m m> • ]■ r '' : '' • i- M!«!!!> I i 1 I itiiiiiiiiiiiiiinuMiii! V I ,r ■ ■ ! ■V 1/ 'V A m i I I * . - i ,!■ ■■■- VJ / i ,; I ini i; -.5 lili .ii« V^ :. ■ '-ll, ''■".';'!''''■; ^ 'iMiiiiiiiitniiiii: .i .iiiKiniimuiuii! ,.,:...,. m\ M ■ J ^ a o a t-" a a -C Ln ru IS 1 00 lO ^ t I X COSMOS: A SKETCH OP PHYSICAL DESCRIPTION OF THE UNIYERSK BY ALEXANDEPv VON HUMBOLDT. THAXSLATED rROM VH3 GEIUIAN, BY E. C. OTTE. Naturae vcro rerum vis atqne majestas in omnibus momcntis fide caret, ei quia mi»do partes ejus ac non totam complectatur ardmo. — Plin., Hist. NaL, lib. vii., c. 1. VOL. Ill, NEW YORK; HARPER & BROTHERS, PUBLISHERS, 329 & 331 PEARL STREET FRANKLIN SQUARE. 1875. CONTENTS OF VOL. III. INTRODUCTION. Historical ileviGW of the attempts made with the object of consWering the Phenomena of the Universe as a Ur.ity of Baturc 5-25 IVgB SPECIAL RESULTS OF OBSERVATIONS IN THE DOMAIN OF COSMICAL PHENOxMENA A. Uranological portion of the physical description of the world. — a. Astrognosy 2G-29 I. The realms of space, and conjectures regarding that which appears to occupy the space intervening between the heavenly bodies 29-41 il. Natural and telescopic vision, 41—73 ; Scintillation of the stars, 73-83 ; Velocity of light, 83-89 ; Results of pho- tometry, 89-102 41-102 III. Number, distribution, and color of the fixed stars, 103- 139; Stellar masses (stellar swarms), 139-143; The Milky Way interspersed v/ith a few nebulous spots, 143-151 103-15 J IV. New stars, and stars that have vanished, 151—160 ; Va- riable stars, whose recurring periods have been determ- ined, 160—177; Variations in the intensity of the light of stars whose periodicity is as yet uninvestigated, 177- 182 151-S32 V. Proper motion of the fixed stars, 182-185 ; Problemat- ical existence of dark cosmical bodies, 185—188 ; Par- allax— measured distances of some of the fixed stars, 188-194; Doubts as to the assumption of a central body for the whole sidereal heavens, 194-199 : 82-199 VI. Multiple, or double stars — Their number and reciprocal distances — Period of revolution of two stars round a common center of gravity ,. . ,. 199-22? JV CONTENTS. TABLES. Photometric Tables of Stars 100-102 Clusters of Stars 141-143 New Stars 155-160 Variable Stars 172-177 Parallaxes 1 93 Elements of Orbits of double Stars , . 213 SPECIAL RESULTS OF OBSERVATION la THE DOMAIN OF COSMICAL PHENOMENA. INTRODUCTION. In accordance with the object I have proposed to myself, and which, as far as my own powers and the present state of science permit, I have regarded as not unattainable, I have, in the preceding volumes of Cosmos, considered Nature ill a two-fold point of view. In the fii-st place, I have en- deavored to present her in the pure objectiveness of external phenomena ; and, secondly, as the reflection of the image im- pressed by the senses upon the inner man, that is, upon hia ideas and feelings. The external world of phenomena has heen delineated un- der the scientific form of a general picture of nature in her two great spheres, the uranological and the telluric or ter- restrial. This delineation begins with the stars, which glim- mer amid nebulae in the remotest realms of space, and, pass- ing from our planetary system to the vegetable covering of the earth, descends to the minutest organisms which float in the atm.osphere, and are invisible to the naked eye. In order to give due prominence to the consideration of the existence of one common bond encircling the whole organic world, of the control of eternal laws, and of the causal connection, as far as yet known to us, of whole groups of phenomena, it was necessary to avoid the accumulation of isolated facts. This precaution seemed especially requisite v/here, in addition to the dynamic action of moving forces, the powerful influence of a specific difi^erence of matter manifests itself in the ter- restrial portion of the universe. T1k> problems presented to us in the sidereal, or uranological sphere of the Cosmos, are, considering their nature, in as far as they admit of being ob- eerved, of extraordinary simplicity, and capable, by means of the attractive force of matter and the quantity of its mass, ©f being submitted to exact calculation in accordance with « CO&xMOB. tlie theory of motion. If, as I believe, we are justified m re garding the revolving meteor-asteroids (aerolites) as portiona of our planetary system, their fall upon the earth constitutes the sole means by which we are brought in contact with cosmical substances of a recognizable heterogeneity.* I hero refer to the cause which has hitherto rendered terrestrial phenomena less amenable to th rules of mathematical de- duction than those mutually disturbing and readjusting move- ments of the cosmical bodies, in which the fundamental forco ©f homojieneous matter is alone manifested. I have endeavored, in my delineation of the earth, to ar- range natural phenomena in such a manner as to indicate their causal connection. In describing our terrestrial sphere, 1 have considered its form, mean density, electro-magnetic currents, the processes of polar light, and the gradations ac- cording to which heat increases with the increase of depth. The reaction of the planet's interior on its outer crust im plies the existence of volcanic activit}^ ; of more or less con- tracted circles of waves of commotion (earthquake waves), and their efiects, which are not always purely dynamic ; and of the eruptions of gas, of mud, and of thermal springs. The upheaval of fire-erupting mountains must be regarded as the highest demonstration of the inner terrestrial forces. "We have therefore depicted volcanoes, both central and chain formations, as generative no less than as destructive agents, and as constantly forming before our eyes, for the most part, periodic rocks (rocks of eruption) ; we have likewise shown, m contrast with this formation, how sedimentary rocks are m the course of precipitation from fluids, which hold their minutest particles in solution or suspension. Such a com- parison of matter still in the act of development and solidi- fication with that already consolidated in the form of strata of the earth's crust, leads us to the distinction of geognostic epochs, and to a more certain determination of the chronolog- ical succession of those formations in which lie entombed ex- tinct genera of animals and plants — the fauna and flora of a former world, whose ages are revealed by the order in whicli they occur. The origin, transformation, and upheaval of ter* restrial strata, exert, at certain epochs, an alternating actior. on all the special characteristics of the physical configura tion of the earth's surface ; influencing the distribution of liuids and solids, and the extension and articulation of eon * Cosmos, vol. i. (Harper's edit.), p ;3-C5, 136, INTRODUCTION. 7 tiiieiital masses in a horizontal and vertical direction. On these relations depend the thermal conditions of oceanic cur- rentis, the meteorological processes in the aerial investment of our planet, and the typical and geographical distribution of organic forms. Such a reference to the arrangement of telluric phenomena presented in the picture of nature, will, I think, suffice to show that the juxtaposition of great, and apparently complicated, results of observation, facilitates our insight into their causal connection. Our impressions of na- ture will, however, be essentially weakened, if the picture fail in warmth of color by the too great accumulation of minor details. In a carefully-sketched representation of the phenomena of the material world, completeness in the enumeration of individual features has not been deemed essential, neither does it seem desirable in the delineation of the reflex of ex- ternal nature on the inner man. Here it was necessary to observe even stricter limits. The boundless domain of the world of thought, enriched for thousands of years by the vig- orous force of intellectual activity, exhibits, among difierent races of men, and in diiferent stages of civilization, sometimes a joyous, sometimes a melancholy tone of mind ;=* sometimes a delicate appreciation of the beautiful, sc«3Cietimes an apa- thetic insensibility. The mind of man is first led to adore the forces of nature and certain objects of the material world ; at a later period it yields to religious impulses of a higher and purely spiritual character.! The inner reflex of the outer world exerts the most varied influence on the myste- rious process of the formation of language, $ in which the original corporeal tendencies, as well as the impressions of surrounding nature, act as powerful concurring elements. Man elaborates •within himself the materials presented to him by the senses, and the products of this spiritual labo • belong as essentially to the domain of the Cosmos as do the phenomena of the external world. As a reflected image of Nature, influenced by the crea- tions of excited imagination, can not retain its truthful purity, there has arisen, besides the actual and external world, an ideal and internal world, full of fantastic and partly sym- bolical myths, heightened by the introduction of fabulous ani- mal forms, whose several parts are derived from the orgau * Cosmos, vol. i., p. 23-25 ; vol. ii., p. 25 and 97. t Ibid., vol. ii., p. 38-43, and 56-GO. X Ibid , vol. i., p. SS'-aSQ; vol ii., p. 112-117. 8 COSMOS. isms of the present world, and sometimes even from the relics of extinct species. =^. Marvelous flowers and trees spring from this mythic soil, as the giant ash of the Edda-Songg, the world-tree Yggdrasil, whose branches tower ahove the heav- ens, while one of its triple roots penetrates to the *' foaming caldron springs" of the lower world. f Thus the cloud-re- gion of physical myths is filled with pleasing or with fearful terms, according to the diversity of character in nations and climates ; and these forms are preserved for centuries in the intellectual domain of successive generations. If the present work does not fully bear out its title, the adoption of which I have myself designated as bold and in- considerate, the charge of incompleteness applies especially to that portion of the Cosmos which treats of spiritual life ; that is, the image reflected by external nature on the inner w^orld of thought and feeling. In this portion of my Avork I have contented myself with dwelling more especially upon, those objects which lie in the direction of long-cherished studies ; on the manifestation of a more or less lively appre- ciation of nature m classical antiquity and in modern times ; on the fragments of poetical descriptions of nature, the col oring of which has been so essentially influenced by individ- uality of national character, and the religious monotheistic view of creation ; on the fascinating charm of landscape painting ; and on the history of the contemplation of the physical universe, that is, the history of the recognition of the universe as a whole, and of the unity of phenomena — a recognition gradually developed during the course of two thousand years. In a work of so comprehensive a character, the object of which is to give a scientific, and, at the same time, an ani- mated description of nature, a first imperfect attempt must rather lay claim to the merit of inciting than to that of sat- isfying inquiry. A Book of Natui'e, worthy of its exalted title, can ne^? er be accomplished until the physical sciences, notwithstanding their inherent imperfectibihty, shall, by theij * M. vou Olfer's TJeherresti vortreltlicher Riescnthiere in Bezieliung auj Ostasialische Sagen in the Abh. der Berl. Akad., 1832, s. 51. On tlie opinion advanced by Empedocles regarding the cause of the extinction of the earliest animal forms, see Hegel's Geschichte der Philosopkie, bd. ii., s. 344. t See, for the world-tree Yggdrasil, and the rushing (foaming) cal dron-spring Hvergelmir, the Deutsche Mi/ihologie of Jacob Grimm, 1844, B. 530, 756; also Mallet's Northern Antiquities (Bohn's edition), 1847 p. 410, 489, and 492, and frontispiece to ditto. f.XTRODUOTiOPr S gradual development and extension, have attained a higher degree of advancement, and until we shall have gained a more extended knowledge of the two grand divisions of the Cosmos — the external world, as made perceptible to us by the senses ; and th-e inner, reflected intellectual world. I tliink I have here sufhciently indicated the reasons which determined me not to give greater extension to the general picture of nature. It remains for this third and fourth volume of iiiy Cos?)ws to supply much that is wanting in the previ- ous portions of the work, and to present those results of ob- servation on which the present condition of scientific opinion is especially grounded. I shall here follow a similar mode of arrangement to that previously adopted, for the reasons which I liave advanced, in the delineation of nature. But, before entering upon the mdividual facts on wdiich special departments of science are based, I would fain ofler a few more general explanatory observations. The unexpected in- dulgence with which my undertaking has been received by a large portion of the public, both at home and abroad, ren- ders it doubly imperative that I should once more define, as distinctly as possible, the fundamental ideas on which the whole work is based, and say something m regard to those demands which I have not even attempted to satisfy, be- cause, according to my view of empirical — i. e., experiment- al— science, they did not admit of being satisfied. These explanatory observations involuntarily associate themselves with historical recollections of the earlier attempts made to discover the one universal idea to which all phenomena, in their causal connection, might be reduced, as to a sole prin- ciple. The fundamental principle* of my work on the Cosmos, as enunciated by me more than twenty years ago, in the French and German lectures I gave at Paris and Berlin, comprehended the endeavor to combine all cosmical phenom- ena in one sole picture of nature ; to show in what manner the common conditions, that is to ^say, the great laws, by which individual groups of these phenomena are governed, have been recognized ; and what course has been pursued in ascending from these law^s to the discovery of their causal connection. Such an attempt to comprehend the plan of the universe — the order of nature — must begin with a gen* eraiization of particular facts, and a knowledge of the con* * Cosmos, vol. i., p. 48-50. and GS-77. 10 COSMOS. ditions under which physical changes regularly anl period' ically manifest themselves ; and must conduct to the thought- iul consideration of the results yielded by empirical observa- tion, but not to " a contemplation of the universe based on speculative deductions and development of thought alone, or to a theory of absolute unity independent of experience.' We are, I here repeat, far distant from, the period when it was thought possible to concentrate all sensuous perceptions into the unity of one sole idea of nature. The true path waa indicated upward of a century before Lord Bacon's time, by Leonardo da Vinci, in these few words : " Cominciare dall' esperienza e per mezzo di quest a scoprirne la ragione."* " Commence by experience, and by means of this discover the reason." In many groups of phenomena we must still content ourselves with the recognition of empirical laws ; but the highest and more rarely attained aim of all natural in- quiry must ever be the discovery of their cauuil connection.^ The most satisfactory and distinct evidence w^ill always ap- pear where the laws of phenomena admit of being referred to miathematical principles of explanation. Physical cosmog- raphy constitutes merely in some of its parts a cosmology. The two expressions can not yet be regarded as identical. The great and solemn spirit that pervades the intellectual * Op. cit., vol. ii, p. 283. t In the lutioJuctory Observations, iu Cosmos, vol. i., p. 50, it should not have been generally stated that '' the ultimate object of the experi- mental sciences is to discover laws, and to trace their progressive gen- eralization." The clause " in many kinds of phenomena" should have been added. The caution with which I have expressed myself in the second volume of this work (p. 313), on the relation borne by Newton lo Kepler, can not, I think, leave a doubt that 1 clearly distinguish be t ween the discoveiy and iuterpretaiion of natural laws, i. e., the explana- tion of phenomena. I there said of Kepler: "The rich abundance of accurate observations furnished by Tycho Brahe, the zealous opponent of the Copernican system, laid the foundation for the discovery of those eternal laws of the planetary movements which prepared imperishable renown for the name of Kepler, and which, interpi'eted by Newton, and proved to be theoretically and necessarily true, have been transferred into the bright and glorious domain of thought, as the intellectual rcc' ognitioji of nature.''^ Of Newton I said (p. 351): "We close it [the , great epoch of Galileo, Kepler, Newton, and Leibnitz] with the figure of the earth as it was then recognized from theoretical conclusions. New ton was enabled to give an explanation of the system of the universe because he succeeded in discovering the force from whose action the laws of Kepler necessarily result." Compare on this subject (" On Laws end Causes") the admirable remarks in Sir John Herschel's address at the (ifteenth meeting of the British Association at Cambridge, 1845, ]i. xhi.; and Edlnb. Rev., yo\. 87, 1848, p. 180-183. INTRODUCTION. U labor, of wlach the limits are here defined, arises from tha Bublime consciousness of striving toward the infinite, and of grasping all that is revealed to us amid the boundless and inexhaustible fullness of creation, development, and bemg. This active striving, which has existed in all ages, must frequently, and under various forms, have deluded men into the idea that they had reached the goal, and discovered the principle which could explain all that is variable in the or- ganic world, and all the phenomena revealed to us by sen- suous perception. After men had for a long time, in accord- ance with the earliest ideas of the Hellenic people, vener- ated the agency of spirits, embodied in hiuTian forms,* in the creative, changing, and destructive processes of nature, the germ of a scientific contemplation developed itself in the physiological fancies of the Ionic school. The first principle of the origin of things, the first principle of all phenomena, was referred to two causesf — either to concrete material prin- ciples, the so-called element?, of Nature, or to processes of rarefaction and condensation, sometimes in accordance with mechanical, sometimes with dynamic views. The hypothe- sis of four or five materially difiering elements, which was probably of Indian origin, has continued, from the era of the didactic poem of Empedocles down to the most recent times, to imbue all opinions on natural philosophy — a primeval evi- dence and monument of the tendency of the human mind to seek a generalization and simplification of ideas, not only with reference to the forces, but also to the qualitative na- ture of matter. In the latter period of the development of the Ionic phys iology, Anaxagoras of Clazomena; advanced from the postu- late of simply dynamic forces of matter to the idea of a spirit independent of all matter, uniting and distributing the homo- geneous particles of which matter is composed. The world- arranging Intelligence {yov^^ controls the coniinuoudy jJro grossing formation of the world, and is the primary source * In the memorable passage {Metaph., xii., 8, p. 1074, Bekker) in which Aristotle speaks of " the relics of an earlier acquired and sabse« quently lost wisdom," he refers with extraordinary freedom and sig- nificance to the veneration of physical forces, and of gods in human Ibrms : "much," says he, "has been mythically added for the 'persua tion of the midtitvde, as also on account of the laws and for other useful ends." + Tlie important difference in these philosophical directions Tjoorroi, is clearly indicated in Arist., Phys. Auscult., 1, 4, p. 187, Bekk. (Coii> pare Brandis, in the Rhcin. Museum filr PhUologie, Juhrg. iii., g. 105.) 12 COSMOS. of all motion, and therefore of all physical phenomena. An- axagoras explains the apparent raiovement of the heavenly bodies frcm east to west by the assumption of a centrifugal force,* on the intermassion of which, as we have already ob- served, the fall of meteoric stones ensues. This hypothesis indicates the origin of those theories of rotatory motion wliich more than two thousand years afterward attained considera- ble cosmical importance from the labors of Descartes, Huy- gens, and Hooke. It would be foreign to the present work to discuss whether the world- arranging Intelligence of the philosopher of Clazomense indicates! the Godhead itself, or the mere pantheistic notion of a spiritual principle animating all nature. In striking contrast with these two divisions of the Ionic school is the mathematical symbolism of the Pjrthagoreans, which in like manner embraced the whole universe. Here, in the world of physical phenomena cognizable by the senses, the attention is solely directed to that which is normal in con- figuration (the five elementary forms), to the ideas of num- bers, measure, harmony, and contrarieties. Things are re- flected in numbers which are, as it were, an imitative repre- sentation {jufX7]0L^) of them. The boundless capacity for rep- etition, and the illimitability of numbers, is tj'pical of the character of eternity and of the infinitude of nature. The essence of things may be recognized in the form of numerical relations ; their alterations and metamorphoses as numerical combinations. Plato, in his Physics, attempted to refer the nature of all substances in the universe, and their difierent stages of metamorphosis, to corporeal forms, and these, again, to the simplest triangular plane figures 4 But in reference * Cosmos, vol. i., p. 133-135 (note), and vol. ii., p. 309, 310 (and note). Simplicius, in a remarkable passage, p. 491, most distinctly contrasts the centripetal with the centrifugal foi'ce. He there says, "■ The heavenly bodies do not fall in consequence of the centrifugal force being supei'ior to the inherent falling force of bodies and to their down- ward tendency." Hence Plutarch, in his work, De Facie in Orbs lAincc, p. 923, compares the moon, in consequence of its not falling to the earth, to "a stone in a sling." For the actual signification of the Kepix(^oriGi^ of Anaxagoras, compare Schaubach, in Anaxag. Clazom. Fragm., 1827, p. 107-109. t Schaubach, Op. cit., p. 151-156, and 185-189. Plants are likewiso Mid to be animated by the intelligence vovg ; Aristot., De Plant., i., p. 8 1 5, Bekk. X Compare on this portion of Plato's mathematical physics, B5ckh, Vn Platnnico Syst. Caslesiium Glohoriim, 1810 ct 1811; Martin, £^«i/p| tur le Tim^e, torn, ii., p. 234-242; and Brandis, in the Gesckichie det O I iichisch-Romischen Philosophie, th. ii., ablh. i., 1844, $ 375. INTRODUCTION. 13 to ultimate principles (the elements, as "it were, of the ele ments), Plato exclaims, with modest diffidence, " God alone, and those whom he loves among men, know what they are." Such a mathematical mode of treating physical phenomena, together with the development of the atomic tlieor}^ and the philosophy of measure and harmony, have long obstructed the development of the physical sciences, and misled fanciful in- quirers into devious tracks, as is shown in the histoiy of the physical contemplation of the universe. *' There dwells a captivating charm, celebrated by all antiquity, in the simple relations of time and space, as manifested in tones, numbers, and lines."* The idea of the harmonious government of the universe re- veals itself in a distinct and exalted tone throughout the writ- ings of Aristotle. All the phenomena of nature are depicted in the Pliysical Lectures (^Auscultationes PliysiccE) as mov- ing, vital agents of one general cosmical force. Heaven and nature (the telluric sphere of phenomena) depend upon the " unmoved motus of the universe."! The " ordainer" and the ultimate cause of all sensuous changes must be regarded as something non-sensuous and distinct from aU matter. $ Unity in the dilierent expressions of material force is raised to the rank of a main principle, and these expressions of force are themselves always reduced to motions. Thus we find already in " the book of the soul"§ the germ of the undulatory theory of light. The sensation of sight is occasioned by a vibration * Cosmos, vol. ii., p. 3ol, note. Compare also Gruppe, Ueber dit Fragmente des Arcliytas, 1840, s. 33. t Aristot.,Po/^■^,vii.,4,p. 13-26,audi^/e^fi'^A.,xii.,7,p. 1072, 10, Bekk.. and xii., 10, p. 1074-5. The pseudo-Aristoteliau work, De Mundo, which Osaiin ascribed to Chrysippus (see Cosmos, vol. ii., p. 28, 29), also contains (cap. 6, p. 397) a very eloquent passage on the world-or- derer and world-snstainer. X The proofs are collected in Eitter, History of Philosophy (Jiohn, 1838-46), vol. iii., p. 180, et seq. § Compare Aristot., De Anima, ii., 7, p. 419. lu this passage the analogy with sound is most distinctly expressed; although in other por- tions of his writings Ai-istotle has greatly modified his theory of vision. Thus, in De Insomniis, cap. 2, p. 459, Bekker, we find the following words: ''It is evident that sight is no less an active than a passive agent, and that vision not only expenences some action from the air (the medium), but itself also acts upon the medium." He adduces in evidence of the- truth of this proposition, that a new and very pure me- tallic mirror will, under certain conditions, when looked at by a woman, retain on its surface cloudy specks that can not be removed withoul difficulty. Compare also Martin, Etudes sur le Timie de Platan., torn ii. p, 159-.163. 14 COSiMOS. — a movement of the medium between the eye and tlio ohjeei Been — and not by emissions from the object or the eye. Hear- ing is compared with sight, as sound is hkewise a consequence of the vibration of the air. Aristotle, while he teaches men to investigate generalities in the particulars of perceptible unities by the force of reflect- ive reason, always includes the whole of nature, and the in- ternal connection not only of forces, but also of organic forms. In liis book on the parts (organs) of animals, he clearly in- timates his behef that throughout all animate beings there is a scale of gradation, in which they ascend from lower to high- er forms. Nature advances in an uninterrupted progressive course of development, from the inanimate or " elementary" to plants and animals; and, "lastly, to that which, though not actually an animal, is yet so nearly allied to one, that on the whole there is little diiference between them."^ In the transition of formations, "the gradations are almost imper- ceptible, "f The unity of nature was to the Stagirite the great problem of the Cosmos. " In this miity," he observes, with singular animation of expression, " there is nothing unconnect- ed or out of place, as in a bad tragedy.''^ The endeavor to reduce all the phenomena of the universe to one principle of explanation is manifest throughout the physical works of this profound philosopher and accurate ob- server of nature ; but the imperfect condition of science, and ignorance of the mode of conducting experiments, i. e., of calling forth phenomena under definite conditions, prevented the comprehension of the causal comiection of even small groups of physical processes. All things were reduced to the ever-recurring contrasts of heat and cold, moisture and dry- ness, primary density and rarefaction — even to an evolution of alterations in the organic world by a species of inner divis- ion (antiperistasis), which reminds us of the modern hypothesis of opposite polarities and the contrasts presented by + and — .' * Arlstot., De jyartihns Anim., lib. iv., cap. .5, p. 681, lin. 12, Bekker. t Aristot., Hist. Anim., lib. ix., cap. 1, p. 588, lin. 10-24, Bekker. When any of the representatives of the four elements in the animal kingdom on our globe fail, as, for instance, those which represent the element of the purest fire, the intermediate stages may perhaps be found to occur in the moon. (Biese, Die Phil, des Aristoteles, bd. ii., s. 18G.) It is singular enough that the Stagirite should seek in another planet Sh.jsQ intermediate links of the chain of organized beings which we find in the extiniit animal and vegetable forms of an earlier world. X Aristot., Mctaph., lib. xiii., cap. 3, p. 1090, lin. 20, Bekker. $ The uv::Trepi7TaGiQ of Aristotle plays an important part in nil hij IM'llODUCTION. 13 The so-called solutions of the problems only reproduce the same, facts in a disguised form, and the otherwise vigorous and concise style of the Stagirite degenerates in his explana- tions of meteorological or optical processes into a self-com- placent difluseness and a somewhat Hellenic verbosity. A3 Aristotle's inquiries were directed almost exclusively to 77io- tio7i, and seldom to differences in matter, we find the funda- mental ilea, that all telluric natural phenomena are to be ascribed to the impulse of the movement of the heavens — the rotation of the celestial sphere — constantly recurring, fondly cherished and fostered, =^ but never declared with ab- solute distinctness and certainty. The impulse to which I refer indicates only the communi- cation of motion as the cause of all terrestrial phenomena. Pantheistic views are excluded ; the Godhead is considered as the highest "ordering unity, ma,nifested in all parts of the universe, defining and determining the nature of all forma- tions, and holding together all thmgs as an absolute power.f The main idea and these teleological views are not applied to the subordinate processes of inorganic or elementary nature, but refer specially to the higher organizations^ of the animal and vegetable world. It is Vt'orthy of notice, that in these theories the Godhead is attended by a number of astral sjnrits, who (as if acquainted with perturbations and the dis- explanations of meteorological processes; so also in the works De Geii' eralione et Intcritn, lib. ii., cap. 3, p. 330; in the Meteorologicis, lib. i., cap. 12, and lib. iii., cap. 3, p. 372, and in the Prohlemce (lib. xiv., cap. 3, lib. viii., No. 9, p. 888, and lib. xiv., No. 3, p. 909), which are at all events based on Aristotelian pnnciples. In the ancient polarity hypoth esis, Kar avrLTzeiuaTaaiv, similar conditions attract each other, and dis similar ones (-j- and — ) repel each other iu opposite directions. (Com pare Ideler. Mctcorol. vctervm Grcec. et Rom., 1832, p. 10.) The op- posite conditions, instead of being destroyed by combining together, I'ather increase the tension. The ibvxpov increases the -Qepjiov ; as in- versely "in the formation of hail, the siuTounding heat makes the cold body 'still colder as the cloud sinks into warmer strata of air." Aristotle explains by his antlperistatic process and the polarity of heat, what modern physics have taught us to refer to conduction, radiation, evap- oration, and changes in the capacity of heat. See the able observations of Paul Ermau iu the Abhandl. der Berliner AJcademie avf das Jahr 182.5, 8. 128. * " By the movement of the heavenly sphere, all that is unstable in natural bodies, and all terrestrial phenomena are produced." — Aristot.^ Miisw., i., 2, p. 339, and De Gener. et Corrvpt., ii., 10, p. 33G. r Aristot., De Coslo, lib. i., c. 9. p. 279 ; hb. ii., c. 3, p. 28G ; lib. ii., c 13, p. 292, Bekker. (Compare Biese, bd. i., s. 3.52-1, 357.) \ Aristot, Phys. Aiiscult., lib. ii., c. 8, p. 199; De Avimn, lib. iii.. c 12, p. 434; De Animal. General., lib. v., c. 1, p 778. Bekker. IG COSxMOS. (ributioii of masses) maintain the planets in tiieir eternal Dib- its.'^ The stars here reveal the image of the divinity in the visible world. "VYe do not here refer, as its title might lead to suppose, to the little pseudo-Aristotelian work entitled the •* Cosmos," undoubtedly a Stoic production. Although it de- gcribes the heavens and the earth, and oceanic and aerial currents, with much truthfulness, and frequently with rhetor- ical animation and picturesque coloring, it shows no tenden- cy to refer cosmical phenomena to general physical princi- ples based on the properties of matter. I have purposely dwelt at length on the most brilliant pe - riod of the Cosmical views of antiquity, in order to contrast the earliest efforts made toward the generalization of ideas with the efforts of modern times. In the intellectual move- ment of centuries, whose influence on the extension of cos- mical contemplation has been defined in another portion of the present work,t the close of the thirteenth and the begin- ning of the fourteenth century were specially distinguished ; but the Opus Majus of Roger Bacon, the Mirror of Nature of Yincenzo de Beauvais, the Physical Geography [Liber Cos- mograpMcus) of Albertus Magnus, the Picture of the World {Imago Mimdi) of Cardinal Petrus d'Alliaco (Pierre d'Ailly), are works which, however powerfully they may have influ- enced the age in which they were wTitten, do not fulfill by their contents the promise of their titles. Among the Italian opponents of Aristotle's physics, Bernardino Telesio of Cosen- za is designated the founder of a rational science of nature. All the phenomena of inert matter are considered by him as the effects of two incorporeal principles (agencies or forces) — heat and cold. All forms of organic life — "animated" * See the passage in Aristot., Meteor., xii., 8, p. 1074, of which there is a remarkable elucidation in the Commentary of Alexander Aphro- iisiensis. The stars are not inanimate bodies, but must be regarded as active and living beings. (Aristot., De Coelo, lib. ii., cap. 12, p. 292.) They are the most divme of created things; ra -deioTepa tuv cpavspuv. (Aristot., De Ccelo, lib. i., cap. 9, p. 278, and lib. ii., cap. 1, p. 284.) In the small pseudo-Aristotelian work De Mundo, which frequently breathes a religious spirit in relation to the preserving almightiness of God (cap. 6, p. 400), the high a?ther is also called divine (cap. 2, p. 392). That which the imaginative Kepler calls moving spirits {animcE motri:e») in his work, Mystermm Cosmographicum (cap. 20, p. 71), is the distort- ed idea of a force (virtus) whose main seat is in the sun {a'n.ima mnn- di), and which is decreased by distance in accordance with the laws of light, and impels the planets in elliptic orbits. (Compai c Apelt, Epoch en der Gesch. dcr Mcnschheit, bd. i., s 274.) ♦ r.namcs, vol ii., p. 241-250. INTRODUCTION. 17 plants and animals — are the effect of these two ever- divided forces, of wliich the one, heat, specially appertains to the ce- lestial, and the other, cold, to the terrestrial sphere. With yet more unhridled fancy, but with a profound spin* of inquiry, Giordano Bruno of Nola attempted to comprehend the whole universe, in three Vv^orks,* entitled De la causa Principio e Uno ; Contemjjlationi circa lo Injinito, U?ii' verso e Mondi innumerahili ; and De JSlinimo et Maximo. In the natural philosophy of Telesio, a cotemporary of Co- pernicus, we recognize at all events the tendency to reduce ' the changes of matter to two of its fundamental forces, which, although " supposed to act from without," yet resemble the fundamental forces of attraction and repulsion in the dy- namic theory of nature of Boscovich and Kant. The cos- mic al views of the Philosopher of Xola are purely meta- physical, and do not seek the causes of sensuous phenomena in matter itself, but treat of "the infinity of space, filled with self - illumined worlds, of the animated condition of those worlds, and of the relations of the highest intelligence — God — to the universe." Scantily endowed with mathematical knowledge, Giorda- no Bruno continued nevertheless to the period of his fearful martyrdom! an enthusiastic admirer of Copernicus, Tycho Brahe, and Kepler. He was cotemporary with Galileo, but did not live to see the invention of the telescope by Hans Lippershey and Zacharias Jansen, and did not therefore wit- ness the discovery of the " lesser Jupiter world," the phases of Venus, and the nebula?. With bold confidence in what he terms the lume intenw, ragioiie naturale, altezza dell' intelletto (force of intellect), he indulged iii happy conjec- tures regarding the movement of the fixed stars, the planet * Compare the acute and learned commentary on the works of the Philosopher of Nola, in the treatise Jordano Bruno par Christian Bar- • tholmess, torn, ii., 1847, p. 129, 149, and 201. t He was burned at Rome on the 17th of February, IGOO. pursuant to the sentence " ut quam clementissime et citra sansuinis effusionem puniretur." Bruno was imprisoned six years in the Plomhi at Venice, and two years in the Inquisition at Rome. When the sentence of death was announced to him, Bruno, calm and unmoved, gave utterance to the following noble expression: " Majori forsitan cum timore sententi- am in me fertis quam ego accipiam." When a fugitive from Italy ia 1580, he taught at Geneva, Lyons, Toulouse, Paris, Oxford, Marburg, Wittenberg (which he calls the Athens of Germany), Prague, and Helm- stedt, where, in 1589, he completed the scientific instruction of Duke Henry Julius of Brunswick- Wolfenbiittel. — Bartholmess, torn . ' , p. 1G7- 178. He also taught at Padua subsequently to 1592. 18 COSMOS. ary nature of comets, and the deviation from the sphericai form observed in the figure of the earth. =^ Greek antiquity- is also replete with uranological presentiments of this na- ture, which were realized in later times. In the development of thought on cosmical relations, of v»diich the main forms and epochs have been already enu- merated, Kepler approached the nearest to a ma.thematical application of the theory of gravitation, more than seventy- eight years before the appearance of Newton's immortal work; Pi'incijna Pltilosojjliioi JS'atitralis. For while the eclectic Simplicius only expressed in general terms " that the heavenly bodies were sustained from falling in conse- quence of the centrifugal force being superior to the inher- ent falling force of bodies and to the downward traction ;" while Joannes Philoponus, a disciple of Ammonius Hermeas, ascribed the movement of the celestial bodies to " a primi- tive impulse, and the continued tendency to fall ;" and while, as we have already observed, Copernicus defined only the general idea of gravitation, as it acts in the sun, as the center of the planetary world, in the earth and in the moon, using these memorable words, " Gravitatem non aliud esse quam appetentiam quandam naturalem partibus inditam a divina providentia opificis universorum, ut in unitatem integrita- temque suam sese conferant, in formam globi coeuntes ;" Kepler, in his introduction to the book De Stella Martis,-f was the first who gave mimerical calculations of the forces of attraction reciprocally exercised upon each other, accord- ing to their relative masses, by the earth and moon. He * Bartliolmess, torn, ii., p. 219, 232, 370. Bruno carefully collected all tlie separate observations made on the celestial phenomenon of the sudden appearance, in 1572, of a new star in Cassiopeia. Much dis- cussion has been directed in modern times to the relation existing be- tween Bruno, his two Calabrian fellow-countrymen, Bernardino Tele- sio and Thomas Oampanella, and the platonic cardinal, Nicolaus Krebs of Cusa. See Cosmos, vol. ii., p. 310, 311, note. t " Si duo lapides in aliquo loco Mundi collocai'entur propinqiii in- vicem, extra orbem virtutis tertii coguati corporis ; illi lapides ad simil- itudinem duorum Magneticorum corporum coirent loco intermedio, qui- libet accedens ad alterum tanto intervallo, quanta est alterius moles in comparatione. Si luna et terra non retinerentur vi aniraali (!) aut alia iliqua Eequipollente, qufelibet in suo circuitu, Terra adscenderet ad Lu- uam quinquagesima quarta parte intervalli, Luna descenderet ad Ter- ram quinquaginta tribus circiter partibus intervalli; ibi jungerentur, posito tamen quod substantia ntri usque sit unius et ejusdem densitatis." —Kepler, Astronomianova, sen Physica ccclestis de Motibus Stellce Mar* tis, 1G09. Introd., fol. v. On the older views regarding gravitation, see Cosmos, vrl. ii., p. 310. INTRODUCTION. IS distinctly adduces tlie tides as evidence^ that the attract; vfr Ibrce of the moon {virtus tractoria) extends to the earth ; and that this force, similar to that exerted by the magnet on iron, would deprive the earth of its water ii the formes should cease to attract it. Unfortunately, this great mai? was induced, ten years afterward, in 1619, prohahly from deference to Galileo, who ascribed the ebb and flow of the ocean to the rotation of the earth, to renounce his correct explanation, and depict the earth in the Harmonice Munch as a living monster, whose whale-like mode of breathing oc- casioned the rise and fall of the ocean in recurring periods of sleeping and waking, dependent on solar time. "VVlien we remember the mathematical acumen that pervades one of the works of Kepler, and of v/hich Laplace has already made honorable mention,! it is to be lamented that the discoverer of the three great laws of all planetary niotion should not have advanced on the path whither he had been led by his views on the attraction of the masses of cosmical bodies. Descartes, who was endowed with greater versatility of physical knowledge than Kepler, and who laid the founda- tion of many departments of mathematical physics, under- took to comprise the whole world of phenomena, the heav- * " Si Terra cessaret attraliere ad se aquas suas, aquae manna? oranes elevareiitur et in corpus Luna? influerent. Orbis virtutis tractorise, qure est in Luna, porrigitur usque act terras, et prolectat aquas quacunque pi verticem loci incidit sub Zonam torridam, quippe in occursura suura quacunque in verticem loci incidit, insensibiliter in maribus inclusis, sensibiliter ibi ubi sunt latissimi alvei Oceani propinqui, aquisque spa- ciosa reciprocationis libertas." (Kepler, 1. c.) " Undas a Luna trahi 7it ferrum a Magnete." .... Kepleri Harmonice Mundi, libri quinque, 1G19, lib. iv., cap. 7 , p. 162. The same work which presents us with so many admirable views, among others, with the data of the establisb inent of the third la^o (that the squares of the periodic times of two planets are as the cubes of their mean distance), is distorted by the wildest flights of fancy on the respiration, nutrition, and heat of tho earth-animal, on the soul, memory {memoria animcB Terrcc), and crea« tive imagination {animce Telluns imaginatio) of this monster. This great rian was so wedded to these chimeras, that he warmly contested his right of priority in the views regarding the earth-animal with the mys- tic author of the Macrocosmos, Robert Fludd, of Oxford, who is report- ed to have participated in the invention of the thermometer. {Harm. Mnndi, p. 252.) In Kepler's writings, the attraction of masses is often confounded with magnetic attraction. " Corpus solis esse magneticum. Virtutem, quae Planetas movet, residere in corpore eolis." — Stella Mar- its, pars iii., cap. 32, 34. To each planet was ascrired a mcgnetic axig^ which constantly pointed to one and tlie same quivvter of the heavens f Apelt, Jok. Kfple/s Astron. IVeltansicht, 1849, s. 73. t Compare Cosmos vol. ii., p. 327 (and note 20 COS3I03. eiily sphere and all that he loiew coiicernmg the ammate and inanimate parts of terrestrial nature, in a work entitled Traite dii Mo7ide, and also Summa PhilosGijliice. The or- ganization of animals, and especially that of man — -a subject to which he devoted the anatomical studies of eleven years^ —was to conclude the work. In his correspondence with Father Merseune, we frequently find him complaining of his glow progress, and of the difficulty of arranging so large a [mass of materials. The Cosinos which Descartes always called " his world'' (son monde) was at length to have been sent to press at the close of the year 1633, when the report of the sentence passed by the Inquisition at Rome on Gali- leo, which was first made generally known four months aft- erward, in October, 1633, by Gassendi and Bouillaud, at once put a stop to his plans, and deprived posterity of a great work, completed with much pains and infinite care. The motives that restrained him from publishing the Cosmos were, love of peaceful retirement in his secluded abode at De venter, and a pious desire not to treat irreverentially the decrees pronounced by the Holy Chair against the planetary movement of the earth. f In 1664, fourteen years after the death of the philosopher, some fragments were first printed under the singular title of Le Mo?tde, ou Traite de la Lu- miere.''t The three chapters which treat of light scarcely, however, constitute a fourth part of the work ; while those sections which originally belonged to the Cosmos of Des- cartes, and treated of the movement of the planets, and their distance from the sun, of terrestrial magnetism, the ebb and flow of the ocean, earthquakes, and volcanoes, have been transposed to the third and fourth portions of the celebrated work, Principes de la PJdlosophie. Notwithstanding its ambitious title, the Ccsmotlicoros of Huygens, which did not appear till after his death, scarcely deserves to be noticed in this enumeration of cosmological efibrts. It consists of the dreams and fancies of a great man on the animal and vegetable worlds, of the most remote cos- raical bodies, and especially of the modifications of form which * See La Vie de M. Descartes (par Baillet), 1691, Part i., p. 10?, End CEuvres de Descartes, publiees par Victor Cousin, torn, i., 1824, p. 101. t Lzttres de Descartes au P. Mersenne, du 19 Nov., 1G33, et du 5 Jan* vier, 1G34. . (Baillet, Fart i., p. 244-247.) X The Latin translation bears the title Mundus sive Dissertaiio de Litmiyie ut ct de aliis Sensmim Ohjectis primariis. See Descartes, Oj.'tiS' ttula posllmma Physica et Mathematlca, Arast., 1704. INTUODUCTION. 21 the liurnaii race may there present. The reader might sup pose he were peiiismg Kepler's Somniuon Astronojnicum, oi Kircher's Iter Extaticus. As Ilnygens, hke the astronomers of our own day, denied the presence of air and water in the moon,*' he is much more embarrassed regarding the exist- ence of mhahitants in the moon than of those in the remoter pLanets, which he assumes to he " surrounded with vapors and clouds." The immortal author of the Pliilosophice Is'aturalis Prin- cipia Matliematica (Newton) succeeded in embracing the whole uranological portion of the Cosmos in the causal con- nection of its phenomena, by the assumption of one all-con- trolling fundamental moving force. He first applied phys- ical astronomy to solve a great problem in mechanics, and elevated it to the rank of a mathematical science. The quantity of matter in every celestial body gives the amount of its attracting force ; a force wdiich acts in an inverse ra- tio to the square of the distance, and determines the amount of the disturbances, which not only the planets, but all the bodies in celestial space, exercise on each other. But the Newtonian theory of gravitation, so worthy of our admira- tion from its simxplicity and generality, is not limited in its cosmical application to the uranological sphere, but com prises also telluric phenomena, in directions not yet fully investigated ; it affords the clew to the periodic movements in the ocean and the atmosphere,! and solves the problems of capillarity, of endosmosis, and of many chemical, elec- * " Lunam aqiiis carei'e et a6re : IManum similitudinem ia Luna nul- 1am reperio. Nam regiones planas qucB montosis multo obscuriores sunt, quasque vulgo pro maribus haberi video et oceanoiizra nomiuibna insiguiri, iu his ipsis, longiore telescopio iuspectis, cavitates exiguas iii- esse comperio rotundas, umbris intus cadentibus ; quod maris siipei-fi- ciei convenire nequit; turn ipsi campi illi latiores nou prorsus a^quabi- lem superficiem prsferuut, cum diligeutius eas intuemur. Quod circa maria esse non possuut, sed materia constare debent minus candicante, quam qua? est partibus asperioribus in quibus rursus qua^dam viridiori liimine caeteras prgecellunt." — Hugenii Cosynotkeoros, ed. alt. 1699, lib. xi , p. 114. Huygens conjectures, however, that Jupiter is agitated by much wind and rain, for " ventorum flatus ex ilia nubium Jovialiura miitabili facie cognoscitur" (lib. i., p. G9). These dreams of Huygens regarding the inhabitants of remote planets, so unworthy of a man versed iu exact mathematics, have, unfortunately, been revived by Emanuel Kant, iu his admirable -work Jllgemeine Naturgeschichte und Theorii det Himmels, l755 (s. 173-192). t See Laplace {des Oscillations de V Atmoiplicre, dn jinx Solaira et Lnnaire) iu the Mecaniqve Celeste, livrt; iv., and iu the Exposition, dn a.yU. dn Monde, 1S24, p. '.391-29o. 22 C0SM0?5. tio-inagiietic, and organic processes. Newton^ even distin.' guished tlie attraction of tiuisses, as manifested in the mo- tion of CGsmical bodies and in the phenomena of the tides, from tnolecular attraction, which acts at infinitely small distances and in the closest contact. Thus we see that among the various attempts which have been made to refer whatever is unstable in the sensuous world to a single fundamental principle, the theory of grav- itation is the most comprehensive and the richest in cosmic- a.1 results. It is indeed true, that notwithstanding the brill- iant progress that has been made in recent times in stoBchi- ometry (the art of calculating with chemical elements and in the relations of volume of mixed gases), all the physical theories of matter have not yet been referred to mathematic- ally-determinable principles of explanation. Empirical laws have been recognized, and by means of the extensively- dif- fused views of the atomic or corpuscular philosophy, many points haA'e been rendered more accessible to mathematical investigation ; but, owing to the unbounded heterogeneous- ness of mattei and the manifold conditions of aggregation of particles, the proofs of these empirical laws can not as yet by any means be developed from the theory of contact-at- traction with that certainty which characterizes the estab- lishment of Kepler's three great empirical laws derived from the theory of the attraction of masses or gravitation. At the time, however, that Newton recognized all move- ments of the cosmical bodies to be the results of one and the same force, he did not, like Kant, regard gravitation as an essential property of bodies,! but considered it either as the * Adjicere jam licet de spirita quodam subtilissimo corpora crassa pervadente et in iisdem lateiite, cujus vi et actionibus particular corpo- rum ad mitumas distanlias se mutuo altrahunt et coutiguoe facta colue- rent. — Newton, Prlncipla Phil. Nat. (ed. Le Sueur et Jacquier, 1760), Scliol. gen., t. iii., p. G7G; compare also Newton's Optics (ed. 1718), Query 31, p. 305, 333, 3G7, 372. (Laplace, Syst. du Monde, p. 384, and Cosmos, vol. i., p. 63 (note).) t Hactenus ph<'jenomena coslonim et maris nostri per vim gravitatia exposui, sed. causam gravitatis nondum assigiiavi. Oritur iitique lueo vis a causa aiiqua, qu^e penetrat ad usque centra solis et planetaiiim, sine virtutis diminutione ; quarque agit non pro quantitate superficieruiu particalarum, in quas agit (ut solent causte mechanicae), sed pro quanti- tate materise solida). — Rationem liarum gravitatis proprietatum ex pha> nomenis nondum potui deducere et hypotheses non fingo. Satis est quod gravitas revera existat et agat secundnm leges a nobis expositas. -—Newton, Principia Phil. Nat., p. C7G. "To tell us that every spe. cies of things is endowed wilt an occult speciiic quality, by which it acts and produces manifest effects is to tell us nothing; but to de)i\e INTRODUCTION. 23 result of Eome higher and still unknown power, or of =' the centrifugal force of the aether, which fills the realms of space, and is rarer within bodies, but increases in density outward. The latter view is set forth in detail in a letter to Robert Boyle* (dated February 28, 1678), which ends with the words, " I seek the cause of gravity in the sether." Eight years afterward, as we learn from a letter he wrote to Hal ley, Newton entirely relmquished this hypothesis of the rarer and denser SBther.f It is especially worthy of notice, that in 1717, nine years before his death, he should have deemed it necessary expressly to state, in the short preface to the sec- ond edition of his Optics, that he did not by any means con- sider gravity as an "essential property of bodies ;"$ while I wo or tln-ee general principles of motion from phenomena, and after- ward to tell us how the propertied and actions of all corporeal things follow from those manifest principles, would be a very great step in phi- losophy, though the causes of those principles were not yet discovered ; and therefore I scruple not to propose the principles of motion, and leave their causes to be found out." — Newton's Optics, p. 377. In a previ- ous portion of the same work, at query 31, p. 351, he writes as follows : " Bodies act one upon another by the attraction of gravity, magnetism, and electricity; and it is not improbable that there may be more at- tractive powers than these. How these attractions may be performed I do not here consider. What I call attraction may be performed by impulse, or by some other means unknown to me. I use tliat word here to signify only in general any force by which bodies tend toward one another, whatsoever be the cause." * " I suppose the rarer sether within bodies, and the denser without them." — Operiim Neictoni, tomus iv. (ed. 1782, Sara. Horsley), p. 386. The above observation was made in reference to the explanation of the discoveiy made by Grimaldi of the diffraction or inflection of light. At the close of Newton's letter to Robert Boyle, February, 1678, p. 94, ho Bays: ''I shall set down one conjecture more which came into my mind: it is about the cause of gravity. . . ." His correspondence with Olden- burg (December, 1675) shows that the great philosopher was not at that time averse to the '' a?ther hypotheses." According to these views, the impulse of material light causes the sather to vibrate ; but the vibra- tions of the eether alone, which Kas some alHnity to a nervous fluid, does not generate light. In reference to the contest with Hooke, consult Horsley, t. iv., p. 378-380. t See Brewster's Life of Sir Isaac Neivfon, p. 303-305. t Newton's words "not to take gravity for an essential property cf bodies" in the " Second Advertisement" contrast with his remarks on the forces of attraction and reoulsion, which he ascribes to all molecu- lar particles, in order, according to the theory of emission, to explain the phenomena of the refraction and repulsion of the rays of light from reflecting surfaces "wnthout their actual contact." (Nev/ton, Optie$, book ii., prop. 8, p. 241, and Brewster, Op. cit., p. 301.) According to Kant (see Die MetapliysiscTien Anfangsgriinde der Naturwissenschafty 1800, s. 28), we can not conceive the existence of matter without these fomea of attraction and repulsion. All physical phcuumena arc thcro 24 c<)SMos. Gilbeit, as early as 1600, regarded magnetism as a ibrcft in* herent in all matter. So midetermined was even Kewtoii, the profound and experienced thinker, regarding the " ulti- mate mechanical cause" of all motion. It is indeed a brilliant effort, worthy of the human mini, lo comprise, in one organic v/hole, the entire science of na* ture from the laws of gravity to the formative impulse (ni- sus formativus) in animated bodies ; but the present imper- fect state of many branches of physical science offers innu- merable difficulties to the solution of such a problem. The imperfectibility of all empirical science, and the boundless- ness of the sphere of observation, render the task of explain- ing the forces of matter by that which is variable in matter, an impracticable one. "VYhat has been already perceived by no means exhausts that which is perceptible. If, simply re- ferring to the progress of science in modern times, we com- pare the imperfect physical knowledge of Gilbert, Robert Boyle, and Hales, with that of the present day, and remem- ber that every few years are characterized by an increasing rkpidity of advance, we shall be better able to imagine the periodical and endless changes wliich all physical sciences are destined to undergo. Kew substances and new forces will be discovered. Although many physical processes, as those of light, heat, and electro-magnetism, have been rendered accessible to a mathematical investigation by being reduced to motion or vi brations, we are still without a solution to those often mooted and perhaps insolvable problems : the cause of chemical dif- ferences of matter ; the apparently irregular distribution of the planets in reference to their size, density, the inclination cf their axes, the eccentricity of their orbits, and the num- fore I'educed by liim, as previously by Goodwin Knight {Philos. Tran^ act. 1748, p. 264), to the conflict of two elementary forces. In the at- omic theories, which were diametrically opposed to Kant's dynamic views, the force of attraction was referred, in accordance with a view specially promulgated by Lavoisier, to the discrete solid elementary molecules of which all bodies are supposed to consist; while the force of repulsion was attributed to the atmospheres of heat surrounding all elementary corpuscles. This hypothesis, which regards the so-called saloric as a constantly expanded matter, assumes the existence of two elemeutaxy substances, as in the mythical idea of two kinds of &ilier. (Newton, Gpiics, qiiery 28, p. 339.) Here the question arises, What causes this caloric matter to expand? Considerations on the density of molecules in comparison with that of their aggregates (the entiro body) lead, according to atomic hypotheses, to the result, that the dis- tance between elementary corpuscles is far greater than their diunetera INTRODUCTION. 25 Der and distaiiGe of their satellites ; the configuration of con- tinents, and the position of their highest mountain chains. Those relations in space, which we have referred to meiely by way of illustration, can at present be regarded only ag something existing in nature, as a fact, but which I can not designate as merely causal, because their causes and mutual connection have not yet been discovered. They are the re- sult of occurrences in the realms of space coeval with tlie formation of our planetary system, and of geognostic process- es in the upheaval of the outer strata of the earth into con- tinents and mountain chains. Our knowledge of the prime- val ages of the world's physical histor}?- does not extend suf- ficiently far to allow of our depicting the present condition of things as one of development.* Wherever the causal connection between phenomena has not yet been fully recognized, the doctrine of the Cosmos, or the physical description of the universe, does not constitute a distinct branch of physical science. It rather embraces the whole domain of nature, the phenomiena of both the celestial and terrestrial spheres, but embraces it only under the single point of view of efforts made toward the knowledge of the universe as a whole."! As, in the " exposition of past events in the moral and political world, the historian| can only di- vine the plan of the government of the v/orld, according to human views, through the signs which are presented to him, and not by direct insight," so also the inquirer into nature, in his investigation of cosmical relations, feels himself pene- trated by a profound consciousness that the fruits hitherto yielded by direct observation and by the careful analysis of phenomena are far from having exhausted the number of impelling, producing, and formative forces. * Cosmos, vol. i., p. 94-97. t Op. ciL, p. 55-62. t Wilhelm von Humboldt, Gesa-nmeUe Werke, bd. i., s. 23. Vol. Ill— R RESULTS OF OBSERVATIONS IN TUB URANOLOGICAL TOE. TION OF THE PHYSICAL DESCRIPTION OF THE WORLD. "We again commence with the depths of cosmical spact, and the remote sporadic starry systems, which appear to tel- escopic vision as faintly shining nchulce. From these we gradually descend to the double stars, revolving round one common center of gravity, and which are frequently bicol- ored, to the nearer starry strata, one of which appears to in- close our own planetary system ; passing thence to the air- and-ocean-girt terrestrial spheroid which we inhabit. We have already indicated, in the introduction to the General Delineation of Nature j^^ that this arrangement of ideas is alone suited to the character of a work on the Cosmos, since v/e can not here, in accordance with the requirements of di- rect sensuous contemplation, begin with our own terrestrial abode, whose surface is animated by organic forces, and pass from the apparent to the true movements of cosmical bodies. The uraiiological, when opposed to the telluric domain of the Cosmos, may be conveniently separated into two di- visions, one of which comprises astt'OgJiosij, or the region of i\\Q fixed stars, and the other our solar and 'planetary sys- tern. It is unnecessary here to describe the imperfect and unsatisfactory nature of such a nomenclature and such class- ifications. Names were introduced into the physical sci- ences before the differences of objects and their strict limita- tions were sufficiently known. f The most important point, however, is the connection of ideas, and the order in which the objects are to be considered. Innovations in the no- menclature of groups, and a deviation from the meaningi liitherto attached to well-known names, only tend to dis- tract and confuse the mind. a. ASTROGNOSY. (The Domain of the Fixed Stars.) Nothing is stationary in space. Even the fixed stars move, as Halleyl endeavored to show in reference to Sirius, • Cosmos, voL i., p. 79-83. f Op. cit., p. 56, 57 X Ilalley, in the P/t/7(7i. Transacl. for \7\7 . \o^ xxx. p. 736. AS'xROGNOSY. 2*7 A.rcturus, and Aldebaran, and as in modern times has been incontrovertibly proved with respect to many others. The bright star Arcturus has, during the 2100 years (since the times of Aristi'lus and Hipparchus) that it has been ob' €erved, changed its position in relation to the neighboring fainter stars 2^ times the moon's diameter. Encke remarks ' that the star fj, Cassiopeise appears to have moved 3i lunar diameters, and 61 Cygni about 6 lunar diameters, if the an- cient observations correctly indicated its position." Conclu- sions based on analogy justify us in behoving that there is every where progressive, and perhaps also rotatory motion. The term " fixed star.s" leads to erroneous preconceptions ; it may have referred, in its earliest meaning among the Greeks, to the idea of the stars being riveted into the crys- tal vault of heaven ; or, subsequently, in accordance with the Roman interpretation, it may indicate iixity or immo- bility. The one idea involuntarily led to the other. In Gre- cian antiquity, in an age at least as remote as that of Anax- imenes of the Ionic school, or of Alcma^on the Pythagorean, all stars were divided into tcojidering [dorpa nXavcJueva or 7i?.avr}Td) and no?i-u'a?ideri72g fixed stars (dizXavelg darspsg or dnXavTi dor pa). '^^ Besides this generally adopted desig- nation of the fixed stars, which Macrobius, in his Sormiium Scijnofiis, Latinized by Sjjhcsra aplanes,\ we frequently meet in Aristotle (as if he wished to introduce a new tech- nical term) with the phrase riveted stars, evdF.defitva dorpa, instead of d~/^avTj,X as a designation for fixed stars. From this form of speech arose the expressions of sidcra infixa t,(Llo of Cicero, Stellas quas 'putamus afixas of Pliny, and as* • Pseudo-Plut., De plac. Philos., ii., 15, 16 ; Stob., Edog. Phys , p 082 ; Plato, in the Tlmceus, p. 40. t Macrob., Sonm. Scip., i., 9-10 ; siellcs. inerrantes, iu Cicero, De AuV. Deorum, 'iu., 20. X The principal passage in wliicb we meet with the technical expres fiitm kv6t6EH£va uarpa, is in Aristot., De CorJo, ii., 8, p. 289, 1. 34, p. 290, 1. 19, Bekker. This altered nonicnclatare forcibly attracted my atten- tion in my investigations into the optics of Ptolemy, and his experi- ments on refraction. Professor Franz, to w^hose philological acquire- ments I am indebted for frequent aid, reminds me that Ptolemy {Syn- tax, vii., 1) speaks of the fixed stai's as aSxed or riveted; uairep Trpo- Grre<^VK6Teg. Ptolemy thus objects to the expression cdalpa un}.avfiQ {orbis inerrans) ; " in as far as the stars constantly preserve their rela live distances, they might rightly be termed dizT^avelq', but in as far as^ the sphei'e in which they complete their course, and in which they seem to have grown, as it were, has an independent motion, the designatioij c^AQt7/f is inappi'opriate if applit-d^to the sphere." V}8 COSMOS. * tra jijtxL of Manilius, which corresponds with our term fixed 6tars> This idea of fixity leads to the secondary idea of immobiHty, of persistence in one spot, and thus the original signification of the expressions injixum or ajjixum sidus waa gradually lost sight of in the Latin translations of the Mid- dle Ages, and the idea of immohihty alone retained. This is already apparent in a highly rhetorical passage of Seneca, regarding the possibility of discovering new planets, in which he says (JXcit. Quccst., vii., 24), " Credis autem in hoc max- imo et pulcherrimo corpore inter innumerabiles stcllas, qua? nocteiTi decore vario distinguunt, qua3 aera minime vacuum et mertem esse patiuntur, quinque solas esse, quibus exer- cere se liceat ; ceteras stare Jixuni ct iimnohilcm 'po'puliunV' "And dost thou believe that in this so great and splendid body, among innumerable stars, which by their various beau- ty adorn the night, not sufiering the air to remain void and unprofitable, that there should be only five stars to whom it is permitted to be in motion, while all the rest remain a fixed and immovable multitude ?" This fixed and immovable mul* titude is nowhere to be found. In order the better to classify the main results of actual observations, and the conclusions or conjectures to which they give rise, in the descrij)tion of the universe, I will sep- arate the astrognostic sphere into the following sections : I. The considerations on the realms of space aiid the bodies by which they appear to be filled. II. Natural and telescopic vision, the scintillation of the stars, the velocity of light, and the photometric experiments on the intensity of stellar light. III. The number, distribution, and color of the stars ; the stellar swarms, and the Milky Way, which is interspersed with a few nebulse. lY. The newly-appeared and periodically-changing stars, and those that have disappeared. V. The proper motion of the fixed stars ; the problematij3al existence of dark cosmical bodies ; the parallax and meas- ured distance of some of the fixed stars. VI . The double stars, and the period of their revolution round a common center of gravity. VII. The nebulse which are interspersed in the Magellania clouds with numerous stellar mass(js, the black spots (coal lags) in the vault of heaven. • Cicei o, X>eiVa^ /Vorvr •, i. J3 ; Pliii., ii. 6 and 21 ; Mauillas, ii., 35 THE REALMS OF SPACE, AND CONJECTURES REG \RDING THAT WHICH APPEARS TO OCCUPY THE SPACE INTERVENING BETWEEN TIIK HEAVENLY BODIES. That portion of the physical description of the universe which treats of what occupies the distant regions of the heavens, filling the space between the globular cosmical bodies, and is imperceptible to our organs, may not unaptly be compared to the mythical commencement of ancient his- tory. In infinity of space as well as in eternity of time, all things are shrouded in an uncertain and frequently deceptive twilight. The imagination is here doubly impelled to draw from its owii fullness, and to give outline and permanence to 4iese indefinite changing forms. =^ This observation will, I trust, safiice to exonerate me from the reproach of confound- ing that which has been reduced to mathematical certainty by direct observation or measurement, with that which is founded on very imperfect induction. Wild reveries belong to the romance of physical astronomy ; yet the mind famil- iar with scientific labors dehghts in dwelling on subjects such as these, which, intimately connected with the present condition of science, and with the hopes which it inspires, have not been deemed unworthy of the earnest attention of the most distinguished astronomers of our day. By the influence of gravitation, or general gravity, as well as by light and radiating heat,t we are brought in contact, as we may with great probability assume, not only with our own Sun, but also with all the other luminous suns of the firma- ment. The important discovery of the appreciable resist- ance which a fluid filling the realms of space is capable of opposing to a comet having a period of revolution of five years, has been perfectly confirmed by the exact accordance of numerical relations. Conclusions based upon analogies may fill up a portion of the vast chasm which separates the certain results of a mathematical natural philosophy from conjectures verging on the extreme, and therefore obscure and barren confines of all scientific development of mind. From the infinity of space — an infinity, however, doubted * Cosmos, vol. i.. p. 87. (Compare the admirable observations of Eacke, Ueber die Aiiordnung des SternsyRtcms, 1844, s. 7.) f Cosmos, vol. 1., p. 154, 155. 30 COSMOS. by Aristotle^— IjIIows the idea of its iiDmcAsui ability , Sep- arate portions only have been rendered accessible to meas- urement, and the numerical results, which far exceed the grasp of our comprehension, become a source of mere puerile gratification to those who delight in high numbers, and im- agine that the sublimity of astronomical studies may be heightened by astounding and terrific images of physical mag- nitude. The distance of CI Cygni from the Sun is 657,000 semi-diameters of the Earth's orbit ; a distance which light takes rather more than ten years to traverse, v/hile it passes from the ^un to the Earth in 8' 17"-78. Sir John Herschel conjectures, from his ingenious combination of photometric calculations,! that if the stars in the great circle of the Milky Way which he saw in the field of his twenty-feet telescope were newly-arisen luminous cosmical bodies, they would have required 2000 years to transmit to us the first ray of light All attempts to present such numerical relations fail, either from the immensity of the unit by which they must be meas- ured, or from the high number yielded by the repetition of this unit. Bessel$ very truly observes that " the distance which light traverses in a year is not more appreciable to us than the distance which it traverses in ten years. There- fore every endeavor must fail to convey to the mind any idea of a magnitude exceeding those that are accessible on the earth." This overpowering force of numbers is as clear- ly m^anifested in the smallest organisms of animal life as in the milky way of those self-luminous suns which we call iixed stars, ^^liat masses of Polythalami;c are inclosed, ac- cording to Ehrenberg, in one thin stratum of chalk ! This eminent investigator of nature asserts that one cubic inch of the Bilin polishing slate, which constitutes a sort of mount ain cap forty feet in height, contains 41,000 millions of tin* microscopic Galioiiella clistans ; while the same volume con- tains more than 1 billion 750,000 millions of distinct indi- viduals of Galionclla fcrniginca.k Such estimates remind as of the treatise named Arcnarius {^aitalT7]g) of Archime- des— of the sand-grains which might fill the universe of space I If the starry heavens, by incalculable numbers, laagnitude, space, duration, and length of periods, impresa * Avistot., De Coelo, 1, 7. p. 276, Bekker. t Sir John Herschel, Outlines of Astronomy, IStf), § 803, p. 541. X Bessel, ill Schumacher's Jahrbuch fur 1839, s. .'30. § p:hrenberg, Ahhandl. der Berl. Akad., 1838, s. 50; also in hie Infu- ttonsthicre, s. 170. IHE PROPAGATION OF LIGHT. 31 man with the conviction of his own insignificance, his phy^" ical weakness, and the ephemeral nature of his existence ; he is, on the other hand, cheered and invigorated by tha consciousness of having been enabled, by the application and development of intellect, to investigate very many important points in reference to the laws of Nature and the sidereal arrangement of the universe. Although not only the propagation of light, but also a special form of its diminished intensity, the resisting medium acting on the periods of revolution of Encke's comet, and the evapoiation of many of the large tails of comets, seem to prove that the regions of space which separate cosmical bod- ies arenot void,^ but filled with some kind of matter ; we must not omit to draw attention to the fact that, among the now current but indefinite expressions of 'Hhe air of lieav- 672," " cosmical (non-luminous) niatter^^ and " ether,'" the latter, which has been transmitted to us from the earliest an- tiquity of Southern and AVestern Asia, has not always ex- pressed the same idea. Among the natural philosophers of India, ether {cbkcisa) was regarded as belonging to the pant- scliata, or five elements, and was supposed to be a fluid of infinite subtlety, pervading the whole universe, and constitu ting the medium of exciting life as Avell as of propagating sound, t Etymologic ally considered, aka'sa signifies, accord- ing to Bopp, " luminous or shining, and bears, therefore, in its fundamental signification, the same relation to the ' ether' of the Greeks as slmiinn: does to burning." In the dogmas of the Ionic philosophy of Anaxagoras and Empedocles, this ether [aldfjp) differed wholly from the act- ual (denser) vapor-charged air {drjp) which surrounds the * Aristotle {Pliys. Auscult., iv., G-10, p. 213-217, Bekker) proves, in opposition to Leucippus aud Democritus, that there is no unjllled space — no vacuum in the universe. t Aka'sa signifies, according to Wilson's Sanscrit Dictionaiy, " the Bubtle and ethereal fluid supposed to fill and pervade the universe, and to be the peculiar vehicle of life and sound." "The word aka'sa (lu- minous, shining) is derived from the root ka's (to shine), to which is added the preposition a. The quintuple of all the elements is called pantschatd, or pantschatra, aud the dead are, eingularly enough, desig- aated as those who have been resolved into the five elements {prdpta pantschatra). Such is the interpretation given in the text of Amara- Koscha, Amarasinha's Dictionary." — (Bopp.) Colebrooke's admirable treatise on the Sdnkhya Philosophy treats of these five elements ; see Transact, of the Asiat. Soc, vol. i., Lond., 1827, p. .31. Strabo refers, according to Megasthenes (xv., § 59, p. 713, Cas.), to the ali-formiuf| fifth element of the Indians, without, however, naming it. 32 COSMOS. earth, and '*' probabl)* extends as far as the moon." It wai of " a fiery nature, a brightly-beaming, pure fire-air,=^ of great subtlety and eternal serenity." This definition perfectly co- incides with its etymological derivation from aWetv, to burn, for which Plato and Aristotle, from a predilection for me- chanical views, singularly enough substituted another {del- Oelv), on account of the constancy of the revolving and rota- tory movement. t The idea of the subtlety and tenuity of the upper ether does not appear to have resulted from a knowledge that the air on mountains is purer and less charged with the heavy vapors of the earth, or that the dens- ity of the strata of air decreases with their increased height. In as far as the elements of the ancients refer less to mate- rial differences of bodies, or even to their simple nature (their incapacity of being decomposed), than to mere conditions of matter, the idea of the upper ether (the fiery air of heaven) has originated in the primary and normal contraries of heavy and light, lower and uj}per, earth and fire. These extremes * Empedocles, v. 216, calls the ether rrafxipavouv, brightly-beamiug, and therefore selt-lumiiious. t Plato, Cratyl., 410 B., where we meet with the expression deLde^fj. Aristot., i>e Casio, 1, 3, p. 270, Bekk., says, in opposition to Anaxagoras: aWepa Trpoauvofiaoav rbv avurarci tokov, utto tov ^eIv ueI tov dldiov ^povov -d^ifievoc ttjv enuvvfilav avru. 'Ava^ayopac di KaraKEXp^jraL tu ov6/j.aTC Tovr(i) ov /coAwj- • bvofiu^et yap alOipa uvtl Tzvpog. We find thia more circumstantially referred to in Anstot., Meteor., 1, 3, p. 339, lines 21-34, Bekk.: " The so-called ether has an ancient designation, which Anaxagoras seems to identify with fire ; for, according to him, the up- per region is full of fire, and to be considered as ether ; in which, in- deed, he is correct. For the ancients appear to have regarded the body which is in a constant state of movement, as possessing a divine natjare, and therefore called it ether, a substance with which we have nothing analogous. Those, however, who hold the space surrounding bodies to be fire no less than the bodies themselves, and who look upon that which lies between the earth and the stars as air, would probably re- linquish such childish fancies if they properly investigated the results of the latest researches of mathematicians." (The same etymology of thia word, implying rapid revolution, is referred to by the Aristotelian, or Stoic, author of the woi'k De Mundo, cap. 2, p. 392, Bekk.) Professor Franz has correctly remarked, " That the play of words in the designa tiou of bodies in eternal motion (acJua uel t^eov) and oithe divine (^eIov] alluded to in the Meteorologica, is strikingly characteristic of the Greek typ-s of imagination, and affords additional evidence of the inaptitude of the ancients for etymological inquiry." Pz'ofessor Buschmann calls at- tention to a Sanscrit term, dschlra, ether or the atmosphere, which looks very like the Greek aldrjp, with which it has been compared by Vana Kennedy, in his Researches into the Origin and Affinity of the principal Languages of Asia and Europe, 1828, [>. 279. This word may also bo referred to the root (as, asch), to which the Indians attach the signiS cation of shining or beaming. COSMICAL ETHER. 38 arc separated by two intermediate elementary conditions, of which the one, water, approximates most nearly to the heavy earth, and the other, air, to the Ughter element of fire. ^ Considered as a medium filling the regions of space, the other oi Empedocles presents no other analogies excepting those of subtlety and tenuity with the ether, by whose trans- verse vibrations modern physicists have succeeded so hap- pily ill explaining, on purely mathematical principles, the propagation of light, with all its properties of double refrac ■ lion, polarization, and interference. The natural philosophy of Aristotle further teaches that the ethereal substance pen- etrates all the living organisms of the earth — both plant's and animals ; that it becomes in these the principle of vital heat, the very germ of a psychical principle, which, uninflu- enced by the body, stimulates men to independent activity.! These visionary opinions draw down ether from the higher regions of space to the terrestrial sphere, and represent it as a highly rarefied substance constantly penetrating through the atmosphere and through solid bodies ; precisely similar to the vibrating light-ether of Hu3^gens, Hooke, and modern physicists- But what especially distinguishes the older Ionic from the modern hypothesis of ether is the original assump- tion of luminosity, a view, however, not entirely advocated by Aristotle. The upper fire-air of Empedocles is expressly termed brightly radiating (frafupavoojv), and is said to be seen by the inhabitants of the earth in certain phenomena, gleaming brightly through fissures and chasms [x^^l^^'^) which occur in the firmament. $ The numerous investigations that have been made in re- cent times regarding the intimate relation between light, heat, electricity, and magnetism, render it far from improba- ble that, as the transverse vibrations of the ether which fills the regions of space give rise to the phenomena of light, the thermal and electro-magnetic phenomena may likewise • Aristot., De Calo, iv., 1, and 3-4, p. 308, and 311-312, Bekk. If the Stagirite withhokls from ether the character of a fifth element, which indeed is denied by Ritter {Geschichte der Philosophie, th. iii., s. 259), and by Martin {Etud-es siir le Timie de Platon., t. ii., p. 150), it ia only because, according to him, ether, as a condition of matter, has no contrary. (Compare Biese, Philosophie des Aristoleles, bd. xi., s. (iQ.^ Among the Pythagoreans, ether, as a fifth element, was represented by the fifth of the regular bodies the dndccahedi-on, composed of twelve pentagons. (iMaitm, t. ii., p. 24")-250.) t See the proofs collected by Biese. op. fit., bd. xi. s, 93. t Cosmoy, vol. i., ]). ir/l. P> 2 34 rosMO?. have tlieir origin in analogous kinds of motion (currents). ]♦, is reserved for future ages to make great discoveries in rel- erence to these subjects. Light, and radiating heat, whicli is inseparable from it, constitute a main cause of motion and organic life, both in the non-luminous celestial bodies and on the surface of our planet.^ Even far from its surface, in the interior of the earth's crust, penetrating heat calls forth electro-magnetic currents, which exert their exciting influ- ence on the combinations and decompositions of matter — on all formative agencies in the mineral kingdom — on the dis- turbance of the equilibrium of the atmosphere — and on the functions of vegetable and animal organisms. If electricity moving in currents develops magnetic forces, and if, in ac- cordance with an early hypothesis of Sir William Herschel,t the sun itself is in the condition of " a perpetual northern light" (I should rather say of an electro-magnetic storm), we should seem warranted in concluding that solar light, trans- mitted in the regions of space by vibrations of ether, may be accompanied by electro-magnetic currents. Direct observations on the periodic changes in the decli- nation, inclination, and intensity of terrestrial magnetism, have, it is true, not yet shown with certainty that these con- ditions are affected by the different positions of the sun or moon, notwithstanding the latter's contiguity to the earth. The magnetic polarity of the earth exhibits no variations that can be referred to the sun, or which perceptibly affect the precession of the equinoxes. | The remarkable rotatory or oscillatory motion of the radiating cone of light of Halley's comet, which Bessel observed from the 12th to the 22d of October, 1835, and endeavored to explain, led this great as- tronomer to the conviction that there existed a 2^olar force, * Compare lli.e fine pnssage on rne influence of the sun's raj^s in Sir Jolm Herscliei's Outlines of Astronomy, p. 237: " By the vivifying ac- tion of tlie sun's rays, vegetables are enabled to draw su})port from in- organic matter, and become, in tfjeir tuni, the support of animals and of man, and the sources of those great deposits of dynamical efficiency tehich are laid uj) for human vse in our coo^ , strata. By them the wa- ters of the sea are made to circulate in vnp t through the air, and ini- gate the land, producing springs and rivers. By them are produced i all disturbances of the chemical equilibrium of the elements of nature, which, by a series of compositions and decompositions, give rise to ne'iv products, and oi'iginate a transfer of materials." t Philos. Transact, for 17.9.5, vol. Ixxxv., p. 318 ; John Herschelj Outf lines of Astr., p. 238; see also Cosmos, vol. i., p. 189. t See Bessel, in Schumacher's Asfr. Nackr., bd. xiii., 183G, No. 300 B. 201. RADIATING HEAT. 35 *' whose action differed considerably from gravitation or the ordinary attracting force of the sun ; since those portions of the comet which constitute the tail are acted upon by a re' fuUive force proceeding from the body of the sun."'^ Tha splendid comet of 1744, which was described by Heinsius, led my deceased friend to similar conjectures. The actions of radiating heat in the regions of space are regarded as less problematical than electro-magnetic phenom- ena. According to Fourier and Poisson, the temperature of the regions of space is the result of radiation of heat from the sun and all astral bodies, minus the quantity lost by absorp- tion in traversing the regions of space filled with ether. f Frequent mention is made in antiquity by the Greek and Roman! writers of this stellar heat ; not only because, from a universally prevalent assumption, the stars aj)pertained to the region of the fiery ether, but because they were supposed to be themselves of a fiery nature§ — the fixed stars and th(? sun being, according to the d£)ctrine of Aristarchus of Samos, of one and the same nature. In recent times, the observa- tions of the above-m.entioned eminent French mathemati- cians, Fourier and Poisson, have been the means of direct- ing attention to the average determination of the tempera- ture of the regions of space ; and the more strongly since the importance of such determinations on account of the radia tion of heat from the earth's surface toward the vault of heaven has at length been appreciated in their relation to all thermal conditions, and to the very habitability of our planet. According to Fourier's Analytic Theory of Heat, the temperature of celestial space {^des cspaccs planetaires ou celestes) is ra,ther below the mean temperature of the poles, or even, perhaps, below the lowest degree of cold hith- erto observed in the polar regions. Fourier estimates it at from —58^ to --76° (from —40° to —48° Reaum.). The icy pole {^pble glacial), or the point of the greatest cold, no more * Bessel, op. ciL, s. 186-192, 229. t Fourier, Th^orie Analytique de la Chaleur, 1822, p. ix. (Annalci de Chimie e.t de Physique, torn, iii., 1816, p. 350; torn, iv., 1817, p. 128; torn, vi., 1817, p. 259 ; torn, xiii., 1820, p. 418.) Poisson, in his Theorii Math6matlque de la Chaleur (§ 196, p. 436, § 200, p. 447, and $ 228, p. 521), attempts to give the numerical estimates of the stellar heat {cho' letcr stellaire) lost by absorption in the ether of the regions of space. X On the heating power of the stars, see Aristot., De Meteor., 1, 3, p. 340, lin. 28 ; and on the elevation of the atmospheric strata at whidi heat is at the minimum, consult Seneca, in Nat. Qncrst., ii., 10: ' Sii periora enim aeris calorem vicinorum siilerum sentiu'H," ^ riut., De plac. Ph»''os., ii , 13. 36 COSMOS. corresponds with the terrestrial pole than does the thermal eqitator, which connects together the hottest points of all meridians with the geographical equator. Arago concludes, from the gradual decrease of mean temperatures, thit the degree of cold at the northern terrestrial pole is — 13^, if the maximum cold observed by Captain Back at Fort Rehance (62° 46' lat.) in Januar}^ 1834, w^ere actually —70° (—56^-6 Cent., or — 45°-3 K-eaum.).^ The lowest temperature that, as far as we know, has as yet been observed on the earth, is probably that noted by Neveroff, at Jakutsk (62° 2' lat.), on the 21st of January, 1838. The instruments used in this observation were compared with his own by Middendorff, whose operations w^ere always conducted with extreme ex- actitude. Neveroff found the temperature on the day above named to be — 76° (or — 48° Reaum.). Among the many grounds of uncertainty in obtaining a numerical result for the thermal condition of the regions of space, must be reckoned that of our inability at present to ascertain the mean of the temperatures of the poles of great- est cold of the two hemispheres, owing to our insufficient ac ■ quaintance wdth the meteorology of the antarctic pole, from which the mean annual temperature must be determined. I attach but little physical probability to the hypothesis of Pois- son, that the different regions of space must have a very va- rious temperature, owing to the unequal distribution of heat- radiatmg stars, and that the earth, daring its motion with the * Arago, Snr la Tempiralure du Pole et des espaces Cilestes, in the Annuaire du Bureau des Long, jwnr 1825, p. 189, et pour 1834, p. 192; also Saigey, Physique du Globe, 1832, p. 60-76. Svvauberg found, from considerations on refraction, that the temperature of the regions of space was — .58^.5. — Berzelius, Jahresbericht fur 1830, s. 54. Arago, from polar observations, fixed it at — 70^ ; and Pectet at — 76°. Saigey, by calculating the decrease of heat in the atmosphere, from 367 observa- tions made by myself in the chain of the Andes and in Mexico, found it — 85°; and from thermometrical measurements made at Mont Blanc, and dui-ing the aeronautic ascent of Gay-Lussac, — 107°-2. Sir John Horschel (Edinburgh Review, vol. 87, 1848, p. 223) gives it at —132°. We feel considerable surprisf , and have our faith in the correctness of the methods hitherto adopted somewhat shaken, when we find that Poisson, notwithstanding that the mean temperature of Melville Island (74° 47' N. lat.) is — 1° 66', gives the mean temperature of the regions of space at only 8°'6, having obtained his data from purely theoretical premises, according to which the regions of space are wai'mer than tha outer limits of the atmosphere (see the work already referred to, $ 227, p. .520) ; while Pouillet Stales it, from actinometric experiments, to ba •IS low as — 223^0. See Comptes Rcndus de V Academic des Sciences. u,m vii., 1838 p. 25-65. TEMPERATURE OF SPACE. 37 whole solar system, receives its interna, heat from without while passing through hot and cold regions.* The question whether the thermal conditions of the celes- tial regions, and the climates of individual portions of space, have sujSered important variations in the course of ages, de pends mainly on the solution of a prohlem warmly discussed by S^ir Wihiam Herschel : whether the nebulous masses are subjected to progressive processes of formation, while the cos- rriical vapor is being condensed around one or more nuclei in accordance "with the laws of attraction ? By such a con- densation of cosmical vaiJor, heat must be liberated, as in every transition of gases and fluids into a state of solidifica- tion.! If, in accordance with the most recent views, and the important observations of Lord R.osse and Mr. Bond, we may assume that all nebulas, iiicluding those which the high- est power of optical instruments has hitherto failed in resolv- ing, are closely crowded stellar swarms, our faith in tliis per- petually augmenting liberation of heat must necessarily be in some degree weakened. But even small consolidated cos- mical bodies Avhich appear on the field of the telescope as distinguishable luminous points, may change their density by combining in larger masses ; and many phenomena pre- sented by our own planetary system lead to the conclusion that planets have been soUdified from a sfate of vapor, and that their internal heat owes its origin to the fomiative pro- cess of conglomerated matter. It may at first sight seem hazardous to term the fearfully low temperature of the regions of space (which varies be- tween the freezing point of mercury and that of spirits of wine) even indirectly henejicial to the habitable climates of the earth and to animal and vegetable life. But in proof of the accuracy of the expression, we need only refer to the ac- tion of the radiation of heat. The sun- warmed surface of our planet, as well as the atmosphere to its outermost strata, freely radiate heat into space. The loss of heat which they experience arises from the difference of temperature between the vault of heaven and the atmospheric strata, and from the feebleness of tlie counter-radiation. How enormous would l?3 this loss of heat,$ if the regions of space, instead of the * See Poisson, ThioHe Mathim. de la Chalenr, p. 438. According to him, the consolidation of the earth's strata began from the center, and advanced gradually toward the surface; 'J 193, p. 429. Compare also Cosmos, vol. i., p. 176, 177. t Cosmos, vol. i., p. 83, 84, 144. X " Were there no atmosphere, a thcrmonietor freely exposed (at suit 38 r jsMOa. temperature they now possess, and which we designate as — 76° of a mercury thermometer, had a temperature of ahout — 1400° or even many thousand times lower I It still remains for us to consider two hypotheses in rela- tion to the existence of a fluid filling the regions of space, cf which one — the less firmly-based hypothesis— -refers to the limited traiisijarency of the celestial regions ; and the other, founded on direct observation and pelding numerical results, is deduced from the regularly shortened periods of revolution of Encke's comet. Olbers in Bremen, and, as Struve has ob- served, Leys de Cheseaux at Geneva, eighty years earlier"^ drew attention to the dilemma, that since we could not con- ceive any point in the infinite regions of space unoccupied by a fixed star, i. e.,du sun, the entire vault of heaven must ap- pear as luminous as our sun if light w^ere transmitted to us in perfect intensity ; or, if such be not the case, we must as- sume that light experiences a diminution of intensity in its passage through space, this diminution being more excessive than in the inverse ratio of the square of the distance. As we do not observe the whole heavens to be almost uniformly illumined by such a radiance of light (a subject considered by Halleyt in an hypothesis which he subsequently rejected), the regions of space can not, according to Cheseaux, Olbers, and Struve, possess perfect and absolute transparency. The results obtained by iSir William Herschel from gauging the Bet) to the heating influence of the earth's radiation, and the cooling power of its own into space, woukl indicate a medium temperature be- tween that of the celestial spaces ( — 132^ Fahr.) and that of the earth's surface below it, 82° Fahr., at the equator, 3p Fahr., in the Polar Sea. Under th.e equator, then, it would stand, on the average, at — 25° Fahr., and in the Polar Sea at — 68° Fahr. The presence of the atmosphere tends to prevent the thermometer so exposed from attaining these ex- treme low temperatures : first, by imparting heat by conduction ; sec- jndly, by impeding radiation outward." — Sir John Herschel, in the Edinburgh Review, vol. 87, 1848, p. 222. "Si la chaleur des espaces planetaires n'existait point, notre atmosphere eprouverait un refroidis- sement, dont on ne peut fix'jr la lim'.te. Probablement la vie des plantea et des animaux serait impassible a la surface du globe, on relcguce dans line etroite zone de cette surface." (Saigey, Physique du Globe, p. 77 .^ * Traits de la Cometc de 1743. avec nne Addition sur la force de la humiere et sa Propagation dans Vither, ct sur la distance des ^toiles fixes; par Loys de Cheseaux (1744). On the transparency of the regions of space, see Olbers, in Bode's Jnhrbuchfur 182G, s. 110-121 ; and Struve, Etudes d'Asir. Stellairc, 1847, p. 83-93, and note 9.5. Compare alsc Sir John Herschel, Outlines of Astronomy, § 798, and Cosmos, vol i., p. 151, 152. t Halley, On the InfinVij of the Sphere of Fixed Stars, in ihe Phiws Transact., vol. xxxi., for t lo year 1720, p. 22-2(3. RESISTING MEDIUM. 39 Btars,^ and iVom his ingenious experimeu.ts on the space-pen- etrating power of his great telescopes, seem to show, that if the light of Sirius in its passage to us through a gaseous or ethereal fluid loses only -g- ^Q-th of its intensity, this assump- tion, which gives the amount of the density of a fluid capa- ble of diminishing light, would suffice to explain the phe- nomena as they manifest themselves. Among the doubts advanced by the celebrated author of "The New Outlines of Astronomy" against the views of Olbers and Struvc, one of the most important is that his twenty-feet telescope shows, tliroughout the greater portion of the Milky Way in both hem- ispheres, the smallest stars projected on a black ground. f A better proof, and one based, as we have already stated, upon direct observation of the existence of a resisting fluid, ^ is alTorded by Encke's comet, and by the ingenious and im- portant conclusion to which my friend Avas led in his observ- ations on this body. This resisting medium miist, however, be regarded as ditferent from the all-penetrating light-ether, because the former is only capable of ofiering resistance in- asmuch as it can not penetrate through solid matter. These observations require the assumption of a tangential force to explain the diminished period of revolution (the diminished major axis of the ellipse), and this is most directly afiorded by the hypothesis of a resisting fluid. § The greatest action * Coamos, vol. i., p. SG, 87. T "Throughout by far ihe larger portion of the extent of the Milky Way ill botli hemispheres, the general blackness (jf the ground of the heavens, on which its stars are projected .... In tliose regions where the zone is clearly resolved into stars, well separated, and seen projected on a hind: ground, and where we look out beyond them into space. . . ." — Sir John Herschel, Outlines of As/'r., p. .537, 539. + Cosmos, vol. i,, p. 8"), 86, 107; compare also Laplace, Essai Philos- ophique sur les ProbabilUes, 1825, p. 133; Arago, in the Anmiaire d?i Bureau des Long, pour 1832, p. 188, pour 183G, \>. 216; and Sir John Herschel, Outlines of Astr., § 577. ^ The oscillatory movement of the emanations from the bead of some comets, as in tliat of 1744, and in Halley's, as observed by Bessel, be- tween the 12th and 22d of October, 1835 (Schumacher, Astron. Nachr., Nos. 300, 302, § 185, 232), "may indeed, in the case of some individ- uals of this class of cosmical bodies, exert an influence on the transla- tory and rotatory motion, and lead us to infer the action of polar forces ("$ 201, 229), which differ from theordinary attracting force of the sun;'' but the regular acceleration observable for sixty-three years in Encke's pomet (whose period of revolution is 3^ years), can not be regarded as the result of incidental emanations. Compare, on this cosmically im- portant subject, Bessel, in Schum.. Astron. Nachr., No. 289, s. G, and No. 310, s. 345-350, with Encke's Treatise on the hypothesis of Iho rf> slstliiic mc'dium, in Schum., No. 305. s. 285-274 40 COSMOS. is manifested during the twenty-five days immedia'.ely pro» ceding and succeeding the comet's perihelion passage. The value of the constant is therefore somewhat different, because in the neighborhood of the sun the highly attenuated but still gravitating strata of the resisting fluid -are denser. Gi- bers maintained"^ that this fluid could not be at rest, but must rotate directly round the sun, and therefore the resist- ance offered to retrograde comets, like Halley's, must differ wholly from that opposed to those comets having a direct course, like Encke's. The perturbations of comets having long periods of revolution; and the difference of their magni tudes and sizes, complicate the results, and render it dilf?- cult to determine what is ascribable to individual forces. The gaseous matter constituting the belt of the zodiacal light may, as Sir John Herschelf expresses it, be merely the denser portion of this comet-resisting medium. Although it may be shown that all nebulae are crowded stellar masses, indistinctly visible, it is certain that innumerable comets fill the regions of space with matter through the evaporation of their tails, some of which have a length of 56,000,000 of miles. Arago has ingeniously shown, on optical grounds, $ that the variable stars which always exhibit white light without any change of color in their periodical phases, might afford a means of determining the superior hmit of the dens- ity to be assunaed for cosmic al ether, if we suppose it to be equal to gaseous terrestrial fluids in its power of refraction. The question of the existence of an ethereal fluid filling the regions of space is closely connected with one warmly agitated by "Wollaston,^ in reference to the definite limit of the atmosphere — a limit which must necessarily exist at the elevation where the specific elasticity of the air is equipoised by the force of gravity. Faraday's ingenious experiments on * Olbers, in Schum., Asir. NacJir., No. 268, s. 58. t Outlines of Astronomy , ^ 55G, 597. X ^^ En assimilant la watiere tres rare qui rempllt les espaces cilestei quant a ses proprietes refringcntes aux gas terrestres, la density de cetti matiere nz saurait depasscr nne certaine limite dont les observations dee iloilcs chcngeantes, p. e. cellcs d'' Algol ou de (3 de Persic, peuvent assigner la valeur?^ — Arago, in the Annnaire pour 1842, p. 336-345. " On com paring the extremely rare matter occupying the regions oif space with terrestrial gases, in respect to its refractive properties, we shall find that the density of this matter can not exceed a definite limit, whose value may be obtained from observations of variable stars, as, for instance, Algol or (3 Tersei." i See WoWaRton, Philos. Transact, for 1822. p 80' Sir.Tnlin TIerschel cyp. cU., ^M, 36. FIRST TELESCOPE. 41 the limits of an atmosphere of mercury (that is, the elevation at which mercmial vapors precipitated on gold leaf cease perceptibly to rise in an air-tilled space) have given consid- erable weight to the assumption of a definite surface of the atmosphere " similar to the surface of the sea." Can any gaseous particles belonging to the region of space blend with our atmosphere and produce meteorological changes ? New- ton*" inclined to the idea that such might be the case. If we regard falling stars and meteoric stones as planetary as- teroids, we may be allowed to conjecture that in the streams of the so-called JNTovember phenomena,! when, as in 1799, 1833, and 1S34, myriads of falling stars traversed the vault of heaven, and northern liglits were simultaneously observed, our atmosphere may have received from the regions of space some elements foreign to it, which were capable of exciting electro-magnetic processes. II. NATURAL AND TELESCOPIC VISION.— SCINTILLATION OF THE STARS —VELOCITY OF LIGHT.— RESULTS OF PHOTOMETRY. The increased power of vision yielded nearly two hundred and fifty years ago by the invention of the telescope, has af- forded to the eye, as the organ of sensuous cosmical contem plation, the noblest of all aids toward a knowledge of the contents of space, and tlie investigation of the configuration, ph^^sical character, and masses of the planets and their sat- ellites. The first telescope was constructed in 1608, seven years after the death of the great observer, Tycho Brahe. Its earliest fruits were the successive discovery of the satel- lites of Jupiter, the Sun's spots, the crescent shape of Venus, the ring of Saturn as a triple planetary formation (planeta tergeminus), telescopic stellar swarms, and the nel3ulae in Andromeda. $ In 163-1, the French astronomer Morin, emi- nent for his observations on longitude, first conceived the idea of mounting a telescope on the index bar of an instrument of measurement, and seeking to discover Arcturus by day.^ * Newton, Princ. Mathem., t. iii. (1760), p. G71: "Tapores qui ej Bole et stellis fixis et caiidis cometarum oriuutur, iiicidere possvnt in at> mosphaeras planetarum " t Cosmos, vol. i., p. 124-135 X See Cosmos, vol. ii., p. 317-335, with notes. § Dclanibre, Histoire de C Astronomie Moderne, torn, ii., p. 255, 239 42 COSMOS. The perfection in the graduation of the arc would have failed entirely, or to a considerable extent, in affording that great- er precision of observation at vv^hich it aimed, if optical and astronomical instruments had not been brought into accord, and the correctness of vision made to correspond with that of measurem 3nt. The micrometer-application of fine tlu'eads stretched in the focus of the telescope, to wliich that instru- ment owes its real and invaluable importance, was first de- vised, six years afterward (1640), by the young and talented Gascoigne.^ While, as I have already observed, telescopic vision, ob- servation, and measurement extend only over a period of about 240 years in the history of astronomical science, we find, without including the epoch of the Chaldeans, Egyp- tians, and Chinese, that more than nineteen centuries have intervened between the age of Timochares and Aristillusf and the discoveries of Galileo, during which period the posi- tion and cou^Tse of the stars were observed by the eye alone, unaided by instruments. AYhen we consider the numerous disturbances which, during this prolonged period, checked the advance of cwilization, and the extension of the sphere of ideas among *,he nations inhabiting the basin of the Medi- terranean, \y** are astonished that Hipparchus and Ptolemy should have been so well acquainted with the precession of the equinoxes., the complicated naovements of the planets, the two principal inequalities of the moon, and the position of the stars ; that Copernicus should have had so great a knowledge of the true Fystem of the universe ; and that Tycho Brahe should have been so familiar with the methods of practical astronomy b-?fore the discovery of the telescope. Long tubes, 272. Mfniu, ia his work, Scientia Longitudinum, which appeared in 1G34, v/lritea .t^ follows: Applicatlo tuhi optlci ad alliidadam pro dellis fixis p-^ompte et accurate mensurandis a me excogitata est. Picard had not, up to the year 1667, employed any telescope on the mural circle: and Hevelius, when Halley visited him at Dantzic in 1679, and admired tha precision of his measurement of altitudes, was observing through Improved slits or openings. (Baily's Catal. of Sfars, p. 38.) * The unfortunate Gascoigue, whose merits remained so long unac- knowledged, lost his life, when scarcely twenty-three years of age, at the battle of Marston Moor, fought by Cromwell against the Royalists. See Derham, in the Philos. Transact., vol. xxx., for 1717-1719, p. 603 -610. To him belongs the merit of a discovery which was long ascribed to Picard and Auzout, and which has given an impulse previously un- known to practical astronomy, the principal object of which is to de- termine poii4ions in the vault of heaven. t Cosmos, vol. ii., p. 177, ITS. DIOPTRIC TUBES. 43 wliich were certainly employed by Arabian astronomers, and very probably also by the Greeks and Romans, may indeed, in some degree, liave increased the exactness of the observa- tions by causing the object to be seen througli diopters or slits. Abul-Hassan speaks very distinctly of tubes, to the extremi- ties of which ocular and object diopters were attached ; and instruments so constructed were used in the observatoiy founded by Hulagu at Meragha. If stars be more easily discovered during twilight by means of tubes, and if a star be sooner revealed to the naked eye through a tube than without it, the reason lies, as Arago has already observed, in the circumstance that the tube conceals a great portion of the disturbing light {rayons 'pertiirhateurs^ diilused in the atmos pheric strata between the star and the eye apphed to the tube. In like mamier, the tube prevents the lateral impression of the faint hght which the particles of air receive at night from all the other stars in the fimiament. The intensity of the imago and the size of the star are apparently augmented. In a fre- qr jntly emendated and much contested passage of Strabo, in which mention is made of locking througli tubes, this " en- larged fomi of the stars" is expressly mentioned, and is erro- neously ascribed to refraction.'^ * The passage in which Strabo (lib. iii., p. 138, Casaub.) atteni[)ts lo rffute the views of Posidoiiius is given as follows, according to the manuscripts: ''The image of the sun is enlarged on the seas at its ris- ing as well as at its setting, because at these times a larger mass of ex- halations rises from the humid element; and the eye, looking through these exhalations, sees images refracted into larger forms, as observed throiigh tubes. The same thing happens when the setting sun or mo""! is seen throu£;h a dry and thin cloud, when those bodies likewise appea. reddish." This passage has recently been pronounced corrupt (see Kramer, in Strahonis Geogi:, 1844, vol. i., p. 211), and 61 vu/mv (through glass spheres) substituted for 61 av?iuv (Schneider, Eclog. Phys., vol. ii., p. 273). The magnilying power of hollow glass spheres, tilled with water (Seneca, i., 6), was, indeed, as familiar to the ancients as the ac- tion of burning-glasses or crystals (Aristoph., Nub., v. 765), and that of Nero's emerald (Plin., xxxvii., 5) ; but these spheres most assuredly could not have been employed as astronomical measuring instruments, (Compare Cosmos, vol. ii., p. 245, and note %•) Solar altitudes, taken through thin, light clouds, or through volcanic vapors, exhibit no trace cf the influence of refraction. (Humboldt, Recueil d^Observ. Asir., vol. i-, p. 123.) Colonel Baeyer observed no angular deviation in the heli- otrope ligii'. on the passage of streaks of mist, or even from artificially »- ephanes {de Vair sec et de Vair humide) par le De placement des Franges, ■ in Moi^iio, Repertoire d'Optique Mod., 1847, p. 159-162. iS C0SM03 rc capacity, which was the same among former generations, as, for instance, the Greeks and Romans, as at the present day. The Pleiades prove that several thousand years ago, even as now, stars wliich astronomers regard as of the sev- enth magnitude, wer3 invisible to the naked eye of average visual power. The group of the Pleiades consists of one star of the third magnitude, Alcyone ; of two of the fourth, Electra and Atlas ; of three of the fifth, Merope, Maia, and Taygeta ; of two between the sixth and the seventh magni- tudes, Pleione and Celseno ; of one between the seventh and the eighth, Asterope ; and of many very minute telescopic stars. I make use of the nomenclature and order of succes sion at present adopted, as the same names were among the ancients in part applied to other stars. The six first-named stars of the third, fourth, and fifth magnitudes were the only ones which could be readily distinguished.^ Of these Ovid says [Fast., iv., 170), " Quae septem dici, sex tamen esse solent." One of the daughters of Atlas, Merope, the only one who was wedded to a mortal, Avas said to have veiled herself for very shame, or even to have wdiolly disappeared. This is probably the star of about the seventh magnitude, which wo call Celseno ; for Hipparchus, in his commentary on Aratus, observes that on clear moonless nights seven stars may ac- tually be seen. Celseno, therefore, must have been seen, for Pleione, which is of equal brightness, is too near to Atlas, a "itar of the fourth magnitude. The little star Alcor, which, according to Triesnecker, is situated in the tail of the Great Bear, at a distance of 11' * Hipparchus says (ad Arati PTicen., 1, p. 190, in Uranologio Petavii), ill refutation of the assertion of Aratus that there were only six stars visible in the Pleiades : " One star escaped the attention of Aratus. For when the eye is attentively fixed on this constellation on a serene and moonless night, seven stars are visible, and it therefore seems strange that Attains, in his description of the Pleiades, should have neglected to notice this oversight on the part of Aratus, as though he regarded the statement as correct." Merope is called the invisible {'Kava» Literate tho image of tiio star toward which the eyo is directed." VISIBILITY OF STARS. 5\ etars faintei than those of the sixth magnitude — have been able to distinguish the satelhtes of Jupiter without a tele- Bcope. The angular distance of the third and brightest sat- eUite from the center of the planet is 4' 42" ; that of the fourth, which is only one sixth smaller than the largest, is 8' 16" ; and all Jupiter's satellites sometimes exhibit, as Ar- ago maintains, =^ a more intense light for equal surfaces than * Arago, in the Annuaire pour 1842, p. 284, and in the Compt€$ Rendus, torn, xv., 1842, p. 750. (Schum., Astron. Nachr., No. 702.) " ^have instituted some calculations of magnitudes, in reference to your conjectures on the visibility of Jupiter's satellites," writes Dr. Galle, in letters addressed to me, " but I have found, contrary to ray expecta- tions, that they are not of the fifth magnitude, but, at most, only of the sixth, or even of the seventh magnitude. The third and brightest sat ellito alone appeared nearly equal in brightness to a neighboring star of the sixth magnitude, which I could scai'cely recognize with the naked eye, even at some distance from Jupiter; so that, considered in refer- ence to the brightness of Jupiter, this satellite would probably be of the fifth or sixth magnitude if it were isolated from the planet. The fourth satellite was at its gi-eatest elongation, but yet I could not estimate it at more than the seventh magnitude. The rays of Jupiter would not pre- vent this satellite from being seen if it were itself brighter. Froin a comparison of Aldebaran w'wh the neighboring star d Tauri, which is easily i^ecognized as a double star (at a distance of 5^ minutes), I should estimate the radiation of Jupit'er at five or six minutes, at least, for or- dinary vision." These estimates coirespond with those of Arago, who is even of opinion that this false radiation may amount in the case of some persons to double this quantity. The mean distances of the four satellites from the center of the main planet are undoubtedly 1' 51", 2' 57", 4' 42", and 8' 16". " Si nous supposons que I'image de Jupiter, dans certains yeux exceptionnels, s'epanouisse seulement par des ray- .ons d'une ou deux minutes d'amplitude, il ne semblera pas impossible que les satellites soient de lems en tems aper^us, sans avoir besoin de recourir k I'artifice de I'amplification. Pour verifier cette conjecture, j'ai fait constniire ime petite lunette dans laquelle I'objectif et I'ocu- laire ont a peu pres le meme foyer, et qui des lors ue grosrit point Cette lunette ne detniit pas entierement les rayons divergents, mats elle en reduit considerablement la longueur. Cela a suffi pour qu'uu satellite convenablement ecarte de la planete, soit devenu visible. Le fait a ete constate par tons les jeunes astronomes de I'Observatoire." ** If we suppose that the image of Jupiter appeal's to the eyes of some persons to be dilated by rays of only one or two minutes, it is net im- possible that the satellites may from time to time be seen without the aid of magnifying glasses. In order to verify this conjecture, I caused a small instrument to be constructed in which the object-glass and tha eye-piece had nearly the same focus, and which, therefore, did not mag nify. This instrument does not entirely destroy the diverging rays, al though it considerably reduces their length. This method has sufficed to render a satelht-3 visible when at a sufficient distance from the planet. This observation has been confirmed by all the young astronomers at the Observa*;ory." (Arago, in iho Comptes Rendus, torn, xv., J 842, ]> rsi.) 52 C0SM03. Jupiter himself; occasionally, however; as shown by recent observations, they appear like gray spots on the planet. The rays or tails, which to our eyes appear to radiate from the planets and fixed stars, and wliich were used, since the ear- liest ages of mankind, and especially among the Egyptians, as pictorial representations to indicate the sliining orbs of lieaven, are at least from five to six minutes in length. (These lines are regarded by Hassenfratz as caustics on the crystalline lens : intersections cles deux coAistiques.) *' The image of the star which we see with the naked eya is magnified by diverging rays, in consequence of which it occupies a larger space on the retina than if it were concen- As a remakable instance of acute %nsion, and of the great sensibility of the retina in some individuals who are able to see Jupiter's satellites with the naked eye, I may instance the case of a master tailor, named Schon, who died at Breslau in 1837, and with reference to whom I have received some interesting communications from the learned and active director of the Breslau Observatoiy, Von Boguslawski. ** After having (since 1820) convinced ourselves, by several rigid tests, that in serene moonless nights Schon was able correctly to indicate the position of sev- eral of Jupiter's satellites at the same time, we spoke to him of the em anations and tails which appeai'ed to prevent others from seeing so clearly as he did, when he expressed his astonishment at these ob* iti'ucting radiations. From the animated discussions between himself and the by-standers regarding the difficulty of seeing the satellites with the naked eye, the conclusion was obvious, that the planet and fixed stars must always appear to Schon like luminous points having no rays. He saw the third satellite the best, and the first very plainly when it was at the greatest digression, but he never saw the second and tho fourth alone. When the air was not in a veiy favorable condition, the satellites appeared to him like faint streaks of light. He never mistook email fixed stars for satellites, probably on account of the scintillating and less constant light of the fonner. Some yeai's before his death Schon complained to me that his failing eye could no longer distinguish Jupiter's satellites, whose position was only indicated, even in cleai' weather, by light faint streaks." These circumstances entirely coin- cide with what has been long known regarding the relative luster of Jupiter's satellites, for the brightness and quality of the light probably exert a greater influence than mere distance from the main planet ou persons of such great perfection and sensibihty of vision. Schon never saw the second nor the fourth satellite. The former is the smallest of all ; the latter, although the largest after the third and the most remote, is periodically obscured by a dark color, and is genei'ally the faintest of all the satellites. Of the third and the first, which were best and most frequently seen by the naked eye, the former, which is the largest of all; is usually the brightest, and of a very decided yellow color ; the latter occasiona.ly exceeds in the intensity of its clear yellow light the luster of the third, which is also much larger. (Madler, Astr., 1846, 6. 231-234, and 439.) Sturm and Airy, inUie Comptes Rendns, t. xx., p. 764-6, show how, under proper conditions of refraction in the orgui; of vision, remote lum'uous j>uin'd mov anpcar as light streaks. NATURAL VISION. 53 trated in a single point. The impression on the nerves is weaker. A very dense starTy swarm, in which scarcely any of the separate stars belong even to the seventh magnitude, may, on the contrary, be visible to the unaided eye in con- sequence of the images of the many different stars crossing each other upon the retina, by which every sensible point of its surface is more powerfully excited, as if by one concen- trated image. "*" * " L'image ipanouie d'une etoile de 7eme grandeur n'ebraule pa3 suiSsamraeut la re tine : elle n'y fait pas naitre une sensation apprecia- ole de lumi<5re. Si l'image n'Hait 'point ipanouie (par des rayons di- vergents), la sensation aurait plus de force, et I'etoile se ven-ait. La premiere classe d'etoiles invisibles a I'aeil nu ne serait plus alors la sep- tieme: pour la trouver, il faudrait peut-etre desceudre alors jusqu'ji la I2eme. Considerons un groupe d'etoiles de 7eme grandeur tellement rapprochees les nnes des autres que les intervallesecliappeutnecessaire- ment k I'ffiil. Si la vision avait de la netteU, si l'image de chaque etoile etait tres petite et bien terminee, I'observateur aperceverait un champ de lumiere dont chaque point aurait Viclat conccntri d'une etoile do 7eme grandeur. U eclat concentri. d'une etoile de 7eme grandeur suflSt a la vision a I'ffiil nu. Le groupe serait done visible a VaiW nu. Di- latons maintenant sur la retine l'image de chaque etoile du groupe ; rempla^ons chaque point de I'ancienne image generale par un petit cer- cle : ces cercles empieteront les uns sur les autres, et les divers points de la retine se trouveront eclaires par de la lumiere venaut simultan - ment de plusieurs ctoiles. Pour peu qu'on y reflechisse, il restera evi- dent qu' excepte sur les bords de l'image generale, I'aire lumineuse ainsi eclairee a precisement, a cause de la superposition des cercles, la memo intensite que dans le cas ou chaque etoile n'eclaire qu'un seul point au fond de Toeil ; mais si chacun de ces points re- aes qui manquent, done encore efFet de I'interference des rayons." On the causes of the scintillation of the stars. " The most remarkable feature in the phenomenon of the stars* sci» tillation is their change of color. This change is of much more frequent occurrence than would appear from ordinaiy observation. Indeed, on shaking the telescope, the image is transformed into a line or circle, and all the points of this line or circle appear of different colors. We have here the results of the superposition of all the images seen when the telescope is at rest. The rays united in the locus of a leus vibrate m SCINTILLATION OF THE STARS. 75 these alterations are more intense in reality than they appeal to the naked eye ; for when the several points of the retina harmony or at variance with one another, and increase or destroy one another according to the various degrees of refraction of the strata through which they have passed. The whole of the red rays alone can desti'oy one another, if the rays to the right and left, above and below them, have passed through unequally refracting media. We have used the term alone, because the difference of refraction necessary to destroy the red ray is not the same as that which is able to destroy the green ray, and vice versa. Now, if the red rays be destroyed, that which re- mains will be white minus red, that is to say, green. If the green, on the other hand, be destroyed by interference, the image will be white minus green, that is to say, red. To understand why planets having large diameters should be subject to little or no scintillation, it must be remem- bered that the disk may be regarded as an aggregation of stars or of small points, scintillating independently of each other, while the images of different colors presented by each of these points taken alone would impinge upon one another and form white. If we place a diaphragm or a cork pierced with a hole on the object-glass of a telescope, the stars present a disk surrounded by a series of luminous rings. On push- ing in the eye-piece, the disk of the star increases in diameter, and a dark point appears in its center; when the eye-piece is made to recede BtiU further into the instrument, a luminous point will take the place of the dark point. On causing the eye-piece to recede still further, a black center wiU be obsei'ved. If, while the center of the image is black, we point the instrument to a star which does not scintillate, it will remain black as before. If, on the other hand, we point it to a scin- tillating star, we shall see the center of the image alternately luminous and dark. In the position in which the center of the image is occu pied by a luminous point, we shah see this point alternately vanish and reappear. This disappearance and reappearance of the central point is a direct proof of the variable interference of the rays. In order to comprehend the absence of light from the center of these dilated im- ages, we must remember that rays regularly refracted by the object- glass do not reunite, and can not, consequently, interfere except in the focus; thus the images produced by these rays will always be uniform and without a central point. If, in a certain position of the eye-piece, a point is observed in the center of the image, it is owing to the inter- ference of the regularly refracted rays with the rays diffracted on the margins of the circular diaphragm. The phenomenon is not constant, for the rays which interfere at one moment no longer do so in the next, after they have passed through atmospheric strata possessing a varying poAver of refraction. We here meet with a manifest proof of the im- portant part played in the phenomenon of scintillation by the unequal refrangibility of the atmospheric strata traversed by ra} s united in a Tery narrow pencil." "It follows from these considerations that scintillation mast necessa- rily be referi'ed to the phenomena of luminous interferences alone The rays emanating from the stars, after traversing an atmosphere composed of strata having different degi-ees of heat, density, and humidity, com- bine in the focus of a lens, where they form images perpetually chang ing in intensity and color, that is to say, the images presented by sciii tillation. There is another form of scintillation, independent of the fo cus (if ih i telescope. Tlie explanations of this phenomenon advaaceJ' 76 cosx\io». are once excited, they retain the impression of light "whica they have received, so that the disappearance, obscuration and change of color m a star are not perceived by us to their full extent. The phenomenon of scintillation is more striking- ly manifested in the telescope when the instrument is shaken, for then different points of the retina are successively excited, and colored and frequently interrupted rings are seen. The principle of interference explains how the momentary colored effulgence of a star may he followed hy its equally instanta- neous disappearance or sudden obscuration, in an atmosphere composed of ever-changing strata of different temperatures, moisture, and density. The undulatory theory teaches us generally that two rays of light (tv\"o systems of waves) em- anating from one source (one center of commotion), destroy each other by inequality of path ; that the light of one ray added to the light of the other produces darkness. When the retardation of one system of waves in reference to the other amounts to an odd number of semi-undulations, both systems endeavor to imxpart simultaneously to the same molecule of ether equal but opposite velocities, so that the effect of their combination is to produce rest in the molecule, and therefore darkness. In some cases, the refrangibility of the different strata of air intersecting the rays of light exerts a greater in- fluence on the phenomenon than the difference in length of their path.* The intensity of scintillations varies considerably in the dif- ferent fixed stars, and docs not seem to depend solely on thei : altitude and apparent magnitude, but also on the nature of their own light. Some, as for instance Vega, flicker less than Arcturus and Prccyon. The absence of scintillation in plan- ets with larger disks is to be ascribed to compensation and to the naturahzing mixture of colors proceeding from different points of the disk. The disk is to be regarded as an aggregate Dy Galileo, Scaliger, Kepler, Descartes, Hooke, Huygeiis, Newton, and John Michel], which I exaniiued in a memoir presented to the Institute in 1840 {Comj^les Rendns, t. x., p. 83), are inadmissible. Thomas Young, to whom we owe the discoveiy ot" the first laws of interference regarded scintillation as an inexplicable phenomenon. The erroneous- ness of the ancient explanation, which supposes that vapors ascend and displace one another, is sufficiently proved by the circumstance that we sea scintillations with the naked eye, which presupposes a displace nient of a minute. The undulations of the margin of the sun are from 4" to 5", and are perhaps owing to chasms or inteiTuplions, and there- fore also to the effect of interference of the rays of liirht." (Fxt'i'aeti from Arago's MSS. of 18i7.) * See Arago, in the Annnairc pour 183! p. 168. SCINTILLATION CF THE STARS. 7"^ ol stars wliich naturally compensate for the light destroyed by interference, and again combine the colored rays into white light. For this reason, we most rarely meet with traces of scintillation in Jupiter and Saturn, hut more frequently in Mercury and Venus, for the apparent diameters of the disks of these last-named planets diminish to 4"'4 and 9"'5. The diameter of Mars may also decrease .to 3"-3 at its conjunc- tion. In the serene cold winter nights of the temperate zone, the scintillation increases the magnificent impression produced by the starry heavens, and the more so from the circumstance fhat, seeini? stars of the sixth and seventh magnitude flicker- ing in various directions, we are led to imagine that we per- ceive more luminous points than the unaided eye is actually capable of distinguishing. Hence the popular surprise at the few thousand stars which accurate catalogues indicate as vis- ible to the naked eye I It was known in ancient times by the Greek astronomers that the flickering; of their light dis- tinguished the fixed stars from the planets ; but Aristotle, in accordance with the emanation and tangential theory of vi- sion, to which he adhered, singularly enough ascribes the scin- tillation of the fixed stars merely to a straining of the eye. '* The riveted stars (the fixed stars)," says he,^ " sparkle, but not the planets ; for the latter are so near that the eye is able to reach them ; but in looking at the fixed stars (rrpo^ 6e rovg fisvovra^), the eye acquires a tremulous motion, owing to the distance and the effort." In the time of Galileo, between 1572 and 1G04 — an epoch remarkable for great celestial events, when three starsf of greater brightness than stars of the first magnitude suddenly appeared, one of which, in Cygnus, remained luminous for twenty-one years — Kepler's attention was specially directed to scintillation as the probable criterion of the non-planetary nature of a celestial body. Although well versed in the sci- ence of optics, in its then imperfect state, he was unable to rise above the received notion of moving vapors, $ In tha Chinese Records of the newly appeared stars, according to the great collection of Ma-tuan-lin, their strong scintillation is occasionally mentioned. T he more equal mixture of the atmospheric strata, in and near the tropics, and the faintness or total absence of scintil- • Aristot., De Ccelo, ii., 8, p. 290, Bekker. t Cosmos, vol. ii., p. 326. t Causa scinlillalionis, in Kepler, De Stella nova in pede Serpentartt^ I/i06, cap. xviii., p. 92-97. - 8 COSMOS. lation of the fixed stars when they have risen 12° or 15* above the horizon, give the vault of heaven a peculiar char« acter of mild effulgence and repose. I have already referred in many of my delineations of tropical scenery to tliis charac- teristic, which was also noticed by the accurate observers Iju Condamine and Bouguer, in the Peruvian plains, and by Garcin,^ in Arabia, India, and on the shores of the Persian. Gulf (near Bender Abassi). As the aspect of the starry heavens, in the season of the serene and cloudless nights of the tropics, specially excited my admiration, I have been careful to note in my journals the height above the horizon at wliich the scintillation of the stars ceased in different hygrometric conditions. Cumana and the rainless portion of the Peruvian coast of the Pacific, before the season of the garita (mist) had set in, were pecul- iarly suited to such observations. On an average, the fixed stars appear only to scintillate when less than 10° or 12^ above the horizon. At greater elevations, they shed a mild, planetary hght ; but this difference is nrost strikingly per- ceived when the same fixed stars are watched in their grad- ual rising or setting, and the angles of their altitudes meas- ured or calculated by the known time and latitude of the place. In some serene and calm nights, the region of scin- tillation extended to an elevation of 20° or even 25° ; but a comiection could scarcely ever be traced between the differ- ences of altitude or intensity of the scintillation and the hy- grometric and thermometric conditions, observable in the low- er and only accessible region of the atmosphere. I have ob- served, during successive nights, after considerable scintilla- tion of stars, having an altitude of G0° or 70^, when Saus- sure's hair-hygrometer stood at 8-5^, that the scintillation en- tirely ceased when the stars were 15° above the horizon, al- though the moisture of the atmosphere was so considerably increased that the hygrometer had risen to 93°. The intri- cate compensatory phenomena of interference of the rays of light are modified, not by the quantity of aqueous vapor con- tained in solution in the atmosphere, but by the unequal dis- tribution of vapors in the superimposed strata, and by the upper currents of cold and warm air, which are not percept- ible in the lower regions of the atmosphere. The scintilla- tion of stars at a great altitude was also strikingly increased {luring the thin yellowish red mist which tinges the heavens * Letire de M. Garcia, Dr. en Med. a M. de Rdanmnr, in Hist, de V Arnd^in/e Rnijale da Sciences, Annee 1743, p. 28-32. SCINTILLATION OP THE STARS. 79 ghcrtiy before an earthquake. These ohservatlons only refei to the serenely bright and rainless seasons of the year with- in the tropics, from 10° to 12° north and south of the equa- tor. The phenomena of light exhibited at the commence- ment of the rainy season, during the sun's zenith-passage, depend on very general, yet powerful, and almost tempestu- ous causes. The sudden decrease of the northeast trade- wind, and the interruption of the passage of regular upper currents from the equator to the poles, and of lower currents from the poles to the equator, generate clouds, and thus daily give rise, at definite recurring periods, to storms of wind and torrents of rain. I have observed during several successive years that in regions where the scintillation of the fixed stars is of rare occurrence, the approach of the rainy season is an- nounced many days beforehand by a flickering light of the stars at great altitudes above the horizon. This phenome- non is accompanied by sheet lightning, and single flashes on the distant horizon, sometimes without any visible cloud, and at others darting through narrow, vertically ascending col- umns of clouds. In several of my writings I have endeav ored to delineate these precursory characteristics and physi- ognomical changes in the atmosphere.* The second book of Lord Bacon's Novum Orgamim gives us the earliest views on the velocity of light and the prob ability of its requiring a certain time for its transmission. He speaks of the time required by a ray of light to traverse the enormous distances of the universe, and proposes tho * See Voyage aux Rigions Equln., t. i., p. 511 and 512, and t. ii., p 202-208; also my Vie^cs of Nature,^. IG, 138. " En Arable, de meme qu'^ Bendei'-Abassi, port fameux du Golfe Persique, I'air est parfaitement serein presque toute I'anuee. Le prin- temps, I'ete, et I'automne se passent, sans qu'on y voie la moindre rosee. Dans COS memes temps tout le monde couche dehors sur le haut des maisons. Quand on est ainsi couche, il n'est pas possible d'exprimer le plaisir qu'on prend k contempler la beaute du ciel, I'eclat des etoiles. C'estune lamiere pui-e, ferme et eclatante, sans etincellement. Ce n'est qu'au milieu de I'hiver que la scintillation, quoique tres foible, s'y fait upercevoir." '' In Arabia," says Gai'cin, "as also at Bender- Abassi, a celebrated port on the Persian Gulf, the air is perfectly serene throughout nearly the whole of the year. Spring, summer, and autumn pass without ex hibiting a trace of dew. Dm'ing these seasons all the inhabitants sleep on the roofs of their houses. It is impossible to describe the pleasure experienced in contemplating the beauty of the sky, and the brightness of the stars, while thus lying in the open air. The light of the stars is pure, steady, and brilliant ; and it is only in the middle of the winter that a slight degi'ce of scintillation is observed." — Garcin, in Hift, dt VAcad. des Sc, 1743 p. 30. so COSMOS. question whether those stars yet exist which we now see shining.* We are astonished to meet with this happy con- jecture in a work whose intellectual author was far behind his cotemporaries in mathematical, astronomical, and phys- ical knowledge. The velocity of rejlected solar light wag first measured by Romer (November, 1G75) by comparing the periods of occultation of Jupiter's satellites ; while the velocity of \\\q direct light of the fixed stars was ascertained (in the autumn of 1727) by means of Bradley's great discov- ery of aberration, which afforded objective evidence of the translatory movement of the earth, and of the truth of the Copernican system. In recent times, a third method of measurement has been suggested by Arago, which is based on the phenomena of light observed in a variable star, as, for instance, Algol in Perseus. f To these astronomical meth- ods may be added one of terrestrial measurement, lately con- ducted with much ingenuity and success by M. Fizeau in the neighborhood of Paris. It reminds us of Galileo's early * In speaking of the deceptions occasioned by the velocity of sound and light, Bacon says : " This last instance, and others of a like nature, have sometimes excited in us a most marvelous doubt, no less than whether the image of the sky and stars is perceived as at the actual moment of its existence, or rather a httle after, and whether there is not (with regard to the visible appearance of the heavenly bodies) a true and apparent place which is observed by astronomers in parallaxes. It appeared so incredible to us that the images or radiations of heavenly bodies could suddenly be conveyed through such immense spaces to the eight, and it seemed that they ought rather to be transmitted in a def- inite time. That doubt, however, as far as regards any great difference between the tiiie and apparent time, was subsequently completely set at rest when we considered . . . ." — The works of Francis Bacon, vol. xiv., Lond., 1831 {Novum Organum), p. 177. He then recalls the cor- rect view he had previously announced precisely in the manner of the ancients. Compare Mrs. Somerville's Connection of the Physical Sci- ences, p. 36, and Cosmos, vol. i., p. 154, 155. t See Arago's explanation of his method in the Annuaire du Bureau des Longit^ides pour 1842, p. 337-343. " L'observation attentive dea phases d'Algol a six mois d'intervalle servira a determiner directement la vitesse de la lumiere de cette etoile. Pres du maximum et du mini- mum le changement d'intensite s'opere lentement ; il est au contraire rapide a certaiues epoques intermediares entre celles qui correspondent aux deux etats extremes, quand Algol, soit en diminuant, soit en aug- mentant d'eclat, passe pour la troisieme grandeur." ' The attentive observation of the phases of Algol at a six-months in* terval will serve to determine directly the velocity of that star's light Near the maximum and the minimum the change of intensity is very Blow; it is, on the contraiy, rapid at certain intermediate epochs b© tween those corresponding to the two extremes, when Algol, either d' minishing or increasing in bnghtuess, appears of the third magnitude SCINTILLATION OF THE STARS. Si and fruitless experiments with two alternately obscured Ian terns. * Horrebow and Du Hamel estimated the time occupied in the passage of light from the sun to the earth at its mean dis- tance, according to Romer's first observationsof Jupiter's satel- lites, at I'V 7", then 11' ; Gassini at 14' 10" ; while Newton* * Newton, Optics, 2d ed. (London, 1718), p. 325. " Light moves from the suu to us in seven or eight minutes of time." Newton com- pares the velocity of sound (1140 feet in I") witli that of light. As, from observations ou the occultatious of Jupiter's satellites (Newton'a death occurred about half a j^ear before Bradley's discovery of aberra- tion), he calculates that light passes from the suu to the earth, a distance, as he assumed, of 70 millions of miles, iu 7' 30" ; this result yields a ve- Jocity of light equal to 155,555 1 miles in a second. The reduction of these [ordinary] to geographical miles (60 to 1°) is subject to variations according as we assume tlie figure of the earth. According to Encke's accurate calculations in the Jahrbtich fur 1852, an equatorial degree is equal to 60-1637 English miles. According to Nesvton's data, we should therefore have a velocity of 134,944 geographical miles. Newton, how- ever, assumed the sun's parallax to be 12". If this, according to Encke's calculation of the transit of Venus, be 8"*57116, the distance is greater, and we obtain for the velocity of light (at seven and a half minutes) 188,928 geographical, or 217,783 ordiuaiy miles, in a second of time ; therefore too much, as before we had too little. It is certainly very re- markable, although the circumstance has been overlooked by Delambre (^Hist. de V Astronomie Moderne, torn, ii., p. 653), that Newton (proba- bly basing his calculations upon more recent English observations of the first satellite) should have approximated within 47" to the true re- sult (namely, that of Struve, which is now generally adopted), while tiie time assigned for the passa2:e of li^ht over the serni-diameter of the earth's orbit continued to vacillate between the veiy high amounts of 11' and 14' 10'', from the period of Romer's discovery iu 1675 to the be- ginning of the eighteenth century. The first treatise in which Romer, the pupil of Picard, communicated his discovery to the Academy, bears the date of November 22, 1675. He found, from observations of forty emersions and immersions of Jupiter's satellites, " a retardation of light amounting to 22 minutes for an interval of space double that of the sun's distance from the earth." (Memoirs de V Acad, de 1666-1699, tom. x., 1730, p. 400.) Cassini does not deny the retardation, but he does not concur in the amount of time given, because, as he erroneously argues, ditferent satellites presented different results. Du Hamel, secretary to the Paris Academy {Regies Scientiamm Acaderuice Historia, 1698, p. 143), gave fi-om 10 to 11 minutes, seventeen years after Romer had left Paris, althoush he refers to him; vet we know, through Peter Horre- bow {Basis Asfronomice sive Triduum Roemeriannm, 1735, p. 122-129), that Romer adhered to the result of 11', when iu 1704, six years before his death, he purposed bringing out a w^ork on the velocity of light; the same was the case with Huy^ens {Tract, de Lnmine, cap. i., p. 7) Cassini's method was very different; he found 7' 5" for the first satel- lite, and 14' 12" for the second, having taken 14' 10" for the basis of his tables for .Tupiter pro pcragrando diametri semissi. The error wa« therefore on the increase. (Compare Hon-ebow, Tridnnm, p. 129 ; Cas- Hini, Hi/potheses et SatcUUes de Jnj^iter in the M^ni. de VArnd., J 666- T) 2 82 COSMOS approximated very remarkably to the truth when he gave it at 7' 30". DeUmhre,=^ who did not take into account any of the observations made in his own time, with the excep- lion of those of the first satellite, found S' 13"-2. Encke has very justly noticed the great importance of undertaking a special course of observations on the occultations of Jupi- ter's satellites, in order to arrive at a correct idea regarding the velocity of light, now that the perfection attained in the construction of telescopes warrants us in hoping that we may obtain trustworthy results. Dr. Busch,t of Konigsberg, who based his calculations on Bradley's observations of aberration, as rediscovered by E.i- gaud of Oxford, estimated the passage of light from the sun to the earth at 8' 12"- 14, the velocity of stellar light at 167,976 miles in a second, and the constant of aberration at 20"'2116 ; but it would appear, from the more recent ob- servations on aberration carried on during eighteen months by Struve with the great transit instrument at Pulkowa,$ that the former of these numbers should be considerably in- 1699, torn, viii., p. 435, 475; Delambre, Hist, de V Astr. Mod., torn, ii., p. 751, 782 ; Du Hamel, Physica, j). 435.) * Delambre, Hist, de VAstr. Mod., torn, ii., p. 653. t Reduction of Bradley's Ohsei-vaiions at Kew and Wansted, 1836, p 22; Schumacher's Astr. Nackr., bd. xiii., 1836, No. 309 (compare Mia- cellaneous Works and Correspondence of the Rev. James Bradley, by Prof. Rigaud, Oxford, 1832). Oil the mode adopted for explaining ab- en-ation in accordance with the theory of undulatory light, see Dopplei-, in the Abhl. der Kdn. buhmischcn Gesellschaft der Wiss., 5te Folge., bd. iii., s. 754-765. It is a point of extreme importance in the history of great astronomical discoveries, that Picard, more than half a centuiy before the actual discovery and explanation by Bradley of the cause of aberration, probably from 1667, had observed a periodical movement of the polar star to the extent of about 20", which could " neither be the effect of parallax or of refraction, and was very regular- at opposite seasons of the year." (Delambre, Hist, de VAstr. Modeme, tom. ii., p. 616.) Picard had nearly ascertained the velocity of direct light before his pupil. Homer, made known that of reflected light. X Schum., Astr. Nachr , bd. xxi., 1844, No. 484 ; Struve, Etudes d'Astr. Stellaire, p. 103, 107 (compare Cosmos, vol. i., p. 153, 154). The re- sult given in the Annvaire pour 1842, p 37, for the velocity of hght in a second, is 308,000 kilomenes, or 77,000 leagues (each of 4000 , metres), which corresponds to 215,834 miles, and approximates most nearly to Struve's recent result, while that obtained at the Pulkowa Observatory is 189,746 miles. On the difference in the aberration of the light of the polar star and that of its companion, and on the doubts recently expressed by Struve, see Madler, Astronomie, 1849, s. 393, WiUiam Richardson gives as the result of the passage of light from the Bun to the earth 8' 19"-28, from which we obtain a velocity of 215,392 miles in a second. {Mem. of the Astron. Soc, vol. iv., Part i.. p. 68 * SCINTILLATION OF THE STARS. 83 creased. The result of these important observations gave 8' 17"-7S ; from which, with a constant of aberration of 20"'4451, and Encke's correction of the smi's parallax in the year 1835, together with his determination of the earth's radius, as given in his Astro7iomischrs Jahrhucli fur 1852, we obtain 166,190 geographical miles for the velocity of light in a second. The probable error in the velocity seems Bcarcely to amount to eight geographical miles. Struvc'a result for the time which light requires to pass from the snn to the earth differs about yy^th from Delambre's (8' 13"*2), which has been adopted by Bessel in the Tab. Regiom., and has hitherto been followed in the Berlin Astronomical Al- manac. The discussion on this subject can not, however, be regarded as wholly at rest. Great doubts still exist as to the earlier adopted conjecture that the velocity of the light of the polar star was smaller than that of its compan- ion in the ratio of 133 to 134. M. Fizeau, a physicist, distinguished alike for his great acquirements and for the delicacy of his experiments, has submitted the velocity of light to a terrestrial measurement, by means of an ingeniously constructed apparatus, in which artificial light (resembling stellar light) generated from oxy- gen and hydrogen is made to pass back, by means of a mir- ror between Suresne and La Butte Montmartre, over a dis- tance of 28,321 feet, to the same point from wdiich it ema- nated. A disk having 720 teeth, w^hich made 12' 6 rotations in a second, alternately obscured the ray of light and allowed it to be seen between the teeth on the margin. It was sup- posed from the marking of a counter (compteur) that the artificial light traversed 56,642 feet, or the distance to and from the stations in y g^ooth part of a second, whence we ob- tain a velocity of 191,460 miles in a second.* This result, therefore, approximates most closely to Delambre's (which was 189,173 miles), as obtained from Jupiter's satellites. Direct observations and ingenious reflections on the ab' sence of all coloration during the alternation of iight in the variable stars — a subject to which I shall revert in the se- * Fizeau gives his result in leagues, reckoning 25 (and o;nsequently 44.'32 metres) to the equatorial degree. He estimates tbd velocity of light at 70,000 such leagues, or about 210,000 miles in thasecond. Of; .he earlier experiments of Fizeau, see Compfes Rendns, torn, xxix., p. 92. In Moigno, Ripert. (VOptiqnc Moderne, Part iii., p. 1162, we find this velocity given at 70,843 leagues (of 25=1°), or about 212,529 miles, which approximates most nearly to the result of Bradley, as given Uy Busch. 84 COSMOS. quel — led Arago tc the result that, accoiimg ;o the undU' iatory theory, rays of light of different color, which conse quently have transverse vibrations of very different length and velocity, move through space with the same rapidity. The velocity of transmission and. refraction differ, therefore, in the interior of the different bodies through which the col- ored rays pass ;* for Arago's observations have shown that • " D'apres la theorie mathematique dans le systeme des ondes, lea rayons de differentes coiileurs, les rayons dont les ondulations sont ine- gales, doivent neanmoins se propager dans I'ether avec la m^me vi tesse. II n'y a pas de diiference k cet egard entre la propagation dea ondes sonores, lesquelles se propagent dans I'air avec la m^me rapidite. Cette egalite de propagation des ondes sonores est bien etablie expen- raeutalement par la similitude d'eftet que produit une musique doniiee k toutes distances du lieu ou I'on I'execute. La principale difBculte, je dirai I'unique difficulte, qu'on eAt elevee centre le systeme des ondes, consistait done k expliquer, comment la vitesse de propagation des ray- ons de differentes couleurs dans les corps differents pouvait etre dissem- blable et servir k rendre compte de I'inegalite de refraction de ces ray- ons ou de la dispersion. On a montre recemment que cette difficulte n'est pas insurmontable; qu'on peut constituer I'ether dans les corps inegalement denses de maniere que des rayons k ondulations dissem- blables s'y propagent avec des vitesses inegales : reste a determiner, si les conceptions des geometres k cet egard sont confonnes a la nature des choses. Voici les amplitudes des ondulations deduites expenmen- talement d'une seiie de faits relatif aux interferences : mm. Violet 0-000423 Jaune 0-000551 Rouge 0-000620 La vitesse de transmission des rayons de diffirentes couleurs dans le* espaces celestes est la meme dans le systeme des ondes et tout-^-faii independante de I'etendue ou de la vitesse des ondulations." " According to the mathematical theory of a system of waves, raya of different colors, having unequal undulations, must nevertheless be traaismitted through ether with the same velocity. There is no differ- ence in this respect from the mode of propagation of waves of sound which are transmitted through the atmosphere with equal velocity. This equahty of transmission in waves of sound may be well demon strated experimentally by the uniformity of effect produced by music at all distant^es from the source whence it emanates. The principal, I may say the only objection, advanced against ti'.e undulatory theory, consisted in the difficulty of explaining how the velocity of the propa- gation of rays of different colors through different bodies could be dis similar, while it accounted for the inequality of the refraction of the mys or of their dispersion. It has been recently shown that this diffi culty is not insurmountable, and that the ether may be supposed to ba tirxnsmitted througli bodies of unequal density in such a manner that rays of dissimilar systems of waves may be propagated through it with iiiieqiial velocities; but it remains to be determined whether the views advanced by geometricians on this question are in unison with the act* UJ',1 nature of tliinjrs. The following; are the lengths of the und'ilat-f*^is VELOCITY OF L-'GIIT. fc'5 refraction in the prism is not altered by the rt lation of the velocity of light to that of the earth's motion. All the meas- urements coincide in the result, that the light of those stars toward which the earth is moving presents the same index of refraction as the lisfht of those from which it is recedinsr. Using the language of the emission hypothesis, this celebra- t3d observer remarks, that bodies send forth rays of all ve- locities, but that among these different velocities one only is capable of exciting the sensation of light. ^ as oxperi men tally deduced from a series of facts in relation to inter- ference : mm. Violet 0-000423 Yellow 0-000551 Red 0-000620 The velocity of the transmission of rays of different colors through ce- lestial space is equal in the system of waves, and is quite independent of the length or the velocity of the undulations." — Arago, MS. of 1849. Compare also the Annuaire pour 1842, p. 333-336. The length of the himinous wave of the ether, and the velocity of the vibrations, determ- ine the chai'acter of the colored rays. To the violet, which is the most refrangible ray, belong 662, while to the red (or least refrangible ray with the gi'eatest length of wave) there belong 451 billions of vibra* tions in the second. * " J'ai'prouve, il y a bien des annees, par des observations directes que les rayons des etoiles vers lesquelles la Terre marche, et les ray- ons des etoiles dont la terre s'eloigne, se I'efractent exactement de la m«^me quantite. Un tel resultat ne peut se concilier avec la thiorie de remission qu'a I'aide d'une addition importante a faire a cette theorie • il faut admettre que les corps lumineux emettent des rayons de toutes les vitesses, et que les seuls rayons d'une vitesse determinee sont visi- bles, qu'eux seuls produisent dans I'oeil la sensat on de lumiere. Dans la tlieorie de I'emission, le rouge, le jaune, le vert, le bleu, le violet so- laires sontrespectivement accompagiies de rayons pareils, mais obscurs par defaut ou par exces de vitesse. A plus de vitesse correspond une nioindre refraction, comme moins de vitesse entraine une refraction plus grande. Ainsi chaque rayon rouge visible est accompagne de rayons obscurs de la meme nature, qui se refractent les uus plus, les autres moins que lui : ainsi il cxiste des rayons dans les strlcs noires de la por- tion rouge du spectre ; la meme chose doit etre admise des stries situ ees dans les portions jaunes, vertes, bleues et violettes." " I showed many years ago, by direct observations, that the rays of those stars toward which the earth moves, and the rays of those stars from which it recedes, are repeated in exactly the same degree. Such a result can not be reconciled with the theory of emission, unless we make the important admission that luminous bodies emit rays of all ve locities, and that only rays of a determined velocity are visible, these alone being capable of impressing the eye with the sensation of light. In the theory of emission, the red, yellow, green, blue, and violet so* lar rays are respectively accompanied by like rays, which are, how- ever, da"k from deficiency or excess of velocity. Excessive velocity it S6 COSMOS. On comparing tlie velocities of solar, stellar, and tcrreS' trial liglit, which are all equally refracted in the prism, with the velocity of the light of frictional electricity, we are disposed, in accordance with Wheatstone's ingeniously con- ducted experiments, to regard the lowest ratio in which the latter exceeds the former as 3 : 2. According to the lowest results of Wheatstone's optical rotatory apparatus, electric light traverses 288,000 miles in a second. =^ If we reckon 189,938 miles for stellar light, according to Struve's observ- sitions on aberration, we obtain the difference of 95,776 miles as the greater velocity of electricity in one second. These results are airparently opposed to the views ad- vanced by Sir William Herschel, according to v/hich solar and stellar lif^ht are regarded as the effects of an electro- magnetic process — a perpetual northern light. I say «j> 'parcntly, for no one will contest the possibility that there may be several very different magneto-electrical processes in the luminous cosmical bodies, in which light — the product of the process — may possess a different velocity of propaga tion. To this conjecture may be added the uncertainty of the numerical result yielded by the experiments of W^heat- stone, who has himself admitted that they are not sufficient- ly estabhshed, but need further confirmation before they can associated with a slight degree of refraction, while a smaller amount of velocity involves a slighter degree of refraction. Thus every visible red ray is accompanied by dark rays of the same nature, of which soma are more, and others less, refracted than the former; there are conse- quently rays in the black lines of the red portion of the spectrum ; and the same must be admitted in reference to the lines situated in the yel low, green, blue, and violet portions." — Arago, in the Comptes Rendus de VAcad. des Sciences, t. xvi., 1843, p. 404. Compare also t. viii., 1839, p. 326, and Poisson, TraiU de Mecanique, ed. ii., 1833, t. i., ^ 168. Ac- cording to the undulatory theory, the stars emit waves of extremely various transverse velocities of oscillations. * Wheatstone, in the Philos. Transact, of the Royal Soc.for 1834, p. 589, 591. From the experiments described in this paper, it would ap pear that the human eye is capable of perceiving phenomena of light, whose duration is limited to the millionth part of a second (p. 591). On the hypothesis referred to in the text, of the supposed analogy be- tween the light of the sun and polar liiilit, see Sir John Herschel's Re- sults of Astron. Observ. at the Cape of Good Hope, 1847, p. 351. Arago, in the Comptes Rendus pour 1838, t. vii., p. 956, has refei'red to the in- genious application of Breguet's improved Wheatstone's rotatoiy ap- paratus for determining between the theories of emission and undula- tion, since, according to the former, light moves more rapidly through water than through air, while, according to the latter, it moves more rapidly through air than through water. 'Compare also Comptes Ren ins pour 1850, t. xxx., p. 483-495, 55G.) VELOCITY OF ELECTRICITY. ST be satisfactorily compared with tlie results deduced from ob* servations on aberration and on the satellites. The attention of physicists has been powerfully attracted to the experiments on the velocity of the transmission of electricity, recently conducted in the United States by Walk* er during the course of his electro-telegraphic determina- tions of the terrestrial longitudes of AYashington, Philadel- phia, New York, and Cambridge. According to Steinheil's description of these experiments, the astronomical clock of the' Observatory at Philadelphia was brought to correspond so perfectly with Morse's writing apparatus on the tele- graphic line, that this clock marked its own course by points on the endless paper fillets of the apparatus. The electric telegraph instantaneously conveys each of these clock times to the other stations, indicating to these the Philadelphia time by a succession of similar points on the advancing pa- per fillets. In this manner, arbitraiy signs, or the instant of a star's transit, may be similarly noted down at the sta- tion by a mere movement of the observer's finger on the stop. "The special advantage of the American method consists," as Steinheil observes, " in its rendering the determination of time independent of the combination of the two senses, sight and hearing, as the clock notes its own course, and indicates the instant of a star's transit (with a mean error, according to Walker's assertion, of only the 70th part of a second). A constant difierence between the compared clock times at Philadelphia and at Cambridge is dependent upon the time occupied by the electric current in twice traversing the closed circle between the two stations." Eighteen equations of condition, from measurements made on conducting wires of 1050 miles, gave for the velocity of transmission of the hydro-galvanic current 18,700 miles,* which is fifteen times less than that of the electric current in^Mieatstone's rotatory disks. As in Walker's remarkable experiments tico ivires were not used, but half of the con- * Steinheil, in Schumacher's Astr. Nachr., No. 679 ('1849), s. 97-100 i Walker, in the Proceedings of ike American Philosophical Society, vol. v., p. 128. (Compare earlier propositions of Pouillet in the Comptcs Re7tdiis, t.xix.,1^. 1386.) The more recent ingenious experiments of Mitchel. Director of the Observatory at Cincinnati (Gould's Astron. Journal, Dec, 1849, p. 3, On the Velocity of the Electric Wave), and tho investigations of Fizeau and Gounelle at Paris, in Api-il, 1850, difier both from Wheatstone's and Walker's results. The experiments re corded in the Comptes Rendus, t. xxx., p. 439, exhibit striking difler i?nce3 betweftii iron and copper as conducting media. 88 COSMOS. duction, to use a conventional mole of expression, passed through the moist earth, we should seem to be justified in concluding that the velocity of the transmission of electricity depends upon the nature as well as the dimensions'^ of the medium. Bad conductors in the voltaic circuit become more powerfully heated than good conductors ; and the experi- mec.ts lately made by Riessf show that electric discharges are phenomena of a very various and complicated nature Ihe \'i3ws prevailing at the present day regarding what is usually termed " connection through the earth" are opposed to the hypothesis of linear, molecular conduction betvi'^een the extremities of the wires, and to the conjectures of the impediments to conduction, of accumulation, and disruption in a current, since what was formerly regarded as interme- diate conduction in the earth is now conjectured to belong exclusively to an equalization or restoration of the electric tension. Although it appears probable, from the extent of accura- cy at present attainable in this kind of observation, that the consta/tt of aberration, and, consequently, the velocity of light, is the same for all fixed stars, the question has fre- quently been mooted Avhether it be not possible that there are luminous cosmical bodies whose light does not reach us, in consequence of the particles of air being turned back by the force of gravitation exercised by the enormous masses of these bodies. The theory of emission gives a scientific form to these imaginative speculations. | I here only refer * See PoggendorfT's Annalen, bd. Ixxiii., 1818, s. 337, and Pouiilet, Comptes Rendns, t. xxx., p. 501. t Riess, in roggendorft''s Ann., bd. 78, s. 433. On the non-conduc tion of the intermediate earth, see the important experiments of Guille- min, Sur le courant dans une pile isoMe ct sans communication enire let poles in the Comptes Rendns, t. xxix., p. 521. " Quand on remplace un fil par la terre, dans les telegraphes electriques, la terre sert pkuot de reservoir commun, que de moyen d'union eiitre les deux extremi- tes du fil." " When the earth is substituted for half the circuit in the electric telegraph, it serves rather as a common resen'oir than as a means of connection between the two extremities of the wire." X Madler, Astr., s. 380; aUD Laplace, according to Moigno, RSperioirt d'Optique Moderne, 1847, L i., p. 72 : " Selon la theorie de I'emission on croit pouvoir demontrer que si le diametre d'une etoile fixe serait 250 fois plus grand que celui du soleil, sa densite restant la me me, I'attrac- tion exercee d sa surface detruirait la quantite de mouvement, de la molecule lumineuse emise, de sorte qu'elie serait invisible a de grandes distances." " It seems demonstrable by the theory of emission that if the diameter of a fixed star be 250 times greater than that of the sun— it3 density remaining the same — th(' attraction exercise.! on th*.' sTn'facf STELLAR LIGHT. 81) to such views because it will be necessan^ in the sequel thai we should consider certain peculiarities ©f motion ascribed to ProcyoU; which appeared to indicate a disturbance from dark cosmical bodies. It is the object of the present portion of this work to notice the different dir3ctions to which scien- tific inquiry had inclined at the period of its composition and publication, and thus to indicate the individual character of an epoch in the sidereal as well as the telluric sphere. The 'photometric relations (relations of brightness) of the self-luminous bodies with which the regions of space are filled, have for more- than two thousand years been an ob- ject of scientific observation and inquiry. The description of the starry firmament did not only embrace determinations of places, the relative distances of luminous cosmical bodies from one another and from the circles depending on the ap- parent course of the sun and on the diurnal movement of the vault of heaven, but it also considered the relative in- tensitv of the light of the stars. The earliest attention of mankind was undoubtedly directed to this latter point, in- dividual stars having received names before they were ar- ransred with others into groups and constellations. Among the wild tribes inhabiting the densely- wooded regions of the Upper Orinoco and the Atabapo, where, from the impene- trable nature of the vegetation, I could only observe high culminating stars for determinations of latitude, I frequently found that certain individuals, more especially old men, had designations for Canopus, Achernar, the feet of the Centaur, and a in the Southern Cross. If the catalogue of the con- stellations known as the Cata&terisms of Eratosthenes can lay claim to the great antiquity so long ascribed to it (between Autolycus of Pitane and Timocharis, and therefore nearly a "Would destroy the amount of motion emitted from the luminous mole- cule, so that it would be invisible at great distances." If, with Sir "^Villiam Herschel, we ascribe to Arcturus an apparent diameter of 0"'l, it follows that the true diameter of this star is only eleven times greater than that of our sun. {Cosmos, vol. i., p. 148.) From the above con- siderations on one of the causes of non-luminosity, the velocity of light must be veiy ditierent in cosmical bodies of difleient dimensions. This has, however, by no means been confirmed by the observations hitherto made. Arago says in the Comptes Rendus. t. viii., p. 326, " Les expe- liences snr I'egale deviation prismatique des etoiles, vers lesquelles la lerrs marche ou dont elle s'eloigne, rend compte de I'egalite de vitesse apparente de toutes les etoiles." "Experiments made on the equaj prismatic deviation of the stars toward which the earth is moving, and from which it is receding, explain the apparent equality of velocity in the rays of all the stars." fiO COSMOS!. * cenlary and a half before the time of Hipparchus), we po» sess in the astronomy of the Greeks a limit for the period when the fixed stars had not yet been arranged according to their relative majrnitudes. In the enumeration of the stars belonging to each constellation, as given in the Catas- tcrisms, frequent reference is made to the number of the largest and most luminous, or of the dark and less easily rec- ognized stars ;^ but we find no relative comparison of the stars contained in the different constellations. The Catas- te?'is7ns are, according to Bernhardy, Baehr, and Letronne, more than two hundred years less ancient than the catalogue of Hipparchus, and are, besides, a careless compilation and a mere extract from the Foeticum AUronomicum (ascribed to Julius Hyginus), if not from the poem 'Epurjg of the older Eratosthenes. The catalogue of Hipparchus, which we pos- sess in the form given to it in the Almagest, contains the ear- liest and most important determination of classes of magni- tude (gradations of brightness) of 1022 stars, and therefore of about one fifth of all the stars in the firmament visible to the naked eye, and ranging from the first to the sixth mag- nitude inclusive. It remains undetermined whether these estimates are all due to Hipparchus, or whether they do not rather appertain in part to the observations of Timocharis or Aristyllus, which Hipparchus frequently used. This work constituted the important basis on which was established the science of the Arabs and of the astronomers of the Middle Ages : the practice, transmitted to the nine- teenth century, of limiting the number of stars of the first magnitude to 15 (although Miidler counts 18, and Hiimker, after a more careful observation of the southern celestial hem- isphere, upward of 20), takes its origin from the classifica- tion of the Almagest, as given at the close of the table of stars in the eighth book. Ptolemy, referring to natural vi- sion, called all stars dark which were fainter than those of his sixth class ; and of this class he singularly enough only instances 49 stars distributed almost equally over both hem- ispheres. Considering that the catalogue enumerates about one fifth of all the fixed stars visible to the naked eye, it should, according to Argelander's investigations, have given * Eratosthenes, Catasterismi, ed. Schaubacli, 1795, and Eratosiher.ica, ed. G. Beruhardy, 1822, p. 110-llG. A distinction is made betwjen rtars laf^TTpovg (/j.Eyd?yOvg) and uiiavpoh^ (cap. 2, 11, 41). Ptolemy flso limits 01 uij^p(po)TOL to those stars whi 'h do not regularly belong to a coa- Btellaiiin. MAGNITUDES OF STARS Di r;40 stars of the sixth magnitude. The nebulous stars (ve- ^e?^oeL6£ig) of Ptolemy and of the Pseudo-Eratosthenian C(i' tastej'isms are mostly small stellar swarms,* appearing like nebulae in the clearer atmosphere of the southern hemisphere. I more particularly base this conjecture on the mention of a nebula in the right hand of Perseus. Galileo, who, like the Greek and Arabian astronomers, Avas unacquainted with the nebula^in Andromeda which is visible to the naked eye, says in his Niincius sidercus that stcllce 7iebuloscB are nothing more than stellar masses scattered in shining groups through the ether {areolcB siKirsim 'per cethera fulgent). i The ex- pression {tC)v [iEyd?i(x)v rd^ig), the order of magnitudes, al- though referring only to luster, led, as early as the ninth cen- tury, to hypotheses on the diameters of stars of different bright- ness ;| as if the intensity of light did not depend on the dis- tance, volume, and mass, as also on the peculiar character of the surface of a cosmical body in more or less favoring the process of light. At the period of the Mongolian supremacy, when, in the flteenth century, astronomy flourished at Samarcand, under Timur Ulugh Beg, photometric determinations were facili- tated by the subdivision of each of the six classes of Hippar- chus and Ptoleniy into three subordinate groups ; distinctions, fur example, being drawn between the small, intermediate, and large stars of the second magnitude — an attempt which reminds us of the decimal gradations of Struve and Argelan der.^ This advance in photometr}^ by a more exact determ- ination of degrees of intensity, is ascribed in Ulugh Beg's tables to Abdurrahman Sufi, v/ho wrote a work " on the knowledge of the fixed stars," and was the hrst who men- tions one of the Maofellanic clouds under the name of the White Ox. Since the discovery and gradual improvement of telescop'c vision, these estimates of the gradations of light have been extended far below the sixth class. The desire cf compa'ring the increase and decrease of light in the newly- * Ptol. Almag., ed Halma, toin. ii., p. 40, and in Eratosth. Catast., cap. 22, p. 18: // 6s KsdaAr/ Kai i/ upTCTj ufOTrror opuTai, Stu Si vE(pe/M6ov( cvaTpofy^ 6oKE~. tlclv opuadac. Thus, too, Geininus, Phcrn. (ed. Hilder, 1590), p. 46. t Cosmos, vol. ii., p. 330, 331. t Muhamedis Alfragani Chronologica et Ast. Elemeuta, 1590, cap. Xiiv., p. 118. § Some MSS. of the Almagest refer to such subdivisions or intermo- diate classes, as they add the words fxEiCuv or eAu(T(tuv to the determ- ination of magnitudes. (Cod. Paiis, No. 2389.) Tycho expressed thia mcrease or dirainullon by points 92 COSMOS. appeared stars in Cygnus and Ophiuchus (tie former of wh'.ch continued luminous for twenty-one years), with the bright- ness of other stars, called attention to photometric determina- tions. The so-called dark stars of Ptolemy, which were he- low the sixth magnitude, received numerical designations according to the relative intensity of their light. " Magni- tudes, from the eighth down to the sixteenth," says Sir John Herschel, " are familiar to those who are in the prajCtice of using powerful instruments.^ But at this fciint degree of brightness, the denominations for the difierent gradations in the scale of magnitudes are very undetermined, for Struve occasionally classes among the twelfth or thirteenth stars which Sir John Herschel designates as belonging to the eighteenth or twentieth magnitudes. The present is not a fitting place to discuss the merits of the very difierent methods which have been adopted for the measurement of light within the last hundred and fifty years, from Auzout and Huygens to Bouguer and Lambert ; and from Sir William Herschel, Humford, and Wollaston, to Stein- heil and Sir John Herschel . It will be sufficient for the ob- ject of this work briefly to indicate the difierent methods. These were a comparison of the shadows of artificial lights, differing in numbers and distance ; diaphragms ; plane-glass- es of different thickness and color ; artificial stars formed by reflection on glass spheres ; the juxtaposition of two seven- feet telescopes, separated by a distance which the observer could pass in about a second ; reflecting instruments in which two stars can be simultaneously seen and compared, when the telescope has been so adjusted that the star directly ob- served gives two images of like intensity ;t an apparatus hav» * Sir John Herschel, Outlines of Astr., p. 520-27. t This is the apphcatiou of redacting sextants to the determination of the intensity of stellar light; of this instrument I made greater use when in the tropics than of the diaphragms recommended to me by Borda. I began my investigation under the clear skies of Cumana, and continued them subsequently till 1803, but under less Divorable condi- tions, on the elevated plateaux of the Andes, and on the coasts of the Pacific, near Guayaquil. I had formed an arbitrary scale, in which 1 marked Sirius, as the brightest of all the fixed stars, equal to 100; the stars of the first magnitude between 100 and 80, those of the second magnitude between 80 and CO, of the third between %^ and 45, of the fourth between 45 and 3C, and those of the fifth between 30 and 20. I especially measured the constellations of Argo and Grus, in which I thought I had observed alterations since the time of LacaiUe. It seemed to me, after a careful combination of magnitudes, using other stars aa intermediate gradations, that Sirius was as much brighter than CanopuSf aa a Centauri than Achernar. My numbers can not, on account of tho rilOTOMETRIC METHODS. 1)3 ing (in front of the object-glass) a mirror and diapliragms, whose rotation is measured on a ring ; telescopes with di- vided object-gldsses, on either half of which the stellar light is received throngh a prism ; astrometers* in which a prism reflects the image of the moon or of Jupiter, and concentrates it through a lens at different distances into a star more or less bright. Sir John Herschel, who has been more zealous- ly engaged than any other astronomer of modern times in making numerical determinations in both hemispheres of the intensity of light, confesses that the practical application of exact photometric methods must still be regarded as a " de- above-menlioned mode of classification, be compared directly with those which Sir John Herschel made public as early as 1838. (See my Recueil cC Observ. Astr., vol. i., p. Ixxi., and Rclat. Hist, cht Voyage anx Rdgions Equin., t. i., p. 518 and 624 ; also Lettre de M. de Humboldt a M. Schumacher en Fcvr., 1839, in the Astr. Kachr., No. 374.) In this letter I wrote as follows : " M. Arago, qui possede des moyens photo- metriques entierement diflfereuts de ceux qui ont ete publies jusqu'ici, m'avait rassure siirla partie des erreurs qui pouvaient pi'ovenir du change- menfd'iuclinaison d'un miroir entame sur la face interieure. II blame d'ailleurs le principe de ma methode et le regarde comme peu suscep- tible de perfectiomiement, iion seulement a cause de la difference des angles eutre I'etoile vue directement et celle qui est amenee par reflex- ion, mais surtout parceque le resultat de la niesure d'iutensite depend de la partie de I'ceil qui se trouve en face de I'oculaire. II y a errenr lorsque la pupille n'est pas tres exactement k la hautem* de la limite in- ferieure de la portion uou entamee du petit miroir." " M. Arago, who possesses photometric data differing entirely from those hitherto pub lished, had instmcted me in x'eference to those errors which might arise from a change of inclination of a mirror silvered on its inner surface. He moreover blames the principle of my method, and regards it as lit- tle susceptible of correctness, not only on account of the difference of Bngles between the star seen dii-ectly and by reflection, but especially because the result of the amount of intensity depends on the part of the eye opposite to tlie ocular glass. There will be an error in the obsen'- ations when the pupil is not exactly adjusted to the elevation of the lower limit of the unplated part of the small mirror." * Compare Steinheil, Elemente der HeUigkeits-Messnngen am S/cr nen- jimviel Mimchen, 1836 (Sebum., Astr. Nachr., No. 609), and John Her- eche], Results of Astronomical Observations made during the Ycarx 1834 -1838 at the Cape of Good Hope (Lend., 1847), p. 353-357, Seidel at- tempted in 1846 to determine by means of Steinheil's photometer the quantities of light of several stars of the first magnitude, which attain the requisite degree of latitude in our northern latitudes. . Assuming Vega to be =1, he finds for Sinus 5-13 ; for Rigel, whose luster appears to be on the increase, 1*30; for Arcturus, 0-84; for Capella, 0-83; for Procyon, 0-71; for Spica, 0-49; for Atair, 0-40; for Aldebaran, 0-36; for Deneb, 0-35; for Regains, 0-34; for Pollux, 0-30; he does not giva the intensity of the light of Betelgeux, on account of its being a varia ble star, as was particularly manifested between 1836 and 1S39. {Out iines, p. 5J3 ) Oi COSMOS. sideratum in astronomy," and that " photometry is yet a. ^^m infancy." The increasing interest taken in variable ssWrs^ and the recent celestial phenomenon of the extraordinary in- crease of light exhibited in the year 1837 in a star of the con- stellation Argo, has made astronomers more sensible of the importance of obtaining certain determinations of light. It is essential to distinguish between the mere arrangement of stars according to their luster, without numerical estimates of" the intensity of light (an arrangement adopted by Sir John Herschel in his Manual of Scientific Lic^uiry iweixircd for the Use of the NavT/), and classifications in which intensity of light is expressed by numbers, under the form of so-called relations of magnitude, or by more hazardous estimates of the quantities of radiated light. =^ The first numerical scale, based on estimates calculated with the naked eye, but improved by an ingenious elaboration of the materialsf probably deservea the preference over any other spproximative method practi- cable in the present imperfect condition of photometrical in ■ struments, however much the exactness of the estimates must be endangered by the var}^ing pov/ers of individual observers — the serenity of the atmosphere — the difierent altitudes of widely-distant stars, which can only be compared by means of numerous intermediate stellar bodies — and above all by the unequal color of the light. Very brilliant stars of the first magnitude, such as Sirius and Canopus, a Centauri and Achcr- nar, Deneb and Yega, on account of their white light, admit far less readily of comparison by the naked eye than fainter stars below the sixth and seventh magnitudes. Such a com- parison is even more difficult when we attempt to contrast yellow stars of intense light, like Procyon, Capella, or Atair, with red ones, like Aldebaran, Arc turns, and Betelgeux.J * Compare, for the numencal data of the photometric results, funi tables of Sir Joha Herschel's Asfr. Ohs. at the Cape, a), p. 341 ; b), p. 367-371 ; c), p. 440 ; and d), in his Outlines of Astr., p. 522-525, 645- 646. For a mere an'augeraent without numbers, see the Manual of Scienfijic Inqviry prepared for the Use of the Navy, 1819, p. 12. In order to improve the old conventional mode of classing the stars accord- ing to magnitudes, a scale of photometric magnitudes, consisting in tlie addition of 0*41, as explained more in detail in Astr. Obs. at the Cape, p. 370, has been added to the vulsfar scale of magnitudes in the Outlines of Astronomy, p. 645, and these scales are subjoined to this portion of tht, present work, together with a list of northern and southern stars. t Argelander, Durchrmisterung des nordl. Himmels zwischen 45*-* 'uni\ 80° Decl. 1846, s. xxiv.-xxvi. ; Sir John Hcrscliel, Astr. Obfcrv. at tht Cape of Good Hope, p. 327, 340, 365. I Op. cit., p. 304, and Outl.. p. .522. rHOTOMETR'i'. 95 Sir Jolin Herscliel lias endeavored to determine the rela- tion between the intensity of solar light and that of a star of the first magnitude by a photometric comparison of the moor, with the double star a Centauri of the southern hemisphere, ^hich is the third in brightness of all the stars. He thus fulfilled (as had been already done by AVollaston) a wish ex- pressed by John Michell=* as early as 1767. Sir John Her- scliel found from the mean of eleven measurements conduct- ed with a prismatic apparatus, that the full moon v/as 27,408 times brighter than a Centauri. According to Wollaston, the light of the sun is 801,072 times brighter than the full moon ;t whence it follows that the light transmitted to us from the sun is to the light which we receive from a Centauri as 22,000 millions to 1. It seems, therefore, very probable, when, in accordance with its parallax, we take into account the distance of the star, that its (absolute) proper luminosity exceeds that of our sun by 2-^-^ times. Wollaston found the brifrhtness of Sirius 20,000 million times famter than that of the sun. From what we at present believe to be the paral- lax of Sirius (0'"230), its actual (absolute) intensity of light exceeds that of the sun 63 times. $ Our sun therefore be- longs, in reference to the intensity of its process of light, to the fainter fixed stars. Sir John Herschel estimates the in- tensity of the light of Sirius to be equal to the light of nearly * Pliilos. Transact., vol. Ivii., fur tlic year 17G7, p. 234. t Wollaston, in the Fhilos. Transact, for 1829, p. 27. Herscliel'a Outlines, p. 553. Wollastou's comparison of the light of the sun with that of the moon was made in 1799, and was based on observations of the shadows thrown Ly lighted wax tapers, while in the experiments made on Sirius in 1826 and 1827, images reflected from thermometer bnlbs were employed. The earlier data of the intensity of the sun'a light, compared with that of the moon, differ widely from the results here given. They were deduced by Michelo and Euler, from theoret- ical grounds, at 450,000 and 374,000, and by Bouguer, from measure- ments of the shadows of the light of wax tapers, at only 300,000. Lam- bert assumes Venus, in her greatest intensity of light, to be 3000 times fainter than the full moon. According to Steinhei], the sun must be 3,286,500 times further removed from the earth than it is, in order to appear like Arcturus to the inhabitants of our planet (Struve, Stellarum Compositarum Mcns2ircB MlcrometriccB, p. clxiii.) ; and, according to Sir John Herschel, the light of Arcturus exhibits only half the intensity of Danopus. — Herschel, Ohserv. at the Cape, p. 34. All these conditions of" intensity, more especially the important comparison of the bright nes3 of the sun, the full moon, and of the ash-colored light of our satel« lite, which varies so greatly according to the different positions of tha '^arth considered as a reflecting body, deserve further and Berioaa ia< vestigation. t (hitl. of Astr., p. 553 ; Astr. O'jserv. at the Cape, p. 363. 06 C0SiM03. two hundred stars of the sixth magnitude. Since it is very probable, from analogy with the experiments already made that all cosmical bodies are subject to variations both in theii movements through space and in the intensity of their light, although such variations may occur at very long and unde- termined periods, it is obvious, considering the dependence '>f all organic hfe on the sun's temperature and on the intens' ity of its light, that the perfection of photometry constitutes a great and important subject for scientific inquiry. Such an improved condition of our knowledge can render it alone possible to transmit to future generations numerical determ- inations of the photometric condition of the firmament. By these means we shall be enabled to explain numerous geog- nostic phenomena relating to the thermal history of our at' mos'pherc, and to the earlier distribution of plants and ani- mals. Such considerations did not escape the inquiring mind of William Herschel, who, more than half a century ago, be- fore the close connection between electricity and magnetism had been discovered, compared the ever-luminous cloud-en velopes of the sun's body with the polar light of our own ter- restrial planet.* Arago has ascertained that the most certain method for the direct measurement of the intensity of light consists in observing the complementary condition of the colored rings Been by transmission and reflection. I subjoin in a note,! in * William Herschel, On the Nature of the Sun and Fixed Stars, in the Philos. Transact, for 1795, p. 62 ; and On the Changes that happen to the Fixed Stars, in the Philos. Transact, for 1796, p. 18G. Compai'e also Sir John Herschel, Observ. at the Cape, p. 350-352. i Extract of a Letter from M. Arago to M. de Humboldt, May, 1850. (a.) Mcsiires Phoiomitriques. " II n'existe pas cle photometre proprement dit, c'est-^-dire d'instru- ment donnant I'iutensite d'une himiere isolee ; le photometre de Les- lie, k I'aide duquel il avait eu I'audace de vouloir comparer la lumiere de la lune a la lumiere du soleil, par des actions calorifiques, est com- plctement dcfectueux. .T'ai prouve, en effet, que ce pretendu photo- metre monte quand on I'expose a la lumiere du soleil, qu'il descend sous Taction de la lumiere du feu ordinaire, et qu'il reste complete' ment stationnaire lorsqu'il re9oit la lumiere d'une lampe d'Argand. Tout ce qu'on a pu faire jusqu'ici, c'est de comparer entr'elles deux lu« mitres en presence, et cette comparaison n'est memo a I'abri de toute objection que lorsqu'on ramene ces deux lumieres k I'egalite par uu aflfaiblissement graduel de la lumiere la plus forte. C'est comme crit©« rium de cette egalite que j'ai employe les anneaux colores. Si on place I'une sur I'autre deux leutilles d'un long foyer, il se forme autour de leur point de contact des anneanx colores tant par voio de redexion quo pai" vol? de transmission. Lcs aimeaux rcllechis sont complcnientairva PHOTOMETRY. 97 his own words, the results of my friend's photometric method, to which he has added an account of the optical principle on which his cyanometer is based. en couleur des anneaux transrais ; ces deux series d'anncaux se neu- tralisent mutuellemeut quand les deux luniieres qui les forment et qui arnvent simultanemeut sur les deux lentilles, sout egales entr'elles. " Daus le cas contraire on voit des traces ou d'auneaux reflechis ou d'anneaux transmis, suivant que la lumiere qui forme les premiers, est plus forte ou plus foible que la lumiere k laquelle on doit les seconds. C'est daus ce sens seulement que les anneaux colores jouent un rolo dans les mcsures de la lumiere auxquelles je me suis livre." {b.) Cyanometre, " Mon cyanometre est line extension de mon polariscope. Ce der» nier instrument, comme tu sais, se compose d'un tube ferme a I'uno do ses extremites par une plaque de cristal de roche perpendiculaire k I'axe, de 5 millimetres d'epaisseur; et d'un prisme done de la double refraction, place du cote de I'oeil. Parmi les couleurs varices que donne cet aj)pareil, lorsque de la lumiere polarisee le traverse, et qu'on fait tourner le prisme sur lui-meme, se trouve par un heureux hasard la nuance du bleu de ciel. Cette couleur bleue fort affaiblie, c'est-a-dii'e tres melangee de blanc lorsque la lumiere est presque neutre, aug- inente d'intensite — progressivement, a mesure que les rayons qui pene trent dans I'instrument, renferment une plus grande proportion de ray ons polarises. " Supposons done que le polariscope soit dirige sur une feuille de pa pier blanc ; qu'entre cette feuille et la lame de cristal de roche il ex iste une pile de plaques de verre susceptible de changer d'inclinaison, CO qui rendra la lumiere eclairaute du papier plus ou moins polarisee ; la couleur bleue fournie par I'instrument va en augmentant avec I'in- clinaison de la pile, et I'on s'arrete lorsque cette couleur parait la meme que celle de la region de I'atmosphere dont on veut determiner la teinte cyanometrique, et qu'on regarde k I'oeil nu immediatement a cote de I'instrument. La mesure de cette teinte estdonnee par I'inclinaison de la pile. Si cette derniere partie de I'instrument se compose du merae nombre de plaques et d'une meme espece de verre, les observations faites daiis divers lieux seront parfaitemeut compai'ables entr'elles." {a.) Photometric Measurements. "There does not exist a photometer properly so called, that is to say, no instrument giving the intensity of an isolated light ; for Leslie's pliotometer, by means of which he boldly supposed that he could com pare the light of the moon with that of the sun, by their caloric actions, IS utterly defective. I found, in fact, that this pretended photometer rose on being exposed to the light of the sun, that it fell when exposed to a moderate fire, and that it remained altogether stationaiy when orought near the light of an Argand lamp. All that has hitherto been done has been to compare two lights when contiguous to one another but even this comparison can not be relied on unless the two lights be equalized, the stronger being gradually reduced to the intensity of the feebler. For the purpose of judging of this inequality I employed col- ored rings. On placing on one another two lenses of a great focal length, colored rings will be formed round their point of contact as Birich by means of reflection as of transmis-^on. The colors of the re- Vol. Ill — E Q8 COSMOS. The so-called relations of the magnitude cf the fixed star^ as given in our catalogues and maps of the stars, sometimes indicate as of simultaneous occurrence that which belongs to very different periods of cosmical alterations of light. Tha order of the letters v^^hich, since the beginning of the seven- teenth century, have been added to the stars in the general- ly consulted tlranometria Bayeri, are not, as was long sup- posed, certain indications of these alterations of light. Arge- iander has ably shown that the relative brightness of the stars can not be inferred from the alphabetical order of the letters, and that Bayer was influenced in his choice of these letters by the form and direction of the constellations.* fleeted rings are complementary to those of the transmitted rings ; these two series of rings neutralize one another when the two lights by^vhich they are formed, and which fall simultau'^ously on the two lenses, are equal. " In the contrary case, we meet y\n\\\ traces of reflected or transmit- ted rings, according as the light by which the former are produced is stronger or fainter than that from which t\± ward of 5000 for the horizon ol Taris. He gives 70,000 for tne whole spher3, including stars of the ninth magnitude. (Asfronomi6, th. iii., s, 54.) These numbers are aii much too high. Argelander finds only 08,000 from lhe first to the eighth magnitude. 108 COSMOS. and who comments on his boldness in attempting", as it were, *' to leave heaven as a heritage to posterity," should hav« enumerated only 1600 stars visible in the fine sky of Italy I^ In this enumeration he had, however, descended to stars of the fifth, while half a century later Ptolemy indicated only 1025 stars down to the sixth magnitude. Since it has ceased to be the custom to class the fixed stars merely according to the constellations to which they belong, and they have been catalogued according to determinations of place, that is, in their relations to the great circles of the equator or the ecliptic, the extension as well as the accuracy of star catalogues has advanced with the progress of science and the improved construction of instruments. No catalogues of the stars compiled by Timocharis and Aristyllus (283 B.C.) have reached us ; but although, as Hipparchus remarks in the fragment " on the length of the year," cited in the sev- enth book of the Almagest (cap. 3, p. xv., Halma), their ob- servations were conducted in a very rough manner [rravv oXoaxf^poJg), there can be no doubt that they both determ- ined the declination of many stars, and that these determin- ations preceded by nearly a century and a half the table of fixed stars compiled by Hipparchus. This astronomer is said to have been incited by the phenomenon of a new star to attempt a survey of the whole firmament, and endeavor to determine the position of the stars ; but the truth of this Srtatement rests solely on Pliny's testimony, and has often been regarded as the mere echo of a subsequently invented tradition.! It does indeed seem remarkable that Ptolemy should not refer to the circumstance, but yet it must be ad- mitted that the sudden appearance of a brightly luminous *■ " Patrociiiatur vastitas cceH, immensa discreta altitudine, in clno at- que septuaginta signa. Hjec sunt i-eriim et animantiura effigies, in quas digessere ccelura periti. In his quidera niille sexcentas adnotavere Stel- las, insignes videlicet efFectu visuve" .... Plin., ii., 41. "Hipparchua nunqucun satis laudatus, ut quo nemo magis approbaverit cognationeui cum bomine siderum animasque nostras partem esse ccEli, novani stel lam et aliam in xvo suo genitam deprehendit, ejusque motu, qua die fulsit, ad dubitationem est adductus, anne hoc saepius fieret moveren* tiirque et eae quas putamus affixas ; itemque ausus rem etiam Deo im- probam, adnumerare posteris Stellas ac sidera ad nomen expungere, or-, ganis excogitatis, per qua) singularum loca atque magnitudines signaret, ut facile discerni posset ex eo, non modo an obirent nascerenturve, sed an omnino aliqua transirent moverenturve, item an crescerent minue* reuturque, coelo in hereditate cunctis relicto, si quisquam qwi cretionem earn caperet inventus esset." — Plin., ii., 26. t Delambre, Hist, de V Astr. Anc, tom. i., p. 290, and Hist, de VAstr A/nd., torn, ii., p. ISvG. NUMBER OF THE FIXED STARS. 109 Star in Cassiopeia (November, 1572) led Tycho Braiie to compose his catalogue of the stars. According to an ingen« ious conjectm-e of Sir John Herschel,* the star referred to by Pliny may have been the new star which appeared in Scorpio in the month of July of the year 134 before our era (as we learn from the Chinese Annals of the reign of Wou-ti, of the Han dynasty). Its appearance occurred exactly six years before the epoch at which, according to Ideler's investiga- tions, Hipparchus compiled his catalogue of the stars. Ed- ward Biot, whose early death proved so great a loss to science, found a record of this celestial phenomenon in the celebra- ted collection of Ma-tuan-lin, which contains an account of all the comets and remarkable stars observed between the years B.C. 613 and A.D. 1222. The tripartite didactic poem of Aratus,t to whom we are indebted for the only remnant of the works of Hipparchus that has come down to us, was composed about the period of Eratosthenes, Timocharis, and Aristyllus. The astronomical non-meteorological portion of the poem is based on the ura- nography of Eudoxus of Cnidos. The catalogue compiled by Hipparchus is unfortunately not extant ; but, according to Ideler,$ it probably constituted the principal part of his work, cited by Suidas, " On the arrangement of the region of the fixed stars and the celestial bodies," and contained 1080 de- terminations of position for the year B.C. 128. In Hippar- chus's other Commentary on Aratus, the positions of the starts, which are determined more by equatorial armilla3 than by the astrolabe, are referred to the equator by right ascension and declination ; while in Ptolemy's catalogue of stars, which is supposed to have been entirely copied from that of Hip- parchus, and which gives 1025 stars, together with five so- called nebulae, they are referred by longitudes and latitudes * Outlines, § 831 ; Etlward Biot, Sur les Etoilcs Extraordinaires oh- servees en Chine, ia the Connnissance des temps pour 1840. t It is worthy of remark that Aratus was mentioned with approba- tion almost simultaneously by Ovid {Amor., i., 15) and by the Ajiostlo Paul at Athens, in an earnest discourse directed against the Epicureans and Stoics. Paul {Acts, ch. xvii., v. 28), although he does not mention Aratus by name, undoubtedly refers to a verse composed by him {Phccn., V 5) on the close communion of mortals with the Deity. X Idelei', Untersnchitngen iiber den Ursprung der Stemnamen, s. xxx.-» X}r5V. Baily, in \\xe Mem. of the Asti-on. Soc, vol. xiii., 1843, p 12 and 15, also treats of the years according to our era, to which we must refer the observations of Aristyllus, as well as the catalogues of the stars com- piled by Hipparchus (128. and not 140, B.C.) and by Ptolon)y (138 A I) ) \10 COSMOS. *,o the ecliptic,^ On comparing the number of fixed stars lU the Hipparch>Ptolemaic Catalogue, Almagest, ed. Hahina, t. ii., p. 83 (namely, for the first mag,, 15 stars ; second, 45 ; thh'd, 208 ; fourth, 474 ; fifth, 217 ; sixth, 49), with the numbers of Argelander as already given, we find, as might be expected, a great paucity of stars of the fifth and sixth magnitudes, and also an extraordinarily large number of those belonging to the third and fourth. The vagueness in the determinations of the intensity of light in ancient and modern times renders direct comparisons of magnitude ex- tremely uncertain. Although the so-called Ptolemaic catalogue of the fixed stars enumerated only one fourth of those visible to the naked eye at Rhodes and Alexandria, and, owing to erroneous re- ductions of the precession of the equinoxes, determined theii positions as if they had been observed in the year 63 of out era, yet, throughout the sixteen hundred years immediately following this period, we have only three original catalogues ci stars, perfect for their time ; that of Ulugh Beg (1437), * Compare Delambre, Hist, de VAstr. Anc, torn, i., p. 184; torn, ii., p. 260. The assertion that Hipparchus, in addition to the riglit ascen- sion and declination of the stars, also indicated their positions in his catalogue, according to longitude and latitude, as was done by Ptolemy, is wholly devoid of probability and in direct variance with the Alma- gesi, book vii., cap. 4, where this reference to the ecliptic is noticed as something new, by which the knowledge of the motions of the fixed stars round the pole of the ecliptic may be faciUtated. The table of stars with the longitudes attached, which Petriis ¥ictorius found in a Medicean Codex, and published with the life of Aratus at Florence in 1567, is indeed ascribed by him to Hipparchus, but without any proof. It appears to be a mere rescript of Ptolemy's catalogue from an old manuscript of the Almagest, and does not give the latitudes. As Ptole- my was imperfectly acquainted with the amount of the retrogression of the equinoctial and solstitial points {Almag., vii., c. 2, p. 13, Halma), and assumed it about ~^^ too slow, the catalogue which he determined for the beginning of the reign of Antoninus (Ideler, o/). cit., s. xxxiv.) indicates the positions of the stai's at a much earlier epoch (for the year G3 A.D.). (Regarding the improvements for reducing stars to the time of Hipparchus, see the observations and tables as given by Encke in Schumacher's y4si!ro7i. Nach'r.. No. 608, s. 113-126.) The earlier epoch to which Ptolemy unconsciously reduced the stars in his catalogue cor- responds tolerably well with the period to which we may refer the Pseudo-Eratosthenian Catasterisms, which, as I have already elsewhere observed, are more recent than the time of Hyginus, who lived in the Augustine age, but appear to be taken from him, and have no conneo tion with the poem of Hermes by the true Eratosthenes. (Erafosiheni- ea, ed. Bernhardy, 1822, p. 114, 116, 129.) These Pseudo-Eratosthe. nian Catasterisms contain, moreover, scarcely 700 individual stars dis» tribute. 1 among the mythical constellations. EARLY CATA'.OGUES. Ill that of Tycho Bralie (1600), and that of Hevelius (1660), During the short intervals of repose which, amid tumultuous revolutions and devastations of war, occurred between the ninth and fifteenth centuries, practical astronomy, undei Arabs, Persians, and Moguls (from Al-Mamun, the son of the great Haroun Al-Raschid, to the Timurite, Mohammed Tar- aghi Ulugh Beg, the son of Shah E-okh), attained an emi- nence till then unknown. The astronomical tables of Ebn- Junis (1007), called the Hakemitic tables, in honor of the Fatimite calif, Aziz Ben-Hakem Biamrilla, afford evidence, as do also the Ilkhanic tables^ of Nassir-Eddin Tusi fwho founded the great observatory at Meragha, near Tauris, 1259), of the advanced knowledge of the planetary motions — the improved condition of measuring instruments, and the mul- tiplication of more accurate methods differing from those em- ployed by Ptolemy. In addition to clepsydras,! pendulum- oscillationsl were already at this period employed in the measurement of time. The Arabs had the great merit of showing how tables might be gradually amended by a comparison with observa- tions. Ulugh Beg's catalogue of the stars, originally written in Persian, was entirely completed from original observations made in the Gymnasium at Samarcand, with the exception of a portion of the southern stars enumerated by Ptolemy,^ * Cosmos, vol. ii., p. 222, 223. The Paris Library contains a manu- script of the Ilkhanic Tables by the hand of the son of Nassir-Eddin. They deidve their name from the title " Ilkhan," assumed by the Tar- tar princes who held rule in Persia. — Reinaud, Introd. de la G4ogr. d'AbouIfeda, 1848, p. cxxxix. t [For an account of clepsydras, see Beclcmmnt's Inventions, vol. i., 2M,ef. seq. (Bohn's edition).] — Ed. t Sedillot fils, Prolegomenes d^es Tahlcs As!r. d' OIo%ig-Beg, 1847, p. cxxxiv., note 2. Delambre, Hist, de I'A.str. du Moyen Age, p. 8. § In my investigations on the relative vakie of astronomical determ- inations of position in Central Asia {Asie Centrale, t. iii., p. 531-596), J have given the latitudes of Samarcand and Bokhara according to the different Arabic and Persian MSS. contained in the Paris Library. I have shown that the foniier is probably more than 39"^ 52', while most of the best manuscripts of Ulugh Beg give 39^ 37', and tlie Kitab aU athual of Alfares, and the Kanum of Albyruni, give 40°. I would again draw attention to the importance, in a geographical no less than an as- tronomical point of view, of determining the longitude and latitude of Samarcand by new and trustworthy observations. Burnes's Travela have made us acquainted with the latitude of Bokhara, as obtained from observations of culmination ot stars, which gave 39° 43' 41". There is, therefore, only an error of from 7 to 8 minutes in the two fine Persian and Arabic MSS. (Nos. 164 and 2460) of the Paris Library. Major Ren- i»ell, wh )se combinations are generally so successful, made an error o/ 112 COSMOS. and not visibl'i in 39^ 52' lat. (?) It contains only 10 19 positions of stars, which are reduced to the year 1437. A subsequent commentary gives 300 other stars, observed by Abu-Bekri Altizini in 1533. Thus we pass from Arabs, Per- sians, and Moguls, to the great epoch of Copernicus, and nearly to that of Tycho Brahe. The extension of navigation in the tropical seas, and in liigh southern latitudes, has, since the beginning of the six- teenth century, exerted a powerful influence on the gradual extension of our knowledge of the firmament, though in a less degree than that effected a century later by the appli- cation of the telescope. Both were the means of revealing new and unknown regions of space. I have already, in other ' w:)rks, considered^ the reports circulated first by Americus Vespucius, then by Magellan, and Pigafetta (the companion of Magellan and Elcano), concerning the splendor of the southern sky, and the descriptions given by Vicente Yaiiez Pinzon and Acosta of the black patches (coal-sacks), and by Anghiera and Andrea Corsali of the Magellanic clouds. A merely sensuous contemplation of the aspect of the heavens here also preceded measuring astronomy. The richness of the firmament near the southern pole, which, as is well known, is, on the contrary, peculiarly deficient in stars, was so much exaggerated that the intelligent Polyhistor Cardanua indicated in this region 10,000 bright stars which were said to have been seen by Vespucius with the naked eye.f Friedrich Houtman and Petrus Theodori of Embden (who, according to Olbers, is the same person as Dircksz Keyser) now first appeared as zealous observers. They measured distances of stars at Java and Sumatra ; and at this period the most southern stars were first marked upon the celestial maps of Bartsch, Hondius, and Bayer, axid by Kepler's in- dustry were inserted in Tycho Brahe's Rudolphine tables. Scarcely half a century had elapsed from the time of Ma- gellan's circumnavigation of the globe before Tycho com menced his admirable observations on the positions of the fixed stars, which far exceeded in exactness all that had hitherto been done in practical astronomy, not excepting even about 19' m determining the latitude of Bokhara. (Humboldt, Asit Ccntrale, t. iii., p. 592, and Sedillot, in the Prolegomenes d'Olovg-Beg, p. cxxiii.-cxxv.) * Cosmos, \o\. ii., p. 285-29C ; Humboldt, Examcn Or'J de V Histain ie ='« Geogr., t. iv., p. 321-33(5 : t. v., p. 226-238. \ Cardnni Paralipomcnn7i,Y\h. viii., c:ip. 10. {Opp , t, \i ., eil Lu. W)7 ZODIACAL SIGNS. 119 groups ; the for.ner mentions tlie constellation of the Beat (" otherwise known as the Celestial Wain, and which alona never sinks into the bath of Oceanos"), Bootes, and the Dog of Orion ; the latter speaks of Sirius and Arcturus, and both refer to the Pleiades, the Hyades, and Orion.* Homer's twice repeated assertion that the constellation of the Bear alone never sinks into the ocean, m.erely allows us to infer that in his age the Greek sphere did not yet comprise the constella- tions of Draco, Cepheus, and Ursa Minor, wliich likewise do not set. The statement does not prove a want of acquaint- ance with the existence of the separate stars forming these three catasterisms, but simply an ignorance of their arrange ment into constellations. A long and frequently misunder- stood passage of Strabo (hb. i., p. 3, Casaub.) on Homer, //., xviii., 485—489, specially proves a fact — important to tho question — that in the Greek sphere the stars were only grad- ually arranged in constellations. Homer has been mijustly accused of ignorance, says Strabo, as if he had known of only one instead of two Bears. It is probable that the lesser one had not yet been arranged in a separate group, and that the name did not reach the Hellenes until after the Phoenicians had sj)ecially designated this constellation, and made use of it for the purposes of navigation. All the scholia on Homer, Hyginus, and Diogenes Laertius ascribe its introduction to Thales. In the Pseudo-Eratosthenian work to which we have already referred, the lesser Bear is called (^olvUt] (or, as it were, the Phoenician guiding star). A century later (01. 71), Cleostratus of Tenedos enriched the sphere with the constellations of Sagittarius, To^orrjg, and Aries, Kpiog. The introduction of the Zodiac into the ancient Greek sphere coincides, according to Letromie, with this period of the domination of the Pisistratidse. Eudemus of Hhodes, one of the most distinguished pupils of Aristotle, and author of a "History of Astronomy," ascribes the introduction of this zo- diacal belt (?) rod ^iDdtanov dia^cjGLg, also ^G)i6wg icvfcXog) to GFlnopides of Cliios, a cotemporary of Anaxagoras.f Tho * Ideler, Untcrs. uher die Stcrnnamen, s. xi., 47, 139, 144, 243 • Lev traune, Sur VOrigine du Zodiaqve Grec, 1340, p. 25. "t Letronne, op. cit., p. 25 ; and Carteron, Analyse des RecTiercties de M. Letronne sur les Representations Zodiacalcs, 1843, p. 119. "It is very doubtful whether Eudoxus (01. 103) ever made use of the word ^oidtaKoq. We first meet with it iu Euclid, and iu the Commentary of Hipparchus on Aratns (01. 160). The name ecliptic, ekXeltttlko^, ia also very recent." Compare Martin in the Commentary to Thconit Smyrnai Platonici Liber de Adionomia, 1849, p. 50, GO. 120 COSMOS. idea of the relation of the planets and fixed stars to the su/t^s course, the division of the ecliptic into twelve equal partu (Dodecatoraeria), originated with the ancient Chaldeans, and very probably came to the Greeks, at the beginning of tlia ^fth, or even in the sixth century before our era, direct from Chaldea, and not from the Valley of the Nile.* The Greeks merely separated from the constellations named in their prim* itive sphere those which were nearest to the ecliptic, and could be used as signs of the zodiac. If the Greeks had bor- rowed from another nation any tiling more than the idea and number of the divisions (Dodecatomeria) of a zodiac — -if they had borrowed the zodiac itself, with its signs — they v/ould not at first have contented themselves with only eleven con- stellations. The Scorpion would not have been divided into two groups ; nor would zodiacal constellations have been in- troduced (some of which, like Taurus, Leo, Pisces, and Virgo, extend over a space of 35° to 48°, while others, as Cancer, Aries, and Capicornus, occupy only from 19° to 23°), which are inconveniently grouped to the north and south of the ecliptic, either at great distances from each other, or, like Tau- rus and Aries, Aquarius and Capricornus, so closely crowded together as almost to encroach on each other. These cir- cumstances prove that catasterisms previously formed were converted into signs of the zodiac. The sign of Libra, according to Letronne's conjecture, was introduced at the time of, and perhaps by, Hipparehus. It is never mentioned by Eudoxus, Archimedes, Autolycus, or even by Hipparehus in the few fragments of liis writings which have been transmitted to us (excepting indeed in one * Letroune, Orig. du Zod., p. 25 ; and Analyse Crit. des Repris. Zod., 1846, p. 15. IJeler and Lepsius also consider it probable " that the knowledge of the Chaldean zodiac, as well in reference to its divi- sions as to the names of the latter, had reached the Greeks in the sev- enth century before our era, although the adoption of the separate signs of the zodiac in Greek astronomical literature was gradual and of a sub- sequent date." (Lepsius, Chrcnologie der u^gypter, 1849, s. 65 and 124.) Ideler is inclined to believe that the Orientals had names^ but not constellations for the Dodecatomeria, and Lepsius regards it as a natural assumption " that the Greeks, at the period when their sphere was for the most part unfilled, should have added to their own the Chaldean constellations, from which the twelve divisions were named." But are we not led on this supposition to inquire why the Greeks had at first only eleven signs instead of introducing all the twelve belong- ing to the Chaldean Dodecatomeria ? If they introduced the twelve eigns, they ai'e hardly likely to hav6 removed one in order to replace i\ at a subseq eu* period i,ODlACAL SIGNS. 121 passage, pDjbaWy falsified by a copyist).* Tlie earliest no- tice of this new constellation occurs in Gemiiius and Yarro scarcely half a century before our era ; and as the Romans, from the time of Augustus to Antoninus, became more strong- ly imbued with a jjredilection for astrological inquiry, thosf, constellations which " lay in the celestial path of the sun'* acquired an exaggerated and fanciful importance The Egyp- tian zodiacal constellations found at Dendera, Esnch, the Propylon of Panopolis, and on some mummy-cases, belong to the first half of this period of the Rorr.an dominion, as was maintained by Visconti and Testa, at a time when the nec- essary materials for the decision of the question had not been collected, and the wildest hypothesis still prevailed regard- ing the signification of these symbolical zodiacal signs, and their dependence on the precession of the equinoxes. The great antiquity which, from passages in Manu's Book of Laws, Yalmiki's E.amayana and Amarasinha's Dictionary, Augustus William von Schlegel attributed to the zodiacal •circles found in India, has been rendered very doubtful by Adolph Holtzmami's ingenious investigations.! * On the passage referred to iu the text, and interpolated by a coi)y ist of Hipparchas, see Letronne, OnV. du Zod., 1810, p. 20. As early as 1812, when I was much disposed to believe that the Greeks had been long acquamted with the sign of Libra, I directed attention in au elaborate memoir (on all the passages iu Greek and Roman writers of antiquity, in which the Balance occurs as a sign of the zodiac) to that passage in Hipparchus (Comment, in Arafum, lib. iii., cap. 2) which re- fers to the {^Tjpiov held by the Centaur (in his fore-foot), as well as to the remarkable passage of Ptolemy, lib. ix., cap. 7 (Halma, t. ii., p. 170). In the latter the Southern Balance is named with the affix Kara 'K.aAdacovc, and is opposed to the pincers of the Scorpion in an observ- ation, which was undoubtedly not made at Babylon, but by some of the astrological Chaldeans, dispersed throughout Syria and Alexandria. ( Vues des Cordilleres et Monumens des Penples Indigenes de V Amirique, t. ii., p. 380.) Buttman maintained, what is very improbable, that the Xr]?ML originally signified the two scales of the Balance, and were sub- sequently by some misconception converted into the pincers of a scor- pion. (Compare Ideler, Untersiichnngen uher die astronomisclien Beo' bachtungen der Allen., s. 374, and Ueber die Sternnameyi, s. 174-177, with Carterou, Recherches de M. Letronne, p. 113.) It is a remarkable circumstance connected with the analogy between many of the names of the twenty-seven '' houses of the moon," and the Dodecatomeria of the zodiac, that we also meet with the sign of the Balance among the Indian Nakschatras (Moon-houses), which are undoubtedly of very great antiquity, {Vues des Cordilleres, t. ii., p. 6-12.) t Compare A. W. von Schlegel, Ueber Sternbilder des Thierhreises i n alten Indien, in the Zeitschrift fur die Kunde des Morgenlandes, bd. \., Heft 3, 1837, and his Con\mcntcUio de Zodlnei Ayitiquitafe ct Origine 1839, with Adolph Holt/ir.ann, Ueber den ihicchischeH Ursprung des Im, Vox III—F 122 C03A103. The artifical group. ng of the stars into constellations, which arose incidentally during the lapse of ages — the fre- quently inconvenient extent and indefinite outline — the com- phcated designations of individual stars in the difierent con- stellations— the various alphabets which have been required to distinguish them, as in Argo — together with the tasteless blending of mythical personages with the sober prose of philo- sophical instruments, chemical furnaces, and pendulum clocks, in the southern hemisphere, have led to many propositions for mapping the heavens in new divisions, without the aid of imaginary figures. This undertaking appears least haz- ardous in respect to the southern hemisphere, where Scorpio, Sagittarius, Gentaums, Argo, and Eridanus alone possess any poetic interest.^ The heavens of the fixed stars {orhis incrrans of Apule- ius), and the inappropriate expression o^ fixed stars {astra fixa of Manilius), reminds us, as we have already observed i\\ the introduction to the Astrognosy,t of the connection, or, rather, confusion of the ideas of insertion, and of absolute im- mobility or fixity. When Aristotle calls the non-wandering celestial bodies {a-nXavr] aarpa) riveted (evdEdefisva), when Ptolemy designates them as ingrafted (npoaTTecpvKoreg), these terms refer specially to the idea entertained by Anaximcnes of the crystalline sphere of heaven. The apparent motion of aU the fixed stars from east to west, while their relative distances remained unchanged, had given rise to this hypoth- esis. " The fixed stars [dnAav?] aarpa) belong to the highel and more distant regions, in which they are riveted, hke nails, dischen Tklerlcreises, 1841, s. 9, 16, 23. " The passages quoted from Amorakoscba and Ramayaua," says the latter writer, "admit of un- doubted interpretation, and speak of the zodiac in the clearest terms; but if these works were composed before the knowledge of the Greek signs of the zodiac could have reached India, these passages ought to be carefully examined for the purpose of ascertaining whether they may not be comparatively modern interpolations." * Compare Buttman, in Berlin Astron. Jahrhuch ficr 1822, s. 93, 01 bers on the more recent constellations in Schumacher's Jahrbucli fui 1840, s. 283-251, and Sir John Herschel, Revision and Rearrangement of the Constellations, with special reference to those of the Southern Hem isphere, in the Memoirs of the Astr. Soc, vol. xii., p. 201-224 (with a very exact distribution of the southern stars from the first to the fourth magnitude). On the occasion of Lalande's formal discussion with Boda ou the introduction of his domestic cat and of a reaper {Messier!), 01 bers complains that in order " to find space in the firmament for Kioj Frederic's glory, Andromeda must lay her right arm in a different plac« from that whicli it had occupied for 3000 years !" t Vide &uvra, p. 20-28, and note. THE FIXED STARS 123 to tlio crystalline heavens ; the planets (darpa -nXavufiEva or ixXavr}Td), v/hich move in an opposite direction, belong to a lower and nearer region."^ As we find in Manilius, in the earliest ages of the Csesars, that the term Stella Jixa was substituted for infixa or affixa, it may be assumed that the schools of Rome attached thereto at first only the original signification of riveted ; but as the word^a;2(fS also embraced the idea of immobility, and might even be regarded as sy- nonymous with immotus and immobilis, we may readily con- ceive that the national opinion, or, rather, usage of speech, should gradually have associated with Stella fixa the idea of immobility, without reference to the fixed sphere to which it was attached. In this sense Seneca might term the Avorld of the fixed stars fixuiii et immobilem iiopulum. Although, according to Stoba^us, and the collector of the " Views of the Philosophers," the designation " crystal vault of heaven" dates as far back as the early period of Anax- imenes, the first clearly-defined signification of the idea on v/hich the term is based occurs in Empedocles. This phi iosopher regarded the heaven of the fixed stars as a solid inass, formed from the ether which had been rendered crys talline and rigid by the action of fire.f According to hia * According to Democritus and his disciple Metrodorus, Stob., Eclog. Phijs., p. 582. t Plat., De plac. Phil., ii., 11; Diog. Laert., viii., 77 ', Acliilles Tat., ad. Arat., cap. 5, Eutt", KpvaTa?Ji6r} tovtov {tuv ovpavov) eivai ^rjaiv, ka rov TTayeTuSovg av'KT.eyevra ; in like manner, we only meet with the expression crystal-like in Diog. Laert., viii., 77 , and Galenus, Hist. Phil., 12 (Sturz, Empedocles Agrigeiit., t. i., p. 321). Lactantius, De Opijicio Dei, c. 17 : " An. si milii quispiam dixerit cencnm esse coelum, aut r«- ircum, aut, ut Empedocles ait, a6rem glaciattim, statimne assentiat quia caelum ex qua materia sit, ignorem." " If any one were to tell me that the heavens are made of brass, or of glass, or, as Empedocles asserts, of frozen air, I should incontinently assent thereto, for I am ignorant of w4iat substance the heavens are composed." We have no early Hel- lenic testimony of the use of this expression of a glass-like or vitreous heaven {ccdum viiret/m), for only one celestial body, the sun, is called by Philolaiis a glass-like body, which throws upon us the rays it has received from the central fire. (The view of Empedocles, referred to in the text, of the reflection of the sun's light from the body of the moon (supposed to be consolidated in the same manner as hailstones) is frequently noticed by Plutarch, apud Euseb. Prcep. Evangel., 1, p. 24, D, and De Facie in Orbe Lunce, cap. 5.) Where Uranos is described as Xa7iK£og and cidrjpeog by Homer and Pindar, the expression refers only to the idea of steadfast, permanent, and imperishable, as in speak- ing of brazen hearts and brazen voices. Volcker uber Homerische Geo- graphic, 1830, s. 5. The earliest mention, before Pliny, of the word KpvaraXAo^ when applied to ice-like, transparent rock-crystal, occurs in Dionysius Perid getes, 781, .^lian, xv., 8, and Strabo, xv.^ p. 717 Ce 124 COSMOS. . theory, the moon is a body conglomerated (Uke hail) by tha action of fire, and receives its light from the sun. The original saub. The opinion that the idea of the crystalline heavens being a gla« cial vault {aer glacintus of Lactantius) arose among the ancients, Irom their knowledge of the decrease of temperature, with the increase of height in the strata of the atmosphere, as ascertained from ascending great heights and from the aspect of snow-covered mountains, is refuted by the circumstance that they regarded the fiery ether as lying beyond the confines of the actual atmosphere, and the stars as warm bodies. (Aristot., Meteor., 1, 3; De Cczlo, 11, 7, p. 289.) In speaking of the music of the spheres (Aristot., De Ccelo, 11, p. 290), which, according to the views of the Pythagoreans, is not perceived by men, because it is continuous, whereas tones can only be heard when they are inter- rupted by silence, Aristotle singularly enough maintains that the move- ment of the spheres generates heat in the air below them, while they are themselves not heated. Their vibrations produce heat, but no sound. " The motion of the sphere of the fixed stars is the most rapid (Aristot., De CcpJo, ii., 10, p. 291) ; as ths sphere and the bodies attached to it are impelled in a circle, the subjacent space is heated by this movement, and hence heat is ditfused to the surface of the earth." (MeicoroL, 1, 3, p. 340.) It has always struck me as a circumstance worthy of remai'k, that the Stagirite should constantly avoid the Vv'ord crystal heaven; for the expression, " riveted stars'^ (hdEde/uiva uorpa), which he uses, in- dicates a general idea of solid spheres, without, however, specifying tho nature of the substance. We do not meet with any allusion to the sub- ject in Cicero, but we find in his commentator, Macrobius {Cic. Som- nium Scipionis, 1, c. 20, p. 99, ed. Bip.), traces of freer ideas on the dim- inution of temperature with the increase of height. According to him, eternal cold prevails in the outermost zones of heaven. " Ita enira noE solum terram sed ipsum quoque ccelum, quod vere mundus vocatur, temperari a sole certissimum est, ut extremitates ejus, quse via soli* longissime recesserunt, omni careant beneficio caloris, et una frigoins perpetuitate torpescant." " For as it is most certain that not only tho earth, but the heavens themselves, which are truly called the universe, are rendered more temperate by the sun, so also their confines, which are most distant from the sun, are deprived of the benefits of heat, and languish in a state of perpetual cold." These confines of heaven (ea; tremitates coeli), in which the Bishop of Hippo (Augustinus, ed. Antv., 1700, i., p. 102, and iii., p. 99) placed a region of icy-cold water near Saturn the highest, and therefore the coldest, of all the planets, art- within the actual atmosphere, for beyond tlie outer limits of this space lies, according to a somewhat earlier expression of Macrobius (1, c. 19, p. 93), the fiery ether which enigmatically enough does not prevent thii eternal cold: " Stelhe supra coelum locat;e, in ipso purissimo aethere sunt, in quo omne quidquid est, lux naturalis et sua est, quae tota cum igne BUG ita sphaerae solis incumbit, ut cceli zonae, quae procul a sole sunt, perpetuo fi-igore oppressae sint." " The stars above the heq^-ens are gituated in the pure ether, in which all things, whatever they may be, have a natural and proper light of their own" (the region of self-lumin- ous stars), " which so impends over the sphere of the sun with all ita fire, that those zones of heaven which are far from the sun are oppress. ed by perpetual cold." My reason for entering so circumstantially intc the physical and meteorological ideas of the Greeks and Romans is sim ply l>e('ause these subjects, except in the works of Ukert, Henri Martiu THE FIXED STARS. 123 idea of transparency, congelation, and solidity would not, ac' cording to the physics of the ancients,^ and their ideas of the solidification of fluids, have referred directly to cold and ice ; but the affinity between KpvaraXXog, upvoq, and KpvaratVG). as well as this comparison with the most transparent of all bodies, gave rise to the more definite assertion that the vault of heaven consisted of ice or of glass. Thus we read in Lae- lantius : "Coelum acrem glaciatum esse" and "vitreum cob- lum." Empedocles undoubtedly did not refer to the glass cf the Phoenicians, but to air, wdiich was supposed to be con- densed into a transparent solid body by the action of the fiery ether. In this comparison Mdth ice {K.pvaraXXog), the idea of transparency predominated ; no reference being here made to the origin of ice through cold, but simply to its conditions of transparent condensation. While poets used the term crystal, prose writers (as found in the note on the passage cited from Achilles Tatius, the commentator of Aratus) lim- ited themselves to the expression crystallme or cry?,tal-likc, tcpvaraXXoELdrjg. In like manner, Txayoq (from nrjyvvoOaL, to become solid) signifies a piece of ice — its condensation be ing the- sole point referred to. The idea of a crystalline vault of heaven was handed down to the Middle Ages by the fathers of the Church, who believed the firmament to consist of from seven to ten glassy strata, incasing one another like the diflerent coatings of an onion. This supposition still keeps its ground in some of the monasteries of Southern Europe, where I was greatly sur- prised to hear a venerable prelate express an opinion m ref- erence to the fall of aerolites at Aigle, which at that time formed a subject of considerable interest, that the bodies we called meteoric stones with vitrified crusts were not portions of the fallen stone itself, but simply fragments of the crys- and the admirable frasjmeut of tlie Mefeorolortia Veterum of Julius Ido- ier, have hitherto beeu very imperfectly, and, for the most part, suptr ficially considered. * The ideas that fire has the power of making rigid ( Aristot., PrcLL, xiv., 11), and that the formation of ice itself may be promoted by bes% are deeply rooted in the physics of the ancients, and based on a fanci- ful theory of contraries {Antiperistasis) — on obscure conceptions of po- larity (of exciting opposite qualities or conditions). {Vide supra, p. 14, and note.) The quantity of hail produced was considered to b* proportional to the degree of heat of the atmospheric strata. (Aristot., Meteor., i., 12.) In the winter fishery on the shores of the Euxin^. warm 'vater was used to increase the ice formed in the neighborhoo( of an uprisht tube. (Alex. Aphrodis., fo\ 83, ayJ Plut,, Dcprimo Frig* do. c. 12. "T 12G COSMOS. tal vault shattered by it in its fall Kepler, from his ccn Eiderations of comets which intersect the orbits of all the planets,^ boasted, nearly two hundred and fifty years ago, that he had destroyed the seventy-seven concentric spheres of the celebrated Girolamo Fracastoro, as well as all tlsr- more ancient retrograde epicycles. The ideas entertaineu by such great thinkers as Eudoxus, Mencschmus, Aristotle, and Apollonius Pergseus, respecting the possible mechanism and motion of these solid, mutually intersecting spheres by which the planets were moved, and the question whether they regarded these systems of rings as mere ideal modes of representation, or intellectual fancies, by means of which diffi- cult problems of the planetary orbits might be solved or de- termined approximately, are subjects of which I have already treated in another place,! and which are not devoid of interest in our endeavors to distinguish the difierent periods of devel- opment which have characterized the history of astronomy. Before we pass from the very ancient, but artificial zodi- acal grouping of the fixed stars, as regards their supposed insertion into solid spheres, to their natural and actual ar- rangement, and to the known laws of their relative distri- bution, it will be necessary more fully to consider some of the sensuous phenomena of the individual cosmical bodies — their extending rays, their apparent, spurious disk, and their differences of color. In the note referring to the invisibility of Jupiter's satellites,! I have already spoken of the influ- ence of the so-called tails of the stars, which vary in num- ber, position, and length in difierent individuals. Indistinct- ness of vision {la vue inclhtincte) arises from numerous or- ganic causes, depending on aberration of the sphericity of * Kepler expressly says, in his Stella Martis, ful. 9 : " Solidos orbes rejeci." ''I have rejected the idea of solid orbs;" and in the Stella Nova, IGOfi, cap. 2, p. 8 : '■' Planetse in puro selhere, periude atque aves in acre cursus sues conficiunt." " The planets perform their course in the pure ether as birds pass through the air." Compare also p. 1*2'2. lie inclined, however, at an earlier period, to the idea of a eolid icy vault of heaven congealed from the absence of solar heat: • Orbis ex aqua factus gelu concreta propter solis absentiam." (Kepler, F.pit. Astr. Copern., i., 2, p. 51.) "Two thousand years before Kepler, Empedocles maintained that the fixed stars were riveted to the crystal heavens, but that the planets were free and unrestrained" {rovq 6e TzXav- Tjrac avfladai). (Pint., plac. Phil., ii., 13; Emped., 1, p. 335, Sturz; Euseb., Prcpp. Evang., xv., 30, col. 1688, p. 839.) It is difficult to con- ceive how, according to Plato in the Tira;.eus ( Tim., p. 40, B ; see Bohn'g edition cf Plato, vol. ii., p. 344; but not according to Aristotle), the fixed Btars, riveted as they are to solid spheres, could rotate independently, ■* Cosr^ns, vol. ii., p 31o, 316. + Vide supra, p. 51, and note. VELOCITY OF LIGHT. IS'/ tne eye, diflractlon at the margins of the pupil, or at the eyelashes, and on the more or less widely-diffused irritabili- ty of the retina from the excited point. =^ I see very regu- * " Les principales causes de la vue indistincte sont : aberration de pphericite de I'oeil, diffraction sur les bords de la pupille, communica- tion d'irritabilite a des points voisins sur la retina. La vue confuse est celle ou le foyer ne torabe pas exactement sur la retine, mais tombe Qu-devant ou dernere la retine. Les queues des etoiles sont I'effet de ja vision indistincte, autant qu'elle depend de la constitution du cristal- lin. D'apres un tres ancien m^moire de Hassenfratz (1809) ' les queues nu nombre de 4 ou 8 qu'offrent les etoiles ou une bougie vue a 25 me- tres de distance, sont les caustiques du cristallin formees par I'intersec- tiou des rayons refractes.' Ces causttques se meuvent a mesure que nous incliuous latete. La propriete de la lunette de terminer I'image fait qu'elle concentre dans un petit espace la lumiere qui sans cela en aurait occupe un plus grand. Cela est vrai pour les etoiles fixes et pour les disques des planetes. La lumiere des etoiles qui n'ont pas de disque reels, cousers'e la me me iutensite, quel que soit le grossissement. Le fond de fair duquel se detache I'etoile dans la lunette, devient plus noir par le grossissement qui dilate les molecules de I'air qu'embrasse le champ de la lunette. Les planetes a vrais disques deviennent elles- memes plus pales par cet effet de dilatation. Qnand la peinture focalo est nette, quand les rayons partis d'tin point de I'objet se sont concen- tres en un seul point dans I'image, i'oculaire donne des resultats satis- faisants. Si au contraire les rayons emancs d'un point ne se reunissent pas au foyer en un seul point, s'ils y ferment nn petit cercle, les images de deux points contigus de I'objet empietent uecessairement Tune eur I'autre ; leurs rayons se coufondent. Cette confusion la lentille ocu- laire ne saurait la faire disparaitre. L'office qu'elle remplit exclusive- ment, c'est de grossir ; elle grossit tout ce qui est dans I'image, les de- fauts comme le reste. Les etoiles n'ayant pas de diametres angulaires sensibles, ceux qu'elles conserveut toujours, tiennent pour la plus grande partie au manque de perfection des instnimens (a la courbure moins reguliere donnce aux deux faces de la lentille objective) et a quelques defauts et aberrations de notre oeil. Plus une etoile semble petite, tout etant egal quant au diametre de I'objectif, au grossissement em- ploye et a I'eclat de I'etoile observee, et plus la lunette a de perfection. Or le meilleur moyen de jnger si les etoiles sont tres petites, si des points sont representes au foyer par des simples points, c'est evidem- ment de viser a des etoiles excessivement rapprochces entr'elles et de voir si dans les etoiles doubles connues les images se confondent, si elles empietent I'uue sur I'autre, ou bien si on les aper^oit bieu nette- ment separees." " The principal causes of indistinct vision are, aberration of the sphe- ricity of the eye, diffraction at the margins of the pupil, and irritation transmitted to contiguous points of the retina. Indistinct vision exists where the focus does not fall exactly ou the retina, but either somewhat before or behind it. The tails of the stars are the result of indistinct- ness of vision, as far as it depends on the constitution of the ciystalline lens. According to a very old paper of Hassenfratz (1809), 'the four or ei"ht tails which surround the stars or a candle seen at a distance >f 25 metres [82 feet], are the caustics formed on the crj-stalline lena by the intersection of r(;fracted rays ' These caustics follow the move 128 COSMOS. larly eiglit rays at angles of 45° in stars from tlie first to the third magnitude. As, according to Hassenfratz, these radi- ations are caustics intersecting one another on the crystal- line lens, they necessarily move according to the direction in which the head is inclined.^ Some of my astronomical friends see three, or, at most, four rays above, and none he- low the star. It has always appeared extraordinary to me that the ancient Egyptians should invariably have given only five rays to the stars (at distances, therefore, of 72°) ; Eo that a star in hieroglyphics signifies, according to Hora- pollo, the number five.f The rays of the stars disappear when the image of the radiating star is seen through a very small aperture made ments of the head. The property of the telescope, in giving a definite outline to images, causes it to concentrate in a small space the light which would otherwise be more widely diffused. This obtains for the fixed stars and for the disks of planets. The light of stars having no actual disks, mahitains the same intensity, whatever may be the mag- nifying power of the instrument. The aerial field from which the star is projected in the telescope is rendered more black by the magnifying property of the instrument, by which the molecules of air included in the field of view are expanded. Planets having actual disks become fainter from this effect of expansion. When the focal image is clearly defined, and when the rays emanating from one point of the object are concentrated into one point in the image, the ocular focus affords satis- factoiy results. But if, on the contrary, the rays emanating from one point do not reunite in the focus into one point, but form a small circle, the images of two contiguous points of the object will necessai'ily im- pinge upon each other, and their rays will be confused. This confusioa. can not be removed by the ocular, since the only part it performs is that of magnifying. It magnifies eveiy thing comprised in the image, including its defects. As the stars have no sensible angular diameters, those which- they present are principally owing to the imperfect con struction of the instrument (to the different curvatures of the two sides of the object-glass), and to certain defects and aberrations pertaining to the eye itself. The smaller the star appears, the more perfect is the instrument, providing all relations are equal as to the diameter of the object-glass, the magnifying power employed, and the brightness of the star. Now the best means of judging whether the stars are very small, and whether the points are represented in the focus by simple points is undoubtedly that of directing the instrument to stars situated very near each other, and of observing whether the images of known double stars are confused, and impinging on each other, or whether they can be seen separate and distinct." (Arago, MS. of 1834 and 1847.) * Hassenfratz, Sur les rayons divergens des Etoiles in Delamotherie Journal de Physique, torn. l*xix., 1809, p. 324. t Horapollinis Niloi Hieroglyphica, ed. Con. Leemans, 1835, cap. 13, p. 20. The learned editor notices, however, in refutation of Jomard'.s assertion {Descr. de VEgypte, tom. vii., p. 423), that a star, as the nu merical hieroglyphic for 5, has not yet been discovered on any momv ment or papyrus-roll. (Horap., p. 194.) RAYS OF THE STARS. 12S witli a needle in a card, and I have myself frequently oL- served both Canopus and Sirius in this manner. The same thing occurs in telescopic vision through powerful instru- ments, when the stars appear either as intensely luminous points, or as exceedingly small disks. Although the fainter scintillation of the fixed stars in the tropics conveys a cer- tain impression of repose, a total absence of stellar radiation would, in my opinion, impart a desolate aspect to the firma- ment, as seen by the naked eye. Illusion of the senses, op- tical illusion, and indistinct vision, probably tend to augment the splendor of the luminous canopy of heaven. Arago long since proposed the question why fixed stars of the first mag- nitude, notwithstanding their great intensity of light, can not be seen when rising above the horizon in the same man- ner as under similar circumstances we see the outer margin of the moon's disk.* Even the most perfect optical instruments, and those hav- ing the highest magnifying powers, give to the fixed stars spurious disks (diametres factices) ; " the greater aperture," according: to Sir John Herschel, " even with the same mag- nifyin^ power, giving the smaller disk."! Occult ations of the stars by the moon's disk show that the period occupied in the immersion and emersion is so transient that it can not be estimated at a fraction of a second of time. The frequent occurrence of the so-called adhesion of the immersed star to the moon's disk i^ a phenomenon depending on inflection of light in no way connected with the question of the spurious diameter of the star. We have already seen that Sir Yfill- iam Herschel, with a majniifying power of 6500, found the diameter of Yega 0"-36. The image of Arcturus was so di- minished in a dense mist tliat the disk was below 0"*2. It IS worthy of notice that, in consequence of the illusion occa- sioned by stellar radiation, Kepler and Tycho, before the in- vention of the telescope, respectively ascribed to Sirius$ a diameter of 4' and of 2' 20". * I found an opinion prevalent among the sailors of the Spanish shipi of the Pacific, that the age of the moon might be determined before the first quarter by looking at it through a piece of silk and counting tha multiplied images. Here we have a phenomenon of diffracfioiu oh* B3rved through tine slits. t Outlines, ^ 8U). Arago has caused the spurious diameter of Aide- baran to increase from 4" to 15" in the instrument by diminisb.ing tlm ol»ject-glass. t Delambre, Hist de V Astr. Moderne, torn, i., p. 193; Aragii, Aunv^ aire, 184-2 p. SfiC. F 2 130 COSMOS. The alternating light and dark rings which surround th« small spurious disks of the stars when magnified two oi three hundred times, and which appear iridescent when seen through diaphragms of different form, are likewise the result of interference and difiraction, as we learn from the observ- ations of Arago and Airy. The smallest objects which can be distinctly seen in the telescope as lummous points, may be employed as a test of the perfection in construction and illuminating power of optical instruments, whether refractors or reflectors. Among these we may reckon multiple stars, such as e Lyrse, and the fifth and sixth star discovered by Struve in 1826, and by Sir John Herschel in 1832, in the trapezium of the great nebula of Orion,=^ forming the quad- ruple star 6 of that constellation. A difference of color in the proper light of the fixed stars, as well as in the reflected light of the planets, was recog- nized at a very early period ; but our knowledge of this re- markable phenomenon has been greatly extended by the aid of telescopic vision, more especially since attention has been so especially directed to the double stars. We do not hero allude to the change of color wliich, as already observed, ac- companies scintillation even in the whitest stars, and still less to the transient and generally red color exhibited by stellar light near the horizon (a phenomenon OAving to the character of the atmospheric medium through which we see it), but to the white or colored stellar light radiated from each cosmical body, in consequence of its peculiar luminous process, and the different constitution of its surface. The Greek astronomers were acquainted with red stars only, while modern science has discovered, by the aid of the tele- * " Two excessively minute and very close companions, to perceive both of which is one of the severest tests which can be applied to a tel- escope." {Outlines, § 837. Compare also Sir John Herschel, Observ- ations at the. Cape, p. 29 ; and Arago, in the Annuaire pour 1834, p. 302-305.) Among the different planetary cosmical bodies by which the illuminating power of a strongly magnifying optical instrument may be tested, we may mention the first and fourth satellites of Uranus, re- discovered by Lassell and Otto Struve in 1847, the two innermost and the seventh satellite of Satuni (Mimas, Enceladus, and Bond's Hyperi- ou),,and Neptune's satelhte discovered by Lassell. The powder of pen- etrating into celestial space occasioned Bacon, in an eloquent passage in praise of Galileo, to whom he erroneously ascribes the invention of telescopes, to compare these instmments to ships which carry men upon an unknown ocean: '' Ut propriora exercere possint cum coslestibua commercia." {Works oj Francis Bacon, 1740, vol. i.. Novum Orga- num, p. 3G1.) COLOU OF THE STARS. 131 ifiope, ill the radiant fields of the starry heaven, as in tha blossoms of the phanerogamia, and in the metallic oxyds, almost all the gradations of the prismatic spectrum between the extremes of refrangibility of the red and the violet ray. Ptolemy enumerates in his catalogue of the fixed stars six [vnoKi^poL) fiery red stars, viz. '.^ Arcturus, Aldebaran, Pol- lux, Antares, a Orionis (in the right shoulder), and Sirius. Cleomedes even compares Antares in Scorpio with the fiery red Mars,t which is called both TTvppbg and TTvpoeidijq. Of the six above-named stars, five still retain a red or red- dish light. Pollux is still indicated as a reddish, but Castoi as a greenish star.$ Sirius therefore affords the only ex- ample of an historically proved change of color, for it has at present a perfectly white light. A great physical revolu- tion^ must therefore have occurred at the surface or in the photosphere of this fixed star (or remote sun, as Aristarchus * The expression VnOKippoQ, which Ptolemy employs indiscriminate- ly to designate the six stars named in his catalogue, implies a slightly- marked transition ivoxn. fiery yellow to fiery red; it therefore refers, strictly speaking, to ^ fiery reddish color. He seems to attach the gen- eral predicate ^avdog, fiery yellow, to all the other fixed stars. {Almag., viii., 3d ed., Halma, torn, ii., p. 94.) Kip^oc is, according to Galen (Metk. Med., 12), a pale fiery red inclining to yellow. Gellius com- pares the word with melinns, which, according to Servius, has the same meaning as " gilvus" and " fulvus." As Sirius is said by Seneca {Nai. Qucesi., i., 1) to be redder thaii Mars, and belongs to the stars called in !he Almagest v-oKippot, there can be no doubt that the word implies llie predominance, or, at all events, a certain proportion of red rays. The assertion that the affix Troi/c/Aof, which Aratus, v. 327, attaches to Sirius, has been translated by Cicero as " rutilus," is erroneous. Cicero says, indeed, v. 348 : " Nam que pedes subter rutilo cum hi mine claret, Fervidus ille Canis stellarum luce refulgens ;*' but " rutilo cum lumine" is not a translation of ttoikHoc, but the mere addition of a free translation. (From letters addressed to me by Pro fessor Franz.) " If," as Arago observes (AnJinaire, 1842, p. 351), " the Roman orator, in using the term rutilus, purposely departs from the strict rendering of the Greek of Aratus, we must suppose that he rec- ognized the reddish character of the light of Sirius." t Cleom., Cycl. Theor., i., ii., p. 59. X Madler, Astr., 1849, s. 391. \ Sir John Herschel, in the Edinh. Review, vol. 87, 1848, p. 189, and in Sebum., Astr. Nachr., 1839, No. 372: " It seems much more likely that in Sirius a red color should be the effect of a medium interfered, than that in the short space of 2000 years so vast a body should have Rctually undergone such a material change in its physical constitution. It may be supposed owing to the existence of some sort of cosmical cloudiness, subject to internal movements, depending on causes of which we are i:rnoiant." (Compare Aragn,in ilie Annuair^ pour 1842. p. 350- 353.) 132 COSMOS. of Sanios called the fixed stars) before the process could have been disturbed by means of which the less refrangible red rays had obtained the preponderance, through the abstraction or absorption of other complementary rays, either in the pho- tosphere of the star itself, or in the moving cosmical clouds by which it is surrounded. It is to be wished that the epoch of the disappearance of the red color of Sirius had been re- corded by a definite reference to the time, as this subject has excited a vivid interest in the minds of astronomers since the great advance made in modern optics. At the time of Tycho Brahe the light of Sirius was undoubtedly already white, for when the new star v/hich appeared in Cassiopeia in 1572, was observed in the month of March, 1573, to change from its previous dazzling white color to a reddish hue, and again became white in January, 1574, the red ap- pearance of the star was compared to the color of Mars and Aldebaran, but not to that of Sirius. M. Sedillot, or other philologists conversant with Arabic and Persian astronomy, may perhaps some day succeed in discovering evidence of the earlier color of Sirius, in the periods intervening from El-Batani (Albategnius) and El-Fergani (Alfraganus) to Ab- durrahman Sufi and Ebn-Junis (that is, from 880 to 1007), and from Ebn-Junis to Nassir-Eddm and Ulugh Beg (from 1007 to 1437). El-Fergani (properly Mohammed Ebn-Kethir El-Fergani), who conducted astronomical observations in the middle of the tenth century at E,akka (Aracte) on the Euphrates, in- dicates as red stars {stcllce riijfcB of the old Latin translation of 1590) Aldebaran, and, singularly enough,^ Capella, which is now yellow, and has scarcely a tinge of red, but he does not mention Sirius. If a.t this period Sirius had been nd longer red, it would certainly be a striking fact that El-Fer * In Mnhamedis Alfragani Chronologica et Astronomica Elementa, ed .Tacobus Christmannus, 1590, cap. 22, p. 97, we i-ead, " Stella rutta in Tauvo Aldebaran; Stella ruffa in Geminis qua? appellatur Hajok, bo«; est Capra," Alhajoc, Aijuk are, however, the ordinary names for Ca- pella Aurigse, in the Arabic and Latin Almagest. Argelander justly ob* serves, in reference to this subject, that Ttolemy, in the astrologicnl work (T£Tpu6LC?iog rvi>Ta^ig), the genuine character of which is testis fied by the style as well as by ancient evidence, has associated planeta with stars according to similarity of color, and has thus connected Mar tirt Stella, Quccvrit sicnt congruit igneo ipsius colori, with Aurigai stella f»r Capella. (Compare Ttol., Qiiadripart. Congtruct., libri iv., Basil l")51, p. 383.) Rircioli {Almageslum Novum, ed. 1650, tom. i., pars i. lib. G, cap. 2, p. 394) also reckons Capella, together with \ntares, Ald« IfHrau, find Arctui-us, among red stag's SIRIU3. 133 gjini, who invariably follows Ptolemy, should not here indi- cate the change of color in so celebrated a star. Negative proofs are, however, not often conclusive, and, indeed. El* Fergani makes no reference in the same passage to the color of Betelgcux {a Orionis), which is now red, as it was in the age of Ptolemy. It has long been acknowledged that, of all the brightest luminous fixed stars of heaven, Sirius takes the first and most important place, no less in a chronological point of view than through its historical association with the earliest development of human civilization in the valley of the Nile. The era of Sethis — the heliacal rising of Sothis (Sirius) — on which Biot has written an admirable treatise, indicates, according to the most recent investigations of Lepsius,=^ the complete arrange- ments of the Egyptian calendar into those ancient epochs, in- cluding nearly 3300 years before our era, " when not only the summer solstice, and, consequently, the beginning of the rise of the Nile, but also the heliacal rising of Sothis, fell on the day of the first water-month (or the first Pachon)." I will collect in a note the most recent, and hitherto unpublished, etymological researches on Sothis or Sirius from the Coptic, Zend, Sanscrit, and Greek, which may, perhaps, be accept- able to those who, from love for the history of astronomy, seek in lano-uaofes and their afiinities monuments of the earlier conditions of knowledge.! * See Chrojiologie dcr ^-Tlgypter. by Richard Lepsiiis, bd. i., 1849, s. inO-195, 213. The complete arraiigeinent of the Egyptian calendar is referred to the earlier part of the year 3285 before our era, i.e., about a century and a half after the building of the great pyramid of Cheojis- Chufu, and 940 years before the periotl generally assigned to the Deluge. (Compare Cosmos, vol. ii., p. 114, 115^ note.) In the calculations based on the circumstance of Colonel Vyse having found that the inclination of the nan'ovv subterranean passage leading into the interior of the pyr- amid very nearly corresponded to the angle 20° 1.5', which in the time of Cheops (Chufu) was attained by the star a Draconis, which indicated t!ie pole, at its inferior culmination at Gizeh, the date of the building of the pyramid is not assumed at 3430 B.C., as given in Cosmos according to Letronne, but at 3970 B.C. {Outlines of Astr., ^ 319.) This difference of 540 years tends to strengthen the assumption that a Drac. vs^as re- garded as the pole star, as in 3970 it was still at a distance of 3° 44' from the pole. t I have extracted the following observations from letters addressed to me by Professor Lepsius (February, 1850). "The P^gyptian name c»f Sirius is Sothis, designated as a female star ; hence ?; l,u)6ig is identi fied in Greek with the goddess Sote (more frequently Sit in hieroglyph, ics), and in the temple of the gi-eat Ramses at Tliebes with Isis-Sothia (Lepsius, Chron. der A^gyj)ter, bd. i., s. 119, 136). The signification of the root is found in Coptic, and is allied with a numerous family of worJ'^ 134 cosxMos. Besides Sirius, Vega, Deiieb, Reguliis, and SjDioa aie at tha present time decidedly white ; and among the small double the members of which, although they apparently differ very widely from each other, admit of being arranged somewhat in the following order. By the three-fold transference of the verbal signification, we obtain from the original meaning, to throw out — projicere (sagiiiam, telum) — first, seminare, to sow; next, extendere,to extend or spread (as spun threads); and, lastly, w^hat is here most important, to radiate light and to shine (as stars and fire). From this series of ideas we may deduce the names of tliG divinities. Satis (the female archer); Sothis, the radiating, and SUh, the fieiy. We may also hieroglyphically explain sit or seti, tha aiTows as well as the ray ; seta, to spin ; setu, scattered seeds. Sothis is especially the brightly radiating, the star regulating the seasons. of the year and periods of time. The small triangle, always represented yellow, which is a symbolical sign for Sothis, is used to designate the radiating sun when arranged in numerous triple rows issuing in a down- ward direction from the sun's disk. Seth is the fiery scorching god, in contradistinction to the warming, fnictifying water of the Nile, the god- dess Satis who inundates the soil. She is also the goddess of the cat- aracts, because the overflowing of the Nile began with the appearance of Sothis in the heavens at the summer solstice. In Vettius Valens the star itself is called 2^0 instead of Sothis; but neither the name nor the subject admits of our identifying Thoth with Seth or Sothis, as Ideler has done. {Handbtich der Chronologie, bd. i., s. 126.)" (Lepsius, bd. i., s. 13G.) I will close these observations taken from the early Egyptian periods with some Hfellenic, Zend, and Sanscrit et^'mologies : " I'f/p, the sun," says Professor Franz, '' is an old root, ditlering only in pronunciation from i9fp, ■&Epog, heat, summer, in which we meet with the same change in the vowel sound as in reipog and repog or repac- The coiTeclness of these assigned relations of the radicals asip and d^ep, ■&epo^, is proved not only by the employment of T^epsiTarog in Aratus, v. 149 (Ideler, Sternname7i, s. 241), but also by the later use of the forms aeipog, eel- pcog, and cetpivog, hot, burning, derived from adp. It is worthy of no- tice that aeLpd or -deiptvu i/mTLa is used the same as ■depivu l/uaTLa, light summer clothing. The form oeipiog seems, however, to have had a wider application, for it constitutes the ordinary term appended to all stars in- fluencing the summer heat: hence, according to the version of the poet Archilochus, the sun was adpiog dorrjp, while Ibycus calls the stars gen- erally aeipia, luminous. It can not be doubted that it is the sun to which Archilochus refers in the words TToTiXovg fi£v avrov aelptog Karavavel u^vg kXkdnrruv. According to Hesychius and Suidas, l,eipLog does indeed signify both the sun and the Dog-star; but I fully coincide with M. Mar- tin, the new editor of Theon of Smyrna, in believing that the passage «f Hesiod (Opera ct Dies, v. 417) refers to the sun, as maintained by Tzetzes and Procfus, and not to the Dog-star. From the adjective cei- pioc, which has established itself as the ' epitheton perpetuum^ of the Dog-star, we derive the verb aeipiov, which may be translated * to sparkle.' Aratus, v. 331, says of Siriiis, b^ia aeipLuei, ' it spai'kles strong- 1}'.' When standing alone, the word "LEiprjv, the Siren, has a totally dif« ferent etymology ; and your conjecture, that it has merely an accidental similarity of sound with the brightly shining star Sirius, is perfectly well •bunded. The opinion of those who, according to Theon SmyniaEua \Liber de Astronomia, ISiO p. 202 '^. derive ILeipjjv from aEipid^eiv (» THE COLOR OF THE STARS 135 Btars, Stmve enumerates about 300 in which both stars are white,* Procyon, Atair, the Pole Star, and more especially |3 UrscB Min. have a more or less decided yellow light. Wt have already enumerated among the larger red or reddish stars Betelgeux, Arcturus, Aldebaran, Antares, and Pollux. K-iim ker finds y Crucis of a fine red color, and my old friend, Cap tain Berard, who is an admirable observer, wrote from Mada gascar in 1847 that he had for some years seen a Crucis grow ing red. The star rj Argus, which has been rendered cele- brated by Sir John Herschel's observations, and to which 1 shall soon refei more circumstantially, is undergoing a change in color as wei as in intensity of light. In the year 1843, Mr. Mackay noticed at Calcutta that this star was similar in color to Arcturus, and was therefore reddish yellow ;t but in letters from Santiago de Chili, in Feb., 1850, Lieutenant Gil- liss speaks of it as being of a darker color than Mars. Sir John Herschel, at the conclusion of his Observations at the Cai^e, gives a list of seventy-six ruhy-colorccl small stars, of the seventh to the ninth magnitude, some of which appear in the telescope like drops of blood. The majority of the vari- able stars are also described as red and reddish,^ the excep- moreover unaccredited form of (jsipiuv), is likewise entirely erroneous. While the motion of heat and light is implied by the expression aeioLoq, the radical of the word Heiprjv represents the flowing tones of this phe nomenon of nature. It appears to me probable that liELprjv is connect- ed with elpsLv (Plato, Cratyl., 398, D, to yap elpeiv 7ieytLv kari), in which the onginal sharp aspiration passed into a hissing sound." (From let ters of Prof. Franz to me, Jannaiy, ]8")0.) The Greek ^e'lp, the sun, easily admits, according to Bo] p. " of be- ing associated with the Sanscrit word svar, which does not indeed sig- nify the sun itself, l)nt the heavens (as somelliiug shining). The ordi- nary Sansciit denoniinatiou for the sun is surya, a contraction of svarya, which is not used. The root svnr si^^nifies in general to shine. The Zend designation for the sun is hvare, wiih the h instead of the s. The Greek i?fp, ■&£po^, and d^epfiog comes from the Sanscnt word gharma (Nom. gharmas), warmth, heat." The acute editor of the Rigveda, Max Miiller, obser\^es, that " the special Indian astronomical name of the Do^.^Xm', Lubdkaka, which sig- nifies a hunUr, when considered in reference to the neighboring con- stellation Orion, seems to indicate an ancient Ajian community of ideas regarding these groups of stars." He is, moreover, principally inclined " to derive 'LeipLog from the Veda word sira (whence the adjective snir- va) and the root sri, to go, to wander; so that the sun and the brig.it- est of the stars, Sirius, were originally called w-anderinsT stars." (Con;- pare also Voit, Etymologische Forscliungen, 1833, s. 130.) * Sti'uve, Stellarum compositarnm MensurcE Mtcromci'ritc^, 1837, J- Ixxiv. et Ixxxiii. t Sir .Tolin Herschel, Ojservntions al fhc C rvc, p. 34. t Madler's ^l5i»-(>7?oi«;V'. s. •J3(J 133 SOSMOS. tions being Algol in Caput Medusre, (3 Lyrce and e Auriga, which have a. pui'e white light. Mira Ceti, in which a pe« liodical change of light was first recognized, has a strong red dish light ;^ but the variability observed in Algol and [i Lyrce proves that this red color is not a necessary condition of a c.liange of light, since many red stars are not variable. The Ikintest stars in which colors can be distinguished belong, ac- cording to Struve, to the ninth and tenth magnitudes. Blue stars were first mentioned by Mariotte,t 1686, in his 2'railS des Couleurs. The light of a L}Ta3 is bluish ; and a smaller stellar mass of 3^ minutes in diameter in the southern hem- isphere consists, according to Dunlop, of blue stars alone. Am:)ng the double stars there are many m which the princi- pal star is white, and the companion blue ; and some in which both stars have a blue light| (as 6 Serp. and 59 Androm.). Occasionally, as in the stellar swarm near k of the Southern Cross, which was mistaken by Lacaille for a nebulous spot, more than a hundred variously-colored red, green, blue, and bluish-green stars are so closely thronged together that they appear in a powerful telescope " like a superb piece of fancy jewelry."^ The ancients believed they could recognize a remarkable symmetry in the arrangement of certain stars of the first magnitude. Thus their attention was especially directed to the four so-called regal stars, which are situated at oppo- site points of the sphere, Aldebaran and Antares, E-egulus and Fomalhaut. We find this regular arranfjement, of which I have already elsewhere treated, || specially referred to in a late Roman writer, Julius Firmicus Maternus,^ who belonged to the age of Constantine. The diflerences of right ascension in these regal stars, stcllce regales, are llh. 57m. and 12h. 49m. The importance formerly attached to this subject is probably owing to opinions transmitted from the East, w^hich gained a footing in the Roman empire un- der the Caesars, together with a strong national predilection, for astrology. The leg, or north star of the Great Bear (the celebrated star of the Bull's leg in the astronomical repre- * Cosmos, vol. ii., p. 330. t Arago, Anmtalre pour 1842, p. 318 I Stnive, StellcB comp., p. Lxxxii. § Sir John Herschel, Observations at the Cape, p. 17, 102. (" Nebula and Clusters, No. 3435.") II HumbokU, Viies des Cordillircs el Afnnumcns des Peiipies Indigenet 7/e V Arn4riqve, torn, ii., p. 5.5. 11 JuJii Firmici Materni Astrcn.,X\\)v\ viii.. Basil, 1551, lib vi., cap ;., p- 150. SOUTHERN STARS. IST Eentatioiis of Dendera, and in the Egyptian Book of tJi^ Dead), is perhaps the star indicated in an obscure passage of Job (ch. ix., ver. 9), in which Arcturus, Orion, and the Plei- ades are contrasted with "the chambers of the south," and in which tlie four quarters of the heavens in hke manner are indicated by these four groups.^ While a large and splendid portion of the southern heav- ens beyond stars having 53^ S. Decl. were unknown in an- cient time?, and even in the earlier part of the Middle Ages, the knowledge of the southern hemisphere was gradually completed about a centuiy before the invention and appli- cation of the telescope. At the time of Ptolemy there were visible on the horizon of Alexandria, the Altar, the feet of the Centaur, the Southern Cross, then included in the Cen- taur, and, according to Pliny, also called Cccsaris Thi'onus, in honor of Augustus,! and Canopus (Canobus) in Argo, which is called Ftolcmceon by the scholiast to Germanicus4 * Lepsins, Chronol. der JEgj/pler, bJ. i., s. 143. In the Hebrew text mention is made o( Asch, the giant (Orion?), the many stars (the Pleiades, Gemut?), and "the Chambers of the South." The Septua- gint gives : 6 ttgluu 'E?ieiu6a aal ^EaTTspov Kal 'ApKvovpov kqI rafxeia VOTOV. The early English translators, like the Germans and Dutch, under- stood the first group referred to in the verse to signify the stars in the Great Bear. Thus we find in Coverdale's version, " He maketh the vvaynes of heaven, the Orions, the vii. stars, and the secret places of the south." — Adam Clarke's Commentary on the Old Testament. — (Tr.) t Ideler, Sternnamen, s. 295. X Martianus Capella changes Ptolemceon into Ptolem(B7ts; both names were devised by the flatterers at the court of the Egyptian sovereigns. Amei'igo Vespucci thought he had seen three Canopi, one of which was quite dark (fosco), Canoprts ingens ct niger of the Latin translation ; most probably one of the black coal -sacks. (Humboldt, Examen Crit. de la Geogr., torn, v., p. 227, 229.) In the above-named Elem. Chronol. et Astron. hy El-Fergaui (p. 100)., it is stated that the Christian pilgrims used to call the Sohel of tlie Arabs (Canopus) the star of St. Catharine, because they had the gratification of observing it, and admiring it as a guiding star when they journeyed from Gaza to Mount Sinai. In a fine episode to the Raniayana, the oldest heroic poem of Indian antiquity, the stars in the vicinity of the South Pole are declai'ed for a singular reason to have been more recently created than the northern. When Brahmiuical Indians were emigrating from the northwest to the couu tries around the Ganires, from the 30th decree of north latitude to the lands of the tropics, where they subjected the original inhabitants to their dominion, they saw unknown stars rising above the horizon aa they advanced toward Ceylon. In accordance with ancient practice, they combined these stars into new constellations. A bold fiction rep. resented the later-seen stars as having been subsequently created by the miraculous power of Visvamitra, who threatened " the ancient god* that he would overcome the northern hemisphere with his more richly 138 COSMOS. Ill the catalogue of the Almagest, Acliernar, a star of tha first magnitude, the last in Eridanus (Achir el-nahr, in Arabic), is also given, although it was 9^ beloAV the hori- zon. A report of the existence of this star must therefore have reached Ptolemy through the medium of those who had made voyages to the southern parts of the Red Sea, or be- tween Ocelis and the Malabar emporium, Muziris.^ Though improvements in the art of navigation led Diego Cam, to- gether with Martin Behaim, along the western coasts of Af- rica, as early as 1484, and carried Bartholomew Diaz in 1487, and Gama in 1497 (on his way to the East Indies), far beyond the equator, into the Antarctic Seas, as far as 35° south lat., the first special notice of the large stars and nebulous spots, the first description of the " Magellanic clouds" and the "coal-sacks," and even the fame of " the wonders of the heavens not seen in the Mediterranean," be- long to the epoch of Vicente Yaiiez Pinzon, Amerigo Ves- pucci, and Andrea Corsali, between 1500 and 1515. The distances of the stars of the southern hemisphere were meas- ured at the close of the sixteenth and the beginning of the seventeenth century. f Laws of relative density in the distribution of the fixed stars in the vault of heaven first began to be recognized when Sir WiUiam Herschel, in the year 1785, conceived the happy idea of counting the number of stars which passed starred southern hemisphere." (A. W. von Schlegel, in the Zeitschrift fiir die Kunde des Morgenlandes, bd. i., s. 240.) While this Indian myth figuratively depicts the astonishment excited in wandering na- tions by the aspect of a new heaven (as the celebrated Spanish poet, Garcilaso de la Vega, says of travelers, " they change at once their coun- try and stars," mudan de pays y de csirellas), we are powerfully re- minded of the impression that must have been excited, even in the rudest nations, when, at a certain part of the earth's surface, they ob- served large, hitherto unseen stars appear in the horizon, as those in the feet of the Centaur, in the Southern Cross, in Eridanus or in Argo, while those with which they had been long familiar at home wholly disappeai'ol. The fixed stars advance towai'd us, and again recede, owing to the pi'ecession of the equinoxes. We have au'eady mentioned that the Southern Cross was 7° above the horizon, m the countries around the Baltic, 2900 years before our era ; at a time, therefore, when \he great pyi-amids had already existed five hundred years. (Compare "Josmos, vol. i., p. 149, and vol. ii., p. 282.) " Canopus, on the other nand, can never have been visible at Berlin, as its distance from the Bouth pole of the ecliptic amounts to only 14°. It would have required a distance of 1° more to bring it within the limits of visibility for our horizon." * Cosmos, vol. ii., p. 571, 572 t Olbors, in Schumacher's Jahrh. fur 1810, s. 249, and Cosmos, vol. i^ p. 51 DISTRIBUTION OF STARS. 13S at difierent heights and in various directions over tlie field of view, of 15' in diameter, of his twenty-feet reflecting tel- escope. Frequent reference has already been made in the present work to his laborious process of "gauging the heav- ens." The field of view each time embraced only iraVo oo-^^* of the whole heavens ; and it would therefore require, ac- cording to Struve, eighty-three years to gauge the whole sphere by a similar process.* In investigations of the par- tial distribution of stars, we must specially consider the class of magnitude to which they photometrically belong. If we limit our attention to the bright stars of the first three or four classes of magnitudes, we shall find them distributed on the whole with tolerable uniformity,! although in the south- ern hemisphere, from e Orionis to a Crucis, they are locally crowded together in a splendid zone in the direction of a great circle. The various opinions e?vpressed by different travelers on the relative beauty of the northern and south- ern hemispheres, frequently, I believe, depends wholly on the circumstance that some of these observers have visited the Southern regions at a period of the year when the finest por- tion of the constellations culminate in the daytime. It fol- lows, from the gaugings of the two Herschels in the north- ern and southern hemispheres, that the fixed stars from the fifth and sixth to the tenth and fifteenth magnitudes (par- ticularh^ therefore, telescopic stars) increase regularly in density as we approach the galactic circle (6 yaXa^iag icv- K?.og) ; and that there are therefore poles rich in stars, and others poor in stars, the latter being at right angles to the principal axis of the Milky Way.. The density of the stellar light is at its minimum at the poles of the galactic circle ; and it increases in all directions, at first slowly, and then rap- idly, in proportion to the increased galactic polar distance. By an ingenious and careful consideration of the results of the gauges already made, Struve found that o?i the average there are 29*4 times (nearly 30 times) as many stars in the center of the Milky Way as in regions surrounding the ga- lactic poles. In northern galactic polar distances of 0^, 30°, 60^, 75°, and 90°, the relative numbers of the stars in a tel- escopic field of vision of 15' diameter are 4*15, 6*52, 17*6S, 30-30, and 122-00. Notwithstanding the great similarity bi the law of increase in the abundance of the stars, we again find in the comparison of these zones an absolute pre« * Etudes d'Asir. Stellaire, note 74.. p. 31. + OtiUincs of Ash-., § 78') 140 COSMOS. ; ponderance^ on the side of the more beautiful southern heavens. "VVhen in 1843 I requested Captain Sdiwiiick (of the En- gineers) to communicate to me the distribution according to right ascension of the 12,148 stars (from the first to the sev- enth inclusive), which, at Bessel's suggestion, he had noted in his Ma2')pa Ccdestis, he found in four groups — ight Ascension, 50° to 140° 3147 stars. 140° 230° 2627 '^ 230° 320° 3523 " 320° 50° 2851 " These groups correspond v^dth the more exact results of the Ktudes Stellaires, according to which the maxima of stars of the first to the ninth magnitude occur in the right ascen- sion 6h. 40m. and. 18h. 40m., and the minima in the right ascension of Ih. 30m. and 13h. 30m. f It is essential that, in reference to the conjectural struc- ture of the universe and to the position or depth of these strata of conglomerate matter, we should distinguish among the countless number of stars with which the heavens are studded, those which are scattered sporadically, and those which occur in separate, indeperident, and crowded groups. The latter are the so-called stellar clusters or sivarins, which frequently contain thousands of telescopic stars in recogniza- ble relations to each other, and which appear to the unaided eye as round nebulse, shining like comets. These are, the uebulous stars of Eratosthenes! and Ptolemy, the nehulosce of the Alphonsine Tables in 1483, and the same of which Galileo said in the Nuncius Sidercics, " Sicut areola? spar- Bim per sethera subfulgcnt." These clusters of stars are either scattered separately throughout the heavens, or closely and irregulai ty crowded together, in strata, as it were, in the Milky Way. and in the Magellanic clouds. The greatest accumulation of globulaT clusters, and the most important in reference t( the config uration of the galactic circle, occurs in a region y f the south- ern heavenss^ betM^cen Corona Aiistralis, Sag: ".tarius, the *" Op. ciL, § 7'Jo, 796; Struve, Eiudcs d'Asir. Sid!., ?. GO, 73 (aii;l note 7o). t Struve, p. 59. Sclnviiick finds in his maps, R. A 0^-90°, 2858 stars; R. A. 90O-180^, 3011 stars; R. A. 180^-270^, 26 8 stars; R. A i!70^-3G0°, 3591 stars; sum total, 12,148 stars to the seve. >.h magnitude t On the nebula m the right hand of Perseus (near .he hilt of hid 8Word), see Eratosth., CaiasL, c. 22, p. 51, Schauhach p John Herschel's Observations at the Cape, $ 105, ] i'JC. CLUSTERS OF STARS. 141 tail of Scorjiio, and the Altar (E,. A. IGh. 4om.--19h ), All clusters in and near the Milky "Way are not, however, round and globular ; there are many of irregular outline, with hut few stars and not a very dense center. In many globular clusters the stars are uniform i:i magnitude, in others they vary. In some few cases they exhibit a fine reddish cen- tral star* (Pt. A. 2h. 10m. ; N *Decl. 5G° 21'). It is a dif- ficult problem in dynamics to understand how such island- worlds, with their multitude of suns, can rotate free and un disturbed. Nebulous spots and clusters of stars appear sub- ject to difl^erent laws in their local distribution, although the former are noAV very generally assumed to consist of very small and still more remote stars. The recognition of these laws must specially modify the conjectures entertained of what has been boldly termed the " structure of the heav- ens." It is, moreover, worthy of notice, that, Avith an in- strument of equal aperture and magnifying power, round nebulous spots are more easily resolved into clusters of stara than oval ones.f I will content myself with naming the following among the isolated systems of clusters and swarms of stars. The Pleiades : doubtless known to the rudest nations from the earliest times ; the iiuirincfs. stars — Pleias, and rov ttXeIv (from fiXelv, to sail), according to the etymology of the old schohast of Aratus, who is probably more correct than those modern writers who would derive the name from irXeog, plenty. The navigation of the Mediterranean lasted from May to the beginning of November, from the early rising to the early setting of the Pbiades. Prcesepe in Cancer : according to Pliny, nuhecula quavi PrcEScina vacant inter Ascllos, a vecpeXiGV of the Pseudo Eratosthenes. The cluster of stars on the sword-hilt of Perseus, frequent- ly mentioned by Greek astronomers. Coma Berenices, like the three former, visible to the naked eye. A cluster of stars near Arcturus (No. 1663), telescopic: R. A. 13h 34m. 12s., N. Decl. 29^ 14' ; more than a thousand stars from the tenth to the twelfth magnitude. Cluster of stars between 7] and ^ Herculis, visible to the naked eye in clear nights. A magnificent object in the tel* esoope (No. 1968), with a singular radiating margin ; R. A * Outlines. § 864-860, p. 591-.59G; Madler's Astr., s. 7fi4 t Observations at the Cape, § 29, p. 19. 142 COSMOS. i6h. 35m. 37s., N. Decl. 36° 47' ; first described l.y Halley m 1714. A cluster of stars near u) Geiitauri , described by Halley as early as 1677 ; appearing to the naked eye as a round cometic object, almost as bright as a star of the fourth or fifth magni- tude ; in pov/erful instruments it appears composed of count- less stars of the thirteenth to the fifteenth magnitude, crowd- ed together and m^ost dense toward the center; R. A. 13h. 16m. 38s., S. Decl. 46° 35' ; No. 3504 in Sir John Herschcl'a catalogue of the clusters of the southern hemisphere, 15' in diameter. [Observations at the Cape, p. 21, 105 ; Outlines of Astr., p. 595.) Cluster of stars near k of the Southern Cross (No. 3435), composed of many-colored small stars from the twelfth to the sixteenth magnitude, distributed over an area of ^'g-^^ ^^ ^ square degree ; a nebulous star, according to Lacaille, but so completely resolved by Sir John Herschel that no nebulous mass remained ; the central star deep red. {Observations at the Cai^e, p. 17, 102, pi. i., fig. 2.) Cluster of stars, 47 Toucani, Bode ; No. 2322 of Sir John rierschel's catalogue, one of the most remarkable objects in the southern heavens. I was myself deceived by it for sev- eral evenings, imagining it to be a comet, when, on my ar- rival at Peru, I saw it in 12° south lat. rise high above the horizon. The visibility of this cluster to the naked eye is in- creased by the circumstance that, although in the vicinity of the lesser Magellanic cloud, it is situated in a part of the heavens containing no stars, and is from 15' to 20' in diam- eter. It is of a pale rose color in the interior, concentrically inclosed by a white margin com.posed of small stars (four teenth to sixteenth magnitude) of about the same magnitude, and presenting all the characteristics of the globular form.* A cluster of stars in Andromeda's girdle, near v of this con- stellation. The resolution of this celebrated nebula into small stars, upward of 1500 of which have been i-ecognized, apper- tains to the most remarkable discoveries in the observing as- tronomy of the present day. The merit of this discovery is due to Mr. George Bond, assistant astronomer! at the OVeervatory * " A stupendous object — a most mai^iificent globular cluster," eayg Sir John Herschel, " completely insulated, upon a ground of the sky per fectly black throughout the,whole breadth ot" the sweep." — Observation* at the Cape, p. 18 and 51, PI. iii., fig. 1 ; Oulllnes, ^ 895, p. G15. t Bond, iu the Memoirs of the American Academy of Arts and Sciences uew £ori',^s, vol. iii., p. 75. CLUSTERS OF STAR3. 143 of Cambridge, United States (March, 1848), and testifies to the admirable illuminating power of the refractor of that Ob- servatory, which has an object-glass fifteen inches in diarri' eter ; since even a reflector with a speculum of eighteen inch es in diameter did not reveal " a trace of the presence of a star."* Although it is probable that the cluster in Adrom- eda was, at the close of the tenth century, already recorded as a nebula of oval form, it is more certain that Simon Ma- fius (Mayer of Guntzenhausen), the same who first observed tlie change of color in scintillation,! perceived it on the 15th of December, 1612 ; and that he was the first who described it circumstantially as a new starless and wonderful cosmical body unknown to Tycho Brahe. Half a century later, Bouil- laud, the author of Astronomia Pliilolaica, occupied himself with the same subject. This cluster of stars, which is 2i^ in length and more than 1° in breath, is specially distinguish- ed by two remarkable very narrow black streaks, parallel to each other, and to the longer axis of the cluster, which, ac- cording to Bond's investigations, traverse the whole length like fissures. This configuration vividly reminds us of the singular longitudinal fissure in an unresolved nebula of the southern hemisphere, No. 3501, which has been described and figured by Sir John Herschcl. (^Observations at tJtc Cape, p. 20, 105, pi. iv., fig. 2.) Notwithstanding the important discoveries for which wc are indebted to Lord Rosse and his colossal telescope, I have not included the great nebula in Orion's belt in this selection of remarkable clusters of stars, as it appeared to me more ap propriate to consider those portions of it which have been re- solved in the section on Nebuke. The greatest accumulation of clusters of stars, although by no means of nebula3, occurs in the Milky Way| [Galaxias^ * OntHfies,^ 874, p. 601. \ Delambre, Hist, de V istr. Moderne, t. i., p. G97. X We arc indebted for the first and only complete description of the Milky Way, in both hemispheres, to Sir John Herschel, in his Results of Astronomical Ohscrvations, made during the Years 1834-1838, at the Cape of Good Hope, ^ 316-335, and still more recently in the Outlines of Astronomy, ^ 787-799. Throughout the whole of that section -of the Cosmos which treats of the directions, ramifications, and various con- tents of the Milky Way, I have exclusively followed the above-named astronomer and physicist. (Compare also Strave, Etudes d'Astr. SteU laire, p. 35-79; Madler, Ast., 1849, uIh?, No. 3686, see p. 114 Vol. TIL- ; 146 COSMOS. Herschel, a twenty-feet instrument penetrates 900, and a forty-feet one 2800 distances of Sirius), the Milky AVay ap- pears as diversified in its sidereal contents as it is irregular and indefinite in its outlines and limits when seen by Hip unaided eye. "While in some parts the Milky Way exhibits throughout a large space, the greatest uniformity in the lighJ and apparent magnitudes of the stars, in others the mosJ brilliant patches of closely-crowded luminous points are in- terrupted by granular or reticular darker* intervals contain- ing but few stars ; and in some of these intervals in the in- terior of the Galaxy not the smallest star (of the 18m. or 20m.) is to be discovered. It almost seems as though, in these regions, we actually saw through the whole starry stratum of the Milky Way. In gauging with a field of view of 15' diameter, fields presenting on an average forty or fifty stars are almost immediately succeeded by others exhibiting from 400 to 500. Stars of the higher magnitudes often oc- cur in the midst of the most minute telescopic stars, while all the intermediate classes are absent. Perhaps those stars which we regard as belonging to the lowest order of mag- uitudes do not ahvays appear as such, solely on account of their enormous distance, but also because they actually have a smaller volume and less considerable development of light. In order rightly to comprehend the contrast presented by the greater brilliancy, abundance, or paucity of stars, it will be necessary to compare regions most widely separated from each other. The maximum of the accumulation and the greatest luster of stars are to be found between the prow of Argo and Sagittarius, or, to speak more exactly, between the Altar, the tail of the Scorpion, the hand and bow of Sagit- tarius, and the right foot of Ophiuchus. "No region of the heavens is fuller of objects, beautiful and remarkable in themselves, and rendered still more so by their mode of as- sociation" and grouping.! Next in brightness to this por- * " Intervals absolutely dark a7id complctety void of any star of the Bmallest telescopic magnitude." — Outlines, p. 536. * " No region of the heavens is fuller of objects, beautiful and rc« -kable in themselves, and rendered still more so by their mode of «»feociation, and by the peculiar features assumed by the iNIilky Way, «vliich are without a parallel in any other part of its course." — Observ- ^iions at the Cape, p. 386. This vivid description of Sir John Herschel entirely coincides with the impressions I have myself experienced. Capt. Jacob, of the Bombay Engineers, in speaking of the intensity of light in the Milky Way, in the vicinity of the Southern Cross, remarks with striking truth, " Such is the general blaze of starlight near the Cross from tliat part of the sky, that a person is immediately madi MILKY WA /. 147 tioii of the southern heavens is the pleasing and lichly-star- red region of our northern hemisphere in Aquila and Cyg- nus, where the Milky Way branches off in different direc- tions. While the Milky Way is the narrowest under the foot of the Cross, the region of laiinimum briirhtness (where there is the greatest paucity of stars in the Galactic zone) is in the neighborhood of Monoceros and Perseus. The magnificent effulgence of the Milky Way in the south- em hemisphere is still further increased by the circumstance, that between the star 7] Argus, which has become so cele- brated in consequence of its variabilit)^, and a Crucis, under the parallels of 59^ and 60^ south lat., it is intersected at an angle of 20^ by the remarkable zone of very large and probably very proximate stars, to which belong the constella- tions Orion, Canis Major, Scorpio, Centaurus, and the South- ern Cross. The direction of this remarkable zone is indi- cated by a great circle passing through e Orionis and the foot of the Cross. The picturesque efiect of the Milky Way, if I may use the expression, is increased in both hemispheres by its various ramifications. It remains undivided for about two fifths of its length. Accordmg to Sir John Herschel's observations, the branches separate in the great bifurcation at a Centauri,^ and not at (3 Cent., as given in our maps of the stars, or, as was asserted by Ptolemy,! in the constella- tion of the Altar ; they reunite again in Cygnus. In order to obtain a general insight into the whole course and direction of the Milky Y\^ay with its subdivisions, we will briefly consider its parts, following the order of their Ilight Ascension. Passing through y and e Cassiopeiee, the Milky Way sends forth toward e Persei a southern branch, which loses itself in the direction of the Pleiades and Hyades. The main stream, which is here ve.iy faint, passes on through Auriga, over the three remarkable stars e, ^, 7], the Hsedi of that constellation, preceding Capell i betv^^een the feet of Gem- ini and the horns of the Bull (where it intersects the eclip« a^va^e of its Laving nsen above the horizon, though he should not be at the time looking at the heavens, by the increase of general illumination of the atmospliere, resembling the effect of the young moon." (See Piazzi Smyth, On the Orhil of a Cejitauri, in the Transact, of the Rayed Soc. of Edinburgh, vol. xvi., p. 445.) * Outlines, ^ 789, 791 ; Observations at the Cape, § 325. t Almagest, lib. viii., cap. 2 (t. ii., p. 84, 90, Halma). Ptolemy's de- Bcription is admirable in some parts, especially when compared with Aiistotle's ti'eatraent of the subject of the Milky Way, in Alefcor (lib i.. p. 29 ?4. according to Ideler's edition). H8 COSMOS. tic nearly in the solstitial colure), and tlience over Orion i club to the neck of Monoceros, intersecting the equinoctial (in 1800) at R. A. 6h. 54m. From this point the brightness considerably increases. At the stern of Argo one branch runs southward to y Argus, where it terminates abruptly The main stream is continued to 33^ S. Decl., where, after separating in a fan-hke shape (20^ in breadth), it again breaks off, so that there is a wide gap in the Milky Way in the line from y to /I Argus. It begins again in a similai fan-like expansion, but contracts at the hind feet of the Cen- taur and before its entrance into the Southern Cross, where it is at its narrowest part, and is only 3° or 4° in width. Soon after this the Milky Way again expands into a bright and broad mass, which incloses (3 Centauri as well as a and (3 Crucis, and in the midst of which lies the black pear- shaped coal-sack, to which I shall more specially refer in the seventh section. In this remarkable region, somewhat below the coal-sack, the Milky Way approaches nearest to the South Pole. The above-mentioned bifurcation, which begins at a Cen- tauri, extended, according to older views, to the constellation Cygnus. Passing from a Centauri, a narrow branch runs northward in the direction of the constellation Lupus, where it seems gradually lost ; a division next shows itself at y ISTormffi. The northern branch forms irregular outlines till it reaches the region of the foot of Ophiuchus, where it wholly disappears ; the most southern branch then becomes the main stream, and passes through the Altar and the tail of the Scorpion, in the direction of the bow of Sagittarius, where it intersects the ecliptic in 276^ long. It next runs in an irregular patchy and winding stream through Aquila, Sagitta, and Vulpecula up to Cygnus ; between £, a, and y, of which constellation a broad dark vacuity appears, which, as Sir John Herschel says, is not unlike the southern coal- sack, and serves as a kind of center for the divergence of three great streams. =^ One of these, which is very vivid and conspicuous, may be traced running backAvard, as it were, through (3 Cygni and g Aquilse, without, however, blending with the stream already noticed, which extends to the foot of Ophiuchus. A considerable offset or protuberant append- age is also thrown oil' by the northern stream from the head * Outlines, p. 531. The strikingly dark spot between a and y Cas- BiopeicO is also ascribed to the contrast with the hrightness by which if is sr.rrounded. See Sfnive, Eludes Stell., note 58. MILKY WAY. 149 of Ceplieus, and therefore near Cassiopeia (from which con^ Btellation we began our description of the Milky Way), to- ward Ursa Minor and the pole. From the extraordinary advancement which the applica- tion of large telescopes has gradually effected in our knowL edge of the sidereal contents and of the differences in the concentration, of light observable in individual portions of the Milky Way, views of merely optical projection have been re- placed by others referring rather to physical conformation. Thomas Wright, of Durham,^ Kant, Lambert, and at first also Sir William Herschel, were disposed to consider the tbrm of the Wilky Way, and the apparent accumulation of the stars within this zone, as a consequence of the flattened form and unequal dimensions of the U'orld-isla7icl (starry stratum) in which our solar system is included. The hy- pothesis of the miiform magnitude and distribution of the fixed stars has recently been attacked on many sides. The bold and gifted investigator of the heavens, Wm. Herschel, i\\ his last Avorks,t expressed himself strongly in favor of the assumption of an annulus of stars ; a view which he had contested in the talented treatise he composed in 1784. The most recent observations have favored the hypothesis of a system of separate concentric rings. The thickness of these rings seems very unequal ; and the different strata, whose combined stronger or fainter light we receive, are undoubt- edly situated at very different altitudes, i. e., at very unequal distances from us ; but the relative brightness of the sep- arate stars which we estimate as of the tenth to the six- teenth magnitude, can not be regarded as affording sufficient data to enable us in a satisfactory manner to deduce numer- ically from them the radius of their spheres of distances. $ In many parts of the Millty Way, the space-penetrating Dower of instrum.ents is sufficient to resolve whole star- clouds, and to show the separate luminous points projected on the dark, starless ground of the heavens. AVe here act* * De Morgan has giveu an extract of the extremely rare work of Thomas Wi-ight of Durham ( Theory of the Universe, London, 1750), p 241 iu the Pkilos. Magazine, ser. iii., No. 32. Thomas Wriglit, to whose researches the attention of astronomers has been so permanently di rected since the beginning of the present century, through the ingen ions speculations of Kant and William Herschel, observed only with o reflector of one foot focal length. t rfiiff, in Will. HerscheVs sdmmtl. Schriften, bd. i. (18-26), s. 78-8i ,• Rtrave, Etudes StelL, p. 35-44. t Encke, in Schumacher's Astr. Nachr., No. 622, 1817 e 3n-3ir 150' COSM(.S. ually look throngli as into free space. " It leads us," say.< Sir John Ilersclicl, "irresistibly to the conclusion that in these r3gions we see fairly through the starry stratum. "=* Tn other regions we see, as it were, through openings and fissures, remote world-islands, or outbranching portions of the annular si^stem ; in other parts, again, the Milky Way has hitherto heen fathoinless, even with the forty-feet telescope. t Investigations on the different intensity of light in the Milky Way, as well as on the magnitudes of the stars, which regu- larly increase in number from the galactic poles to the circle itself (an increase especially observable for 30° on either side of the Milky Way in stars below the eleventh magnitude,t and therefore in -j-fths of all the stars), have led the most recent investigator of the southern hemisphere to remarkable viev/s and probable results in reference to the form of the galactic annular system, and what has been boldly called the sun's 2^lace in the world-island to which this annular system belongs. The place assigned to the sun is eccentric, and probably near a point where the stratum bifurcates or spreads itself out into two sheets, § in one of those desert re- gions lying nearer to the Southern Cross than to the oppo- site node of the Milky AVay.il "The depth at which our system is plunged in the sidereal stratum constituting the galaxy, reckoning from the southern surface or limit of that * Outlines, p. 536, 537, where we find the following words on the same subject : " In such cases it is equally impossible not to perceive that we are looking through a sheet of stars nearly of a size, and cf no great thickness compared with the distance wliich separates them from us." t Struve, Etudes StelL, p. 63. Sometimes the largest instruments reach a portion of the heavens, in which the existence of a stany stra^ turn, shining at a remote distance, is only announced by " a uniform dotting or stippling of the field of view." See, in Observations at the Cape, p. 390, the section " On some indications of very remote telo. scopic branches of the Milky Way, or of an independent sidereal sys- tem or systems beai'ing a resemblance to such branches." t Observations at the Cape, $ 314. $ Sir WiUiam Herschel, in the Philos. Transact, for 1785, p. 21 ; Sir John Ilerschel, Observations at the Cape, ^ 293. Compare also Struve, Dcscr. de V Ouscrvatoire de Poulkova, 1845, p. 267-271. II "I think," says Sir .lohn Ilei-schel, "it is impossible to view this splendid zone fi'om a Centauri to the Cross without an impression amounting almost to conviction that the Milky Way is not a mere stra- tum, but annular; or, at least, that our system is placed within one of the poorer or almost vacant parts of its general mass, and that eccen- trically, so as to be much nearer to the region about the Cross than te that diametrically opposite to it." (Mary Somerville, On the Conner **on of the Physical Sciences, 1846, p. 419.) NEW STARS. 151 ft1rat\im. is about equal to that distance which, on a genera, average, corresponds to the light of a star of the ninth oi tenth magnitude, and certainly does not exceed that corre spending to the eleventh."=^ Where, from the peculiar nature of individual problems, measurements and the direct evi- dence of the senses fail, we see but dimly those results which intellectual contemplation, urged forward by an intuitive im- pulse, is ever striving to attain. IV. NLW STARS AND STARS THAT HAVE VANISHED.— VARIABLE STARS, WHOSE RECURRING PERIODS HAVE BEEN DETERMINED.— VARIA- TIONS IN THE INTENSITY OF THE LIGHT OF STARS WHOSE PERI ODICITY IS AS YET UNINVESTIGATED. New Stars. — The appearance of hitherto unseen stars in the vault of heaven, especially the sudden appearance of strongly-scintillating stars of the first magnitude, is an oc- currence in the realms of space which has ever excited as- tonishment. This astonishment is the greater, in proportion as such an event as the sudden manifestation of what was before invisible, but which nevertheless is supposed to have previously existed, is one of the very rarest phenomena in nature. While, in the three centuries from 1500 to 1800, as many as forty-two comets, visible to the naked eye, hav appeared to the inhabitants of the northern hemisphere-, on an average, fourteen in every hundred years — only eight new stars have been observed throughout the same period. The rarity of the latter becomes still more striking when we extend our consideration to yet longer periods. From the completion of the Alphonsine Tables, an important epoch in the history of astronomy, down to the time of William Herschel — that is, from 1252 to 1800 — the number of ^-m- hle comets is estimated at about sixty-three, while that of new stars does not amount to more than nine. Consequent- ly, for the period during which, in the civilized coimtries of Europe, we may depend on possessing a tolerably correct enumeration of both, the proportion of new stars to comets visible to the naked eye is as one to seven. We shall pres- ently show that if from the tailless comets we separate the pew stars which, according to the records of Ma-tuan-lin. * Chsrrvations at the Cape, $ 31?. 152 COSMOS. have been observed in China, and go back to tl e middle «f the second century before the Christian era, that for about 2000 years scarcely more than twenty or twenty-two of such phenomena can be adduced with certainty. Before I proceed to general considerations, it seems not inappropriate to quote the narrative of an €>ye-witness, and, by dwelling on a particular instance, to depict the vividness of the impression produced by the sight of a new star. " On my return to the Danish islands from my travels in Germa- ny/' says Tycho Brahe, " I resided for some time with my uncle, Steno Bille (ut aulicse vitas fastidium lenirem), in the old and pleasantly situated monastery of Herritzwadt ; and here I made it a practice not to leave my chemical labora- tory until the evening. Raising my eyes, as usual, during one of my walks, to the well-known vault of heaven, I ob- served, with indescribable astonishment, near the zenith, in Cassiopeia, a radiant fixed star, of a magnitude never be- fore seen. In my amazement, I doubted the evidence of my senses. However, to convince myself that it was no illusion, and to have the testimony of others, I summoned my assist- ants from the laboratory, and inquired of them, and of all the country people that passed by, if they also observed the star that had thus suddenly burst forth. I subsequently heard that, in Germany, wagoners and other common peo- ple first called the attention of astronomers to this great phe- nomenon in the heavens — a circumstance which, as in the case of non-predicted comets, furnished fresh occasion for the usual raillery at the expense of the learned. " This new star," Tycho Brahe continues, " I found to be without a tail, not surrounded by any nebula, and perfectly like all other fixed stars, with the exception that it scintil- lated more strongly than stars of the first magnitude. Its brightness was greater than tliat of Sirius, a Lyra3, or Jupi- ter. For splendor, it was only comparable to Venus when nearest to the earth (that is, when only a quarter of her disk is illuminated). Those gifted with keen sight could, when the air was clear, discern the new star in the daytime, and even at noon. At night, when the sky was overcast, so that all other stars were hidden, it was often visible through the clouds, if they were not very dense (nubes non admo- dum densas). Its distances from the nearest stars of Cassi- opeia, which, throughout the whole of the following year, 1 measured with great care, convinced me of its perfect immo- bility. Already, in December, 1572, its brilUancy began to A^VV STARS. 153 diminisii,. and the star gradually reser.iLled Jupiter; but by January, 1573, it had become less bright than that planet. Successire photometric estimates gave the following results : for February and March, equahty with stars of the first mag- nitude (stellarum atHxarum primi honoris — for Tycho Bralie Beems to have disliked using Manilius's expression of stellae fixse) ; for April and May, with stars of the second magni- tude ; for July and August, with those of the third ; for Oc- tober and jNTovember, those of the fourth magnitude. To- ward the month of November, the new star was not bright- er than the eleventh in the lower part of Cassiopeia's chair The transition to the fifth and sixth magnitude took place between December, 1573, and February, 1574. In the fol- lowing month the new star disappeared, and, after having ehone seventeen months, was no longer discernible to the naked eye." (The telescope was not invented until tliirty seven years afterward.) The gradual diminution of the star's luminosity was, more over, invariably regular ; it was not (as is the case in the present day with 7] Argus, though indeed that is not to be called a 7ieiv star) interruptejd by several periods of rekind ling or by increased intensity of light. Its color also changed with its brightness (a fact which subsequently gave rise to many erroneous conclusions as to the velocit}'' of colored rays hi their passage through space). At its first appearance, as long as it had the brilliancy of Venus and Jupiter, it was for two months white, and then it passed through yellow into red. In the spring of 1573, Tycho Brahe compared it to Mars ; afterward he thought that it nearly resembled Be- telgeux, the star in the right shoulder of Orion. Its color, for the most part, was like the red tint of Aldebaran. In the spring of 1573, ^nd especially in May, its white color re- turned (albedinem quandam sublividam induebat, qualis Sa- tumi stellcc subesse videtur). So it remained in January, 1571 ; being, up to the time of its entire disappearance in the month of March, 1574, of the fifth magnitude, and white, but of a duller whiteness, and exhibiting a remarkably strong fecintillation in proportion to its faintness. The circumstantial minuteness of these statements^ is of * De admiranda Nova 8 tela, anno 1572, exorta in Tyclionis Brah* Attronomicc instaurat]an- ets at a distance of less than a diameter of the moon. — Tychonis Pro- gymnasmata, p. 324-330; contrast with Ideler, Handhnch der Mathe- matischen und Technisclien Chronologie, bd. ii., s. 399-407. t Progymn., p. 324-330. Tycho Brahe, in his theory of the forma- tion of new stars from the Cosmical vapor of the Milky Way, builds much on the remarkable passages of Aristotle on the connection of tiff t TEMPORARY STARS. 155 transition of the cosmical vapor into clusters of stars, of an agglomerative force, of a concentration to a central nucleus, and of hypotheses of a gradual formation of solid bodies out of a vaporous fluid — views which were generally received in the beginning of the nineteenth century, but which at pres- ent, owinsf to the ever-changing fluctuations in the world of thought, are in many respects exposed to new doubts. Among newly-appeared temporary stars, the following (though with variable degrees of certainty) may be reckoned. I have arranged them according to the order in which the/ respectively appeared. (a) 134 B.C in Scorpio. (b) 123 A.D in Ophiuchus. (c) 173 " in Centaurus (d) 369 " ? (e) 3S6 " in Sagittarius. (/) 389 " in Aquila. (o-) 393 " in Scorpio. (h) 827 " in Scorpio. (^) 945 " between Ccphcus and Cassiopeia. {k) 1012 " in Aries. (/) 1203 " in Scorpio. (?7i) 1230 " in Ophiuchus. (?^) 1264 " • between Cepheus and Cassiopeia. (o) 1572 " in Cassiopeia. 0^) 1578 " (q) 1584 " in Scorpio. (r) 1600 " in Cygnus. (s) 1604 '• in Ophiuchus. (t) 1609 ''• (u) 1670 " in Yulpes. {v) 1848 " in Ophiuchus. EXPLANATORY REM.VRKS. (a) This star first appeared in .July, 134 years before our era. We have taken it from the Chinese Records of Ma-tuan-lin, for the transla* tion of which we are indebted to the learned linguist Edward Biot {Connaissance des Temps pour Van 1846, p. 61). Its place was between ^ and p of Scorpio. Among the extraordinary foreign-looking stars of these records, called also guest-stars {iioiles holes, " Ke-sing," strangers of a singular aspect), which are distinguished by the observers from comets with tails, fixed new stars and advancing tailless comets are cer- Sainly sometimes mixed up. But in the recoi'd of their motion (Ke-sing tails of comets (the vapory radiation from their nuclei) with the galaxj to which I have a'ready alluded. {Cosmos, vol. i., p. 103.) 156 coSxMOS. of 1092, 1181, and 1458), and hi the absence of any s..ch record, as also in the occasional addition, '* the Ke-sing dissolved" (disappeared), there is contained, if not an infallible, yet a veiy important criterion. Besideg, we must bear in mind that the light of the nucleus of all comets, wheth* er with or without tails, is dull, never scintillates, and exhibits only a mild radiance, while the luminous intensity of what the Chinese call extraordinary (stranger) stars has been compared to that of Venus — a circumstance totally at variance with the nature of comets in general, and especially of those without tails. The star which appeared in 134 B.C., under the old Han dynasty, may, as Sir John Herschel remarks, have been the new star of Hipparchns, which, according to the state- ment of Pliny, induced him to commence his catalogue of the stars. Delambre twice calls this statement a fiction, "une historiette." {Hisi de VAstr. Anc, tom. i., p. 290; and HisL de VAstr. Mod., tom. i., p. 18G.; Since, according to the express statement of Ptolemy (Almag., vii., p. 2 13, Halma), the catalogue of Hipparchus belongs to the year 128 B.C., and Hipparchus (as I have already remarked elsewhere) carried on his observations in Rhodes (and perhaps also in Alexandria) from 162 to 127 B.C., there is nothing in-econcilable with this conjecture. It is very probable that the great Nicean astronomer had pursued his observations for a considerable period before he conceived the idea of forming a reg- ular catalogue. The words of Pliny, " suo sevo genita," apply to the whole term of his life. After the appearance of Tycho Brahe's star in 1572, it was much disputed whether the star of Hipparchus ought to be classed among new stars, or comets without tails. Tycho Brahe himself was of the former opinion {Progymn., p. 319-325). The words " ejus- que motu addubitationem adductus" may undoubtedly lead to the sup- position of a faint, or altogether tailless comet; but Pliny's rhetorical style admitted of such vagueness of expression. {b) A Chinese observation. It appeared in December, A.D. 123, between a Hercnlis and a Ophiuchi. Ed. Biot, fi'om Ma-tuan-hn. (It is also asserted that a new star appeared in the reign of Hadrian, about A.D. 130.) (c) A singular and very large star. This also is taken from Ma-tuan- lin, as well as the three following ones. It appeared on the 10th of December, 173, between a and (i Centauri and at tlie end of eight months disappeared, after exhibiting the five colors one after another. '' Succesdvement''^ is the term employed by Ed. Biot in his translation. Such an expression would almost tend to suggesta series of colors similar to those in the above-described star of Tycho Brahe ; but Sir John Herschel more correctly takes it to mean Q colored scintillation (0?f^/2«cs, p. 563), and Arago interprets in the same way a nearly similar expression employed by Kepler when speaking of the new star (1604) in Ophiuchus. ( Annuaire pour 1842, p. 347.) {d) This star was seen from March to August, 369. (e) Between A and 0 Sagittarii. In the Cliinese Record it is expressly observed, " where the star remained (i. e., without movement) from April to July, 386. (/) A new star, close to a Aquilse. In the year 389, in the reign of the Emperor Honorius, it shone forth with the brilliancy of Venus, ac« cording to the statement of Cuspiuianus, who had himself seen it. It totally disappeared in about three weeks.* * Other accounts place the appearance in the year 388 or 398 Jacques Cassini, EUmens d' Astronomic, 1740 (Etoiles No-ivellcs), p. 59 TEMPORARY STARS. It>'/ {g) March, 393. This star was also in Scorpio^ in the tail of that coustellation. l^rom the Records of Ma-tuau-lin. (/i) The precise year (827) is doubtful. It may witt more certainty fee assigned to the first half of the ninth centuiy, when in the reign of Calif Al-Mamun, the two famous Arabian astronomers, Haly and Gia- far Ben Mohammed Albumazar, observed at Babylon a new star, whose light, according to their report, " equaled that of the moon in her quar- ters." This natural phenomenon likewise occurred in Scorpio. The star disappeared after a period of four months. (i) The appearance of this star (which is said to have shone forth in tlie year 945, under Otho the Great), like that of 1264, is vouched for iolely by the testimony of the Bohemian astronomer Cypinanus Leovi- tius, who asserts that he derived his statements concerning it from a manuscript chronicle. He also calls attention to the fact that these two phenomena (that in 945 and that in 12G4) took place between the con- stellations of Cepheus and Cassiopeia, close to the Milky Way, and near the spot where Tycho Brahe's star appeared in 1572. Tycho Brahe {Progym.y p. 331 and 709) defends the credibility of Cyprianus Leovi- tius against the attacks of Pontauus and Camerarius, who conjectured that the statements arose from a confusion of new stars with long-tailed comets. {k) According to the statement of Hepidannus, the monk of St. Gall (who died A.D. 1088, whose annals extend from the year A.D, 709 to 1044), a new star of unusual magnitude, and of a brilUancy that dazzled the eye (oculos verberans), was, for three months, from the end of May in the year 1012, to be seen in the south, in the constellation of Aries. In a most singular manner it appeared to vary in size, and occasionally it could not be seen at all. " Nova stella apparuit insolitoe magnitudinis, aspectu fulgurans et oculos verberans non sine teiTore. Qute mirum in modum aliquando contractior, aliquando diffasior, etiam extinguebatur interdum. Visa est autem per tres menses in intimis finibus Austri, ul- ti'a omnia signa quie videntur in coelo." (See Hepidanni, Annales bre- ves, in Duchesne, HlstoricE Francorum Scriptores, t. iii., 1641, p. 477. Compare also Schnuirer, Chronik der Seuchen, th. i., s. 201.) To the manuscript made use of by Duchesne and Goldast, which assigns the phenomenon to the year 1012, modern historical criticism has, howev- er, preferred another manuscript, which, as compared with the former, exhibits many deviations in the dates, throwing them six years back. Thus it places the appearance of this star in 1006. (See Annales San.' gallenses majorcs, in Veriz, Momiment a Germanics kisiorica Scnptomm, t. i., 1826, p. 81.) Even the authenticity of the writings of Hepidannus has been called into question by modern critics. The singular phenom- enon of variability has been termed by Chladni tiie conflagration and extinction of a fixed star. Hind {Notices of the Astron. Soc, vol. viii., 1848, p. 156) conjectures that this star of Hepidannus is identical with a new star, which is recorded in Ma-tuan-lin, as having been seen in China, in February, 1011, between a and ^ of Sagittarius. But in thai case thex'e must be an error in Ma-tuan-lin, not only in the statement of the year, but also of the constellation in which the star appeared. (/) Toward the end of July, 1203, in the tail of Scorpio. According to the Chinese Record, this new star was "of a bluish-white color, without luminous vapor, and resembled Saturn." ( Edouard Biot, in the Connaissance des Temps pour 1846, p. 68.) (wi) Another Chinese observation, from Ma-tuan-lin, whose astronom- ical records, containing an accurate account of the positions '^f comets 58 COSMOS. and fixt^d stars, go back to the year 613 B.C., to the times of Thalei and the expedition of Colusus of Samos. This new star appeared in the middle of December, 1230, between Ophiuchus and the Serpent. It dissolved toward the end of March, 1231. (») This is the star mentioned by the Bohemian astronomer, Cypri an:is Leovitius (and referred to under the ninth star, in the year 945) About the same time (July, 1264), a great comet appeai-ed, whose tail swept over one half of the heavens, and which, therefore, could not be mistaken for a new star suddenly appearing between Cepheus and Ga;*- aiopeia. (o) This is Tycho Brahe's star of the 11th of November, 1572, in the Chair of Cassiopeia, R. A. 3° 26' ; DecL 63° 3' (for 1800). (p) February, 1578. Taken from Ma-tuan-lin. The constellation is not given, but the intensity and radiation of the light must have been extraordinary, since the Chinese Record appends the remark, " a star as large as the sun !" (q) On the 1st of July, 1584, not far from tt of Scorpio ; also a Chinese observation. (r) According to Bayer, the star 34 of Cygnus. Wilhelm Jansen, the celebrated geographer, who for a time had been the associate of Tycho Brahe in his observations, \vas the first, as an inscription on his celes- tial globe testifies, to di'aw attention to the new star in the breast of the Swan, near the beginning of the neck. Kepler, who, after the death of Tycho Brahe, was for some time prevented from carrying on any observations, both by his travels and want of instruments, did not ob- serve it till two yeai's later, and, indeed (what is the more surprising, since the star was of the third magnitude), then first heard of its exist- ence. He thus writes: " Cum niense Main, anni 1602, primum litteria monerer de novo Cygni phsenomeno." (Kepler, De Stella Nova teriii honoris in Cygno, 1606, which is appended to the work De Stella Nova in Serpent., p. 152, 154, 164, and 167.) In Kepler's treatise it is no- where said (as we often find asserted in modern works) that this star of Cygnus upon its first appearance was of the first magnitude. Kep- ler even calls it " parva Cygni stella," and speaks of it throughout as one of the third magnitude. He determines its position in R. A. 300^ 46' ; Deck 36^ 52' (therefore for 1800 : R. A. 302'^ 36' ; Deck -f-37° 27 ). The star decreased in brilliancy, especially after the year 1619, and van ishedin 1621. Dominique Cassiui (see Jacques Cassini, EMmens cV Astr., p. 69) saw it, in 1655, again attain to the third magnitude, and then dis- appear. Hevelius observed it again in November, 1665, at first ex- tremely small, then larger, but never attaining to the third magnitude. Between 1677 and 1682 it decreased to the sixth magnitude, and as such it has remained in the heavens. Sir John Herschel classes it among the variable stars, in which he differs from Argelander. («) After the star of 1572 iu Cassiopeia, the most famous of the new stars is that of 1604 in Ophiuchus (R. A. 259^ 42' ; and S. Deck 21° 15', for 1800). With each of these stars a great name is associated. The star in the right foot of Ophiuchus was originally discovered, on the 10th of October, 1604, not by Kepler himself, but by his pupil, the Bohemian astronomer, John Bronowski. It was larger than all stars of the firs! order, greater than Jupiter and Saturn, but smaller ttan Venus. Her» Hciiis asserts that he had previously seen it on the 27th of September Its brilliancy was less than that of tlie new star discovered by Tyclu Brahe in 1572. Moreover, unlike the latter, it was not discernible in the da3^time. But its scintillation was considerably greater, and esj)e« TEMPORARY STARS. 159 cially excitt and his Astronomy, s. 416. § Vide note t, p. 186 I! Vide supra, p. 88, and note ; Laplace, in Zach's AUg. Geogr Epkem., bd. iv., s. 1; Madler, Asir., s. 393. 188 COSMOS. may well be assumed, there exist, in tLe regions of space, dark invisible bodies in which the process of light-producing vibration does not take place, these dark bodies can not fall within the sphere of our own planetary and cometary system, or, at all events, their mass can only be very small, since their existence is not revealed to us by any appreciable dis- turbances. The inquiry into the quality and direction oithe ^notion cf the Jixed stars (both of the t7'iie motion proper to them, and also of their ajJj^arcfit motion, produced by the change in the place of observation, as the earth moves in its orbit), the determijiation of the distances of the fixed stars from the sun by ascertaining their j^;ar<2//a.7;, and the conjecture as to the part in, universal sioace toicard ivldch our planetary system is moving, are three problems in astronomy which, through the means of observa'^ion already successfully em- ployed in their partial solution, are closely connected with each other. Every improvement in the instruments and methods which have been used for the furtherance of any one of these difficult and complicated problems has been beneficial to the others. I prefer commencing with the par- allaxes and the determination of the distances of certain fixed stars, to complete that which especially relates to our j)res ent knov/ledge of isolated fixed stars. As early as the beginning of the seventeenth centur)% Galileo had suggested the idea of measuring the " certainly very unequal distances of the fixed stars from the solar sys- tem," and, indeed, with great ingenuity, was the first to point out the means of discovering the parallax ; not by de- termining the star's distance from the zenith or the pole, "but by the careful comparison of one star with another very near it." He gives, in very general terms, an account of the mi- crometrical method which William Herschel (1781), Struve, and Bessel subsequently made use of. " Perche io non credo," says Galileo,^ in his third dialogue (Giornata terza), *' clie tutte le stelld siano sparse in una sferica superficie egual- niente distanti da ilu centro ; ma stimo, che le loro lonta- nanze da noi siano talmente varie, che alcune ve ne possanc esser 2 e 3 volte piu remote di alcune altre ; talche quando El trovasse col telescopio qualche 'picciolissirtia Stella vici- * Opere di Galileo Galilei, vol. xii., Milano, 1811, p. 20G. This ro- markable passage, which expresses tlie possibility and ihe project of a measurement, was pointed out by Arago see his Annuaire 2')our 18 1:2 p. 382. DISTANCES OF THE STARS. Ibll niibsima ad alcuna delle maggiori, e die pero quella fussc al- tissima, j^otrebbe accadere che qualche sensibil niutazione succedesse tra di loro.'^ " Wherefore I do not "believe," saya Galileo, in liis third discourse (Giornata terza), ''that all the stars are scattered over a spherical superficies at equal dis- tances from a common center ; but I am of opinion that their distances from us are so various that some of them may ha two or tln^ee times as remote as others, so that when som-i minute star is discovered by the telescope close to one of the larger, and yet the former is highest, it may be that some sensible change might take place among them." The in- troduction of the Copernican system imposed, as it were, the necessity of numerically determining, by means of measure- ment, the change of direction occasioned in the position of the fixed stars by the earth's semi-annual change of place in its course round the sun. Tycho Brahe's angular determina- tions, of which Kepler so successfully availed liimself, do not manifest any perceptible change arising from parallax in the. apparent positions of the fixed stars, although, as I have already stated, they are accurate to a minute of the arc. For this the Copernicans long consoled themselves with the reflection that the diameter of the earth's orbit (1651 mill- ions of geographical miles) was insignificant when compared to the immense distance of the fixed stars. The hope of being able to determine the existence of par allax must accordingly have been regarded as dependent on the perfection of optical and measuring instruments, and on the possibility of accurately measuring A-ery small angles. As long as such accuracy was only secure within a minute, the non-observance of parallax merely testified to the fact that the distance of the fixed stars must be more than 343 S times the earth's mean distance from the sun, or semi-di- ameter of its orbit.* This loicer limit of distances rose to 206,265 semi-diameters when certainty to a second M'as at- tained in the observations of the great astronomer, James Bradley ; and in the brilliant period of Frauenhofer's instru- ments (by the direct measurement of about the tenth part of a second of arc), it rose still higher, to 2,062,648 mean distances of the earth. The labors and the ingeniously con- trived zenith apparatus of Newton's great cotemporary, Hob- ort Hooke (1669), did not lead to the desired end. Picard, florrebow (who worked out Romer's rescued observations). * Bessel, in Schumacher's Jahrb fur 1839, s. 511. 190 COSMOS mid FlamsteaJ believed that they had discovered parallaxei ef several seconds, whereas they had confounded the proper motions of the stars with the true changes from parallax. On the other hand, the ingenious John Michell [Phil. Trans. 1767, vol. Ivii., p. 234-2G4) was of opinion that the paral- laxes of the nearest fixed stars must be less than 0' -02, and in that case could only " become perceptible when magnified 12,000 times." In consequence of the widely-difiused opin- ion that the superior brilliancy of a star must invariably in- dicate a greater proximity, stars of the first magnitude, as, for instance, Vega, Aldebaran, Sirius, and Procyon, were, M^th little success, selected for obserA-ation by Calandrelli and the meritorious Piazzi (1805). These observations must be classed with those which Brinkley published in Dublin (1815), and which, ten years afterward, were refuted by Pond, and especially by Airy. An accurate and satisfactory knowledge of parallaxes, founded on micrometric measure- ments, dates only from between the years 1832 and 1838 Although Peters,* in his valuable work on the distance? of the fixed stars (184G), estimates the number of parallaxes liitherto discovered at 33, we shall content ourselves with re ferring to 9, which deserve greater, although very different, degrees of confidence, and which we shall consider in .the probable order of their determinations. The first place is due to the star 61 Cygni, which Bessel has rendered so celebrated. The astronomer of Koniofsbers: determined, in 1812, the large proper motion of this double star (below the sixth magnitude), but it was not until 1838 that, by means of the heliometer, he discovered its parallax. Between the months of August, 1812, and November, 1813, my friends Arago and Mathieu instituted a series of numer ous observations for the purpose of finding the parallax oi the star 61 Cygni, by measuring its distance from the zenith. In the course of their labors they arrived at the very correct conclusion that the parallax of this star was less than half a second.! So late as 1815 and 1816, Bessel, to use his own * Struve, Astr. Stell., p. 104. t Arago, in the Connaissance des Temps four 1834, p. 281 : " Noua obsei-vAmes avec beaucoup de soin, M. Mathieu et moi, pendant le mois d'Aofit, 1812, et pendant le mois de Novembre suivant, la hauteur augulaire de I'etoile audessus de I'horizon de Paris. Cette hauteur, k la secoude epoque, ne surpasse la hauteur angulaire sL la premiere que de 0"*66. Une parallaxe absolue d'une seule seconde aurait necessaire- inent amene entre ces deux hauteurs unc difference de l"-2. Nos ob* eervations n'indiquent done pus que le I'ayon de I'orbite terreste, que DISTANCES OF THE STARS. 19J fiords, " had arrived at no available result. "=^ The ohserva- tioiis taken from August, 1S37, to October, 1838, by means of the great heliometer erected in 1829, first led him to tha parallax of 0"-3483, which corresponds with a distance of 592,200 mean distances of the earth, and a period of 9i . years for the transmission of its light. Peters confirmed this result in 1842 by finding 0"-3490, but subsequently changed Bessel's result into 0"-3744 by a correction for temperature. i The parallax of the finest double star of the southern hem- isphere {a Centauri) has been calculated at 0"-9128 by the observations of Henderson, at the Cape of Good Hope, in 39 millions de lieues soient vns de la 61^ du Cygiie sous im angle de plus d'une demi-seconde. Mais une base vue perpendiculaiiemeut sou- tend un angle d'une demi-seconde quand on est eloigne de 412 mille fois sa longueur. Done la 61^ du Cygne est au moins a une distance de la terre egale a 412 mille fois 39 millions de lieues." *' Duiing tha month of August, 1812, and also during the following November, Mr Mathieu and myself very carefully observed the altitude of the star above the horizon, at Paris. At the latter period its altitude only ex- ceeded that of the former by 0"-66. An absolute parallax of only a single second would necessarily have occasioned a difference of l"-2 between these heights. Our observations do not, therefore, show that a semi-diameter of the earth's orbit, or thirty -nine millions of leagues, are seen from the star 61 of Cygnus, at an angle of more than 0"*5. But a base viewed perpendicularly subtends an angle of 0"*.5 only when it is observed at a distance of 412,000 times its length. Therefore the star 6 1 Cygui is situated at a distance from our earth at least equal to four hundred and twelve thousand times thirty-nine millions of leagues." * Bessel, in Schum., Jahrb. 1839, s. 39-49, and in the Astr. Nachr., No. 366, gave the result 0"-3136 as a first approximation. His later aiid final result was 0''-3483. (^Astr. Nachr., No. 402, in bd. xvii., s. 274.) Peters obtained by his own obsen^ations the following, almost identical, result of 0"-3490. (Struve, Astr. Slell., p. 99.) The alteration which, after Bessel's death, was made by Peters in Bessel's calculations of the angular measurements, obtained by the Konigsberg heliometer, arises from the circumstance that Bessel expressed his intention {Astr. Nachr., bd. xvii., s. 267) of investigating further the influence of temperature on the results exhibited by the heliometer. This purpose he had, iu fact, partially fulfilled in the first volume of his Astro nomische Untersuch' ungen, but he had not applied the corrections of temperature to the ob- servations of parallax. This application was made by the eminent as- tronomer Peters {Ergdnzungscheft zu den Astr. Nachr., 1849, s. 56), and tlie result obtained, owing to the corrections of temperature, was 0''-3744 instead of 0"-3483. t This result of 0"'3744 gives, according to Argelander, as the dis- tance of the double star 61 Cygni from the sun, 550,900 mean distances of the earth from the sun, or 45,576,000 miles, a distance which light traverses iu 3177 mean days. To judge from the three consecutive statements of parallax given by Bessel, 0" 3136, 0"-3483, and 0"-3744, this celebrated double star has apparently come gradu.nlly nearer to u» in liglit passages amounting respectively to 10, O}, and Sr^ yeai-a 192 COSMOS. 1832, and by those of Maclear in 1839>' According to this Btatement, it is the nearest of all the fixed stars that havo yet been measured, being three times nearer than 61 Cygni. The parallax of a Lyras has long been the object of Struve's observations. The earlier observations (1836) gavcf between 0"-07 and 0"-18 ; later ones gave 0"-2613, and a distance of 771,400 mean distances of the earth, with a period of twelve years for the transmission of its light. | But Peters found the distance of this brilliant star to be much greater, since he gives only 0"-103 as the parallax. This result contrasts with another star of the first magni- tude (a Centauri), and one of the sixth (61 Cygni). The parallax of the Polar Star has been fixed i)y Peters at 0"'106, after many comparisons of observations made be- tween the years 1818 and 1838 ; and this is the more sat- isfactory, as the same comparisons give the aberration at 20"-455.§ The parallax of Arcturus, according to Peters, is 0"'127. Riimker's earlier observations with the Hamburg meridian circle had made it considerably larger. The parallax of an- other star of the first magnitude, CapcUa, is still less, bemg, according to Peters, 0"-046. The star No. 1830 in Groombridge's Catalogue, which, according to Argelander, showed the largest proper motion of all the stars that hitherto have been observed in the firm- ament, has a parallax of 0"-226, according to 48 zenith distances which were taken with much accuracy by Peters during the years 1842 and 1843. Faye had believed it to be five times greater, l"-08, and therefore greater than the parallax of a Centauri. |1 * Sir John Herschel, Outlines, p. 545 and 551. Madler {Astr., s. 425j gives ill the case of a Centauri the paj-ajlax 0"-9213 instead of 0"-9128. t Striive Btell. compos. Mms. Microm., p. clxix.-clxxii. Airy makes the paralkx of a Lyra?, which Peters had previously reduced to 0"-l, fitill lower; indeed, too small to be measurable by our present instru- "meuta, {Mem. of the Royal Astr. Soc, vol. x., p. 270.) \ Stnive, On the Micrametrical Admeasurements by tJie Great Refract oral Dorpat (Oct., 1839), in Schum., Astr. Nachr., No. 396, s. 178. i Peters, in Struve, Astr. StelL, p. 100. II Id., p. 101. DISTANCES OF THE STARS. 195 Fixed Star. Parallax. Probable Error. Name of Observer. a Centauri 61 Cygni 0" 0" 0" 0" 0" 0" 0" 0"- 0" • 913 3744 230 226 133 127 207 106 046 0"070 0"020 Henderson and Maciear. Bessel. Henderson Peters. Peters. Peters. Peters. Peters. Peters. Sirius 1830, Groombridge. t Ursag Maj Arcturus 0"-l4l 0"-106 0''073 0"-038 0"-0l2 0"-200 a Lyree Polaris Capella It does not in general follow from the results hitherto ob- tained that the brightest stars are likewise the nearest to ns. Although the parallax of a Centauri is the greatest of all at present known, on the other hand, Vega Lyrse, Arcturus, and especially Capella, have parallaxes from three to eight times less than a star of the sixth magnitude in Cygnus, More- over, the two stars which after 2151 Puppis and e Indi show the most rapid proper motion, viz., the star just mentioned in the Swan (with an annual motion of 5"" 123), and No. 1830 of Groombridge, which in France is called Argelander's Btar (with an annual motion of 6" '974), are three and four times more distant from the sun than a Centauri, which has a proper motion of 3""58. Their volume, raiass, intensity of light, =^ proper motion, and distance from our solar system, stand in various complicated relations to each other. Al- though, therefore, generally speaking, it may be probable that the brightest stars are nearest to us, still there may be cer- tain special very remote stars, whose photospheres and sur- faces, from the nature of their physical constitution, maintain a very intense luminous process. Stars which from their brilUancy we reckon to be of the first magnitude, may be further distant from us than others of the fourth, or even of the sixth magnitude. "When we pass by degrees from the consideration of the great starry stratum of Avhich our solar system is a part, to the particular subordinate systems of our planetary world, or to the still lower systems of Jupiter's and Saturn's moons, we perceive central bodies surrounded by masses in which the successive order of magnitude and of in- tensity of the reflected light does not seem to depend on dis- tance. The immediate connection subsisting between our still imperfect knowledge of parallaxes, and our knowledge c^ * On the proportion of the amount of proper motion to the proximity of the bnghter stars,, see Struvr, SUlL compos. Mcnsurce Microm., p cLxir. Vol. Ill -I 194 COSMOS. the -whole structural configuration of the universe, lends a pt> culiar charm to those investigations which relate to the dis- tances of the fixed stars. Human ingenuity has invented for this class of investiga- tions methods totally different from the usual ones, and which, being based on the velocity of light, deserve a brief mention in this place. Savary, whose early death proved such a loss to the physical sciences, had pointed out how the aberration of light in double stars might be used for determining the parallaxes. If, for instance, the plane of the orbit which the secondary star describes around the central body is not at right angles to the line of vision from the earth to the double star, but coincides nearly with this line of vision itself, then the secondary star in its orbit will likewise appear to describe nearly a straight line, and the points in that portion of its orbit which is tm*ned toward the earth will all be nearer to the observer than the corresponding points of the second half, which is turned away from the earth. Such a division into two halves produces not a real, but an apparent unequal velocity, with which the satellite in its orbit recedes from, or approaches, the observer. If the semi-diameter of this orbit were so great that light would require several days or weeks to traverse it, then the time of the half revolution through its more remote side will prove to be longer than the time in the side turned toward the observer. The sum oi the two unequal times will always be equal to the true pe- riodic time ; for the inequalities caused by the velocity of light reciprocally destroy each other. From these relations of du- ration, it is possible, according to Savary's ingenious method of changing days and parts of days into a standard of length (on the assumption that light traverses 14,356 millions of geograpliical miles in twenty-four hours), to arrive at tlie absolute magnitude of a semi-diameter of the earth's orbit , and the distance of the central body and its parallax may b« then deduced from a simple determination of the angle under which the radius appears to the observer.^ In the same way that the determination of the parallaxe?. mstructs us as to the distances of a small number of the fixed Btars, and as to the place which is to be assigned to them in the regions of space, so the knowledge of the measure and duration of proper motion, that is to say, of the changes which take place in the positions of self-luminous stars.; throws some * Savary, ill tlie Connaissancc ties Temps pour 1830, p. 5G-69, and p. 163-171; and Struve, ibid., d. clxiv\ PROPER MOTION OF THE STARS. . 195 light Oil two mutually dependent problems; namely, tlie mo- tion of tlie solar system,* and the position ol" the center of gravity in the heaven of the fixed stars. That which can only be reduced in so very incomplete a manner to numerical relations, must for that very reason be ill calculated to throw any clear light on such causal connection. Of the two prob- lems just mentioned, the first alone (especially since Arge- iander's admirable investigation) admits of being solved with a certain degree of satisfactory precision ; the latter has been considered with much acuteness by Madler, but, according to the confession of this astronomer himself,! his attempted solution is, in consequence of the many mutually compensa- ting forces which enter into it, devoid " of any thing like evi- dence amounting to a complete and scientifically certain proof." After carefully allowing for all that is due to the preces- sion of the equinoxes, the nutation of the earth's axis, the aberration of light, and the change of parallax caused by the v earth's revolution round the sun, the remaining annual mo- tion of the fixed stars comprises at once that which is the consequence of the trandation in space of the ivhole solaj system, and that also which is the result of the actual propei motion of the fixed stars. In Bradley's masterly labors on nutation, contained in his great treatise of the year 1748, we meet with the first hint of a translation of the solar system, and in a certain sense, also, with suggestions for the most deshable methods of observing iX.X " For if our own solar system be conceived to change its place with respect to ab- solute space, this might, in process of time, occasion an ap- parent change in the angular distances of the fixed stars; and in such a case, the places of the nearest stars being more affected than of those that are very remote, their relative positions might seem to alter, though the stars themselves were really immovable. And, on the other hand, if our own system be at rest, and any of the stars really in motion, this might likewise vary their apparent positions, and the more so, the nearer they are to us, or the swifter their motions are or the more proper the direction of the motion is, to be ren- dered perceptible by us. Since, then, the relative places of • Cosmos, vol. i., p. 146. T Madler, Astronomie, s. 414. X Arago, ill his Annuaire pour 1842, p. 383, was tiie first to call aU tention to this remarkable passage of Bradley's. See, in the same An waite, the section on the translation of the entire solar system, p. 38'J- 3.99. l\)6 COSMOS. the stars may be changed from such a variety .of causes, con» sidering that amazing distance at which it is certain some of them are placed, it may require the observations of many ages to determine the la-v^'s of the apparent changes even of a single star ; much more difficult, therefore, it must be to settle the laws relating to all the most remarkable stars." After the time of Bradley, the mere possibility, and the greater or less probability, of the movement of the solar sys- tem, were in turn advanced in the v/ritings of Tobias Mayer, Lambert, and Lalande ; but William Herschel had the great merit of being the first to verify the conj ecture by actual ob- servations (1783, 1805, and 1806). He found (what has been confirmed, and more precisely determined by many later and more accurate inquiries) that our solar system moves to- ward a point near to the constellation of Hercules, in H. A. 260° 44', and N. Decl. 26° 16' (reduced to the year 1800). Argelander, by a comparison of 3 1 9 ^tars, and with a refer- ence to Lmidahl's investigations, found it for 1800 : E,. A. 257° 54''1, Decl. +28° 49'-2 ; for 1850, R.A. 258° 23'-5, Decl. +28° 45'-6. Otto Struve (from 392 stars) made it to be for 1800 : E.. A. 261° 26'-9, Decl. +37° 35'-5 ; for 1850, 261° 52'-6, Decl. 37° 33'-0. According to Gauss,=^the point in question falls within a quadrangle, whose extremes are, R, A. 258° 40', and Decl. 30° 40'; U. A. 258° 42', Decl. + 30° 57'; U. A. 259° 13', Decl. +31° 9'; K. A. 260° 4', Decl. +30° 32'. It still remained to inquire what the result would be if the observations were directed only to those stars of the south- ern hemisphere which never appear above the horizon in Eu- rope. To this inquiry Galloway has devoted his especial attention. He has compared the very recent calculations (1830) of Johnson at St. Helena, and of Henderson at the Cape of Good Hope, with the earlier ones of Lacaille and Bradley (1750 and 1757). The resultf for 1790 was R. A. 260° 0', Decl. 34° 23' ; therefore, for 1800 and 1850, 260° 5', +34° 22', and 260° 33', +34° 20'. This agreement with the results obtained from the northern stars is extremely sat- isfactory. If, then, the progressive motion of our solar system may be considered as determined within moderate limits, the * In a letter addressed to me. See Schura., Astr. Nackr., No. 622, %. 348. t Galloway, on tlie Motion of the Solar System, in the Phtlos. Triid 1500 equal to the six gi'eater stars of the Pleiades, are manifestly incorrect. The ingenious cosmological treatise of John Michell ends with a veiy bold attempt to explain the scintillation of the fixed stars by a kind of " pulsation in material eSluxes of light" — an elucidation not more happy than that which Simon Marius, one of the discoverers of Jupiter's satellites (eee Cosmos, vol. ii., p. 320) has given at the end of his Munius Joviaii^ (1614). But Michell has the merit of having called attention to the fact (p. 263) that the scintillation of stars is always accompanied by a change of color. '' Besides their brightness, there is in the scintillation cf the fixed stai's a change of color." ( Vide supra.) DOUBLE &TAR3. 203 The importance of Christian Mayer's lahors has, long after his death, heen thankfully and publicly acknowledged by Struve and Madler. In his two treatises, Vertheidigung neuer Beobaclitmigen von Fixstern-trabanteyi (1778), and Dissertatio de novis in Cado sidereo Phcenomenis (1779), eighty double stars are described as observed by him, of which sixty-seven are less than 32" distant from each other. Most of these were first discovered by Christian Mayer him- self, by means of the excellent eight-feet telescope of the Man heim Mural (Quadrant ; " many even now constitute very difficult objects of observation, wliich none but very power- ful instruments are capable of representing, such as p and 71 Herculis, e 5 Lyrte, and w Piscium." Mayer, it is true as was the practice long after his time), only measured dis- tances in right ascension and declination by meridian instru- ments, and pointed out, from his own observations, as well as from those of earlier astronomers, changes of position ; but from the numerical value of these, he omittCvd to deduct what (in particular cases) was due to the proper motion of the stars. ^' These feeble but praiseworthy beginnings were followed by Sir William Herschel's colossal work on the multiple stars, which comprises a period of more than twenty-five years ; for althouo^h Herschel's first catalofjue of double stars was published four years after Christian Mayer's treatise on the same subject, yet the observations of the former go back as far as 1779 — indeed, even to 1776, if we take into consider- ation the investigations on the trapezium in the great nebula of Orion. Almost all w^e at present know of the manifold formation of the double stars has its origin in Sir Wilhara Herschel's work. In the catalogues of 1782, 1783, and 1804, he has not only set dov>ai and determined the position and distance of 846 double stars,! for the most part first dis- covered by himself, but, what is far more important than any augmentation of number, he applied his sagacity and power of observation to all those points which have any bearing on their orbits, their conjectured periodic times, their brightness, contrasts of colors, and classification according to the amount * Struve, in the Recveil des Actcs de la Siance pulliqne de VAcad. iT.p. des Scv^^es de St. Petersbourg, le 29 D^c, 183-2, p. 48-50. Mad. er, Astr. , s. 478. t Philos. Transact, for the Year 1782, p. 40-126; for 1783, p. 112- 124 ; for 1804, p. 87. Regai'ding the observations on which Sir Will- iam Herschel founded his views respecting the 846 double stcfs, see Madler, in '^chnxnachev^s, Jahrbucli fur 1839, s. 59, nnd his Untersuchnrt> ffeu icier die Flxsiern-Systeme, th. i., 1817, s. 7. 204 COSMOS. of their mutual distances. Full of imagination, yet always proceeding with great caution, it was not till the year 1794, v/hile distinguishing between optically and physically double BtaiSj that he threw out his preliminary suggestions as to the natu re of the relation of the larger star to its smaller com- panion. Nine years afterward, he first explained his viewa of the whole system of these phenomena, in the 93d volume of the Philosopliical Tra7isactio7is. The idea of partial Btar-systems, in which several suns revolve round a common center of gravity, was then firmly established. The stupen- dous influence of attractive forces, which in our solar system extends to Neptune, a distance 30 times that of the earth (or 2488 millions of geographical miles), and which com- pelled the great comet of 1680 to return in its orbit, at the distance of 28 of Neptune's semi-diameters (853 mean dis- tances of the earth, or 70,800 millions of geographical miles), is also manifested in the motion of the double star 61 Cygni, vvdiich, with a parallax of 0"'-3744, is distant from the sun 18,240 semi-diameters of Neptune's orbit (^. e., 550,900 earth's mean distances, or 45,576,000 millions of geograph- ical miles). But although Sir William Herschel so clearly discerned the causes and general connection of the phenome- na, still, in the first few years of the nineteenth century, the angles of position derived from his own observations, owing to a want of due care in the use of the earlier catalosfues, were confined to epochs too near together to admit of perfect certainty in determining the several numerical relations oi the periodic times, or the elements of their orbits. Sir John Herschel himself alludes to the doubts regarding the accu- racy of the assigned periods of revolution of a Geminorum (334 years instead of 520, according to Miidler),^ of y Vir- ginis (708 instead of 169), and of y Leonis (1424 of Struve's great catalogue), a splendid golden and reddish-green double star (1200 years). iVfter William Herschel, the elder Struve (from 1813 to 1842) and Sir John Herschel (from 1819 to 1838), availing themselves of the great improvements in astronomical in- struments, and especially in micrometrical applications, have, with praiseworthy diligence, laid the proper and special foun- * Madler, ihid., tli. i., s. 255. For Castor we have two old observa«i lions of Bradley, 1719 and 1759 (the former taken in conjunction with i'oud, the latter with Maskelyne), and two of the elder Herschel, taken ill tiie years 1779 and 1803. For the period of revolution af y Virginis, see Madler, Fixstern-Syat th. ii.. s. 23 1-40. 18-18 DOUBLE STARS 20l dation of this important branch of astrono;ny. In 1820, StiTive published his first Dorpat Table of doubb stars, 796 in number. This was followed in 1824 by a second, con* taining 3112 double stars, down to the ninth magnitude, in distances under 32", of which only about one sixth had been before observed. To accomplish this work, nearly 120,000 fixed stars wore examined by raieans of the great Fraun* hofer refractor. Struve's third table of multiple stars ap- peared in the year 1837, and forms the important Avork Stel- laniTTi cojnpositarwn Mensurce Micrometricoi.'^ It contains 2787 double stars, several imperfectly observed objects being carefully excluded. Sir John Herschel's unwearied diligence, during his four years' residence in Feldhausen, at the Cape of Good Hope, which, by contributing to an accurate topographical knowl- edge of the southern hemisphere, constitutes an epoch in astronomy,! has been the means of enriching this numbei by the addition of more than 2100 double stars (which, with few exceptions, had never before been observed). All these African observations were taken by a twenty-feet reflecting telescope ; they were reduced for the year 1830, and are included in the six catalogues which contain 3346 double stars, and were transmitted by Sir John Herschel to the As- tronomical Society for the sixth and ninth parts of their val- uable Memoirs.X In these European catalogues are laid down the 380 double stars which the above celebrated as- tronomer had observed in 1825, conjointly with Sir James South. "VVe trace in this historical sketch the gradual advance made by the science of astronomy toward a thorough knowl- edge ofjJCirtial, and especially of binary systems. The num- ber of double stars (those both optically and physically double) may at present be estimated with some certainty at about 6000, if we include in our calculation those observed by Bes- sel with the excellent Fraunhofer heliometer, by Argelan- der§ at Abo (1827-1835), by Encke and Galle' at Berlin * Strnve, Mensurcs Micrnm., p. 40 and 234-248. On the whole. 2641-|-146, i. e., 2787 double stars have been observed. (Madler, ia Schum., Jahrb., 1839, s. 64.) + Sir John Herschel, Astron. Observ. at the Cape of Good Hope, p. 165-303. X Ibid., p. 167 and 242. $ Argelander, in order carefully to investigate their proper motion^ examined a great number of fixed stars. See his essay, entitled "-DLX. Stellarmn fixariim posltiones mcdiiP, ineunte anno 1830, ex observ. Aboa habiUs {Ifelsingfarsi?, 1825)." Mad'er {Astr., s. 625) estimates th» 206 COSMOS. (183G and iS39), by Preuss and Otto Struve in Pulkowi (since the catalogue of 1837), by Madl(;r in Dorpat, and by Mitchell in Cincinnati (Ohio), with a seventeen-feet Munich refractor. How many of these 6000 stars, which appear to the naked eye as if close together, may stand in an imme- diate relation of attraction to each other, forming systems of their own, and revolving in closed orbits — or, in other words, liow many are so-called jp7i7/S2C«Z {i-evolving) double stars — is an important problem, and difficult of solution. More re- volving companions are gradually but constantly being dis- covered. Extreme slowness of motion, or the direction of the plane of the orbit as presented to the eye, being such as to render the position of the revolving star unfavorable for ob- servation, may long cause us to class physically double stars among those which are only optically so ; that is, stars of which the proximity is merely apparent. But a distinctly- ascertained appreciable motion is not the only criterion. The perfectly uniform motion in the realms of space {i. e., a com- mon progressive movement, hke that of our solar system, in- cluding the earth and moon, Jupiter, Saturn, Uranus, and Neptune, with their satellites), which in the case of a con- siderable number of multiple stars has been proved by Arge- lander and Bessel, bears evidence that the principal stars and their companions stand in undoubted relation to each other in separate partial systems. Miidler has made the in- teresting remark, that whereas, previous to 1836, among 2640 double stars that had been catalogued, there were only 58 in which a difference of position had been observed ivith certainty, and lOo in which it might be regarded as more or less prohahle ; at present, the proportion of physically double stars to optically double stars has changed so greatly in favor of the former, that among the 6000 double stars, according to a tabic published in 1849, 650 are known in which a change of relative position can be incontestably proved. =^ The earliest comparison gave one sixteenth, the number of multiple stars in tlie uortlieni hemisphere, discovered at Piilkowa since 1837, at not less than 600. * The number of fixed stars in which proper motion has been un. doubtedly discovered (though it may be conjectured in the case of all) is slightly greater than the number of double stars in which change of position hdiS been observed. (Madler, Astr., s. 394, 490, and 520-540.) Results obtained by the application of the Calculus of Probabilities, ac cording as the several reciprocal distances of the double stai's are be- tween 0" and 1", 2" and 8", or 10" and 32", are given by Stnive, in his Mens. Miirom., p. xciv. Distances less than 0' -8 have been taken, am/ DOUBLE STARS 20*7 most recent gives one ninth, as the proportion of the cosmic* al bodies which, by an observed motion both of the primary star and the companion, are manifestly proved to be phys' ically double stars. Yery little has as yet been numerically determined re garding the relative distribution of the binary star-system3 throughout space, not only in the celestial regions, but even on the apparent vault of heaven. In the northern hemi- sphere, the double stars most frequently occur in the direc- tion of certain constellations (Andromeda, Bootes, the Great Bear, the Lynx, and Orion). For the southern hemisphere Sir John Ilerschel has obtained the unexpected result, " that in the extra-tropical regions of this hemisphere the number of multiple stars is far smaller than that in the correspond- - ing portion of the northern." And yet these beautiful south- ern regions have been explored, under the most favorable circumstances, by one of the most experienced of observers, v/ith a brilliant twenty-feet reflecting telescope, which sep- arated stars of the eighth magnitude at distances even of three quarters of a second. =* The frequent occurrence of contrasted colors constitutes an extremely remarkable peculiarity of multiple stars. Struve, in his great workf pubhshed in 1837, gave the following re suits with regard to the colors presented by six hundred of the brighter double stars. In 375 of these, the color of both principal star and companion .was the same and equally in- tense. In 101, a mere difference of intensity could be dis- cerned. The stars with perfectly different colors were 120 in number, or one fifth of the whole ; and in the remaining four fifths the principal and companion stars were uniform in color. In nearly one half of these six hundred, the princi- pal star and its companion were white. Among those of different colors, combinations of yellow with blue (as in i Cancri), and of orange v/ith green (as in the ternary star 7 Andromedai),! are of frequent occurrence. Arago was the first to call attention to the fact that the diversity of color in the binary systems principally, or at least in very many cases, has reference to the complementary col- giperimouts with very complicated systems have confirmed the aatrc;!: 9mer ia the hope that these estimates are mostly correct within C ''"? Struve, uher Dappelsteriie nach Dot-pater Beob., s. 29.) * Sir John Herschel, Observations at thz Cape, p. 1()G. ■f Stnive, Mensura Microm., p. Ixxvii. to Ixxxiv. t Sir John Herschel, Outlines of Asfr., p. .579. £08 COSM DS. ors — the subjective colors, which, when miited; form white.* It is a well known optical phenomenon that a faint white light appears green when a strong red light is brought neaj it, and that a white light becomes blue when the stronger surrounding light is yellowish. Arago, however, with his usual caution, has reminded us of the fact that even though the green or blue tint of the companion star is sometimes the result of contrast, still, on the whole, it is impossible to deny the actual existence of green or blue stars. f There are in- * Two glasses, which exhibit complementary colors when placed one upon the other, are used to exhibit white images of the sun. During my long residence at the Observatory at Paris, my I'riend very success- fully availed himself of this contrivance, instead of using shade glasses to observe the sun's disk. The colors to be chosen are red and green, yellow and blue, or green and violet. " Loi-squ'uue lumiere forte i. 33-36, m\di M ensures Microm., p. Ixxxiii., enumerates sixty-three doubla etarsin which both the principal and companion are blue or bluish, and in which, therefore, the colca's can not be the effect of contrast. When we are forced to compare together the colors of double stars, as report" ed by several astronomers, it is particularly striking to observe how fre« quently the companion of a red or orange-colored star is reported by gome obser\-ers as blue, and by others as green. t Ai'ago, Annvaire pour 1831, p. 302. t Vide supra, p. 13Q-13G. 210 COSMOS. a corresponding dilTerence in brightness. In two cases-— ir ^ Bootis and y Leonis — wliicli, from their great brightness, can easily be measured by powerful telescopes, even in the daytime, the former consists of two white stars of the third and fourth magnitudes, and the latter of a principal star of the second, and of a companion of the 3* 5th magnitude. This is usually called the brightest double star of the north- ern hemisphere, whereas a Centauri^ and a Crucis, in the southern hemisjDhere, surpass all the other double stars in brilliancy. As in ^Bootis, so also in a Centauri and y Leonis, we observe the rare combination of two great stars with only a slightly different intensity of light. No unanimity of opinion yet prevails respecting the vari- able brightness in multiple stars, and especially in that of companions. We have already! several times made mention of the somewhat irregular variability of luster in th^ orange- colored principal star in a Herculis. Moreover, the fluctua- tion in the brightness of the nearly equal yellowish stars (of the third magnitude) constituting the double star y Virginis and Anon. 2718, observed by Struve (1831-1833), probably indicates a very slow rotation of both suns upon their axes.} Whether any actual change of color has ever taken place in double stars (as, for instance, in y Leonis and y Delphini) ; whether their white light becomes colored, and, on the other hand, whether the colored light of the isolated Sirius has be- come white, still remain undecided questions. § Where the disputed differences refer only to faint tones of color, we should take into consideration the power of vision of the observer, find, if refractors have not been employed, the frequently red- dening influence of the metallic speculum. Among the multiple systems we may cite as ternaries, ^ Libra?, ^ Cancri, 12 Lyncis, 11 Monoc. ; as quaternaries, 102 and 2G81 of Struve's Catalogue, a Andromedce, e Lyrse : in 0 Orionis, the famous trapezium of the greater nebula of * "This superb double star (a Cent.) is beyond all comparison the most striking object of the kind in the heavens, and consists of two in- dividuals, both of a high ruddy or c-range color, though that of tho smaller is of a somewhat more somber and brownish cast." (Sir .Toha Ilerschel, Observations at the Cape of Good Hope, p. 300.) And, ac- cording to the important observations taken by Captain Jacob, of tho Bombay Engineers, between the years 1846 and 1848, the principal star is estimated of the first magnitude, and the satellite from the 2'5th to the third magnitude. {Transact, of tin Royal Soc. of Ed'mh., vol. xv' 1849. p. 451.) t Vide supra, p. 165, 166, and note. X Struve, Uehcr Dopjjelsf. nnch Dorp Bcoh., s. 33. $ Ibid., s. 3«: DOUBLE STARS. 21 J Orion, we have a combination of six— probably a system sub- ject to peculiar physical attraction, since the five smaller stars (6*3m. ; 7m. ; 8m. ; 11 -Sm. ; and 12m.) follow the prop- er motion of the principal star, 4-7m. No change in their relative positions has yet been observed.* In the ternaiy combinations of ^ Librae and ^ Cancri, the periodical move- ment of the two companions has been recognized with great certainty. The latter system consists of three stars of the third magnitude, differing very little in brightness, and the nearer companion appears to have a motion ten times moro rapid than the remoter one. Tho number of the double stars, the elements of whose orbits it has been found possible to determine, is at present stated at from fourteen to sixteen. f Of these, ^ Herculis has twice completed its orbit since the epoch of its first dis- covery, and during this period has twice (1802 and 1831) presented the phenomenon of the apparent occultation of one fixed star by another. For the earliest measurements of the orbits of double stars, we are indebted to the industry of tSavary {^ Ursse Maj.), Encke (70 Ophiuchi), and Sir John Herschel. These have been subsequently followed by Bes- sel, Struve, Miidler, Hind, Smyth, and Captain Jacob. Sa- vary's and Enc];c's methods require four complete observa- tions, taken at sufficient intervals from each other. The shortest periods of revolution are thirty, forty-two, fifty-eight, and seventy-seven years ; consequently, intermediate be- tween the periods of Saturn and Uranus ; the longest that have been determined with any degree of certainty exceed five hundred years, that is to say, are nearly equal to three times the period of Le Terrier's Neptune. The eccentricity of the elliptical orbits of the double stars, according to tho investigations hitherto made, is extremely considerable, re- sembling that of comets, increasing from 0-62 (cr Coronee) up to 0"95 (a Centauri). The least eccentric interior comet — that of Faye — has an eccentricity of 0'55, or less than that of the orbits of the two double stars just mentioned. Ac- cording to Madler's and Hind's calculations, rj Coronse and Castor exhibit much less eccentricity, which in the former is 0'29, and in the latter 0*22 or 0-24. In these double stars the two suns describe ellipses which come very near to those of * Miidler, Asfr., s. 517. Sir John Herschel, OntL, p. 568. t Compare Miidler, Untersuck. uber die Fixstern-Systeme, th. i., s 225-275 ; in. ii., s. 235-240 ; and his Astr., s. 511 Sir Johu Herschel, OatL, p. 573. 212 COSMOS. two of the smaller principal planets in our solar system, th« eccentricity of the orbit of Pallas being 0 24, and that of Juno, 0'25. If, with Encke, we consider one of the two stars in a bi- nary system, the brighter, to be at rest, and on this supposi- tion refer to it the motion of the companion, then it follows from the observations hitherto made that the companion de scribes round the principal star a conic section, of which the latter is the focus ; namely, an ellipse in which the radius vector of the revolving cosmical body passes over equal su- perficial areas in equal times. Accurate measurements of the angles of position and of distances, adapted to the determ- ination of orbits, have already shown, in a considerable num- ber of double stars, that the companion revolves round the principal star considered as stationary, impelled by the same gravitating forces which prevail in our own solar system. This firm conviction, which has only been thoroughly attain- ed within the last quarter of a century, marks a great epoch in the history of the development of higher cosmical knowl- edge. Cosmical bodies, to which long use has still preserved the name oi fixed stars, although they are neither riveted to the vault of heaven nor motionless, have been observed to occult each other. The knowledge of the existence of partial systems of independent motion tends the more to en- large our view, by showing that these movements are them- selves suboidinate to more general movements animating tha regions of space. DOUBLE STARS. Elements of the Orbits of Double Stabb. 213 Name. Semi-Major Axis. Eccentricity. Period of ReTolution in years. Calculator. (1) ^UrsaeiMaj 3"-857 0-4164 58-262 Savary, 1830. 3''-278 2"-295 0-3777 04037 60 720 61-300 John Herschel. Tables of 1849. Madler, 1847. (2) p Ophiuchi 4"-328 0 4300 73-862 Encke, 1832. (3) CHerculis r'-208 04320 30-22 Madler, 1847 (4) Castor 8"-086 5"-692 07582 0-2194 252-66 51977 John Herschel. Tables of 1849. Madler, 1847. 6"-300 0-2405 632-27 Hind, 1849. (5) y Virginis 3"-580 3"-863 0-8795 0-8806 182-12 169 44 John Herschel. Tables of 1849. Madler, 1847. (S « Cer.tauri 15"-500 09500 77 00 Captain Jacob, 1843. INDEX TO VOL. III. AciiBOMATic telescopes, 63 Adalbert, Prince, of Prussia, his observa- tions on the undulation of the stars, 59. Alcor, a star of the constellation Ursa Ma- jor, employed by the Persians as a test of vision, 49, 50, 200. Alcyone, one of the Pleiades, imagined the center of gravity of the solar sys- tem by Madler, 198. Alphonsine Tables, date of their construc- tion, 151. Anasagoras of Clazomenae, his theory of the world-arranging intelligence, 11 ; ■ origin of the modern theories of rota- tory motion, 12. Andromeda's girdle, nebula in, 142. Arago, M., letters and communications of, to M. Humboldt, 46, 49, 67, 68, 73, 96, 207-209 ; on the etiect of telescopes on the visibility of the stars, 69 ; on the velocity of light, 80, 84 ; on photometry, 92, 96 ; his cyanometer, 97, Aratus, a fragment of the work of Ilip- parchns preserved in, 109. Archimedes, his " Arenarius," 30. Arcturus, true diameter of, 89. Argelander, his view of the number of the fixed stars, 105, 106 ; his additions to Bessel's Catalogue, 115 ; on period- ically variable stars, 166. 17 Argus, changes in color and brilliancy of, 135, 178, 179. Aristotle, his distinct apprehension of the unity of nature, 13-15; his defective solution of the problem, 15 ; doubts the infinity of space, 29, 30 ; his idea of the generation of heat by the movement of 5ie spheres, 124. Astrognosy, the domain of the fixed stars, 26-28. Astronomy, the observation of groups of fixed stars, the first step in, 118 ; very bright single stars, the first named, 89. Atmosphere, limits of the, 40, 41 ; eflecta of an untransparent, 104. Augustine, St., cosmical views of, 124. Autolycus of Pitane, era of, 89, 90. Auzout's object-glasses, 62. Bacon, Lord, the earliest views on the ve- locity of light found in his "Novum Organum,' 79. Faily, Francis, his revision of De Lalande's Catalogue, 115. Bayer's lettering of the stars of any con- stellation not an evidence of tlieir rel- ative brightness, 98. B6rard, Captain, on the change of color of the star y Crucis, 135. Berlin Academy, star maps of the, 116. Bessel, on repulsive force, 34, 35 ; his star maps have been the principal means of the recognition of seven new planets, 116 ; calculation of the orbits of douKa stars by, 211. Binary stars, 199. Blue stars, 136 ; less frequent than red, 209. Blue and green suns, the probable cause of their color, 208. Bond, of the Cambridge Observatory, United States, his resolution of the neb- ula in Andromeda's girdle into small stars, 142. Brewster, Sir David, on the dark lines of the prismatic spectra, 44. British Association, their edition of La- lande's Catalogue, 115. Bruno, Giordano, his cosmical views, 17 ; his martyrdom, 17. Busch, Dr., his estimate of the velocity oi hght incorrect, 82. Catalogues, astronomical, their great im- portance, 113, 114 ; future discoveries of planetary bodies mainly dependent on their completeness, 114 ; list of, 114, 115 ; Halley's, Flamstead's, and others, 114 ; Lalande's, Harding's, Bessel's, 115 Catf^terisms of Eratosthenes, 89, 90. a Centauri, Piazzi Smyth on, 146, 147, 185; the nearest of the fixed stars that have yet been measured, 191, 192. Central body for the whole sidereal heav- ens, existence of, doubtful, 197. Chinese record of extraordinary stars (of Ma-tuan-lin), 109, 155-159 ; deserving of confidence, 162. Clusters of stars, or stellar swarms, 14C ; hst of ih.9. principal, 141-143. Coal-sacks, a portion of the Milky Way in the southern hemisphere so called, 137. Colored rings aflTord a direct measure of the intensity of light, 96. Colored stars, 130 ; evidence of change of color in some, 131, 132; Sir John Herschel's hypothesis, 131 ; difference of color usually accompanied by differ- ence of brightness, 209. Comets, information regarding celestial space, derived from observation on, 31, 39 ; number of visible ones, 151. Concentric rings of stars, a view favored by recent observation, 149. Constellations, arrangement of stars into^ very gradual, 119. Conti'asted coters of double stars, 207. Cosmical contemplation, extension of, is the Middle Ages, 16. ne INDEX. Cosiiiical vnpor, question as to condensa- tion of; 37 ; Tvcho Brahe's and Sir Will- iam llerschers theories, 154. •' Cosmos," a pseudo-Aiistotelian work, 16. Crystal vault of heaven, date of the desig- nation, 123 ; its signification according to Erapedocles, 1'^ ; the idea favored by the Fathers of the Church, 125. Cyanometer, Arago's, 97. Dark cosmical bodies, question of, 164, 187. Dolambre on the velocity of light, 82. Descartes, his cosmical views, 19, 20 ; sup- presses his work from detbrence to tlie Inquisition, 20. Dioptric tubes, the precursors of the tele- scope, 43. Direct and reflected light, 45. Distribution of the fixed stars, according to right ascension, 140. Dorpat Table (Struve's) of multiple stars, 205, Double stars, the name too indiscrimin- ately applied, 199, 200 ; distribution into optical and physical. 200 ; pointed out by Galileo as useful in determining the parallax, 200 ; vast increase in their ob- served number, 201, 205 ; those earliest described, 201 ; number in wiiich a change of position has been proved, 206 ; greater number of double stars in the northern than in the southern hem- isphere, 207 ; occurrence of contrasted colors, 207 ; calculation of theix orbits, 211 ; table of the elements, 213. Earth-animal, Kepler and Fludd's fancies regarding the, 19. Edda-Songs, allusion to, 8. Egypt, zodiacal constellationa of, their date, 121. Egyptian calendar, period of the complete arrangement of the, 133. Ehrenberg on the incalculable number of animal organisms, 30. Electrical light, velocity of transmission of, 86. Electricity, transmission o^ through the earth, 88. Elements, Indian origin of the hypothesis of four or five, 11. Emanations Irom the head of some com- ets, 39. Encke, his accurate calculation of the equivalent of an equatorial degree, 81 ; on the star-maps of the BerUn Academy, 116 ; an early calculator of the orbits of double stars, 2i 1 ; his theory of their motion, 212. Encke's comet, cocsiderations on space, derived from periods of revolution of, 27 ; a resisting medium proved from observation on, 39, Ether, different meanings of, in the East and the West, 31, 32. Etlier (Akd'sa, in Sanscrit), ore of the In- dian five elements, 31 r.lher, the, fiery, 35. Euler's ccmparative estmiate of the light of the sun and moon^ 95. Fixed stars, the term erroneous, 27, 123 ; scintillation of the, 73 ; variations in iU intensity, 76 ; our sun one of the fainter fixed stars, 95; photometric arrango ment of, 99; their number, 105; num- ber •sisible at Berlin with the naked eye, 107; at Alexandria, 107; Struve and Herschel's estimates, 116; grouping of the, 117 ; distribution of the, 140; prop- er motion of the, 182; parallax, 188; number of, in which proper motion has been discovered, greater than of thoso in which change of position has been observed, 206, 207. Fizeau, M., his experiments on the veloc- ity of light, 80, 83. Fonnula tor computing variation nf light of a star, by Argelander, 168, 169. Galactic circle, average number of stars in, and beyond the, 139. Galileo indicates the means of discover- ing the parallax, 188. Galle, Dr., on Jupiter's satellites, 50 ; on the photometric arrangement of the fixed stars, 99. Garnet star, the, a star in Cepheus, so called by William Herschel, 166. Gascoigne applies micrometer threads to the telescope, 42. Gauging the heavens, by Sir William Her- schel, 138, 139 ; length of time neces- sary to complete the process, 139. Gauss, on the point of translation in space of the whole solar system, 196. Gilliss, Lieutenant, on the change of color of the star rj Argiis, 135. Gravitation, not an essential property of bodies, but the result of some higher and still unknown power, 22, 23. Greek sphere, date of the, 119, 121. Green and blue suns, 208. Groups of fixed stars, recognized even by the rudest nations, 117 ; usually the same groups, as the Pleiades, the Great Bear, the Southern Cross, &c., 117, 118. Halley asserted the motion of Sirius and other fixed stars, 26, 27. Hasscnfratz, his description of the raya of stars as caustics on the crj'stalliae lens, 52, 127. Heat, radiating, 35. Hepidannus, monk of Saint Gall, a new star recorded by, 157, 162. Herschel, Sir William, on the vilifying action of the sun's rays, 34 ; his estimate of the number of the fixed stars, 116, 117; his "gauging the heavens," and its result, 138, 139. Herschel, Sir John, on the transmission of light, 30; on the influence of the sun's rays, 34 ; compares the sun to a per- petual northern light, 34 ; on the at- mosphere, 37 ; on the blackness of the ground of the heavens, 39 ; on stan seen in daylight, 57 ; on photousctry. INDEX. 2n 5».», [jhotometric arrangement of the lixed stars, 99 ; on the number of stars actually registered, 106 ; on the cause of the red color of Sirius, 131, 13:2; on the Milky Way, 145 ; on the sun's place, 150 ; on the determined periods of vari- able stars, 166 ; number of double stars the elements of whose orbits have been determined, 211. Hieroglyphical signification of a star, ac- cording to Horapollo, 128. Hind's discovery of a new reddish-yellow star of the fifth magnitude, in Ophiu- chus, 160 ; has since sunk to the eleventh magnitude, 160 ; calculation of the or- bits of double stars by, 211. Ilipparchus, on the number of the Plei- ades, 48 ; his catalogue contains the earliest determination of the classes of magnitude of the stars, 90 ; a fragment of his work preserved to us in Aratua, 109. Holtzmann, on the Indian zodiacs, 121. Homer, not an authority on the state of Greek astronomy in his day, 119, 123. HumboMt, Alexander von, works of, quoted in various notes : Ansichten der Natur, 79. Asie Centrale, 111, 112. Essai sur la G4ogr. des Plantee, 58. Examen Critique de I'Histoire de la G6ographie, 49, 112, 137. Lettre a M. Schumacher, 93. Regueil d'Observations Astrono- miques, 43, 47, 93. Relation Historique du Voyage aux Regions Equinoxiales, 56, 58, 79, 93. Vue des Cordilleres et Monumens des Peuples Indigenes de I'Amer- ique, 121, 136. Humboldt, WUhelm von, quoted, 25. Huygens, Christian, his ambitious but un- satisfactory Cosmotheoros, 20; exam- ined the Milky Way, 144. Huygens, Constantin, his improvements in the telescope, 62. Hvergelmir, the caldron-spring of the Ed- da-Songs, 8. Indian fiction regarding the stars of the Soutliem hemisphere, 138. Indian theory of the live elements (Pant- schatd), 31. Indian zodiacs, their high antiquity doxibt- ful, 121. Jacob, Capt., on the intensity of light in the Milky Way, 146; calculation of the orbits of double stars, by, 211. Joannes Philoponus, on gra^^tation, 18. Jupiter's satellites, estimate of the magni- tudes of, 50 ; case in which they were •s ifiible by the naked eye, 52 ; occulta- tions of, observed by daylight, 62. Kepler, his approach to the mathematical application of the theory of gravitation, 18 ; rejects the idea of sohd orbs, 126. f.alande, liis Catalogue, revised by Baily, 115. Vol. ITT — K liassell's telescope, discoveries made by means of, 65. Lepsius, on the Egyptian name (Sothis) ot Sirius, 134. Leslie's photometer, defects of, 96. Libra, the constellation, date of its intro- duction into the Greek sphere, 120. Light, always refracted, 44 ; prismatic spectra diifer in number of dark linea according to their source, 44, 45 ; polar- ization of, 45 ; velocity of, 79 ; ratio of solar, lunar, and stellar, 95 ; variation of, in stars of ascertained and unascer- tained periodicity, 168, 177. Light of the sun and moon, Euler's and Slichelo's estimates of the comparative, 95. Limited transparency of the celestial re- gions, 38. Macrobius, " Sphrera aplanes" of, 27. Madler, on Jupiter's satellites, 52 ; on the determined periods of variable stars, 166; on future polar stars, 181 ; on non- luminous stars, 187 ; on the center of gravity of the solar system, 198. Magellanic clouds, known to the Arabs, 91. Magnitude of the stars, classes of, 90, 91. Mains, his discoveries regarding light, 4c\ " Mappa coelestis" of Schwinck, 140. Ma-tuan-lin, a Chinese astronomical rec- ord of, 109. Mayer, Christian, the first special observer of the fixed stars, 202. Melville Island, temperature of, 36. Michell, John, 95 ; applies the calculus of probabilities to small groups of stars, 2 ination of the inten.sity of stellar ligh^ Reflecting and refracting telescopes. Si. Regal stars of the ancients, 136. Resisting medium, proved by obsenri- tions on Encke's and other comets, 'i% Right ascension, distribution of stars »?• cording to, by Schwinck, 140. Pdngs, colored, measurement of the in* tensity of light by, 96. Rings, concentric, of stars, the hypothppJa of, favored by the most recent obaen'v tions, 149. Rosse's, Lord, his great telescope, 65 ; iU serrices to astronomy, 66. Ruby-colored stars, 135. Saint Gall, the monk of, observed a ncrr star distant from the MiUsy Way, 162. Saussure asserts that stars may be seen in daylight on the Alps, 57 ; the asser- tion not supported by other travelers' experience, 58. Savary, on the application of the aberra- tion of light to the determination of the parallaxes, 194 ; an early calculator of the orbits of double stars, 211. Schlegel, A. W. von, probably mistaken as to the high antiquity of the Indiaa zodiacs, 121. Schwinck, distribution of the fixed stara in his " Mappa coelestis," 140. Scintillation of the stars, 73 ; variations in its intensity, 76 ; mentioned in the Chinese records, 77 ; httle observed in tropical regions, 77, 78 ; always accom- panied by a change of color, 202. Seidel, his attempt to determine the quan- tities of light of certain stars of the firat ma^^itude, 93. Selfluminous cosmical bodies, or suns, 199. Seneca, on discovering new planets, 23 Simplidus, the Eclectic, contrasts the cen- tripetal and centrifugal forces, 12 ; hia vague view of gravitation, 18. Sirius, its absolute intensity of light, 95, historically proved to have changed ita color, 131 ; its association with the ear- liest development of civilization in the valley of the Nile, 133 ; etymological re- searches concerning, 133, 134. Smyth, Capt. W. H., calculations of tho orbits of double stars by, 211. Smyth, Piazzi, on the Milky Way, 146, 147 ; on a Centauri, 185. Sotliis, the Egyptian name of Sirius, 133, 134. South, Sir James, observation of 380 dou- ble stars by, in conjunction with Sir John Herschel, 205. Southern constellations known to Ptol« emy, 137. Southern Cross, formerly visible on the shores of the Baltic, 138. Southern hemisphere, in parts remark- ably deficient in constellations, 112; dis- tances of its stars, first measured about the end of the sixteenth century, 138 INDEX. 211.' fcptiry, conjectures regardinj;, 29; com- pared to the nij-thic period of history, 20 ; fallacy of attempts atmeasureraent of, 30 ; portions between cosmical bod- ies not void, 31 ; its probable low tem- perature, 35. Spectra, the prismatic, 44; difference of the dark lines of, according to their sources, 45. " Sphtera aplanes" of Macrobius, 27. Spurious diameter of stars, 130. Star of the Magi, Ideler's explanation of the, 154. Star of St. Catharine, 137. Star systems, partial, in which several suns revolve about a common center of gravity, 204. Stars, division into wandering and non- wandering, dates at least from the early Greek period, 27; magnitude and visi- bility of the, 48 ; seen through shafts of chimneys, 57 ; undulation of the, 58, 59 ; observation of, by daylight, 66 ; scintillation of the, 73 ; variations in its intt^nsity, 76 ; the brightest the earliest named, 89; rays of, 52, 127, 128 ; color of, 130 ; distribution of, 140 ; concentric rings of, 149 ; variable, 161 ; vanished, 163 ; periodically changeable, 164 ; non- luminous, of doubtful existence, 187 ; ratio of colored stars, 209. Steinheil's experiments on the velocity of the transmission of electi'icity, 87 ; his photometer, 93. Stellar clusters or swarms, 140. Struve on the velocity of light, 82; his estimate of the number of the tixed stars, 117 ; on the Milky Way, 139; his Dorpat Tables, 20o ; on the contrasted colors of multiple stars, 207 ; calcula- tion of the orbits of double stars by. 211. Sun, the, described as " a perpetual north- ern light" by Sir William Herschel, 34 ; in intensity of light merely one of the fainter tixed stars, 95 ; its place prob- ably in a comparatively desert region of the stariy stratum, and eccentric, 1.50. Suns, self-luminous cosmical bodies, 199. Fable of photometric aiTangeraent of 190 fixed stars, 100 ; of 17 stars of first mag- nitude, 102 ; of the variable stars, by Argelander, 172, and explanatory re- marks, 172-177 ; of ascertained paral- laxes, 193 ; of the elements of the or- bits of double stars, 213. Telescope, the principle of, known to the Arabs, and probably to the Greeks and Romans, 42, 43 ; discoveries by its means, 61 ; successive improvements of the, 62; enormous focal length of some, 63 ; Lord Rosse's, 65 ; Bacon's comparison of, to discovery ships, 130 ; penetrating power of the, 145, 146. Telesio, Bernardino, of Cosenza, his views of the phenomena of inert matter, 16. Temperature, low, of celestial space, 35; uncn'tainty of results vet obtained, 36; ita influence on the climate 'A the earth, 37. Temporary stars, list of, 155 ; notes to, 155-160. Ternary stars, 210. Timur Ulugh Beg, improvements in prac- tical asti'onomy in the time of, 91. Translation in space of the whole solai system, 195 ; first hinted by Bradlej', 195; verified by actual observation by William Herschel, 196; Argelander, Struve, and Gauss's views, 196. Trapezium in the great nebula of Orion, investigated by Sir Wm. Herschel, 203. Tj'cho Brahe, his vivid description of the appearance of a new star, 152 ; his the- ory oi' the formation of such, 154. "Ultimate mechanical cause" of all mo- tion, unknown, 24, 25. Undulation of the stars, 58, 59. Undulations of rays of light, varioua lengths of, 84. Unity of nature distinctly taught by Aria- totle, 13-15. Uranological and telluric domain of the Cosmos, 26. Uranus observed as a star by Flamstcad and others, 114. Vanished stars, 163 ; statements about such to be received with great caution, 163. Variable brightness of multiple and dou- ble stars, 209. Variable stars, 160-161 ; mostly of a red color, 165; irregularity of their periods, 167 ; table of, 172. Velocity of light, 79 ; method's of determ- ining, 80; applied to tlie determination of the parallax, 195. Visibility of objects, 55 ; how modified, 56. Vision, natural and telescopic, 41; aver- age natural, 47, 48 ; remarkable in- stances of acute natural, 52, 55. Wheatstone's experiments with revolv- iivg mirrors, 45 ; velocity of electrical light determined by, 86. White Ox, name given to the nebula now known as one of the Magellanic clouds, 91. ■ Wollaston's photometric researches, 95. Wright, of Durham, hisview of the origin of the Ibrm of the Milky Way, 149. Yggdrasil. the World-tree of the Edd«- Songs, 8. Zodiac, period of its introduction into the Greek sphere, 119 ; its origin among the Chaldeans, 120 ; the Greeks borrowed from them only the idea of the division, and filled its signs with their own catas torisms, 120; great antiquity of the In- dian very doubtful, 121. Zodiacal lidit, Sir John Herschel on tha 40. THE END. \ ''^:> i's iTSff " B ~:-i t ,d ')p / IIMi