. 4. 9. 8. 27. It is the same series which is found in the Timaeus, where the subject of the arithmetical division of the world — spirit (p. 35, Steph., Davis's trans., Bohn's Class. Lib.), which Demiurgus propounds, is treated of. Plato Lad, indeed, considered the two geometrical progressions 1. 2. 4. 8 and 1. 3. 9. 27 together, and thus alternately taken each successive number from one of the two series, whence resulted the above-mentioned succession 1. 2. 3. 4. 9 Compare Bockh in the Studien von Daub und Creu- zer, bd. iii., p. 34-43 ; Martin, Etudes sur le Time'e, torn, i., p. 384, and torn, ii., p. 64. (Compare also Prevost, Sur V Ame d'apres Platon, in the M6m. del' Acad, de Berlin for 1802, p. 90 and 97 ; the same in the Bibli- oiheqne Britannique, Sciences et Arts, torn, xxxvii.,1108, p. 153.) $ See the acute work of Professor Ferdinand Piper, Von der Harmo- nie der Sphdren, 1850, p. 12-18. The supposed relation of the seven vowels of the old Egyptian language to the seven planets, and Gustav Seyfiarth's conception, already disproved by Zoega's and Tolken's in- vestigations, of the astrological hymns, rich in vowels, of the Egyptian priests, according to passages of Pseudo-Demetrius Phakereus (perhaps Demetrius of Alexandria), an epigram of Eusebius, and a C4nostic man- ilO cosmos. At the close of the sixteenth century, all the Pythagorean and Platonic views of the system of the universe were again reanimated in the person of the imaginative Kepler. He, in the first instance, constructed the planetary system in the Mysterium Cosmograjiliicum, in accordance with the prin- ciple of the five regular solids, which may be imagined as situated between the planetary spheres, then in the Harmo- nice Mundi, according to the intervals of tone. ^ Convinced of the regularity of the relative distances of the planets, he believed that he had solved the problem by a happy combi- nation of his earlier and later views. It is extremely re- markable that Tycho Brahe, who in other respects is found to be so strictly attached to actual observation, had already expressed the opinion (controverted by Rothmann) that the revolving cosmical bodies were capable of vibrating the ce- lestial air (what we now call resisting medium) so as to pro- duce tones. f But the analogies between the relations of tone and the distances of the planets, which Kepler so long and laboriously endeavored to trace out, remained, in his opinion, as it appears to me, entirely with the domain of abstract speculation. He congratulated himself upon having, to the greater glorification of the Creator, discovered musical rela- tions of number in the relations of cosmical space ; as if, in poetic enthusiasm, he makes "Venus, together with the Earth, sound sharp in aphelion and flat in perihelion ; the highest tone of Jupiter and that of Venus must coincide in flat accord." In spite of these merely symbolical expres- sions, so frequently employed, Kepler says positively, "Jam soni in ccelo nulli existunt, nee tarn turbulentus est motus, ut ex attritu aurce, ccelestis eliciatur stridor. $ {Harmonice Mundi, lib. v., cap. 4.) The thin and clear celestial air (aura ccelestis) is also mentioned here again. The comparative consideration of the planetary intervals with the regular bodies which would fill these intervals, en- uscript in Leyden, have been minutely treated of with critical erudition by the younger Ideler (Hermapion, 1841, pars i., p. 198-214). Com- pare also Lobeck, Aglaoph., torn, ii., p. 932. * On the gradual development of the musical ideas of Kepler, vide Apelt's Commentary of the Harmonice Mundi, in his work ; Johann Kepler's Weltansichl, 1849, p. 76-116. (Compare also Delambre, Hist, de V Astronom. Mod., torn, i., p. 352-360.) t Cosmos, vol. ii., p. 316. t [Now there are no such things as sounds among the heavenly bodies, nor is their motion so turbulent as to elicit noise from the at- trition of the celestial air.] THE PLANETS. Ill couraged Kepler to extend his hypothesis even so far as the region of fixed stars.* The circumstance which, on the oc- casion of the discovery of Ceres, and the other so-called small planets, first forcibly recalled to mind Kepler's Pythagorean arguments, was his almost forgotten conjecture as to the prob- able existence of a yet unseen ])lanet in the great planetless chasm between Mars and Jupiter. (" Motus semper distan- tiam pone sequi videtur ; atque ubi magnus hiatus erat inter orbes, erat et inter motus. "f ) " I have become more daring," he says, in the introduction to the Mi/slcrium Cosmograph- icum, " and place a new planet between Jupiter and Mars, as also (a conjecture which was less fortunate, and' remained long unnoticed^) another planet between Venus and Mercu- ry ; neither of these have been seen, probably on account of their extreme smallness.^ Kepler subsequently found that * Tycho had denied the existence of the crystalline spheres, in which the planets were supposed to be fixed. Kepler praised the undertak- ing, but he still adhered to the opinion that the sphere of fixed stars was a solid globular shell of two German miles in thickness, upon which are the twelve fixed stars, which are all situated at equal distances from us, and have a peculiar relation to the corners of an icosahedron. The fixed stars "lumina sua ab intus emittunt;" " emit light from their own bodies;" he also considered for a long time that the planets were self- luminous, until Galileo taught him better ! Although he, like many other of the ancients and Giordano Bruno, considered the fixed stars to be suns like our own, still he was not much inclined to entertain the opinion, which he had well considered, that all fixed stars are sur- rounded by planets, as I had formerly stated them to be. (Cosmos, vol. ii., p. 328.) Compare Apelt, Commentary to the Harmonice, p. 21-24. t [" There seems to be always a close relation, between the motion and the distance [of the planets]; that is to say, where there is a great interval between their orbs, the same exists also between their mo- tions."] % It was not until the year 1821 that Delambre, in the Hist, de VAs- tron. Mod., torn, i., p. 314, directed attention to the planets which Kep- ler conjectured to lie between Mercury and Venus, in the extracts which are complete with regard to astronomy, but not with regard to astrology, from Kepler's collected works (p. 314-615). "On n'a fait aucune attention a. cette supposition de Kepler, quand on a forme des projets de decouvrir la planete qui (selon une autre de ces predic- tions) devait circuler entre Mars et Jupiter." " No attention was paid to that supposition of Kepler's when projects were formed for discover- ing the planet, which (according to another of his predictions) ought to revolve between Mars and Jupiter." § The remarkable passage respecting a space to be filled up between Mars and Jupiter [hiatus] is in Kepler's Prodromus Dissertationum Cos- mographicarum, continens Mt/sierium Cosmo grapkicum de admirabili proportions Orbium Ccelesthtm, 1596, p. 7: "Cum igitur hac non succe- deret, alia via, mirum quam audaci, tentavi aditum. Inter Jovem et Martem interposui novum planetam, itemque alium inter Venerem et 112 COSMOS. he did not require these new planets for his solar system founded upon the properties of the regular solids ; it was only necessary to modify the distances of the old planets a little arbitrarily. (" Non reperies novos et incognitos planetas, ut paulo antea, interpositos, non ea mihi probatur audacia ; sed illos veteres parum admodum luxatos."* — Myst. Cosmogr., p. 10.) The ideal tendencies of Kepler were so analogous to those of the Pythagorean school, and still more to those of Plato expressed in the Timceus,\ that in the same way as Plato (Cratyl., p. 409) assumed, in addition to the differ- ences of tone in the planetary spheres, those of color, Kepler likewise instituted some experiments (Astron. Opt., cap. 6, p. 261) for the purpose of detecting the colors of the planets. Even the great Newton, always so precise in his conclusions, was inclined, as Prevost has already remarked {Mem. de V Acad, de Berlin for 1802, p. 77 and 93), to reduce the di- Mercurium, quos duos forte ob exilitatem non videamus, iisque sua tempora periodica ascripsi. Sic enim existimabam me aliquam aequal- itatem proportionum effecturum, quae proportiones inter binos versus Solem ordine minuerentur, versus fixas augescerent ; ut propior est Terra Veneri quantitate orbis terrestris, quam Mars Teme, in quanti- tate orbis Martis. Verum hoc pacto neque unius planeUe interpositio sufficiebat ingenti hiatu, Jovem inter et Martem : manebat enim major Jovis ad ilium novum proportio, quam est Saturni ad Jovem. Rursus alio modo exploravi." " When this plan therefore failed, I tried to reach my aim in another way, of, I must confess, singular boldness. Between Jupiter and Mars I interposed a new planet, and another also between Venus and Mercury, both which it is possible are not visible on account of their minuteness, and I assigned to them their respective periods. For in this way I thought that I might in some degree equal- ize their ratios, which ratios regularly diminished toward the Sun, and enlarged toward the fixed stars, as the Earth is nearer to Venus than Mars is to the Earth. But even in this way the interposition of one planet did not supply the great chasm between Jupiter and Mars, for the ratio between Jupiter and the supposed new planet still remained greater than between Saturn and Jupiter. Again I tried in another way." Kepler was twenty-five years of age when he wrote this. It may be seen how his restless mind formed hypotheses, and again quick- ly forsook them, to deceive himself with others. He always retained a hopeful faith in being able to discover numerical laws where matter had aggregated under the manifold disturbances of attractive forces (disturbances whose combinations are incalculable, as are so many past events and formations on account of our ignorance of the accompanying conditions), aggregated into globes, revolving in orbits, sometimes sim- ple and almost parallel, sometimes grouped together and surprisingly complicated. * ["You will not find new and unknown planets, as I said before ; that boldness I do not approve of; but you will find the old ones a little altered in position."] t [Plato's Works translated, vol. ii., Bonn's Classical Library.] THE PLANETS. 113 mensions of the seven colors of the spectrum to the diatonic scale.* The hypothesis of yet unknown members of the planetary series calls to mind the opinion of Hellenic antiquity, that there were far more than five planets ; these were, indeed, all that had been observed, but many others might remain unseen, on account of the feebleness of their light and their position. Such a doctrine was especially attributed to Arte- midorus of Ephesus.f Another old Hellenic, and perhaps even Egyptian belief, appears to have been, that " the celes- tial bodies which we now see were not all visible in earlier times." Connected with such a physical, or, much rather, historical myth, is the remarkable form of the praise of a high antiquity which some races ascribed to themselves. Thus the pre-Hellenic Pelasgian inhabitants of Arcadia called themselves Proselenes, because they boasted that they came into the country before the Moon accompanied the Earth. Pre-Hellenic and pre-lunarian were synonymous. The appearance of a star was represented as a celestial event, as the Deucalionic flood was a terrestrial event. Apuleius (Apologia, vol. ii., p. 494, ed. Oudendorp ; Cosmos, vol. ii., p. 189, note) extends the flood as far as the Gatulean mount- ains of Northern Africa. Apollonius Rhodius, who, accord- ing to Alexandrian custom, was fond of imitating old models, speaks of the early colonization of the Egyptians in the val- * Newtoni Opnscula Mathematica, Philosophica et Philologica, 1744, torn, ii., Opusc. xviii., p. 246: " Chordam musice divisam potius aclhi- bui, noil tantum quod cum phamominis (lucis) optiine convenit, sed quod fortasse, aliquid circa colorum harmonias (quarum pictores non penitus ignari sunt), sonorum concordantiis fortasse analogas, involvat. Quemadmodum verisimilius videbitur animadvertenti affinitatem, qua? est inter extimam Purpuram (Violarura colorein) ac Rubedinem, colo- rum extremitates, qualis inter octavae terminos (qui pro unisonis quo- dammodo haberi possunt) reperitur." " I preferred employing the di- visions of the musical chord, not only because they harmonize best with the phenomena [of light], but because it is possible there may be some latent analogy between the harmonies of colors (with which painters are not altogether unacquainted) and the concords of sounds. This will appear more probable to any one who shall notice the similarity of relations between violet and red, the extreme colors [on the spec- trum], and the highest and lowest notes of the octave, which somehow may be considered as in unison." — Compare also Prevost, in the M6m. de VAcad. de Berlin for 1802, p. 77 and 93. t Seneca, Nat. Qu and the larg- est of Jupiter's satellites, the third, gi.¥ of the diameter of their primaries. A wide distinction must be drawn between this consideration of a relative magnitude and that of an ab- solute magnitude. The Earth's Moon, relatively so large (1816 miles in diameter), is absolutely smaller than all four of Jupiter's satellites (3104, 2654, 2116, and 1900 miles in diameter). The sixth satellite of Saturn differs very little in magnitude from Mars (3568 miles).* If the problem of tel- escopic visibility depended only upon the diameter, and was not, at the same time, determined by the proximity of the disks of the primaries, the great distance and the nature of the reflecting surfaces, it would be necessary to consider as the smallest of the secondary planets the first and second of Saturn's satellites (Mimas and Enceladus), and the two satel- lites of Uranus ; but it is safer to represent them merely as the smallest luminous points. It has hitherto appeared more certain that, upon the whole, the smallest of all planetary bodies (primaries and satellites) are to be found among the small planets. f The density of the satellites is by no means always less than that of their primaries, as is the case with the Earth's Moon (whose density is only 0-619 of that of our Earth) and * Outlines, § 548. t See Madler's attempt to estimate the diameter of Vesta (2T>4 geo- graphical miles) with a thousand-fold magnifying power in ins Astro- nomie, p. 218, THE PLANETS. 133 the third satellite of Jupiter. The densest of this group of satellites, the second, is even denser than Jupiter himself, while the third and largest appears to be of equal density with the primary. The masses also do not increase in at all the same ratio as the distances. If the planets have been formed from revolving rings, then the greater or less dense aggregation round a nucleus must have been caused by pe- culiar causes, which may, perhaps, always remain unknown to us. The orbits of the secondary planets which belong to the same group have very different degrees of eccentricity. In the Jovial system, the orbits of the first and second satellites are nearly circular, while the eccentricities of those of the third and fourth satellites amount to 0- 00 13 and 0 0072. In the Saturnian system, the orbit of the satellite nearest to the primary (Mimas) is considerably more eccentric than the orb- its of Enceladus and Titan, the largest and first discovered, whose orbit was so accurately determined by Bessel. The eccentricity of the orbit of the sixth satellite of Saturn is only 0*02922. According to all these data, which are among those that may be relied upon, Mimas only is more eccentric than the Earth's Moon (0* 05484) ; the latter possesses the pecul- iarity that its orbit round the Earth has a greater eccentric- ity, in comparison with that of its primary, than any other satellite. Mimas revolves round Saturn in an orbit whose eccentricity is 0*068, while that of the orbit of its primary is 0*056 ; but the orbit of our Moon has an eccentricity of 0*054, while the eccentricity of that of the Earth is only 0*016. With regard to the distances of the satellites from their primaries, compare Cosmos, vol. i., p. 94-98. The distance of the sat- ellite nearest to Saturn (Mimas) is now no longer taken as 80,088 geographical miles, but as 102,400 ; whence its dis- tance from the ring, this being calculated as 24,188 miles broad, and at a distance of 18,376 miles from the surface of the planet, will be 28,000 miles.* Remarkable anomalies, together with a certain correspondence, are also presented in the position of the orbits of the satellites in the Jovial sys- tem, in which very nearly all the satellites move in the plane of the equator of their primary. In the group of Saturnian satellites, seven of them revolve almost in the plane of the ring, while the outermost (the eighth, Japetus) is inclined to- ward their plane 12° 14'. * In the earlier data {Cosmos, vol. i., p. 97) the equatorial diameter was taken as a basis. 134 cosmos. In this general consideration of the planetary revolutions in the universe, we have descended from the higher — though probably not the highest^ system — from that of the Sun to the subordinate partial systems of Jupiter, Saturn, Uranus, and Neptune. In the same way that, from the striving to- ward generalization of views, which is innate in thoughtful, and, at the same time, imaginative men, the unsatisfied cos- mical presentiment of a translatory motionf of our solar sys- tem through space appears to suggest the idea of a higher relation and subordination, so the possibility has been con- ceived that the satellites of Jupiter may be again central bodies to other secondary ones, which, on account of their smallness, are unseen. In that case, the individual mem bers of the partial systems, which are chiefly situated among the group of exterior principal planets, would have other and similar partial systems subordinate to them. Repetitions of form in recurring organizations, as well as the self-created images of the fancy, are certainly pleasing to a systematic mind ; but in every serious investigation, it is imperatively necessary to distinguish between the ideal and the actual Cosmos — between the possible, and that which has been dis- covered by actual observation. SPECIAL ENUMERATION OF THE PLANETS AND THEIR MOONS, AS PARTS OF THE SOLAR SYSTEM. It is, as I have already often remarked, the especial object of a physical description of the ivorld to bring together all the important and well-established numerical results which have been obtained in the domain either of sidereal or ter restrial phenomena up to the middle of the nineteenth cen tury. All that has form and motion should here be repre sented as something already created, existing, and definite The grounds upon which the obtained numerical results ai founded ; the cosmological conjectures respecting genetic de velopment, which during thousands of years have been called into existence by the ever-changing conditions of mechanical and physical knowledge — these do not, in the strictest sense of the word, come within the range of empirical investiga- tion. {Cosmos, vol. i., p. 47—49, 71, and 83.) * Compare Cosmos, vol. iii., p. 196. t I have fully treated of the translatory motion of the Sun in the de- lineation of nature. (Cosmos, vol. i., p. 145-149. Compare also vol. iii., p. 184.) THE SUN. 135 The Sun. Whatever relates to the dimensions, or to the present views as to the physical constitution of the central body, has been already given. {Cosmos, vol. iv., p. 59-88.) It only re- mains to add in this place some remarks, according to the most recent observations, upon the red figures and masses of red clouds, which were specially treated of at page 70. The important phenomena which the total eclipse of the Sun of July 28, 1851, presented in Eastern Europe, have still more strengthened the opinion put forward by Arago in 1842, that the red mountain, or cloud-like projections upon the edge of the eclipsed Sun, belong to the outermost gaseous envelope of the central body.*1 These projections became visible on the Moon's western edge as it proceeded in its motion toward the east {Annuaire dn Bureau des Longitudes for 1842, p. 457), and disappeared again when they were covered on the oppo- site by the eastern edge of the Moon. On a subsequent occasion, the intensity of the light of these projections became so considerable, that they could be per- ceived within the corona through telescopes, when veiled by their clouds, and even with the naked eye. The form of some of the projections, which were mostly ruby or peach-colored, changed with perceptible rapidity dur- ing the total obscuration ; one of these projections appeared to be curved at its summit, and presented to many observers the appearance of a freely-suspended detached cloudf near the point, and resembling a column of smoke curved back at the top. The height of most of these projections was estimated at from V to 2'; at one point it is said to have been more. Besides these tap-formed projections, from three to five of which were counted, there were also observed ribbon-like streaks of a carmine color, extended lengthways, which ap- peared to rest upon the Moon, and were often serrated. $ * Cosmos, vol. iv., p. 70, note X and §, and p. 79. t Compare the observations of the Swedish mathematician, Bigerus Vassenius, at Gottenburg, during the total eclipse of May 2, 1733, and the commentary upon them by Arago, in the Annuaire du Bureau des Longitudes for 184G, p. 441 and 4G2. Dr. Galle, who observed on the 28th of July at Frauenburg, 6aw "the freely-suspended cloud connect- ed with the curved, hook-formed gibbosity by three or more threads." t Compare what a very expert observer, Captain Berard, saw at Tou- lon upon the 8th of July, 1842. "II vit une bande rouge tres mince, dentelee irregulierement." (Annuaire die Bureau des Longitudes, p. 416.) " He saw a very narrow red band irregularly serrated." 136 cosmos. That part of the Moon's edge which was not projected upon the Sun's disk again became perceptible, especially during the egress.* A group of Sun-spots was visible, though some minutes distant from the edge of the Sun, where the largest red, hook-formed projection was developed. On the opposite side, not far from the feeble eastern projection, there was also a Sun-spot near the edge. It is scarcely possible that these funnel-shaped depressions can have furnished the material constituting the red gaseous exhalations, on account of the distance above mentioned ; but as the whole surface of the Sun appears to be covered with pores, perhaps the most probable conjecture is, that the same emanation of vapor and gas, which, rising from the body of the Sun, forms the fun- nels,! pours through these, which appear to us as Sun-spots * This outline of the Moon, clearly perceived by four observers dur- ing the total eclipse of the Sun on the 8th of July, 1842, was never pre- viously described as having been seen during similar eclipses. The possibility of seeing an exterior outline appears to depend upon the light which is given by the third outermost envelope of the Sun and the ring of light (corona). " La Lune se projette en partie sur l'atmo- sphere du Soleil. Dans la portion de la lunette ou l'image de la Lune se forme, il n'y a que la lumiere provenant de l'atmosphere terrestre. La Lune ne fournit rien de sensible, et, semblable a un ecran, elle ar- rete tout ce qui provient de plus loin et lui correspond. En dehors de cette image, et precisement a partir de son bord, le champ est eclaire a la fois par la lumiere de l'atmosphere terrestre et par la lumiere de V atmosphere solairc. Supposons que ces deux lumieres reunies forment un total plus fort de ^L que la lumiere atmospherique terrestre, et, des ce moment, le bord de la Lune sera visible. Ce genre de vision peut prendre le nom de vision negative ; c'est en effet par une moindre intensity de la portion du champ de la lunette ou existe l'image de la Lune, que le contour de cette image est aper9ii. Si l'image etait plus intense que le reste du champ, la vision serait positive." — Arago, Annuaire du Bureau des Longitudes, p. 384. " The Moon is projected partially upon the at- mosphere of the Sun. In that portion of the telescope where the image of the Moon is formed, no other light enters except that of the terres- trial atmosphere. The Moon gives no sensible light, and, like a screen, it stops all that which comes from beyond and corresponds with it. Outside the image, and immediately round its edge, the field is lighted simultaneously by the light of the terrestrial atmosphere and by that of the solar atmosphere. If we suppose that these two lights collectively are J- stronger than the light of the terrestrial atmosphere, the Moon's edge will be directly visible. This kind of vision may be designated a negative vision, for it is, in fact, by the less intensity of that portion of the field of the telescope in which is the image of the Moon, that the outline of this image is perceptible. If this image were more intense than the remaining part of the field, the vision would be positive." (Compare also, on this subject, Cosmos, vol. iii., p. 56, note *.) * Cosmos, vol. iv., p. 63-o"7. MERCURY. 137 or smaller pores, and, when illuminated, present the appear- ance of red columns of vapor, and clouds of various forms in the third envelope of the Sun. Mercury. yVTien it is remembered how much the Egyptians* occu- pied themselves with the planet Mercury (Set-Horus), and the Indians with their Buddha, f since the earliest times ; how, under the clear heaven of Western Arabia, the star- worship of the race of the AseditesJ was exclusively directed to Mercury ; and, moreover, that Ptolemy was able, in the 19 th book of the Almagest, to make use of fourteen observa- tions of this planet, which reach back to 261 years before our era, and partly belong to the Chaldeans, § it is certainly astonishing that Copernicus, who had reached his seventieth year, should have lamented, when on his death-bed, that with all his endeavors, he had never seen Mercury. Still the Greeksll justly characterized this planet by the name of (ot'lX(j(x>v) the sparkling, on account of its occasionally very intense light. It presents phases (variable form of the illu- minated part of the disk) the same as Venus, and, like the latter, appears to us as a morning and evening star. Mercury is, in his mean distance, little more than 32 mill- ions of geographical miles from the Sun, exactly 0-3870938 parts of the mean distance of the Earth from the Sun. On account of the great eccentricity of its orbit (0'2056163), the distance of Mercury from the Sun in perihelion is 25 millions, in aphelion 40 millions of miles. He completes his revolu- tion round the Sun in 87 mean terrestrial days and 23h. 15m. 46s. Schroter and Harding have estimated the rota- tion at 24h. 5m. from the uncertain observation of the form of the southern cusp of the crescent, and from the discovery of a dark streak, which was darkest toward the east. According to Bessel's determination on the occasion of the transit of Mercury on May 5, 1832, the true diameter amounts to 2684 geographical miles,TI i. e., 0-391 parts of the Earth's diameter. * Lepsius, Chronologic der JEgypter, th. i., p. 92-96. t Cosmos, vol. iv., p. 93, note t, p. 92. t Ibid., vol. ii., p. 221. § Lalande, in the Mini, de V Acad, des Sciences for 1766, p. 498 ; De- lambre, Histoire de V Astron. Ancienne, torn, ii., p. 320. || Cosmos, vol. iv., p. 93. II On the occasion of the transit of Mercury on the 4th of May, 1832, Madler and William Beer {Beitrdge zur Phys. Kenntniss der himm- lischen Korper, 1841, p. 145) found the diameter of Mercury 2332 miles ; 138 cosmos. The mass of Mercury was determined by Lagrange upon very bold assumptions as to the reciprocity of the relations of distances and densities. A means of improving this element was first afforded by Encke's Comet of short period of rev- olution. The mass of this planet was fixed by Encke at 4"3"65 TsT °f the Sun's mass, or about Ti.T of the Earth's. La- place# gave the mass of Mercury as 2025 3T0 according to La- grange ; but the true mass is only ^ of that assigned by La- grange. By this correction, also, the previous hypothesis of the rapid increase of density in the planets, in proportion as they were nearer to the Sun, was disproved. When, with Hansen, the material contents of Mercury are assumed to be T|o those of the Earth, the resulting density of Mercury is 1-22. " These determinations," adds my friend, the author of them, " are to be considered only as first attempts, which, nevertheless, come much nearer the truth than the numbers assumed by Laplace." Ten years ago the density of Mer- cury was taken as nearly three times greater than the dens- ity of the Earth— as 2*56 or 2-94, when the Earth =1-00. Venus. The mean distance of this planet from the Sun, expressed in fractional parts of the Earth's distance from the Sun, i. e., 60 million geographical miles, is 0,7233317. The period of its sidereal, or true revolution, is 224 days, 16h. 49m. 7s. No principal planet comes so near the Earth as Venus. She can approach the Earth to within a distance of 21,000,000 miles, but can also recede from it to a distance of 144,000,000 miles. This is the reason of the great variability of her ap- but in the edition of the Astronomie of 1849, Madler has given the pref- erence to Bessel's result. * Laplace, Exposition du Syst. du Monde, 1824, p. 209. The cele- brated author admits, however, that in the determination of the mass of Mercury, he founded his opinion upon the " hypothese tres precaire qui suppose les densites de Mercure et de la Terre reciproques a leur moyenne distance du Soleil." " The very precarious hypothesis which supposes the densities of Mercury and the Earth reciprocal to their mean distance from the Sun." I have not considered it necessary to mention either the chain of mountains, 61,826 feet in height, which Schroter states that he saw upon the disk of Mercury and measured, and which Kaiser (Sternenhimmel, 1850, § 57) doubts the existence of, or the vis- ibility of an atmosphere round Mercury during his transit over the Sun, asserted by Lemonnier and Messier (Delambre, Hist, de V Astronomie au dixhuitieme siecle, p. 222), or the temporary darkening of the surface of the planet. On the occasion of the transit which I observed in Peru on the 8th of November, 1802, I very closely examined the outline of the planet during the egress, but observed no indications of an envelope VENUS. 139 parent diameter, which by no means alone determines the degree of brilliancy.* The eccentricity of the orbit of Verms expressed, as in all cases, in fractional parts of half the major axes, is only 0-00686182. The diameter of this planet is 6776 geographical miles; the mass ^otVto' the material contents 0*957, and the density 0-91 in comparison to the Earth. Of the transits of the two inferior planets first announced by Kepler after the appearance of his Rudolphine tables, that of Venus is of most importance for the theory of the whole planetary system, on account of the determination of the Suns parallax, and the distance of the Earth from the Sun deduced from the latter. According- to Encke's thor- ough investigation of the transit of Venus in 1769, the Sun's parallax is 8"-57116. (Berliner Jahrbuch for 1852, p. 323.) A new examination of the Sun's parallax has been under- taken since 1849, by command of the government of the United States, at the suggestion of Professor Gerling of Mar- burg. The parallax is to be obtained by means of observa- tions of Venus near the eastern and western stationary points, as well as by micrometer measurements of the differences in the right ascension and declination of well-determined fixed stars in very different latitudes and longitudes. (Schum., Astr. Nachr., No. 599, p. 363, and No. 613, p. 193.) The astronomical expedition, under the command of the learned Lieutenant Gilliss, has proceeded to Santiago in Chili. The rotation of Venus was long subject to great doubt. Dominique Cassini, 1669, and Jacques Cassini, 1732, found * " That point of the orbit of Venus in which she can appear to us with the brightest light, so that she may be seen at noon even with the naked eye, lies between the inferior conjunction and the greatest di- gression, near the latter, and near the distance of 40° from the Sun, or from the place of the inferior conjunction. On the average, Venus ap- pears with the finest light when distant 40° east or west from the Sun, in which case her apparent diameter (which in the' inferior conjunction can increase to 66") is only 40", and the greatest breadth of her illu- minated phase measures scarcely 10". The degree of proximity to the Earth then gives the small luminous crescent such an intense light, that it throws shadows in the absence of the Sun." — Littrow, Theoretische Astronomie, 1834, th. ii., p. 68. Whether Copernicus predicted the ne- cessity of a future discovery of the phases of Venus, as is asserted in Smith's Optics, sec. 1050, and repeatedly in many other works, has re- cently become altogether doubtful, from Professor de Morgan's strict examination of the work De Revolvtionibus, as it has come down to us. — See the letter from Adams to the Rev. R. Main, on the 7th of Sep- tember, 1846, in the Report of the Royal Astronomical Society, vol. vii., No. 9, p. 142. (Compare also Cosmos, vol. ii., p. 325.) 140 COSM08. it 23h. 20m., while Bianchini* of Home. 1726, assumed the slow rotation of 24i days. More accurate observations by De Vico, from 1840 to 1842, afford, by means of a great number of spots upon Venus, as the mean value of irer period of ro- tation, 23h. 21' 21"-93. These spots are not very distinct, and are mostly variable ; they seldom appear at the boundary of the separation be- tween light and shadow in the crescent-shaped phase of the planet, and both the Herschels, father and son, are conse- quently of opinion that they do not belong to the solid sur- face of the planet, but more probably to an atmosphere. f The changeable form of the horns of the crescent, especially the southern, has been taken advantage of by La Hire, Schroter, and Madler, partly for the estimation of the height of mountains, partly and more especially for the determina- tion of the rotation. The phenomena of this changeability are of such a nature that they do not require for their ex- planation the assumption of the existence of mountain- peaks, twenty geographical miles in height (121,520 feet), as Schroter of Lilienthal stated, but merely elevations like those which our planet presents in both continents. $ With the little that we know with certainty of the appearance of the surfaces of the planets near the Sun, Mercury, and Ve- nus, and their physical constitution, the phenomenon of an a^h-colored light, sometimes observed in the dark parts, and * Delambre, Hist, de VAstron. au dixhuitieme siecle, p. 256-258. The result obtained by Bianchini was supported by Hussey aud Flaugergues; Hansen also, whose authority is justly so great, considered it to be the more probable until 1836. (Schumacher's Jahrbuch for 1837, p. 90.) t Arago, on the remarkable observation at Lilienthal on the 12th of August, 1700, in the Annuaire for 1842, p. 539. "Ce qui favorise aussi la probability de 1'existence d'une atmosphere qui enveloppe Venus c'est le resultat optique obtenu par l'emploi d'une lunette prismatique. L'intensite de la lumiere de l'interieur dii croissant est serrsiblement plus faible que celle des points situes dans la partie circulaire du disque de la planete." — Arago, Manuscripts of 1847. "That circumstance which also favors the probability of the existence of an atmosphere surrounding Venus is the optical result obtained by employing a pris- matic telescope. The intensity of the light of the interior of the cres- cent is sensibly weaker than that of the points situated in the circular part of the planet's disk." $ Wilhelm Beer and Madler, Beitruge zur Physischen Kenntniss der Himmlischen Korper, p. 148. The so-called moon of Venus, which Fontana, Dominique Cassini, and Short declared that they had seen, for which Lambert calculated tables, and which was said to have been seen in the center of the Sun's disk, full three hours after the egress of Venus, belongs to the astronomical myths of an uncritical age. THE MOON. 141 mentioned by Christian Mayer, "William Herschel,* and Harding, also remains exceedingly mysterious. It is not probable that at so great a distance the reflected light of the Earth should produce an ash-colored illumination upon Ve- nus as upon our Moon. Hitherto there has been no flatten- ing observed in the disks of the two inferior planets, Mercu- ry and Venus. The Earth. The mean distance of the Earth from the Sun is 12,032 times greater than the diameter of the Earth ; therefore, 82,728,000 geographical miles, uncertain as to about 360,000 miles (-5-^0). The period of the sidereal revolution of the Earth round the Sun is 365d. 6h. 9' 10"-7496. The eccentricity of the Earth's orbit amounts to 0,01679226 ; its mass is 3-57^3-51- ; its density in relation to water, 544. Bes- sel's investigation of ten measurements of degrees gave for the flattening of the Earth 29 9Y5 3- The length of a geo- graphical mile, sixty of which are contained in one equato- rial degree, 951,807 toises, and the equatorial and polar di- ameters, 6875*6 and 6852-4 geographical miles. [Cosmos, vol. i., p. 65, note.) "We restrict ourselves here to numerical data referring to the Earth's figure and motions : all that refers to its physical constitution is deferred until the con- cluding terrestrial portion of the Cosmos. The Moon of the Earth. The mean distance of the Moon from the Earth is 207,200 geographical miles ; the period of sidereal revolution is 27d. 7h. 43' 11"5; the eccentricity of her orbit, 0-0548442 ; her diameter is 1816 geographical miles, nearly one fourth of the Earth's diameter; her material contents j\ those of the Earth ; the mass of the Moon is, according to Lindeman, TT?Tir (according to Peters and SchidlofTsky, -g'T) of the mass of the Earth ; her density, 0619, therefore nearly three fifths of the density of the Earth. The moon has no perceptible flattening, but an extremely slight prolongation on the side toward the Earth, estimated theoretically. The rotation of the Moon upon its axis is completed exactly in the same time in which it revolves round the Earth, and this is probably the case with all other secondary planets. The sunlight reflected from the Moon is in all zones more o Philos. Transact., 1795, vol. lxxxvi., p. 214. 142 cosmos. feeble than the sunlight which is reflected by a white cloud in the daytime. When, in determining geographical longi- tudes, it is often necessary to take the distance of the Moon from the Sun, it is not unfrequently difficult to distinguish the Moon between the more intensely luminous masses of cloud. Upon mountain-heights, which lie between 12,791 and 17,057 feet above the level of the sea, and where, in the clear mount- ain air, only feathery cirri are to be seen in the sky, I found the detection of the Moon's disk was much more easy, be- cause the cirrus reflects less sunlight on account of its loose texture, and the moonlight is less weakened by its passage through the rarer strata of air. The relative degree of in- tensity of the Sun's light to that of the full Moon deserves a new investigation, as Bouguer's universally received determ- ination, 3 ooVo ?r> differs so widely from the certainly less prob- able one of Wollaston, g- ooVoo"-* The yellow moonlight appears white by day, because the blue strata of air through which we see it presents the com- plementary color to yellow. f According to the numerous ob- servations which Arago made with his polariscope, the moon- light contains polarized light ; it is most perceptible during the first quarter and in the gray spots of the Moon's surface ; for example, in the great, dark, sometimes rather greenish ele- vated plains, the so-called Mare Crisium. Such elevated plains are generally intersected by metallic veins, in whose polyhedric figure the surfaces are inclined at that angle which is necessary for the polarization of the reflected sun- light. The dark tint of the surrounding space appears, in addition, to make the phenomenon still more obvious. With regard to the luminous central mountain of the group Aris- tarchus, upon which it has been frequently erroneously sup- posed that volcanic action has been seen, it did not present any greater polarization of light than other parts of the Moon. In the full Moon no admixture of polarized light was observ- * Cosmos, vol. iii., p. 95, and note t. t " La lumiere de la Lune est jaune, tandis que celle de Venus est blanche. Pendant le jour la Lune parait blanche, parcequ'a la lumiere du disque lunaire se mele la lumiere bleue de cette partie de l'atmo- sphere que la lumiere janne de la Lune traverse." — Arago, in Handschr. of 1847. " The light of the Moon is yellow, while that of Venus is white. The Moon appears white during the day, because the blue light of that part of the atmosphere which the yellow light of the Moon traverses, mixes with the light of the lunar disk." The most refrangible rays of the spectrum, from blue to violet, unite with the less refrangible, fmm red to green, to form white. (Cosmos, vol. iii., p. 208, note *.) the moon's light. 143 able ; but during a total eclipse of the Moon (31st of May, 1848), Arago detected indubitable signs of polarization in the reddened disk of the Moon, the latter being a phenomenon of which we shall speak further on. (Comities Hcnclus, torn, xviii., p. 119.) That the moonlight is capable of 'producing heat, is a dis- covery which belongs, like so many others of my celebrated friend Melloni, to the most important and surprising of our century. After many fruitless attempts, from those of La Hire to the sagacious Forbes,* Melloni was fortunate enough to observe, by means of a lens {lentille a cchellons) of three feet in diameter, which was destined for the meteorological station on Vesuvius, the most satisfactory indications of an el- evation of temperature during different changes of the Moon. Mosotti-Lavagna and Belli, professors of the Universities of Pisa and Pavia, were witnesses of these experiments, which gave results differing in proportion to the age and altitude of the Moon. It had not at that time (Summer, 1848) been determined what the elevation of temperature produced by Melloni's thermoscope, expressed in fractional parts of the centigrade thermometer, amounted to.f * Forbes, On the Refraction and Polarization of Heat, in the Trans- act, of the Royal Society of Edinburgh, vol. xiii., 1836, p. J31. t Lettre de M. Melloni a M. Arago sur la Puissance calorifique dc la Lumiere de la Lune, in the Comptes Rendus, torn, xxii., 1846, p. 541-544 Compare also, on account of the historical data, the Jahresbericht der Physicalischen Gesellschaft zu Berlin, bd. ii., p. 272. It had always appeared sufficiently remarkable to me, that, from the earliest times, when heat was determined only by the sense of feeling, the Moon had first excited the idea that light and heat might be separated. Among the Indians the Moon was called, in Sanscrit, the King of the stars of cold ('sitala, hima), also the cold-radiating (himdrfsii), while the Sun was called a creator of heat {niddghakara). The spots upon the Moon, in which Western nations supposed they discerned a face, represent, according to the Indian notion, a roebuck or a hare ; thence the San- scrit name of the Moon (mrigadhara}, roebuck-bearer, or (,sa'sabhrit), hare-bearer. (Schtitz, Five Hymns of the Bhatti-Kdvya, 1837, p. 19-23.) Among the Greeks it was complained " that the sunlight reflected from the Moon should lose all heat, so that only feeble remains of it were transmitted by her." (Plutarch, in the dialogue " De Facia quce in OrbeLuna apparel, Moralia," ed. Wyttenbach, torn, iv., Oxon., 1797, p. 793.) In Macrobius (Comm. in Soimiium Scip., i., 19, ed. Lud. Janus, 1848, p. 105) it is said, " Luna speculi instar lumen cpao illustratur . . . rursus emittit, nullum tamen ad nos preferentem sensum caloris : quia lucis radius, cum ad nos de origine sua, id est de Sole, pervenit, natu- ram secum ignis de quo nascitur devehit; cum vero in Lume corpus in- funditur et inde resplendet, solam refundit claritatem, non calorem." The same in Macrobius, Saturnal., lib. vii., cap. 16, ed. Bipont, torn. ii., p. 277. 144 cosmos. The ash-gray light with which a part of the Moon's disk shines when, some days before or after the new Moon, she presents only a narrow crescent, illuminated by the Sun, is earth-light in the Moon, " the reflection of a reflection." The less the Moon appears illuminated for the Earth, so much the more is the Earth luminous for the Moon. But our planet shines upon the Moon with an intensity 13|- times greater than the Moon upon the Earth ; and this light is sufficiently bright to become again perceptible to us by a second reflec- tion. By means of the telescope, mountain-peaks are distin- guished in the ash-gray light of the larger spots and isolated brightly-shining points, even when the disk is already more than half illuminated.^ These phenomena become particu- larly striking between the tropics and upon the high mount- ain-plains of Quito and Mexico. Since the time of Lambert and Schroter, the opinion has become prevalent that the ex- tremely variable intensity of the ash-gray light of the Moon depends upon the greater or less degree of reflection of the sunlight which falls upon the Earth, according as it is reflect- ed from continuous continental masses, full of sandy deserts, grassy steppes, tropical forests, and barren rocky ground, or from large ocean surfaces. Lambert made the remarkable observation (14th of February', 1774) of a change of the ash- colored moonlight into an olive green color, bordering upon yellow. " The Moon, which then stood vertically over the Atlantic Ocean, received upon its night side the green terres- trial light, which is reflected toward her when the sky is clear by the forest districts of South America."! The meteorological condition of our atmosphere modifies the intensity of the earth-light, which has to traverse the * Madler, Astron., $ 112. t See Lambert, Sur la Lumiere Cendrie de la Lune, in the M6m. de V Acad, de Berlin, anne"e 1773, p. 46 : " La Terre, vue des planetes, pour- ra paraitre d'une lumiere verdatre, a peu pres comme Mars nous parait d'une couleur rougeatre." " The Earth, seen from the planets, may appear of a green color, much the same as Mars affords to us of a reddish color." We will not, however, on that account, conjecture with this acute man that the plauet Mars may be covered with a red vegetation, such as the rose-red bushes of Bougainvillaea. (Hum- boldt, Views of Nature, -p. 334.) " When in Central Europe the Moon, shortly before the neto Moon, stands in the eastern heavens during the morning hour, she receives the earth-light principally from the large plateau surfaces of Asia and Africa. But if, after the new Moon, it stands during the evening in the west, it can only receive the reflection in less quantities from the narrower American continent, and principally from the wide ocean." — Wilhelm Beer and Madler, Der Mond nach seincn Cosmischen Verhdltnissen, § 106, p. 152. the moon's light. 145 double course from the Earth to the Moon, and from thence to our eye. " Thus, when we have better photometric in- struments at our command, we may be able," as Arago re- marks,* " to read in the Moon the history of the mean con- dition of the diaphaneity of our atmosphere." The first cor- rect explanation of the nature of the ash-colored light of the Moon is ascribed by Kepler (ad Vitellionem Paralipomena, quibits Astro nomicc pars Optica traditicr, 1604, p. 254) to his highly venerated teacher Miistlin, who had made it known in a thesis publicly defended at Tubingen in 1596. Galileo spoke (Sidcreus Nimcius, p. 26) of the reflected terrestrial light as a phenomenon which he had discovered several years previously ; but a century before Kepler and Galileo, the ex- planation of terrestrial light visible to us in the Moon had not escaped the all-embracing genius of Leonardo da Vinci. His long-forgotten manuscripts furnished a proof of this.f In the total eclipse of the Moon, the disk very rarely dis- appears entirely ; it did so, according to Kepler's earliest ob- servation, X on the 9th of December, 1601, and more recently, on the 10th of June, 1816; in the latter instance so as not to be visible from London, even by the aid of telescopes. The cause of this rare and extraordinary phenomenon must be a * Stance de V Academic des Sciences, le 5 Aoiit, 1833, " M. Arago sig- uale la comparaison de l'intensite lumineuse de la portion de la Luno que les rayons solaires eclairent directemeut, avec celle de la partie du meme astre qui recoit seulement les rayons reflechis par la Terre. II croit d'apres les experiences qu'il a cleja tentees a cet egard, qu'on pourra, avec des instrumens perfectionnes, saisir dans la lumiere cendre'e les differences de l'eclat plus on moins nuageux de l'atmosphere de notre globe. 11 n'est done pas impossible, malgre tout ce qu'un pareil resultat exciterait de surprise au premier coup d'oeil, qu'un jour les me- teorologistes aillent puiser dans l'aspect de la Lune des notions pre- cieuses sur Vtlat moyen de diaphanite de l'atmosphere terrestre, dans les hemispheres qui successivement concourrent a la production de la lu- miere cendree." " M. Arago pointed out the comparison between the luminous intensity of that portion of the Moon which is illuminated di- rectly by the solar rays, and that portion of the same body which re- ceives only the rays reflected by the Earth. After the experiments which he has already made in reference to this subject, he is of opinion that with improved instruments it will be possible to detect in the ashy light indications of the differences in brightness, more or less cloudy, ol the atmosphere of our globe. It is not, therefore, impossible, not- withstanding the surprise which such a result may excite on the first view, that one day meteorologists will derive valuable ideas as to the mean state of the diaphaneity of our atmosphere in the hemispheres which successively contribute to the production of the ashy light." t Venturi, Essai sur les Ouvrages de Leonard de Vinci, 1797, p. 11. X Kepler, Paralip. vel Astronomies pars Optiae, 1604. p. 297. Vol. IV.— G 146 cosmos. peculiar and not sufficiently investigated diaphanic condition of individual strata of our atmosphere. Hevelius states dis- tinctly that, during a total eclipse on the 25th of April, 1642, the sky was covered with brilliant stars, the atmosphere per- fectly clear, and yet, with the different magnifying powers which he employed, not a vestige of the Moon could be seen. In other cases, likewise very rare, only separate parts of the Moon are feebly visible. During a total eclipse, the disk gen- erally appears red ; and, indeed, in all degrees of intensity of color, even passing, when the Moon is far distant from the Earth, into a fiery and glowing red. While lying at anchor off the island of Baru, not far from Carthagena de Indias, half a century ago (29th of March, 1801), I observed a total eclipse, and was extremely struck with the greater luminous intensity of the Moon's disk under a tropical sky than in my native north.* The whole phenomenon is known to be a consequence of refraction, since, as Kepler very correctly ex- presses himself (Paralip Astron. ]jars Optica, p. 893), the Sun's rays are innectedf by their passage through the at- * " On comjoit que la vivacite de la lumiere rouge ue depend par uniquement de l'etat de l'atmosphere, qui refracte, plus ou moins affai- blis, les rayons solaires, en les enflechissant dans le cone d'ombre, mais qu'elle est modifiee surtout par la transparence variable de la partie de l'atmosphere a traverslaquelle nous apercevons la Lune eclipsee. Sous les tropiques, une grande sei'enite du ciel, line dissemination uniforme des vapeurs diminuent l'extinction de la lumiere que le disque lunaire nous renvoie." — Humboldt, Voyage aux Regions Equinoxiales, torn, iii., p. 544 ; and Recueil d'Observ. Astronomiques, vol. ii., p. 145. " It may easily be understood that the intensity of the red light does not depend solely upon the state of the atmosphere, which refracts more or less feebly the solar rays by inflecting them into the shadow cone, but that it is especially modified by the variable transparency of that part of the atmosphere across which we perceive the eclipsed Moon. Under the tropics a great serenity of sky, a uniform dissemination of vapors, diminish the extinction of the light which the lunar disk sends toward us." Arago observes : " Les rayons solaires arrivent a notre satellite par l'eftet d'une refraction et a la suite d'une absorption dans les couches les plus bases de l'atmosphere terrestre ; pourraient-ils avoir une autre teinte que le rouge?" — Annuaire for 1842. p. 528. "The solar rays reach our planet by the effect of a refraction, and subsequently to an absorption (partial) in the lower strata of the Earth's atmosphere. How can they have any other colors than red ?" t Babinet declares the reddening to be a consequence of diffraction, in a memoir as to the different share of the white, blue, and red Lights which are produced by the inflection. See his Reflections upon the Total Eclipse of the Moon on the 19th of March, 1848, in Moigno'a Re- pertoire d'Optique Moderne, 1850, torn, iv., p. 1C56. " La lumiere dif- fractee qui penetre dans l'ombre de la Terre, predoraine toujours et memo a ete seule sensible. Elle est d'autant plus rouge ou orangee THE MOON. 117 mosphere, and thrown into the shadow cone. The reddened or glowing disk is moreover never uniformly colored. Home places always appear darker, and are, at the same time, con- tinually changing color. The Greeks had formed a peculiar and curious theory with respect to the different colors which the eclipsed Moon was said to present according to the hour at which the eclipse took place. ^ During *he long dispute as to the probability or improba- bility of an atmospheric envelope round the Moon, accurate occult observations have proved that no refraction takes place on the surface of the Moon, and that, consequently, the assumption made by Schrbterf of the existence of a lunar atmosphere and a lunar tivilight are disproved. " The comparison of the two values of the Moon's diameter which may be respectively deduced from direct measurement, or from the length of time that it remains before a fixed star during the occultation, teaches us that the light of a fixed star is not pe?'-ceptibly deflected from its rectilinear course at qu'elle se trouve plus pres da centre de l'ombre geometrique ; car se sont les rayons les moins refrangibles qui se propagent le plus abon- dammentpar diffraction, a. mesure qu'on s'eloigne de la propagation en ligne droite." " The diffracted light which penetrates into the Earth's shadow always predominated, and was, indeed, alone seusible. It was the more red or orange in proportion as it was nearer to the geomet- rical center of the shadow ; for those rays which are least refrangible ure those which are propagated most abundantly by diffraction, in pro portion as they differ from a rectilinear course." The phenomena of diffraction take place as well in a vacuum, according to the acute in vestigations of Magnus (on the occasion of a discussion between Airy and Faraday). Compare, in reference to the explanations by diffrac tion in general, Arago in the Annuaire for 1846, p. 452-455. * Plutarch {De Facie in Orbe Lnnce), Moral., ed. Wytten., torn, iv., p. 780-783 : " The fiery, charcoal-like, glimmering (avdpano£L6r)e) coloi of the eclipsed Moon (about the midnight hour) is, as the mathemati- cians affirm, owing to the change from black into red and bluish, and is by no means to be considered as a character peculiar to the earthy surface of the planet." Also Dio Cassius (lx., 26, ed. Sturz, p. iii., p 779), who occupied himself especially with eclipses of the Moon, and the remarkable edicts of the Emperor Claudius, which predicted the di- mensions of the eclipsed portion, directs attention to the very different colors which the Moon assumed during the conjunction. He says (lxv., 11, torn, iv., p. 185, Sturtz), "Great was the excitement in the camp of Vitellius in consequence of the eclipse which took place that night. The mind was filled with melancholy apprehensions, not so much at the eclipse itself, although that might appear to predict misfortune to an unquiet mind, but much more from the circumstance that the Moon displayed blood-red, black, and other gloomy colors." t Schroter, Selenotopographische Fragmente, th. i., 1791, p. 668; th. ii., 1802, p. 52. 148 cosmos. that moment in which it touches the Moon's edge. If a re- fraction took place at the edge of the Moon, the second de- termination of her diameter must give a value smaller by twice the amount of the refraction than the former ; but, on the contrary, both determinations correspond so closely in repeated determinations, that no appreciable difference has ever been detected."* The ingress of stars, which may be particularly well observed at the dark edge, t^kes place suddenly, and without gradual diminution of the star's brill- iancy ; just so the egress or reappearance of the star. In the case of the few exceptions which have been described, the cause may have consisted in accidental changes of our atmosphere. If, however, the Earth's Moon is destitute of a gaseous envelope, the stars must appear then, in the absence of all diffuse light, to rise upon a black sky ;f no air-wave can there convey sound, music, or language. To our imagina- tion, so apt presumptuously to stray into the unfathomable, the Moon is a voiceless wilderness. The phenomenon of apparent adherence on and within the Moon's edge,:}: sometimes observed in the occultation of stars, can scarcely be considered as a consequence of irradiation, which, in the narrow crescent of the Moon, on account of the very different intensity of the light in the ash-colored part of the Moon, and in that which is immediately illumin- ated by the Sun, certainly makes the latter appear as if sur- rounding the former. Arago saw, during a total eclipse of the Moon, a star distinctly adhere to the slightly luminous disk of the Moon during the conjunction. It still continues to be * Bessel, Ueber eine angenommene Atmosphdre des Mondes in Schu- macher's Aslron. Nachr., No. 263, p. 416-420. Compare also Beer and Madler, Der Monde, § 83 and 107, p. 133 and 153; also Arago, in the Annuaire for 1846, p. 346-353. The frequently mentioned proof of the existence of an atmosphere round the Moon, derived from the greater or less perceptibility of small superficial configurations and " the Moon- clouds moving round in the valleys," is the most untenable of all, on account of the continually-varying condition (darkening and brighten- ing) of the upper strata of our own atmosphere. Considerations as to the form of one of the Moon's horns on the occasion of the solar eclipse on the 5th of September, 1793, induced William Herschel to decide against the assumption of a lunar atmosphere. (Philos. Transact., vol. lxxxiv., p. 167.) t Madler, in Schumacher's Jahrbuch for 1840, p. 188. $ Sir John Herschel (Outlines, p. 247) directs attention to the ingress of such double stars as can not be seen separately by the telescope, on account of the too great proximity of the individual stars of which they consist. THE MOON. 149 a subject of discussion between Arago and Plateau whether the phenomenon here mentioned depends upon deceptive per- ception and physiological causes,* or upon the aberration of sphericity and refrangibility of the eye.f Those cases in which it has been asserted that a disappearance and reap- pearance, and then a repeated disappearance, have been ob- served during an occupation, may probably indicate the in- gress to have taken place at a part of the Moon's edge which happened to be deformed by mountain declivities and deep chasms. The great differences in the reflected light from particular regions of the illuminated disk of the Moon, and especially the absence of any sharp boundary between the inner edge of the illuminated and ash-colored parts in the Moon's phases, led to the formation of several very rational theories as to the inequalities of the surface of our satellite, even at a very remote period. Plutarch says distinctly, in the small but very remarkable work On the Face in the Moon, that we may suppose the spots to be partly deep chasms and valleys, partly mountain peaks, " which cast long shadows, like Mount Athos, whose shadow reaches Lemnos."$ The spots cover about two fifths of the whole disk. In a clear atmosphere, and under favorable circumstances in the position of the * Plateau, Sur V Irradiation, in the M6m. de V Acad. Royale des Sci- ences et Belles-Leltres de Bruxelles, torn. xi.,p. 142, and the supplement- ary volume"" of Poggendorff's Annalen, 1842, p. 79-128, 193-232, and 405 and 443. "The probable cause of the irradiation is an irritation produced by the light upon the retina, and spreads a little beyond the outline of the image." t Arago, in the Comptes Rendus, torn, viii., 1839, p. 713 and 883. " Le^phenomenes d'irradiation signales par M. Plateau sont regard es par M. Arago comme les effets des aberrations de refraugibilite et de sphericite de l'oeil, combines avec l'indistinction de la vision, conse- quence des circonstances dans lesquelles les observateurs se sont places. Des mesures exactes prises sur des disques noirs a fond blanc et des disques blancs a fond noir, qui etaient places au Palais du Luxembourg, visibles a l'observatoire, n'ont pas indique les effets de l'irradiation." " The phenomena of irradiation pointed out by M. Plateau are regarded by M. Arago as the effects of the aberration of sphericity and refrangi- bility of the eye, combined with the indistinctness of vision consequent upon the circumstances in which the observers are placed. The exact measurement taken of the black disks upon a white ground, and the white disks upon a black ground, which were placed upon the palace of Luxembourg, and visible at the Observatory, did not present any phenomena of irradiation." % Plutarch, Moral., ed. Wytten., torn, iv., p. 786-789. The shadow of Athos, which was seen by the traveler Pierre Belon {Observations de Singularitis trouvies en Grece, Asie, etc., 1554, liv. i., chap. 25), reached the brazen cow in the market-town Myrine in Lemnos. 150 COSMOS. Moon, some of the spots are visible to the naked eye ; the ridge of the Apennines, the dark, elevated plain Grimaldus, the inclosed Mare C?'isium, and Tycho* crowded round with numerous mountain ridges and craters. It has been affirmed, not without probability, that it was especially the aspect of the Aj^ennine chain which induced the Greeks to consider the spots on the Moon to be mountains, and at the same time to associate with them the shadow of Mount Athos, which in the solstices reached the Brazen Cow upon Lemnos. Another very fantastic opinion was that of Agesi- nax, disputed by Plutarch, according to which the Moon's disk was supposed, like a mirror, to present to us again, ca- toptrically, the configuration and outline of our continent, and the outer sea (the Atlantic). A very similar opinion ap- pears to have been preserved to this time as a popular belief among the people in Asia Minor. f By the careful application of large telescopes, it has grad- * For proofs of the visibility of these four objects, see in Beer and Madler, Der Mond., p. 241, 338, 191, and 290. It is scarcely necessary to mention that all which refers to the topography of the Moon's surface is derived from the excellent work of my two friends, of whom the second, William Beer, was taken from us but too early. The beautiful Uebersichtsblatt, which Madler published in 1837, three years after the large map of the Moon, consisting of three sheets, is to be recommended for the purpose of more easily becoming acquainted with the bearings. t Plut, De Facie in Orbe Lunce, p. 726-729, Wytten. This passage is, at the same time, not without interest for ancient geography. — See Humboldt, Examen Critique de V Hist, de la Geogr., torn, i., p. 145. With regard to other views of the ancients, see Anaxagoras and De- mocritus, in Plut., De Plac. Philos., ii., 25 ; Parmenides, in Stob., p. 419, 453, 516, and 563, ed. Heeren; Schneider, Eclogue Physicce, vol. i., p. 433-443. According to a very remarkable passage in Plutarch'%Z,z/e of Nicias, cap. 42, Anaxagoras himself, who calls " the mountainous Moon another Earth," had made a drawing of the Moon's disk. (Com- pare also Origines, Philosophumena, cap. 8, ed. Mulleri, 1851, p. 14.) I was once very much astonished to hear a very well-educated Per- sian, from Ispahan, who certainly had never read a Greek book, men- tion, when I showed him the Moon's spots in a large telescope in Paris, the hypothesis of Agesinax (alluded to in the text) as to the reflection, as a widely-diffused popular belief in his country. " What we see there in the Moon," said the Persian, "is ourselves; it is the map of our Earth." One of the interlocutors in Plutarch's Moon-dialogue would not have expressed himself otherwise. If it can be supposed that men are inhabitants of the Moon, destitute of water and air, the Earth, with its spots, would also present to them such a map upon a nearly black shy by day, with a surface fourteen times greater than that which the full Moon presents to us, and always in the same position. But the constantly varying clouds and obscurities of our atmosphere would con- fuse the outlines of the continents. — Compare Madler's A stron., p. 169 and Sir John Herschel, Outlines, § 436. THE MOON. 151 ually become possible to construct a topographical chart of the Moon, based upon actual observations ; and since, in the opposition, the entire half-side of the Earth's satellite presents itself at the same moment to our investigation, we know more of the general and merely formal connection of the mountain groups in the Moon, than of the orography of a whole terres- trial hemisphere containing the interiors of Africa and Asia. Generally the darker parts of the disk -are the lower and more level ; the brighter parts, reflecting much sunlight, are the more elevated and mountainous. Kepler's old description of the two as sea and land has long been given up ; and the accuracy of the explanation, and the opposition, was already doubted by Hevel, notwithstanding the similar nomenclature introduced by him. The circumstance principally brought forward as disproving the presence of surfaces of water on the Moon was, that in the so-called seas of the Moon, the smallest parts showed themselves, upon closer examination and very different illumination, to be completely uneven, pol- yhedric, and consequently giving much 'polarized light. Ar- ago has pointed out, in opposition to the arguments which have been derived from the irregularities, that some of these surfaces may, notwithstanding the irregularities, be covered with water, and belong to the bottoms of seas of no great depth, since the uneven, craggy bottom of the ocean of our planet is distinctly seen when viewed from a great height, on account of the preponderance of the light issuing from be- low its surface over the intensity of that which is reflected from it. (Annuaire du Bureau des Longitudes for 1836, p. 339—343.) In the work of my friend, which will shortly appear, on astronomy and photometry, the probable absence of water upon our satellite will be deduced from other optical grounds, which can not be developed in this place. Among the low plains, the largest surfaces are situated in the north- ern and eastern parts. The indistinctly bounded Oceanus Procellarum has the greatest extension of all these, being 360,000 geographical miles. Connected with the Mare Im- brium (64,000 square miles), the Marc JSfubium, and, to some extent, with the Marc Humor u m, and surrounding in- sular mountain districts (the Rijrticci, Kepler, Copernicus, and the Carpathians), this eastern part of the Moon's disk presents the most decided contrast to the luminous south- western district, in which mountain is crowded upon mount- ain.* In the northwest region, two basins present them- * Beer and Madler, p. 273. 152 cosmos, selves as being more shut in and isolated, the Mare Crisium (12,000 square miles) and the Mare Tranquillitatis (23,200 square miles). The color of these so-called seas is not in all cases gray. The Mare Crisium is gray mixed with dark green ; the Mare Serenitatis and Mare Humorum are likewise green. Near the Hercynian mountains, on the contrary, the isolated cir- cumvallation Lichtenberg presents a pale reddish color, the same as Palus Somnii. Circular surfaces, without central mountains, have for the most part a dark steel-gray color, bordering upon bluish. The causes of this great diversity in the tints of the rocky surface, or other porous materials which cover it, are extremely mysterious. While, to the northward of the Alpine mountains, a large inclosed plain, Plato (called by Hevel Lacus niger major), and still more Grimaldus in the equatorial region, and Endymion on the northwest edge, are the three darkest spots upon the whole Moon's disk, Aris- tarchus, with its sometimes almost star-like shining points, is the brightest and most brilliant. All these alternations of light and shade affect an iodized plate, and may be repre- sented in Daguerreotype, by means of poAverful magnifiers, with wonderful truthfulness. I myself possess such a moon- light 'picture of two inches diameter, in which the so-called seas and ring-formed mountains are distinctly perceptible ; it was executed by an excellent artist, Mr. "Whipple, of Boston. If the circular form is striking in some of the seas ( Cris- ium, Serenitatis, and Humorum), it is still more frequently — indeed, almost universally, repeated in the mountainous part of the disk, especially in the configuration of the enor- mous mountain-masses which occupy the southern hemisphere from the pole to near the equator, where the mass runs out in a point. Many of the annular elevations and inclosed plains (according to Lohrmann, the largest are more than 4000 square miles in extent) form connected series, and, in- deed, in the direction of the meridian, between 5° and 40° south latitude.^ The northern polar region contains com- paratively few of these crowded mountain circles. In the western edge of the northern hemisphere, on the contrary, they form a connected group between 20° and 50° north latitude. The North Pole itself is within a few degrees of the Mare Frigoris, and thus, like the whole level northeast- ern space, including only a few isolated annular mountains {Plato, Mairan, Aristarch, Copernicus, and Kepler), pre- * Schumacher's Jahrbuch for 1841, p. 270. THE MOON. 153 Bents a great contrast to the South Pole, entirely covered with mountains. Here lofty peaks shine during whole lunations in eternal light, in the strictest sense of the word ; they are true light islands, which become perceptible, even with feeble magnifying powers.* As exceptions to this type of circular and annular configu- rations, so universally predominant upon the Moon, are the actual mountain-chains which occur almost in the middle of the northern half of the Moon {Apennines, Caucasus, and Al})s). They extend from south to north in a slight curve to- ward the west, through nearly 32° of latitude. Innumer- able mountain crests and extraordinary sharp peaks are here thronged together. Few annular mountains, or crater-like depressions, are intermingled (Conon, Hadley, Calippits), and the whole resembles more the configuration of our mount- ain-chains upon the Earth. The lunar Alps, which are in- ferior in height to the lunar Caucasus and Apennines, pre- sent a remarkable bro.id transverse valley, which intersects the chain from southeast to northwest. It is surrounded by mountain peaks which exceed in height that of Teneriffe. The relative height of the elevations in proportion to the diameters of the Moon and the Earth, gives the remarkable result, that since in the four times smaller satellite the high- est peaks are only 3836 feet lower than those of the Earth, the lunar mountains amount to ¥i¥, the mountains on the Earth to tjVt °f the planetary diameters. f Among the 1095 points of elevation already measured upon the Moon, I find 39 are higher than Mont Blanc (16,944 feet), and six higher than 19,000 feet. The measurements were effected either by light tangents (by determining the distance of the illumin- ated mountain peak on the right side of the Moon from the boundary of the light) or by the length of the shadows. The former method was already made use of by Galileo, as is seen from his letter to the Father Grienberger upon the Montu- osita della Lu?m. According to Madler's careful measurements by means of the length of the shadows, the culminating points of the * Madler, Astron., p. 166. t The highest peak of the Himalayas, and (up to the present time!) of the whole Earth, Kinchin- junga, is, according to Waugh's recent measurement, 4406 toises, or 28,178 English feet; the highest peak among the Moon's mountains is, according to Madler, 3800 toises (ex- actly four geographical miles). The diameter of the Moon is 1816, that of the Earth 6872 geographical miles ; whence it follows for the Moon ¥ix, for the Earth yy-g-p G 2 154 cosmos. Moon are in descending order at the south edge, very near the Pole, Dor/el and Leibnitz, 24,297 feet ; the annular mountain Neivton, where a part of the deep hollow is never lighted, neither by the Sun nor the Earth's disk, 23,830 feet ; Casa- tus, eastward of Newton, 22,820 feet ; Calippus, in the Cau- casian chain, 20,396 feet; the Apennines, between 17,903 and 19,182 feet. It must be remarked here, that in the en- tire absence of a general niveau-line (the plane of equal dis- tance from the center of a cosmical body, as is presented on our planet by the level of the sea), the absolute heights are not to be compared strictly with each other, since the six numerical results here given properly express only the differ- ences between the peaks and the immediately surrounding plains or hollows. # It is, however, very remarkable that Galileo likewise assigned to the loftiest lunar mountains the height of about four geographical miles (24,297 feet), " in- circa miglia quatro," and, in accordance with the extent of his hypsometric knowledge, considered them higher than any of the mountains on the Earth. An extremely remarkable and mysterious phenomenon which the surface of our satellite presents, and which is only optically connected with a reflection of light, and not hyp- sometrically with a difference of elevation, consists in the nar- row streaks of light which disappear when the illuminating rays fall obliquely ; but in the full Moon, quite in opposition to the Moon-spots, become most visible as systems of rays. They are not mineral veins, cast no shadow, and run with equal intensity of light from the plains to elevations of more than 12,780 feet. The most extensive of these ray-systems commences from Tycho, where more than a hundred streaks of light may be distinguished, mostly several miles broad. Similar systems which surround the Aristarchus, Kepler, Co- pernicus, and the Carpathians, are almost all in connection with each other. It is difficult to conjecture, by the aid of induction and analogy, what special transformations of the surface give rise to these luminous, ribbon-like rays, proceed- ing from certain annular mountains. The frequently mentioned type of circular configuration, almost every where preponderating upon the Moon's disk, in the elevated plains which frequently surround central mount- ains ; in the large annular mountains and their craters (22 are counted close together in Bayer, and 33 in Albategnius) * For the six heights which exceed 19,182 feet, see Beer and Mad- ter. p. 99, 125, 234, 242, 330, and 331. THE MOON. 155 must have early induced a deep-thinker like Robert Hooke to ascribe such a form to the reaction of the interior of the Moon upon the exterior — "the action of subterranean lire, and elastic eruptive vapors, and even to an ebullition in eruptive bubbles." Experiments with thickened boiling lime solutions appeared to him to confirm his opinion ; and the cir- cumvallations, with their central mountains, were at that time already compared with " the forms of iEtna, the Peak of TeneriHe, Hecla, and the Mexican volcanoes described by Gage."* One of the annular plains of the Moon reminded Galileo, as he himself relates, of the configuration of countries entirely surrounded by mountains. I have discovered a passagef in which he compares these annular plains of the Moon with the great inclosed basin of Bohemia. Many of the plains are, in fact, not much smaller, for they have a diameter of from 100 to 120 geographical miles. $ On the contrary, the real an- nular mountains scarcely exceed 8 or 12 miles in diameter. Conon in the Apennines is 8 ; and a crater which belongs to the shining region of Aristarchus is said to present a breadth of only 25,576 feet, exactly the half of the diameter of the crater of Rucu-Pichincha, in the table-land of Quito, meas- ured trigonometric ally by myself. Since we have in this place adhered to comparisons with well-known terrestrial phenomena and relations of magnitude, it is necessary to remark that the greater part of the plains and annular mountains of the Moon are to be considered in the first place as craters of elevation, without continuous phenomena of eruption in the sense of the hypothesis of Leo- pold von Buch. What, according to the European standard, * Robert Hooke, Micrographia, 1667, Obs. lx., p. 242-246. " Theso seem to me to have been the effects of* some motions within the body of the Moon, analogous to our earthquakes, by the eruption of which, as it has thrown up a brim or ridge round about higher than the am- bient surface of the Moon, so has it left a hole or depression in the mid- dle, proportionably lower." Hooke says of his experiment with boil- ing alabaster, that " presently ceasing to boyl, the whole surface will appear all over covered with small pits, exactly shaped like those of the Moon. The earthy part of the Moon has been undermined, or heaved up by eruptions of vapors, and thrown into the same kind of figured holes as the powder of alabaster. It is not improbable, also, that there may be generated within the body of the Moon divers such kind of internal fires and heats as may produce exhalations " t Cosmos, vol. ii., p. 319, note. % Beer and Madler, p. 126. Ptolemseus is 96 miles in diameter Alphons and Hipparchus. 76 miles. 156 cosmos. we call great upon the Earth — the elevation crater of Rocca Monsina, Palma, Teneriffe, and Santorin — becomes insignifi- cant when compared with Ptolemy, Hipparchus, and many- others of the Moon. Palma has only 24,297 feet diameter ; Santorin, according to Captain Graves, new measurement, 33,148 feet; Teneriffe, at the utmost, 53,298 feet: conse quently, only one eighth or one sixth of the two craters of elevation of the Moon just mentioned. The small crater of the Peak of Teneriffe and Yesuvius (from 319 to 426 feet in diameter) could scarcely be seen by the aid of telescopes. The by far greater number of the annular mountains have no central mountain ; and where there is one, it is described as being dome-formed or level {Hevelius, Macrobius), not as an erupted cone with an opening* The active volcanoes which are stated to have been seen in the right side of the Moon (May 4, 1783) ; the phenomena of light in Plato, which Bianchini (August 16, 1725) and Short (April 22, 1751) ob- served, are here mentioned only as of historical interest, since the sources of deception have long been fathomed, and lie in the more powerful reflection of the terrestrial light which certain parts of the surface of our planet throw upon the ash- colored night side of the Moon.t * Arzachel and Hercules are supposed to be exceptions : the former to have a crater upon its summit, the second a lateral crater. These points, important in a geognostic point of view, deserve fresh investi- gation with more perfect instruments. (Schroter, Selenotopographische Fragmente, th. ii., tab. 44 and 68, fig. 23.) Hitherto no signs have ever been detected of lava streams collected in deep hollows. The radiated lines which issue from Aristoteles in three directions are ranges of hills. (Beer and Madler, p. 236.) t Op. cit., p. 151. Arago, in the Annuaire for 1842, p. 526. (Com- pare also Immanuel Kant, Schriften der Physiscken Geograpkie, 1839, p. 393-402.) According to recent and more complete investigations, the temporary changes said to have been observed upon the surface of the Moon (the formation of new central mountains and craters in the Mare Crisium, Hevelius, and Cleomedes), are illusions of a similar na- ture to the supposed volcanic eruptions pei'ceptible to us upon the Moon. (See Schroter, Selenotopographische Fragmente, th. i., p. 412-523 ; th. ii., p. 268-272.) The question, what is the smallest object whose height can be measured with the instruments which are at present at our com- mand? is in general difficult to answer. According to the report of Dr. Robinson upon the beautiful reflecting telescope of Lord Rosse, extents of 220 feet (80 to 90 yards) are discerned with the greatest distinctness. Madler calculates that, in his observations, shadows of 3" were capable of being measured ; a length which, under certain presuppositions as to the position of a mountain, and the altitude of the Sun, would indicate a mountain elevation of 120 feet. However, he points out. at the same time, that the shadows must have a certain degree of breadth in order to be visible and measurable. The shadow of the great pyramid of THF. MOON. 157 Attention has been repeatedly, and with justice, directed to the fact, that in the absence of water upon the Moon (even the rills, very narrow, mostly rectilinear hollows,* are not riv- ers), we must represent to ourselves the surface of the Moon as being somewhat similarly constituted as was the Earth in its primitive and most ancient condition, while yet uncovered flotz strata, by bowlders and detritus, which were spread out by the transporting force of the ebb and flood or currents. Sun and Earth floods are naturally wanting ; where the liquid element is absent, slight coverings of decomposed conglomer- ates are scarcely conceivable. In our mountain-chains, up- heaved upon fissures, partial groups of elevations are begin- ning gradually to be discovered here and there, forming, as it were, egg-shaped basins. How entirely different the Earth's surface would have appeared to us if it were divested of the flotz and tertiary formations ! The Moon, by the variety of its phases, and the more rapid change of its relative position in the sky, animates and beau- tifies the aspect of the firmament under every zone more than all the other planets. She sheds her agreeable light upon men, more especially in the primitive forests of the tropical world, and the beasts of the forests. f The Moon, in virtue Cheops, according to the known dimensions of this monument (super- ficial extent), would be, even at the point of commencement, scarcely one ninth of a second broad, and consequently invisible. (Madler, in Schumacher's Jahrbuch for 1841, p. 264.) Arago calls to mind that, with a 6000-fold magnifying power, which, nevertheless, could not be applied to the Moon with proportionate results, the mountains upon the Moon would appear to us just as Mont Blanc does to the naked eye when seen from the Lake of Geneva. * The rills do not occur frequently; are, at the utmost, thirty miles long; sometimes forked (Gassendi); seldom resembling mineral veins (Triesnecker) ; always luminous; do not cross mountains transversely; are peculiar to the level landscapes ; are not characterized by any pe- culiarities at the terminal points, without becoming broader or narrow- er. (Beer and Madler, p. 131, 225, and 249.) t See my Essay upon the Nocturnal Life of Animals in the Primaeval Forest, in the Views of Nature, Bonn's ed., p. 198. Laplace's reflections upon a perpetual moonlight {Exposition du Systeme du Monde, 1824, p. 232) have met with a disproval in the Mem. of Liouville sur un caspar- ticulier du problem des Trois Corps. Laplace says, " Quelques partisans des causes finales ont imagine que la Lune a ete donnee a la Terre pour l'eclairer pendant les nuits ; dans ce cas, la nature n'aurait point atteint le but qu'elle se serait propose, puisque nous sommes souvent prives a la fois de la lumiere du Soleil et de celle de la Lune. Pour y parvenir, il eUt surh* de mettre a l'origine la Lune en opposition avec le Soleil dans le plan meme de Pecliptique, a une distance egale a la centieme partie de la distance de la Terre an Soleil, et de dormer a la Lune et a la Terre des vitesses paralleles et proportionnelles a leurs distances a 158 cosmos. of the attractive force which she exercises in common with the Sun, excites motion in our ocean — the liquid portion of the Earth — gradually changes the surface by periodical floods, and the outlines of continental coasts, by the destructive agen- cy of the tides, hinders or favors the labor of men ; affords the greater part of the material from which sandstones and conglomerates are formed, and which are again covered by the rounded, loose, transported detritus.^ Thus the Moon, as one of the sources of motion, continues to act upon the ge- ognostic relations of our planet. The indisputable! influence cet astre. Alors la Lune, sans cesse en opposition au Soleil, eUt decrit autour de lui une ellipse semblable a celle de la Terre ; ces deux astres se seraient succede l'un a l'autre sur l'horizon ; et comme a cette dis- tance la Lune n'eut point ete eclipsee, sa lumiere aurait certainement remplace celle du Soleil." " Several partisans of final causes have im- agined that the Moon has been given to the Earth to light it during the night ; in that case, nature would not have attained the object which she had proposed, because we are frequently deprived at the same time of the light of the Sun and Moon. To have attained this end, it would have been sufficient in the beginning to place the Moon in opposition with the Sun, in the same plane of the ecliptic, at a distance equal to the hundredth part of the distance of the Earth from the Sun, and to give to the Moon and the Earth velocities parallel and proportional to their distances from that body. Then the Moon, constantly in opposi- tion to the Sun, would have described an ellipse round it like that of the Earth ; these two bodies would have succeeded each other in the horizon, and as at that distance the Moon would never have been eclipsed, its light would certainly have replaced that of the Sun." Liou- ville finds, on the contrary, " Que, si la Lune avait occupe a l'origine la position particuliere que l'illustre auteur de la Mecanique Cileste lui assigne, elle n'aurait pu s'y maintenir que pendant un temps tres court." " That if the Moon had occupied at the beginning the particular posi- tion assigned to her by the illustrious author of the Mecanique Celeste, she would not have been able to maintain it for more than a very short time." * On the Transporting Power of the Tides, see Sir Henry de la Beche, Geological Manual, 1833, p. 111. t Arago, Sur la question de savoir si la Lune exerce sur notre Atmo- sphere une influence appreciable, in the Annuaire for 1833, p. 157-206. The principal advocates of this opinion are Scheibler {Unter&nch. uber Einfluss des Mondes auf die Vcrdnderun gen in unserer Atmosphdre, 1830, p. 20); Flaugergues (Zicanzigjdhrige Beobachtungen in Viviers, Bill- Universelle, Sciences et Arts, torn, xl., 1829, p. 265-283, and in Kastncr's Archivf. die ges. Naturlehre, bd. xvii., 1829, sees. 32-50); and Eisenlohr (Poggend., Annalen der Physik, bd. xxxv., 1835, p. 141-160, and 309- 329). Sir John Herschel considers it very probable that a very high temperature prevails upon the Moon (far above the boiling-point of water), as the surface is uninterruptedly exposed for fourteen days to the full action of the Sun. Therefore, in the opposition, or some few days after, the Moon must be, in some small degree, a source of heat for the Earth; but this heat, radiating from a body far below the tem- perature of ignition, can not reach the surface of the Earth, since it is MARS. 150 of the satellite upon atmospheric pressure, aqueous depositions, and the dispersion of clouds, will be treated of in the last and purely telluric part of the Cosmos. Mars. The diameter of this planet, notwithstanding its considera- bly greater distance from the Sun, is only 0'519 of the Earth's, or 3568 geographical miles. The eccentricity of his orbit is 0*0932 168, next to Mercury the greatest of all the planetary orbits ; and also on this account, as well as from its proximi- ty to the Earth, the most suitable for Kepler's great discove- ry of the elliptical form of the planetary orbits. His period of rotation* is, according to Madler and "VYilhelm Beer, 24h. 37m. 23s. His sidereal revolution round the Sun occupies 1 year 32 Id. 17h. 30m. 41s. The inclination of Mars' 's orbit toward the Earth's equator is 24° 44' 24"; his mass, IFI}IT ' his density, in comparison to that of the Earth, 0-958. The mass of Mars will be hereafter corrected by means of the dis- turbances which he may experience from his influence with the Comet of De Vico, in the same way that the close approach of Encke's Comet was taken advantage of to ascertain the mass of Mercury. The flattening of Mars, which (singularly enough) the great Kbnigsberg astronomer permanently doubted, was first recog- nized by William Herschel (1784). With regard to the amount of the flattening, however, there was long considerable uncer- absorbed in the upper strata of our atmosphere, where it converts visi- ble clouds into transparent vapor." The phenomenon of the rapid dis- persion of clouds by the full Moon, when they are not extremely dense, is considered by Sir John Herschel " as a meteorological fact, which," he adds, "is confirmed by Humboldt's own experience and the uni- versal belief of the Spanish sailors in the tropical seas of America." — See Report of the Fifteenth Meeting of the British Association for the Advancement of Science, 1846, Notices, p. 5; and Outlines, p. 201. * Beer and Madler, Beitrdge zur Phys. Kenntniss des Sonnensy stems, 1841, p. 113, from observations in 1830 and 1832 ; Madler, Astronomie, 1849, p. 206. The first considerable improvement in the data for the period of rotation, which Dominique Cassini found 24h. 40m., was the result of laborious observations by William Herschel (between 1777 and 1781), which gave24h. 39m. 21-7s. Kunowsky found, in 1821,241). 36m. 40s., very near to Madler's result. Cassini's oldest observation of the rotation of a spot upon Mars (Delambre, Hist, de V Astron. Mod., torn, ii., p. 694) appears to have been soon after the year 1670; but in the very rare Treatise, Kern, Diss, de Scintillaiione Stellarum, Wittenb., 1686, § 8, I find that the actual discoverers of the rotations of Mars and Jupiter are stated to have been " Salvator Serra and Father iEgidius Franciscus de Cottignez. astronomers of the Collegio Romano." 160 CCSMOS. tainty. It was stated by William Herschel to be TJF ; accord- ing to Arago's more accurate measurement,^ with one of Ro- chon's prismatic telescopes, in the first instance (before 1824), only in the proportion of 189 : 194, i. e., -§%.j ; by a subsequent measurement (1847), -Jj ; still, Arago is inclined to consider the flattening somewhat greater. If the study of the Moon's surface calls to mind many ge- ognostic relations of the surface of the Earth, so, on the con- trary, the analogies which Mars presents with the Earth are entirely of a meteorological nature. Besides the dark spots — some of which are blackish ; others, though in very small numbers, yellowish-red, f and surrounded by the greenish con- trast colors, so-called seas$ — there are seen upon the disk of Mars two white, brilliant, snow-like spots, \ either at the poles which are determined by the axis of rotation, or at the poles of cold alternately. They were recognized as early as 1716 by Philip Maraldi, though their connection with climatic changes upon the planet was first described by the elder Herschel, in the seventy-fourth volume of the Philosophical Transactio?is for 1784. The white spots become alternately larger or smaller, according as the poles approach their win- ter or summer. Arago has measured, by means of his polari- scope, the intensity of the light of these snoiv zones, and found it twice as great as that of the remaining part of the disk. The Physikalisch-astronomischen Beitragen of Madler and Beer contain some excellent graphic representations!! of the north and south hemispheres of Mars ; and this remarkable phenomenon, unparalleled throughout the whole planetary system, is there investigated with reference to all the changes of seasons, and the powerful action of the polar summer upon the melting snow. Careful observations, during a period of ten years, have also taught us that the dark spots upon Mars preserve a constant form and relative position. The period- ical formation of snow-spots, as meteoric depositions depend- ent upon change of temperature, and some optical phenom- ena which the dark spots present as soon as they have, by the rotation of the planet, reached the edge of the disk, make the existence of an atmosphere upon Mars more than probable. * Laplace, Expos, du Syst. du Monde, p. 36. Schroter's very imper- fect measurement of the diameter of the planet gave Mars a flattening of only -gL. t Beer and Madler, Beitrage, p. 111. X Sir John Herschel, Outlines, § 510. § Beer and Madler, Beitrage, p. 117-125. H Madler, in Schumacher's Astr. Nachr., No. 192. THE SMALL PLANETS. H) I The Small Planets. We have already, in the general consideration* of the planetary bodies, characterized the group of small planet?, (asteroids, planetoids, co-planets, telescopic or idtra-zodiacal planets) under the name of an intermediate group, which, to a certain extent, forms a zone of separation between the four interior planets (Mercury, Venus, the Earth, and Mars), and the four exterior planets of our solar system (Jupiter, Sat- urn, Uranus, and Neptune). Their most distinctive features consist in their interlaced, greatly inclined, and extremely ec- centric orbits ; their extraordinary smallness, as the diameter of Vesta does not appear to equal even the fourth part of the diameter of Mercury. When the first volume of the Cosmos appeared (1845), only four of the small planets were known : Ceres, Pallas, Juno, and Vesta, discovered by Piazzi, Olbers, and Harding (between January 1, 1801, and March 29, 1S07) ; at the present time (July, 1851), the number of the small planets has already increased to 14 ; they form numerically * Cosmos, vol. iv., p. 101. With regard to the chronology of the dis- coveries of the small planets, compare p. 100 and 131 ; their relations of magnitude to the meteor-asteroids (aerolites), p. 105. With respect to Kepler's conjecture of the existence of a planet in the great chasm between Mars and Jupiter — a conjecture, however, which by no means led to the discovery of the first of the small planets ( Ceres), compare p. Ill, 116, and 117, note t. The bitter reproach which has been thrown upon a highly esteemed philosopher, " because at a time when he might have known of Piazzi's discovery certainly five mouths before, but was unacquainted with it, he denied not so much the probability, as much more the necessity of a planet being situated between Mars and Jupi- ter," appears to me to be little justifiable. Hegel, in his Disserlatio de Orhitis Planetarum, composed in the spring and summer of 1801, treats of the ideas of the ancients of the distances of the planets ; and when he quotes the arrangement of which Plato speaks in the Timceus (p. 35, Steph.), 1.2. 3. 4. 9. 8. 27 (compare Cosmos, vol. iv., p. 109, note $), he denies the necessity of a chasm. He says only, "Qua? series si verior naturcc ordo sit, quam arithmetica progressio, inter quar- tum et quintum locum magnum esse spalium, neque ibi planetam de- siderari apparet." " If the order of nature is more precise than an arithmetical progression, there appears to be a great space between the fourth and fifth place, and that no planet is required there." (He- gel's Werke, bd. xvi., 1834, p. 28; and Hegel's Leben von Rosenkranz , 1844, p. 154.) Kant, in his ingenious work, Naturgcschichte desHim- mels, 1755, says merely that at the time of the formation of the planets, Jupiter occasioned the smallness of Mars by the enormous attractive force which the former possessed. He only once mentions, and then in a very indecisive manner, " the members of the solar system which are situated far from each other, and between which the intermediate parts have not yet been discovered." Immanuel Kant, Sdmmtliche Werke, th. vi., 1839 p. 87, 110, and 196.) 162 cosmos. the third part of all the 43 known planetary bodies, i. e., of all principal and secondary planets. Although the attention of astronomers was long directed in the solar regions to increasing the number of the members of partial systems — the Moons which revolve round principal planets — and to the planets to be discovered in the furthest regions beyond Saturn and Uranus, now, since the accidental discovery of Ceres by Piazzi, and especially since the foreseen discovery of Astrea by Encke, as well as the great improve- ments in the star-charts* (those of the Berlin Academy con- tain all stars as far as the 9th, and partly to the 10th mag- nitudes), a nearer space presents to us the richest, and per- haps inexhaustible field for astronomical industry. It is an especial merit of the Astronomischen Jahrbuch, which is published in my native town by Encke, the Director of the Berlin Observatory, with the assistance of Dr. Wolfers, that the ephemerides of the increasing host of small planets are treated of with particular completeness. Up to the present time, the region nearest to the orbit of Mars appears to be the most filled ; but the breadth of this measured zone is in itself more considerable than the distance of Mars from the Sun,f " when the difference of the radii-vectores in the near- est perihelion (Victoria) and the most distant aphelion (Hy- giea) is taken into consideration." The eccentricities of the orbits, of which those of Ceres, Egeria, and Vesta are the smallest, and Juno, Pallas, and Iris the greatest, have already been alluded to| above, as well as their degrees of inclination toward the ecliptic, which decreases from Pallas (34° 37') and Egeria (16° 33') to Hy- giea (3° 47'). A tabular view of the elements of the small planets follows here, for which I am indebted to my friend Dr. Galle. * With regard to the influence of improved star-charts upon the dis- covery of the small planets, see Cosmos, vol. hi., p. 116. t D'Arrest, Ueber das System der Kleinen Planeten zwiscken Mars una Jupiter, 1851, p. 8. t Cosmos, vol. iv., p. 102 and 172. THE SMALL PLANETS. 103 m T-i < w X w a H H O o pa CO T3 • _ CO cm ^ co ? ct 1ft i .—1 Ift 00 rH L0 > o o i-H cm r— i a r-l o CO 00 CO CM CO CJ o 00 CO l-H o CO a> Ch f^ 1ft co t^ T3 _ o CO Ift •^ co t^ r- -fl ■ ■ m 00 r-l CO u Ch- o LO o l-H o l-H 00 8> r-l CO »- CJ CO o o r-l 00 CO r-l ip o o ib co oo l^ CO T3 rH CI O op 00 CO d c 3 rH no oo H l-H CD o CO o o o o CO CO CO CO LO IO CJ o CJ LO i-s C 3 CJ ift l-H i-H 00 CM rH r^J o ift o rH CO t- o CO 13 . . l-H rH LO t^ -Tl oo Of a e i-H lo 00 1—1 i— 1 >> 13 •-a o CO CI o o l-H o CO 00 o co IO 00 CO LO CJ CO rH o CO 1—1 LO r^ O a 1> 00 CO CO »ft t^ "3* CM 1— 1 rH CO Ci ct CJ .5 "B CI LO l-H O CI o 00 o CO o CO IO CO 00 CO CO o CO l-H LO CD ^ co 1 — I ■«*< l-H CI l-H x) i-H CO rH l-H o feH *H ift t~ CO 00 C3 o "*« LO • cj CO •<*• a I-H LO t^ t^ 'O c *-> l-H LO CO o Po CO o 1—1 TH o LO CO >ft c< 00 00 r^t l-H LO r-l 3 l-l Vi l-H i-H rH o < eg o. o c 1 o rH LO bi V CI CO 03 . . 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The discovery of a fifteenth new planet (Eunomia) has just been announced. It was discovered by De Gasparis upon the 19th of July, 1851. The elements, which have been calculated by Rumker, are the following : Epoch of mean longitude in mean Greenwich time. } n t 1 "ft Mean longitude 321° 25' 29" Longitude of perihelion 27 35 38 Longitude of ascending node 293 52 55 Inclination 11 48 43 Eccentricity 0*188402 Half major axis 2-64758 Mean of motion 823-630 Period of revolution 1574 days. The mutual relation of the orbits of the asteroids and the enumeration of the individual pairs of orbits, has been made the subject of acute investigation, first by Gould* in 1848, and more recently by D'Arrest. The latter says, " The strongest evidence of the intimate connection of the whole group of small planets appears to be, that if the orbits are supposed to be represented materially as hoops, they all hang together in such a manner that the whole group may be replaced by anj given one. If it so happened that Iris, which Hind discov- ered in August, 1847, was still unknown, as many other bod- ies in this region certainly are, the group would consist of two separate parts — a result which must appear so much the more unexpected, as the zone which these orbits occupy in the solar system is wide."f We can not take leave of this wonderful group of planets without mentioning, in this fragmentary enumeration of the individual members of the solar system, the bold view of a gifted and deeply investigating astronomer as to the origin of the asteroids and their intersecting orbits. A result deduced from the calculations of Gauss, that Ceres approaches extreme- ly near to Pallas in her ascending passage through the plane of that planet's orbit, led Olbers to form the conjecture that " both planets, Ceres and Pallas, maybe fragments of a sin- gle large principal planet which has been destroyed by some natural force, and formerly occupied the gap between Mars and Jupiter, and that the discovery of an additional number of similar fragments which describe elliptical orbits round the Sun, in the same region, may be expected. "$ * Benjamin Althorpe Gould (now at Cambridge, Massachusetts, U. S.), Untersuchungen uber die gegenseitige Lage der Bahnen zwischen Mars und Jupiter. 1848, p. 9-12. t D'Arrest, op. cit., p. 30. X Zach, Monatl. Corresp., bd. vi., p. 88. JUPITER. 165 The possibility of determining by calculation, even approx- imativcly, the epoch of such a cosmical event, which it is sup- posed would be at the same time the epoch of the formation of the small planets, remains more than doubtful, from the complication produced by the already large number of the " fragments" known, the peculiar retrogression of the apsides, and motion of the nodes.* Olbers describes the region of the nodes of the orbits of Ceres and Pallas as corresponding to the northern wing of the Virgin and the constellation of the Whale. Certainly Juno was discovered in the latter by Harding, though accidentally, in the construction of a star- catalogue, scarcely two years after the discovery of Pallas, and even Vesta in the latter, after a long search during five years, conducted upon hypothesis. This is not the place to determine whether these results alone are sufficient to estab- lish the hypothesis. The cometary clouds, in which the small planets were at first supposed to be enveloped, have disap- peared on investigation with more perfect instruments. The considerable changes of light to which they were said to be subject were ascribed by Olbers to their irregular figure as being " fragments of a single destroyed planet."! Jupiter. The mean distance of Jupiter from the Sun, expressed in fractional parts of the Earth's distance from the central body, amounts to 5-202767. The true mean diameter of this plan- et, the largest of all, is 77,176 geographical miles ; equal, therefore, to 11 255 terrestrial diameters, about one fifth great- er than the diameter of the more remote Saturn. His side- real revolution occupies lly. 314d. 20h. 2m. 7s. The flattening of Jupiter, according to the measurements by Arago with the prismatic micrometer (which were intro- duced into the Exposition du Systhne du Blonde, p. 38), is as 167 : 177, consequently T^.j, which agrees very closely with the later determination (1839) of Beer and Madler,$ * Gauss, Monatl. Corresp., bd. xxvi., p. 299. t Mr. Daniel Kirkwood (of the Pottsville Academy) has ventured upon the undertaking of restoring the exploded primitive planet from the fragmentary remains in the same maimer as the animals of the prim- itive Earth. He finds for it a diameter greater than Mars (of more than 4320 geographical miles), and the slowest rotation of all the prin- cipal planets — a length of day of fifty-seven hours and a half. (Report of the British Assoc, 1830, p. xxxv.) X Beer and Madler, Beitrdge zur Phys. Kenntniss der Hirnl. Korper, p. 104-106. Older and less certain observations by Hnssey gave J^, 166 cosmos. who found the flattening to he between T|-.T and ^{-e- Han- sen and Sir John Herschel give the preference to y1^. The earliest observation of the flattening, by Dominique Cassini, is older than the year 1666, as I have already pointed out elsewhere. This circumstance has an especial historical im- portance, on account of the influence which, according to Sir David Brewster's acute remark, the discovery of this flatten- ing by Cassini exercised upon Newton's ideas as to the figure of the Earth. The Principia Philosophies Naturalis bears witness to this, but the epochs at which the Principia and Cassini's observation of equatorial and polar diameters of Jupiter appeared, might excite chronological doubts.*1 As the mass of Jupiter after that of the Sun is the most important element of the whole planetary system, its accurate determination, which has recently been effected through the disturbances of Juno and Vesta, as well as by the elongation of his satellites, especially the fourth,! must be considered as one of the most productive improvements of calculating astron- omy. The value of the mass of Jupiter is greater now than formerly; that of Mercury, on the contrary, smaller. The former, together with that of the four satellites, is to"t4^"T9' while Laplace gave it as j-osVoT--!- Jupiter's period of rotation is, according to Airy, 9h. 55' 21"'3 mean solar time. Dominique Cassini first found it (1665) to be between 9h. 55m. and 9h. 56m., by means of a spot which was visible^ for many years, even indeed to 1691, and was always of the same color and outline. The greater part of these spots are of greater blackness than the streaks upon Jupiter. They do not, however, appear to belong to Laplace (Syst. du Monde, p. 266) found it theoretically between -^V and T5^, with increasing density of the strata. * Newton's immortal work, Philosophies Naturalis Principia Mathe matica, appealed as early as May, 1687, and the papers of the Paris Academy did not contain the notice of Cassini's determination of the flattening (y^) until the year 1691 ; so that Newton, who might cer- tainly have known of Richer's pendulum-experiment at Cayenne, from the account of the journey printed in 1679, must have become acquaint- ed with the configuration of Jupiter by verbal intercourse and the act- ive correspondence of that time. With regard to this subject, and the only apparent early acquaintance of Huygens with the pendulum-ex- periment of Richer, compare Cosmos, vol. i., p. 165, note, and vol. ii., p. 146, note. t Airy, in the Mem. of the Royal Astron. Soc, vol. ix., p. 7 ; vol. x., p. 43. X As early as the year 1824. (Laplace, op. cit., p. 207.) § Delambre, Hist, de V Astron. Mod., torn, ii., p. 754. JUPITER. 167 the surface of the planet itself, as they sometimes have a dif- ferent velocity from that of the equatorial regions. Accord- ing to a very experienced observer, Heinrich Schwabe, of Des- sau, the dark, more sharply-bounded spots have been several years in succession exclusively peculiar to the two gray gir- dles bordering upon the equator, sometimes the north and sometimes the south. The process of spot-formation is, there- fore, locally variable. Schwabe's observations, made in No- vember, 1834, likewise show, that the spots on Jupiter, seen with a 280-fold magnifying power in a Fraunhofer telescope, sometimes resemble the small nucleoid spots surrounded by a halo upon the Sun. But still their darkness is less than that of the satellite shadows. The nucleus is probably a part of the body of Jupiter itself, and if the atmospheric opening remains fixed above the same spot, the motion of the spots gives the true rotation. They also separate sometimes, like the Sun-spots, as Dominique Cassini discovered as early as 1665. In the equatorial zone of Jupiter are situated two broad 'principal streaks or girdles, of a gray or grayish-brown col- or, which become paler toward the edges, and finally disap- pear entirely. Their boundaries are very irregular and va- riable ; both are separated by an intermediate bright equa- torial streak. Toward the poles, also, the whole surface is cov- ered with numerous, narrower, paler, frequently interrupted, even finely branched streaks, always parallel to the equator. " These phenomena," says Arago,* "are most easily explain- * " On sait qu'il existe au-dessus et au-dessous de l'equateur de Ju- piter deux bandes moins brillantes que la surface generate. Si on les examine avec uue lunette, elles paraissent moins distiuctes a mesure qu'elles s'eloignent du centre, et meme elles deviennent tout-a-fait in- visibles pres des bords de la planete. Toutes ces apparences s'expli- quent en admettant l'existence d'une atmosphere de nuages inter- rompue aux environs de l'equateur par une zone diaphaue, produite peut-etre par les vents alises. L'atmosphere de nuages reflechissant plus de lumiere que le corps solide de Jupiter, les parties de ce corps que l'on verra a travers la zone diaphane, auront moins d'eclat que le reste et formeront les bandes obscures. A mesure qu'on s'eloignera du centre, le rayon visuel de l'observateur traversera des epaisseurs de plus en plus grandes da la zone diaphane, en sorte qu'a la lumiere reflechie par le corps solide de la planete s'ajoutera la lumiere reflechie par cette zone plus epaisse. Les bandes seront par cette raison moins obscures en s'eloignant du centre. Enfin aux bords memes la lumiere reflechie par la zone vue dans la plus grande epaisseur pourra faire disparattre la difference d'intensite qui existe entre les quantites de lumiere reflechie par la planete et par l'atmosphere de nuages ; on cessera alors d'aper- cevoir les bandes qui n'existent qu'en vertu de cette difference. On 168 cosmos. able by assuming the existence of an atmosphere partially condensed by strata of clouds, in which, however, the region resting upon the equator is free from vapor and diaphanous probably in consequence of the trade-winds. Since, as Will- iam Herschel already assumed in a treatise in the 83d vol. of the Philosoiriiical Transactions, which appeared in 1793, the cloud-surface reflects a more intense light than the sur- face of the planet, so that part of the ground which we see through the clearer air must have less light (appear darker) than the strata of clouds reflecting large quantities of light. On that account gray (dark) and clear bands alternate with each other ; the former appear so much the less dark-colored in proportion to the distance from the center, when, the visual radius of the observer being directed obliquely toward the edge of the planet, at a small angle, they are seen through a larger and thicker mass of atmosphere, reflecting more light. observe dans les pays de montagnes quelque chose d'analogue : quand on se trouve pres d'un foret de sapin, elle parait noire ; mais a mesure qu'on s'en eloigne, les couches d'atinosphere interposees deviennent de plus en plus epaisses et reflechissent de la lumiere. La difference de teinte entre la foret et les objets voisins diminue de plus en plus, elle finit par se confondre avec eux, si l'on s'en eloigne d'une distance con- venable." (From Arago's Reports on Astronomy, 1841.) " It is known that there exist above and below the equator of Jupiter two bands less brilliant than the general surface. If these are examined with a tel- escope, they appear less distinct in proportion as the distance from the center increases, and they even become quite invisible near the edges of the planet. All these appearances may be explained by admitting the existence of an atmosphere of clouds, interrupted near the equator by a transparent zone, produced, perhaps, by the trade-winds. The at- mosphere of clouds reflects more light than the solid body of Jupiter. Those parts of him which are seen through the transparent zone would have less brightness than the remainder, and would form obscure bands. In proportion as the distance from the center increases, the visual ray of the observer traverses greater and greater thicknesses of the trans- parent zone, in such a way that to the light reflected by the solid body of the planet is added the light reflected by the denser zone. The bands would be, from this reason, less obscure the greater the distance from the center. Finally, at the very edges of the planet's disk, the light reflected by the zone, seen in its greatest thickness, would cause the difference of intensity which existed between the quantities of light reflected by the planet and by the atmosphere of clouds to disappear, and the bauds which exist only in virtue of that difference would cease to be visible. Something analogous is observed in mountainous coun- tries; in the neighborhood of a forest of fir-trees they appear black, but in proportion as the observer removes to a greater distance, the interposed atmospheric strata become thicker and thicker, and reflect light. The difference of tint between the forest and the objects near diminishes more and more, and ends by their being confounded to- gether on removing to a sufficient distance." THE SATELLITES OF JUPITER. 109 The Satellites of Jupiter. Even so early as the brilliant epoch of Galileo, the correct opinion was formed that the subordinate planetary system of Jupiter might present, in many relations of "Space and time, a picture in miniature of the Solar System. This view, rap- idly diffused at that time, as well as the discovery, shortly afterward, of the phases of Venus (February, 1610), contrib- uted greatly to the general introduction of the Copernican system. The quadruple group of satellites of Jupiter is the only one of the exterior principal planets which has not been increased by any new discovery, during a period of nearly two centuries and a half, since the epoch of their first dis- covery by Simon Marius on the 29th of December, 1609. The following table contains the periods of sidereal revo- lution of the satellites of Jupiter, their mean distances ex- pressed in diameters of the primary, their diameters in geo- graphical miles, and their masses as parts of the mass of Jupiter. Satellites. Period of Rev- olution. Distance from Jupiter. Diameter in Geogr. Miles. Mass. 1 o 3 4 d. h. m. 1 18 28 3 13 14 7 3 14 16 16 32 6,049 9,623 15,350 26,998 2116 1900 3104 2656 0-0000173281 0-0000232355 0-0000884972 0-0000426591 If I_ 1047'8 T 7 expresses the mass of Jupiter with his satel- lites, then his mass without the satellites is nI/ng, only about c oV o smaller. The comparisons of the magnitudes, distances, and ec- centricities with other satellite systems has already been given (Cosmos, vol. iv., p. 105-127). The luminous in- tensity of Jupiter's satellites is various, and not in propor- tion to their volume, since, as a general rule, the third and the first, whose relation of magnitude is as 8 : 5, appear the brightest. The smallest and densest of all — the second — is generally brighter than the larger fourth, which is ordinarily called the least luminous. Accidental (temporary) fluctua- tions in the luminous intensity have, as already remarked, been ascribed sometimes to changes of the surface, sometimes to obscurations in the atmosphere of the satellites.* They all appear, moreover, to reflect a more intense light than the primary. When the Earth is situated between Jupiter and the Sun, and the satellites, therefore, moving from east to * Sir John Herschel, Outlines, At the instigation of Arago, Leverrier commenced, in the Bummer of 1845, hia investigations of the theory of Uranus. The results of this in- igation he laid before the Institute! on the 10th of November, 181."), the 1st of June, 31st of August, and 5th of October, 1846, and published them at the same time ; but the most extensive and important of Lever* tier's labors which contained the solution of the whole problem appeared in the Connaissance des Temps pour Van 1849. Adams laid the first results which he had obtained for the disturbing planet before Profes- sor Challis in September, 1845, without having them printed, and. to gether with some alterations in October of the same year, before the astronomer royal, still without making them public. The latter re- ceived the final results of Adams, witli fresh corrections referring to a decrease of the distance, in the commencement of September, 184G. The young Cambridge geometrician expresses himself upon the chro- nological succession of the investigations which were directed to one and the same object with as much modesty as self-denial : " I mention these earlier dates merely to show that my results were arrived at in- dependently and previously to the publication of M. Leverrier, and not with any intention of interfering with his just claims to the honor of the discovery ; for there is no doubt that his researches were first pub- lished to the world, and led to the actual discovery of the planet by Dr. Galle; so that the facts stated above can not detract in the slightest degree from the credit due to M. Leverrier." Since, in the history of the discovery of Neptune, mention is frequently made of an early share which the great Konigsberg astronomer took in the hope already ex- pressed by Alexis Bouvard (the author of the tables of Uranus) in the year 1834, "of the disturbance of Uranus by a yet unknown planet," it will, perhaps, not be unacceptable to many readers of the Cosmos if I introduce here part of a letter which Bessel wrote to me on the 8th of May, 1840 (therefore two years before his conversation with Sir John Herschel, during his visit to Collingwood) : "You request me I i give you information as to the planet beyond. Uranus. I could indeed refer you to friends in Konigsberg who, from misunderstanding, fancy that they know more about the matter than I do myself. 1 chose as the subject of a public lecture delivered upon the 28th of February, 1840, tho development of the connection between astronomical obaerta- tions and astronomy. The public know no difference between the two; consequently, their opinion was to be corrected. The indication of the development of astronomical knowledge from observations naturally led to the remark that we can by no means affirm thai our theory ex- plains all the motions of the planets. Uranus afforded a proof oi this, the old observations of which do not at all accord with elements which coincide with the later observations from 1783 to 1820. f believe that 180 COSMOS. ously directed to the same important end, present in their laudable competition so much the more interest, as they testi- fy, by the selection of means, to the present distinguished con- dition of higher mathematical knowledge. The Satellites op Neptune. "While in exterior planets the existence of a ring presents itself only in one solitary instance, and its rarity permits of the conjecture that the organ and formation of an unconnect- ed girdle depends upon the conjunction of peculiar and diffi- cultly fulfilled conditions, so, on the contrary, the existence of satellites accompanying the exterior planets (Jupiter, Saturn, Uranus) is a phenomenon as universal as the former is rare. Lassell discovered with certainty* the first satellite of Nep- tune so soon as the commencement of August, 1847, in his large twenty-feet reflector, with a 24-inch aperture. Las- sell's discovery was confirmed by Otto Struvef at Pulkowa I once told you that I have worked much upon this subject, but have come to no other result than the certainty that the present theory, or, much rather, its application to the solar system, as we are acquainted with it, was insufficient to solve the mystery. Nevertheless, it must not, on that account, be considered upon my opinion to be unsolvable. We must first know accurately and completely what has been observed of Uranus. By the aid of one of my young hearers, Flemming, I have had all the observations reduced and compared, and thus the existing facts now lie before me complete. While the old observations do not agree with the theory, the more recent ones agree still less ; for now the error is a whole minute, and increases annually about 7" to 8", so that it will soon be much greater. I was therefore of opinion that the time might come when the solution of this mystery might perhaps be found in the discovery of a new planet whose elements might be ascer- tained by its influences upon Uranus, and confirmed by those exerted upon Saturn. That this time has already arrived I am far from Baying, but I shall examine now how far the existing facts can carry us. This is an investigation which I have pursued for so many years, and on ac- count of which I have followed so many views, that its results espe- cially interest me, and shall therefore be brought to an end as soon as possible. I have great confidence in Flemming, who will, in Dantzic, to which place he has been called, continue the same reduction of ob- servations for Saturn and Jupiter which he has now made for Uranus. It is, in my opinion, fortunate that he has (for the present) no means of observation, and has no lectures to deliver. A time will indeed come when he must institute observations with a definite aim; then he should no longer want the means of carrying them out any more than he does the ability to do so." * The first letter in which Lassell announced the discovery was on the 6th of August, 1847. (Schumacher, Astr. Nachr., No. 611, p. 165.) t Otto Struve, in the Astr. Nachr., No. 629. August Struve, in Dor- pat, calculated the orbit of the first satellite of Neptune from the observ- ations at Pulkowa. COMETS. 181 (September 11th to December 20th, 1847), and Bond,* the director of the observatory at Cambridge (U. S.), (September 16th, 1817). The Pulkowa observations gave : the period of rotation of Neptune's satellite, 5d. 21h. 7m. ; the inclina- tion of its orbit to the plane of the ecliptic, 34° 1' ; the dis- tance from the center of the primary, 210,000 geographic- al miles ; the ?nass,T-i\-u^. Three years afterward (August 14th, 1850), Lassell discovered a second satellite, for the ex- amination of which he employed a magnifying power of 628. t This last discovery has not, I believe, been confirmed by other observers. III. THE COMETS. The comets, which Xenocrates and Theon of Alexandria call light-clouds, and which, according to an old Chaldean belief, Apollonius Myndius considered to " ascend periodically from great distances in long-regulated orbits," though subject to the attractive force of the central body, form a peculiar and separate group in the solar regions. They are distin- guished from the planets, properly so called, not merely by the eccentricity of their orbits, and, what is still more import- ant, their intersection of the planetary orbits ; they also pre- sent a variability of figure, a change of outline, which in some instances has been observable during the space of a few hours , as, for example, in the Comet of 1744, so accurately described by Hensius, and at the last appearance of Halley's Comet in 1835. Before Encke had discovered the existence of inte- rior comets of short periods of revolution, whose orbits were inclosed within those of the planets, dogmatic speculations, founded upon false analogies as to the increasing eccentricity, magnitude, and decreasing density in proportion to the dis- tance from the Sun, led to the opinion that planetary bodies of enormous volume would be discovered beyond Saturn, re- volving in eccentric orbits, and " forming an intermediate group between planets and comets, and, indeed, that the last exterior planet ought to be called a comet, since perhaps its orbit intersected that of Saturn, the planet next to it."$ Such * W. C. Bond, in the Proceedings of the American Academy of Arts and Sciences, vol. ii., p. 137 and 140. t Schum., Astr. Nachr., No. 729, p. 143. t " By means of a series of intermediate members," says Immanuel 182 cosmos. an opinion of the connection of forms in the universe, analo- gous to the frequently misemployed doctrine of transition in organic nature, was shared by Immanuel Kant, one of the greatest minds of the eighteenth century. At two epochs, twenty-six and ninety-one years after the Naturgeschichte des Himmeh was dedicated to the great Frederick by the Konigsberg philosopher, Uranus and Neptune were discovered by William Herschel and Galle ; but the orbits of both plan- ets have a less degree of eccentricity than that of Saturn ; if even the latter is 0-056, so, on the contrary, Neptune, the outermost of all known planets, moves in an orbit whose ec- centricity is 0-008, nearly the same as that of Venus (0.006). In addition to this, Uranus and Neptune present none of the predicted cometary characters. As, in more recent times (since 1819), the discovery of Encke's Comet was gradually followed by those of five inte- rior comets, forming, as it were, a peculiar group, the semi- major axis of whose orbits for the most part resembles those of the small planets, the question was raised as to whether the group of interior comets may not, as is conjectured by Olbers, in his hypothesis respecting the small planets, origin- ally have formed a single cosmical body ; whether the large comet may not have been separated into several by the influ- ence of Mars, in the same way that such a separation, as it were a bipartition, took place under the eye of the observer in the year 1846, on the occasion of the last return of the interior comet of Biela. Certain similarities in their elements have induced Professor Stephen Alexander, of the College of New Jersey, to institute investigations* as to the possibility Kant, " the last planets beyond Saturn would gradually pass into com- ets, and so the last species would be connected with the first. The law according to which the eccentricity of the planetary orbits is propor- tionate to the distances of the planets from the Sun. supports this con- jecture. The eccentricity increases with the distance, and, consequent- ly, the more distant planets approach nearer to the definition of com- ets. The last planet and the first comet may he called that body which in its perihelion intersects the orbit of the adjoining planet, perhaps that of Saturn. Our theory of the mechanical formation of the cosmical bodies is also clearly proved by the magnitudes of the planetary masses which increase with the distance from the Sun." — Kant, NaiurgQ: sckichte des Himmeh (1755), in his Sdmmtliche Werke, th. vi., p. 88 and 195. At the commencement of the fifth section (p. 131). ho speaks of the former cometary nature which Saturn was supposed to have pos- sessed. * Stephen Alexander. "On the Similarity of arrangement of the As- teroids and the Comets of short period, and the possibility of tlu'ij- common origin," in Gould's Astronom. Journal, No. 19. p. 147. mid No COMET*. 183 of a common origin of the asteroids between Mars arid Ju- piter, with some or even all of the comets. The grounds of analogy which have been deduced from the nebulous envel- opes of the asteroids must, according to all more recent and accurate observations, be renounced. The orbits of the small planets are not parallel to each other ; that of Pallas certain- ly presents the phenomenon of an extreme inclination ; but, with all the want of parallelism between their own orbits, still they do not intersect in a comet ary manner any one of the orbits of the large older, i. e., earlier discovered planets. This circumstance, so extremely essential in every assumption of a primitive projectile direction and projectile velocity, ap- pears, besides the difference in the physical constitution of the interior comets, and the entirely vaporless small planets, to render the similarity of origin of both kinds of cosmical bodies very improbable. Laplace, also, in his theory of planetary genesis from rings of vapor revolving round the Sun, in which matter aggregates into spheres around a nucleus, considered it necessary to separate the comets from the planets : " Dans Vhypothese cles zones de vapeurs et d'un noyau s'accroissant par la condensation de V atmosphere qui Venvironne, les co- mctes sont etr anger es au systeme planetaire."* " According to the hypothesis of zones of vapor, and of a nucleus increas- ing by the condensation of the atmosphere which surrounds them, the comets are strangers to the planetary system." "We have already directed attention, in the Delineations of Nature,^ to the fact that the comets at the same time pos- sess the smallest mass, and occupy the largest space, of any bodies in the solar regions ; in their number, also, they ex- ceed all other planetary bodies ; the theory of probabilities, applied to the data of the equable distribution of the orbits, the boundaries, the perihelions, and the possibility that some 20, p. 181. The author distinguishes, with Hind (Schum., Astr. Nachr., No. 724), "the comets of short period, whose semi-axes are all nearly the same with those of the small planets between Mars and Jupiter ; and the other class, including the comets whose mean distance or semi- axis is somewhat less than that of Uranus." He concludes the first es- say with this remark: " Different facts and coincidences agree in indi- cating a near appulse, if not an actual collision, of Mars with a large comet in 1315 or 1316, that the comet was thereby broken into three parts, whose orbits (it may be presumed) received even then their pres- ent form, viz., that still presented by the Comets of 1812, 1815, and 1846, which are fragments of the dissevered comet." * Laplace, Expos, du Syst. du Monde (ed. 1824), p. 414. t On Comets: in the Delineation of Nature, ste Cosmos, vol. i., p 100-110. 184 cosmos. remain invisible, indicates the existence of many thousands. We except the aerolites or meteoric asteroids, as their nature is still enveloped in great obscurity. Among the comets, those must be distinguished whose orbits have been calcula- ted by astronomers, and such of which there are only incom- plete observations, or mere indications recorded. As, accord- ing to Galle's last accurate enumeration, 178 had been cal- culated up to the year 1847, so it may be admissible to adopt as the total number, with those which have been merely in dicated, the assumption of six or seven hundred observed com- ets. When the Comet of 1682, predicted by Halley, appeared again in 1759, it was considered very remarkable that three comets should be visible in the same year. At the present time, the investigation of the heavens is carried on simultane- ously at several parts of the globe, and with such energy, that in each of the years 1819, 1825, and 1840, four were discovered and calculated; in 1826, five; and in 1846, even eight. Of comets visible with the naked eye, more have been ob- served recently than during the latter part of the previous century ; but among them, those which have a great brill- iancy in the head and tail still remain, on account of their unfrequency, remarkable phenomena. It will not be with- out interest to enumerate how many comets, visible in Europe to the naked eye, have appeared during the last centuries.* The epoch in which they were most numerous was the six- teenth century, during which twenty-three such comets were seen. The seventeenth numbered twelve, and of these only two during its first half. In the eighteenth century only eight appeared, but nine during the first fifty years of the nineteenth century. Among these, the most beautiful were those of 1807, 1811, 1819, 1835, and 1843. In earlier ages, thirty or forty years have frequently passed without such a spec- tacle presenting itself in a single instance. In the years, however, during which comets seldom appear, there may be a number of large comets whose perihelia are situated be- yond the orbits of Jupiter and Saturn. Of the telescopic comets, there are at the present time, upon an average, at least two or three discovered annually. In three successive months (1840) Galle discovered three new comets : from J.764 to 1798, Messier discovered twelve ; from 1801 to 1827, Tons discovered twenty-seven. Thus Kepler's expression as to the * la the 6even half centuries from 1500 to 1850, altogether 52 comets have appeared which were visible to the naked eye; in separate succes- COMETS. 185 number of comets in the universe appears to hold good : %u jrisccs in oceano. Of not less importance is the careful catalogue of comets which have appeared in China, and which Edward Biot has made known from the collection of Ma-tuan-lin. It reaches back beyond the foundation of the Ionic school of Thales and the Lydian Alyattes, and comprises, in two sections, the place of the comets from 613 years before our own era until 1222 years afterward, and then from 1222 to 1644, the period in sion during seven equal periods, 13, 10, 2, 10, 4, 4, and 9. The follow- ing are the individual years : 1500—1550 13 Com. 1600—1650 1607 1618 2 Corn. 1700—1750 1702 1744 1784 (2) 4 Com. 1550—1600 10 Com. 1650—1700 1652 1664 1665 1668 1672 1680 1682 1686 1689 1696 10 Com. 1750—1800 1759 1766 1769 1781 4 Com. 1800—1850 1807 1811 1819 1823 1830 1835 1843 1845 1847 9 Com. Of the 28 Comets visible to the naked eye which are here enumei*ated in the sixteenth century (the epoch of Apianus, Girolamo Fracastoro, Landgravine William IV. of Hesse, Mastlin, and Tycho), 10 were de- scribed by Pingre, namely, those of 1500, 1505, 1506, 1512, 1514, 1516, 1518, 1521, 1522, and 1530; further, the Comets of 1531, 1532, 1533, 1556, 1558, 1569, 1577, 1580, 1582, 1585, 1590, 1593, and 1596. i86 cosmos. which the dynasty of Ming ruled. I repeat here (see Cos- 9710s, vol. i., p. 99), that while from the middle of the third to the end of the fourteenth century it was necessary to cal- culate comets exclusively from the Chinese observations, the calculation of Halley's Comet, on its appearance in the year 1456, was the first calculation which was made from alto- gether European observations, those of Regiomontanus. These latter were again followed by the very accurate observations of Apianus at Ingoldstadt, upon the occasion of the reappear- ance of Halley's Comet in August of the year 1531. In the interval (May, 1500) appeared a magnificently brilliant com- et.* rendered famous by African and Brazilian travels of dis- covery, which was called in Italy Signor Astone, the great Asia. Laugierf has detected, by similarity of the elements in the Chinese observations, a seventh appearance of Hal- ley's Comet (that of 1378) ; as well as that the third comet of 1840, discovered by*Gal]e,$ on the 6th of March, appears to be identical with that of 1097. The Mexicans also con- nected events in their records with comets and other ob- servations of the heavens. The Comet of 1490, which I discovered in the Mexican manuscript of St. Tellier, and of which an engraving is inserted in my Monumens des Peuples indigenes de V Amerique, I have found, singularly enough, to be mentioned as having been observed in December of that year only in the Chinese comet-register. \ The Mexi- cans had inserted it in their register twenty-eight years be- fore the first appearance of Cortez upon the coasts of Vera Cruz (Chalchinhcuecan). I have, in the Delineations of Nature (Cosmos, vol. i., p. 101), treated fully of the configuration, alterations of form, * This is the " evil-disposed" comet to which was ascribed the death of the celebrated Portuguese discoverer Bartholomams Diaz, by ship- wreck, as he was sailing to the Cape of Good Hope; Humboldt, Ex- amen Crit. de VHist. de la Giogr., torn, i., p. 296, and torn, v., p. 80. (Sousa, Asia Poring., torn, i., p. i., cap. v., p. 45.) t Laugier, in the Connaissance des Temps pour Van 1846, p. 99. Compai'e also Edward Biot, Rcckerches sur les Anciennes Apparitions Chinoises de la Comete de H alley anterieures a Vannee 1378, op. cit., p. 70-84. \ Upon the comet discovei'ed by Galle in March, 1840, see Schu- macher, Astr. Nachr., bd. xviii., p. 188. § See my Vues des Cordilleres (ed. in folio), pi. lv., fig. 8, p. 281, 282 The Mexicans had also a very correct view of the cause of a solar eclipse. The same Mexican manuscript, written at least a quarter of a century before the arrival of the Spaniards, represents the Sun as al- most entirely covered by the Moon's disk, and with stars visible at the same time. COMETS. 187 light, and color of comets, the emanations from their heads which, hent backward,5* form the tails, from the observations of Hensius (1744), Bessel, Struve, and Sir John Herschel. Besides the magnificent Comet of 1843,f which could be seen by Bowring, in Chihuahua (N.W. America), as a small white cloud from nine o'clock in the morning until sunset, and by Amici, in Parma, at full noon, 1° 23' eastward of the Sun,$ the first comet of the year 1847, discovered by * This formation of the tail at the anterior part of the comet's head, which has occupied Bessel's attention so much, was the opinion of New- ton and Winthrop (compare Newton's Principia, p. 511, and Philos. Transact., vol. lvii., for the year 17G7, p. 140, tig. 5). Newton consid- ered that the tail was developed most considerably and longer near the Sun, because the cosmical ether (which we call, with Encke, the resist- ing medium} was the densest there, and the particular caudce, strongly heated and supported by the ether, ascended more easily. Winthrop considered that the principal effect did not take place until some time after the perihelion passage, because, according to the law established by Newton (Principia, p. 424 and 466), the maxima are universally re- tarded (in periodical changes of heat as well as in ocean tides). t Arago, in the Annuaire for 1844, p. 395. The observation was made by the younger Amici. X With regard to the Comet of 1843, which appeared with unexam- pled splendor in Northern Europe during the month of March, near Orion, and approached nearer to the Sun than any hitherto observed and calculated comet, all the details are collected in Sir John Herschel's Outlines of Astronomy , § 589-597 ; and in Peirce, American Almanac for 1844, p. 42. On account of physiognomical resemblances whose uncertainty was already shown by Seneca (Nat. Quasi., lib. h\, caps, xi. andxvii.),it was at first considered to be identical with the comets of 1668 and 1689 ( Cosmos, vol. i., p. 139, note; Galle, in Olbers's Come- tenbahnen, Nos. 42 and 50). Boguslawski (Sebum., Astr. Nachr., No. 545, p. 272) believes on the contrary, that its previous appearances were with a revolution of 147 years, those of 1695, 1548, and 1401 ; he even calls it the Comet of Aristotle, " because he traces it back to ihe year 371 before our era, and, together with the talented Hellenist Thiersch, of Munich, considers it to be a comet which is mentioned in the Mete- orologicis of Aristotle, book i., cap. vi." But I would call to mind that the name Comet of Aristotle is vague and indefinite. If that one is meant which Aristotle states to have disappeared in Orion, and which he connects with the earthquake in Achaia, it must not be forgotten that this comet is stated by Callisthenes to have appeared before, by Diodorus after, and by Aristotle at the time of the earthquake. The sixth and eighth chapters of the Meteorology treat of four comets whose epochs of appearance are characterized by the archons at Athens, and by unfortunate events. In this place those are mentioned in order: the western comet which appeared on the occasion of the great earth- quake at Achaia, accompanied with floods (cap. vii.,8); then the comet which appeared during the time of the Archon Eucles, the son of Mo- Ion; afterward (cap. vi., 10) the Stagirite comes again to the western comet, that, of the great earthquake, and at the same time calls the Ar- chon Asteus — a name which incorrect readings have changed into Aris- 188 cosmos. Hind near Capella, has very recently been visible at London, near the Sun, on the day of its perihelion. taeus, and which was, on that account, erroneously considered by Phigre, in his Cometographie, to signify one and the same person as Aristher.es or Alcisthenes. The brilliancy of this comet of Asteus diffused itself over the third part of the sky ; the tail, which was called its way (odor), was also 60° in length. It extended nearly as far as Orion, where it gradually disappeared. In cap. vii., 9, the comet is mentioned which appeared simultaneously with the famous fall of aerolites near iEgos Potamos {Cosmos, vol. i., p. 117), and which can scarcely be a confu- sion with the aerolite- cloud described by Damachos, which shone for 70 days, and poured forth falling stars. Finally, Aristotle mentions (cap. vii., 10) a comet which appeared at the time of the Archon Ni- comachus, to which was ascribed a storm near Corinth. These four ap- pearances of comets occurred during the long period of 32 Olympiads : viz., the fall of aerolites, according to the Parian Chronicle, 01. 78, 1 (468 B.C.), under the Archon Theagenides; the great comet of Asteus, which appeared at the time of the earthquake at Achaia, and disap- peared in the constellation of Orion, in Ol. 101, 4 (373 B.C.): Eucles, the son of Molon, erroneously called Euclides Diodorus (xii., 53), in Ol. 88, 2 (427 B.C.), as is also confirmed by the commentary of Jo- hannes Philoponus ; the comet of Nicomachus, in Ol. 109, 4 (341 B.C.). The date assigned by Pliny for the juba effigies mutata in kastam, is Ol. 108 (Plinius, ii., 25). Seneca also agrees in connecting the comet of Asteus {Ol. 101, 4) immediately with the earthquake in Achaia, as he mentions the downfall of Bura and Helice, which towns Aristotle does not expressly mention, in the following manner: " Effigiem ignis longi fuisse, Callisthenes tradit, antequam Burin et Helicen mare ab- sconderet. Aristoteles ait, non trabem illam, sed cometam fuisse." " Callisthenes affirms that the fiery shape appeared long before the sea overwhelmed Buris and Helice. Aristotle says that this was not a meteor, but a comet." (Seneca, Nat. Qucest., vii., 5.) Strabo (viii., p. 384, Cas.) places the downfall of these two frequently mentioned towns two years before the battle of Leuctra, whence again results the date, Ol. 101, 4. Finally, after Diodorus Siculus had more fully de- scribed this event as having occurred under the Archon Asteus (xv., 48, 49), he places the brilliant comet which threw shadows (xv., 50) under the Archon Alcisthenes, a year later, Ol. 102, 1 (372 A.C.), and as a prediction of the decline of the Lacedaemonian rule; but the later Diodorus had the habit of transferring an event from one year to an- other ; and the oldest and most reliable witnesses, Aristotle and the Parian Chronicle, speak in favor of the epoch of Asteus before that of Alcisthenes. Now since the assumption of a period of revolution for the beautiful Comet of 1843 of 147f years, leads Boguslawski to assign to its appearances the dates 1695, 1548, 1401, and 1106, up to the year 371 before our era, the comet of the earthquake of Achaia corresponds with it, according to Aristotle, within two — according to Diodorus, to within one year; which, if we could know any thing of the similarity of the orbit, is, when taking into consideration the probable disturban- ces during a period of 1214 years, certainly a very small error. When Pingre, in the Cometographie (1783, torn, i., p. 259-262), relying upon Diodorus and the Archon Alcisthenes instead of Asteus, places the comet in question in Orion, in Ol. 102, and still in the commencement of July, 371 before Christ, instead of 372, the reason perhaps lies'in the COMETS. 189 For the explanation of what has been said above of the re- mark of Chinese astronomers on the occasion of their observ- ation of the Comet of March, 837, in the dynasty of Thang, I insert here a translation from Ma-tuan-lin of the verbal statement of the law of direction of the tail. It is said there, "In general, the tail of a comet which is situated eastward from the Sun is directed toward the east, calculating from the nucleus ; but if the comet appears to the west of the Sun, the tail turns toward the west."* Fracastoro and Appia- nus say, still more correctly, "that a line produced through the head of a comet in the direction of the axis of the tail meets the Sun." The words of Seneca are also characteristic : " The tails of comets fly from the Sun's rays." {Nat. Qucest., vii., 20.) While, among the yet known planets and comets, the periods of rotation dependent upon the half-major axis, the shortest and the longest of the planets, are in the propor- tion of 1 : 683, the proportion in the case of the comets is as 1:2670. Mercury (87d-97) is here compared with Neptune circumstance that, like some other astronomers, he characterizes the first year before the Christian era as anno 0. It is to be observed, in conclusion, that Sir John Herschel assumes for the Comet of 1843, seen in full daylight near the Sun, an entirely different period of revolution, one of 175 years, which leads to the years 1668, 1493, and 1318, as the dates of its previous appearances. (Compare Outlines, p. 208-372, with Galle, in Olbers's Cometenbahncn, p. 208; and Cosmos, vol. i., p. 137.) Other combinations by Peirce and Clausen lead to periods of revolution of even 214 or 74 years: a sufficient proof how hazardous it is to trace back the Comet of 1843 to the archonship of Asteus. The mention of a comet under the archonship of Nicomachus, in the Meteorol., lib. i., cap. vii., 10, has at least the advantage of showing us that this work was written when Aristotle was at least 44 years of age. It has al- ways appeared to me remarkable that the great man, as he was already 14 years old at the time of the earthquake at Achaia, and of the appear- ance in Orion of the great comet with a tail 60° in length, should speak with so little animation of so brilliant an object, and content himself with enumerating it among the other comets " which had appeared in his time." The astonishment incx-eases when, in the same chapter, the statement is found that he had seen with his own eyes something misty, even a feeble haza (k6/j.tj), round a fixed star in the hip-bone of the Dog (perhaps Procyon in the small Dog), (Meteorol., i., 6, 9). Aristotle also speaks (i., 6,11) of his observation of the occultation of a star in Gemini by the disk of Jupiter. With regard to the vaporous or nebulous en- velope of Procyon (?), it recalls to my mind a phenomenon of which frequent mention is made in the old Mexican annals according to the Codex Tellerianvs. " This year," it is said there, " Citlalcholoa smoked again;" this is the name of the planet Venus, also called Tlazoteotl in the Aztec language (see my Vncs des Cordilleres, torn, ii., p. 303) : this is probably, in the Grecian as well as the Mexican sky, a phenomenon of atmospheric refraction — the appearance of small halos. * Edward Biot, in the Comptes Rendus, torn, xvi., 1843, p. 751. 190 COSMOS. (60,126d'7), and the Comet of Encke (3-3 years) with the Comet of 1680 (8814 years), observed by Gottfried Kirch at Coburg, Newton, and Halley. The distance of the fixed star nearest to our solar system (a Centauri) from the aphelion (point of greatest distance from the Sun) of the last-named comet is determined by Encke in an excellent treatise. The small velocity of its motion (ten feet in a second) in this out- ermost part of its orbit, the greatest proximity which the Comet of Lexell and Burckhardt (1770) has attained to the earth (six times the distance of the Moon), and the Comet of 1680 (and still more that of 1843) to the Sun, I have al- ready treated of in. Cosmos, vol. i., p. 109, and vol. iv., p. 53-55. The second comet of the year 1819, which ap- peared, in Europe, suddenly to break forth from out of the Sun's rays in considerable magnitude, passed, according to the calculation of its elements, across the Sun's disk on the 26th of June ;* unfortunately, its passage was not observed. This must also have been the case with the Comet of 1823, which, besides the ordinary tail turned from the Sun, had also another turned directly toward it. If the tails of both comets had a considerable length, vaporous parts of them must have mixed with our atmosphere, as certainly often hap- pens. The question has been raised as to whether the won- derful mists of 1783 and 1831, which covered a great part of the Continent, %vere consequences of such an admixture ?t While the quantity of radiant heat received by the Comets of 1680 and 1843 in such close proximity to the Sun has been compared to the focal temperature of a 32-inch burn- ing mirror,$ a highly-deserving^ astronomical friend of mine * Galle, in the Supplement to Olbers's Cometenhahnen, p. 221, No. 130. (With respect to the probable passage of the two-tailed comet of 1823, see Edinb. Rev., 1848, No. 175, p. 193.) The treatise shortly be- fore quoted in the text, containing the true elements of the Comet of 1680, contradicts Halley's fantastic idea, according to which, with a presumed period of 575 years, it had appeared at all the great epochs of the human race: at the time of the Deluge according to Hebrew tra- ditions, in the age of Ogyges according to Greek traditions, at the Tro- jan war, on the destruction of Nineveh, on the death of Julius Caesar, &c. The period of revolution resulting from Encke's calculation is 8814 years. The least distance from the surface of the Sun was, on the 17th of December, 1680, only 128,000 geographical miles ; consequently, 80,000 less than the distance of the Earth from the Moon. The aphe- lion is 853-3 times the distance of the Earth from the Sun, and the proportion of the smallest to the greatest distance from the Sua is as 1 : 140,000. t Arago, in the Annuaire for 1832, p. 236-255. X Sir John Herschel, Outlines, § 592. § Bernhard von Lindenau, in Schum., Astr. Nachr., No. 698, p. 25- COMETS. 191 maintains that " all comets which are without a solid nu- cleus (on account of their extremely small density) have no solar heat, only the temperature of cosmical space. "^ If we take into consideration the numerous and striking analogies of the phenomena which, according to Melloni and Forbes, luminous and non-luminous sources of heat present, it ap- pears difficult, in the present state of our physical reasoning, not to assume that processes go on in the Sun itself which si- multaneously produce radiant light and radiant heat by vi- brations of the ether (waves of different lengths). The dark- ening of the Moon by a comet, stated to have taken place in the year 1454, which the Jesuit Pontanus, the first trans- lator of the Byzantine author, George Phranza, believed that he had discovered in a monkish manuscript, has long been mentioned in many astronomical works. This statement of the passage of a comet between the Earth and Moon in 1454 is quite as erroneous as that asserted by Lichtenberg of the Comet of 1770. The Chronicon of Phranza first ap- peared complete at Vienna in 1796, and it is said there ex- pressly, that in the year of the world 6962, while an eclipse of the Moon took place, a comet like a mist appeared and came near to the Moon quite in the ordinary manner, ac- cording to the order and circular orbits of the heavenly luminaries. The year of the world ( = 1450) is incorrect, as Phranza says distinctly the eclipse of the Moon and the appearance of the comet were seen after the taking of Con- stantinople (May the 19th, 1453), and an eclipse of the Moon actually happened upon the 12th of May, 1454. (See Jacobs, in Zach's Monatl. Corresp., bd. xxiii., 1811, p. 196-202.) The relation of Lexell's Comet to the satellites of Jupiter, and the perturbation which it suffers from them without in fluencing their periods of revolution (Cosmos, vol. i., p. 110), have been more accurately investigated by Leverrier. Mes- sier discovered this remarkable comet as a feeble nebulous spot in Sagittarius upon the 14th of June, 1770 ; but eight days after, its nucleus shone as brightly as a star of the 2d magnitude. Before the perihelion passage, no tail was vis- ible ; afterward it developed itself by slight emanations scarcely one degree in length. Lexell found for his comet an elliptic orbit, and the period of rotation of 5585 years, which Burckhardt confirmed in his excellent prize essay According to Clausen, it had approached the Earth upon the 1st of. July, 1770, to a distance of 363 times the Earth's ra- M Cosmos, vol. iii . p 36 and 37, .92 cosmos. dius (1,244,000 geographical miles, or six times the Moon's distance). That the comet was not seen before March, 1776, and not later than October, 1781, according to Lexell's pre- vious conjecture, is analytically demonstrated by Laplace, in the fourth volume of the Mecanique Celeste, from the per- turbations occasioned by the Jovial system on the occasion of the approximations in the years 1767 and 1779. Lever- rier finds that, according to one hypothesis respecting the cometary orbits, this comet passed through orbits of the sat- ellites in 1779 ; according to another, that it remained at a considerable distance without the fourth satellite.* The molecular conditions of the head or nucleus, so seldom possessing a definite outline, as well as the tail of the com- ets, is rendered so much the more mysterious from the fact that it causes no refraction, and, as was proved by Arago's important discovery (Cosmos, vol. i., p. 105, and note), that the cometary light contains a portion of polarized light, and consequently reflected sun-light. Although the smallest stars are seen in undiminished brilliancy through the vaporous em- anations of the tail, and even through the center of the nu- cleus itself, or at least in very great proximity to the center, (per centrum non aliter quam per nubem ulteriora cernatur : Seneca, Nat. Qucest., vii., 18) ; so, on the contrary, the an- alysis of the cometary light in Arago's experiments, during which I was present, shows that the vaporous envelopes are capable! of reflecting light, notwithstanding their extremely slight density, and that these bodies have " an imperfect transparency,! since light does not pass through them unim- peded." In this group of vaporous bodies, the solitary in- stances of great luminous intensity, as in the Comet of 1843, or the star-like shining of a nucleus, excite so much the more astonishment when it is assumed that their light proceeds solely from a reflection of the solar rays. Is there not, how- ever, in addition to this, a peculiar light-producing process going on in the comets ? The brush-like membered tails emanating from the comets, and consisting of vapory matter of millions of miles in length, diffuse themselves in space, and form, perhaps, either the re- sisting mediumh itself, which gradually contracts the orbit * Leverrier, in the Complex Rendus, torn, xix., 1844, p. 982-993. t Newton considered that the most brilliant comets shone only with reflected sun-light. " Splendent cometa,1," says he, " luce Solis a se reflexa." (Princ. Mathem., ed. Le Seur et Jaquier, 1760, torn, hi., p. 577.) \ Bessel, in Schum. Jahrbnch for 1837, p. 169. $ Cosmos, vol. i., p. 106, and vol. iii., p. 39. COMETS. 193 of Encke's Comet, or they mix with the old cosmical matter which has not aggregated into spheres, or condensed into the rings, and which appears to us as the zodiacal light. We see, as it were, before our eyes, material particles disappear, and can scarcely conjecture where they again collect. How- ever probable may be the condensation, in the neighborhood of the central body of our system, of a gaseous fluid filling space, still, in the case of the comets, whose nuclei, accord- ing toValz, diminish in the perihelion, this fluid, condensed there, can scarcely be looked upon as pressing upon a vesicu- lar vapory envelope.* Although in the streamers of the comets the outlines of the reflecting portion of the vapory envelope is generally very indefinite, the circumstance that, in some individuals (for example, Halley's Comet at the 2d of January, 1836, at the Cape of Good Hope), a sharpness of outline has been observed on the anterior parabolic part of the body, such as our masses of clouds seldom present, is so much the more striking and instructive as to the molecular condition of these bodies. The celebrated observer at the Cape compared the unusual appearance, testifying to the in- tensity of the mutual attraction of the particles, with that of an alabaster vessel strongly illuminated in the interior.! Since the appearance of the astronomical part of my De- lineation of Nature, the cometary world has presented a phenomenon whose mere possibility could scarcely have been suspected beforehand. Biela's Comet, an interior one of short period, 6| years in its revolution, has separated into two comets of similar figure though unequal dimensions, both having a head and tail. So long as they could be observed, they did not unite again, and proceeded on their course sep- arately, almost parallel with each other. Hind had, on the * Valz, Esstxi sur la Determination de la Densite de V Ether dans I'espace PlanUaire, 1830, p. 2; and Cosmos, vol. i., p. 106. The so-carefully observing and always unprejudiced Hevelius had also directed atten- tion to the increase in the size of the cometary nuclei, with increased distance from the Sun. (Pingre, Comilographie, torn, ii., p. 193.) The determinations of the diameter of Encke's Comet in the perihelion is very difficult, if accuracy is desired. The comet is a nebulous mass, in which the center, or one point of it, is the brightest, even prominently bright. From this point, which, however, presents no appearance of a disk, and can not be called a comet-head, the light decreases very rapid- ly all around, and at the same time the vapor elongates toward one disk, so that this elongation appears as a tail. The measurements, therefore, refer to this mass of vapor, whose circumference, without having really definite boundaries, decreases in perihelion. \ Sir John Herschel, Results of Astronomical Observations at the Cap*- of Good Hope, 1847, $ 366, pi. XV. and xvi. Vol. IV— I J 94 cosmos. 19th of December, 1845, already remarked a kind of pro- tuberance toward the north ; but on the 21st there was, ac- cording to Encke's observation in Berlin, still no signs of a separation visible. The subsequent separation was first de- tected in North America on the 29th of December, 1845 ; in Europe, not until the middle and end of January, 1846. The new smaller comet proceeded toward the north. The distance of the two was at first 3', afterward (February 20th), according to Otto Struve's interesting drawing, 6'.* The luminous intensity varied in such a manner that the gradu- ally increasing secondary comet for some time exceeded the principal comet in brightness. The nebulous envelopes which surrounded each of the nuclei had no definite outlines : that of the larger comet, indeed, showed a less luminous protuber- ance toward S.S.W. ; but the space between the two comets was seen at Pulkowa quite free from nebulous matter. f A few days later, Lieutenant Maury, in Washington, remarked, with a nine-inch Munich refractor, rays which proceeded from the larger older comet to the smaller new one, so that a kind of bridge-like connection was produced for some time. On the 24th of March, the smaller comet was scarcely percepti- ble, on account of the decreasing luminous intensity. The larger one only was seen up to the 16th or 20th of April, when this also disappeared. I have described the wonderful phenomenon in detail. $ so far as it could be observed. Un- fortunately, the actual separation and the immediately previ- ous condition of the older comet escaped observation. Did the separated comet become invisible only on account of dis- tance and feeble luminosity, or did it resolve itself? Will it be again detected as an attendant, and will the Comet of Biela present similar anomalies at other reappearances ? The formation of a new planetary body by separatio?i nat- urally excites the question whether, in the innumerable com- ets revolving round the Sun, several have not originated by a similar process, or do not daily originate so ? whether they * The subsequent (5th of March) increase of distance seen to the ex- tent of 9° 19' was, as Plautatnour has shown, merely apparent, and de- pendent upon the approximation to the Earth. Both parts of the double comet remained at the same distance from each other from February until the 10th of March. t '' Le 19 Fevrier, 1846, on apercoit le fond noirdu ciel qui separe les deux cometes." — Otto Struve, in the Bulletin Physico-mathimatique de C Acad, des Science 8 de St. Pttesbourg, torn, vi., No. 4. + Compare Outlines, § 580-583 ; Galle, in Olbers's Come/enbahncn, p. 232. COMETS. 195 may not acquire different orbits by retardation, i. c, unequal velocity of revolution, and the unequal influence of perturba- tions ? In a treatise already alluded to, Stephen Alexander has attempted to explain the genesis of all the interior com- ets by the assumption of such an hypothesis, certainly but in- adequately founded. In antiquity, also, similar occurrences appear to have been observed, but not sufficiently described. Seneca states, upon the authority, as he himself says, of an unreliable witness, that the comet which was considered to have caused the destruction of the two towns of Helice and Bura separated into two parts. He adds ironically, why has no one seen two comets unite to form one ?* The Chinese astronomers speak of " three dome-formed comets," which ap- peared in the year 896, and pursued their course together.! Among the great number of calculated comets, there are, up to the present time, eight known, whose period of revolu- tion is shorter than that of Neptune. Of these eight, six are interior comets, i.e., such whose aphelia are within the orbit of Neptune, viz., the comets of Encke (aphelion, 4-09), of De Vico (5-02), Brorsen (564), Faye (5-93), Biela (6-19), and D'Arrest (6*44). If the distance of the Earth from the Sun is taken as = 1 , the orbits of all these six interior com- ets have aphelia which are situated between Hygeia (3*15), and a limit which is nearly \\ the Earth's distance from the Sun beyond Jupiter. The two other comets, likewise of a shorter period of revolution than Neptune, are the 74-year Comet of Olbers, and the 76-year Comet of Halley. Up to the year 1819, when Encke first discovered the existence of an interior comet, these two latter ones were those of the shortest period among the then calculated comets. Olbers's Comet of 1815, and Halley's Comet are, since the discovery of Neptune, situated in their aphelia only 4 and 5| times the Earth's distance from the Sun — beyond the limits which would allow of their being considered interior comets. Al- though the term interior comet may suffer alteration from the * " Ephorus non religiosissima? fidei, 6aepe decipitur, stepe decipit. Si- cut hie Cometem, qui omnium mortalium oculis custoditus est, quia in- gentis rei traxit eventus, cum Helicen et Burin ortu suo merserit, ait ilium discessisse in duas Stellas : quod praeter ilium nemo tradidit. Quia enim posset observare illud momentum, quo Cometes solutus et in duas partes redactus est? Quomodem autem, si est qui viderit Cometem in duas dirimi, nemo vidit fieri ex duabus?" — Seneca, Nat. Qucest., lib. vii., cap. 16. t Edward Biot, Reckerches sur les Cometes de la Collection de Ma' tuan-lin, in the Comptes Reyidus, torn, xx., 1845, p. 334. 196 cosmos. discovery of Trans-neptunian planets since the boundary which determines whether a comet is to be called an interioi one is changeable, still this term is preferable to that of com- ets of shoi't period, from the fact that it is in each epoch of our knowledge dependent upon something definite. The six interior comets now accurately calculated certainly vary in their periods of revolution only from 3*3 to 7*4 years ; but if the return of the comet discovered by Peters at Naples, upon the 26th of June, 1846 (the 6th comet of the year 1846, with a half-major axis of 6*32), after a period of 16 years, should be confirmed,* it may be foreseen that intermediate members, in reference to the duration of the period of revolution, will gradually be discovered between the Comets of Faye and Olbers. Then it would be difficult in future to fix a limit for the shortness of the period. Here follows the table in which Dr. Galle has arranged the elements of the six interior comets. * Galle, in Olbers's Methode der Cometenbahnen, p. 232, No. 174. The comets of Colla and Bremiker, of the years 1845 and 1840, present el- liptical orbits with proportionately not very short periods of revolution. (I allude to the 3065 and 8800 years of the Comets of 1811 and 1680.) 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CO -3 ; : ! : r- c c cj a £ I-; «-" T1 CO CO "E O co CO CO a o o ♦*« : o : : § § _ C S . 3 £3 M " H • — ' ^-* *s « is :?o 4) l d ,, -, a c „fc. -13.^,6 « ♦-> **§ § b»'rS — I ® .2 J5 CO &i O CO CB Q ^HJhU KPui quans ovum lapis visus fuit) immensio maguitu dini, ponderis egregii. Decern fuisse reperta centilibralia sexa ferunt." •'You will perhaps inquire what accompanied that terrific commotion of nature. On the plain of Crema, where never before was seen a stone the size of an egg, there fell pieces of rock of enormous dimensions and of immense weight. It is said that ten of these were found weighing a hundred pounds each. Birds, sheep, and even fish were killed." Under all these exaggerations, it may still be seen that the meteoric cloud out of which the stones fell must have been of uncommon black- ness and thickness. The " pavo" was undoubtedly a long and broad AEROLITKS. 221 large fire-ball, which moved from S.E. to N.W.,was seen at one o'clock in the afternoon at Alencon, Falaise, and Caen, while the sky was quite clear. Some moments afterward there was heard near Aigle (Dep. de L'Orne) an explosion in a small, dark, almost motionless cloud, lasting for five or six minutes, which was followed three or four times by a noise like a cannon and a rattle of muskets, mixed with a number of drums. At each explosion, parts of the vapor, of which the cloud consisted, were removed. No appearance of light was visible in this instance. There fell at the same time upon an elliptical surface, whose major axis, from S.E. to N.W., had a length of six miles, a great number of meteoric stones, the largest of which weighed only 17-J pounds. They were hot but not red,* smoked visibly, and, what is very strik- tailed fire-ball. The terrible noise in the meteoric cloud is here repre- sented as the thunder accompanying the lightning (?). Anghiera him- self received in Spain a fragment, the size of a fist {ex frustris disrup- torum saxorum), and showed it to King Ferdinand the Catholic, in the presence of the famous warrior Gouzalo de Cordova. His letter ends with the words, " Mira super hisce prodigiis conscriptafanatice, physice, theologice ad nos missa sunt ex Italia. Quid portendant, quomodocjue giguantur, tibi utraque servo, si aliquando ad nos veneris." " From these prodigies Italy has furnished us with many a marvel of supersti- tion, physic, and theology ; what they portend, and how they are to come to pass, you will learn whenever you come to us." (Written from Burgos to Fagiardus.) Cardanus {Opera, ed. Lugd., 1663, torn, iii., lib. xv., cap. lxxii., p. 279) affirms, still more accurately, that 1200 aerolites fell among them, one of 120 pounds' weight, iron gray, of great density. The noise is said to have lasted two hours: " ut mi- rum sit, tamtam molem in aere sustineri potuisse ;" " it is marvelous that such a mass could be supported in the air." He considered the tailed fire-ball to be a comet, and en-s in the date of the phenomenon by a year : " Vidimus anno 1510." Cardanus was at that time nine or ten years old. * Recently, on the occasion of the fall of aerolites at Brauuau (July 14th, 1847), the fallen masses of stone were so hot, that after six hours they could not be touched without causing a burn. I have already treated {Asie Centrale, torn, i., p. 408) of the analogy which the Scyth- ian myth of sacred gold presents with a fall of meteors. "5. As the Scythians say, theirs is the most recent of all nations; and it arose in the following manner. The first man that appeared in this country, which was a wilderness, was named Targitaus : they say that the par- ents of this Targitaus, in my opinion relating what is incredible — they say, however, that they were Jupiter and a daughter of the River Bo- rysthenes; that such was the origin of Targitaus; and that he had three sons, who went by the names of Lipoxais, Apoxais, and the youngest, Colaxais ; that during their reign a plow, a yoke, an ax, and a bowl of golden workmanship dropping down from heaven, fell on the Scythian territory; that the eldest, seeing them first, approached, intending to take them up, but as he came near, the gold began to burn; when he had retired the second went up, and it did the same again ; according- 222 cosmos. ing, they were more easily broken during the first day after the fall than subsequently. I have intentionally given more time to this phenomenon, in order to be able to compare it with another of the 13th of September, 1768. About half past four o'clock in the afternoon of the above-mentioned day, a dark cloud was seen near the village of Luce (Dep. d'Eure et Loire), four miles westward of Chartres, in which a noise was heard like a cannon shot, and at the same time a hissing was perceived in the air, caused by the fall of a black stone moving in a curve. The stone, which had penetrated into the Earth, weighed 7-ilbs., and was so hot that it could not be touched. It was very imperfectly analyzed by Lavoisier, Fougeroux, and Cadet. No phenomena of light were per- ceived throughout the whole occurrence. As soon as the observation of periodic falls of shooting stars was commenced, and their appearance on certain nights ex- pected, it was remarked that the frequency of the meteors in- creased with the length of time from midnight, and that the greatest number fell between two and five in the morning. Already, on the occasion of the great fall of meteors at Cu- mana in the night of the 11th and 12th of November, 1799, « ly, the burning gold repulsed these ; but when the youngest went up the third, it became extinguished, and he carried the things home with him; and that the elder brothers, in consequence of this giving way, surrendered the whole authority to the youngest. 6. From Lipoxais, they say, are descended those Scythians who are called Auchatae ; from the second, Apoxais, those who are called Catiari and Traspies ; and from the youngest of them, the royal race, who are called Paralataa But all have the name of Scoloti, from the surname of their king; but the Grecians call them Scythians. 7. The Scythians say that such was their origin ; and they reckon the whole number of years from their first beginning, from King Targitaus to the time that Darius crossed over against them, to be not more than a thousand years, but just that num- ber. This sacred gold the kings watch with the gi'eatest care, and an- nually approach it with magnificent sacrifices to render it propitious. If he who has the sacred gold happens to fall asleep in the open air on the festival, the Scythians say he can not survive the year, and on this account they give him as much land as he can ride round on horseback in one day. The country being very extensive, Colaxais established three of the kingdoms for his sons, and made that one the largest in which the gold is kept. The parts beyond the north of the inhabited districts the Scythians say can neither be seen nor passed through, by reason of the feathers shed there ; for that the earth and air are full of feathers, and that it is these which intercept the view." — Herodotus, iv., 5 and 7 (translation, Bonn's Classical Library, p. 238). But is the myth of sacred gold merely an ethnographical myth — an allusion to three kings' sons, the founders of three races of Scythians ? an allusion to the prominent position which the race of the youngest son, the Paralatae, attained? (Brandstatter, Scythica, de aurea Caterva, 1837, p. 69 and 81.) AEROLITES. 223 my fellow-travelers saw the greatest swarm of shooting stars between half past two and four o'clock. A very meritorious observer of the phenomena of meteors, Conlvier-Gravier, con- tributed an important essay to the Institute at Paris upon la variation horaire des etoilcs filantcs. It is difficult to con- jecture the cause of such an hourly variation, an influence of the distance from the hour of midnight. If, under differ- ent meridians, the shooting stars do not become especially visible until a certain early hour, then, in the case of their cosmical origin, we must assume, what is still but little prob- able, viz., that these night, or, rather, early morning hours, are especially adapted to the recognition of the shooting stars, while in other hours of the night more shooting stars pass by before midnight invisible. We must still long and pa- tiently collect observations. The principal characters of the solid masses which fall from the air I believe I have treated of with tolerable com- pleteness [Cosmos, vol. i., p. 129), in reference to their chem- ical relations and the granular structure, especially investi- gated by Gustav Rose in accordance with the state of our knowledge in the year 1845. The successive labors of How- ard, Klaproth, Thenard, Vauquelin, Proust, Berzelius, Stro- meyer, Laugier, Dufresnoy, Gustav and Heinrich Rose, Bous- singault, Rammelsberg, and Shepard, have afforded a rich material,* and yet two thirds of the fallen meteoric stones, which lie at the bottom of the sea, escape our observation. Although it is striking that, under all zones, at points most distant from each other, the aerolites have a certain jyhys- iognomic resemblance — in Greenland, Mexico, and South America, in Europe, Siberia, and Hindostan — still, upon a closer investigation, they present very great differences. Many contain T9/¥ of iron ; others (Siena) scarcely t|q ; nearly all have a thin black, brilliant, and, at the same time, veined coating : in one (Chantonnay) this crust was entire- ly wanting. The specific gravity of some meteoric stones amounts to as much as 4-28, while the carbonaceous stone of Alais, consisting of crumbling lamella;, showed a specific gravity of only 1*94. Some (Juvenas) have a doleritic struc- ture, in which crystallized olivin, augite, and anorthite are to be recognized separately ; others (the masses of Pallas) afford merely iron, containing nickel and olivin ; and others, # The metals discovered in meteoric stones are nickel, by Howard; cobalt, by Stromeyer ; copper and chromium, by Laugier ; tin. by Bcr- ze'.hi6. 224 cosmos. again (to judge from the proportions of tho ingredients), are aggregates of hornblende and albite (Chateau-Renard), or of hornblende and labrador (Blansko and Chantonnay). According to the general summary of results given by a Bagacious chemist, Professor Rammelsberg, who has recently occupied himself uninterruptedly, and as actively as success- fully, with the analysis of aerolites and their composition from simple minerals, " the separation of the masses fallen from the air into meteoric iron and meteoric stones is not to be admitted in its strictest sense. Meteoric iron is sometimes found, though seldom, with silicates intermixed (the Siberian mass weighed again by Heis of 1270 Russian pounds, with grains of olivin), and, on the other hand, many meteoric stones contain metallic iron. "A. The meteoric iron, whose fall it has been possible to observe only a few times (Hradschrina, near Agram, on the 26th of May, 1751, Braunau, 14th of July, 1847), while most analogous masses have already laid long upon the surface of the earth, possesses in general very similar physical and chem- ical properties. It almost always contains sulphuret of iron mixed with it in finer or coarser particles, which, however, do not appear to be either iron pyrites or magnetic pyrites, but a sulphuret of iron.* The principal mass of such a me- teoric iron is also not pure metal, but consists of an alloy of iron and nickel, so that this constant presence of nickel (on the average 10 per cent., sometimes rather more, sometimes rather less) serves justly as an especial criterion for the me- teoric nature of the whole mass. It is only an alloy of two isomorphous metals, not a combination in definite proportions. There are also present in minute quantity, cobalt, manganese, magnesium, copper, and carbon. The last-mentioned sub- stance is partly mixed mechanically, as difficultly combusti- ble graphite ; partly in chemical combination with iron, and therefore analogous to many kinds of bar-iron. The princi- pal mass of the meteoric iron contains also always a peculiar combination of 'phosphorus ivith iron and nickel, which, on the solution of the iron in hydrochloric acid, remains in the form of silver- white, microscopic, crystalline needles and lam- inae. " B. The meteoric stones, properly so called, it is customary to divide into two classes, according to their external appear- ance. The stones of one class present, in an apparently ho- mogeneous mass, grains and splinters of meteoric iron, which * Rammelsberg, in Poggendorff, Annalen, vol. lxxiv., 1849, p. 442. AEROLITE 825 are attracted by the magnet, and possess entirely the nature of that found in larger masses. To this class belong, for ex- ample, the stones of Blansko, Lissa, Aigle, Ensisheim, Chan- tonnay, Klein- Wenden near Nordhausen, Erxleben, Chateau- Renard, and Utrecht. The stones of the other class are free from metallic admixtures, and present rather a crystalline mixture of different mineral substances ; as, for example, the stones of Juvenas, Lontalax, and Stannern. " Since the time that Howard, Klaproth, and Vauquelin first instituted the chemical investigation of meteoric stones, for a long time no regard was paid to the fact that they might be mixtures of separate combinations ; but they were examined only for their total constituents, and it was consid- ered sufficient to draw out the iron by the magnet. After Mohs had directed attention to the analogy between some aerolites and certain telluric rocks, Nordenskjold endeavored to prove that the aerolite of Lontalax, in Finland, consisted of olivin, leucite, and magnetic iron ore ; but the beautiful observations of Gustav Rose first placed it beyond doubt that the stone of Juvenas consists of magnetic pyrites, augite, and a feldspar very much resembling labrador. Guided by this, Berzelius endeavored, in a more extended essay (Kongl. Veten- skaps-Academiens Handlingar fur 1834), to eliminate, also by chemical methods, the mineralogical nature of the sepa- rate combinations in the aerolites of Blansko, Chantonnay, and Alais. The road happily pointed out by him beforehand has subsequently been abundantly followed. " a. The first and more numerous class of meteoric stones, those with metallic iron, contain this disseminated through them, sometimes in larger masses, which occasionally form a skeleton, and thus constitute the transition to those meteoric masses of iron in which, as in the Siberian mass of Pallas, the other materials disappear more considerably. On account of the constant 'presence of olivin, they are rich in magnesia. The olivin is that part of the meteoric stone which is decom- posed when it is treated with acids. Like the telluric, it is a silicate of magnesia and protoxide of iron. That part which is not attacked by acids is a mixture of feldspathic and au- gitic matter, whose nature admits of being determined solely by calculation from its total constituents, as labrador, horn- blende, augite, or oligoclas. " (3. The second much rarer class of meteoric stones have been less examined. They contain partly magnetic iron ore, olivin, and some feldspathic and augitic matter ; gome of K 2 226 cosmos. them consist merely of the two last-mentioned simple miner- als, and the feldspar tribe is then represented by anorthite.* Chrome iron ore (oxyd of chromium and protoxyd of iron) is found in small quantity in all meteoric stones ; phosphoric acid and titanic acid, which Rammelsberg discovered in the very remarkable stone of Juvenas, perhaps indicate apatite and titanite. " Of the simple substances hitherto detected in the meteoric stones, there are 18 :f oxygen, sulphur, phosphorus, carbon, silicium, aluminum, magnesium, calcium, potassium, sodi- um, iron, nickel, cobalt, chromium, manganesium, copper, tin, and titanium. The proximate constituents are, (a.) metallic: nickel-iron, a combination of phosphorus with iron and nickel, sulphuret of iron and magnetic pyrites ; (b.) oxy- dized : magnetic iron ore and chrome iron ore ; (c.) silicates : olivin, anorthite, labrador, and augite." In order to concentrate the greatest number of important facts separated from hypothetic conjectures, it still remains for me to develop the manifold analogies which some mete- oric stones present as rocks with older, so-called trap rocks (dolerites, diorites, and melaphyren), with basalts and more recent lava. These analogies are so much the more strik- ing, as "the metallic alloy of nickel and iron, which is con- stantly contained in certain meteoric masses," has not hither- to been discovered in telluric minerals. The same distin- guished chemist whose friendly communications I have made use of in these last pages, enters fully into this subject in a special treatise, $ the results of which will be more appropri- ately discussed in the geological part of the Cosmos. * Shepard, in Silliman's American Journal of Science and Arts, ser. ii., vol. ii., 1846, p. 377 ; Rammelsberg, in Poggend., Ann., bd. lxxiii., 1848, p. 377. t Compare Cosmos, vol. i., p. 130. X Zeitschrift der Dentschen Geolog. Gesellschaft, bd. i., p. 232. All the matter in the text from p. 224 to p. 226, which is between inverted commas, was taken from the manuscript of Professor Rammelsberg (May, 1851). CONCLUSION. In concluding the uranological part of the 'physical de- scHptio?i of the universe, in taking a retrospect of what I have attempted (I do not say accomplished), after the exe- cution of so difficult an undertaking, I think it necessary once more to call to mind that this execution could have been ef fected only under those conditions which have been indicated in the Introduction to the third volume of Cosmos. The attempt to carry out such a cosmical treatment of the subject is limited to the representation of space and its material con- tents, whether aggregated into spheres or not. The character of the present work differs, therefore, essentially from the more comprehensive and excellent elementary icorks on astronomy which the various literatures of modern times possess. As- tronomy, as a science, the triumph of mathematical reason- ing, based upon the sure foundation of the doctrine of gravi- tation and the perfection of the higher analysis (a mental in- strument of investigation), treats of phenomena of motion measured according to space and time ; locality (position) of the cosmical bodies in their mutual and perpetually-varying relations to each other ; change of form, as in the tailed comets ; change of light, as the sudden appeara?ice or total extinction of the light of distant suns. The quantity of mat- ter present in the universe remains always the same ; but from what has already been discovered in the telluric sphere of physical laws of nature, we see working in the eternal round of material phenomena an ever-unsatisfied change, presenting itself in numberless and nameless combinations. Such an exercise of force by matter is called forth by its at least apparent heterogeneity. Exciting motion in immeas- urably minute spaces, this heterogeneity of matter compli- cates all the problems of terrestrial phenomena. The astronomical problems are of a simpler nature. Hitherto unencumbered by the above-mentioned complica- tions, directed to the consideration of the qtiantities of pon- derable matter (masses), to the oscillations producing light and heat — the mechanics of the heavens has, precisely on account of this simplicity, in which every thing is reducod to 228 coSiMos. motion, remained in all its branches amenable to mathemat- ical treatment. This advantage gives to the elementary works on theoretical astronomy a great and entirely peculiar charm. In them is reflected what the intellectual labors of later centuries have achieved by the analytical methods ; how configuration and orbits are determined ; how, in the phenomena of planetary motion, only small oscillations about. a mean condition of equilibrium can take place ; how the planetary system, from its internal arrangement, works its preservation and permanence by the compensation of 'per- turbations. The examination of the means of forming a general con ception of the universe, the explanation of the complicated celestial phenomena, do not belong to the plan of this work. The physical description of the universe relates to what fills space, and organically animates it, in both spheres of urano- logical and telluric relations. It adheres to the consideration of the discovered laws of nature, and treats of them as ac- quired facts, as immediate results of empirical induction. In order to carry out the work of the Cosmos within the appro- priate limits, and not with too great extension, it must not be attempted to establish theoretically the connection of phe- nomena. In this limitation of the plan laid down beforehand, I have, in the astronomical volume of Cosmos, applied so much the more care to the individual facts and their arrange- ment. From the consideration of universal space, its tem- perature, the degree of its transparency, and the resisting medium which fills it, I have passed on to natural and tele- scopic vision, the limits of visibility, the velocity of light, ac- cording to the difference of its sources, the imperfect meas- urements of luminous intensity, and the new optical means of distinguishing direct from reflected light. Then follows the heaven of fixed stars ; the numerical statement of its self-luminous suns so far as their position is determined ; their probable distribution ; the changeable stars which reappear at well-defined periods ; the proper motion of the fixed stars ; the assumption of the existence of dark cosmical bodies, and their influence upon the motion of the binary stars; the nebulous spots, in so far as these are not remote and very dense swarms of stars. The transition from the sidereal part of uranology — from the heaven of the fixed stars to our solar system, is merely a transition from the universal to the particular. In the class of binary stars, self-luminous cosmical bodies move about CONCLUSION. 229 a common center of gravity. In our solar system, which is constituted of very heterogeneous elements, dark cosmical bodies revolve round a self-luminous one, or much rather again round a common center of gravity, which at different times is situated within and without the central body The individual members of the solar system are of dissimilar na- ture— more dissimilar than for many centuries astronomers were justified in supposing. They arc principal and sec- ondary planets ; among the principal planets a group whose orbits intersect each other ; an innumerable host of comets ; the ring of the zodiacal light ; and, with much probability, the periodic meteor-asteroids. It still remains to state here fully, as actual relations, the three great laws of planetary motion, discovered by Kepler. First laiv : each orbit of a planetary body is an ellipse, in one of whose foci the Sun is situated. Second law : each planetary body describes in equal times equal sectors round the Sun. Third law : the squares of the times of revolu- tion of two planets are as the cubes of their mean distances. The second law is sometimes called the first, because it was discovered earlier. (Kepler, Astronomia Nova, seu Physica Cozlestis, tradita Commentariis de Motibus stellce tylartis, ex observ. Tychonis Br alii elaborata, 1602 ; compare cap. xl. with cap. lix.) The first two laws would be applicable if there were only a single planetary body ; the third and most important, which was discovered nineteen years after- ward, fixes the motions of two planets to one law. (The manuscript of the Harmonice Miindi, which appeared in 1619, was already completed on the 27th of May, 1618.) While the laws of planetary motions were empirically dis- covered at the commencement of the seventeenth century ; while Newton first discovered the force, of whose action Kep- ler's laws were to be considered as necessary consequences ; so the end of the eighteenth century has had the merit of de- monstrating the stability of the planetary system by the new path which the perfected calculation of infinitesimals opened to the investigation of astronomical truths. The principal elements of this stability are, the invariability of the major axes of the planetary orbits, proved by Laplace (1773 and 1784), Lagrange, and Poisson ; the long periodic change (comprised within narrow limits) of the eccentricity of two larger planets more distant from the sun, Jupiter and Saturn, themselves only y^T of the mass of the all-governing central body ; finally, the arrangement that, according to the eternal 230 cosmos. plan of creation, and the nature of the formation of the planets, they have all a translatory and rotatory motion in one direction ; that this motion takes place in orbits of slight and but little varying ellipticity, in planes of moderate dif- ferences of inclination ; and that the periods of the planeta- ry revolutions have among each other no common measure. Such elements of stability, as it were the maintenance and duration of the planets' existence, are dependent upon the condition of mutual action with a separate circle. If, by the entry of a cosmical body coming from without, and not pre- viously belonging to the planetary system, that condition was disturbed (Laplace, Expos, du Syst. du Monde, p. 309 and 391), then this disturbance, as the consequence of new attractive forces, or of a collision, might certainly become destructive to the existing system, until finally, after long con- flict, a new equilibrium was produced. The arrival of a comet upon an hyperbolic orbit from a great distance, even when want of mass is made up for by immense velocity, can excite apprehension only in an imagination which is not sus ceptible of the earnest assurances of the calculation of proba- bilities. The wandering clouds of the interior comets are not more dangerous to our solar system than the great incli- nation of the orbits of some of the small planets between Mars and Jupiter. Whatever must be characterized as mere probability, lies beyond the domain of a physical description of the universe ; science must not wander into the cloud- land of cosmological dreams. INDEX TO VOL. IV. Abdurrahman Sufi, his notice of neb- ulous spots, 15, 44. Absence of solar spots and bad harvests, supposed connection of, Sir William Herschel on, 68. Acosta, on the black specks of the south- ern hemisphere, 50. Adams and Leverrier, claims of, to the discovery of Neptune, 179. Aerolites, of extraterrestrial cosmical origin, 199; fall of, 219. Alphoneine Tables, their date, 15. Anaxagoras of Clazomene, on meteoric stones, 2U6. Andromeda, nebula in, its discovery, 16 ; further researches, 17, 18 ; not noticed by Huygens, 38. Anghiera. See Peter Martyr. Annular nebula?, rare, 32. April, falling stars in, 214. Apsides, line of motion of, 123. Arabian uotices of the Magellanic Clouds, 15, 44. Arago, on the physical constitution of the Sun, 62. Arago and Plateau, different views of, on irradiation, 148. rj Argus, nebula round, its magnificent effulgence, 41. Asterion, spiral nebula in, 42. Asteroids, 57 ; numerical data, 213 ; Ol- bers's conjecture as to their origin. 164. Astraea, discovery of, 100 ; elements, 163. Atmosphere, lunar, disproved, 147. August, falling stars in, 214. Axes of rotation, inclination of, 121. Axial rotation of the planets, periods of, 120. Bessel, on the planet beyond Uranus, 179. Biela's Comet, separation of, into two parts, 193 ; elements, 197. Black specks in the southern hemisphere, 50. Bode, on solar spots. 66; his law of plan- etary distance, 116. Bond, nebulaj resolved by, 32, 39. Brorsen's Comet, elements, 197. Cadamosto seeks for a south polar star, 23. Canes Venatici, spiral nebula in Asterion, one of, 42 ; a most remarkable phe- nomenon, 42. Canopi, three, of Vespucci, 46. Cape Catalogue (or Southern Catalogue) of Sir John Herschel, 26. Cape Clouds, or Magellanic Clouds, 43 ; southern clouds vaguely so called, 45. Cassini, on nebula?, 19 ; on the Sun'a spots, 65. Ceres, discovery of, 100; elements, 163. Chinese statements as to the obliquity of the ecliptic, 125; as to comets, 186; as to falling stars and meteoric stones, 206. Classification of nebula), 19, 32; of plan- ets, 101. Coal-bags, or coal-sacks, in the southern hemisphere, 50. Colored glasses, early use of, by Belgian pilots, 65. Comet of Aristotle, 187. Comet of Colla and Bremiker, 196. Comet, Halley's, 186, 195. Comet, Olbers's, 195. Comets, orbits of, indicate the limits of the solar system. 57 ; called light- clouds by the Greeks, 181 ; hypothesis of their similarity to asteroids, 182 ; number discovered annually, 184 ; re- appearance of Halley's Comet, 186 ; Chinese statements, 186; Comet of Aris- totle, 187; tails of comets, 189, 192; ra- diant heat, 191 ; LexelFs Comet, 191 ; Biela's Comet, 193; numerical data, 195; elements of the six interior com- ets, 197 ; inclination of the orbits, 198 ; Chaldean opinions on, 200. Craters of the Moon, 155. Crema, great fall of aerolites at, 220. Cusa, Cardinal de, his remarkable views of the physical constitution of the Sun, 62; on the motion of the Earth, 64. Cygnus, nebula in, 46. D'Arrest's Comet, elements, 197. Days and hours, planetary, 94. December, falling stars in, 216. De Hoces discovers the southern ex- tremity of the new continent, 46. Densities of the planets, 119. De Vico's Comet, elements, 197. Dione, a satellite of Saturn, 174. Distances of the planets from the Sun, 107. Double nebula}, 32. Double stars differ in their natural char- acter from our solar system, 53. Dunlop, his observations of nebulffi at Paramatta, 22, 26. Earth, the, distance, and other numerical data. 141; nutation. i05, 125. Earth-light, what, 144 ; known to Leon- ardo da Vinci, 145. Egeria, discovery of, 101 ; elements, 163. Elliptical nebulas, named the normal type, 31. 232 COSMOS. Enceladus, a satellite of Saturn, 174. Encke's Comet, elements, 197; its reap- pearance, 198. Epochs, main, of planetary discovery, 57. Eccentricity of the planetary orbits, 127. Exterior planets, 102. Fabricius first observes the solar spots, 64. Faculae and shallows, 86. Fage's Comet, elements, 197. Falling stars, 204. Faraday on atmospheric magnetism, 84. Fire-balls, 198. Flora, discovery of, 101 ; elements, 163. Fontaney, the Jesuit, on the Magellanic Clouds, 47. Galileo, his controversy with Marius, 16 ; his Mundus Jovialis, 17 ; use of colored glasses neglected by, 65. Geminus mentions nebulous stars, 15. Gnomons, ancient, 127. Halley's observations on nebulae, 19. Halley's Comet, reappearances of, 186. Heat, rays of, 83. Heat possessed by the Moon's light, 143. Hebe, discovery of, 101 ; elements, 163. Heis's observations on shooting stars, 212. Herschel, Sir William, his estimate of the extent of nebulous spots, 14; bis dis- coveries, 21 ; on the nebula of Orion, 40; on solar spots, G7; opposed to the assumption of a lunar atmosphere, 147. Herschel, Sir John, on nebulae and stellar clusters, 27, 31 ; on irregular nebulous masses, 35 ; on the nebula in Orion, 38 ; on the nebula round tj Argus, 41 ; on the nebula in Vulpes, 41 ; his descrip- tion of the Magellanic Clouds, 47 ; on the black specks and coal-bags of the southern hemisphere, 51 ; on the heat of the Moon's surface, 131. Herschel, Miss, discovery of a nebula by, 31. Hipparchus mentions nebulous stars, 15. Houzeau's observations on the zodiacal light, 204. Humboldt, Alexander von, works of, quoted in various notes : Asie Centrale, 222. De Distributione Geograpbica Plan- tarum, 123. Examen Critique de l'Histoire de la Geographie du Nouveau Conti- nent, 15, 28, 45, 151. Kleinen Schriften, 114. Voyage aux Regions Equinoxiales, 215. Vues des Cordilleres et Monumens des Peuples Indigenes de l'Ame- rique, 98. Huygens discovers the nebula in the sword of Orion, 19, 37. Hygeia, discovery of, 101 ; elements, 163. Hyperion, a satellite of Saturn, 174. Intensity of the solar light on the planets, 130. Interior comets, 197. Interior planets, 103 Irene, discovery of, 101 ; elements, 163. Iris, discovery of, 101 ; elements, 163. Irregular nebulous masses, 33 ; situate near the Milky Way, 34 ; extraordinary size and singular forms, 36. Isaac, Aben Sid Hassan, introduces the Latinized term nebulosaj into the Al- phonsine Tables, 15. Jacob, Captain, on the nebula round 17 Argus, 41. Japetus, a satellite of Saturn, 174. July, falling stars in, 214. Juno, discovery of, 100; elements, 163. Jupiter, numerical data, 165; streaks, or girdles, 167. Jupiter's satellites, numerical data, 169. Kant's speculations on nebulae and star- formation, 20. Kepler on planetary distances, 110 ; laws of planetary motion discovered by, 229. Lacaille, his classification of nebulae, 19. Lambert's speculations on nebulae, 20. Lassell, discovery of a satellite of Saturn by, 174; of satellites of Neptune by, 180. Laurentius stream of failing stars, 214. Le Gentil's study of nebulas, 20. Leonardo da Vinci. Earth-light known to, 145. Leverrier and Adams, claims to the dis- covery of Neptune, 179. Lexell's Comet, 191. Light, time required to traverse the radius of the Earth's orbit, 60; solar and arti- ficial, 82 ; difference of intensity in the different planets, 130. Light, zodiacal. See Zodiacal light. I Light-clouds, comets so styled by the Greeks, 181. I Lucerna Mundi, the Sun, 59. J Lunar atmosphere disproved, 147. i Lunar spots, 149. Magellanic Clouds, early notices of, 15; termed Cape-clouds by the Portu- guese, 43 ; general adoption of the name, 46 ; described by Sir John Her- schel, 48; not connected with one an- other, 48; nor with the Milky Way, 48. Magnitude, absolute and apparent, of planets, 105. Map of the Moon, 151. Mars, numerical data, 159 ; meteorologic- al analogies with the Earth, 159. Masses of the planets, 1 18. May, falling stars in, 214. Mayer, of Gunzenhausen (Simon Marius), first describes a nebula, 16. Mercury, distance, diameter, mass, densi- ty of, 137. Messier, his discoveries regarding nebu- lae, 21. Meteor asteroids, 57. Meteoric stones, 57 ; seldom fall from a clear 6ky, 219 ; remarkable falls of, 219 ; analysis, 223. Metis, discovery of, 101 ; elements, 163. INDEX. 233 Michell conceives nil nebulae to be stellar clusters, 20. Milky Way, Huygens on the, 38. Mimas, a satellite of Saturn, 174. Moon, myths respecting the, 113, 115 ; estimate of the heat of its surface, 130 ; numerical data, 141; moonlight, 142; capable of producing heat, 143 ; styled by the Indians, King of the stars of cold, 143 ; eclipses, 145 ; predictions from the color of the eclipsed body, 147 ; lunar twilight disproved, 147 ; probably a voiceless wilderness, 148 ; irradiation, 148; spots, 149; supposed to reflect the surface of our planet, 150; topographical chart, 151 ; 6o-called seas, 151 ; mountains, 153 ; comparison of height with the mountains of the Earth, 153; ray -systems, 154; annular plains, 154 ; craters of elevation, 155 ; rills, 157 ; influence on the Earth, 157. Mountains of the Moon, 153. Mundus Jovialis, a work by Galileo, 16. Nebula, the first isolated, discovered, 16. Nebulas, Lacaille's classification of, 19 ; discoveries of the Herschels, 21 ; of the Earl of Rosse and others, 22 ; probably no essential physical distinction be- tween, and clusters of stars. 23 ; ques- tion of the existence or non-existence of a self-luminous, vaporous matter, 24 ; elliptical, 31 ; annular, 32 ; planetary, 33 ; nebulous stars, 34 ; galaxy of, not confirmed by recent observation, 36. Nebular theory, the, 20 ; independent of the theory of sidereal aggregation, 21. Nebulous masses, regular, 29 ; irregular, 33 ; these latter mostly situate near the Milky Way, 34 ; extraordinary size of some, and singular forms of others, 36. Nebu'ous spots, 13 ; number whose posi- tions have been determined, 14 ; early notices of, 14 ; Galileo's discoveries, 17 ; Huygens, 19; Lacaille, 19; other in- vestigators, 20; the discoveries of the Herschels. 21 ; the Earl of Rosse, 22 ; Sir John Herschel's distribution of, 27. Nebulous stars, mentioned by Hippar- chus, Geminus, and Ptolemy, 15 ; a modern division of regular nebulae, 34. Neptune, considerations on the distance of, 178 ; numerical data, 178 ; claims to the discovery of, 178. Neptune, satellites of, 180. Northern Catalogue of the Herschels, 25. Northern hemisphere possesses many nebulae, and but few clusters of stars, 27. November period, meteors of the, 209, 215. Nubecula Major and Minor, 20, 46. Number and epoch of discovery of the principal planets, 89. Nutation of the Earth's axis, 105, 125. October, falling stars in, 214. Olbers's conjecture as to the asteroids being fragments of a single destroyed planet, 164 ; on shooting stars, 216. Orbits, inclination of, planetary, 121 ; cometary, 198. Orion, nebula in the sword of, 18, 36 ; in the head of, 36 ; trapezium not sur- rounded by a nebula, 39 ; new stars discovered in the trapezium, 39, Pallas, discovery of, 100 ; elements, 161. Parthenope, discovery of, 101 ; elements, 163. Penumbras of the solar body, 67. Periodic meteors, number of, observed at different hours, and in different months, 213. Perpetual spring, its undesirable nature, 123. Perseus, falling stars issuing from, 210. Peruvian seven-day week, an error, 98. Peter Martyr, his description of the Ma- gellanic Clouds, 46 ; on a fall of aero- lites, 219. Photosphere of the nebulous stars, 34 ; of the Sun, 62. Picard investigates the nebula in Orion, 19. Pisces, nebulous region of, 28. Planetary discovery, epochs of, 58. Planetary motion, three great laws of, 228. Planetary nebulae, 33; mainly found in the southern hemisphere, 33. Planetary system, stability of, how de- monstrated, 229. Planets and their satellites, general con- siderations, 88 ; principal planets, 89 ; discovery, 89 ; names, 91 ; planetary signs, not of ancient date, 94 ; days and metals named from, 94 ; early conjec- tures that other planets remained to be discovered, 99 ; periods of discovery since the invention of the telescope, 100 ; classification hi two groups, 102 ; exterior, generally larger than the in tenor, 103 ; absolute and apparent mag nitudes, 104 ; arrangement and dis- tances. 107 ; assumed laws, by Titius and Bode, and Wurm, 116; masses, 118 ; densities, 119 ; periods of revolu tion, and axial rotation, 120; inclina- tion, 121 ; eccentricity, 127 ; intensity of the Sun's light, 130. Planets, secondary, numerical data, 131. Planets, the small, numerical data, 160 ; table of elements, 163 ; Olbers's con- jecture as to their origin, 164. Plateau on irradiation, 148. Principal planets, 89. Proselenes, astronomical myth of the, 113. Ptolemy mentions nebulous stars, 15. Regular nebulas, classification of, 29. Revolution, periods of, of the planets, 120 ; of comets, 195. Rhea, a satellite of Saturn, 174. Robinson, Dr., nebulae resolved by, 22. Rosse, Earl of, discoveries by means of his powerful telescope, 22 ; his caution, 23. Sabbath, used as a name for the whol« week, 95. 234 COSMOS. Sagittarius, nebula in, 41. Sanscrit names of planets, 93. Satellites, general considerations on, 131. Saturn, numerical data, 170 ; rings, 171 ; eccentric position, 172. Saturn's satellites, numerical data, 174. Schwabe's observations on the solar spcts, 85 ; on the eccentric position of Saturn, 172. Scythian myth of a fall of gold (meteors), 221. Seas (so called) of the Moon, 151. Secondary planets, 131. Shooting stars, upper limits of the height of, unascertained, 217 ; various colors, 217 ; magnitudes, 219. Sidera Borlonia and Sidera Austriaca, 64. Sidereal aggregation, theory of, 21. Sidereal periods of revolution and axial rotation of the planets, 120. Sirius, and other fixed stars, estimates of the distance of, 55. Small planets, 160. Snow spots in Mars, 160. Solar system, difference between, and the system of double stars, 53 ; its limits in- dicated by the orbits of comets, 57 ; its constituents, 57. South, Sir James, nebulas resolved by, 22. South polar star, search for a, 29. Southern Catalogue of the Herschels, 25. Southern Cross, planetary nebula in, 33 ; black spot in, 46, 51. Southern hemisphere, with fewer nebulas, possesses relatively more clusters of stars than the northern, 29 ; the Magel- lanic Clouds, 15, 45. Spiral nebula in Asterion, 42. Spots, solar, 72, 86 ; lunar, 149 ; on Mars, 160. Star catalogues, early, 47 ; the Herschels', 25 ; the Northern, 26 ; the Southern, 26. Star clusters, 17 ; predominate in the southern hemisphere, 27. Star-formation theory, the, 21 ; inde- pendent of the nebular theory, 21. Stellar clusters, probably no essential physical difference between, and nebu- las, 23 ; in the northern and the south- ern hemispheres, 27. Sternhaufen, star clusters, 17. Suhel, a vague term of the Arabian astron- omers, 46. Sun, domain of the, 53 ; its constituents 57; translatory motion, 134. Sun, considered as the central body, 59 ; numerical data, 60 ; conjectures as to its physical character, 61 ; envelopes, 62 ; penumbras, 67 ; protuberances, 70, 135 ; distribution of solar spots, 72 ; chronological list of remarkable ap- pearances of, 74 ; intensity of solar light, 79 ; comparison of artificial light, 82 ; rays of light and rays of heat, 83 ; Schwabe's table of occurrence of solar spots, 86. Telescope, discoveries of planets since the invention of the, 100 ; the Earl of Rosse's, 22. Tethys, a satellite of Saturn, 174. Titan, a satellite of Saturn, 174. Titius, on the law of planetary distances, 116. Transits of Venus, 139. Trapezium of Orion, discovery of new stars in, 39. Uranus, numerical data, 175. Uranus, satellites of, peculiarity of their motion, 176 ; their number undeterm- ined, 177. Ursa Major, planetary nebula in, 33. Ursa Minor, /3 and y, 29. Venus, distance, brilliancy, rotation, trans- its, spots, mountains of, 138. Vespucci searches for a south polar star, 29 ; his mention of the Magellanic Clouds, 45. Vesta, discovery of, 100 ; elements, 163. Victoria, discovery of, 101 ; elements, 163. Virgo, nebulous region of, 28. Volcanoes of the Moon, 156. Vulpes, nebula in, 41. Week, or seven-day period, early diffused among the Semitic nations, 95 ; the Peruvian, an error, 98. White Ox, the large Magellanic Cloud, so called by the Arabians, 15, 43. Wilson, on solar spots, 66. Wurm, his correction of Bode's law of planetary distance, 118. Zodiacal light, early speculations on, 25; later opinions, 202 ; observations by the author and others, 203. 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