COSMOS: 
 
 A SKETCH 
 
 A PHYSICAL DESCRIPTION OF THE UNIVERSE. 
 
 ALEXANDER VON HUMBOLDT. 
 
 TKANSLATED FBOM THE GEHMAN, 
 
 BY E. C. OTTE. 
 
 Nataraa vero rerum vis atquo majestas in omnibus momentis fide caret, si quis modo 
 partes ejus ac non totam complectatur animo. Plin., Hist. Nat., lib. vil, c. L 
 
 VOL. III. 
 
 NEW YORK: 
 
 HARPER & BROTHERS, PUBLISHERS, 
 329 & 331 PEARL STREET, 
 
 FRANKLIN SQUARE. 
 
 1858.
 
 CONTENTS OF VOL. III. 
 
 INTRODUCTION. 
 
 nv 
 
 Historical Review of the attempts made with the object of 
 considering the Phenomena of the Universe as a Unity 
 of Nature 6-25 
 
 SPECIAL RESULTS OF OBSERVATIONS IN THE 
 DOMAIN OF COSMICAL PHENOMENA 
 
 A. URANOLOGICAL PORTION of the physical description of the 
 
 world. a. ASTROGNOSY 26-28 
 
 I. The realms of space, and conjectures regarding that which 
 
 appears to occupy the space intervening between the 
 heavenly bodies 29-41 
 
 II. 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 with a few nebulous spots, 
 143-151 103-151 
 
 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- 
 182 151-182 
 
 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, 194-199 182-199 
 
 VI. Multiple, or double stars Their number and reciprocal 
 
 distances. Period of revolution of two stars round a 
 common center of gravity 199-21.*
 
 IV CONTENTS. 
 
 TABLES. 
 
 Fag. 
 
 Photometric Tables of Stars 100-102 
 
 Clusters of Stars 141-143 
 
 New Stars 155-160 
 
 Variable Stars 172-177 
 
 Parallaxes 193 
 
 Elements of Orbits of double Stars ... 213
 
 SPECIAL RESULTS OF OBSERVATION 
 
 IN 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 stata 
 of science permit, I have regarded as not unattainable, I 
 have, in the preceding volumes of Cosmos, considered Nature 
 in a two-fold point of view. In the first 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 his 
 ideas and feelings. 
 
 The external world of phenomena has been 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 atmosphere, 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 where, in addition to 
 the dynamic action of moving forces, the powerful influence 
 of a specific difference of matter manifests itself in the ter- 
 restrial portion of the universe. Tho 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- 
 served, of extraordinary simplicity, and capable, by means of 
 the attractive force of matter and the quantity of its mass, 
 of being submitted to exact calculation in accordance with
 
 the theory of motion. If, as I believe, we are justified in re- 
 garding the revolving meteor-asteroids (aerolites) as portions 
 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 here 
 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 force 
 of homogeneous 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, 
 I 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 activity ; of more or less con- 
 tracted circles of waves of commotion (earthquake waves), 
 and their effects, 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, 
 in contrast with this formation, how sedimentary rocks are 
 in 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 which 
 they occur. The origin, ransformation, 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 
 fluids and solids, and the extension and articulation of con 
 
 Cotmos, vol. i. (Harper's edit.), p 33-65, 136.
 
 INTRODUCTION. 7 
 
 tinental masses in a horizontal and vertical direction. On 
 these relations depend the thermal conditions of oceanic cur- 
 rents, 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 different 
 races of men, and in different stages of civilization, sometimes 
 a joyous, sometimes a melancholy tone of mind ;* sometimes 
 a delicate appreciation of the beautiful, sometimes 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 organ- 
 
 * Cosmos, vol. i., p. 23-25 ; vol. ii., p. 25 and 97. 
 
 t Ibid., vol. ii., p. 38-43, and 56-60. 
 
 \ Ibid, vol. i., p. 357-359; 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-Songs, the 
 world-tree Yggdrasil, whose branches tower above the heav- 
 ens, while one of its triple roots penetrates to the " foaming 
 caldron springs" of the lower world. t Thus the cloud-re- 
 gion of physical myths is filled with pleasing or with fearful 
 forms, 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 
 world of thought and feeling. In this portion of my work 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 in 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 Nature, worthy of its exalted 
 title, can nerer be accomplished until the physical sciences, 
 notwithstanding their inherent imperfectibility, shall, by theii 
 
 * M. von Olfer's Ueberreste vorweltlicher Riesenthiere in Beziehung auj 
 Ostasiatische Sagen in the Abh. der Berl. ATead., 1832, s. 51. On the 
 opinion advanced by Empedocles regarding the cause of the extinction 
 of the earliest animal forms, see Hegel's Geschichte der Philosophic, 
 bd. ii., 8. 344. 
 
 t See, for the world-tree Yggdrasil, and the rushing (foaming) cal- 
 dron-spring Hvergelmir, the Deutsche Mylhologie of Jacob Grimm, 1844, 
 B. 530, 756; also Mallet's Northern Antiquities (Bohn's edition), 1847 
 p. 410, 489, aud 492, and frontispiece to ditto.
 
 INTRODUCTION. 9 
 
 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 the inner, reflected intellectual world. 
 
 I think I have here sufficiently 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 my Cosmos 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 have advanced, in the delineation of nature. But, 
 before entering upon the individual facts on which special 
 departments of science are based, I would fain offer 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 in 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 laws 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 
 eralization of particular facts, and a knowledge of the con- 
 
 * Cotmot. vol. i., p. 48-50, and 68-77.
 
 10 COSMOS. 
 
 ditions under which physical changes regularly and period- 
 ically manifest themselves ; and must conduct to the thought- 
 ful 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 was 
 indicated upward of a century before Lord Bacon's time, by 
 Leonardo da Vinci, in these lew words : " Cominciare dall' 
 esperienza e per mezzo di questa 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 causal connection. t 
 The most satisfactory and distinct evidence will always ap- 
 pear where the laws of phenomena admit of being referred 
 to mathematical 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. tit., vol. ii. p. 283. 
 
 t In the Introductory Observations, in 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 
 to Kepler, can not, I think, leave a doubt that I clearly distinguish be- 
 tween the discovery and interpretation 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, interpreted by Newton, 
 and proved to be theoretically and necessarily true, have been transferred 
 into the bright and glorious domaiu of thought, as the intellectual rec- 
 ognition 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 
 and Causes") the admirable remarks in Sir John Herschel's address at 
 the fifteenth meeting of the British Association at Cambridge, 1845, p. 
 rlii. ; and Edinb. Rev., vol. 87, 1848, p. 180-183.
 
 INTRODUCTION. 11 
 
 labor, of which the limits are here defined, arises from the 
 sublime 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 being. 
 
 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 human 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 causes! either to concrete material prin- 
 ciples, the so-called elements 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 differing 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 Clazomense 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 (vovg) controls the continuously pro- 
 gressing 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 subse- 
 quently lost wisdom," he refers with extraordinary freedom and sig- 
 nificance to the veneration of physical forces, and of gods in human 
 forms : " much," says he, " has been mythically added for the persua* 
 tion of the multitude, as also on account of the laws and for other useful 
 ends." 
 
 t The important difference in these philosophical directions rpdiroi, 
 is clearly indicated in Arist., Phys. Auscult., 1, 4, p. 187, Bekk. (Com- 
 pare Brandis, in the Rhein. Museum fur Philologie, Jahrg. iii., 8. 105.)
 
 12 COSMOS. 
 
 of all motion, and therefore of all physical phenomena. An- 
 axagoras explains the apparent movement of the heavenly 
 bodies from east to west by the assumption of a centrifugal 
 force,* on the intermission 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 which 
 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 thg world- arranging Intelligence of the 
 philosopher of Clazomenae 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 Pythagoreans, 
 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 (fj,ifj,7)aig) of them. The boundless capacity for rep- 
 etition, and the illimitability of numbers, is typical 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 different 
 stages of metamorphosis, to corporeal forms, and these, again, 
 to the simplest triangular plane figures. J 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 force. He there says, 
 " The heavenly bodies do not fall in consequence of the centrifugal force 
 being superior to the inherent falling force of bodies and to their down- 
 ward tendency." Hence Plutarch, in his work, De Fade in Orbe 
 Ltmte, 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 
 nepiXupT)ai.s of Anaxagoras, compare Schaubach, in Anaxag. Clazom. 
 Fragm., 1827, p. 107-109. 
 
 t Schaubach, Op. cit., p. 151-156, and 185-189. Plants are likewise 
 said to be animated by the intelligence i>ot5f ; Aristot., De Plant., i., p. 
 815, Bekk. 
 
 t Compare, on this portion of Plato's mathematical physics, B6ckh, 
 De Platonico Syst. Caelestium Globorum, 1810 et 1811; Martin, Eludei 
 tur le Timie, torn, ii., p. 234-242; and Brandis, in the Geschichte der 
 GricchiKh-Rdmuchsn Philosophic, th. ii., abth. i., 1844, $ 375.
 
 INTRODUCTION. 13 
 
 to ultimate principles (the elements, as it were, of the ele 
 ments), Plato exclaims, with modest diffidence 1 , " 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 theory, 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 history 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 Physical Lectures (Auscultationes Physicce) 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 all matter.^ Unity 
 in the different 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. 351, note. Compare also Gruppe, Ueber die 
 Fragmente des Archytas, 1840, s. 33. 
 
 t Aristot.,Poto., vii., 4, p. 1326, and Metapk., xii., 7, p. 1072, 10, Bekk., 
 and xii., 10, p. 1074-5. The pseudo-Aristotelian work, De Mundo, 
 which Osann ascribed to Chrysippus (see Cotmot, vol. ii., p. 28, 29), 
 also contains (cap. 6, p. 397) a very eloquent passage on the world-or- 
 derer and tcorld-sustainer. 
 
 t The proofs are collected in Ritter, History of Philotophy (Bohn, 
 1838-46), vol. iii., p. 180, et seq. 
 
 Compare Aristot., De Anima, ii., 7, p. 419. In this passage the 
 analogy with sound is most distinctly expressed, although in other por- 
 tions of his writings Aristotle 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 experiences 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 without 
 difficulty. Compare also Martin, Etudes sur le Timfe de Platun., torn 
 ii. p. 159-163.
 
 14 COSMOS. 
 
 a movement of the medium between the eye and the object 
 Been and not by emissions from the object or the eye. Hear- 
 ing is compared with sight, as sound is likewise 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 his book on the parts (organs) of animals, he clearly in- 
 timates his belief 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 difference between them."* In the 
 transition of formations, " the gradations are almost imper- 
 ceptible."! The unity of nature was to the Stagirite the great 
 problem of the Cosmos. " In this unity," 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 connection 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 . 
 
 * Aristot., De partibus Amm., 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 oar 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. 186.) 
 It is singular enough that the Stagirite should seek in another planet 
 those intermediate links of the chain of organized beings which we find 
 in the extinct animal and vegetable forms of an earlier world. 
 
 t Aristot., Metaph., lib. xiii., cap. 3, p. 1090, lin. 20, Bekker. 
 
 The uvrnrepiiraait of Aristotle plays an important part in all hit
 
 INTRODUCTION. 15 
 
 The so-calle"d 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 diffuseness and a somewhat Hellenic verbosity. As 
 Aristotle's inquiries were directed almost exclusively to mo- 
 tion, and seldom to differences in matter, we find the funda- 
 mental idea, 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, manifested in all parts of the 
 universe, defining and determining the nature of all forma- 
 tions, and holding together all things 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 worthy of notice, that in these 
 theories the Godhead is attended by a number of astral 
 spirits, who (as if acquainted with perturbations and the dis- 
 
 explanatious of meteorological processes ; so also in the works De Gen- 
 eralione et Interitu, lib. ii., cap. 3, p. 330 ; in the Meteorologicis, lib. i., 
 cap. 12, and lib. iii., cap. 3, p. 372, and in the Problems (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 principles. In the ancient polarity hypoth- 
 esis, /car* avrnrepiaTaaiv, similar conditions attract each other, and dis- 
 similar ones (-J- and ) repel each other in opposite directions. (Com 
 pare Ideler, Meteorol. veterum Grcsc. et Rom., 1832, p. 10.) The op- 
 posite conditions, instead of being destroyed by combining together, 
 rather increase the tension. The ipvxpov increases the -Qeppov ; as in- 
 versely "in the formation of hail, the surrounding heat makes the cold 
 body still colder as the cloud sinks into warmer strata of air." Aristotle 
 explains by his antiperistatic 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 Erman in the Abhandl. tier Berliner Akademie aufdasJahr 1825, 
 s. 128. 
 
 * " By the movement of the heavenly sphere, all that is unstable in 
 natural bodies, and all terrestrial phenomena are produced." Aristot., 
 Mtteor., i., 2, p. 339, and De Gener. et Corrupt., ii., 10, p. 336. 
 
 t Aristot., De Casio, lib. i., c. 9, p. 279 ; lib. ii., c. 3, p. 286 ; lib. ii., c 
 13, p. 292, Bekker. (Compare Biese, bd. i., s. 352-1, 357.) 
 
 t Aristot., Phys. Auscult., lib. ii., c. 8, p. 199; De Anima, lib. iii., o 
 12, p. 434 ; De Animal. General., lib. v., c. 1, p. 778, Bekker.
 
 16 COSMOS. 
 
 tribution of masses) maintain the planets in their eternal oib- 
 its.* The stars here reveal the image of the divinity in the 
 visible world. We 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- 
 scribes 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.f 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 Vincenzo de Beauvais, the Physical Geography (Liber Cos- 
 mographictis) of Albertus Magnus, the Picture of the World 
 (Imago Mundi) of Cardinal Petrus d'Alliaco (Pierre d'Ailly), 
 are works which, however powerfully they may have influ- 
 enced the age in which they were written, 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 Casio, lib. ii., cap. 12, p. 292.) 
 They are the most divine of created things ; TO. -Qeiorepa TUV <j>avepuv. 
 (Aristot., De Casio, lib. i., cap. 9, p. 278, and lib. ii., cap. 1, p. 284.) 
 
 ip. 6, p. 400), me nigh anner is also called divine (cap. 
 That which the imaginative Kepler calls moving spirits (anima motruai) 
 in his work, Mysterium Cotmographicum (cap. 20, p. 71), is the distort- 
 ed idea of a force (virtus') whose main seat is in the sun (anima mun- 
 di), and which is decreased by distance in accordance with the laws of 
 light, and impels the planets in elliptic orbita. (Compare Apelt, Epoch 
 en der Gesch. der Mcnechheit, bd. i., e. 274.) 
 * Cotmot, vol. ii., p. 241-250.
 
 INTRODUCTION. 17 
 
 plants and animals are the effect of these two ever-divided 
 forces, of which the one, heat, specially appertains to the ce- 
 lestial, and the other, cold, to the terrestrial sphere. 
 
 "With yet more unbridled fancy, but with a profound spirit 
 of inquiry, Giordano Bruno of Nola attempted to comprehend 
 the whole universe, in three works,* entitled De la causa 
 Principio e Uno; Contcmplationi circa lo Infinite, Uni- 
 verso e Atondi innumerabili ; and De Minima 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- 
 mical views of the Philosopher of Nola 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 
 martyrdomf 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 nebulse. "With bold confidence in what 
 he terms the lume interno, ragione naturale, altezza dell' 
 intclletto (force of intellect), he indulged in 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, 1600, pursuant 
 to the sentence " ut qnam clementissime et citra sanguinis effusionem 
 puniretur." Bruno was imprisoned six years in the Piombi 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 in 
 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 Duko 
 Henry Julius of Brunswick- Wolfenbuttel. Bartholmess, torn . i , p. 167- 
 178. He also taught at Padua subsequently to 1592.
 
 18 COSMOS. 
 
 ary nature of comets, and the deviation from the spherical 
 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 
 which the main forms and epochs have been already enu- 
 merated, Kepler approached the nearest to a mathematical 
 application of the theory of gravitation, more than seventy- 
 eight years before the appearance of Newton's immortal 
 work, Principia Philosophies Naturalis. 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 MartisJ 
 was the first who gave numerical calculations of the forces 
 of attraction reciprocally exercised upon each other, accord- 
 ing to their relative masses, by the earth and moon. He 
 
 * Bartholmess, torn, ii., p. 219, 232, 370. Bruno carefully collected 
 all the 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 Campanella, and the platonic cardinal, Nicolaus Krebs 
 of Cusa. See Cosmos, vol. ii., p. 310, 311, note. 
 
 t " Si duo lapides in aliquo loco Mundi collocarentur propinqui in- 
 vicem, extra orbem virtutis tertii cognati 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 animali (!) aut alia 
 aliqua aequipollente, quselibet in suo circuitu, Terra adscenderet ad Lu- 
 nam quinquagesima quarta parte intervalli, Luna descenderet ad Ter- 
 rarn quinquaginta tribus circiter partibus intervalli; ibi jungerentur, 
 posito tamen quod substantia utriusque sit unius et ejusdem densitatis." 
 Kepler, A&tronomia nova, seu Physica ccclestis de Motibus Stella Mar- 
 tis, 1609. Introd., fol. v. On the older views regarding gravitation, 
 see Cosmos, vrl. ii., p. 310.
 
 INTRODUCTION. 19 
 
 distinctly adduces the tides as evidence* that the attractiv& 
 force 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 if the forme] 
 should cease to attract it. Unfortunately, this great man 
 was induced, ten years afterward, in 1619, probably 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 Mundt 
 as a li ving 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. When we 
 remember the mathematical acumen that pervades one of the 
 works of Kepler, and of which Laplace has already made 
 honorable mention,t it is to be lamented that the discoverer 
 of the three great laws of all planetary motion 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 attrahere ad se aquas suas, aquae marinse omnes 
 elevarentur et in corpus Luna? iufluerent. Orbis virtutis tractoriae, qua? 
 est in Luna, porrigitur usque ad terras, et prolectat aquas quacunque 
 in verticem loci incidit sub Zonam torridam, quippe in occursum suum 
 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 
 ut ferrum a Magnete." .... Kepleri Harmonice Mundi, libri quinque, 
 1619, lib. iv., cap. 7, p. 162. The same work which presents us with 
 so many admirable views, among others, with the data of the establish- 
 ment of the third law (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 the 
 earth-animal, on the soul, memory (memoria animce Terra), and crea- 
 tive imagination (anima Tdluris imaginatio) of this monster. This great 
 man 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 Macrocosmcs, Robert Fludd, of Oxford, who is report- 
 ed to have participated in the invention of the thermometer. (Harm. 
 Mitndi, 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 solis." Stella Mar 
 tit, pars iii., cap. 32, 34. To each planet was ascribed a magnetic axis, 
 which constantly pointed to one and the same quarter of the heavens. 
 CApelt, Joh. Kepler's Astron. Weltansicht, 1849, 8. 73. 
 
 t Compare Cosmos, vol. ii., p. 327 (and iiole
 
 20 COSMOS. 
 
 enly sphere and all that he knew concerning the animate 
 and inanimate parts of terrestrial nature, in a work entitled 
 Traite du Monde, and also Summa Philosophies. 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 Mersenne, we frequently find him complaining of hia 
 slow progress, and of the difficulty of arranging so large a 
 mass of materials. The Cosmos 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 
 Deventer, and a pious desire not to treat irreverentially the 
 decrees pronounced by the Holy Chair against the planetary 
 movement of the earth. t In 1664, fourteen years after the 
 death of the philosopher, some fragments were first printed 
 under the singular title of Le Monde, ou Traite de la Lu- 
 miere."i. 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 Philosophic. 
 
 Notwithstanding its ambitious title, the Cosmotheoros of 
 Huygens, which did not appear till after his death, scarcely 
 deserves to be noticed in this enumeration of cosmological 
 efforts. It consists of the dreams and fancies of a great man 
 on the animal and vegetable worlds, of the most remote cos- 
 mical bodies, and especially of the modifications of form which 
 
 See La Vie de M. Descartes (par Baillet), 1691, Part i., p. 197, 
 End CEuvret de Descartes, publiees par Victor Cousin, torn, i., 1824, 
 p. 101. 
 
 t Lsttres de Descartes au P. Mersenne, du, 19 Nov., 1633, et du 5 Jan- 
 vier, 1634. (Baillet, Part i., p. 244-247.) 
 
 \ The Latin translation bears the title Mundus give Dissertalio de 
 Lwmine itt et de aliis Sensuum Objectis primariis. See Descartes, Optu~ 
 cula posthuma Physka et Mathematica, Amst., 1704.
 
 INTRODUCTION. 21 
 
 the human race may there present. The reader might sup- 
 pose he were perusing Kepler's Somnium Astronomicum, or 
 Kircher's Iter Extaticus. As Huygens, like 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 inhabitants in the moon than of those in the remoter 
 planets, which he assumes to be " surrounded with vapors 
 and clouds." 
 
 The immortal author of the Philosophic Naturalis Prin- 
 cipia Mathematica (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 which 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 simplicity 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 aqnis carere et afire : Marium similitudinem in Luna nul- 
 lam reperio. Nam regiones planas quae montosis multo obscuriores 
 eunt, quasque vulgo pro maribus haberi video et oceanorum nominibus 
 insigniri, in his ipsis, longiore telescopic inspectis, cavitates exiguas in- 
 esse comperio rotundas, umbris intus cadentibus; quod maris superfi- 
 ciei convenire nequit; turn ipsi campi illi latiores non prorsus eequabi- 
 lem superficiem praDferunt, cum diligentius eas intuemur. Quod circa 
 maria esse non possunt, sed materia constare debent minus candicante, 
 quam qute est partibus asperioribus in quibus rursus quanlam viridiori 
 lumine caeteras prsecellunt." Hugenii Cosmotheorog, 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 Jovialium 
 mutabili facie cognoscitur" (lib. i., p. 69). These dreams of Huygens 
 regarding the inhabitants of remote planets, so unworthy of a man versed 
 iu exact mathematics, have, unfortunately, been revived by Emauuel 
 Kant, in his cdmirable work Allgemeine Naturgeschichte und Theorie 
 dtt Himmelt, 1755 (s. 173-192). 
 
 t See Laplace (des Oscillations de t 'Atmotphlre, du flux Solaire et 
 Lunaire} iu the Micanique Celeste, livre iv., and in the Exposition d* 
 Syst. du Monde, 1824, p. 291-296.
 
 22 COSMOS. 
 
 tro-magnetic, and organic processes. Newton* even distin- 
 guished the attraction of masses , as manifested in the mo- 
 tion of cosmical bodies and in the phenomena of the tides, 
 from molecular 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- 
 al results. It is indeed true, that notwithstanding the brill- 
 iant progress that has been made in recent times in strechi- 
 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 have been rendered more accessible to mathematical 
 investigation ; but, owing to the unbounded heterogeneous- 
 ness of matter 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 spiritu quodam subtilissimo corpora crassa 
 pervadente et in iisdem latente, cujus vi et actiouibus particulaj corpo- 
 rum ad minimas distantias se mutuo attrahunt et contiguae facta cohac- 
 rent. Newton, Principia Phil. Nat. (ed. Le Sueur et Jacquier, 1760), 
 Schol. gen., t. iii., p. 676; compare also Newton's Optics (ed. 1718), 
 Query 31, p. 305, 353, 367, 372. (Laplace, Syst. du Monde, p. 384, and 
 Cosmos, vol. i., p. 63 (note).) 
 
 t Hactenus phaenomena coelorum et maris nostri per vim gravitatis 
 exposui, sed causam gravitatis nondum assignavi. Oritur utique haec 
 vis a causa aliqua, qua: penetrat ad usque centra solis et planetarum, 
 sine virtutis dimiuutione ; quaeque agit non pro quantitate superficierum 
 particularum, in quas agit (ut solent causae mechanics), sed pro quanti- 
 tate materiae solidao. Rationem harum gravitatis proprietatum ex phae- 
 nomenis nondum potui deducere et hypotheses non fingo. Satis est 
 quod gravitas revera existat et agat secundum leges a nobis expositas. 
 Newton, Principia Phil. Nat., p. 676. " To tell us that every spe- 
 cies of things is endowed witlr. an occult specific quality, by which it 
 acts and produces manifest effects, is to tell us nothing ; but to derive
 
 INTRODUCTION. 23 
 
 result of some 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 relinquished this hypothesis of the rarer 
 and denser sether.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 ;"J while 
 
 two or three general principles of motion from phenomena, and after- 
 ward to tell us how the properties 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 that word 
 lio <; to signify only in general any force by which bodies tend toward 
 on^ another, whatsoever be the cause." 
 
 * " I suppose the rarer sether within bodies, and the denser without 
 them." Operum Newtoni, tomus iv. (ed. 1782, Sam. Horsley), p. 386. 
 The above observation was made in reference to the explanation of the 
 discovery made by Grimaldi of the diffraction or inflection of light. At 
 the close of Newton's letter to Robert Boyle, February, 1678, p. 94, he 
 says : " 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 " aether hypotheses." According to these views, 
 the impulse of material light causes the aether to vibrate ; but the vibra- 
 tions of the sether alone, which fias some affinity 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 Newton, p. 303-305. 
 
 t Newton's words " not to take gravity for an essential property of 
 bodies" in the " Second Advertisement" contrast with his remarks on 
 the forces of attraction and repulsion, 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 "without their actual contact." (Newton, Optict, 
 book ii., prop. 8, p. 241, and Brewster, Op. cit., p. 301.) According 
 to Kant (see Die Metaphysischen Anfangsgrunde der Naturwissenschaft, 
 1800, s. 28), we can not conceive the existence of matter without these 
 forces of attraction and repulsion. All physical phenomena are there-
 
 24 COSMOS. 
 
 Gilbert, as early as 1600, regarded magnetism as a force in- 
 herent in all matter. So undetermined was even Newton, 
 the profound and experienced thinker, regarding the " ulti- 
 mate mechanical cause" of all motion. 
 
 It is indeed a brilliant effort, worthy of the human mind, 
 to comprise, in one organic whole, 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. What 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 
 rapidity of advance, we shall be better able to imagine the 
 periodical and endless changes which all physical sciences 
 are destined to undergo. New 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 
 of their axes, the eccentricity of their orbits, and the num- 
 
 fore reduced by him, as previously by Goodwin Knight (Pkilos. Trant- 
 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 
 taloric as a constantly expanded matter, assumes the existence of two 
 elementary substances, as in the mythical idea of two kinds of tether. 
 (Newton, Optics, query 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 entire 
 body) lead, according to atomic hypotheses, to the result, that the dis- 
 tance between elementary corpuscles is i'ar greater than, their diameterg.
 
 INTRODUCTION. 25 
 
 her and distance 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 merely 
 by way of illustration, can at present be regarded only as 
 something existing in nature, as a fact, but which I can net 
 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 the 
 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 history 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 phenomena 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. "f 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 world, 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. cit., p. 55-62. 
 
 t Wilhelra von Humboldt, Gesammdte Werke, bd. i., s. 23. 
 
 VOL. III. B
 
 RESULTS OF OBSERVATIONS IN THE URANOLOGICAL POR- 
 TION OF THE PHYSICAL DESCRIPTION OF THE WORLD. 
 
 WE again commence with, the depths of cosmical space, 
 and the remote sporadic starry systems, which appear to tel- 
 escopic vision as faintly shining nebulce. 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,* that this arrangement of ideas is 
 alone suited to the character of a work on the Cosmos, since 
 we 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 uranological, when opposed to the telluric domain 
 of the Cosmos, may be conveniently separated into two di- 
 visions, one of which comprises astro^nosy, or the region of 
 the fixed stars, and the other our solar and planetary sys- 
 tem. 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 meanings 
 hitherto 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 
 
 t Halley, in the Philos. Transact, for 1717, vol. xxx., p. 736.
 
 A8TROGNOSY. 27 
 
 Arcturus, 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- 
 served, changed its position in relation to the neighboring 
 fainter stars 2 times the moon's diameter. Encke remarks 
 " that the star \i Cassiopeise appears to have moved 31 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 believing that there is 
 every where progressive, and perhaps also rotatory motion. 
 The term " fixed stars" 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 fixity 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 Alcmseon the Pythagorean, 
 all stars were divided into wandering (darpa TrAavcjjueva or 
 TrAavT/rd) and non-wandering fixed stars (drr^avelg aarepeg 
 or dTrXavfj darpa).* Besides this generally adopted desig- 
 nation of the fixed stars, which Macrobius, in his Somnium 
 Scipionis, Latinized by Sphcera aplanesj we frequently 
 meet in Aristotle (as if he wished to introduce a new tech- 
 nical term) with the phrase riveted stars, Ivdedeneva darpa, 
 instead of a^Xavr],% as a designation for fixed stars. From 
 this form of speech arose the expressions of sidera infixa 
 cado of Cicero, Stellas quas ^nctamus affixas of Pliny, and as- 
 
 9 Pseudo-Plut., De plac. Philos., ii., 15, 16 ; Stob., Eclog. Phys., p. 
 582 ; Plato, in the Timeeus, p. 40. 
 
 t Macrob., Sown. Scip., i., 9-10 ; slellce inerrantes, in Cicero, De Nat. 
 Deorum, iii., 20. 
 
 t The principal passage in which we meet with the technical expres- 
 sion hdedspeva uarpa, is in Aristot., De Caelo, ii., 8, p. 289, 1. 34, p. 290, 
 1. 19, Bekker. This altered nomenclature forcibly attracted my atten- 
 tion in my investigations into the optics of Ptolemy, and his experi- 
 ments on refraction. Professor Franz, to whose philological acquire- 
 ments I am indebted for frequent aid, reminds me that Ptolemy (Syn- 
 tax, vii., 1) speaks of the fixed stars as affixed or riveted; uanep Trpo- 
 OTreQvKOTee. Ptolemy thus objects to the expression a<j>aipa air'Xavfjc 
 (orltig inerrans) ; " in as far as the stars constantly preserve their rela 
 live distances, they might rightly be termed airhavtiq ; but in as far an 
 the sphere in which they complete their course, and in which they seem 
 to have grown, as it were, has an independent motion, the designation 
 O7r/laf!?f is inappropriate if applied to the sphere."
 
 tra fixa of Manilius, which corresponds with our term fixed 
 stars.* This idea of fixity leads to the secondary idea of 
 immobility, of persistence in one spot, and thus the original 
 signification of the expressions infixum or affixum sidus was 
 gradually lost sight of in the Latin translations of the Mid- 
 dle Ages, and the idea of immobility alone retained. This 
 is already apparent in a highly rhetorical passage of Seneca, 
 regarding the possibility of discovering new planets, in which 
 he says (Nat. Queest., vii., 24), " Credis autem in hoc max- 
 imo et pulcherrimo corpore inter innumerabiles Stellas, quae 
 noctem decore vario distinguunt, quse ae'ra minime vacuum 
 et inertem esse patiuntur, quinque solas esse, quibus exer- 
 cere se liceat ; ceteras stare fixum et immobilempopulum?" 
 "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 suffering 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 description of the universe, I will sep- 
 arate the astrognostic sphere into the following sections : 
 
 I. The considerations on the realms of space and 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 nebulae. 
 
 IV. The newly-appeared and periodically-changing stars, 
 and those that have disappeared. 
 
 V. The proper motion of the fixed stars ; the problematical 
 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 nebulas which are interspersed in the Magellanic 
 clouds with numerous stellar masses, the black spots (coal 
 bags) in the vault of heaven. 
 
 * Cicero, De Nat Deorutn, i., 13 ; Plin., ii., 6 and 24 ; Manillas, ii., 35
 
 THE REALMS OF SPACE, AND CONJECTURES REGARDING THAT WHICH 
 APPEARS TO OCCUPY THE SPACE INTERVENING BETWEEN THE 
 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 cosmic al 
 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 own fullness, and to give outline and permanence to 
 these indefinite changing forms.* This observation will, I 
 trust, suffice 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 delights 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 
 Encke, Ueber die Anordnung des Sternsystems, 1844, s. 7.) 
 t Cotmot, vol. i., p. 154, 155.
 
 30 COSMOS. 
 
 by Aristotle* follows the idea of its immeasurability. 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 61 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, while it passes 
 from the Sun 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 manifested in the smallest organisms of animal life as in 
 the milky way of those self-luminous suns which we call 
 fixed stars. What masses of Polythalami 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 the 
 microscopic Galionella distans ; while the same volume con- 
 tains more than 1 billion 750,000 millions of distinct indi- 
 viduals of Galionella ferruginea.k Such estimates remind 
 us of the treatise named Arenarius (tpafifiirrj^) of Archime- 
 des of the sand-grains which might fill the universe of 
 space ! If the starry heavens, by incalculable numbers, 
 magnitude, space, duration, and length of periods, impress 
 
 * Aristot., De Casio, 1, 7, p. 276, Bekker. 
 
 t Sir John Herschel, Outlines of Astronomy, 1849, 803, p. 541. 
 j Bessel, in Schumacher's Jahrluchfur 1839, s. 50. 
 $ Ehrenberg, Abhandl. der Berl. Akad., 1838, s. 59 ; also in his Info 
 rionsthiere, B. 170.
 
 THE PROPAGATION OP LIGHT. 31 
 
 man with the conviction of his own insignificance, his phys- 
 ical weakness, and the ephemeral nature of his existence ; 
 he is, on the other hand, cheered and invigorated by the 
 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 
 evaporation of many of the large tails of comets, seem to 
 prove that the regions of space which separate cosmical bod- 
 ies are not 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 " the air of Jieav- 
 en" " cosmical (non-luminous) matter" and " ether" the 
 latter, which has been transmitted to us from the earliest an- 
 tiquity of Southern and Western Asia, has not always ex- 
 pressed the same idea. Among the natural philosophers of 
 India, ether (aka'sa) was regarded as belonging to the pant- 
 scJiata, 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 well as of propagating 
 sound.f Etymologically 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 shining does to burning." 
 
 In the dogmas of the Ionic philosophy of Anaxagoras and 
 Empedocles, this ether (alOr^p) differed wholly from the act- 
 ual (denser) vapor-charged air (drjp) which surrounds the 
 
 * Aristotle (Phys. Auseu.lt., iv., 6-10, p. 213-217, Bekker) proves, in 
 opposition to Leucippus and Democritus, that there is no unfilled space 
 no vacuum in the universe. 
 
 t Akd'sa signifies, according to Wilson's Sanscrit Dictionary, " the 
 subtle and ethereal fluid supposed to fill and pervade the universe, and 
 to be the peculiar vehicle of life and sound." " The word dlcd'sa (lu- 
 minous, shining) is derived from the root ka's (to shine), to which is 
 added the preposition d. The quintuple of all the elements is called 
 pantsckatd, or pantschatra, and the dead are, singularly enough, desig- 
 nated 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 Sankhya Philosophy treats of these five elements ; see 
 Transact, of the Asiat. Soc., vol. i., Loud., 1827, p. 31. Strabo refers, 
 according to Megasthenes (xv., $ 59, p. 713, Gas.), to the all-forming 
 fifth element of the Indians, without, however, naming it.
 
 32 COSMOS. 
 
 earth, and " probably extends as far as the moon." It was 
 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 aWeiv, to burn, 
 for which Plato and Aristotle, from a predilection for me- 
 chanical views, singularly enough substituted another (del- 
 6elv), on account of the constancy of the revolving and rota- 
 tory movement.! 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 upper, earth vxAfire. These extremes 
 
 * Empedocles, v. 216, calls the ether irapfavouv, brightly-beaming, 
 and therefore self-luminous. 
 
 t Plato, Cratyl., 410 B., where we meet with the expression aetdsrip. 
 Aristot., De Casio, 1, 3, p. 270, Bekk., says, in opposition to Anaxagoras: 
 aidtpa rrpoffuvofiaaav TOV UVUTUTU TOTTOV, U.TTO TOT delv act rbv aldiov 
 Xpovov -QfUfvoi. TTJV snuwpiav avru. 'Avagayopaf t)e KaraKixpilfai ru 
 ov6/j.aTi TovTCf) ov KO^uf bvoftd&t yap aWepa avrl irvpoc.. We find this 
 more circumstantially referred to in Aristot., 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 nature, 
 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 this 
 word, implying rapid revolution, is referred to by the Aristotelian, or 
 Stoic, author of the work De Mundo, cap. 2, p. 392, Bekk.) Professor 
 Franz has correctly remarked, "That the play of words in the designa- 
 tion of bodies in eternal motion (aufta uei dtov') and of the divine (tfftov) 
 alluded to in the Meteoroloeica, is strikingly characteristic of the Greek 
 type of imagination, and affords additional evidence of the inaptitude of 
 the ancients for etymological inquiry." Professor Buschmann calls at- 
 tention to a Sanscrit term, dschtra, ether or the atmosphere, which looks 
 very like the Greek aidr/p, with which it has been compared by Vans 
 Kennedy, in his Researches into the Origin and Affinity of the principal 
 Languages of Asia and Europe, 1828, p. 279. This word may also be 
 ich 
 
 referred to the root (as, asch), to which the Indians attach the signifi 
 cation of shining or beaming.
 
 COSMICAL ETHER. 33 
 
 are separated by two intermediate elementary conditions, of 
 which the one, water, approximates most nearly to the heavy 
 earth, and the other, air, to the lighter element of fire.* 
 
 Considered as a medium filling the regions of space, the 
 ether of 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 in explaining, on purely mathematical principles, the 
 propagation of light, with all its properties of double refrac- 
 tion, polarization, and interference. The natural philosophy 
 of Aristotle further teaches that the ethereal substance pen- 
 etrates all the living organisms of the earth both plants 
 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 Huygens, 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 (-rrafi^avouv), and is said to be 
 seen by the inhabitants of the earth in certain phenomena, 
 gleaming brightly through fissures and chasms (^da/zara) 
 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 Ccelo, iv., 1, and 3-4, p. 308, and 311-312, Bekk. If 
 the Stagirite withholds from ether the character of a fifth element, 
 which indeed is denied by Ritter (Geschichte der Philosophic, th. iii., s. 
 259), and by Martin (Etudes sur le Timte de Platan., t. ii., p. 150), it ia 
 only because, according to him, ether, as a condition of matter, has no 
 contrary. (Compare Biese, Philosophic des Aristoteles, bd. xi., s. 66.) 
 Among the Pythagoreans, ether, as a fifth element, was represented by 
 the fifth of the regular bodies, the dodecahedron, composed of twelve 
 pentagons. (Martin, t. ii., p. 245-250.) 
 
 t See the proofs collected by Biese, op. cit., bd. xi., s. 93. 
 
 t Cosmos, vol. i., p. 153. 
 
 B2
 
 34 COSMOS. 
 
 have their origin in analogous kinds of motion (currents). It 
 is reserved for future ages to make great discoveries in ref- 
 erence to these subjects. Light, and radiating heat, which 
 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. t 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 polar force, 
 
 Compare the fine passage on me influence of the sun's rays in Sir 
 n Herschel's Outlines of Astronomy, p. 237 : " By the vivifying ac- 
 tion of the sun's rays, vegetables are enabled to draw support from in- 
 
 organic matter, and become, in their turn, the support of animals and 
 of man, and the sources of those great deposits of dynamical efficiency 
 which are laid up for human use in our coo 1 , strata. By them the wa- 
 ters of the sea are made to circulate in v*pT through the air, and irri- 
 gate the land, producing springs and rivers. By them are produced 
 all disturbances of the chemical equilibrium of the elements of nature, 
 which, by a series of compositions and decompositions, give rise to new 
 products, and originate a transfer of materials." 
 
 t Philos. Transact, for 1795, vol. Ixxxv., p. 318 ; John Herschel, Out- 
 lines of Astr., p. 238; see also Cosmos, vol. i., p. 189. 
 
 t See Bessel, in Schumacher's Astr. Nachr., bd. xiii., 1836, 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- 
 pulsive force proceeding from the body of the sun."* The 
 splendid comet of 1744, which was described by Heinsius, 
 led my deceased friend to similar conjectures. 
 
 T/te 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, t 
 Frequent mention is made in antiquity by the Greek and 
 RomanJ writers of this stellar heat ; not only because, from 
 a universally prevalent assumption, the stars appertained to 
 the region of the fiery ether, but because they were supposed 
 to be themselves of a fiery nature the fixed stars and the 
 sun being, according to the doctrine of Aristarchus of Samos, 
 of one and the same nature. In recent times, the observa- 
 tions of the above-mentioned 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 espaces planetaires 
 ou celestes) is rather 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 (pole glacial), or the point of the greatest cold, no more 
 
 * Bessel, op. cif., 8. 186-192, 229. 
 
 t Fourier, Thforie Analytique de la Chaleur, 1822, p. ix. (Annalet 
 de Chimie et 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 Thlorie 
 Mathematiqve de la Chaleur ( 196, p. 436, $ 200, p. 447, and $ 228, p. 
 521), attempts to give the numerical estimates of the stellar heat (cha- 
 leur stellaire) lost by absorption in the ether of the regions of space. 
 
 t 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 which 
 heat is at the minimum, consult Seneca, in Nat. Qu&st., ii., 10: ''So- 
 periora enim afiris calorem vicinoruin siderum sentiurt." 
 
 $ Plut., Deplac. Philos., ii., 13.
 
 corresponds with the terrestrial pole than does the thermal 
 equator, which connects together the hottest points of al] 
 meridians with the geographical equator. Arago concludes, 
 from the gradual decrease of mean temperatures, that the 
 degree of cold at the northern terrestrial pole is 13, if the 
 maximum cold ohserved by Captain Back at Fort Reliance 
 (62 46' lat.) in January, 1834, were actually 70 ( 56-6 
 Cent., or 45 0> 3 Reaum.).* The lowest temperjtlure 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 were 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 with 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- 
 radiating stars, and that the earth, during its motion with the 
 
 * Arago, Sur la Temperature du P6le et des espaces Celestes, in the 
 Annuaire du Bureau des Long, pour 1825, p. 189, et pour 1834, p. 192; 
 also Saigey, Physique du Globe, 1832, p. 60-76. Swanberg 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 during the aeronautic ascent of Gay-Lussac, 107-2. Sir John 
 Herschel (Edinburgh Review, vol. 87, 1848, p. 223) gives it at 132. 
 We feel considerable surprise, 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 warmer than the 
 outer limits of the atmosphere (see the work already referred to, $ 227, 
 p. 520) ; while Pouillet states it, from actinometric experiments, to be 
 as low as 223-6. See Comptet Rendus de I' Academic det Science!, 
 torn, vii., 1838, p. 25-65.
 
 TEMPERATURE OF SPACE. 37 
 
 whole solar system, receives its internal 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 suffered important variations in the course of ages, de 
 pends mainly on the solution of a problem warmly discussed 
 by Sir William Herschel : whether the nebulous masses are 
 subjected to progressive processes of formation, while the cos- 
 mic al vapor is being condensed around one or more nuclei in 
 accordance with the laws of attraction ? By such a con- 
 densation of cosmical vapor, heat must be liberated, as in 
 every transition of gases and fluids into a state of solidifica- 
 tion. t If, in accordance with the most recent views, and 
 the important observations of Lord Rosse and Mr. Bond, we 
 may assume that all nebulae, including those which the high- 
 est power of optical instruments has hitherto failed in resolv- 
 ing, are closely crowded stellar swarms, our faith in this per- 
 petually augmenting liberation of heat must necessarily be 
 in some degree weakened. But even small consolidated cos- 
 mical bodies which 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 solidified from a state of vapor^ and 
 that their internal heat owes its origin to the formative 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 beneficial 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 the counter-radiation. How enormous would 
 be this loss of heat.J if the regions of space, instead of the 
 
 * See Poisson, Tklorie Maih6m. de la Chaleur, p. 438. According 
 to him, the consolidation of the earth's strata began from the center, ana 
 advanced gradually toward the surface ; $ 193, p. 429. Compare also 
 Cosmos, vol. i., p. 176, 177. t Cosmos, vol. i., p. 83, 84, 144. 
 
 t " Were there no atmosphere, a thermometer freely exposed (at sun-
 
 38 COSMOS. 
 
 temperature they now possess, and which we designate as 
 76 of a mercury thermometer, had a temperature of about 
 1400 or even many thousand times lower ! 
 
 It still remains for us to consider two hypotheses in rela- 
 tion to the existence of a fluid filling the regions of space, 
 of which one the less firmly-based hypothesis -refers to the 
 limited transparency of the celestial regions ; and the other, 
 founded on direct observation and yielding numerical results, 
 is deduced from the regularly shortened periods of revolution 
 of Encke's comet. Olbers in Bremen, and, as Struve has ob- 
 served, Loys 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., a sun, the entire vault of heaven must ap- 
 pear as luminous as our sun if light were 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 Halleyf 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 Sir William Herschel from gauging the 
 
 p 
 
 set) to the heating influence of the earth's radiation, and the cooling 
 power of its own into space, would 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, 3* Fahr., in the Polar Sea. 
 Under the 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- 
 ondly, 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 6prouverait un refroidis- 
 sement, dont on ne peut fixer la limite. Probablement la vie des plantes 
 et des animaux serait impossible a la surface du globe, ou releguee dans 
 une etroite zone de cette surface." (Saigey, Physique du Globe, p. 77.) 
 
 * Traiti de la Comete de 1743, avec une Addition sur la force de la 
 Lumiere et sa Propagation dans l'6ther, ct sur la distance des etoiles fixes; 
 par Loys de Cheseaux (1744). On the transparency of the regions of 
 space, see Olbers, in Bode's Jahrbuckfur 1826, s. 110-121 ; and Struve, 
 Etudes d'Astr. Slellaire, 1847, p. 83-93, and note 95. Compare also 
 Sir John Herschel, Outlines of Astronomy, $ 798, and Cosmos, vol. i., p. 
 151, 152. 
 
 t Halley, On the Infinity of the Sphere of Fixed Stars, in the Philos. 
 Transact., vol. xxxi., for tfie year 1720, p. 22-26.
 
 RESISTING MEDIUM. 39 
 
 stars,* and from his ingenious experiments 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 T 7 tb 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 Struve, one 
 of the most important is that his twenty -feet telescope shows, 
 throughout the greater portion of the Milky Way in both hem- 
 ispheres, the smallest stars projected on a black ground. t 
 
 A better proof, and one based, as we have already stated, 
 upon direct observation of the existence of a resisting fluid,} 
 is afforded by Encke's comet, and by the ingenious and im- 
 portant conclusion to which my friend was led in his observ- 
 ations on this body. This resisting medium must, however, 
 be regarded as different from the all-penetrating light-ether, 
 because the former is only capable of offering 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 afforded 
 by the hypothesis of a resisting fluid. The greatest action 
 
 * Cosmos, vol. i., p. 86, 87. 
 
 t "Throughout by far the larger portiou of the extent of the Milky 
 Way in both hemispheres, the general blackness of the ground of the 
 heavens, on which its stars are projected .... In those regions where 
 the zone is clearly resolved into stars, well separated, and seen projected 
 on a black ground, and where we look out beyond them into space. . . ." 
 Sir John Herschel, Outlines of Astr., p. 537, 539. 
 
 t Cosmos, vol. i., p. 85, 86, 107 ; compare also Laplace, Essai Philos- 
 ophique sur les Probability's, 1825, p. 133 ; Arago, in the Annuaire du 
 Bureau des Long, pour 1832, p. 188, pour 1836, p. 216; and Sir John 
 Herschel, Outlines of Astr., $ 577. 
 
 The oscillatory movement of the emanations from the head of some 
 comets, as in that 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 the ordinary attracting force of the sun ;" 
 but the regular acceleration observable for sixty-three years in Encke's 
 comet (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. 6, and 
 No. 310, s. 345-350, with Encke's Treatise on the hypothesis of the re- 
 sisting medium, in Schum., No. 305, s. 265-274
 
 40 COSMOS. 
 
 is manifested during the twenty-five days immediately pre- 
 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. 01- 
 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 diffi- 
 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 limit of the dens- 
 ity to be assumed for cosmical 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 WolJaston, 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 
 
 * Gibers, in Schum., Astr. NacJir., No. 268, a. 58. 
 
 t Outlines of Astronomy, $ 556, 597. 
 
 t "En assimilant la mature ires rare qui remplit les espaces celestes 
 quant a ses proprietes refringentes aux gas terrestres, la densite de cette 
 matiere nt saurait depasser itne certaine limite dont les observations des 
 eloilcs chcngeantes, p. e. celles d 1 Algol oudc/3 de Persic, peuvent assigner 
 la valeur." Arago, in the Annuaire pour 1842, p. 336-345. " On com 
 paring the extremely rare matter occupying the regions of 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 Persei." 
 
 See Wollaston, Philos. Transact, for 1822, p. 89,' Sir John Herschel, 
 op. eit., $ 34, 36.
 
 FIRST TELESCOPE, 41 
 
 the limits of an atmosphere of mercury (that is, the elevation 
 at which mercurial vapors precipitated on gold leaf cease 
 perceptibly to rise in an air-filled 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 November phenomena,! when, as in 1799, 
 1833, and 1834, myriads of falling stars traversed the vault 
 of heaven, and northern lights 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 the investigation of the configuration, 
 physical 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 nebulae in 
 Andromeda. J In 1634, 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 Arcfurus by day.$ 
 
 * Newton, Princ. Mathem., t. iii. (1760), p. 671: "Vapores qui ex 
 sole et stellis fixis et caudis cometarum oriuiitur, incidere posswit in at- 
 mosphaeras planetarum " t Cosmos, vol. i., p. 124-135. 
 
 t See Cosmos, vol. ii., p. 317-335, with notes. 
 
 $ Delambre, Histoire de C Astronomic Moderne, torn, ii., p. 255, 269
 
 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 which it aimed, if optical and 
 astronomical instruments had not been brought into accord, 
 and the correctness of vision made to correspond with that 
 of measurement. The micrometer-application of fine threads 
 stretched in the focus of the telescope, to which 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 course of the stars were observed by the eye alone, 
 unaided by instruments. When we consider the numerous 
 disturbances which, during this prolonged period, checked the 
 advance of civilization, and the extension of the sphere of 
 ideas among the nations inhabiting the basin of the Medi- 
 terranean, we are astonished that Hipparchus and Ptolemy 
 should have been so well acquainted with the precession of 
 the equinoxes, the complicated movements 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 system of the universe ; and that Tycho Brahe 
 should have been so familiar with the methods of practical 
 astronomy before the discovery of the telescope. Long tubes, 
 
 272. Morin, in his work, Seientia Longitudinum, which appeared in 
 1634, writes as follows: Applicatio tubi optici ad alkidadam pro slellit 
 fans prompte 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 
 the precision of his measurement of altitudes, was observing through 
 improved slits or openings. (Daily's Catal. of Stars, p. 38.) 
 
 * The unfortunate Gascoigne, 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 positions in the vault of heaven. 
 
 t Cosmos, vol. iL, p. 177, 1F8.
 
 DIOPTRIC TUBES. 43 
 
 which were certainly employed by Arabian astronomers, and 
 very probably also by the Greeks and Romans, may indeed, 
 in some degree, have increased the exactness of the observa- 
 tions by causing the object to be seen through 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 observatory 
 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 perturbateurs) diffused in the atmos 
 pheric strata between the star and the eye applied to the tube. 
 In like manner, the tube prevents the lateral impression of the 
 faint light which the particles of air receive at night from all 
 the other stars in the firmament. The intensity of the image 
 and the size of the star are apparently augmented. In a fre- 
 quently emendated and much contested passage of Strabo, in 
 which mention is made of looking through tubes, this " en- 
 larged form of the stars" is expressly mentioned, and is erro- 
 neously ascribed to refraction.* 
 
 * The passage in which Strabo (lib. iii., p. 138, Casaub.) attempts to 
 refute the views of Posidonius 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 
 through lubes. The same thing happens when the setting sun or moon 
 is seen through a dry and thin cloud, when those bodies likewise appear 
 reddish." This passage has recently been pronounced corrupt (see 
 Kramer, in Strabonis Geogr., 1844, vol. i., p. 211), and 81 vdAwv (through 
 glass spheres) substituted for 61 avhuv (Schneider, Eclog. Phyt., vol. ii., 
 p. 273). The magnifying power of hollow glass spheres, filled 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 J.) Solar altitudes, taken 
 through thin, light clouds, or through volcanic vapors, exhibit no trace 
 of the influence of refraction. (Humboldt, Recveil d'Obterv. Astr., vol. 
 i., p. 123.) Colonel Baeyer observed no angular deviation in the heli- 
 otrope light on the passage of streaks of mist, or even from artificially 
 developed vapors, and therefore fully confirms Arago's experiments. 
 Peters, at Pulkowa, in no case found a diiference of 0"'017 on compar- 
 ing groups of stellar altitudes, measured in a clear sky, and through 
 light clouds. See his Recherche* sur la Parallaxe des Etoiles, 1848, p. 
 80, 140-143 ; also Struve's Etudes Stellaires, p. 98. On the application 
 of tubes for astronomical observation in Arabian instruments, see Jour-
 
 44 COSMOS. 
 
 Light, from whatever source it comes whether from th 
 sun, as solar light, or reflected from the planets ; from the 
 fixed stars ; from putrescent wood ; or as the product of the 
 vital activity of glow-worms always exhibits the same con- 
 ditions of refraction.* But the prismatic spectra yielded by 
 different sources of light (as the sun and the fixed stars) ex- 
 hibit a difference in the position of the dark lines (raies du 
 spectre) which Wollaston first discovered in 1808, and the po- 
 sition of which was twelve years afterward so accurately de- 
 termined by Fraunhofer. While the latter observer counted 
 600 dark lines (breaks or interruptions in the colored spec- 
 trum), Sir David Brewster, by his admirable experiments with 
 nitric oxyd, succeeded, in 1833, in counting more than 2000 
 lines. It had been remarked that certain lines failed in the 
 spectrum at some seasons of the year ; but Sir David Brew- 
 ster has shown that this phenomenon is owing to different al- 
 titudes of the sun, and to the different absorption of the rays 
 of light in their passage through the atmosphere. In the spec- 
 dam, Sur V Obseroatoire de Meragha, p. 27 ; and A. Sedillot, Mem. sur 
 les Instruments Astronomiques des Arabes, 1841, p. 198. Arabian astron- 
 omers have also the merit of having first employed large gnomons with 
 small circular apertures. In the colossal sextant of Abu Mohammed 
 al-Chokandi, the limb, which was divided into intervals of five minutes, 
 received the image of the sun. " A midi les rayons du soleil passaient 
 par une ouverture pratique dans la voflte de 1'observatoire qui couvrait 
 {'instrument, suivaut le tuyau, et formaient sur la concavite du sextant 
 une image circulaire, dont le centre donnait, sur 1'arc gradue, le com 
 plement de la hauteur du soleil. Cet instrument differe de notre mural, 
 qu'en ce qu'il etait garni d'un simple tuyau au lieu d'une lunette." " At 
 noon, the rays of the sun passed through an opening in the dome of the 
 observatory, above the instrument, and, following the tube, formed in 
 the concavity of the sextant a circular image, the center of which marked 
 the sun's altitude on the graduated limb. This instrument in no way 
 differed from our mural circle, excepting that it was furnished with a 
 mere tube instead of a telescope." Sedillot, p. 37, 202, 205. Dioptric 
 rulers (pinnulce) were used by the Greeks and Arabs in determining 
 the moon's diameter, and were constructed in such a manner that the 
 circular aperture in the moving object diopter was larger than that 
 of the fixed ocular diopter, and was drawn out until the lunar disk, seen 
 through the ocular aperture, completely filled the object aperture. 
 Delambre, Hist, de VAstron. du Moyen Age, p. 201 ; and S6dillot, p. 198. 
 The adjustment of the dioptric rulers of Archimedes, with round aper- 
 tures or slits, in which the direction of the shadows of two small cylin- 
 ders attached to the same index bar was noted, seems to have been orig- 
 inally introduced by Hipparchus. (Baily, Hist, de VAstron. Mod., 2d 
 ed., 1785, torn, i., p. 480.) Compare also Theon Alexandria, Bas., 1538, 
 p. 257, 262; Les Hypotyp. de Prochis Diadockus, ed. Halma, 1820, p 
 107, 110 ; and Ptolem. Almag., ed. Halma, torn, i., Par., 1813, p. Ivii. 
 * According to Arago. See Moigno, Rtpert. d'Optique Moderne, 1847 
 p. 153.
 
 POLARIZATION OF LIGHT. 45 
 
 tra of the light reflected from the moon, from Venus, Mars, 
 and the clouds, we recognize, as might be anticipated, all the 
 peculiarities of the solar spectrum ; but, on the other hand, 
 the dark lines in the spectrum of Sirius differ from those of 
 Castor and the other fixed stars. Castor likewise exhibits dif- 
 ferent lines from Pollux and Procyon. Amici has confirmed 
 this difference, which was first indicated by Fraunhofer, and 
 has ingeniously called attention to the fact that in fixed stars, 
 which now have an equal and perfectly white light, the dark 
 lines are not the same. A wide and important field is thus 
 still open to future investigations,* for we have yet to distin- 
 guish between that which has been determined with certain- 
 ty and that which is merely accidental and depending on the 
 absorbing action of the atmospheric strata. 
 
 We must here refer to another phenomenon, which is pow- 
 erfully influenced by the specific character of the source of 
 light. The light of incandescent solid bodies, and the light 
 of the electric spark, exhibit great diversity in the number 
 and position of Wollaston's dark lines. From Wheatstone's 
 remarkable experiments with revolving minors, it would ap- 
 pear that the tight of frictional electricity has a greater veloc- 
 ity than solar light in the ratio of 3 to 2 ; that is to say, a ve- 
 locity of 95,908 miles in one second. 
 
 The stimulus infused into all departments of optical science 
 by the important discovery of polarization,! to which the in- 
 genious Malus was led in 1808 by a casual observation of the 
 light of the setting sun reflected from the windows of the Pa- 
 lais du Luxembourg, has aflbrded unexpected results to sci- 
 ence by the more thorough investigation of the phenomena of 
 double refraction, of ordinary (Huygens's) and of chromatic po- 
 larization, of interference, and of diffraction of light. Among 
 these results may be reckoned the means of distinguishing 
 between direct and reflected light, $ the power of penetrating, 
 
 * On the relation of the dark lines on the solar spectrum in the Da- 
 guerreotype, see Comptes Rendus des S6ance de I'Acadtmie des Science*, 
 torn, xiv., 1842, p. 902-904, and torn, xvi., 1843, p. 402-407. 
 
 t Cosmos, vol. ii., p. 332. 
 
 t Arago's investigation of cometary light may hero be adduced as an 
 instance of the important difference between proper and reflected light. 
 The formation of the complementary colors, red and green, showed by 
 the application of his discovery (in 1811) of chromatic polarization, that 
 the light of Halley's comet (1835) contained reflected solar light. I was 
 myself present at the earlier experiments for comparing, by means of 
 the equal and unequal intensity of the images of the polariscope, the 
 proper light of Capella with the splendid comet, as it suddenly emerged 
 from the rays of the sun at the beginning of July, 1819. (See Annuaire
 
 46 COSMOS. 
 
 as it were, into the constitution of the body of the eun and 
 of its luminous envelopes,* of measuring the pressure of at- 
 
 du Bureau des Long, pour 1836, p. 232 ; Cosmos, vol. i., p. 105 ; aud Bes- 
 eel, in Schumacher's Jahrbuchfur 1837, 1G9.) 
 
 * Lettre de M. Arago a M. Alexandre de Humboldt, 1840, p. 37 : "A 
 1'aide d'un polariscope de mon invention, je reconnus (avant 1820) quo 
 la lumiere de tous les corps terrestres incandescents, solides ou liquides, 
 est de la lumiere naturelle, tant qu'elle emane du corps sous des inci- 
 dences perpendiculaires. La lumiere, au contraire, qui sort de la surface 
 incandescente sous un angle aigu, offre des marques manifestos de po- 
 larisation. Je ne m'arrete pas a te rappeler ici, comment je d6duisis 
 de ce fait la consequence curieuse que la lumiere ne s'eugendre pas 
 seulement a la surface des corps ; qu'une portion nalt dans leur sub- 
 ttance ineme, cette substance fut-elle du platine. J'ai seulement besoin 
 de dire qu'en repetant la meme serie d'epreuves, et avec les mmes 
 instruments sur la lumiere que lance une substance gazeuse enflammee, 
 on ne lui trouve, sous quelque incllnaison que ce soit, aucun des carac- 
 teres de la lumiere polarisee; que la lumiere des gaz, prise a la sortie 
 de la surface enflammee, est de la lumiere naturelle, ce qui n'empeche 
 pas qu'elle ne se polarise ensuite completement si on la soumet a des 
 reflexions ou a des refractions conveuables. De la une methode trea 
 simple pour decouvrir a 40 millions de lieues de distance la nature du 
 soleil. La lumiere proveuant du hard de cet astre, la lumiere emanee 
 de la matiere solaire sous un angle aigu, et nous arrivant sans avoir 
 eprouve en route des reflexions ou des refractions sensibles, offre-t-elle 
 des traces de polarisation, le soleil est un corps solide ou liquide. S'il 
 n'y a, au contraire, aucun indice de polarisation dans la lumiere du bord, 
 la parte incandescente du soleil est gazeuse. C'est par cet euchainement 
 methodique d'observations qu'on peut arriver a des notions exactes sur 
 la constitution physique -du soleil." 
 
 " By the aid of my polariscope I discovered (before 1820) that the 
 light of all terrestrial objects in a state of incandescence, whether they 
 be solid or liquid, is natural as long as it emanates from the object in 
 perpendicular rays. The light emanating from an incandescent surface 
 at an acute angle presents, on the other hand, manifest proofs of polar- 
 ization. I will not pause to remind you that this circumstance has led 
 me to the remarkable conclusion that light is not generated on the sur- 
 face of bodies only, but that some portion is actually engendered within 
 the substance itself, even in the case of platinum. I need only here ob- 
 serve, that in repeating the same series of experiments (aud with the 
 same instruments) on the light emanating from a burning gaseous sub- 
 stance, I could not discover any characteristics of polarized light, what- 
 ever might be the angle at which it emanated ; and I found that the light 
 of gaseous bodies is natural light when it issues from the burning sur- 
 face, although this circumstance does not prevent its subsequent com- 
 plete polarization, if subjected to suitable reflections or refractions. 
 Hewoe we obtain a most simple method of discovering the nature of the 
 sun at a distance of 40 millions of leagues. For if the light emanating 
 from the margin of the sun, and radiating from the solar substance at an 
 acute angle, reach us without having experienced any sensible reflec- 
 tions or refractions in its passage to the earth, and if it offer traces of 
 polarization, the sun must be a solid or a liquid body. Put if, on the 
 contrary, the light emanating from tke sun's margin giv- no indications 
 of polarization, the incandescent portion of the sun inuetbe %aeuu. it
 
 POLARIZATION OF LIGHT. 47 
 
 mospheric strata, and even the smallest amount of water they 
 contain, of scrutinizing the depths of the ocean and its rocks 
 by means of a tourmaline plate,* and, in accordance with 
 Newton's prediction, of comparing the chemical compositionf 
 of several substances^ with their optical effects. It will be 
 sufficient to mention the names of Airy, Arago, Biot, Brew- 
 ster, Cauchy, Faraday, Fresnel, John Herschel, Lloyd, Ma- 
 lus, Neumann, Plateau, Seebeck, to remind the sci- 
 entific reader of a succession of splendid discoveries and of 
 their happy applications. The great and intellectual labors 
 of Thomas Young more than prepared the way for these im- 
 portant efforts. Arago's polariscope and the observation of 
 the position of colored fringes of diffraction (in consequence 
 of interference) have been extensively employed in the pros- 
 ecution of scientific inquiry. Meteorology has made equal 
 advances with physical astronomy in this new path. 
 
 However diversified the power of vision may be in differ- 
 ent persons, there is nevertheless a certain average of organ- 
 is by means of such a methodical sequence of observations that we may 
 acquire exact ideas regarding the physical constitution of the sun." 
 (On the Envelopes of the Sun, see Arago, in the Annuaire pour 1846, 
 p. 464.) I give all the circumstantial optical disquisitions which I have 
 borrowed from the manuscript or printed works of my friend, in his 
 own words, in order to avoid the misconceptions to which the variations 
 of scientific terminology might give rise in retranslating the passages 
 into French, or any other of the various languages in which the Cosmos 
 has appeared. 
 
 * " Sur 1'effet d'une lame de tourmaline taillee parallelement aux 
 aretes du prisme servant, lorsqu'elle est convenablement situee, a 61i- 
 miner en totalite les rayons reflechis par la surface de la mer et meles 
 la lumiere provenant de 1'ecueil." " On the effect of a tourmaline plate 
 cut parallel to the edges of the prism, in concentrating (when placed in 
 a suitable position) all the rays of light reflected by the surface of the 
 sea, and blended with the light emanating from the sunken rocks." 
 See Arago, Instructions de la Bonite, in the Annuaire pour 1836, p. 339 
 
 343. 
 
 t " De la possibilit6 de d6terminer les pouvoirs refringents des corps 
 d'apres leur composition chimique." On the possibility of determining 
 the refracting powers of bodies according to their chemical composition 
 
 applied to the ratio of the oxygen to the nitrogen in atmospheric air, 
 to the quantity of hydrogen contained in ammonia and in water, to car- 
 bonic acid, alcohol, and the diamond). See Biot ct Arago, Mtmoire 
 sur les Ajfinites des Corps pour la Lumiere, Mars, 1806; also Mlmoirts 
 Mathem. et Phys. de V Inslilut, t. vii., p. 327-346 ; and my M6moire gur 
 les Refractions Astronomiques dans la Zone Torride, in the Recueit 
 d'Obsew. Astron., vol. i., p. 115 and 122. 
 
 t Experiences de M. Arago sur la puissance Refractive des Corps D\- 
 aphanes (de I' air sec ct de I' air humide) par le Replacement des Franges, 
 iu Moigno, Repertoire d'Oplique Mod., 1847, p. 159-K52.
 
 48 COSMOS. 
 
 fc capacity, which was the same among former generation!, 
 as, for instance, the Greeks and Romans, as at the present 
 day. The Pleiades prove that several thousand years ago, 
 even as now, stars which astronomers regard as of the sev- 
 enth magnitude, wera 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 hetween 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), 
 
 " Qua; septem dici, sex tamen esse solent." 
 
 One of the daughters of Atlas, Merope, the only one who 
 was wedded to a mortal, was said to have veiled herself for 
 very shame, or even to have wholly disappeared. This is 
 probably the star of about the seventh magnitude, which we 
 call Celajno ; 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 
 star 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 Phcen., 1, p. 190, in Uranologio Pctavii), 
 in 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 (nava<j>avjjf') in 
 the Catasterisms (XXIII.) ascribed to Eratosthenes. On a supposed 
 connection between the name of the veiled (the daughter of Atlas) with 
 the geographical myths in the Meropis of Theopompus, as well as with 
 the great Saturnian Continent of Plutarch and the Atlantis, see my Ex 
 amen Grit, de VHist. de la Geographic, t. i., p. 170. Compare also Ideler 
 Untersuchungen fiber den Ursprung imd die Bedeutung der Sternnamen, 
 1809, p. 145; and in reference to astronomical determination of place, 
 consult Madler, Unttrsucli. ubet die Fixstern-Systeme, th. ii., 1848, s. 38 
 and 166 ; also Baily in the Mem. of the Astr. Soc., vol. xiii., p. 33.
 
 VISIBILITY OF STARS. 49 
 
 48 from Mizar, is, according to Argelander, of the fifth 
 magnitude, but overpowered by the rays of Mizar. It was 
 called by the Arabs Saidak, " the Test," because, as the Per- 
 sian astronomer Kazwini* remarks, " It was employed as a 
 
 * See Ideler, Sternnamen, s. 19 and 25. Arago, in manuscript notices 
 of the year 1847, writes as follows: " On observe qu'une lumiere forte 
 fait disparaltre une lumiere faible placee dans le voisinage. Quelle 
 peut en etre la cause ? II est possible physiologiquement que 1'ebran- 
 lement communique k la retine par la lumiere forte s'etend au del& des 
 points que la lumiere forte a frappes, et que cet ebranlement secon- 
 daire absorbe et neutralise en quelque sorte 1'ebranlement provenant de 
 la seconde et faible lumiere. Mais sans entrer dans ces causes physio- 
 logiques, il y a une cause directe qu'on peut indiquer pour la dispari- 
 tion de la faible lumiere : c'est que les rayons provenant de la grande 
 n'ont pas seulement forme une image nette sur la retine, mais se sont 
 disperses aussi sur toutes les parties de cet organe cause des imper- 
 fections de transparence de la cornee. Les rayons du corps plus bril- 
 lant a en traversant la cornee se comportent comme en traversant un 
 corps legerement depoli. Une partie des ces rayons refractes reguliere- 
 ment forme 1'image neme de a, 1'autre partie disperses eclaire la totalite 
 de la retine. C'est done sur ce fond lumineux que se projette 1'image 
 de 1'objet voisin b. Cette derniere image doit done ou disparaltre ou 
 etre affaiblie. De jour deux causes contribuent 1'affaiblissement des 
 etoiles. L'une de ces causes c'est 1'image distincte de cette portion de 
 ratmosphere comprise dans la direction de 1'etoile (de la portion aeri- 
 enne placee entre 1'oeil et 1'etoile) et sur laquelle 1'image de 1'etoile vient 
 de se peindre ; 1'autre cause c'est la lumiere diffuse provenant de la dis- 
 persion que les defauts de la cornee imprlment aux rayons emanants de 
 tous les points de 1'atmosphere visible. De nuit les couches atmosphe- 
 riques interposees entre 1'oeil et 1'etoile vers laquelle on vise, n'agissent 
 pas ; chaque etoile du firmament forme une image plus nette, mais une 
 partie de leur lumiere se trouve dispersee a, cause du manque de dia- 
 phanite de la cornee. Le me me raisonnement s'applique 4 une deux- 
 icme, troisieme .... millidme etoile. La retine se trouve done eclai- 
 ree en totalite par une lumiere diffuse, proportionnelle au nombre de 
 ces etoiles et a leur eclat. On con^oit par 1& que cette somme de lu- 
 miere diffuse affaiblisse ou fasse entierement disparaitre 1'image do 
 1'etoile vers laquelle on dirige la vue." 
 
 " We find that a strong light causes a fainter one placed near it to dis- 
 appear. What can be the cause of this phenomenon ? It is physiolog- 
 ically possible that the vibration communicated to the retina by strong 
 light may extend beyond the points excited by it; and that this secondary 
 vioration may in some degree absorb and neutralize that arising from the 
 second feeble light. Without, however, entering upon these physiologic- 
 al considerations, there is a direct cause to which we may refer the disap- 
 pearance of the feeble light, viz., that the rays emanating from the strong 
 light, after forming a perfect image on the retina, are dispersed over all 
 parts of this organ in consequence of the imperfect transparency of the 
 cornea. The rays of the more brilliant body a, in passing the cornea, 
 are affected in th.2 same manner as if they were transmitted through a 
 body whose surface was not perfectly smooth. Some of these regularly 
 refracted rays form the image a, while the remainder of the dispersed 
 rays illumine the whole jf the retina. On this luminous ground the 
 VOL. III. C
 
 60 COSMOS. 
 
 test of the power of vision." Notwithstanding the low po- 
 sition of the Great Bear under the tropics, I have very dis- 
 tinctly seen Alcor, evening after evening, with the naked 
 eye, on the rainless shores of Cumana, and on the plateaux 
 of the Cordilleras, which are elevated nearly 13,000 feet 
 above the level of the sea, while I have seen it less frequent- 
 ly and less distinctly in Europe and in the dry atmosphere 
 of the Steppes of Northern Asia. The limits within which 
 the naked eye is unable to separate two very contiguous ob- 
 jects in the heavens depend, as Madler has justly observed, 
 on the relative brilliancy of the stars. The two stars of the 
 third and fourth magnitudes, marked as a Capricorni, which 
 are distant from each other six and a half minutes, can with 
 ease be recognized as separate. Galle thinks that and 6 
 Lyrse, being both stars of the fourth magnitude, may be dis- 
 tinguished in a very clear atmosphere by the naked eye, al- 
 though situated at a distance of only three and a half min- 
 utes from each other. 
 
 The preponderating effect of the rays of the neighboring 
 planet is also the principal cause of Jupiter's satellites re- 
 maining invisible to the naked eye ; they are not all, how- 
 ever, as has frequently been maintained, equal in brightness 
 to stars of the fifth magnitude. My friend, Dr. Galle, has 
 found from recent estimates, and by a comparison with 
 neighboring stars, that the third and brightest satellite is 
 probably of the fifth or sixth magnitude, while the others, 
 which are of various degrees of brightness, are all of the sixth 
 or seventh magnitude. There are only few cases on record 
 in which persons of extraordinarily acute vision that is to 
 say, capable of clearly distinguishing with the naked eye 
 
 image of the neighboring object b is projected. This last imago must 
 therefore either wholly disappear or be dimmed. By day two causes 
 contribute to weaken the light of the stars ; one is the distinct image 
 
 of that portion of the atmosphere included in the direction of the star 
 (the aerial field interposed between the eye and the star), and on which 
 the image of the star is formed, while the other is the light diffused by 
 the dispersion which the defects of the cornea impress on the rays em- 
 anating from all points of the visible atmosphere. At night, the strata 
 of air interposed between the eye and the star to which we direct the 
 instrument, exert no disturbing action ; each star in the firmament forms 
 a more perfect image, but a portion of the light of the stars is dispered 
 in consequence of the imperfect transparency of the cornea. The same 
 reasoning applies to a second, a third, or a thousandth star. The retina, 
 then, is entirely illumined by a diffused light, proportionate to the num- 
 ber of the stars and to their brilliancy. Hence we may imagine that 
 the aggregate of this diffused light must either weaken, or entirely ob- 
 literate the imago of tlie star toward which the eye is directed."
 
 VISIBILITY OF STARS. 51 
 
 gtars fainter than those of the sixth magnitude have been 
 able to distinguish the satellites of Jupiter without a tele- 
 scope. The angular distance of the third and brightest sat- 
 ellite 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 Compte* 
 Rendus, torn, xv., 1842, p. 750. (Schutn., Astron. Nachr., No. 702.) 
 " I 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 my 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- 
 ellite alone appeared nearly equal in brightness to a neighboring star 
 of the sixth magnitude, which I could scarcely 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 greatest 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. From a 
 comparison of Aldebaran \vith the neighboring star 6 Tauri, which is 
 easily recognized as a double star (at a distance of 5J minutes), I should 
 estimate the radiation of Jupitr at five or six minutes, at least, for or- 
 dinary vision." These estimates correspond 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 1'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 terns en terns aper9us, sans avoir besoin de 
 recourir a 1'artifice de 1'amplification. Pour verifier cette conjecture, 
 j'ai fait construire une petite lunette dans laquelle 1'objectif et 1'ocu- 
 laire ont a peu pres le menie foyer, et qni des lors lie grossit point. 
 Cette lunette ne detruit pas eutierement les rayons divergents, mais 
 elle en reduit considerablement la longueur. Cela a suffi your qu'un 
 satellite convenablement 6cart6 de la plandte, soil devenu visible. Le 
 fait a ete constate par tous les jeunes astronomes de 1'Observatoire." 
 " If we suppose that the image of Jupiter appears to the eyes of some 
 persons to be dilated by rays of only one or two minutes, it is nit 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 caased 
 a small instrument to be constructed in which the object-glass and the 
 eye-piece had nearly the same focus, and which, therefore, did not mag 
 itify. This instrument does not entirely destroy the diverging rays, al 
 though it considerably reduces their length. This method has sufficed 
 to render a satellite visible 'when at a sufficient distance from the planet. 
 This observation has been confirmed by all the young astronomers at 
 the Observatory." (Arago, in the Comptes Rendus, torn, xv., 1842, p.
 
 52 COSMOS. 
 
 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 which were used, since the ear- 
 liest ages of mankind, and especially among the Egyptians, 
 as pictorial representations to indicate the shining orbs of 
 heaven, are at least from five to six minutes in length. 
 (These lines are regarded by Hassenfratz as caustics on the 
 crystalline lens : intersections des deux caustiques.} 
 
 " The image of the star which we see with the naked eye 
 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 vision, 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 
 Schbn, 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 Observatory, Von Boguslawski. " After having 
 (since 1820) convinced ourselves, by several rigid tests, that in serene 
 moonless nights Schbn 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 appeared to prevent others from seeing so 
 clearly as he did, when he expressed his astonishment at these ob- 
 structing 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 Schbii 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 the 
 fourth alone. When the air was not in a very favorable condition, the 
 satellites appeared to him like faint streaks of light. He never mistook 
 small fixed stars for satellites, probably on account of the scintillating 
 and less constant light of the former. Some years before his death 
 Schbn complained to me that his failing eye could no longer distinguish 
 Jupiter's satellites, whose position was only indicated, even in clear 
 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 on 
 persons of such great perfection and sensibility of vision. Schbii 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 generally 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 occasionally exceeds in the intensity of its clear yellow light the 
 luster of the third, which is also much larger. (Madler, Astr., 1846, 
 s. 231-234, and 439.) Sturm and Airy, in the Complex Rendut, t. xx., 
 p. 764-6, show how, under proper conditions of refraction in the organ 
 of vision, remote luminous poin'a may appear as light streaks.
 
 NATURAL VISION. 53 
 
 trated in a single point. The impression on the nerves is 
 weaker. A very dense starry 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 fpanouie d'ane etoile de 7eme grandeur n'ebranle pas 
 suffisamment la retine : elle n'y fait pas naitre une sensation apprecia- 
 ole de lumiere. Si 1'image n'etait point epanouie (par des rayons di- 
 vergents), la sensation aurait plus de force, et 1'etoile se verrait. La 
 premiere classe d'etoiles invisibles a 1'ceil nu ne serait plus alors la sep- 
 tieme: pour la trouver, il faudrait peut-etre descendre alors jusqu'a la 
 12etne. Considerons un groupe d'etoiles de 7eme grandeur tellement 
 rapproch6es les unes des autres que les intervalles echappent necessaire- 
 ment a 1'oeil. Si la vision avait de la nettete, si 1'image de chaque etoile 
 etait tres petite et bien termin&e, 1'observateur aperceverait un champ 
 de lumiere dont chaque point aurait Veclat concentre d'une etoile de 
 7eme grandeur. I? eclat concentre d'une etoile de 7eme grandeur suffit 
 a la vision a 1'oeil nu. Le groupe serait done visible a I'ojil nu. Di- 
 latons maintenant sur la retine 1'image de chaque etoile du groupe ; 
 remplasons chaque point de 1'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 etoiles. Pour peu qu'on y reflechisse, il restera evi- 
 dent qu' excepte sur les bords de 1'image g6nerale, 1'aire lumineuse 
 ainsi eclairee a precisement, a cause de la superposition des cercles, la 
 mme inteusite que dans le cas ou chaque etoile n'eclaire qu'un seul 
 point au fond de 1'ceil ; mais si chacun de ces points re<joit une lumiere 
 6gale en intensity a la lumiere concentree d'une etoile de 7eme gran- 
 deur, il est clair que 1'epanouissement des images individuelles des 
 fetoiles contigues ne doit pas empecher la visibilite de 1'ensemble. Les 
 instruments telescopiques ont, quoiqu'a un beaucoup momdre degre, le 
 defaut de donner aussi aux etoiles un diamitre sensible et factice. Avec 
 ces instruments, comme & 1'ceil nu, on doit done apercevoir des groupes, 
 composes d'etoiles inferieures en intensite a celles que les memea lu- 
 nettes ou telescopes feraient apercevoir isolement." 
 
 " The expanded image of a star of the seventh magnitude doen not 
 cause sufficient vibration of the retina, and does not give rise to an ap- 
 preciable sensation of light. If the image were not expanded (by di- 
 vergent rays), the sensation would be stronger and the star discernible. 
 The lowest magnitude at which stars are visible would not therefore 
 be the seventh, but some magnitude as low perhaps as the twelfth de- 
 gree. Let us consider a group of stars of the seventh magnitude so 
 close to one another that the intervals between them necessarily escape 
 the eye. If the sight were very clear, and the image of each star small 
 and well defined, the observer would perceive a field of light, each 
 point of which would be equal to the concentrated brightness of a star 
 of the seventh magnitude. The concentrated light of a star of the sev- 
 enth magnitude is sufficient to be seen by the naked eye. The group, 
 therefore, would be visible to the naked eye. Let us now dilate the
 
 54 COSMOS. 
 
 Telescopes, although in a much less degree, unfortunately 
 also give the stars an incorrect and spurious diameter ; but, 
 according to the splendid investigations of Sir William Her- 
 echel,* these diameters decrease with the increasing power 
 of the instrument. This distinguished observer estimated 
 that, at the excessive magnifying power of 6500, the appar- 
 ent diameter of Vega Lyrae still amounted to 0"36. In ter- 
 restrial objects, the form, no less than the mode of illumina- 
 tion, determines the magnitude of the smallest angle of vision 
 for the naked eye. Adams very correctly observed that a 
 long and slender staff can be seen at a much greater distance 
 than a square whose sides are equal to the diameter of the 
 staff. A stripe may be distinguished at a greater distance 
 than a spot, even when both are of the same diameter. Ara- 
 go has made numerous calculations on the influence of form 
 (outline of the object) by means of angular measurement of 
 distant lightning conductors visible from the Paris Observa- 
 tory. The minimum optical visual angle at which terres- 
 trial objects can be recognized by the naked eye has been 
 gradually estimated lower and lower from the time when 
 Robert Hooke fixed it exactly at a full minute, and Tobias 
 Mayer required 34" to perceive a black speck on white pa- 
 per, to the period of Leeuwenhoek's experiments with spi- 
 der's threads, which are visible to ordinary sight at an angle 
 of 4" - 7. In the recent and most accurate experiments of 
 Hueck, on the problem of the movement of the crystalline 
 
 image of each star of the group on the retina, and substitute a small 
 circle for each point of the former general image ; these circles will 
 impinge upon one another, and the different points of the retina will 
 be illumined by light emanating simultaneously from many stars. A 
 slight consideration will show, that, excepting at the margins of the 
 general image, the luminous air has, in consequence of the superposi- 
 tion of the circles, the same degree of intensity as in those cases where 
 each star illumines only one single point of the retina ; but if each of 
 these points be illumined by a light equal in intensity to the concen- 
 trated light of a star of the seventh magnitude, it is evident that the 
 dilatation of the individual images of contiguous stars can not prevent 
 the visibility of the whole. Telescopic instruments have the defect, 
 although in a much less degree, of giving the stars a sensible and spu. 
 rious diameter. We therefore perceive with instruments, no less than 
 with the naked eye, groups of stars, inferior in intensity to those which 
 the same telescopic or natural sight would recognize if they were iso- 
 lated." Arago, in the Annuaire du Bureau des Longitudes pour Van 
 1842, p. 284. 
 
 * Sir William Herschel, in the Philos. Transact, for 1803, vol. 93, 
 p. "225, and for 1805, vol. 94, p. 184. Compare also Arago, in the An 
 nuairepour 1842, p. 360-374.
 
 VISIBILITY OP OBJECTS. 55 
 
 lens, white lines on a black ground were seen at an angle 
 of l"-2; a spider's thread at 0"-6 ; and a fine glistening 
 wire at scarcely 0"'2. This problem does not admit gen- 
 erally of a numerical solution, since it entirely depends on 
 the form of the objects, their illumination, their contrast with 
 the back-ground, and on the motion or rest, and the nature 
 of the atmospheric strata in which the observer is placed. 
 
 During my visit at a charming country-seat belonging to 
 the Marquess de Selvalegre at Chillo, not far from Q,uito, 
 where the long-extended crests of the volcano of Pichincha 
 lay stretched before me at a horizontal distance, trigonomet- 
 rically determined at more than 90,000 feet, I was much 
 struck by the circumstance that the Indians who were stand- 
 ing near me distinguished the figure of my traveling com- 
 panion Bonpland (who was engaged in an expedition to the 
 volcano) as a white point moving on the black basaltic sides 
 of the rock, sooner than we could discover him with our tel- 
 escopes. The white moving image was soon detected with 
 the naked eye both by myself and by my friend the unfor- 
 tunate son of the marquess, Carlos Montufar, who subsequent- 
 ly perished in the civil war. Bonpland was enveloped in a 
 white cotton mantle, the poncho of the country ; assuming 
 the breadth across the shoulders to vary from three to five 
 feet, according as the mantle clung to the figure or fluttered 
 in the breeze, and judging from the known distance, we found 
 that the angle at which the moving object could be distinctly 
 seen varied from 7" to 12". White objects on a black ground 
 are, according to Hueck's repeated experiments, distinguish- 
 ed at a greater distance than black objects on a white ground. 
 The light was transmitted in serene weather through rar- 
 efied strata of air at an elevation 15,360 feet above the 
 level of the sea to our station at Chillo, which was itself sit- 
 uated at an elevation of 8575 feet. The ascending distance 
 was 91,225 feet, or about 17 miles. The barometer and 
 thermometer stood at very different heights at both stations, 
 being probably at the upper one about 17*2 inches and 46'4, 
 while at the lower station they were found, by accurate ob- 
 servation, to be 22-2 inches and 65-7. Gauss's heliotrope 
 light, which has become so important an element in German 
 trigonometrical measurements, has been seen with the naked 
 eye reflected from the Brocken on Hohenhagen, at a distance 
 of about 227,000 feet, or more than 42 miles, being fre- 
 quently visible at points in which the apparent breadth of a 
 three-inch mirror was only 0"'43.
 
 56 COSMOS. 
 
 The visibility of distant objects irf modified by the absorp- 
 tion of the rays passing from the terrestrial object to the* 
 naked eye at unequal distances, and through strata of air 
 more or less rarefied and more or less saturated with moist- 
 ure ; by the degree of intensity of the light diffused by the 
 radiation of the particles of air ; and by numerous meteoro- 
 logical processes not yet fully explained. It appears from 
 the old experiments of the accurate observer Bouguer that 
 a difference of ^th in the intensity of the light is necessary 
 to render objects visible. To use his own expression, we 
 only negatively see mountain-tops from which but little light 
 is radiated, and which stand out from the vault of heaven in 
 the form of dark masses ; their visibility is solely owing to 
 the difference in the thickness of the atmospheric strata ex- 
 tending respectively to the object and to the horizon. Strong 
 ly-illumined objects, such as snow-clad mountains, white 
 chalk cliffs, and conical rocks of pumice-stone, are seen pos- 
 itively. 
 
 The distance at which high mountain summits may be 
 recognized from the sea is not devoid of interest in relation 
 to practical navigation, where exact astronomical determina- 
 tions are wanting to indicate the ship's place. I have treat- 
 ed this subject more at length in another work,* where I 
 considered the distance at which the Peak of Teneriffe might 
 be seen. 
 
 The question whether stars can be seen by daylight with 
 the naked eye through the shafts of mines, and on very high 
 mountains, has been with me a subject of inquiry since my 
 early youth. I was aware that Aristotle had maintained! 
 
 * Humboldt, Relation Hist, du Voyage aux Regions Equinox., torn. 
 i., p. 92-97; and Bouguer, Traiti d'Optique, p. 360 and 365. (Com- 
 pare, also, Captain Beechey, in the Manual of Scientific Inquiry for the 
 Use of the Royal Navy, 1849, p. 71.) 
 
 t The passage in Aristotle referred to by Buffon occurs in a work 
 where we should have least expected to find it De Generat. Animal., 
 \. i., p. 780, Bekker. Literally translated, it runs as follows : " Keen- 
 ness of sight is as much the power of seeing far as of accurately distin- 
 guishing the differences presented by the objects viewed. These two 
 properties are not met with in the same individuals. For he who holds 
 his hand over his eyes, or looks through a tube, is not, on that account, 
 more or less able to distinguish differences of color, although he will see 
 objects at a greater distance. Hence it arises that persons in cavern* 
 or cisterns are occasionally enabled, to see stars." The Grecian 'Ooiiy/za- 
 ra, and more especially (ppeara, are, as an eye-witness, Professor Franz, 
 observes, subterranean cisterns or reservoirs which communicate with 
 the light and air by means of a vertical shaft, and widen toward the bot- 
 tom, like the neck of a bottle. Pliny (lib. ii., cap. 14) ays, " Altituda
 
 FISIBILITT OP STARS. 57 
 
 that stars might occasionally be seen from ctverns and cis- 
 terns, as through tubes. Pliny alludes to the same circum- 
 stance, and mentions the stars that have been most distinctly 
 recognized during solar eclipses. While practically engaged 
 in mining operations, I was in the habit, during many years, 
 of passing a great portion of the day in mines where I could 
 see the sky through deep shafts, yet I never was able to ob- 
 serve a star ; nor did I ever meet with any individual in 
 the Mexican, Peruvian, or Siberian mines who had heard of 
 stars having been seen by daylight ; although in the many 
 latitudes, in both hemispheres, in which I have visited deep 
 mines, a sufficiently large number of stars must have passed 
 the zenith to have afforded a favorable opportunity for their 
 being seen. Considering this negative evidence, I am the 
 more struck by the highly credible testimony of a celebrated 
 optician, who in his youth saw stars by daylight through the 
 shaft of a chimney.* Phenomena, whose manifestation de- 
 pends on the accidental concurrence of favoring circum- 
 stances, ought not to be disbelieved on account of their 
 rarity 
 
 The same principle must, I think, be applied to the asser- 
 tion of the profound investigator Saussure, that stars have 
 been seen with the naked eye in bright daylight, on the de- 
 clivity of Mont Blanc, and at an elevation of 12,757 feet 
 " Ctuelques-uns des guides m'ont assure avoir vu des etoiles 
 en plein jour ; pour moi je n'y songeais pas, en sorte que je 
 n'ai point ete le temoin de ce phenomene ; mais I' assertion 
 uniforme des guides ne me laisse aucun doute sur la rea- 
 lite. II faut d'ailleurs etre entitlement a 1'ombre d'une epais- 
 seur considerable, sans quoi 1'air trop fortement eclaire fait 
 evanouir la faible clarte des etoiles." " Several of the guides 
 assured me," says this distinguished Alpine inquirer, "that 
 
 cogit minores videri Stellas ; affixas ccelo-solis fulgor interdiu non cerni, 
 quum aeque ac noctu luceant ; idque manifesto m fiat defectu soils et prce- 
 altis puteis." Cleomedes ( Cycl. Theor., p. 83, Bake) does not speak of 
 stars seen by day, but asserts " that the sun, when observed from deep 
 cisterns, appears larger, on account of the darkness and the damp air." 
 * " We have ourselves heard it stated by a celebrated optician that 
 the earliest circumstance which drew his attention to astronomy waa 
 the regular appearance, at a certain hour, for several successive days, 
 of a considerable star, through the shaft of a chimney." John Herschel, 
 tlines of Astr., 61. The chimney-sweepers whom I have ques- 
 
 Ontlines of Astr., $ 61. The chimney-sweepers whom I have ques- 
 tioned agree tolerably well in the statement that " they have never seen 
 stars by day, but that, when observed at night, through deep shafts, the 
 sky appeared quite near, and the stars larger." I will not enter upon 
 any discussion regarding the connection between these two illusions. 
 
 C 2
 
 58 COSMOS 
 
 they had seen stars at broad daylight : not having myself 
 been a witness of this phenomenon, I did not pay much at- 
 tention to it, but the unanimous assertions of the guides left 
 me no doubt of its reality.* It is essential, however, that 
 the observer should be placed entirely in the shade, and that 
 he should even have a thick and massive shade above his 
 head, since the stronger light of the air would otherwise dis- 
 perse the faint image of the stars." These conditions are 
 therefore nearly the same as those presented by the cisterns 
 of the ancients, and the chimneys above referred to. I do 
 not find this remarkable statement (made on the moniing of 
 the 2d of August, 1787) in any other description of the Swiss 
 mountains. Two well-informed, admirable observers, the 
 brothers Hermann and Adolph Schlagentweit, who have re- 
 cently explored the eastern Alps as far as the summit of the 
 Gross Glockner (13,016 feet), were never able to see stars 
 by daylight, nor could they hear any report of such a phe- 
 nomenon having been observed among the goatherds and 
 chamois-hunters. Although I passed many years in the 
 Cordilleras of Mexico, Quito, and Peru, and frequently in 
 clear weather ascended, in company with Bonpland, to ele- 
 vations of more than fifteen or sixteen thousand feet above 
 the level of the sea, I never could distinguish stars by day- 
 light, nor was my friend Boussingault more successful in his 
 subsequent expeditions ; yet the heavens were of an azure so 
 intensely deep, that a cyanometer (made by Paul of Geneva) 
 which had stood at 39 when observed by Saussure on Mont 
 Blanc, indicated 46 in the zenith under the tropics at ele- 
 vations varying between 17,000 and 19,000 feet.f Under 
 the serene etherially-pure sky of Cumana, in the plains near 
 the sea-shore, I have frequently been able, after observing an 
 eclipse of Jupiter's satellites, to find the planet again with 
 the naked eye, and have most distinctly seen it when the 
 gun's disk was from 18 to 20 above the horizon. 
 
 The present would seem a fitting place to notice, although 
 cursorily, another optical phenomenon, which I only observed 
 once during my numerous mountain ascents. Before sunrise, 
 on the 22d of June, 1799, when at Malpays, on the decliv- 
 ity of the Peak of Teneriffe, at an elevation of about 11,400 
 feet above the sea's level, I observed with the naked eye 
 
 * Consult Saussure, Voyage dans les Alpes (Neuchatel, 1779, 4to), 
 torn, iv., 2007, p. 199. 
 
 t Humboldt, Essai sur la G6ographie des Plantes, p. 103. Compare 
 also my Voy. aux Regions Equinox, torn, i., p. 143, 248.
 
 UNDULATION OP THE STARS. 5 
 
 cars near the horizon flickering with a singular oscillating 
 motion. Luminous points ascended, moved laterally, and 
 feii back to their former position. This phenomenon lasted 
 only from seven to eight minutes, and ceased long before the 
 sun's disk appeared above the horizon of the sea. The same 
 .motion was discernible through a telescope, and there was 
 no doubt that it was the stars themselves which moved.* 
 Did this change of position depend on the much-contested 
 phenomenon of lateral radiation ? Does the undulation of 
 the rising sun's disk, however inconsiderable it may appear 
 when measured, present any analogy to this phenomenon in 
 the lateral alteration of the sun's margin ? Independently 
 of such a consideration, this motion seems greater near the 
 horizon. This phenomenon of the undulation of the stars 
 was observed almost half a century later at the same spot 
 by a well-informed and observing traveler, Prince Adalbert 
 of Prussia, who saw it both with the naked eye and through 
 a telescope. I found the observation recorded in the prince's 
 manuscript journal, where he had noted it down, before he 
 learned, on his return from the Amazon, that I had wit- 
 nessed a precisely similar phenomenon.! I was never able 
 to detect any trace of lateral refraction on the declivities 
 of the Andes, or during the frequent mirages in the torrid 
 plains or Llanos of South America, notwithstanding the het- 
 erogeneous mixture of unequally-heated atmospheric strata. 
 As the Peak of Tenerifie is so near us, and is so frequently 
 
 * Humboldt, in Fr. von Zach's Monatliche Correspondenz zur Erd- 
 und Himmels-Kunde, bd. i., 1800, s. 396 ; also Voy. aux R6g. Equin., 
 torn, i., p. 125 : " On croyait voir de petites fusses lancees dans 1'air. 
 Des points lumineux eleves de 7 a 8 degres, paraissent d'abord se mou- 
 voir dans le sens vertical, mais puis se convertir en une veritable oscil- 
 lation horizontale. Ces images lumineux etaient des images de plu- 
 sieurs etoiles agrandies (en apparence) par des vapeurs et revenant au 
 meme point d'ou elles etaient partis." " It seemed as if a number of 
 sinall rockets were being projected in the air ; luminous points, at an 
 elevation of 7 or 8, appeared moving, first in a vertical, and then os- 
 cillating iu a horizontal direction. These were the images of many 
 stars, apparently magnified by vapors, and returning to the same point 
 from which they had emanated." 
 
 t Prince Adalbert of Prussia, Aus meinem Tagebuche, 1847, s. 213. 
 Is the phenomenon I have described connected with the oscillations 
 of 10"-12", observed by Carlini, in the passage of the polar star over 
 the field of the great Milan meridian telescope ? (See Zach's Corres- 
 
 endance Astronomique et Giog., vol. ii., 1819, p. 81.) Brandes (Geh- 
 's Umgearb. Phys. Wortersb., bd. iv., s. 549) refers the phenomenon 
 to mirage. The star-like heliotrope light has also frequently been seen, 
 by the admirable and skillful observer, Colonel Baeyer, to oscillate to 
 and fro in a horizontal direction.
 
 60 COSMOS. 
 
 ascended before sunrise by scientific travelers provided with 
 instruments, I would hope that this reiterated invitation on 
 my part to the observation of the undulation of the stars 
 may not be wholly disregarded. 
 
 I have already called attention to the fact that the basis 
 of a very important part of the astronomy of our planetary 
 system was already laid before the memorable years 1608 
 and 1610, and therefore before the great epoch of the in- 
 vention of telescopic vision, and its application to astronom- 
 ical purposes. The treasure transmitted by the learning of 
 the Greeks and Arabs was augmented by the careful and 
 persevering labors of George Purbach, Regiomontanus (i. e. } 
 Johann Miiller), and Bernhard Walther of Niirnberg. To 
 their efforts succeeded a bold and glorious development of 
 thought the Copernican system ; this, again, was followed 
 by the rich treasures derived from the exact observations of 
 Tycho Brahe, and the combined acumen and persevering 
 spirit of calculation of Kepler. Two great men, Kepler and 
 Galileo, occupy the most important turning-point in the his- 
 tory of measuring astronomy ; both indicating the epoch that 
 separates observation by the naked eye, though aided by 
 greatly improved instruments of measurement, from tele- 
 scopic vision. Galileo was at that period forty-four, and 
 Kepler thirty-seven years of age ; Tycho Brahe, the most 
 exact of the measuring astronomers of that great age, had 
 been dead seven years. I have already mentioned, in a pre- 
 ceding volume of this work (see vol. ii., p. 328), that none of 
 Kepler's cotemporaries, Galileo not excepted, bestowed any 
 adequate praise on the discovery of the three laws which 
 have immortalized his name. Discovered by purely empir- 
 ical methods, although more rich in results to the whole do- 
 main of science than the isolated discovery of unseen cos- 
 mical bodies, these laws belong entirely to the period of nat- 
 ural vision, to the epoch of Tycho Brahe and his observa- 
 tions, although the printing of the work entitled Astronomia 
 nova seu Physica codestis de motibus Stella Martis was 
 not completed until 1609, and the third law, that the squares 
 of the periodic times of revolution of two planets are as the 
 cubes of their mean distances, was first fully developed in 
 1619, in the Harmonice Mundi. 
 
 The transition from natural to telescopic vision which 
 characterizes the first ten years of the seventeenth century 
 was more important to astronomy (the knowledge of the re- 
 gions of space) than the year 1492 (that of the discoveries
 
 ASTRONOMICAL DISCOX ERIB3. t51 
 
 of Columbus) in respect to our knowledge of terrestrial space. 
 It not only infinitely extended our insight into creation, but 
 also, besides enriching the sphere of human ideas, raised 
 mathematical science to a previously unattained splendor, 
 by the exposition of new and complicated problems. Thus 
 the increased power of the organs of perception reacts on 
 the world of thought, to the strengthening of intellectual 
 force, and the ennoblement of humanity. To the telescope 
 alone we owe the discovery, in less than two and a half 
 centuries, of thirteen new planets, of four satellite-systems 
 (the four moons of Jupiter, eight satellites of Saturn, four, 
 or perhaps six of Uranus, and one of Neptune), of the sun's 
 spots and faculse, the phases of Venus, the form and height 
 of the lunar mountains, the wintery polar zones of Mars, the 
 belts of Jupiter and Saturn, the rings of the latter, the inte- 
 rior planetary comets of short periods of revolution, together 
 with many other phenomena which likewise escape the na- 
 ked eye. While our own solar system, which so long seemed 
 limited to six planets and one moon, has been enriched in 
 the space of 240 years with the discoveries to which we 
 have alluded, our knowledge regarding successive strata of 
 the region of the fixed stars has unexpectedly been still more 
 increased. Thousands of nebulae, stellar swarms, and double 
 stars, have been observed. The changing position of the 
 double stars which revolve round one common center of 
 gravity has proved, like the proper motion of all fixed starb, 
 that forces of gravitation are operating in those distant re- 
 gions of space, as in our own limited mutually-disturbing 
 planetary spheres. Since Morin and Gascoigne (not indeed 
 till twenty-five or thirty years after the invention of the tel- 
 escope) combined optical arrangements with measuring in- 
 struments, we have been enabled to obtain more accurate 
 observations of the change of position of the stars. By this 
 means we are enabled to calculate, with the greatest pre- 
 cision, every change in the position of the planetary bodies, 
 the ellipses of aberration of the fixed stars and their paral- 
 laxes, and to measure the relative distances of the double 
 stars even when amounting to only a few tenths of a sec- 
 onds-arc. The astronomical knowledge of the solar system 
 has gradually extended to that of a system of the universe. 
 We know that Galileo made his discoveries of Jupiter's 
 satellites with an instrument that magnified only seven diam- 
 eters, and that he never could have used one of a higher 
 power than thirty-two. One hundred and seventy years later,
 
 62 COSMOS. 
 
 we find Sir William Herschel, in his investigations on the 
 magnitude of the apparent diameters of Arcturus (0 //- 2 within 
 the nebula) and of Vega Lyrte, using a power of 6500. Since 
 the middle of the seventeenth century, constant attempts 
 have been made to increase the focal length of the telescope. 
 Christian Huygena, indeed, in 1655, discovered the first sat- 
 ellite of Saturn, Titan (the sixth in distance from the center 
 of the planet), with a twelve-feet telescope ; he subsequent- 
 ly, however, examined the heavens with instruments of a 
 greater focal length, even of 122 feet ; but the three object- 
 glasses in the possession of the Royal Society of Londonj 
 whose focal lengths are respectively 123, 170, and 210 feet, 
 and which were constructed by Constantin Huygens, brother 
 of the great astronomer, were only tested by the latter, as 
 he expressly states,* upon terrestrial objects. Auzout, who 
 in 1663 constructed colossal telescopes without tubes, and 
 therefore without a solid connection between the object-glass 
 and the eye-piece, completed an object-glass, which, with a 
 focal length of 320 feet, magnified 600 times.f The most 
 useful application of these object-glasses, mounted on poles, 
 was that which led Dominic Cassini, between the years 1671 
 and 1684, to the successive discoveries of the eighth, fifth, 
 fourth, and third satellites of Saturn. He made use of ob- 
 ject-glasses that had been ground by Borelli, Campani, and 
 Hartsoeker. Those of the latter had a focal length of 266 
 feet. 
 
 During the many years I passed at the Paris Observatory, 
 I frequently had in my hands the instruments made by Cam- 
 pani, which were in such great repute during the reign of 
 Louis XIV. ; and when we consider the faint light of Saturn's 
 satellites, and the difficulty of managing instruments, worked 
 by strings only,| we can not sufficiently admire the skill and 
 the untiring perseverance of the observer. 
 
 * The remarkable artistical skill of Constantin Huygens, who was 
 private secretary to King William the Third, has only recently been 
 presented in its proper light by Uytenbrock in the " Oratio de fratribiis 
 Christiano atque Constantino Hugenio, artis dioptricae cultoribus," 1838; 
 and by Prof. Kaiser, the learned director of the Observatory at Leyden 
 (in Schumacher's Astron. Nachr., No. 592, s. 246). 
 
 t See Arago, in the Annuaire pour 1844, p. 381. 
 
 t " Nous avons place ces grands verres, tantot sur un grand m&t, tan- 
 tot sur la tour de bois venue de Marly ; enfiu nous les avons mis dans 
 un tuyau monte sur un support en forme d'6chelle & trois faces, ce qui 
 a eu (dans la decouverte des satellites de Saturne) le succSs que nous 
 en avions esp6r&." " We sometimes mounted these great instruments 
 on a high pole," says Dominique Caasini, " and sometimes on the wood-
 
 TELESCOPES. 63 
 
 The advantages which were at that period supposed to 
 be obtainable only by gigantic length, led great minds, as is 
 frequently the case, to extravagant expectations. Auzout 
 considered it necessary to refute Hooke, who is said to have 
 proposed the use of telescopes having a length of upward of 
 10,000 feet (or nearly two miles),* in order to see animals 
 in the moon. A sense of the practical inconvenience of op- 
 tical instruments having a focal length of more than a hund- 
 red feet, led, through the influence of Newton (in following 
 out the earlier attempts of Mersenne and James Gregory of 
 Aberdeen), to the adoption, especially in England, of shorter 
 reflecting telescopes. The careful comparison made by Brad- 
 ley and Pond, of Hadley's five-feet reflecting telescopes, with 
 the refractor constructed by Constantin Huygens (which 
 had, as already observed, a focal length of 123 feet), fully 
 demonstrated the superiority of the former. Short's expens- 
 ive reflectors were now generally employed until 1759, when. 
 John Dollond's successful practical solution of the problem 
 of achromatism, to which he had been incited by Leonhard 
 Euler and Klingenstierna, again gave preponderance to re- 
 fracting instruments. The right of priority, which appears 
 to have incontestably belonged to the mysterious Chester 
 More, Esq., of More Hall, in Essex (1729), was first made 
 known to the public when John Dollond obtained a patent 
 for his achromatic telescopes. f 
 
 The triumph obtained by refracting instruments was not, 
 however, of long duration. In eighteen or twenty years after 
 the construction of achromatic instruments by John Dollond, 
 by the combination of crown with flint glass, new fluctua- 
 
 en tower that had been brought from Marly ; and we also placed them 
 in a tube mounted on a three-sided ladder, a method which, in the dis- 
 covery of the satellites of Saturn, gave us all the success we had hoped." 
 Delambre, Hist, de VAstr. Moderne, torn, ii., p. 785. Optical instru- 
 ments having such enormous focal lengths remind us of the Arabian in- 
 struments olmeasurement -quadrants with a radius of about 190 feet, 
 upon whose graduated limb the image of the sun was received as in the 
 gnomon, through a small round aperture. Such a quadrant was erect- 
 ed at Samarcand, probably constructed after the model of the older sex- 
 tants of Al-Chokandi (which were about 60 feet in height). Compare 
 Sedillot, P 'rottgomenes det Tables d'Oloug-Beg, 1847, p. Ivii. and cxxix. 
 
 * See Delambre, Hist, de VAstr. Mod., t. ii., p. 594. The mystic 
 Capuchin monk, Schyrle von Rheita, who, however, was well versed 
 in optics, had already spoken in his work, Oculus Enoch et Elite (Autv., 
 1645), of the speedy practicability of constructing telescopes that should 
 magnify 4000 times, by means of which the lunar mountains might b 
 accurately laid down. Compare also Cosmos, vol. ii., p. 323 (note). 
 
 t Edinb. Encyclopedia, vol. xx., p. 479.
 
 tions of opinion were excited by the just admiration award- 
 ed, both at home and abroad, to the immortal labors of a 
 German, William Herschel. The construction of numerous 
 seven-feet and twenty-feet telescopes, to which powers of 
 from 2200 to 6000 could be applied, was followed by that of 
 his forty-feet reflector. By this instrument he discovered, in 
 August and September, 1789, the two innermost satellites 
 of Saturn Enceladus, the second in order, and^soon after- 
 ward, Mimas, the first, or the one nearest to the ring. The 
 discovery of the planet Uranus in 1781 was made with 
 Herschel's seven-feet telescope, while the faint satellites of 
 this planet were first observed by him in 1787, with a twen- 
 ty-feet "front view" reflector.* The perfection, unattained 
 till then, which this great man gave to his reflecting tele- 
 scopes, in which light was only once reflected, led, by the 
 uninterrupted labor of more than forty years, to the most 
 important extension of all departments of physical astron- 
 omy in the planetary spheres, no less than in the world of 
 nebulae and double stars. 
 
 The long predominance of reflectors wus followed, in the 
 earlier part of the nineteenth century, by a successful emu- 
 lation in the construction of achromatic refractors, and heli- 
 ometers, paralactically moved by clock-work. A homoge- 
 neous, perfectly smooth flint glass, for the construction of 
 object-glasses of extraordinary magnitude, was manufactured 
 in the institutions of Utzschneider and Fraunhofer at Mu- 
 nich, and subsequently in those of Merz and Mahler ; and in 
 the establishments of Guinand and Bontems (conducted for 
 MM. Lerebours and Cauchoix) in Switzerland and France. 
 It will be sufficient in this historical sketch to mention, by 
 way of example, the large refractors made under Fraunho- 
 fer's directions for the Observatories of Dorpat and Berlin, 
 in which the clear aperture was 9' 6 inches in diameter, with 
 a focal length of 14 '2 feet, and those executed by Merz and 
 Mahler for the Observatories of Pulkowa and Cambridge, in 
 the United States of America ;t they are both adjusted with 
 
 * Consult htruve, Etudes d'Astr. Stellaire, 1847, note 59, p. 24. I 
 have retained the designations of forty, twenty, and seven-feet Herschel 
 reflecting telescopes, although in other parts of the work (the original 
 German) I have used French measurements. I have adopted these 
 designations not merely on account of their greater convenience, but 
 also because they have acquired historical celebrity from the important 
 labors both of the elder and younger Herschel in England, and of the 
 latter at Feldhausen, at the Cape of Good Hope. 
 
 t See Schumacher's Astr. Nachr., No. 371 and 611. Cauchoix and
 
 TELESCOPES. 65 
 
 object-glasses of 15 inches in diameter, and a focal length 
 of 22-5 feet. The heliometer at the Konigsberg Observa- 
 tory, which continued for a long time to be the largest in 
 existence, has an aperture of 6'4 inches in diameter. This 
 instrument has been rendered celebrated by the memorable 
 labors of Bessel. The well-illuminated and short dyalitic 
 refractors, which were first executed by Plosl in Vienna : 
 and the advantages of which were almost simultaneously 
 recognized by Rogers in England, are of sufficient merit to 
 warrant their construction on a large scale. 
 
 During this period, to the efforts of which I have refer- 
 red, because they exercised so essential an influence on the 
 extension of cosmical views, the improvements made in in- 
 struments of measurement (zenith sectors, meridian circles, 
 and micrometers) were as marked in respect to mechanics as 
 they were to optics and to the measurement of time. Among 
 the many names distinguished in modern times in relation 
 to instruments of measurement, we will here only mention 
 those of Ramsden, Troughton, Fortin, Reichenbach, Gam- 
 bey, Ertel, Steinheil, Repsold, Pistor, and Oertling ; in rela- 
 tion to clironometers and astronomical pendulum clocks, we 
 may instance Mudge, Arnold, Emery, Earnshaw, Breguet, 
 .Rirgens^n, Kessels, "Winnerl, and Tiede ; while the noble la- 
 Ws of \Yilliam and John Herschel, South, Struve, Bessel, 
 and Dawes, in relation to the distances and periodic motions 
 of the double stars, specially manifest the simultaneous per- 
 fection acquired in exact vision and measurement. Struve's 
 classification of the double stars gives about 100 for the num- 
 ber whose distance from one another is below 1", and 336 
 for those between 1" and 2" ; the measurement in every case 
 being several times repeated.* 
 
 During the last few years, two men, unconnected with 
 any industrial profession the Earl of Rosse, at Parson's 
 Town (about fifty miles west of Dublin), and Mr. Lassell, at 
 Starfield, near Liverpool, have, with the most unbounded 
 liberality, inspired with a noble enthusiasm for the cause of 
 science, constructed under their own immediate superintend- 
 ence two reflectors, which have raised the hopes of astron- 
 omers to the highest degree. t Lassell's telescope, which has 
 
 Lerebours have also constructed object-glasses of more than 13 - 3 inches 
 in diameter, and nearly 25 feet focal length. 
 
 * Struve, Stellarum duplicium el multiplicium Mensurce Micrometricee, 
 p. 2, 41. 
 
 t Mr. Airy has recently given a comparative description of the meth- 
 ods of constructing these two telescopes, including an account of the
 
 66 COSMOS. 
 
 an aperture only two feet in diameter, with a focal length 
 of twenty feet, has already been the means of discovering 
 one satellite of Neptune, and an eighth of Saturn, besides 
 which two satellites of Uranus have been again distinguish- 
 ed. The new colossal telescope of Lord Rosse has an aper- 
 ture of six feet, and is fifty-three feet in length. It is mount- 
 ed in the meridian between two walls, distant twelve feet 
 011 either side from the tube, and from forty-eight to fifty-six 
 feet in height. Many nebulae, which had been irresolvable 
 by any previous instruments, have been resolved into stellar 
 swarms by this noble telescope ; while the forms of other 
 nebulae have now, for the first time, been recognized in their 
 true outlines. A marvelous effulgence is poured forth from 
 the speculum. 
 
 The idea of observing the stars by daylight with a tele- 
 scope first occurred to Morin, who, with Gascoigne (about 
 1638, before Picard and Auzout), combined instruments of 
 measurement with the telescope. Morin himself says,* "It 
 was not Tycho's great observations in reference to the posi- 
 tion of the fixed stars, when, in 1582, twenty-eight years 
 before the invention of the telescope, he was led to compare 
 Venus by day with the sun, and by night with the stars," 
 but " the simple idea that Arcturus and other fixed stars 
 might, like Venus, when once they had been fixed in the 
 field of the telescope before sunrise, be followed through the 
 heavens after the sun had risen, that led him to a discovery 
 which might prove of importance for the determination of 
 longitude at sea." No one was able before him to distin- 
 guish the fixed stars in the presence of the sun. Since the 
 
 mixing of the metal, the contrivances adopted for casting and polishing 
 the specula and mounting the instruments. Abatr. of the Astr. Soc., 
 vol. ix., No. 5, March, 1849. The effect of Lord Rosse's six feet metal- 
 lic reflector is thus referred to (p. 120): "The astronomer royal, Mr. 
 Airy, alluded to the impression made by the enormous light of the tel- 
 escope ; partly by the modifications produced in the appearances of 
 nebulas already figured, partly by the great number of stars seen even 
 at a distance from the Milky Way, and partly from the prodigious brill- 
 iancy of Saturn. The account given by another astronomer of the ap- 
 pearance of Jupiter was, that it resembled a coach-lamp in the tele- 
 scope; and this well expresses the blaze of light which is seen in the 
 instrument." Compare also Sir John Herschel, Oull. of Astr., 870. 
 " The sublimity of the spectacle afforded by the magnificent reflecting 
 telescope constructed by Lord Rosse of some of the larger globular clus- 
 ters of nebulae, is declared by all who have witnessed it to be such as 
 no words can express. This telescope has resolved or rendered resolv- 
 able multitudes of nebula? which had resisted all inferior powers." 
 * Delambre, Hist, de V Astr on. Moderne, t. ii., p. 255.
 
 TELESCOPES. 67 
 
 employment, by Homer, of great meridian telescopes in 1691, 
 observations of the stars by day have been frequent and fruit- 
 ful in results, having been, in some cases, advantageously 
 applied to the measurement of the double star's. Struve 
 states* that he has determined the smallest distances of ex- 
 tremely faint stars in the Dorpat refractor, with a power of 
 only 320, in so bright a crepuscular light that he could read 
 with ease at midnight. The polar star has a companion of 
 the ninth magnitude, which is situated at only 18" distance : 
 it was seen by day in the Dorpat refracting telescope by 
 Struve and Wrangel,f and was in like manner observed on 
 one occasion by Encke and Argelander. 
 
 Many conjectures have been hazarded regarding the cause 
 of the great power of the telescope at a time when the dif- 
 fused light of the atmosphere, by multiplied reflection, ex- 
 erts an obstructing action.^ This question, considered as an 
 
 * Strove, Metis. Microm., p. xliv. 
 
 t Schumacher's Jahrbuchfur 1839, s. 100. 
 
 j La lumiere atmospherique diffuse ne peut s'expliquer par le reflet 
 des rayons solaires sur la surface de separation des couches de difleren- 
 tes densites dont on suppose 1'atmosphere composee. En eflet, suppo- 
 sons le soleil place a 1'horizon, les surfaces de separation dans la direc- 
 tion du zenith seraient horizontales, par consequent la reflexion serait 
 horizontale aussi, et nous ne verrions aucune lumiere au zenith. Dana 
 la supposition des couches, aucun rayon ne nous arriverait par voie 
 d'une premiere reflexion. Ce ne seraient que les reflexions multiples 
 qui pourraient agir. Done pour expliquer la lumiere diffuse, il faut se 
 figurer 1'atmosphere composee de molecules (spheriques, par exemple) 
 dont chacune uonne une image du soleil a peu pres comme les boulea 
 de verres que nous plasons dans nos jardius. L'air pur est bleu, par- 
 ceque d'apres Newton, les molecules de 1'air ont Vepaisseur qui convi- 
 ent a la reflexion des rayons bleus. II est done naturel que les petites 
 images du soleil que de tous cotes reflechissent les molecules sphe- 
 riques de 1'air et qui sont la lumiere diffuse aient une teinte bleue : 
 mais ce bleu n'est pas du bleu pur, c'est uu blanc dans lequel le bleu 
 predomine. Lorsque le ciel n'est pas dans toute sa purete et que 1'air 
 est me!6 de vapeurs visibles, la lumiere diffuse resoit beaucoup de 
 blanc. Comme la lune est jaune, le bleu de 1'air pendant la nuit est un 
 peu verdatre, c'est-a-dire, melange de bleu et de jaune." 
 
 " We can not explain the diffusion of atmospheric light by the reflec- 
 tion of solar rays on the surface of separation of the strata of different 
 density, of which we suppose the atmosphere to be composed. In fact, 
 if we suppose the sun to be situated on the horizon, the surfaces of sep- 
 aration in the direction of the zenith will be horizontal, and consequent- 
 ly the reflection would likewise be horizontal, and we should not be 
 able to see any light at the zenith. On the supposition that such strata 
 exist, no ray would reach us by means of direct reflection. Repeated 
 reflections would be necessary to produce any effect. In order, there- 
 fore, to explain the phenomenon of diffused light, we must suppose the 
 atmosphere to be composed of molecules (of a spherical form, for in
 
 68 COSMOS. 
 
 optical problem, excited the strongest interest in the mind of 
 Bessel, whose too early death was so unfortunate for the 
 cause of science. In his long correspondence with myself, he 
 frequently reverted to this subject, admitting that he could 
 not arrive at any satisfactory solution. 1 feel confident it 
 will not be unwelcome to my readers if I subjoin, in the 
 form of a note, some of the opinions of Arago,* as expressed 
 
 stance), each of which presents an image of the sun somewhat in the 
 game manner as an ordinary glass ball. Pure air is blue, because, ac- 
 cording to Newton, the molecules of the air have the thickness neces 
 sary to reflect blue rays. It is therefore natural that the small images of 
 the sun, reflected by the spherical molecules of the atmosphere, should 
 present a bluish tinge ; this color is not, however, pure blue, but white, 
 in which the blue predominates When the sky is not perfectly pure 
 and the atmosphere is blended with perceptible vapors, the diffused 
 light is mixed with a large proportion of white. As the moon is yellow, 
 the blue of the air assumes somewhat of a greenish tinge by night, or, 
 in other words, becomes blended with yellow." MSS. of 1847. 
 
 * D'vn des Effcts dcs Lunettes sur la Visibility des etoiles. (Lctlre de 
 M. Arago a M. de Humboldt en Die., 1847.) 
 
 " L'ceil n'est done que d'une sensibilite circonscrite, bornee. Quand 
 la lumiere qui frappe la retine, n'a pas assez d'intensite, 1'oeil ne sent 
 rien. C'est par un manque d'intensite que beaucoup d.' etoiles, mdme 
 dans les nuits les plus profondes echappent a nos observations. Les lu- 
 nettes ont pour effet, quant aux etoiles, d'augmenter 1'intensite de 1'image. 
 Le faisceau cylindrique de rayons paralleles venant d'une etoile, qui 
 s'appuie sur la surface de la lentille objective, et qui a cette surface cir- 
 culaire pour base, se trouve considerablement resserre a la sortie de la 
 lentille oculaire. Le diametre du premier cylindre est au diametre 
 du second, comme la distance focale de 1'objectif est a la distance fo- 
 cale de Poculaire, ou bieu comme le diametre de 1'objectif est au dia- 
 metre de la portion d'oculaire qu'occupe le faisceau emergent. Les iii- 
 tensites de lumiere dans les deux cylindres en question (dans les deux 
 cylindres, incident et emergent) doiveut etre entr'elles comme les eten- 
 dues superficielles des bases. Ainsi la lumiere emergente sera plus con- 
 densee, plug intense que la lumiere naturelle tombant sur 1'objectif, dans 
 le rapport de la surface de cet objectif a la surface circulaire de la base 
 du faisceau emergent. Le faisceau Emergent, quand la lunette grosrit, 
 etant plus etroit que le faisceau cylindrique qui tombe sur 1'objectif, il 
 est evident que la pupille, quelle que soit son cMverture, recueillera plus 
 de rayons par 1'intermediaire de la lunette que sans elle. La lunette 
 augmentera done toujours 1'intensite de la lumiere des ttoilei. 
 
 " Le cas le plus favorable, quant a 1'effet des lunettes, est evidemment 
 celui ou 1'ceil re9oit la totalite du faisceau emergent, le cas ou ce fais- 
 ceau a moins de diametre que la pupille. Alors toute la lumiire que 
 1'objectif embrasse, concourt, par 1'entremise du telescope, a la forma- 
 tion de 1'image. A 1'ceil nu, au contraire, une portion seule de cetto 
 meme lumiere est mise a profit ; c'est la petite portion que la surface 
 de la pupille decoupe dans le faisceau incident naturel. L'intensit^ do 
 1'image telescopique d'une etoile est done & 1'intensite de 1'image & 
 1'ceil nu, comme la surface de 1'objectif est a celle de la pupille. 
 
 " Ce qui precede est relatif a la visibilite d'uu seul point, d'uno seulo
 
 TELESCOPES. 69 
 
 in one of the numerous manuscripts to which I was permit- 
 ted free access during my frequent sojourn in Paris. Ac- 
 
 etoile. Venons a 1'observation d'un objet ayant des dimensions an 
 gulairw seusibles, a 1'observation d'une planete. Dans les cas les plus 
 lavorables, c'est-a-dire lorsque la pupille re^oit la totalite du pinceaa 
 emergeut, 1'intensite de 1'image de ckaque point de la planete se calcu- 
 lera par la proportion que nous venons de donner. La quantite totalt 
 de lumiere concourant a former V ensemble de 1'image a Tceil nu, sera 
 done aussi a la quantite totale de lumiere qui forme 1'image de la pla- 
 nete A 1'aide d'uue lunette, comme la surface de la pupille est 4 la sur- 
 face de 1'obiectif. Les intensites comparatives, non plus de pointe 
 isoles, mais des deux images d'une planete, qui se forment sur la retina 
 a 1'oeil nu, et par I'iutermediaire d'une lunette, doivent evidemment 
 diminuer proportionuellement aux etendues superficielles de ces deux im- 
 ages. Les dimensions lineaires des deux images sont entr'elles comme 
 le diametre de 1'objectif est au diametre du faisceau emergent. Le 
 nouibre de fois que la surface de 1'image amplifiee surpasse la surface 
 de 1'image a 1'oeil nu, s'obtiendra done en divisant le carre du diametre 
 de 1'objeclifpa.r le carre du diametre du faisceau Emergent, ou bien la sur- 
 face de I'objeclif par la surface de la base circulaire du faisceau emergent. 
 " Nous avons deja obtenu le rapport des quantites totales de lumiere 
 qui engendrent les deux images d'une planete, en divisant la surface de 
 1'objectif par la surface de la pupille. Ce nombre est plus petit que le 
 quotient auquel on arrive en divisant la surface de 1'objectif par la sur- 
 face du faisceau Emergent. II en resulte, quant aux planetes, qu'une 
 lunette lait moins gagtier en intensite de lumiere, qu'elle ne fait perdre 
 en agrandissaut la surface des images sur la retine; 1'intensite de ces 
 images doit done aller continuellement en s'afiaiblissant a mesure que 
 le pouvoir amplificatif de la lunette ou du telescope s'accroit. 
 
 " L'atmosphere peut etre consideree comme une planete a dimen- 
 sions indefiuies. La portion qu'on en verra dans une lunette, subira 
 done aussi la loi d'affaiblissement que nous venons d'indiquer. Le rap* 
 port entre 1'intensite de la lumiere d'une planete et le champ de lumiere 
 atinospherique a travers lequel on la verra, sera le memo a 1'ceil nu et 
 dans les lunettes de tous les grossissements, de toutes les dimensions. 
 Les lunettes, sous le rapport de Vintensite, ne favorisent done pas la visi- 
 bilite des planetes. 
 
 " II n'eu est point ainsi des etoiles. L'intensite de 1'image d'une etoile 
 est plus forte avec une lunette qu'a I'o3il nu ; au contraire, le champ de 
 la vision, uuiformement eclaire dans les deux cas par la lumiere atmos- 
 pherique, est plus clair a I'osil nu que dan la lunette. II y a done deux 
 raisons, sans sortir des considerations d'intensite, pour que dans une lu- 
 
 ette de 1'image de 1'etoile predomine sur celle de 1'atmosphere, nota- 
 
 lement plus qu'a I'oail nu. 
 
 " Cette predominance doit aller graduellement en augmentant avec 
 le grossissement. En efiet, abstraction faite de certaine augmentation 
 du diametre de 1'etoile, consequence de divers effets de diffraction ou 
 d 1 'interferences, abstraction faite aussi d'une plus forte reflexion que la 
 lumiere subit sur les surfaces plus obliques des oculaires de tres courts 
 foyers, V intensite dc la lumiere de Vetoile est constante tant que 1'ouver- 
 ture de 1'objectif ne varie pas. Comme ou 1'a vu, la clarte du champ 
 de la lunette, au contraire, diminue sans cesse a mesure que le pouvoir 
 amplificatif s'accroit. Done toutes autres circoustances restant egales, 
 uue etoile sera d'autant p. 1 '!* visible, sa predouiiuence sur la lumiere tin
 
 70 COSMOS. 
 
 cording to the ingenious explanation of my friend, high rnag 
 nify ing powers facilitate the discovery and recognition of the 
 
 champ du telescope sera d'autaut plus tranchee qu'on lera usage d'un 
 grossissemont plus fort." 
 
 " The eye is endowed with only a limited sensibility ; for when the 
 light which strikes the retina is not sufficiently strong, the eye is not 
 sensible of any impression. In consequence of deficient intensity, many 
 stars escape our observation, even in the darkest nights. Telescopic 
 glasses have the effect of augmenting the intensity of the images of the 
 stars. The cylindrical pencil of parallel rays emanating from a star, 
 and striking the surface of the object-glass, on whose circular surface it 
 rests as on abase, is considerably contracted on emerging from the eye- 
 piece. The diameter of the first cylinder is to that of the second as 
 the focal distance of the object-glass is to the focal distance of the eye- 
 piece, or as the diameter of the object-glass is to the diameter of tho 
 part of the eye-piece covered by the emerging rays. The intensities 
 of the light in these two cylinders (the incident and emerging cylin- 
 ders) must be to one another as the superficies of their bases. Thus, 
 the emerging light will be more condensed, more intense, than the nat- 
 ural light falling on the object-glass, in the ratio of the surface of this 
 object-glass to the circular surface of the base of this emerging pencil. 
 As the emerging pencil is narrower in a magnifying instrument than the 
 cylindrical pencil falling on the object-glass, it is evident that the pupil, 
 whatever may be its aperture, will receive more rays, by the interven- 
 tion of the telescope, than it could without. The intensity of the light 
 of the stars will, therefore, always be augmented when seen through a 
 telescope. 
 
 " The most favorable condition for the use of a telescope is undoubt 
 edly that in which the eye receives the whole of the emerging rays, 
 and, consequently, when the diameter of the pencil is less than that of 
 the pupil. The whole of the light received by the object-glass then co- 
 operates, through the agency of the telescope, in the' formation of the 
 image. In natural vision, on the contrary, a portion only of this light 
 is rendered available, namely, the small portion which enters the pupil 
 naturally from the incident pencil. The intensity of the telescopic im 
 age of a star is, therefore, to the intensity of the image seen with the 
 naked eye, as the surface of the object-glass is to that, of the pupil. 
 
 " The preceding observations relate to the visibility of one point or 
 one star. We will now pass on to the consideration of an o*bject having 
 sensible angular dimensions, as, for instance, a planet. Under the most 
 favorable conditions of vision, that is to say, when the pupil receives 
 the whole of the emerging pencil, the intensity of each point of the plan- 
 et's image may be calculated by the proportions we have already given. 
 The total quantity of light contributing to form the whole of the image, 
 as seen by the naked eye, will, therefore, be to the total quantity of the 
 light forming the image of the planet by the aid of a telescope, as the 
 surface of the pupil is to the surface of the object-glass. The compar- 
 ative intensities, not of mere isolated points, but of the images of a plan- 
 et formed respectively on the retina of the naked eye, and by the in- 
 tervention of a telescope, must evidently diminish proportionally to the 
 superficial extent of these two images. The linear dimensions of the 
 two images are to one another as the diameter of the object-glass is to 
 that of the emerging pencil. We therefore obtain the number of times 
 that the surface of the magnified image exceeds the surface of the iui-
 
 TELESCOPES. 71 
 
 fixed stars, since they convey a greater quantity of intense 
 light to the eye without perceptibly enlarging the image ; 
 
 age when seen by the naked eye by dividing the square of the diameter 
 of the object-glass by the square of the diameter of the emerging pencil, or 
 rather the surface of the abject-glass by the surface of the circular bate 
 of the emerging pencil. 
 
 " By dividing the surface of the object-glass by the surface of the pu 
 pil, \ve have already obtained the ratio of the total quantities of light 
 produced by the two images of a planet. This number is lower than 
 the quotient which we obtain by dividing the surface of the object- 
 glass by the surface of the emerging pencil. It follows, therefore, with 
 respect to planets, that a telescope causes us to gain less in intensity of 
 light than is lost by magnifying the surface of the images on the retina; 
 the intensity of these images must therefore become continually fainter, 
 in proportion as the magnifying power of the telescope increases. 
 
 " The atmosphere may be considered as a planet of indefinite dimen- 
 sions. The portion of it that we see in a telescope will therefore also 
 be subject to the same law of diminution that we have indicated. The 
 relation between the intensity of the light of a planet and the field of at- 
 mospheric light through which it is seen, will be the same to the naked 
 eye and in telescopes, whatever may be their dimensions and magnify- 
 ing powers. Telescopes, therefore, do not favor the visibility of planets 
 in respect to the intensity of their light. 
 
 " The same is* not the case with respect to the stars. The intensity 
 of the image of a star is greater when seen with the telescope than with 
 the naked eye ; the field of vision, on the contrary, uniformly illumined 
 in both cases by the atmospheric light, is clearer in natural than in tel- 
 escopic vision. There are two reasons, then, which, in connection with 
 the consideration of the intensity of light, explain why the image of a 
 star preponderates in a telescope rather than in the naked eye over that 
 of the atmosphere. 
 
 " This predominance must gradually increase with the increased 
 magnifying power. In fact, deducting the constant augmentation of 
 the star's diameter, consequent upon the different effects of diffraction 
 or interference, and deducting also the stronger reflection experienced 
 by the light on the more oblique surfaces of ocular glasses of short focal 
 lengths, the intensity of the light of the star is constant as long as the 
 aperture of the object-glass does not vary. As we have already seen, 
 the brightness of the field of view, on the contrary, diminishes inces- 
 santly in the same ratio in which the magnifying power increases. All 
 other circumstances, therefore, being equal, a star will be more or less 
 visible, and its prominence on the field of the telescope will be more 
 or less marked, in proportion to the magnifying powers we employ." 
 Arago, Manuscript 0/1847. 
 
 I will further add the following passage from the Annuaire du Bu- 
 reau des Long, pour 1846 (Notices Scient. par M. Arago), p. 381 : 
 
 " L'experience a montre que pour le commun des hommes, deux 
 espaces eclaires et contigus ne se distingueut pas 1'un de Pautre, a inoius 
 que leurs intensites comparatives ne presentent, au minimum, une dif 
 ference de $$. Quand une lunette est tournee vers le firmament, son 
 champ semble nniformement eclaire : c'est qu' alors il existe, dans un 
 plan passant par le foyer et perpendiculaire a 1'axe de 1'objectiC un 
 image indefinie de la region atmospherique vers laquelle la lunette est 
 dirigee. Supposous qu'un astre. c'est-a-dire uu objet situe bieii au-
 
 72 COSMOS. 
 
 while, in accordance with another law, they influence the 
 aerial space on which the fixed star is projected. The tele- 
 scope, by separating, as it were, the illuminated particles of 
 air surrounding the object-glass, darkens the field of view, 
 and diminishes the intensity of its illumination. We are en- 
 abled to see, however, only by means of the difference be- 
 tween the light of the fixed star and of the aerial field or the 
 mass of air which surrounds the star in the telescope. Plan- 
 etary disks present very different relations from the simple 
 ray of the image of a fixed star ; since, like the aerial field 
 (fair aerienne), they lose in intensity of light by dilatation 
 in the magnifying telescope. It must be further observed, 
 that the apparent motion of the fixed star, as well as of the 
 planetary disk, is increased by high magnifying powers. 
 This circumstance may facilitate the recognition of objects 
 by day, in instruments whose movements are not regulated 
 paralactically by clock-work, so as to follow the diurnal mo- 
 tion of the heavens. Different points of the retina are suc- 
 cessively excited. " Very faint shadows are not observed," 
 Arago elsewhere remarks, " until we can give them motion." 
 
 In the cloudless sky of the tropics, during the driest sea- 
 son of the year, I have frequently been able to find the pale 
 disk of Jupiter with one of Dollond's telescopes, of a magni- 
 fying power of only 95, when the sun was already from 15 
 to 18 above the horizon. The diminished intensity of the 
 light of Jupiter and Saturn, when seen by day in the great 
 Berlin refractor, especially when contrasted with the equally 
 reflected light of the inferior planets, Venus and Mercury, 
 frequently excited the astonishment of Dr. Galle. Jupiter's 
 delA de 1'atmosphere, se trouve dans la direction de la lunette : son 
 image ne sera visible qu'autant qu'elle augmentera de ^Vi au moins, 
 1'intensite de la portion de 1'image focale indifinie de 1'atmosphere, sur 
 laquelle sa propre image limitfe ira se placer. Sans cela le champ 
 visuel continuera a paraitre partout de la meme intensity." 
 
 " Experience has shown that, in ordinary vision, two illuminated and 
 contiguous spaces can not be distinguished from each other unless their 
 comparative intensities present a minimum difference of inj-th. When 
 a telescope is directed toward the heavens, its field of view appears 
 uniformly illumined: there then exists in a plane passing through the 
 focus, and perpendicular to the axis of the object-glass, an indefinite im- 
 age of the atmospheric region toward which the instrument is pointed. 
 If we suppose a star, that is to say, an object very far beyond the atmos- 
 phere, situated in the direction of the telescope, its image will not be 
 visible except it exceed, by at least g^-th, the intensity of that portion 
 of the indefinite focal image of the atmosphere on which its limited 
 proper image is thrown. Otherwise the visual field will continue to 
 appear esery where of the same intensity. '
 
 SCINTILLATION OF THE STARS. 73 
 
 occultations have occasionally been observed by daylight, 
 with the aid of powerful telescopes, as in 1792, t by Flau- 
 gergues, and in 1820, by Struve. Argelander (on the 7th 
 of December, 1849, at Bonn) distinctly saw three of the sat 
 ellites of Jupiter, a quarter of an hour after sunrise, with 
 one of Fraunhofer's five-feet telescopes. He was unable to 
 distinguish the fourth ; but, subsequently, this and the other 
 satellites were observed emerging from the dark margin of 
 the moon, by the assistant astronomer Schmidt, with the 
 eight-feet heliometer. The determination of the limits of 
 the telescopic visibility of small stars by daylight, in differ- 
 ent climates, and at different elevations above the sea's level, 
 is alike interesting in an optical and a meteorological point 
 of view. 
 
 Among the remarkable phenomena whose causes have been 
 much contested, in natural as well as in telescopic vision, we 
 must reckon the nocturnal scintillation of the stars. Accord- 
 ing to Arago's investigations, two points must be specially dis- 
 tinguished in reference to this phenomenon* firstly, change 
 
 * The earliest explanations given by Arago of scintillation occur in 
 the appendix to the 4th book of my Voyage avx Regions Equinoxialet, 
 torn, i., p. 623. I rejoice that I am able to enrich this section on nat- 
 ural and telescopic vision with the following explanations, which, for 
 the reasons already assigned, I subjoin in the original text. 
 
 Des causes de la scintillation des ttoiles. 
 
 lation, c'est le changement de couleur. Ce changement est beaucoup 
 plus frequent que 1'observation ordinaire 1'indique. En effet, en agi- 
 tant la lunette, on transforme 1'image dans uue ligne ou un cercle, et 
 tous les points de cette ligne ou de ce cercle paraissent de couleure dif- 
 ferentes. C'est la resultante de la superposition de toutes ces images 
 que 1'on voit, lorsqu'on laisse la lunette immobile. Les rayons qui so 
 reunissent au foyer d'une lentille, vibrent d'accord ou en disaccord, 
 s'ajoutent ou se detruisent, suivant que les couches qu'ils ont traver- 
 sees, ont telle ou telle refringence. L'ensemble des rayons rouges petit 
 se detruire seul, si ceux de droite et de gauche, et ceux de haut et de 
 bas, ont traverse des milieux inegalement refringents. Nous avons dit 
 seul, parceque la difference de refringence qui correspond a la destruc 
 tion du rayon rouge, n'est pas la meme que cella qui amene la destruc- 
 tion du rayon vert, et reciproquement. Main tenant, si des rayons rou ges 
 sont detruits, ce qui reste sera le blanc moins le rouge, c'est-a-dire du 
 vert. Si le vert au contraire est detruit par interference, 1'image sera 
 du blanc moins le vert, c'est-a-dire du rouge. Pour expliquer pourquoi 
 les planetes a grand diametre ne scintillent pas ou tres peu, il faut se 
 rappeler que le disque peut tre consider^ comme une aggregation 
 d'^toiles ou de petits points qui scintillent isol^ment; mais les images 
 de differentes couleurs que chacun de ces points pris isol^ment don- 
 nerait, empietant les unes sur les autres, formeraient du blanc. Lors- 
 qu'on place un diaphragme ju un bouchou perce d'uii trou sur 1'objec- 
 VOL III. D
 
 74 COSMOS. 
 
 in the intensity of the light, from a sudden decrease to perfect 
 extinction and rekindling ; secondly, change of color. Both 
 
 tif d'une lunette, les etoiles acquiere'nt un disque entoure d'une serie 
 d'anneaux lumineux. Si 1'on enfonce 1'oculaire, le disque de 1'eioilo 
 augmente de diamctre, et il se produit dans son centre un trou obscur ; 
 si on 1'enfonce davantage, un point lumineux se substitue au point noir. 
 Un nouvel enfoncemeut donne naissance a un centre noir, etc. Pro 
 nons la lunette lorsque le centre de 1'image est noir, et visons a uno 
 toile qui ne sciatillo pas : le centre restera noir, comme il l'6tait au- 
 paravant. Si au contraire on dirige la lunette & une 4toile qui scintille, 
 on verra le centre de 1'image lumineux et obscur par intermittence. 
 Dans la position ou le centre de 1'image est occup6 par un point lumi- 
 neux, on verra ce point disparaltre et renaitre successivement. Cette 
 disparition ou reapparition du point central est la preuve directe de 
 I' interference variable des rayons. Pour bien concevoir 1'absence de 
 lumiere au centre de ces images dilatees, il faut se rappeler quo les 
 rayons regulierement refractes par 1'objectif ne se reunisseut et ne peu- 
 vent par consequent interferer qu'au foyer : par consequent les images 
 dilatees que ces rayons peuvent produire, resteraient toujours pleines 
 (sans trou). Si dans une certaine position de 1'oculaire un trou se pre- 
 sente au centre de 1'image, c'est que les rayons r6gulierement refrac- 
 ted inierferent avec des rayons diffractes sur les bords du diaphragme 
 circulaire. Le phenomene n'est pas constant, parceque les rayons qui 
 interferent dans un certain moment, n'interferent pas un instant apres, 
 lorsqu'ils ont traverse des couches atmospheriques dont le pouvoir r6- 
 fringent a varie. On trouve dans cette experience la preuve manifesto 
 du role que joue dans le ph^nomene de la scintillation 1'inegale refran- 
 gibilit^ des couches atmospheriques traversees par les rayons dont le 
 faisceau est tres etroit. II r^sulte de ces considerations que 1'explica- 
 tion des scintillations ne pent etre rattachee qu'aux phenomenes des 
 interference* lumineuses. Les rayons des etoiles, apres avoir traverse 
 nne atmosphere ou il existe des couches in^galement chaudes, inegale- 
 ment denses, inegalement humides, vont se reiinir au foyer d'une len- 
 tille, pour y former des images d'intensite et de couleurs perp6tuelle- 
 ment changeantes, c'est--dire des images telles que la scintillation les 
 presente. II y a aussi scintillation hors du foyer des lunettes. Les ex- 
 plications proposers par Galileo, Scaliger, Kepler, Descartes, Hooke, 
 Huygens, Newton et John Michell, que j'ai examin6 dans un tnemoife 
 presente a 1'Institut en 1840 (Comptes Rcndus, t. x., p. 83), sont inad- 
 missibles. Thomas Young, auquel nous devons les premieres lois des 
 interferences, a cru inexplicable le phenomene de la scintillation. La 
 faussete de 1'ancienne explication" par des vapeurs qui voltigent et d6- 
 placent, est deja prouvee par la circonstance que nous voyons la scin- 
 tillation des yeux, ce qui supposerait un deplacement d'une minute. 
 Les ondulations du bord du soleil sont de 4" a 5", et peut-etre des pie- 
 ces qui manquent, done encore effet de 1'interference des rayons." 
 
 On the causes of the scintillation of the stars. 
 
 " The most remarkable feature in the phenomenon of the stars' scin- 
 tillation is their change of color. This change is of much more frequent 
 occurrence than would appear from ordinary observation. Indeed, on 
 shaking the telescope, the image is transformed into a line or circle, and 
 nil the points of this line or circle appear of different colors. We havo 
 here the results of the superposition of all the images seen when the 
 toleacope is at rest. The rays united in the focus of a leas vibrate in
 
 SCINTILLATION OF THE STARS. 75 
 
 these alterations are more intense in reality than they appear 
 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 
 destroy ono 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 
 still 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 will be observed. If, while the center of the image is 
 black, we point the instrument to a star which does not scintillate, it 
 will remain bkck 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 shall 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 
 power 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 rays united in a 
 very narrow pencil." 
 
 " It follows from these considerations that scintillation mast necessa- 
 rily be referred to the phenomena of luminous interferences alone The 
 rays emanating from the stars, after traversing an atmosphere composed 
 of strata having different degrees 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 scin- 
 tillation. There is another form of scintillation, independent of the fo 
 cus of the telescope. The explanations of this phenomenon advanced
 
 76 COSMOS. 
 
 are once excited, they retain the impression of light which 
 they have received, so that the disappearance, obscuration 
 and change of color in 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 be followed by 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 (two 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 impart 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 does not seem to depend solely on their 
 altitude and apparent magnitude, but also on the nature of 
 their own light. Some, as for instancfe Vega, flicker less than 
 Arcturus and Procyon. The absence of scintillation in plan- 
 ets with larger disks is to be ascribed to compensation and to 
 the naturalizing mixture of colors proceeding from different 
 points of the disk. The disk is to be regarded as an aggregate 
 
 oy Galileo, Scaliger, Kepler, Descartes, Hooke, Huygens, Newton, and 
 John Michell, which I examined in a memoir presented to the Institute 
 in 1840 (Comptes Rendus, t. x., p. 83), are inadmissible. Thomas 
 Young, to whom we owe the discovery of 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 
 see scintillations with the naked eye, which presupposes a displace 
 ment of a minute. The undulations of the margin of the sun are from 
 4" to 5", and are perhaps owing to chasms or interruptions, and there- 
 fore also to the effect of interference of the rays of light." (Extrac/i 
 from Arago's MSS. of 1847.) 
 
 * See Arago, in the Annuaire pour 1831 p. 1C8.
 
 SCINTILLATION CP THE STARS. 77 
 
 of stars which 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, but 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 
 that, seeing 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 ! 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 (rrpdf 6e rouf 
 fj,VovTa$), the eye acquires a tremulous motion, owing to the 
 distance and the effort." 
 
 In the time of Galileo, between 1572 and 1604 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.J In the 
 Chinese Records of the newly appeared stars, according to 
 the great collection of Ma-tuan-lin, their strong scintillation 
 is occasionally mentioned. 
 
 The 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 scintillationis, in Kepler, De Stella nova in pede Serpcntara, 
 1606, cap. xviii., p. 92-97.
 
 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 iny delineations of tropical scenery to this charac- 
 teristic, which was also noticed by the accurate observers La 
 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 which 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 garua (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 light; but this difference is most 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 
 connection 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 60 or 70, when Saus- 
 sure's hair-hygrometer stood at 85, 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 
 during the thin yellowish red mist which tinges the heavens 
 
 * Lettre de M. Garcin, Dr. en Med. a M. de RSavmur, in Hist, de 
 TAcadtmie Royale des Sciences,' Annie 1743, p. 28-32.
 
 SCINTILLATION OF THE STARS. 79 
 
 Bhort\y before an earthquake. These observations only refer 
 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 Organum 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 the 
 
 * See Voyage aux Regions Equin., t. i., p. 511 and 512, and t. ii., p. 
 202-208; also my Views of Nature, p. 16, 138. 
 
 En Arabie, de meme qu'a Bender-Abassi, port fameux du Golfe 
 
 Persique, 1'air est parfaitement serein presque toute 1'annee. Le prin- 
 temps, l'et, et 1'automne se passent, sans qu'on y voie la moindre rosee. 
 Dans ces raemes temps tout le monde couche dehors sur le haut dea 
 maisons. Quand on est ainsi couche, il n'est pas possible d'exprimer le 
 plaisir qu'on prend 4 contempler la beaute du ciel, 1'eclat des etoiles. 
 C'est une lumiere pure, ferme et eclatante, sans 4tincellement. Ce n'est 
 qu'au milieu de 1'hiver que la scintillation, quoique tres foible, s'y fait 
 apercevoir." 
 
 " In Arabia," says Garciu, "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. During 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 degree of scintillation is observed." Garcin, in Hist, dt 
 PAcad. de* Sc., 1743, p. 30.
 
 80 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 reflected solar light was 
 first measured by Homer (November, 1675) by comparing 
 the periods of occultation of Jupiter's satellites ; while the 
 velocity of the 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 percei ved as at the actual 
 moment of its existence, or rather a little 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 true and apparent time, was subsequently completely set 
 at rest when we considered . . . ." The works of Francis Bacon, vol. 
 xiv., Lond., 1831 (Novum Organutn), 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 Longitudes pour 1842, p. 337-343. " L'observation attentive des 
 phases d'Algol i 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 certames epoques interme'diares entre celles qui correspondent 
 aux deux etats extremes, quand Algol, soil en diminuant, soit en aug- 
 mentant d'dclat, 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 
 slow ; it is, on the contrary, rapid at certain intermediate epochs be- 
 tween those corresponding to the two extremes, when Algol, either di 
 minishing or increasing in Brightness, appears of the third magnitude.
 
 SCINTILLATION OF THE STARS. 81 
 
 and fruitless experiments with two alternately obscured lan- 
 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 observations of Jupiter's satel- 
 lites, at 14' 7", then 11' ; Cassini at 14' 10" ; while Newton* 
 
 * Newton, Optics, 2d ed. (London, 1718), p. 325. " Light moves 
 from the sun to us in seven or eight minutes of time." Newton com- 
 pares the velocity of sound (1140 feet in 1") with that of light. As, 
 from observations on the occultations of Jupiter's satellites (Newton's 
 death occurred about half a year before Bradley's discovery of aberra- 
 tion), he calculates that light passes from the sun to the earth, a distance, 
 as he assumed, of 70 millions of miles, in 7' 30" ; this result yields a ve- 
 locity of light equal to 155,555| miles in a second. The reduction of 
 these [ordinary] to geographical miles (60 to 1) is subject to variations 
 according as we assume the figure of the earth. According to Encke's 
 accurate calculations in the Jahrbuch fur 1852, an equatorial degree is 
 equal to 69-1637 English miles. According to Newton'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 ordinary miles, in a second of time ; 
 therefore too much, as before we had too h'ttle. It is certainly very re- 
 markable, although the circumstance has been overlooked by Delambre 
 (Hist, de V Astronomic 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 
 the time assigned for the passage of light over the semi-diameter of the 
 earth's orbit continued to vacillate between the very high amounts of 
 11' and 14' 10", from the period of Earner's discovery in 1675 to the be- 
 ginning of the eighteenth century. The first treatise in which RSmer, 
 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 VAcad. de 1666-1699, torn, 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, 
 different satellites presented different results. Du Hamel, secretary to 
 the Paris Academy (Regies Scientiarum Academics Historia, 1698, p. 
 143), gave from 10 to 11 minutes, seventeen years after RSmer had left 
 Pans, although he refers to him ; yet we know, through Peter Horre- 
 bow (Basis Astronomic sive Trvluum Roemerianum, 1735, p. 122-129), 
 that Romer adhered to the result of 11', when in 1704, six years before 
 his death, he purposed bringing out a work on the velocity of light; 
 the same was the case with Huygens (Tract, de Lumine, 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 Jupiter pro pcragrando diametri semissi. The error waa 
 therefore on the increase. (Compare Horrebow, Triduum, p. 129 ; Gas- 
 sini, Hypotheses et Satellites de Jupiter iu the M6m de VAcad., 166G- 
 
 D 2
 
 82 COSMOS. 
 
 approximated very remarkably to the truth when he gave 
 it at 7' 30". Delambre,* who did not take into account any 
 of the observations made in his own time, with the excep- 
 tion of those of the first satellite, found 8' 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 Bi- 
 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,t 
 that the former of these numbers should be considerably in- 
 
 1699, torn, viii., p. 435, 475; Delambre, Hist, de VAstr. Mod., toin. ii., 
 p. 751, 782 ; Du Hamel, Physica, p. 435.) 
 
 * Delambre, Hist, de VAstr. Mod., torn, ii., p. 653. 
 
 t Reduction of Bradley's Observations at Kew and Wangled, 1836, p. 
 22; Schumacher's Astr. Nachr., bd. xiii., 1836, No. 309 (compare Mis- 
 cellaneous Works and Correspondence of the Rev. James Bradley, by 
 Prof. Rigaud, Oxford, 1832). On the mode adopted for explaining ab- 
 erration in accordance with the theory of undulatory light, see Doppler, 
 in iheAbhl. derKon. bohmischen 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 century 
 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 I' Astr. Moderns, torn, ii., p. 
 616.) Picard had nearly ascertained the velocity of direct light before 
 his pupil, R6mer, made known that of reflected light. 
 
 \ Schum., Astr. Nachr , bd. xxi., 1844, No. 484 ; Struve, Eludes d'Astr. 
 Stellaire, p. 103, 107 (compare Cosmos, vol. i., p. 153, 154). The re- 
 suit given in the Annuaire pour 1842, p 87, for the velocity of light 
 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 01 the polar star and that of its companion, and on the doubts 
 recently expressed by Struve, see Madler, Astronomic, 1849, s. 393. 
 William 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 
 milei in a second. (Mem. of the Astren. Soc., vol. iv., Part i.. p. 68.)
 
 SCINTILLATION OF THE STARS. 83 
 
 creased. The result of these important observations gave 
 8' 17"'78 ; from which, with a constant of aberration of 
 20"-4451, and Encke's correction of the sun's parallax in the 
 year 1835, together with his determination of the earth's 
 radius, as given in his Astronomisches Jahrbuch fur 1852, 
 we obtain 166,196 geographical miles for the velocity of 
 light in a second. The probable error in the velocity seems 
 scarcely to amount to eight geographical miles. Struve's 
 result for the time which light requires to pass from the sun 
 to the earth differs about 7TTr 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 which it ema- 
 nated. A disk having 720 teeth, which 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 T ^ 7 ?th 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 light in the 
 variable stars a subject to which I shall revert in the se- 
 
 * Fizean gives his result in leagues, reckoning 25 (and consequently 
 4452 metres) to the equatorial degree. He estimates the velocity of 
 light at 70,000 such leagues, or about 210,000 miles in the second. On 
 the earlier experiments of Fizeau, see Comptes Rendvt, torn, xxix., p. 92. 
 In Moigno, Rupert. tfOptique 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 by 
 Busch.
 
 84 COSMOS. 
 
 quel led Arago to the result that, according to the undu- 
 latory 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, les 
 rayons de differentes couleurs, les rayons dont les ondulations sont ine- 
 gales, doivent neanmoins se propager dans I'ether avec la meme vi- 
 tesse. H n'y a pas de difference a cet egard entre la propagation des 
 ondes sonores, lesquelles se propagent dans 1'air avec la memo rapidite. 
 Cette 6galit6 de propagation des ondes sonores est bien etablio experi- 
 mentalement par la similitude d'effet que produit une musique donnee 
 & toutes distances du lieu ou 1'on 1'execute. La principale difficulte, 
 je dirai 1'unique difficulte, qu'on cut elev6e contre le systeme des ondes, 
 consistait done a expliquer, comment la vitesse de propagation des ray- 
 ons de differentes couleurs dans les corps differents pouvait etre dissem- 
 blable et servir a rendre compte de 1'inegalite de refraction de ces ray- 
 ons ou de la dispersion. On a montre r6cemment que cette difBculte 
 n'est pas insurmontable ; qu'on peut constituer I'ether dans les corps 
 inegalement denses de maniere que des rayons a ondulations dissem- 
 blables s'y propagent avec des vitesses inegales : reste a determiner, si 
 les conceptions des geometres a cet egard sont conformes a la nature 
 des choses. Voici les amplitudes des ondulations deduites experimen- 
 talement d'une serie de fails relatif aux interferences : 
 
 mm. 
 
 Violet 0-000423 
 
 Jaune 0-000551 
 
 Rouge 0-000620 
 
 La vitesse de transmission des rayons de diffe>entes couleurs dans le 
 espaces celestes est la meme dans le systeme des ondes et tout-a-fait 
 Ind^pendante de 1'etendue ou de la vitesse des ondulations." 
 
 " According to the mathematical theory of a system of waves, rayi 
 of different colors, having unequal undulations, must nevertheless be 
 transmitted through ether with the same velocity. There is no differ- 
 ence hi this respect from the mode of propagation of waves of sound 
 which are transmitted through the atmosphere with equal velocity. 
 This equality of transmission in waves of sound may be well demon 
 strated experimentally by the uniformity of effect produced by music 
 at all distances from the source whence it emanates. The principal, I 
 may say the only objection, advanced against the 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 thd "^fraction of the 
 rays or of their dispersion. It has been recently shown* that this diffi 
 culty is not insurmountable, and that the ether may be supposed to bo 
 transmitted through bodies of unequal density in such a manner that 
 rays of dissimilar systems of waves may be propagated through it with 
 unequal velocities ; but it remains to be determined whether the views 
 advanced by geometricians on this question are in unison with the act- 
 ual nature of things. The following are the lengths of the undulations
 
 VELOCITY OF LIGHT. 85 
 
 refraction in the prism is not altered by the relation 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 light of those from which it is receding. 
 Using the language of the emission hypothesis, this celebra- 
 ted 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 experimentally 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 rajs 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 
 luminous wave of the ether, and the velocity of the vibrations, determ- 
 ine the character 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 greatest 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 Stoiles vers lesquelles la Terre marche, et les ray- 
 ons des etoiles dont la terre s'eloigne, se refractent exactement de la 
 meme quantite. Un tel resultat ne pent se concilier avec la tkforie de 
 remission qu'a 1'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 determined sont visi- 
 bles, qu'eux seuls produisent dans Tcei! la sensation de lumiere. Dans 
 la theorie de 1'emission, le rouge, le jaune, le vert, le bleu, le violet so- 
 laires sont respectivement accompagnes de rayons pareils, mais obscurs 
 par defaut ou par exces de vitesse. A plus de vitesse correspond une 
 moindre refraction, comtne 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 uns plus, les autres 
 moins que lui : ainsi il existe des rayons dans les stries noiret 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 emistion, 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, dark from deficiency or excess of velocity. Excessive velocity is
 
 86 COSMOS. 
 
 On comparing the velocities of solar, stellar, and terres- 
 trial light, which are all equally refracted in the prism, 
 with the velocity of th& 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- 
 ations on aberration, we obtain the difference of 95,776 miles 
 as the greater velocity of electricity in one second. 
 
 These results are apparently opposed to the views ad- 
 vanced by Sir William Herschel, according to which solar 
 and stellar light are regarded as the effects of an electro- 
 magnetic process a perpetual northern light. I say ap- 
 parently, 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 Wheat- 
 stone, who has himself admitted that they are not sufficient- 
 ly established, 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 some 
 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, Traite de Mccanique, 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 eve 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 light, see Sir John Herschel's Re- 
 mit* of Aitron. Observ. at the Cape of Good Hope, 1847, p. 351. Arago, 
 in the Comptes Rendus pour 1838, t. vii., p. 956, has referred to the in- 
 genious application of Breguet's improved Wheatstone's rotatory 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- 
 dus pour 1850, t. xxx., p. 489-495, 556.)
 
 VELOCITY OF ELECTRICITY. 87 
 
 be satisfactorily compared with the 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 Washington, 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, arbitrary 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 difference 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 Wheatstone's rotatory disks. As in Walker's remarkable 
 experiments two zvires were not used, but half of the con- 
 
 * Steinheil, in Schumacher's Astr. Naekr., No. 679 (1849), s. 97-100; 
 Walker, in the Proceedings of the American Philosophical Society, vol. 
 v., p. 128. (Compare earlier propositions of Pouillet in the Comptes 
 Rendus, t. xix., p. 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 the 
 investigations of Fizeau and Gounelle at Paris, in April, 1850, differ 
 both from Wheatstone's and Walker's results. The experiments re- 
 corded in the Comptes Rendut, t. xxx., p. 439, exhibit striking differ 
 ences between iron and copper as conducting media.
 
 88 COSMOS. 
 
 duction, to use a conventional mode 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- 
 ments lately made by Eiessf show that electric discharges 
 are phenomena of a very various and complicated nature. 
 The views prevailing at the present day regarding what is 
 usually termed " connection through the earth" are opposed 
 to the hypothesis of linear, molecular conduction between 
 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 
 constant of aberration, and, consequently, the velocity of 
 light, is the same for all fixed stars, the question has fre- 
 quently been mooted whether 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 PoggendorflPs Annalen, bd. Ixxiii., 1848, s. 337, and Pouillet, 
 Comptes Rendus, t. xxx., p. 501. 
 
 t Riess, in PoggendorfTs Ann., bd. 78, s. 433. On the non-conduc 
 tion of the intermediate earth, see the important experiments of Guille- 
 miu, Sur le courant dans une pile isolte ct sans communication entre let 
 pdles in the Comptes Rendus, t. xxix., p. 521. " Quand on remplace 
 un fil par la terre, dans les telegraphes electriques, la terre sort plut6t 
 de reservoir commun, quo de moyen d'union entre 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 reservoir than as a 
 means of connection between the two extremities of the wire." 
 
 t Madler, Astr., a. 380; also Laplace, according to Moigno, Repertoire 
 d'Optique Moderne, 1847, t. i., p. 72 : " Selon la theorie de l'6mission 
 on croit pouvoir demontrer que si le diametre d'une 6toile fixe serait 250 
 fois plus grand que celui du soleil, sa densite restant la meme, 1'attrac- 
 tion exercee a sa surface detruirait la quantite de mouvement, de la 
 moldcule lumineuse Praise, de sorte qu'elle serait invisible a de gramles 
 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 
 its density remaining the same the attraction exercised on the surface
 
 STELLAR LIGHT. 89 
 
 to such views because it will be necessary in the sequel that 
 we should consider certain peculiarities ef motion ascribed 
 to Procyon, 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 directions 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- 
 tensity 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- 
 ranged Avith 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 Catasterisjns 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 
 William Herschel, we ascribe to Arcturus an apparent diameter of 0"-1, 
 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 very different in cosmical bodies of different 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- 
 riences sur 1'egale deviation prismatique des etoiles, vers lesquelles la 
 terre marche ou dont elle s'eloigne, rend compte de I'6galit6 de vitesse 
 apparente de toutes les etoiles." "Experiments made on the equal 
 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 ray of all the stars."
 
 90 COSMOS. 
 
 century and a half before the time of Hipparchus), we pos- 
 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 magnitudes. In the enumeration of the 
 stars belonging to each constellation, as given in the Catas- 
 terisms, 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- 
 terisms 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 Poeticum Astronomicum (ascribed 
 to Julius Hyginus), if not from the poem 'Epju^f 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 Madler counts 18, and Riimker, 
 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. Schaubach, 1795, and Eratotthenica, 
 ed. G. Bernhardy, 1822, p. 110-116. A distinction is made between 
 stars hafinpovc (jieyuTiOvf) and afjtavpovf (cap. 2, 11, 41). Ptolemy also 
 limits ol {ipopfyuToi to those stars which do not regularly belong to a con- 
 stellation.
 
 MAGNITUDES OF STARS. 91 
 
 640 stars of .the sixth magnitude. The nebulous stars (ve- 
 deXoeLdds') of Ptolemy and of the Pseudo-Eratosthenian Ca- 
 iasterisms 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, was unacquainted with the 
 nebula in Andromeda which is visible to the naked eye, says 
 in his Nuntius sidereus that stellce nebulosts are nothing 
 more than stellar masses scattered in shining groups through 
 the ether (areolce, sparsim per cethera fulgent).^ The ex- 
 pression (r&v fj,eydA.d)v raft^), 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 ;J 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 
 fifteenth century, astronomy nourished at Samarcand, under 
 Timur Ulugh Beg, photometric determinations were facili- 
 tated by the subdivision of each of the six classes of Hippar- 
 chus and Ptolemy into three subordinate groups ; distinctions, 
 for 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 photometry, by a more exact determ- 
 ination of degrees of intensity, is ascribed in Ulugh Beg's 
 tables to Abdurrahman Sufi, who wrote a work " on the 
 knowledge of the fixed stars," and was the first who men- 
 tions one of the Magellanic clouds under the name of the 
 White Ox. Since the discovery and gradual improvement 
 of telescopic vision, these estimates of the gradations of light 
 have been extended far below the sixth class. The desire 
 of comparing the increase and decrease of light in the newly- 
 
 * Plot. Almas., ed Halma, torn, ii., p. 40, and in Eratosth. Catast., 
 cap. 22, p. 18: rj de KtQa/.Tj Kai ij apnr) uvaifTOf dparai, 6ia de ve0e?.u<5otf 
 avarpo<j>jjc do/ccl TLGIV opuadai. Thus, too, Geminus, Pheen. (ed. Hilder, 
 1590), p. 46. t Cosmos, vol. ii., p. 330, 331. 
 
 t Muhamedis Alfragani Chronologica et Ast. Elementa, 1590, cap. 
 xxiv., p. 118. 
 
 $ Some MSS. of the Almagest refer to such subdivisions or interme- 
 diate classes, as they add the words pei&v or ehdaauv to the determ- 
 ination of magnitudes. (Cod. Paris, No. 2389.) Tycho expressed thia 
 increase or diminution by points.
 
 92 COSMOS. 
 
 appeared stars in Cygnus and Ophiuchus (tie former of which 
 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 practice of 
 using powerful instruments.* But at this faint degree of 
 brightness, the denominations for the different 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 different 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, K-umford, and Wollaston, to Stein- 
 heil and Sir John Herschel. It will be sufficient for the ob- 
 ject of this work briefly to indicate the different 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 application of reflecting 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 favorable 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 I 
 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 60, of the third between 60 and 45, of the 
 fourth between 45 and 30, 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 Lacaille. It seemed 
 to me, after a careful combination of magnitudes, using other stars as 
 intermediate gradations, that Sirius was as much brighter than Canopus, 
 as a Centauri than Achernar. My numbers can not, on accoupt of tho
 
 PHOTOMETRIC METHODS. 93 
 
 ing (iii front of the object-glass) a mirror and diaphragms, 
 whose rotation is measured on a ring ; telescopes with di- 
 vided object-glasses, on either half of which the stellar light 
 is received through 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-mentioned mode of classification, be compared directly with 
 those which Sir John Herschel made public as early as 1838. (See my 
 Recneil d'Observ. Astr., vol. i., p. Ixxi., and Rclat. Hist, du Voyage aux 
 Regions Equin., t. i., p. 518 and 624; also Lettre de M. de Humboldt a 
 M. Schumacher en Fevr., 1839, in the Astr. Nachr., No. 374.) In this 
 letter I wrote as follows : " M. Arago, qui possede des moyens photo- 
 metriques entierement difierents de ceux qui ont ete publics jusqu'ici, 
 m'avait rassure sur la partie des erreurs qui pouvaient provenir du change- 
 ment d'inclinaison d'un miroir entame sur la face interieure. H blame 
 d'ailleurs le principe de ma methode et le regarde comme peu suscep- 
 tible de perfectionnement, non seulement a cause de la difference des 
 angles entre 1'etoile vue directement et celle qui est amenee par reflex- 
 ion, mais surtout parceque le resultat de la mesure d'intensite dfepend 
 de la partie de 1'ceil qui se trouve en face de 1'oculaire. II y a erreur 
 lorsque la pupille n'est pas tres exactement a la hauteur de la limite in- 
 ferieure de la portion non eutamee du petit miroir." " M. Arago, who 
 possesses photometric data differing entirely from those hitherto pub- 
 lished, had instructed me in reference 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 
 angles between the star seen directly and by reflection, but especially 
 because the result of the amount of intensity depends on the part of the 
 eye opposite to the ocular glass. There will be an error in the observ- 
 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 Helligkeils-Messungen am Sternen- 
 himmel Munchen, 1836 (Schum., Astr. Nachr., No. 609), and John Her- 
 schel, Results of Astronomical Observations made during the Years 1834 
 -1838 at the Cape of Good Hope (Lond., 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 Sirius 5-13 ; for Rigel, whose luster appears 
 to be on the increase, 1-30; for Arcturus, 0-84; for Capella, 0-83; for 
 Procyon, 071; for Spica, 0-49; for Atair, 0-40; for Aldebaran, 0-36; 
 for Deneb, 0-35; for Regulns, 0-34; for Pollux, 0-30; he does not give 
 the intensity of the light of Betelgeux, on account of its being a varia- 
 ble star, as was particularly manifested between 1836 and 1839. (Ont 
 tiite*, p. 523 )
 
 94 COSMOS. 
 
 eideratum in astronomy," and that " photometry is yec /*. * 
 infancy." The increasing interest taken in variable swrs, 
 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 Inquiry prepared for 
 the Use of the Navy), 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 materials! probably deserves 
 the preference over any other approximative method practi- 
 cable in the present imperfect condition of photometrical in- 
 struments, however much the exactness of the estimates must 
 be endangered by the varying powers of individual observers 
 the serenity of the atmosphere the different 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 Acher- 
 nar, Deneb and Vega, 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, Arcturus, and Betelgeux.J 
 
 * Compare, for the numerical data of the photometric results, four 
 tables of Sir John Herschel's Astr. Obs. 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 arrangement without numbers, see the Manual of 
 Scientific Inquiry 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 the 
 addition of 0-41, as explained more in detail in Astr. Obs. at the Cape, p. 
 370. has been added to the vulgar scale of magnitudes in the Outlines of 
 Astronomy, p. 645, and these scales are subjoined to this portion of the 
 present work, together with a list of northern and southern stars. 
 
 t Argelander, Durchmusterung des nordl. Himmels zwischen 45 und 
 80 Decl. 1846, s. xxiv.-xxvi. ; Sir John Herschel, Astr. Obscrv. al the 
 Cape of Good Hope, p. 327, 340, 365. 
 
 t Op. cit., p. 304, aud Outl., p. 522.
 
 PHOTOMETRY. 95 
 
 Sir John Herschcl has 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, 
 which is the third in brightness of all the stars. He thus 
 fulfilled (as had been already done by "Wollaston) a wish ex- 
 pressed by John Michell* as early as 1767. Sir John Her- 
 schel found from the mean of eleven measurements conduct- 
 ed with a prismatic apparatus, that the full moon was 27,408 
 times brighter than a Centauri. According to Wollaston, the 
 light of the sun is 801,072 times brighter than the full moon ;f 
 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 2f- times. Wollaston found the 
 brightness of Sirius 20,000 million times fainter 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 times4 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 
 
 * Philos. Transact., vol. Ivii., for the year 1767, p. 234. 
 
 t Wollaston, in the Philos. Transact, for 1829, p. 27. Herschel'a 
 Outlines, p. 553. Wollaston'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 by lighted wax tapers, while in the experiments 
 made on Sirius in 1826 and 1827, images reflected from thermometer 
 bulbs 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 Steinheil, 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 
 Compositarnm Mcnsuree Micrometricee, p. clxiii.); and, according to 
 Sir John Herschel, the light of Arcturus exhibits only half the intensity 
 of 3anopus. Herschel, Observ. at the Cape, p. 34. All these conditions 
 of intensity, more especially the important comparison of tho bright 
 ness 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 the 
 earth considered as a reflecting body, deserve further and serious in- 
 vestigation. 
 
 \ Quit. <>f Astr., p. 553 ; Aslr. Observ. at the Cape, p. 363.
 
 96 COSMOS. 
 
 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 their 
 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 
 of all organic life 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- 
 mosphere, 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 
 seen by transmission and reflection. I subjoin in a note,t 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. 186. Gomparo 
 also Sir John Herschel, Obsero. at the Cape, p. 350-352. 
 
 t Extract of a Letter from M. Arago to M. de Humboldt, May, 1850. 
 
 (a.) Mesurcs Photom6triqucs. 
 
 " II n'existe pas de photometre proprement dit, c'est-a-dire d'instru- 
 ment donuant 1'intensite d'une lumiere isol^e ; le photometre de Les- 
 lie, a 1'aide duquel il avail eu 1'audace de vouloir comparer la lumiere 
 de la lune a la lumiere du soleil, par des actions calonfiques, est com- 
 pletement defectueux. .T'ai prouve, en effet, que ce preteudu photo- 
 metre monte quand on 1'expose a la lumiere du soleil, qu'il descend 
 sous 1'action 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- 
 mieres en presence, et cette comparaison n'est meme a 1'abri de toute 
 objection que lorsqu'on ramene ces deux lumieres a I'egalit^ par un 
 amublissement graduel de la lumiere la plus forte. C'est comme crite- 
 rium de cette egalit6 que j'ai employ^ les anneaux colores. Si on place 
 I'une sur 1'autre deux lentilles d'un long foyer, il se forme autour de 
 leur point de contact des anneaux colored tant par voie de reflexion que 
 par voi 5 de transmission. Les anueaux reflechia sout conipleineutaires
 
 PHOTOMETRY. 97 
 
 his own words, the results of my friend's photometric method, 
 to which he has added an account of the optical principle 
 oa which his cyanometer is based. 
 
 en couleur des anneaux transmis; ces deux series d'anneaux se neu- 
 tralisent mutuellement qoand les deux lumieres qui les Ibrment et qui 
 arrivent simultanement sur les deux lentilles, sont egales entr'elles. 
 
 " Dans le cas contraire on voit des traces ou d'anneaux reflechis ou 
 d'anneaux transrais, suivant quo la lumiere qui forme les premiers, est 
 plus forte ou plus foible que la lumiere a laquelle on doit les seconds. 
 C'est dans ce sens settlement que les anneaux colores jouent un role 
 dans les mesures de la lumiere auxquelles je me suis livre." 
 
 (6.) Cyanometre. 
 
 " Mon cyanometre est une extension de mon polariscope. Ce der- 
 nier instrument, comma tu sais, se compose d'un tube ferme 1'une de 
 ses extremites par une plaque de cristal de roche perpendiculaire a 
 I'axe, de 5 millimetres d'epaisseur ; et d'un prisme doue de la double 
 refraction, place du cote de 1'oeil. Parmi les couleurs variees que 
 donne cet appareil, lorsque de la lumiere polarisee le traverse, et qu'on 
 fait tourner le prisme sur lui-meme, se trouve par un heureux basard la 
 nuance du bleu de ciel. Cette couleur bleue fort afiaiblie, c'est-4-dire 
 tres melangee de blanc lorsque la lumiere est presque neutre, aug- 
 mente d'intensite progressivement, a mesure que les rayons qui pene- 
 trent dans 1'instrumeut, 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 eclairante du papier plus ou nioins polarisee ; 
 la couleur bleue fournie par 1'instrument va en augmentant avec 1'in- 
 clinaison de la pile, et 1'on s'arrete lorsque cette couleur parait la meme 
 que celle de la region de 1'atmosphere dont on veut determiner la teinte 
 cyanometrique, et qu'ou regarde & 1'ceil nu immecliatement a cote de 
 1'instrumeut. La mesure de cette teiute est don nee par 1'inclinaison de 
 la pile. Si cette derniere partie de 1'instrument se compose du meme 
 nombre de plaques et d'une meme espece de verre, lea observations 
 faites dans divers lieux seront parfaitement comparables 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 
 photometer, 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 stationary when 
 brought 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 wdl be formed round their point of contact as 
 much by means of reflection as of transmission. The colors of the r& 
 VOL, III E
 
 98 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. The 
 order of the letters which, since the beginning of the seven- 
 teenth century, have been added to the stars in the general- 
 ly consulted Uranometria Bayeri, are not, as was long sup- 
 posed, certain indications of these alterations of light. Arge- 
 lander 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 which 
 they aro formed, and which fall simultaneously on the two lenses, are 
 equal. 
 
 " In the contrary case, we meet with 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 the latter are formed. It is 
 only in this manner that colored rings can ba said to come into play in 
 those photometric measurements to which I bavi diracted my atten- 
 tion." 
 
 (b.) Cyanometer. 
 
 " My cyanometer is an extension of my polariscope. This latter in- 
 strument, as you know, consists of a tube closed at ono end by a plate 
 of rock crystal, cut perpendicular to its axis, and 5 millimetres in thick- 
 ness ; and of a double refracting prism placed near the part to which 
 the eye is applied. Among the varied colors yielded by this apoaratus, 
 when it is traversed by polarized light and the prism turns on itself, wo 
 fortunately find a shade of azure. This blue, which is very faint, that 
 is to say, mixed with a large quantity of white when the light is almost 
 neutral, gradually increases in intensity in proportion to the quantity of 
 polarized rays which enter the instrument. 
 
 " Let us suppose the polariscope directed toward a sheet of white 
 paper, and that between this paper and the plate of rock crystal there 
 is a pile of glass plates capable of being variously inclined, by which 
 means the illuminating light of the paper would be more or less polar- 
 ized ; the blue color yielded by the instrument will go on increasing 
 with the inclination of the pile ; and the process must be continued un- 
 til the color appears of the same intensity with the region of the atmos- 
 phere whose cyanometrical tinge is to be determined, and which is 
 seen by the naked eye in the immediate vicinity of the instrument. 
 The amount of this color is given by the inclination of the pile ; and if 
 this portion of the apparatus consist of the same number of plates formed 
 of the same kind of glass, observations made at different places may 
 readily be compared together." 
 
 * Argelander, Defde Uranomelria: Bayeri, 1842, p. 14-23. "In ea- 
 dem classe littera prior majorem splendorem nullo modo indicat" ( 
 9). Bayer did not, therefore, show that the light of Castor was more 
 intense in 1603 than that of Pollux.
 
 PHOTOMETRIC SCALE. 99 
 
 PHOTOMETRIC ARRANGEMENT OF THE FIXED STARS. 
 
 I close this section with a table taken from Sir John Herschel's Out 
 ines of Astronomy, p. 645 and 64G. I am indebted for the mode of its 
 arrangement, and for the following lucid exposition, to my learned 
 friend Dr. Galle, from whose communication, addressed to me in March, 
 1850, I extract the subjoined observations : 
 
 " The numbers of the photometric scale in the Outlines of Astron- 
 omy have been obtained by adding throughout 0-41 to the results calcu- 
 lated from the vulgar scale. Sir John Herschel arrived at these more 
 exact determinations by observing their " sequences" of brightness, and 
 by combining these observations with the average ordinary data of mag- 
 nitudes, especially on those given in the catalogue of the Astronomical 
 Society for the year 1827. See Observ. at the Cape, p. 304-352. The 
 actual photometric measurements of several stars as obtained by the 
 Astrometer (op. cit., p. 353), have not been directly employed in this 
 catalogue, but have only served generally to show the relation existing 
 between the ordinary scale (of 1st, 2d, 3d, &c., magnitudes) to the act- 
 ual photometric quantities of individual stars. This comparison has 
 given the singular result that our ordinary stellar magnitudes ( 1, 2, 3 . . .) 
 decrease in about the same ratio as a star of the first magnitude when 
 removed to the distances of 1, 2, 3 ... by which its brightness, accord- 
 ing to photometric law, would attain the values 1, Jth, ^th, -pg-th . . . 
 (Observ. at the Cape, p. 371, 372 ; Outlines, p. 521, 522) ; in order, how- 
 ever, to make this accordance still greater, it is only necessary to raise 
 our previously adopted stellar magnitudes about half a magnitude (or, 
 more accurately considered, 0-41), so that a star of the 2-00 magnitude 
 would in future be called 2-41, and star of 2-50 would become 2-91, 
 and so forth. Sir John Herschel therefore proposes that this " photo- 
 metric" (raised) scale shall in future be adopted (Observ. at the Cape, 
 p. 372, and Outlines, p. 522) a proposition in which we can not fail to 
 concur ; for while, on the one hand, the difference from the vulgar scale 
 would hardly be felt (Observ. at the Cape, p. 372), the table in the Out- 
 lines (p. (>45) may, on the other hand, serve as a basis for stars down 
 to the fourth magnitude. The determinations of the magnitudes of the 
 stars according to the rule, that the brightness of the stars of the first, 
 second, third, fourth magnitude is exactly as 1, jth, ith, -p^th ... as is 
 now shown approximatively, is therefore already practicable. Sir John 
 Herschel employs a Centauri as the standard star of the first magnitude 
 for his photometric scale, and as the unit for the quantity of light (Out- 
 lines, p. 523; Observ. at the Cape, p. 372). If, therefore, we take the 
 square of a star's photometric magnitude, we obtain the inverse ratio 
 of the quantity of its light to that of a Centauri. Thus, for instance, if 
 K Orionis have a photometric magnitude of 3, it consequently has ^th 
 of the light of a Centauri. The number 3 would at the same time in- 
 dicate that K Orionis is 3 times more distant from us than a Centauri, 
 provided both stars be bodies of equal magnitude and brightness. If 
 another star, as, for instance, Sirius, which is four times as bright, were 
 chosen as the unit of the photometric magnitudes indicating distances, 
 the above conformity to law would not be so simple and easy of recog- 
 nition. It is also worthy of notice, that the distance of a Centauri has 
 been ascertained with some probability, and that this distance is the 
 smallest of any yet determined. Sir John Henchel demonstrates ( Out- 
 lines, p. 521) the inferiority of other scales to the photometric, which
 
 100 COSMOS. 
 
 progresses in order of the squares, 1, th, th, J ff th ... He likewise 
 treats of geometric progressions, as, for instance, 1, 1, Jth, |th, ... or 1, 
 ^d, th, ^th. .... The gradations employed by yourself in your ob- 
 servations under the equator, during your travels in America, are ar- 
 ranged in a kind of arithmetical progression (Recueil d'Observ. Atlron., 
 vol. i., p. Ixxi., and Schumacher's Astron. Nachr., No. 374). These 
 scales, however, correspond less closely than the photometric scale of 
 progression (by squares) -with the vulgar scale. In the following table 
 the 190 stars have been given from the Outlines, without reference to 
 their declination, whether southern or northern, being arranged solely 
 in accordance with their magnitudes." 
 
 List of 190 stars from the first to the third magnitude, arranged accord- 
 ing to the determinations of Sir John Herschel, giving the ordinary 
 magnitudes with greater accuracy, and likewise the magnitudes in ac- 
 cordance with his proposed photometric classification : 
 
 STARS OF THE FIRST MAGNITUDE. 
 
 Star. 
 
 Magnitude. 
 
 Star. 
 
 Magnitude. 
 
 Sirius 
 
 Vulg. 
 
 008 
 
 0-29 
 059 
 077 
 082 
 1-0 
 10 
 1-0 
 
 Phot. 
 
 0-49 
 
 0-70 
 1-00 
 1-18 
 1-23 
 1-4 
 1-4 
 1-4 
 
 a Orionis 
 
 Vulg. 
 
 1-0 
 1-09 
 1-1 
 1-17 
 1-2 
 1-2 
 1-28 
 1-38 
 
 Phot. 
 
 1-43 
 150 
 15 
 1-58 
 1-6 
 1-6 
 1 69 
 1-79 
 
 tl Argus (Var.) 
 
 a Eridani 
 
 Canopus 
 
 Aldebaran 
 
 a Centauri.... . . 
 
 8 Centauri 
 
 Arcturus 
 
 a Crucis 
 
 Rigel 
 
 An tares 
 
 Capella 
 
 a Aquila? ......... 
 
 a. Lyra? 
 
 Spica 
 
 Procyon 
 
 
 STARS OF THE SECOND MAGNITUDE. 
 
 Star. 
 
 Magnitude. 
 
 Star. 
 
 Magnitude. 
 
 Fomalhaut 
 
 Vulg.l Phot 
 
 1-541-95 
 1-57 1-98 
 1-6 2-0 
 1-6 20 
 1-66207 
 1-73214 
 l-84 ! 225 
 1-862-27 
 1-872-28 
 1-90 ! 231 
 1-94|235 
 1-95236 
 1-96:2-37 
 2-01242 
 2-03 2 44 
 2-072-48 
 2-082-49 
 2182-59 
 2-18259 
 2-18259 
 
 a Triang austr. 
 
 2^ 
 2-26 
 2-28 
 228 
 229 
 230 
 232 
 233 
 234 
 2-36 
 2-40 
 241 
 2-42 
 243 
 2-45 
 2-46 
 2-46 
 2-48 
 
 M 
 
 Phot. 
 
 264 
 2-67 
 269 
 2-69 
 270 
 271 
 273 
 2-74 
 275 
 2-77 
 281 
 2-82 
 2-83 
 284 
 2-86 
 2-87 
 28"" 
 289 
 291 
 
 ft Crucis 
 
 e Sagittarii 
 
 Pollux 
 
 3 Tauri 
 
 Regulus 
 
 Polaris 
 
 a Gruis . .. ....... 
 
 6 Scorpii 
 
 
 a Hydra 
 
 e Orionis 
 
 6 Canis 
 
 e Can is 
 
 a Pavonis 
 
 
 y Leonis 
 
 a Cygni 
 
 8 Gruis 
 
 Castor 
 
 a Arietis ........ 
 
 E Ursse (Var ) 
 
 a Sagittarii 
 
 a Ursae (Var ) 
 
 6 Argus 
 
 f Orionis 
 
 Ursae 
 
 8 Argus . ... . . 
 
 8 Andromeda? 
 
 
 /? Ceti 
 
 
 A Argus . ........ 
 
 e Argus 
 
 
 i? Ursae (Var ) 
 
 y Andromedse 
 
 y Orionis 

 
 PHOTOMETRIC SCALE. 
 
 STARS OF THE THIRD MAGNITUDE. 
 
 101 
 
 
 
 Masmtmle. 
 
 
 Magnitude. 
 
 y Cassiopeiae 
 
 Vulg. 
 
 J 52 
 254 
 2-54 
 2-57 
 2-58 
 259 
 259 
 2-61 
 2-62 
 2-62 
 2 62 
 263 
 263 
 263 
 263 
 265 
 265 
 2-68 
 269 
 2-71 
 2-71 
 2-72 
 2-77 
 2-78 
 2-80 
 280 
 2-82 
 2-82 
 2-85 
 2-85 
 286 
 2-88 
 
 Phot. 
 
 2-93 
 2-95 
 2-95 
 2-98 
 2-99 
 300 
 300 
 3-02 
 3-03 
 3-03 
 3-03 
 3-04 
 3-04 
 3-04 
 3-04 
 306 
 3-06 
 3-09 
 3-10 
 3-12 
 3-12 
 3-13 
 3-18 
 3-19 
 3-21 
 3-21 
 3-23 
 323 
 326 
 326 
 3-27 
 'VQ 
 
 f Sagittarii 
 
 Vulg. 
 
 3-01 
 3-01 
 302 
 305 
 3-06 
 307 
 3-08 
 3-08 
 3-09 
 311 
 3-11 
 312 
 313 
 3-14 
 3-14 
 3-15 
 3-17 
 3-18 
 320 
 320 
 322 
 322 
 3-23 
 324 
 3-26 
 3-26 
 326 
 326 
 327 
 327 
 3-28 
 3 28 
 3-29 
 330 
 331 
 331 
 3-^2 
 332 
 332 
 332 
 333 
 334 
 335 
 335 
 3-35 
 335 
 33G 
 336 
 336 
 337 
 
 Phot. 
 
 342 
 3-42 
 343 
 346 
 347 
 348 
 349 
 349 
 350 
 352 
 352 
 353 
 354 
 355 
 355 
 356 
 358 
 359 
 361 
 3-61 
 3 63 
 3-63 
 3-64 
 365 
 3-67 
 367 
 3-67 
 367 
 368 
 368 
 369 
 369 
 370 
 3-71 
 372 
 372 
 373 
 373 
 373 
 373 
 374 
 375 
 3-76 
 3 76 
 376 
 376 
 377 
 377 
 377 
 a-78 
 
 a Andromedae ..... 
 
 77 Bootis 
 
 6 Centauri 
 
 77 Draconis 
 
 a Cassiopeiae ........ 
 
 TT Ophiuchi 
 
 /3 Canis 
 
 i3 Draconis 
 
 * Orionis 
 
 3 Librae 
 
 y Geminorum 
 
 y Virginis 
 
 i Orionis . . 
 
 u Argns . . 
 
 Algol (Var ) 
 
 3 Arietis 
 
 
 y Pegasi 
 
 
 6 Sa^ittarii 
 
 (3 Leonis 
 
 a Libras 
 
 a Ophiuchi ... ... 
 
 * Sagittarii 
 
 3 Cassiopeiae 
 
 3 Lupi 
 
 y Cygni . ... 
 
 e Virginis 1 . 
 
 a Pegasi 
 
 a Columbae 
 
 3 Pegasi 
 
 i9- Aurigae . 
 
 y Centauri 
 
 3 Herculis 
 
 a Coronas 
 
 i Centauri 
 
 y Ursae 
 
 6 Capricorni 
 
 e Scorpii 
 
 6 Corvi 
 
 f Argus 
 
 a Can. ven. 
 
 B Ursa 
 
 3 Ophiuchi 
 
 Phcenicis 
 
 6 Cygni 
 
 Argus 
 
 e Persei 
 
 Bootis 
 
 TJ Tauri 
 
 Lupi 
 
 3 Eridani 
 
 Centauri 
 
 & Argus 
 
 Canis 
 
 3 Hydri 
 
 Aquarii 
 
 f Persei 
 
 Scorpii . . 
 
 f Herculis 
 
 Cygni 
 
 E Corvi 
 
 TI Ophiuchi 
 
 2893-30 
 290331 
 290.331 
 2913-32 
 2 92 3 33 
 294335 
 2943-35 
 2 95 3 36 
 296337 
 2-96337 
 2-973-38 
 *-973-38 
 298339 
 298,339 
 2 99 3 40 
 2-99340 
 3-003-41 
 3003-41 
 
 i Aurigae 
 
 y Corvi 
 
 y Urs. Min 
 
 a Cephei 
 
 T) Pegasi 
 
 6 Centauri 
 
 3 Arae 
 
 a Serpentis 
 
 a Toucani 
 
 6 Leonis 
 
 3 Caprieorni 
 
 K Argus 
 
 p Argus 
 
 3 Corvi 
 
 Aquilae 
 
 B Scorpii 
 
 3 Cygni 
 
 f Centauri 
 
 y Persei.. 
 
 C Ophiuchi .. 
 
 u Ursae.. . 
 
 a Aquani 
 
 
 
 Tf Scorpii 
 
 
 3 Leporis 
 
 6 Cassiopeias 
 
 y Lupi 
 
 d Centauri 
 a Leporis ............. 
 
 I Persei 
 
 ^ Ursse 
 
 6 Ophiuchi .. 
 
 e Aurigae (Var.) ..
 
 102 
 
 Star. 
 
 M^utudp. 
 
 Star. 
 
 MHgmtii.l..-. 
 
 v Scorpii 
 
 Vulg. 
 
 3-37 
 337 
 339 
 3-40 
 340 
 340 
 3-41 
 3-41 
 342 
 3-42 
 3-42 
 343 
 343 
 343 
 344 
 344 
 344 
 
 Phot 
 
 3-78 
 3-78 
 3-80 
 3-81 
 381 
 3-81 
 3-82 
 3-82 
 383 
 383 
 383 
 3-84 
 384 
 3-84 
 385 
 385 
 385 
 
 <5 Geminorum 
 
 Z& 
 
 3-45 
 3-45 
 345 
 3-45 
 3-46 
 346 
 3-46 
 3-46 
 3-47 
 348 
 348 
 349 
 349 
 350 
 350 
 3-50 
 
 Phot. 
 
 3-85 
 3-86 
 386 
 3-86 
 3-86 
 3-87 
 3-87 
 387 
 3-87 
 3-88 
 389 
 389 
 3-90 
 3-90 
 391 
 391 
 391 
 
 i Orionis 
 
 o Orionis ... 
 
 y Lyncis 
 
 (3 Cephei 
 
 
 tfUrsae 
 
 
 f Hydra 
 
 rr Sagittarii ...... 
 
 y Hydrae 
 
 TT Herculis . 
 
 f3 Triang. austr 
 
 /3 Can. min. 1 
 
 t Ursae 
 
 f Tauri 
 
 tj Aurigae ... 
 
 (5 Draconis 
 
 y Lyrae ......... 
 
 p Geminorum 
 
 T) Geminorum 
 
 y Bootis 
 
 y Cephei 
 
 e Geminorum 
 
 K Ursas 
 
 a Muscae 
 
 e Cassiopeiae .... 
 
 a Hydri? 
 
 1? Aquilae 
 
 T Scorpii 
 
 a Scorpii 
 
 6 Herculis 
 
 r Argus 
 
 " The following short table of the photometric quantities 
 of seventeen stars of the first magnitude (as obtained from 
 the photometric scale of magnitudes) may not be devoid of 
 interest :" 
 
 Sirius 4-165 
 
 7i Argus 
 
 Canopus 2-041 
 
 aCentauri 1-000 
 
 Arcturus 0-718 
 
 Rigel 0-661 
 
 Capella 0-510 
 
 aLyrae 0-510 
 
 Procyon 0-510 
 
 " The following is the photometric quantity of stars strict- 
 ly belonging to the 1st, 2d 6th magnitudes, in which 
 
 the quantity of the light of a Centauri is regarded as the 
 unit :" 
 
 a Orionis .... 
 a Eridani .... 
 Aldebaran. . 
 j3 Centauri . . . 
 a Crucis 
 Antares .... 
 a Aquilae .... 
 Spica . . 
 
 0-489 
 .0-444 
 0-444 
 0-401 
 .0-391 
 .0-391 
 .0-350 
 0-312 
 
 
 
 Magnitude on 
 the vulgar scale. 
 
 1-00 
 2-00 
 3-00 
 
 Quantity 
 of light 
 
 0-500 
 0-172 
 0-086 
 
 Magnitude on 
 the vulgar scale. 
 
 4-00 
 5-00 
 6-00 
 
 Quantity 
 of light. 
 
 0-051 
 0-034 
 0-024
 
 III. 
 
 NUMBER, DISTRIBUTION, AND COLOR OF THE FIXED STARS. STEL- 
 LAR MASSES (STELLAR SWARMS). THE MILKY WAY INTERSPERSED 
 WITH A FEW NEBULOUS SPOTS. 
 
 We have already, in the first section of this fragmentary 
 Astrognosy, drawn attention to a question first mooted by 
 Olbers.* If the entire vault of heaven were covered with 
 innumerable strata of stars, one behind the other, as with a 
 wide-spread starry canopy, and light were undiminished in 
 its passage through space, the sun would be distinguishable 
 only by its spots, the moon would appear as a dark disk, 
 and amid the general blaze not a single constellation would 
 be visible. During my sojourn in the Peruvian plains, be- 
 tween the shores of the Pacific and the chain of the Andes, 
 I was vividly reminded of a state of the heavens which, 
 though diametrically opposite in its cause to the one above 
 referred to, constitutes an equally formidable obstacle to hu- 
 man knowledge. A thick mist obscures the firmament in 
 this region for a period of many months, during the season 
 called el tiempo de la garua. Not a planet, not the most 
 brilliant stars of the southern hemisphere, neither Canopus, 
 the Southern Cross, nor the feet of the Centaur, are visible. 
 It is frequently almost impossible to distinguish the position 
 of the moon. If by chance the outline of the sun's disk be 
 visible during the day, it appears devoid of rays, as if seen 
 through colored glasses, being generally of a yellowish red, 
 sometimes of a white, and occasionally even of a bluish green 
 color. The mariner, driven onward by the cold south cur- 
 rents of the sea, is unable to recognize the shores, and in the 
 absence of all observations of latitude, sails past the harbors 
 which he desired to enter. A dipping needle alone could, 
 as I have elsewhere shown, save him from this error, by the 
 local direction of the magnetic curves. f 
 
 Bouguer and his coadjutor, Don Jorge Juan, complained, 
 long before me, of the " unastronomical sky of Peru." A 
 graver consideration associates itself with this stratum of 
 vapors, in which there is neither thunder nor lightning, in 
 consequence of its incapacity for the transmission of light or 
 electric charges, and above which the Cordilleras, free and 
 cloudless, raise their elevated plateaux and snow-covered 
 
 * Vide supra, p. 38, and note. 
 
 t Cotmos, vol. i., p. 178, and note.
 
 104 COSMOS. 
 
 summits. According to what modern geology has taught us 
 to conjecture regarding the ancient history of our atmosphere, 
 its primitive condition, in respect to its mixture and density, 
 must have been unfavorable to the transmission of light. 
 When we consider the numerous processes which, in the pri- 
 mary world, may have led to the separation of the solids, 
 fluids, and gases around the earth's surface, the thought in- 
 voluntarily arises how narrowly the human race escaped be- 
 ing surrounded with an untransparent atmosphere, which, 
 though perhaps not greatly prejudicial to some classes of 
 vegetation, would yet have completely veiled the whole of 
 the starry canopy. All knowledge of the structure of the 
 universe would thus have been withheld from the inquiring 
 spirit of man. Excepting our own globe, and perhaps the 
 sun and the moon, nothing would have appeared to us to 
 have been created. An isolated triad of stars the sun, the 
 moon, and the earth would have appeared the sole occu- 
 pants of space. Deprived of a great, and, indeed, of the sub- 
 limest portion of his ideas of the Cosmos, man would have 
 been left without all those incitements which, for thousands 
 of years, have incessantly impelled him to the solution of 
 important problems, and have exercised so beneficial an in- 
 fluence on the most brilliant progress made in the higher 
 spheres of mathematical development of thought. Before 
 we enter upon an enumeration of what has already been 
 achieved, let us dwell for a moment on the danger from 
 which the spiritual development of our race has escaped, and 
 the physical impediments which would have formed an im- 
 passable barrier to our progress. 
 
 In considering the number of cosmical bodies which fill 
 the celestial regions, three questions present themselves to 
 our notice. How many fixed stars are visible to the naked 
 eye ? How many of these have been gradually catalogued, 
 and their places determined according to longitude and lat- 
 itude, or according to their right ascension and declination ? 
 "What is the number of stars from the first to the ninth and 
 tenth magnitudes which have been seen in the heavens by 
 means of the telescope ? These three questions may, from 
 the materials of observation at present in our possession, 
 be determined at least approximatively. Mere conjectures 
 based on the gauging of the stars in certain portions of the 
 Milky Way, differ from the preceding questions, and refer to 
 the theoretical solution of the question : How many stars 
 might be distinguished throughout the whole heavens with
 
 NUMBER OF THE FIXED STARS. 105 
 
 Herschel's twenty-feet telescope, including the stellar light, 
 " which is supposed to require 2000 years to reach oui 
 earth ?"* 
 
 The numerical data which I here publish in reference to 
 this subject are chiefly obtained from the final results of my 
 esteemed friend Argelander, director of the Observatory at 
 Bonn. I have requested the author of the Durchmusterung 
 des nordlichen Himmeh (Suney of the Northern Heav- 
 ens) to submit the previous results of star catalogues to a 
 new and careful examination. In the lowest class of stars 
 visible to the naked eye, much uncertainty arises from or- 
 ganic difference in individual observations ; stars between 
 the sixth and seventh magnitude being frequently confound- 
 ed with those strictly belonging to the former class. We 
 obtain, by numerous combinations, from 5000 to 5800 as the 
 mean number of the stars throughout the whole heavens vis- 
 ible to the unaided eye. Argelanderf determines the distri- 
 
 * On the space-penetrating power of telescopes, see Sir John Her- 
 schel, Outlines of Astr., 803. 
 
 t I can not attempt to include in a note all the grounds on which 
 Argelander's views are based. It will suffice if I extract the following 
 remarks from his own letters to me: "Some years since (1843) you 
 recommended Captain Schwink to estimate from his Mappa Coelestis 
 the total number of stars from the first to the seventh magnitude in- 
 clusive, which the heavens appeared to contain ; his calculations give 
 12,1 48 stars for the space between 30 south and 90 north declination ; 
 and consequently, if we conjecture that the proportion of stars is the 
 same from 30 S. D. to the South Pole, we should have 16,200 stars of 
 the above-named magnitudes throughout the whole firmament. This 
 estimate seems to me to approximate very nearly to the truth. It is 
 well known that, on considering the whole mass, we find each class 
 contains about three times as many stars as the one preceding. (Struve, 
 Catalogvs Sldlarum duplicium, p. xxxiv. ; Argelander, Banner Zonen, 
 s. xxvi.) I have given in my Uranometria 1441 stars of the sixth mag- 
 nitude north of the equator, whence we should obtain about 3000 for 
 the whole heavens; this estimate does not, however, include the stars 
 of the 6-7 mag., which would be reckoned among those of the sixth, if 
 only entire classes were admitted into the calculation. I think the 
 number of the last-named stars might be assumed at 1000, according 
 to the above rule, which would give 4000 stars for the sixth, and 12 000 
 for the seventh, or 18,000 for the first to the seventh inclusive. From 
 other considerations on the number of the stars of the seventh magni- 
 tude, as given in my zones namely, 2257 (p. xxvi.), and allowing for 
 those which have been twice or oftener observed, and for those which 
 have probably been overlooked, I approximated somewhat more nearly 
 to the truth. By this method I found 2340 stars of the seventh magni- 
 tude between 45 and 80 N. D., and, therefore, nearly 17,000 for the 
 whole heavens. Struve, in his Description de V Observatoire de Paul- 
 kova, p. 268, gives 13,400 for the number of stars down to the seventh 
 magnitude in the region of the heavens explored by him (from 15 
 E 2
 
 106 COSMOS. 
 
 bution of the fixed stars according to difference of magnitude, 
 down to the ninth, in about the following proportion . 
 
 to +90), whence we should obtain 21,300 for the whole firmament. 
 According to the introduction to Weisse's Catal. e Zonis Regiomonta- 
 nit, dcd., p. xxxii., Struve found in the zone extending from 15 to 
 -{-15 by the calculus of probabilities, 3903 stars from the first to the 
 seventh, and therefore 15,050 for the entire heavens. This number is 
 lower than mine, because Bessel estimated the brighter stars nearly 
 half a magnitude lower than I did. We can here only arrive at a mean 
 result, which would be about 18,000 from the first to the seventh mag- 
 nitudes inclusive. Sir John Herschel, in the passage of the Outlines of 
 Astronomy, p. 521, to which you allude, speaks only of ' the whole num- 
 ber of stars already registered, down to the seventh magnitude inclu- 
 sive, amounting to from 12,000 to 15,000.' As regards the fainter stars, 
 Struve finds within the above-named zone (from 15 to +15), for 
 the faint stars of the eighth magnitude, ] 0,557 ; for those of the ninth, 
 37,739 ; and, consequently, 40,800 stars of the eighth, and 145,800 of the 
 ninth magnitude for the whole heavens. Hence, according to Struve, 
 we have, from the first to the ninth magnitude inclusive, 15,100+ 
 40,800+145,800=201,700 stars. He obtained these numbers by a 
 careful comparison of those zones or parts of zones which comprise the 
 same regions of the heavens, deducing by the calculus of probabilities 
 the number of stars actually present from the numbers of those com- 
 mon to, or different in, each zone. As the calculation was made from 
 a very large number of stars, it is deserving of great confidence. Bes- 
 sel has enumerated about 61,000 different stars from the first to the 
 ninth inclusive, in his collective zones between 15 and +45, after 
 deducting such stars as have been repeatedly observed, together with 
 those of the 9 - 10 magnitude; whence we may conclude, after taking 
 into account such as have probably been overlooked, that this portion 
 of the heavens contains about 101,500 stars of the above-named magni- 
 tudes. My zones between -j-45 and -|-80 contain about 22,000 stars 
 (Durchmu sterung des ndrdl. Himmels, s. xxv.), which would leave about 
 19,000 after deducting 3000 for those belonging to the 9-10 magnitude. 
 My zones are somewhat richer than Bessel's, and I do not think we can 
 fairly assume a larger number than 2850 for the stars actually existing 
 between their limits (+45 and +80), whence we should obtain 
 130,000 stars to the ninth magnitude inclusive, between 15 and 
 -J-80 . This space is, however, only 0-62181 of the whole heavens, 
 and we therefore obtain 209,000 stars for the entire number, supposing 
 an equal distribution to obtain throughout the whole firmament ; these 
 numbers, again, closely approximate to Struve's estimate, and, indeed, 
 not improbably exceed it to a considerable ttent, since Struve reck- 
 oned stars of the 9-10 magnitude among thosrof the ninth. The num- 
 bers which, according to my view, may be ashamed for the whole firm- 
 ament, are therefore as follows : first mag., 20 ; second, 65 ; third, 190 ; 
 fourth, 425; fifth, 1100; sixth, 3200; seventh, 13,000; eighth, 40,000; 
 ninth, 142,000 ; and 200,000 for the entire number of stars from the 
 first to the ninth magnitude inclusive. 
 
 If you would contend that Lalande {Hist. Celeste, p. iv.) has given 
 the number of stars observed by himself with the naked eye at 6000, I 
 would simply remark that this estimate contains very many that have 
 been repeatedly observed, and that after deducting these, we obtain 
 only about 3800 stars for the portion of the heavens between 26 30*
 
 NUMBER OF THH FIXED STARS. 107 
 
 1st Mag. SdMag. 3d Mag. 4th Mag. 5th Mag. 
 
 20 65 190 425 1100 
 
 6th Mag. 7th Mag. 8th Mag. 9th Mag. 
 
 3200 13,000 40,000 142,000 
 The number of stars distinctly visible to the naked eye 
 (amounting in the horizon of Berlin to 4022, and in that of 
 Alexandria to 4638) appears at first sight strikingly small.* 
 If we assume the moon's mean semi-diameter at 15' 33"' 5, 
 it would require 195,291 surfaces of the full moon to cover 
 the whole heavens. If we further assume that the stars are 
 uniformly distributed, and reckon in round numbers 200,000 
 stars from the first to the ninth magnitude, we shall have 
 nearly a single star for each full-moon surface. This result 
 explains why, also, at any given latitude, the moon does not 
 more frequently conceal stars visible to the naked eye. If the 
 calculation of occultations of the stars were extended to those 
 of the ninth magnitude, a stellar eclipse would, according to 
 Galle, occur on an average every 44' 30", for in this period 
 the moon traverses a portion of the heavens equal in extent 
 to its own surface. It is singular that Pliny, who was un- 
 doubtedly acquainted with Hipparchus's catalogue of stars, 
 
 and +90 observed by Lalande. As this space is 723 1 of the whole 
 heavens, we should again have for this zone 5255 stars visible to the 
 naked eye. An examination of Bode's Uranography (containing 17,240 
 stars), which is composed of the most heterogeneous elements, does not 
 give more than 5600 stars from the first to the sixth magnitude inclusive, 
 after deducting the nebulous spots and smaller stars, as well as those 
 of the G-7th magnitude, which have been raised to the sixth. A simi- 
 lar estimate of the stars registered by La Caille between the south pole 
 and the tropic of Capricorn, and varying from the first to the sixth mag- 
 nitude, presents for the whole heavens two limits of 3960 and 5900, and 
 thus confirms the mean result already given by yourself. You will 
 perceive that I have endeavored to fulfill your wish for a more thor- 
 ough investigation of these numbers, and I may further observe that M. 
 Heis, of Aix-la-Chapelle, has for many years been engaged in a very 
 careful revision of my Uranometrie. From the portions of this work 
 already complete, and from the great additions made to it by an observ 
 er gifted with keener sight than myself, I find 2836 stars from the first 
 to the sixth magnitude inclusive for the northern hemisphere, and there- 
 fore, on the presupposition of equal distribution, 5672 as the number 
 of stars visible throughout the whole firmament to the keenest unaided 
 vision." {From the Manuscripts of Professor Argelander, March, 1850.) 
 * Schubert reckons the number of stare, from the first to the sixth 
 magnitude, at 7000 for the whole heavens (which closely approximates 
 to the calculation made by myself in Cosmos, vol. i., p. 150), and up- 
 ward of 5000 for the horizon of Paris. He gives 70,000 for the whole 
 sphere, including stars of the ninth magnitude. (Astronomic, th. in., s. 
 54.) These numbers are all much too high. Argelander finds only 
 58,000 from the 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 have 
 enumerated only 1600 stars visible in the fine sky of Italy !* 
 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 (navv 
 oAoo^epoif), 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 
 statement 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 
 
 * " Patrocinatur vastitas cceli, immensa discreta altitudine, in duo at- 
 que septuaginta signa. Haec sunt rerum et animantium effigies, in quas 
 digessere ccelum periti. In his quidem mille sexcentas adnotavere stel- 
 las, iusignes videlicet effectu visuve" .... Plin., ii., 41. "Hipparchus 
 nunquam satis laudatus, ut quo nemo magis approbaverit cognationera 
 cum homine siderum animasque nostras partem esse coeli, novam stel 
 lam et aliam in aevo suo genitam deprehendit, ejusque motu, qua die 
 fulsit, ad dubitationem est adductus, anne hoc saepius fieret moveren- 
 turque et ese quas putamus affixas ; itemque ausus rem etiam Deo im- 
 probam, adnumerare posteris Stellas ac sidera ad nomen expungere, or- 
 ganis excogitatis, per quse 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- 
 renturque, coelo in hereditate cunctis relicto, si quisquam qvi cretioneru 
 earn caperet inventus esset." Plin., ii., 26. 
 
 t Delambre, Hist, de VAstr. Anc., torn, i., p. 290, and Hist, de VAstr. 
 Mod., torn, ii., p. 186.
 
 NUMBER OF THE FIXED STARS. 109 
 
 star in Cassiopeia (November, 1572) led Tycho Brahe to 
 compose his catalogue of the stars. According to an ingen- 
 ious conjecture 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,f 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 stars, 
 which are determined more by equatorial armillse 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 ; Edward Biot, Sur les Etoilet Extraordinaire* ob- 
 servles en Chine, in the Connaissance des temps pour 1846. 
 
 t It is worthy of remark that Aratus was mentioned with approba- 
 tion almost simultaneously by Ovid (Amor., i., 15) and by the Apostle 
 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. 
 
 \ Ideler, Untersuchungen fiber den Unsprung der Stemnamen, s. xxx. 
 xxxv. Daily, in the Mem. of the Astron. 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 Ptolemy (138 
 AD.).
 
 110 COSMOS. 
 
 to the ecliptic.* On comparing the number of fixed stars m 
 the Hipparcho-Ptolemaic Catalogue, Almagest, ed. Halma, 
 t. ii., p. 83 (namely, for the first mag., 15 stars ; second, 45 ; 
 third, 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 their 
 positions as if they had been observed in the year 63 of our 
 era, yet, throughout the sixteen hundred years immediately 
 following this period, we have only three original catalogues 
 of stars, perfect for their time ; that of Ulugh Beg (1437), 
 
 * Compare Delambre, Hist, de I'Astr. Anc., torn, i., p. 184; torn, ii., 
 p. 260. The assertion that Hipparchus, in addition to the right 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- 
 gest, 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 facilitated. The table of 
 stars with the longitudes attached, which Petrus Victorius 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 T ^ too slow, the catalogue which he determined 
 for the beginning of tne reign of Antoninus (Ideler, op. cit., B. xxxiv.) 
 indicates the positions of the stars at a much earlier epoch (for the year 
 63 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 Astron. Nachr., 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 connec- 
 tion with the poem of Hermes by the true Eratosthenes. (Eratostheni- 
 ea, ed. Bernhardy, 1822, p. 114, 116, 129.) These Pseudo-Eratosthe- 
 nian Catasterisms contain, moreover, scarcely 700 individual stars dis- 
 tributed among the mythical constellations.
 
 EARLY CATALOGUES. -Ill 
 
 that of Tycho Brahe (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, under 
 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 Rokh), 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 (who 
 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,f pendulum- 
 oscillationsj 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, 4 
 
 * 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 derive their name from the title " Ilkhan," assumed by the Tar- 
 tar princes who held rule in Persia. Reinaud, Introd. de la Gfogr. 
 d'Aboulfeda, 1848, p. cxxxix. 
 
 t [For an account of clepsydras, see Beckmann's Inventions, voL i., 
 341, et seq. (Bohn's edition).] Ed. 
 
 t Sedillot fils, Prolegomenes des Tables Astr. d' Oloug-Beg, 1847, p. 
 cxxxiv., note 2. Delambre, Hist, de I' Astr. du May en Age, p. 8. 
 
 $ In my investigations on the relative value of astronomical determ- 
 inations of position in Central Asia (Asie Centrale, t. iii., p. 581-596), I 
 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 former is probably more than 39 52', while most 
 of the best manuscripts of Ulugh Beg give 39 37', and the Kitab aL- 
 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 Travels 
 have made us acquainted with the latitude of Bokhara, as obtained from 
 observations of culmination of 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- 
 nell, whoso combinations are generally so successful, made an error of
 
 112 COSMOS. 
 
 and not visible in 39 52' lat. (?) It contains only 1019 
 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 
 high 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 
 works, 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 Yanez 
 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 Cardanus 
 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, and 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' in determining the latitude of Bokhara. (Humboldt, A fie 
 Centrale, t. iii., p. 592, and Sedillot, in the Proligorllenes d' Olov.g-Beg, 
 p. cxxiii.-cxxv.) 
 
 * Cosmos, vol. ii., p. 285-29C ; Humboldt, Examen Crit. de VHisloirt 
 de la Gtogr., t. iv., p. 321-336 : t. v., p. 226-238. 
 
 t Cardani Paralipomenon, lib. viii., cap. 10. (Opp., t. ix., ed. Lugd . 
 1663, p. 508.)
 
 PROGRESS OP ASTRONOMY. 113 
 
 the laborious observations of the Landgrave "William IV. at 
 Cassel. Tycho Brahe's catalogue, as revised and published 
 by Kepler, contains no more than 1000 stars, of which one 
 fourth at most belong to the sixth magnitude. This cata- 
 logue, and that of Hevelius, which was less frequently em- 
 ployed, and contained 1564 determinations of position for the 
 year 1660, were the last which were made by the unaided 
 eye, owing their compilation in this manner to the capricious 
 disinclination of the Dantzig astronomer to apply the telescope 
 to purposes of measurement. 
 
 This combination of the telescope with measuring instru- 
 ments the union of telescopic vision and measurements 
 at length enabled astronomers to determine the position of 
 stars below the sixth magnitude, and more especially between 
 the seventh and the twelfth. The region of the fixed stars 
 might now, for the first time, be said to be brought within 
 the reach of observers. Enumerations of the fainter tele- 
 scopic stars, and determinations of their position, have not 
 only yielded the advantage of making a larger portion of the 
 regions of space known to us by the extension of the sphere 
 of i nervation, but they have also (what is still more import- 
 ant) indirectly exercised an essential influence on our knowl- 
 edge of the structure and configuration of the universe, on 
 tiiv.- discovery of new planets, and on the more rapid determ- 
 ination of their orbits. When William Herschel conceived 
 the happy idea of, as it were, casting a sounding line in the 
 depths of space, and of counting during his gaugings the stars 
 which passed through the field of his great telescope,* at 
 different distances from the Milky Way, the law was discov- 
 ered that the number of stars increased in proportion to their 
 vicinity to the Milky Way a law which gave rise to the 
 idea of the existence of large concentric rings filled with 
 millions of stars which constitute the many-cleft Galaxy. 
 The knowledge of the number and the relative position of 
 the faintest stars facilitates (as was proved by Galle's rapid 
 and felicitous discovery of Neptune, and by that of several 
 of the smaller planets) the recognition of planetary cosmic al 
 bodies which change their positions, moving, as it were, be- 
 tween fixed boundaries. Another circumstance proves even 
 more distinctly the importance of very complete catalogues 
 of the stars. If a new planet be once discovered in the 
 vault of heaven, its notification in an older catalogue of po- 
 
 Cosmos, vol. i., p. 87-89.
 
 114 COSMOS. 
 
 eitions will materially facilitate the difficult calculation of 
 its orbit. The indication of a new star which has subse- 
 quently been lost sight of, frequently affords us more assist- 
 ance than, considering the slowness of its motion, we can 
 hope to gain by the most careful measurements of its course 
 through many successive years. Thus the star numbered 964 
 in the catalogue of Tobias Mayer has proved of great im- 
 portance for the determination of Uranus, and the star num- 
 bered 26,266 in Lalande's catalogue* for that of Neptune 
 Uranus, before it was recognized as a planet, had, as is now 
 well known, been observed twenty-one times ; once, as al- 
 ready stated, by Tobias Mayer, seven times by Flamstead, 
 once by Bradley, and twelve times by Le Monnier. It may 
 be said that our increasing hope of future discoveries of plan- 
 etary bodies rests partly on the perfection of our telescopes 
 (Hebe, at the time of its discovery in July, 1847, was a star 
 of the 8-9 magnitude, while in May, 1849, it was only of the 
 eleventh magnitude), and partly, and perhaps more, on the 
 completeness of our star catalogues, and on the exactness 
 of our observers. 
 
 The first catalogue of the stars which appeared after the 
 epoch when Morin and Gascoigne taught us to combine tele- 
 scopes with measuring instruments, was that of the southern 
 stars compiled by Halley. It was the result of a short resi- 
 dence at St. Helena in the years 1677 and 1678, but, singu- 
 larly enough, does not contain any determinations below the 
 sixth magnitude.! Flamstead had, indeed, begun his great 
 Star Atlas at an earlier period ; but the work of this cele- 
 brated observer did not appear till 1712. It was succeeded 
 by Bradley's observations (from 1750 to 1762), which led to 
 the discovery of aberration and nutation, and have been ren- 
 dered celebrated by the Fundamenta Astronomice of our 
 countryman Bessel (1818),^ and by the stellar catalogues of 
 
 * Bally, Cat. of those stars in the "Histoire Celeste" of Jerome de 
 Lalande,for which tables of reduction to the epoch 1800 have been pub- 
 lished by Prof. Schumacher, 1847, p. 1195. On what we owe to the 
 perfection of star catalogues, see the remarks of Sir John Herschel in 
 Cat. of the British Assoc., 1845, p. 4, 10. Compare also on stars that 
 have disappeared, Schumacher, Astr. Nachr., No. 624, and Bode, Jahrb. 
 fur 1817, s 249. 
 
 t Memoirs of the Royal Astron. Soc., vol. xiii., 1843, p. 33 and 168. 
 
 t Bessel, Fundamenta Astronomies pro anno 1755, deducta ex observa- 
 tionibus viri incomparabilis James Bradley in Specula astronomica Ore- 
 novicensi, 1818. Compare also Bessel, Tabula Regiomontancn reduclio- 
 num observationum astronomicarum ab anno 1750 usque ad annum 1850 
 computatoE (1830).
 
 STAR CATALOGUES. 115 
 
 La Caille, Tobias Mayer, Cagnoli, Piazzi, Zach, Pond, Taylor, 
 Groombridge, Argelander, Airy, Brisbane, and Riimker. 
 
 We here only allude to those works which enumerate a 
 great and important part* of the stars of the seventh to the 
 tenth magnitude which occupy the realms of space. The 
 catalogue known under the name of Jerome de Lalandt's, 
 but which is, however, solely based on observations made by 
 his nephew, Francois de Lalande, and by Burckhardt between 
 the years 1789 and 1800, has only recently been duly appre- 
 ciated. After having been carefully revised by Francis Baily, 
 under the direction of the " British Association for the Ad- 
 vancement of Science" (in 1847), it now contains 47,390 
 stars, many of which are of the ninth, and some even below 
 that magnitude. Harding, the discoverer of Juno, catalogued 
 above 50,000 stars in twenty-seven maps. Bessel's great 
 work on the exploration of the celestial zones, which comprises 
 75,000 observations (made in the years 1825-1833 between 
 15 and +45 declination), has been continued from 1841 
 to 1844 with the most praiseworthy care, as far as +80 
 decl., by Argelander at Bonn. Weisse of Cracow, under the 
 auspices of the Academy of St. Petersburgh, has reduced 
 31,895 stars for the year 1825 (of which 19,738 belonged to 
 the ninth magnitude) from Bessol's zones, between 15 and 
 + 15 decl. ;t and Argelander' s exploration of the northern 
 heavens from +45 to +80 decl. contains about 22,000 
 well-determined positions of stars. 
 
 * I here compress into a note the numerical data taken from star cat- 
 alogues, containing lesser masses and a smaller number of positions, 
 with the names of the observers, and the number of positions attached : 
 La Caille, in scarcely ten months, during the years 1751 and 1752, with 
 instruments magnifying only eight times, observed 9766 southern stars, 
 to the seventh magnitude inclusive, which were reduced to the year 
 1750 by Henderson ; Tobias Mayer, 998 stars to 1756 ; Flamstead, orig- 
 inally only 2866, to which 564 were added by Daily's care (Mem. of the 
 Astr. Soc., vol. iv., p. 1291-64); Bradley, 3222, reduced by Bessel to 
 the year 1755; Pond, 1112; Piazzi,,7646 to 1800; Groombridge, 4243, 
 mostly circumpolar stars, to 1810 ; Sir Thomas Brisbane, and Rflmker, 
 7385 stars, observed in New Holland in the years 1822-1828 ; Airy, 2156 
 stars, reduced to the year 1845 ; Riimker, 12,000 on the Hamburg hori- 
 zon; Argelander (Cat. of Abo), 560; Taylor (Madras), 11,015. The 
 British Association Catalogue of Stars (1845), drawn up under Baily's 
 superintendence, contains 8377 stars from the first to 7i magnitudes. 
 For the southern stars we have the rich catalogues of Henderson, Fal- 
 lows, Maclear, and Johnson at St. Helena. 
 
 t Weisse, Positiones media stellarum fixarum in Zonis Regiomontanit 
 a Bessclio inter 15 ct -J-15 decl. observatanim ad annum 1825 re 
 dvcla (1846); with an important Preface by Struve.
 
 116 COSMOS. 
 
 I can not, I think, make mere honorable mention of the 
 great work of the star maps of the Berlin Academy than by 
 quoting the words used by Encke in reference to this un- 
 dertaking, in his oration to the memory of Bessel : '' With 
 the completeness of catalogues is connected the hope that, 
 by a careful comparison of the different aspects of the heav- 
 ens with those stars which have been noted as fixed points, 
 we may be enabled to discover all moving celestial bodies, 
 whose change of position can scarcely, owing to the faint- 
 ness of their light, be noted by the unaided eye, and that 
 we may in this manner complete our knowledge of the so- 
 lar system. While Harding's admirable atlas gives a per- 
 fect representation of the starry heavens as far as Lalande's 
 Histoire Celeste, on which it is founded, was capable of af- 
 fording such a picture Bessel, in 1824, after the comple- 
 tion of the first main section of his zones, sketched a plan 
 for grounding on this basis a more special representation of 
 the starry firmament, his object being not simply to exhibit 
 what had been already observed, but likewise to enable as- 
 tronomers, by the completeness of his tables, at once to rec- 
 ognize every new celestial phenomenon. Although the star 
 maps of the Berlin Academy of Sciences, sketched in ac- 
 cordance with Bessel's plan, may not have wholly completed 
 the first proposed cycle, they have nevertheless contributed 
 in a remarkable degree to the discovery of new planets, since 
 they have been the principal, if not the sole means, to which, 
 at the present time (1850), we owe the recognition of seven 
 new planetary bodies."* Of the twenty-four maps designed 
 to represent that portion of the heavens which extends 15 
 on either side of the equator, our Academy has already con- 
 tributed sixteen. These contain, as far as possible, all stars 
 down to the ninth magnitude, and many of the tenth. 
 
 The present would seem a fitting place to refer to the 
 average estimates which have been hazarded on the num- 
 ber of stars throughout the whole heavens, visible to us by 
 the aid of our colossal space-penetrating telescopes. Struve 
 assumes for Herschel's twenty-feet reflector, which was em- 
 ployed in making the celebrated star-gauges or sweeps, that 
 a magnifying power of 180 would give 5.800,000 for the 
 number of stars lying within the zones extending 30 on ei- 
 ther side of the equator, and 20,374,000 for the whole heav- 
 ens. Sir Wilh'am Herschel conjectured that eighteen mill- 
 
 * Encke, Geddchtnissrede auf Bessel, s. 13.
 
 DISTRIBUTION OF THE FIXED STARS. 117 
 
 ions of stars in the Milky Way might be seen by his still 
 more powerful forty-feet reflecting telescope.* 
 
 After a careful consideration of all the fixed stars, wheth- 
 er visible to the naked eye or merely telescopic, whose po- 
 sitions are determined, and which are recorded in catalogues, 
 we turn to their distribution and grouping in the vault of 
 neaven. 
 
 As we have already observed, these stellar bodies, from 
 the inconsiderable and exceedingly slow (real and apparent) 
 change of position exhibited by some of them partly owing 
 to precession and to the different influences of the progression 
 of our solar system, and partly to their own proper motion 
 may be regarded as landmarks in the boundless regions of 
 space, enabling the attentive observer to distinguish all bod- 
 ies that move among them with a greater velocity or in an 
 opposite direction consequently, all which are allied to tel- 
 escopic comets and planets. The first and predominating 
 interest excited by the contemplation of the heavens is di- 
 rected to the fixed stars, owing to the multiplicity and over- 
 whelming mass of these cosmical bodies ; and it is by them 
 that our highest feelings of admiration are called forth. 
 The orbits of the planetary bodies appeal rather to inquiring 
 reason, and, by presenting to it complicated problems, tend 
 to promote the development of thought in relation to astron- 
 omy. 
 
 Amid the innumerable multitude of great and small stare, 
 which seem scattered, as it were by chance, throughout the 
 vault of heaven, even the rudest nations separate single 
 (and almost invariably the same) groups, among which cer- 
 tain bright stars catch the observer's eye, either by their 
 proximity to each other, their juxtaposition, or, in some cases, 
 by a kind of isolation. This fact has been confirmed by re- 
 cent and careful examinations of several of the languages of 
 so-called savage tribes. Such groups excite a vague sense 
 of the mutual relation of parts, and have thus led to their 
 receiving names, which, although varying among different 
 races, were generally derived from organic terrestrial ob- 
 jects. Amid the forms with which fancy animated the 
 waste and silent vault of heaven, the earliest groups thus 
 distinguished were the seven-starred Pleiades, the seven stars 
 of the Great Bear, subsequently (on account of the repetition 
 of the same form) the constellation of the Lesser Bear, the 
 
 * Compare Struve, Etudes d'Astr. Sttllaire, 1847, p. 66 and 72 ; Cot- 
 mo$, vol. i., p. 100; ami Madlec Astr., 4te Aufl., $ 417.
 
 118 COSMOS 
 
 belt of Orion (Jacob's stafT), Cassiopeia, the Swan, the Soor 
 pion, the Southern Cross (owing to the striking difference 
 in its direction before and after its culmination), the South- 
 ern Crown, the Feet of the Centaur (the Twins, as it were, 
 of the Southern hemisphere), &c. 
 
 "Wherever steppes, grassy plains, or sandy wastes present 
 a far-extended horizon, those constellations whose rising or 
 setting corresponds with the busy seasons and requirements 
 of pastoral and agricultural life have become the subject of 
 attentive consideration, and have gradually led to a symbol- 
 izing connection of ideas. Men thus became familiarized 
 with the aspect of the heavens before the development of 
 measuring astronomy. They soon perceived that besides 
 the daily movement from east to west, which is common to 
 all celestial bodies, the sun has a far slower proper motion in 
 an opposite direction. The stars which shine in the even- 
 ing sky sink lower every day, until at length they are wholly 
 lost amid the rays of the setting sun ; while, on the other 
 hand, those stars which were shining in the morning sky 
 before the rising of the sun, recede further and further from 
 it. In the ever-changing aspect of the starry heavens, suc- 
 cessive constellations are always coming to view. A slight 
 degree of attention suffices to show that these are the same 
 which had before vanished in the west, and that the stars 
 which are opposite to the sun, setting at its rise, and rising 
 at its setting, had about half a year earlier been seen in its 
 vicinity. From the time of Hesiod to Eudoxus, and from 
 the latter to Aratus and Hipparchus, Hellenic literature 
 abounds in metaphoric allusions to the disappearance of the 
 stars amid the sun's rays, and their appearance in the morn- 
 ing twilight their heliacal setting and rising. An atten- 
 tive observation of these phenomena yielded the earliest ele- 
 ments of chronology, which were simply expressed in num- 
 bers, while mythology, in accordance with the more cheerful 
 or gloomy tone of national character, continued simultane- 
 ously to rule the heavens with arbitrary despotism. 
 
 The primitive Greek sphere (I here again, as in the his- 
 tory of the physical contemplation of the universe,* follow 
 the investigations of my intellectual friend Letronne) had be- 
 come gradually filled with constellations, without being in 
 any degree considered with relation to the ecliptic. Thus 
 Homer and Hesiod designate by name individual stars and 
 
 * Cosmos, vol. ii., j>. 167
 
 ZODIACAL SIGNS. 119 
 
 groups ; the former mentions the constellation of the Bear 
 (" otherwise known, as the Celestial Wain, and which alone 
 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, merely allows us to infer that in 
 his age the Greek sphere did not yet comprise the constella- 
 tions of Draco, Cepheus, and Ursa Minor, which 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 (lib. i., p. 3, Casaub.) on Homer, II., 
 xviii., 485-489, specially proves a fact important to the 
 question that in the Greek sphere the stars were only grad- 
 ually arranged in constellations. Homer has been unjustly 
 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 Phoanicians 
 had specially 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 <&otviKTj (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^OTT/C, and Aries, K.pi6$. 
 
 The introduction of the Zodiac into the ancient Greek 
 sphere coincides, according to Letronne, with this period of 
 the domination of the Pisistratidae. Eudemus of Rhodes, one 
 of the most distinguished pupils of Aristotle, and author of a 
 "History of Astronomy," ascribes the introduction of this zo- 
 diacal belt (TI TOV fadiaicov dia^dxrig, also wt Jio^ /cvwAof) to 
 (Enopides of Chios, a cotemporary of Anaxagoras.f The 
 
 * Ideler, Unters. uber die Sternnamen, s. xi., 47, 139, 144, 2 13 Le- 
 tronne, Sur V Origins du Zodiaque Grec, 1340, p. 25. 
 
 t Letronne, op. cit., p. 25 ; and Carteron, Analyse de Rechercn.es de 
 tl. Letronne sur les Representations Zodiacales, 1843, p. 119. "It ia 
 Yery doubtful whether Eudoxus (Ol. 103) ever made use of the word 
 Cudianof. We first meet with it in Euclid, and in the Commentary of 
 Hipparchus on Aratus (Ol. 160). The name ecliptic, eKfautTiicdf, is 
 also very recent." Compare Martin in the Commentary to Thconi* 
 Smyrn<ri Plalonici Liber de Aslronotnia, 1849, p. 50, GO.
 
 120 COSMOS. 
 
 idea of the relation of the planets and fixed stars to the sun'* 
 course, the division of the ecliptic into twelve equal parts 
 (Dodecatomeria), originated with the ancient Chaldeans, and 
 very probably came to the Greeks, at the beginning of the 
 fifth, 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 thing more than the idea and 
 number of the divisions (Dodecatomeria) of a zodiac if they 
 had borrowed the zodiac itself, with its signs they would 
 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 Capricornus, 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, Hipparchus. It 
 is never mentioned by Eudoxus, Archimedes, Autolycus, or 
 even by Hipparchus in the few fragments of his writings 
 which have been transmitted to us (excepting indeed in one 
 
 * Letronne, Orig. du Zod., p. 25 ; and Analyse Crit. des Reprtt. 
 Zod., 1846, p. 15. Ideler 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 d*te." (Lepsius, Chronologic der ^Egypter, 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 
 signs, they are hardly likely to hava removed one in order to replace it 
 at a subseq :en* period.
 
 ZODIACAL SIGNS. 121 
 
 passage, probably falsified by a copyist).* The earliest no- 
 tice of this new constellation occurs in Geminus and Varro 
 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 predilection for astrological inquiry, those 
 constellations which " lay in the celestial path of the sun" 
 acquired an exaggerated and fanciful importance The Egyp- 
 tian zodiacal constellations found at Dendera, Esneh, the 
 Propylon of Panopolis, and on some mummy-cases, belong to 
 the first half of this period of the Roman 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, Valmiki's Ramayana and Amarasinha's Dictionary, 
 Augustus "William von Schlegel attributed to the zodiacal 
 circles found in India, has been rendered very doubtful by 
 Adolph Holtzmann's ingenious investigations.! 
 
 * On the passage referred to in the text, and interpolated by a copy 
 ist of Hipparchus, see Letronne, Orie. du Zod., 1840, p. 20. As early 
 as 1812, when I was much disposed to believe that the Greeks had 
 been long acquainted with the sign of Libra, I directed attention in an 
 elaborate memoir (on all the passages in Greek and Roman writers of 
 antiquity, in which the Balance occurs as a sign of the zodiac) to that 
 passage in Hipparchus (Comment, in Aratum, lib. iii., cap. 2) which re- 
 fers to the tiripiov 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 KOTO 
 
 f , 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 Cordilleret et Monument des Peuples Indigenes de I'Amerique, 
 t. ii., p. 380.) Buttman maintained, what is very improbable, that the 
 7/A<u originally signi6ed the two scales of the Balance, and were sub- 
 sequently by some misconception converted into the pincers of a scor- 
 pion. (Compare Ideler, Untersuchungen uber die astronomischen Beo- 
 bachtungen der Alien., 8. 374, and Ueber die Sternnamen, s. 174-177, 
 with Carteron, 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. ( Vites des Cordilleres, t. ii., p. 6-12.) 
 
 t Compare A. W. von Schlegel, Ueber Sternbilder des Thierkreises im 
 alien Indien, in the Zeitschrift fur die Kunde det Morgenlandes, bd. i., 
 Heft 3, 1837, and his Commentatio de Zodiari Antiquitate et Origins, 
 1839, with Adolph Holtzmaun, Ueber den Griechtichen Ursprung det In 
 
 Vo*. III. F
 
 122 COSMOS. 
 
 The artifical grouping of the stars into constellations, 
 which arose incidentally during the lapse of ages the fre- 
 quently inconvenient extent and indefinite outline the com- 
 plicated designations of individual stars in the different 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, Centaurus, Argo, and Eridanus alone possess any 
 poetic interest.* 
 
 The heavens of the fixed stars (orbis inerrans of Apule- 
 ius), and the inappropriate expression of fixed stars (astro, 
 fixa of Manilius), reminds us, as we have already observed 
 in the introduction to the Astrognosy,f 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 (dnXavrj darpa) riveted (ivdede^iva), when 
 Ptolemy designates them as ingrafted (TrpoanefivKorec;), these 
 terms refer specially to the idea entertained by Anaximenes 
 of the crystalline sphere of heaven. The apparent motion 
 of all the fixed stars from east to west, while their relative 
 distances remained unchanged, had given rise to this hypoth- 
 esis. " The fixed stars (drrAavr/ aarpa) belong to the higher 
 and more distant regions, in which they are riveted, like nails, 
 
 dischcn Thierkreises, 1841, s. 9, 16, 23. " The passages quoted from 
 Amorakoscha and Ramayana," 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. Jahrbuchfur 1822, s. 93, Ol- 
 bers on the more recent constellations in Schumacher's Jahrbuch fur 
 1840, s. 283-251, and Sir John Herschel, Revision and Rearrangement 
 of the Constellations, with special reference to those^ of the Southern Hem- 
 uphere, 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 Bode 
 on the introduction of his domestic cat and of a reaper (Messier!), Ol- 
 bers complains that in order " to find space in the firmament for Kirg 
 Frederic's glory, Andromeda must lay her right arm in a different place 
 from that which it had occupied for 3000 years !" 
 
 t Vide supra, p. 26-28, and note.
 
 THE FIXED STARS. 123 
 
 to the crystalline heavens ; the planets (aarpa 
 or TrAavT/rd), which move in an opposite direction, belong to 
 a lower and nearer region."* As we find in Manilius, in 
 the earliest ages of the Caesars, that the term Stella fixa was 
 substituted for infixa or affiza, it may be assumed that the 
 schools of Rome attached thereto at first only the original 
 signification of riveted ; but as the word Jixus 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 world 
 of the fixed stars fixum et immobilem populum. 
 
 Although, according to Stobseus, 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 
 which the term is based occurs in Empedocles. This phi- 
 losopher regarded the heaven of the fixed stars as a solid 
 mass, formed from the ether which had been rendered crys- 
 talline and rigid by the action of fire.f According to his 
 
 * According to Democritus and his disciple Metrodorus, Stob., Eclog. 
 Phys., p. 582. 
 
 t Plut., De plac. Phil., ii., 11; Diog. Laert., viii., 77; Achilles Tat., 
 ad. Arat., cap. 5, EMTT, Kpvara^un TOVTOV (TOV ovpavbv) elvai (fujaiv, ix 
 TOV KayeTudovc. ffv/.AeyevTO ; in like manner, we only meet with the 
 expression crystal-likti in Diog. Laert., viii., 77, and Galenus, Hist. Phil., 
 I'-i (Sturz, Empedocles Agrigent., t. i., p. 321). Lactautius, De Opificio 
 Dei, c. 17 : " An, si milii quispiam dixerit tcncum esse ccelum, aut vi- 
 treum, aut, ut Empedocles ait, aCrem glacialum, statimne assentiat quia 
 cajliim 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 
 what 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 (cesium vitreum'), for only one celestial body, the sun, is called 
 by PhilolaUs 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. Prtep. Evangel., 1, p. 
 24, D, and De Facie in Orbe Lunte, cap. 5.) Where Uranos is described 
 as xaZiceof and otdrjpeof 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. V61cker uber Homerische Geo- 
 graphie, 1830. s. 5. The earliest mention, before Pliny, of the word 
 Kov<Tra/lAof when applied to ice-like, transparent rock-crystal, occurs in 
 Uionysius Periegetes, 781, Lilian, xv., 8, and Strabo, xv., p. 717 Ca-
 
 124 COSMOS. 
 
 theory, the moon is a body conglomerated (like hail) by the 
 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 (atr glacintvs of Lactantius) arose among the ancients, from 
 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 Casio, 11, 7, p. 289.) In speaking of the 
 music of the spheres (Aristot., De Casio, 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 Caelo, 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, 
 aud hence heat is diffused to the surface of the earth." (Meteorol., 1, 3, 
 p. 340.) It has always struck me as a circumstance worthy of remark, 
 that the Stagirite should constantly avoid the word crystal heaven; for 
 the expression, " riveted stars" (kv6ede[ieva aarpa), which he uses, in- 
 dicates a general idea of solid spheres, without, however, specifying the 
 nature of the substance. We do riot 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 enim not 
 solum ten-am sed ipsum quoque coelum, quod vere mundus vocatur, 
 temperari a sole certissimum est, ut extremitates ejus, quae via solis 
 longissime recesserunt, omni careant beneficio caloris, et una frigoris 
 perpetuitate torpescant." " For as it is most certain that not only the 
 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 perjpetual cold." These confines of heaven (ex- 
 tremitates cceli), 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, are 
 within the actual atmosphere, for beyond the 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 this 
 eternal cold: " Stellte supra coalum locate, in ipso purissimo asthere suut, 
 in quo omne quidquid est, lux naturalis et sua est, quae tota cum igne 
 suo its sphasrae solis incumbit, ut cceli zonas, quas procul a sole suut, 
 perpetno frigore oppressae sint." " The stars above the heavens are 
 situated 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 its 
 fire, that those zones of heaven which are far from the sun are oppress- 
 ed by perpetual cold." My reason for entering so circumstantially into 
 the physical and meteorological ideas of the Greeks and Romans is sim- 
 ply because these subjects, except in the works of Ukert, Henri Martin,
 
 THB FIXED STARS. 125 
 
 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 jcpvaroAAof, fpuoc, and *pwrr<uv&>. 
 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 Lac- 
 tantius : " Ccelum aerem glaciatum esse" and " vitreum coe- 
 lum." Empedocles undoubtedly did not refer to the glass of 
 the Phoenicians, but to air, which was supposed to be con- 
 densed into a transparent solid body by the action of the fiery 
 ether. In this comparison with ice (cpvoTaAAof), 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 crystalline or crystal-like, 
 Kpvo-a/J.oi6fi$. In like manner, Trayoc (from tr^ywaBfu, 
 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 different 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 in 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 fragment of the Meteorologia Vetenm of Julias Ide- 
 ler. have hitherto been very imperfectly, and, for the most part, super 
 ficially considered. 
 
 * The ideas that fire has the power of making rigid (Aristot., ProbL, 
 xiv.. 11). and that the formation of ice itself may be promoted by beat, 
 are deeply rooted in the physics of the ancients, and based on a fanci- 
 ful theory of contraries (AnJiperittatit) on obscure conceptions of po- 
 larity (of exciting opposite qualities or conditions). ( Vide mpra, p. 
 14, and note.) The quantity of hail produced was considered to be 
 proportional to the degree of heat of the atmospheric strata. (Aristot., 
 Meteor., i.. 12.) In the winter fishery on the shores of the Euxin-s 
 warm water was used to increase the ice formed in the neighborhood 
 of an upright tube. (Alex. Aphrodu., foL 86, and Plat, De\ 
 do, c. 12.)
 
 126 COSMOS. 
 
 tal vault shattered by it in its fall. Kepler, from his con- 
 siderations 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 tki? 
 more ancient retrograde epicycles. The ideas entertained 
 by such great thinkers as Eudoxus, Mensechmus, Aristotle, 
 and Apollonius Pergaeus, 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,t and which are not devoid of interest 
 in our endeavors to distinguish the different 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 different individuals. Indistinct- 
 ness of vision (la vue indistincte) arises from numerous or- 
 ganic causes, depending on aberration of the sphericity of 
 
 * Kepler expressly says, in his Stella Mortis, fol. 9 : " Solidos orbes 
 rejeci." "I have rejected the idea of solid orbs;" and in the Stella 
 Nova, 1606, cap. 2, p. 8: " Planetse in puro aethere, perinde atque 
 aves in aftre cursus suos conficiunt." " The planets perform their 
 course in the pure ether as birds pass through the air." Compare also 
 p. 122. He inclined, however, at an earlier period, to the idea of a 
 solid icy vault of heaven congealed from the absence of solar heat : 
 " Orbis ex. aqua factus gelu concreta propter solis absentiam." (Kepler, 
 Epit. 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" (roif Se Trhav- 
 firae avtiadai). (Plut., plac. Phil., ii., 13; Eraped., 1, p. 335, Sturz; 
 Euseb., Preep. Evang., xv., 30, col. 1688, p. 839.) It is difficult to con- 
 ceive how, according to Plato in the Titnueus ( Tim., p. 40, B ; see Bohn's 
 edition of Plato, vol. ii., p. 344; but not according to Aristotle), the fixed 
 stars, riveted as they are to solid spheres, could rotate independently. 
 
 t Cosmos, vol. ii., p 315, 316. t Vide supra, p. 51, and note.
 
 VELOCITY OF LIGHT. 
 
 tne eye, diffraction 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- 
 
 * "Le3 principales causes de la vue iudistincte sont: aberration de 
 sphericite de 1'oeil, diffraction sur les bords de la pupille, communica- 
 tion d'irritabilite 4 des points voisius sur la retine. La vue confuse est 
 celle ou le foyer ne tombe pas exactement sur la retine, mais tombe 
 au-clevant ou derriere la retine. Les queues des etoiles sont 1'effet de 
 la vision iudistincte, autant qu'elle depend de la constitution du cristal- 
 lin. D'apres un tres ancien m^moire de Hassenfratz (1809) ' les queues 
 au nombre de 4 ou 8 qu'offrent les etoiles ou une bougie vue 4 25 me- 
 tres de distance, sont les caustiques du cristallin formees par 1'interseo 
 tiou des rayons refractes.' Ces caustiques se meuvent a mesure que 
 nous iuclinons la tete. La propriete de la lunette de terminer 1'image 
 lait qu'elle concentre dans un petit espace la lumiere qui sans cela en 
 aurait occupe uu plus grand. Cela est vrai pour les etoiles fixes el 
 pour les disques des planetes. La lumiere des etoiles qui n'ont pas de 
 disque reels, conserve la me me intensite, quel que soil le grossissement. 
 Le foud de 1'air duquel se detache 1'etoile dans la lunette, devient plus 
 noir par le grossisseraent qui dilate les molecules de 1'air qu'embrasse 
 le champ de la lunette. Les planetes a vrais disques deviennent elles- 
 m^mes plus pales par cet effet de dilatation. Quand la peinture focale 
 est uette, quand les rayons partis <fun point de 1'objet se sont concen- 
 tr6s en un seul point dans 1'image, 1'oculaire donne des resultats satis- 
 faisants. Si au contraire les rayons emanes d'un point ne se reiinissent 
 pas au foyer en un seul point, s'ils y forment un petit cercle, les images 
 de deux points contigus de 1'objet empietent necessairement 1'une sur 
 1'autre; leurs rayons se confondeut. Cette confusion la lentille ocu- 
 laire ue saurait la faire disparaitre. L'office qu'elle remplit exclusive- 
 ment, c'est de grossir ; elle grossit tout ce qui est dans 1'image, les de- 
 fauts comme le reste. Les etoiles n'ayant pas de diametres angulaires 
 sensibles, ceux qu'elles conservent toujours, tiennent pour la plus grande 
 partie au manque de perfection des instrumens (. la courbure moins 
 reguliere donnee aux deux faces de la lentille objective) et & quelques 
 defauts et aberrations de notre ceil. Plus une 6toile semble petite, 
 tout etant egal quant au diametre de 1'objectif, au grossiasement em- 
 ploy6 et A 1'eclat de Petoile observee, et plus la lunette a de perfection. 
 Or le meilleur moyen de juger si les etoiles sont tres petites, si des 
 points sont representes au foyer par des simples points, c'est evidem- 
 ment de viser ^. des etoiles excessivement rapproch6es entr'elles et de 
 voir si dans les etoiles doubles connues les images se confondent, si 
 elles empietent 1'une sur 1'autre, ou bien si on les apercoit bien nette- 
 ment separees." 
 
 " The pi-incipal 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 crystalline 
 lens. According to a very old paper of Hassenfratz (1809), ' the four 
 or eight tails which surround the stars or a candle seen at a distance 
 of 25 metres [82 feet], are the caustics formed on the crystalline lens 
 by the intersection ofrefracted rays.' These caustics follow the move*
 
 128 COSMOS. 
 
 laxly eight rays at angles of 45 in stars from the 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 ahove, and none be- 
 IOAV 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) ; 
 so 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, maintains 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- 
 factory 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 necessarily im- 
 pinge upon each other, and their rays will be confused. This confusion 
 can not be removed by the ocular, since the only part it performs is 
 that of magnifying. It magnifies every 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 Delam6therie, 
 Journal de Physique, torn. Ixix., 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, torn, vii., p. 423), that a star, as the nu- 
 merical hieroglyphic for 5, has not yet been discovered on any monu- 
 ment or papyrus-roll. (Horap., p. 194.)
 
 RAYS OF THE STARS. 129 
 
 with a needle in a card, and I have myself frequently ob- 
 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- 
 nifying power, giving the smaller disk."t Occultations 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 is 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 Will- 
 iam Herschel, with a magnifying power of 6500, found the 
 diameter of Vega 0"'36. The image of Arcturus was so di- 
 minished in a dense mist that 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". 
 
 of the Pacific, that the age of the moonTmight be determinecl before 
 first quarter by looking at it through a piece of silk and counting the 
 multiplied images. Here we have a phenomenon of diffraction ob- 
 served through fiue slits. 
 
 t Outlines, $ 816. Arago has caused the spurious diameter of Alde- 
 baran to increase from 4" to 15" in the instrument by diminishing the 
 object-glass. 
 
 t Delambre, Hist, de I'Astr. Moderne, torn, i., p. 193 ; Arago, 
 mre, 1842, p. 366. 
 
 F2
 
 130 COSMOS. 
 
 The alternating light and dark rings which surround the 
 email spurious disks of the stars when magnified two or 
 three hundred times, and which appear iridescent when seen 
 through diaphragms of different form, are likewise the result 
 of interference and diffraction, as we learn from the observ- 
 ations of Arago and Airy. The smallest objects which can 
 be distinctly seen in the telescope as luminous 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 here 
 allude to the change of color which, 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 owing to the 
 character of the atmospheric medium through which we see 
 it), but to the white or colored stellar light radiated from 
 each cosmic al 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 
 loth 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 Saturn (Mimas, Enceladus, and Bond's Hyperi- 
 on), and Neptune's satellite discovered by Lassell. The power 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 instruments to ships which cany men upon 
 an unknown ocean : " Ut propriora exercere possiut cum ccelestibus 
 commercia." ( Works of Francis Bacon, 1740, vol. i., Novum Orga- 
 num, p. 361.)
 
 COLOR OF THE STABS. 131 
 
 Biope, in the radiant fields of the starry heaven, as in the 
 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 
 (vnoictppoi) 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,f which is called both Trvppdf and nvpoeidfj^. 
 
 Of the six above-named stars, five still retain a red or red- 
 dish light. Pollux is still indicated as a reddish, but Castor 
 as a greenish star.J 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 vnonififtof, which Ptolemy employs indiscriminate- 
 ly to designate the six stars named in his catalogue, implies a slightly- 
 marked transition from fiery yellow to fiery red; it therefore refers, 
 strictly speaking, to a. fiery reddish color. He seems to attach the gen- 
 eral predicate av66f, fiery yellow, to all the other fixed stars. (Almag., 
 viii., 3d ed., Halma, torn, ii., p. 94.) ~K.if>f>6( is, according to Galen 
 (Meth. Med., 12), a pale fiery red inclining to yellow. Gellius com- 
 pares the word with melinus, which, according to Servius, has the same 
 meaning as " gilvus" and " fulvus." As Sirius is said by Seneca (Nat. 
 Quasi., i., 1) to be redder than Mars, and belongs to the stars called in 
 the Almagest vnoKifipoi, there can be no doubt that the word implies 
 the predominance, or, at all events, a certain proportion of red rays. 
 The assertion that the affix 7roi*c/^of , which Aratus, v. 327, attaches to 
 Sirius, has been translated by Cicero as " rutilus," is erroneous. Cicero 
 says, indeed, v. 348: 
 
 " Namque pedes subter rutilo cum lumine claret, 
 Fervidus ille Canis stellarum luce refulgena ;" 
 
 but " rutilo cum lumine" is not a translation of iroiK&of, but the mere 
 addition of a free translation. (From letters addressed to me by Pro- 
 fessor Franz.) " If," as Arago observes (Annuaire, 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. 
 
 t Madler, Aslr., 1849, s. 391. 
 
 $ Sir John Herschel, in the Edinb. Review, vol. 87, 1848, p. 189, and 
 in Schum., A$tr. 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 
 actually 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 ignorant." (Compare Arago, in the Annuaire pour 1842. p. 350- 
 353.)
 
 132 COSMOS. 
 
 of Samos called the fixed ttars) 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 which 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-Eddin 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 Rakka (Aracte) on the Euphrates, in- 
 dicates as red stars (stellcn ruffce, 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 at this period Sirius had been no 
 longer red, it would certainly be a striking fact that El-Fer 
 
 * In Muhamedis Alfragani Chronologica et Astronomica Elementa, ed. 
 Jacobus Christmannus, 1590, cap. 22, p. 97, we read, " Stella ruffa in 
 Tauro Aldebaran ; Stella ruffa in Geminit quse appellatur Hajok, hoc 
 est Capra." Alhajoc, Aijuk are, however, the ordinary names for Ca- 
 pella Aurigae, in the Arabic and Latin Almagest. Argelander justly ob- 
 serves, in reference to this subject, that Ptolemy, in the astrological 
 work (Tcrpu&CAof cvvTagif), the genuine character of which is testi- 
 fied by the style as well as by ancient evidence, has associated planets 
 with stars according to similarity of color, and has thus connected Mar 
 tis stella, Quce urit slcut congruit igneo ipsius colori, with Auriga? stella 
 or Capella. (Compare Ptol., Quadripart. Construct., libri iv., Basil, 
 1551, p. 383.) Riccioli (Almageslum Novum, ed. 1650, torn, i., pars i. 
 lib. 6, cap. 2, p. 394) also reckons Capella, together with Antares, Aide 
 baran, and Arcturus, among red stars.
 
 SIRIUS. 133 
 
 gani, 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 Betelgeux (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 
 Sothis 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 languages and their affinities monuments of the earlier 
 conditions of knowledge. t 
 
 10-195, 3. e compete arrangement o te gyptan caen 
 referred to the earlier part of the year 3285 before our era, i. e., 
 a century and a half after the building of the great pyramid of Ch 
 Chufu, and 940 years before the period generally assigned to the D 
 
 See Chronologie der^Egypter, by Richard Lepsius, bd. i., 1849, s. 
 190-195, 213. The complete arrangement of the Egyptian calendar is 
 
 i. e., about 
 f Cheops- 
 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 narrow subterranean passage leading into the interior of the pyr- 
 amid very nearly corresponded to the angle 26 15', which in the time 
 of Cheops (Chufu) was attained by the star a Draconis, which indicated 
 the 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 diflerence 
 of 540 years tends to strengthen the assumption that a Drac. was 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 Egyptian name 
 of Sirius is Sothis, designated as a female star ; hence q Hudif is identi- 
 fied in Greek with the goddess Sole (more frequently Sit in hieroglyph- 
 ics), and in the temple of the great Ramses at Thebes with Isis-Sothis 
 (Lepsius, Ckron. der ^gypter,bd. i., s. 119, 136). The signification of 
 the root is found in Coptic, and is allied with a numerous family of words,
 
 134 . COSMOS. 
 
 Besides Sirius, Vega, Deneb, Regulus, and Spica are at the 
 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 (sagittam, telurn) first, 
 seminare, to sow; next, eztendere, to extend or spread (as spun threads); 
 and, lastly, what is hero most important, to radiate light and to shine 
 (as stars and fire). From this series of ideas we may deduce the names 
 of the divinities, Satis (the female archer); Sothis, the radiating, and 
 Seth, the fiery. We may also hieroglyphically explain sit or seti, the 
 arrows as well as the ray ; seta, to spin ; setu, scattered seeds. Sothit 
 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, ia 
 contradistinction to the warming, fructifying 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 2i?0 instead of Sothis ; but neither the name nor the 
 subject admits of our identifying Thoth with Seth or Sothis, as Ideler 
 has done. (Handbuch der Chronologic, bd. i., 8. 126.)" (Lepsius, bd. 
 i., s. 136.) 
 
 I will close these observations taken from the early Egyptian periods 
 with some Hellenic, Zend, and Sanscrit etymologies : " Se/p, the sun," 
 says Professor Franz, " is an old root, differing only in pronunciation 
 from tfep, &pog, heat, summer, in which we meet with the same change 
 in the vowel sound as in relpof and repof or repaf. The correctness of 
 these assigned relations of the radicals aelp and &ep, depof, is proved 
 not only by the employment of tfepetTarof in Aratus, v. 149 (Ideler, 
 Sternnamen, s. 241), but also by the later use of the forms aeipof, aei- 
 piof, and asipivof, hot, burning, derived from oeip. It is worthy of no- 
 tice that oeipd or deipiva Ifiana is used the same as tiepiva iftdria, light 
 summer clothing. The form oelpiof 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 aeipioc aarrip, while Ibycus calls the stars gen- 
 erally adpia, luminous. It can not be doubted that it is the sun to which 
 Archilochus refers in the words iroJUoiif /*v avrov aeipioe Karavavel 6i>f 
 kXXufiTruv. According to Hesychius and Suidas, Set'ptof 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 
 of Hesiod (Opera et Dies, v. 417) refers to the sun, as maintained by 
 Tzetzes and Proclus, and not to the Dog-star. From the adjective oei- 
 piof, which has established itself as the ' epilheton perpetuum' of the 
 Dog-star, we derive the verb aeipidv, which may be translated ' to 
 sparkle.' Aratus, v. 331, says of Sirius, bt-a aeipiuei, ' it sparkles strong- 
 ly.' When standing alone, the word Setpjyv, 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 
 founded. The opinion of those who, according to Theon Smyrna^us 
 (Liber de Astronomia, 1850, p. 202), derive 'Zeipfjv from oeipid&iv (a
 
 THE COLOR OF THE STARS 135 
 
 stars, Struve enumerates about 300 in which both stars are 
 white.* Procyon, Atair, the Pole Star, and more especially 
 ft Ursae Min. have a more or less decided yellow light. "We 
 have already enumerated among the larger red or reddish stars 
 Betelgeux, Arcturus, Aldebaran, Antares, and Pollux. Rum 
 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 77 Argus, which has been rendered cele- 
 brated by Sir John Herschel's observations, and to which 1 
 shall soon refer more circumstantially, is undergoing a change 
 in color as well 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 
 Cape, gives a list of seventy-six ruby-colored 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, f the excep- 
 
 moreover unaccredited form of acipiav'), is likewise entirely erroneous. 
 While the motion of heat and light is implied by the expression aeipiof, 
 the radical of the word Zeipijv represents the flowing tones of this phe 
 nomenon of nature. It appears to me probable that "Zeipriv is connect- 
 ed with elpeiv (Plato, Cratyl., 398, D, TO yap slpetv hiyeiv kar'C), in which 
 the original sharp aspiration passed into a hissing sound." (From let 
 ters of Prof. Franz to me, January, 1850.) 
 
 The Greek 2e<p, the sun, easily admits, according to Bopp, " of be- 
 ing associated with the Sanscrit word star, which does not indeed sig- 
 nify the sun itself, but the heavens (as something shining'). The ordi- 
 nary Sanscrit denomination for the sun is surya, a contraction of svdrya, 
 which is not used. The root svar signifies in general to shine. The 
 Zend designation for the sun is hvare, with the h instead of the s. The 
 Greek $fp, $^pof, and i?ep//6f comes from the Sanscrit word gharma 
 (N 7 om. gharmas'), warmth, heat." 
 
 The acute editor of the Rigveda, Max MQller, observes, that " the 
 special Indian astronomical name of the Dog-star, Lubdkaka, which sig- 
 nifies a hunter, when considered in reference to the neighboring con- 
 stellation Orion, seems to indicate an ancient Arian community of ideas 
 regarding these groups of stars." He is, moreover, principally inclined 
 " to derive Zetptof from the Veda word rira (whence the adjective sair- 
 ya) and the root tri, to go, to wander ; so that the sun and the bright- 
 est of the stars, Sirius, were originally called wandering stars." (Com. 
 pare also Pott, Etymologische Forschungen, 1833, s. 130.) 
 
 * Stvuve, Stellarum compositarum Mensuree Micrometricts, 1837, ]X 
 Ixxiv. et Ixxxiii. 
 
 t Sir John Herschel, Observation! at (he Cape, p. 34. 
 
 t Madler's Attronomie, s. 436.
 
 136 SOSMOS. 
 
 tions being Algol in Caput Medusae, ft Lyraj and e Auriga, 
 which have a pure white light. Mira Ceti, in which a pe- 
 riodical change of light was first recognized, has a strong red- 
 dish light ;* but the variability observed in Algol and ft Lyrse 
 proves that this red color is not a necessary condition of a 
 change of light, since many red stars are not variable. The 
 faintest 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 Traite 
 des Couleurs. The light of a Lyrse 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. 
 Among the double stars there are many in which the princi- 
 pal star is white, and the companion blue ; and some in which 
 both stars have a blue lightj (as 6 Serp. and 59 Androm.). 
 Occasionally, as in the stellar swarm near 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, Regulus 
 and Fomalhaut. We find this regular arrangement, of 
 which I have already elsewhere treated, II specially referred 
 to in a late Roman writer, Julius Firmicus Maternus,1T who 
 belonged to the age of Constantine. The differences of 
 right ascension in these regal stars, stellce regales, are llh. 
 57m. and 12h. 49m. The importance formerly attached to 
 this subject is probably owing to opinions transmitted from 
 the East, which gained a footing in the Roman empire un- 
 der the Caesars, together with a itrong 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, Annuaire pour 1842, p. 348. 
 
 t Struve, Stella comp., p. Lxxxii. 
 
 $ Sir John Herschel, Observations at the Cape, p. 17, 102. (" Nebula 
 and Clusters, No. 3435.") 
 
 II Humboldt, Vues des CordUleres et Monument des Peuples Indigenes 
 de VAmerique, torn, ii., p. 55. 
 
 IT Julii Firmici Maierni Astron., libri viii., Basil, 1551, lib. vi., cap 
 i., p. 150.
 
 SOUTHERN STARS. 137 
 
 sentations of Dendera, and in the Egyptian Book of the 
 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 the four quarters of the heavens in like 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 times, and even in the earlier part of the Middle Ages, 
 the knowledge of the southern hemisphere was gradually 
 completed about a century 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 Ccesaris Thronus, 
 in honor of Augustus,! and Canopus (Canobus) in Argo, 
 which is called Ptolemceon by the scholiast to Germanicus.J 
 
 * Lepsius, Chronol. der ^Egypter, bd. i., s. 143. In the Hebrew 
 text mention is made of Asch, the giant (Orion?), the many stars (the 
 Pleiades, Gemut?), and "the Chambers of the South." The Septua- 
 gint ^ives : 6 iroiuv 'EAetd<5a /cat 'Ecmepov Kal 'ApKrovpov /cat ra^eta 
 vorov. 
 
 The early English translators, like the Germans and Dutch, under- 
 go >d 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 
 waynes 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. 
 
 t Martianus Capella changes Ptolemceon into Ptolemceus; both names 
 were devised by the flatterers at the court of the Egyptian sovereigns. 
 Amerigo Vespucci thought he had seen three Canopi, one of which was 
 quite dark (fosco), Canopus ingens et 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. by El-Fergani (p. 100), it is stated that the Christian pilgrims 
 used to call the Sohel of the 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 Ramayana, the oldest heroic poem of Indian antiquity, 
 the stars in the vicinity of the South Pole are declared for a singular 
 reason to have been more recently created than the northern. When 
 Brahminical Indians were emigrating from the northwest to the coun 
 tries around the Ganges, from the 30th degree 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 as 
 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 gods 
 that he would overcome the northern hemisphere with his more richly-
 
 138 COSMOS. 
 
 In the catalogue of the Almagest, Achernar, a star of the 
 first magnitude, the last in Eridanus (Achir el-nahr, in 
 Arabic), is also given, although it was 9 below 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 Yanez 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. t 
 
 Laws of relative density in the distribution of the fixed 
 stars in the vault of heaven first began to be recognized 
 when Sir William 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 Zeilschrift 
 fur die Kunde des Morgcnlandes, bd. i., B. 240.) While this Indian 
 myth figuratively depicts the astonishment excited in wandering na- 
 ' , by the aspect of i 
 
 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," mttdan de pays y de estrellas), 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 Eridauus or in Argo, 
 while those with which they had been long familiar at home wholly 
 disappeared. The fixed stars advance toward us, and again recede, 
 owing to the precession of the equinoxes. We have already mentioned 
 that the Southern Cross was 7 above the horizon, in the countries 
 around the Baltic, 2900 years before our era; at a time, therefore, when 
 the great pyramids had already existed five hundred years. (Compare 
 Cosmog, vol. i., p. 149, and vol. ii., p. 282.) " Cauopus, on the other 
 hand, can never have been visible at Berlin, as its distance from the 
 south 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 Olbers, in Schumacher's Jahrb.f&r 1840, s.249, and Cosmos, vol. i., 
 p. 51.
 
 DISTRIBUTION OF STARS. 139 
 
 at different heights and in various directions over the 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 ^^ T V^? tn 
 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, t although in the south- 
 ern hemisphere, from Orionis to a Crucis, they are locally 
 crowded together in a splendid zone in the direction of a 
 great circle. The various opinions expressed 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- 
 ticularly, therefore, telescopic stars) increase regularly in 
 density as we approach the galactic circle (6 yaAafmf KV- 
 /cAof) ; 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 on the average 
 there are 29-4 tunes (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, 17'68, 
 30-30, and 122-00. Notwithstanding the great similarity 
 in the law of increase in the abundance of the stars, we 
 again find in the comparison of these zones an absolute pre- 
 
 * Etudes tfAstr. Stellaire, note 74, p. 31. 
 t Outlines of Astr., 785
 
 140 COSMOS. 
 
 ponderance* on the side of the more beautiful southern 
 heavens. 
 
 When in 1843 I requested Captain Schwinck (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 Mappa Caslestis, he found in four groups 
 Right Ascension, 50 to 140 3147 stars. 
 140 230 2627 " 
 230 320 3523 " 
 320 50 2851 " 
 
 These groups correspond with the more exact results of the 
 Etudes Stellaires, according to which the maxima of stars 
 of the first to the ninth magnitude occur in the right ascen- 
 sion 6h. 40m. and. I8h. 40m., and the minima in the right 
 ascension of Ih. 30m. and 13h. 30m. t 
 
 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, independent, and crowded groups. 
 The latter are the so-called stellar dusters or swarms, which 
 frequently contain thousands of telescopic stars in recogniza- 
 ble relations to each other, and which appear to the unaided 
 eye as round nebulae, shining like comets. These are, the 
 nebulous stars of EratosthenesJ and Ptolemy, the nebulosce 
 of the Alphonsine Tables in 1483, and the same of which 
 Galileo said in the Nuncius Sidereus, " Sicut areolee spar- 
 sim per sethera subfulgent." 
 
 These clusters of stars are either scattered separately 
 throughout the heavens, or closely and irregularly crowded 
 together, in strata, as it were, in the Milky Way, and in the 
 Magellanic clouds. The greatest accumulation of globular 
 clusters, and the most important in reference to the config- 
 uration of the galactic circle, occurs in a region of the south- 
 ern heavens^ between Corona Australis, Sagittarius, the 
 
 * Op. cit., 795, 796 ; Struve, Eludes cTAstr. Stell., p. 66, 73 (and 
 note 75). 
 
 t Struve, p. 59. Schwinck finds in his maps, R. A. 0-90, 2858 
 stars; R. A. 9QO-180 , 3011 stars; R. A. 180-270, 2688 stars; R. A 
 270-360, 3591 stars ; sura total, 12,148 stars to the seventh magnitude 
 
 t On the nebula in the right hand of Perseus (near the hilt of his 
 sword), see Eratosth., Catant., c. 22, p. 51, Schaubach. 
 
 $ John Herschel's Observations at the Cape, $ 105, p. 136.
 
 CLUSTERS OF STARS. 141 
 
 tail of Scorpio, and the Altar (R. A. 16h. 45m.-l9h.). All 
 clusters in and near the Milky Way are not, however, round 
 and globular ; there are many of irregular outline, with but 
 few stars and not a very dense center. In many globular 
 clusters the stars are uniform in magnitude, in others they 
 vary. In some few cases they exhibit a fine reddish cen- 
 tral star* (R. A. 2h. 10m. ; N Decl. 56 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 different laws in their local distribution, although the 
 former are now 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, with an in- 
 strument of equal aperture and magnifying power, round 
 nebulous spots are more easily resolved into clusters of stars 
 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 mariner's stars Pleias, and rov 
 rrAetv (from TrAetv, to sail), according to the etymology of 
 the old scholiast of Aratus, who is probably more correct than 
 those modern writers who would derive the name from rrAeof, 
 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. 
 
 Prsesepe in Cancer : according to Pliny, nubecula quam 
 Prczsepia vacant inter Asellos, a ve</>eA*ov 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. I3h. 34m. 12s., N. Decl. 29 14' ; more than a thousand 
 stars from the tenth to the twelfth magnitude. 
 
 Cluster of stars between 77 and Herculis, visible to the 
 naked eye in clear nights. A magnificent object in the tel- 
 escope (No. 1968), with a singular radiating margin ; R. A. 
 
 Outlines, $ 864-869, p. 591-596; Madler's Astr., s. 764. 
 t Observation at the Cape, $ 29, p. 19.
 
 142 COSMOS. 
 
 16h. 35m. 37s., N. Dccl. 36 47' ; first described by Halley 
 in 1714. 
 
 A cluster of stars near w Centauri ; 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 powerful instruments it appears composed of count- 
 less stars of the thirteenth to the fifteenth magnitude, crowd- 
 ed together and most dense toward the center; R. A. 13h. 
 16m. 38s., S. Decl. 46 35' ; No. 3504 in Sir John Herschel's 
 catalogue of the clusters of the southern hemisphere, 15' in 
 diameter. (Observations at the Cape, p. 21, 105 ; Outlines 
 ofAstr., 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 Jj-th of a 
 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 Cape, p. 17, 102, pi. i., fig. 2.) 
 
 Cluster of stars, 47 Toucani, Bode ; No. 2322 of Sir John 
 Herschel'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 composed 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 vecognized, 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 astronomerf at the Observatory 
 
 * " A stupendous object a most magnificent glolular cluster," says 
 Sir John Herschel, " completely insulated, upon a ground of the sky per- 
 fectly black throughout the whole breadth of the sweep." Observations 
 at the Cape, p. 18 and 51, PI. iii., fig. 1 ; Outlines, $ 895, p. 615. 
 
 t Bond, in the Memoirs of the American Academy of Arts and Sciences, 
 iiew series, vol. iii., p. 75.
 
 CLUSTERS 9F STARS. 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 diam- 
 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- 
 rius (Mayer of Guntzenhausen), the same who first observed 
 the change of color in scintillation,! perceived it on the 1 5th 
 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 Philolaica, occupied himself 
 with the same subject. This cluster of stars, which is 2^- 
 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 Herschel. (Observations at the 
 Cape, p. 20, 105, pi. iv., fig. 2.) 
 
 Notwithstanding the important discoveries for which we 
 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 Nebulae. 
 
 The greatest accumulation of clusters of stars, although 
 by no means of nebulas, occurs in the Milky WayJ (Galaxias, 
 
 * Outlines, $ 874, p. 601. 
 
 t Delambre, Hist, de VAstr. Moderne, t. i., p. 697. 
 
 t We are indebted for the first and only complete description of the 
 Milky Way, in both hemispheres, to Sir John Herschel, in his Results 
 of Astronomical Observations, 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 Struve, Etudes d'Astr. Stel- 
 laire, p. 35-79 ; Madler, Ast., 1849, 213 ; Cosmos, vol. i., p. 103, 150.) 
 I need scarcely here remark that in my description of the Milky Way, 
 in order not to confuse certainties with uncertainties, I have not refer- 
 red to what I had myself observed with instruments of a very inferior
 
 144 COSMOS. 
 
 the celestial river of the Arabs*), which forms almost a great 
 circle of the sphere, and is inclined to the equator at an an- 
 gle of 63. The poles of the Milky Way are situated in Right 
 Ascension 12h. 47m., N. Decl. 27 ; and R. A. Oh. 47m., S. 
 Decl. 27 ; the south galactic pole therefore lies near Coma 
 Berenices, and the northern between Phoenix and Cetus. 
 While all planetary local relations are referred to the eclip- 
 tic the great circle in which the plane of the sun's path in- 
 tersects the sphere we may as conveniently refer many of 
 the local relations of the fixed stars, as, for instance, that of 
 their accumulation or grouping, to the nearly complete circle 
 of the Milky Way. Considered in this light, the latter is to 
 the sidereal world what the ecliptic is to the planetary world 
 of our solar system. The Milky Way cuts the equator in 
 Monoceros, between Procyon and Sinus, R. A. Gh. 54m. (for 
 1800), and in the left hand of Antinous, R. A. 19h. 15m. 
 The Milky Way, therefore, divides the celestial sphere into 
 two somewhat unequal halves, whose areas are nearly as 8 
 to 9. In the smaller portion lies the vernal solstice. The 
 Milky Way varies considerably in breadth in different parts 
 of its course.f At its narrowest, and, at the same time, most 
 brilliant portion, between the prow of Argo and the Cross, 
 and nearest to the Antarctic pole, its width is scarcely 3 or 
 4 ; at other parts it is 16, and in its divided portion, be- 
 tween Ophiuchus and Antinous, as much as 22.$ William 
 Herschel has observed that, judging from his star-gaugings, 
 the Milky Way would appear in many regions to have 6 or 
 7 greater width than we should be disposed to ascribe to 
 it from the extent of stellar brightness visible to the naked 
 eye." 
 
 Huygens, who examined the Milky Way with his twenty- 
 three feet refractor, declared, as early as the year 1656, that 
 the milky whiteness of the whole Galactic zone was not to 
 
 illuminating power, in reference to the very great inequality of the 
 light of the whole zone, during my long residence iu the southern hem- 
 isphere, and which I have recorded in my journals. 
 
 * The comparison of the ramified Milky Way with a celestial river 
 led the Arabs to designate parts of the constellation of Sagittarius, whose 
 bow falls in a region rich in stars, as the cattle going to drink, and to 
 associate with them the ostrich, which has so little need of water. (Ide- 
 ler, Untersuchungen uber den Ursprung und die Dedeutung der Sternna* 
 men, 78, 183, and 187 ; Niebuhr, Beschreibung von Arabien, e. 112.) 
 
 t Outlines, p. 529; Schubert, Ast., th. iii., s. 71. 
 
 t Struve, Etudes d'Astr. Stellaire, p. 41. 
 
 $ Cosmos, vol. L, p. 150.
 
 MILKY WAY. 145 
 
 be ascribed to irresolvable nebulosity. A more careful ap- 
 plication of reflecting telescopes of great dimensions and pow- 
 er of light has since proved, with more certainty, the cor 
 rectness of the conjectures advanced by Democritus and Ma- 
 nilius, in reference to the ancient path of Phaeton, that this 
 milky glimmering light was solely owing to the accumu 
 lated strata of small stars, and not to the scantily inter 
 spersed nebulae. This effusion of light is the same at points 
 where the whole can be perfectly resolved into stars, and 
 even in stars which are projected on a black ground, wholly 
 free from nebulous vapor.* It is a remarkable feature of 
 the Milky "Way that it should so rarely exhibit any globular 
 clusters and nebulous spots of a regular or oval form ;t while 
 both are met with in great numbers at a remote distance 
 from it ; as, for instance, in the Magellanic clouds, where 
 isolated stars, globular clusters in all conditions of condensa- 
 tion, and nebulous spots of a definite oval or a wholly irreg- 
 ular form, are intermingled. A remarkable exception to 
 the rarity of globular clusters in the Milky Way occurs in a 
 region between R. A. 16h. 45m. and 18h. 44m., between the 
 Altar, the Southern Crown, the head and body of Sagitta- 
 rius, and the tail of the Scorpion.^ We even find between 
 and 6 of the latter one of those annular nebulae, which are 
 of such extremely rare occurrence in the southern hemi- 
 sphere. 
 
 In the field of view of powerful telescopes (and we must 
 remember that, according to the calculations of Sir William 
 
 * "Stars standing on a clear black ground." (Observations at the 
 Cape, p. 391.) " This remarkable belt (the Milky Way, when exam- 
 ined through powerful telescopes) is found (wonderful to relate !) to 
 consist entirely of stars scattered by millions, like glittering dust on the 
 )lack ground of the general heavens." Outlines, p. 182, 537, and 539. 
 
 t " Globular clusters, excepting in one region of small extent (be- 
 tween 16h. 45m. and 19h. in R. A.), and pebulce of regular elliptic 
 forms, are comparatively rare in the Milky Way, and are found con- 
 gregated in the greatest abundance in a part of the heavens the most 
 remote possible from that circle." (Outlines, p. 614.) Huygens him- 
 self, as early as 1656, had remarked the absence of nebulosity and of 
 all nebulous spots in the Milky Way. In the same place where he 
 mentions th 3 first discovery and delineation of the great nebulous spots 
 in the belt of Orion, by a twenty-eight feet refractor (1656), he says 
 (as I have already remarked in vol. h., p. 330, and note), viam lacteam 
 perspicillis inspectam nullas habere nebulas, and that the Milky Way, like 
 all that has been regarded as nebulous stars, is a great cluster of stars 
 The passage is to be found in Hugenii Opera varia, 1724, p. 540. 
 
 t Observations at the Cape, $ 105, 107, and 328. On the annular nel> 
 ulsB, No. 3686, see p. 114. 
 
 VOL. Ill ?
 
 146 . COSMOS. 
 
 Herschel, a twenty-feet instrument penetrates 900, and a 
 forty-feet one 2800 distances of Sinus), the Milky Way ap- 
 pears as diversified in its sidereal contents as it is irregular 
 and indefinite in its outlines and limits when seen by the 
 unaided eye. While in some parts the Milky Way exhibits, 
 throughout a large space, the greatest uniformity in the light 
 and apparent magnitudes of the stars, in others the most 
 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- 
 nitudes do not always 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. t Next in brightness to this por- 
 
 * " Intervals absolutely dark and completely void of any ttar of the 
 smallest telescopic magnitude." Outlines, p. 536. 
 
 t " No region of the heavens is fuller of objects, beautiful and re- 
 markable in themselves, and rendered still more so by their mode of 
 association, and by the peculiar features assumed by the Milky Way, 
 which are without a parallel in any other part of its course." 'Observ- 
 ations at the Cape, p. 386. This vivid description of Sir John Hersche] 
 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 that part of the sky, that a person is immediately made
 
 MILKY WAY. 147 
 
 tion of the southern heavens is the pleasing and richly-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 minimum brightness (where 
 there is the greatest paucity of stars in the Galactic zone) is 
 in the naighborhood of Monoceros and Perseus. 
 
 The magnificent effulgence of the Milky Way in the south- 
 ern hemisphere is still further increased by the circumstance 
 that between the star r\ Argus, which has become so cele- 
 brated in consequence of its variability, and a Crucis, undei 
 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 effect 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. According 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,t 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 Way with its subdivisions, we 
 will briefly consider its parts, following the order of their 
 Right Ascension. Passing through y and e Cassiopeiae, 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 very faint, passes on through 
 Auriga, over the three remarkable stars e, , rj, the Hsedi of 
 that constellation, preceding Capell a, between the feet of Gem- 
 ini and the horns of the Bull (where it intersects the eclip- 
 
 aware of its having risen above the horizon, though he should not be at 
 the time looking at the heavens, by the increase of general illumination 
 of the atmosphere, resembling the effect of the young moon." (See 
 Piazzi Smyth, On the Orbit of a Centauri, in the Transact, of the Royal 
 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- 
 scription is admirable in some parts, especially when compared with 
 Aristotle's treatment of the subject of the Milky Way, in Meteor (lib 
 i., p. 29, 34, according to Ideler's edition).
 
 148 COSMOS. 
 
 tic nearly in the solstitial colure), and thence over Orion's 
 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-like 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 A Argus. It begins again in a similar 
 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 o and 
 ft 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 
 Normse. 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 e, 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 backward, as it were, 
 through j3 Cygni and f Aquilae, 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 off by the northern stream from the head 
 
 * Outlines, p. 531. The strikingly dark spot between a and y Cas- 
 siopeia; is also ascribed to the contrast with the brightness by which it 
 is surrounded. See Struve, Eludes Stell., note 58.
 
 MILKY WAY. 149 
 
 of Cepheus, and therefore near Cassiopeia (from which con- 
 stellation 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 
 form 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 world-island (starry 
 stratum) in which our solar system is included. The hy- 
 pothesis of the uniform magnitude and distribution of the 
 fixed stars has recently been attacked on many sides. The 
 bold and gifted investigator of the heavens, Wm. Herschel, 
 in his last works,! 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 differentjiltitudes, 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 Milky Way, the space-penetrating 
 power of instruments is sufficient to resolve whole star- 
 clouds, and to show the separate luminous points projected 
 on the dark, starless ground of the heavens. We here act- 
 
 * De Morgan has given an extract of the extremely rare work of 
 Thomas Wright of Durham ( Theory of the Universe, London, 1750), p 
 241 in the Philot. Magazine, ser. iii., No. 32. Thomas Wright, to whose 
 researches the attention of astronomers has been so permanently di 
 reeled since the beginning of the present century, through the ingen 
 ions speculations of Kant and William Herschel, observed only with a 
 reflector of one foot focal length. 
 
 t Pfaff, in Will. HertchePi sdmmtl. Schriften, bd. i. (1826), a. 78-8l ; 
 Struve, Etvdet Stell., p. 35-44. 
 
 $ Encke, in Schumacher's Attr. Nochr., No. 622, 1847 341-34C
 
 150 COSMOS. 
 
 ually look through as into free space. " It leads us," says 
 Sir John Herschel, " irresistibly to the conclusion that in 
 these regions we see fairly through the starry stratum."* 
 In other regions we see, as it were, through openings and 
 fissures, remote world-islands, or outhranching portions of the 
 annular system ; in other parts, again, the Milky Way has 
 hitherto been, fathomless, even with the forty-feet telescope. f 
 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, J 
 and therefore in |^ths of all the stars), have led the most 
 recent investigator of the southern hemisphere to remarkable 
 views and probable results in reference to the form of the 
 galactic annular system, and what has been boldly called 
 the sun's place 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 Way.ll "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 of 
 no great thickness compared with the distance which 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 starry stra- 
 tum, 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 tele- 
 scopic branches of the Milky Way, or of an independent sidereal sys- 
 tem or systems bearing a resemblance to such branches." 
 
 t Observations at the Cape, 314. 
 
 $ Sir William Herschel, in the Philos. Transact, for 1785, p. 21 ; Sir 
 John Herschel, Observations at the Cape, 293. Compare also Struve, 
 Descr. de I' Observatoire de Poulkova, 1845, p. 267-271. 
 
 || " I think," says Sir John Herschel, " it is impossible to view this 
 splendid zone from 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 to 
 that diametrically opposite to it." (Mary Somerville, On the Connec- 
 *ion of the Physical Sciences, 1846, p. 419.)
 
 NEW STARS. 151 
 
 stratum, is about equal to that distance which, on a general 
 average, corresponds to the light of a star of the ninth or 
 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. 
 
 NEW 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, have 
 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 visi- 
 ble 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 countries 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 
 new stars which, according to the records of Ma-tuan-lin, 
 * Observations at the Cape, $ 315.
 
 152 COSMOS. 
 
 have been observed in China, and go back to the middle o" 
 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 eye-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 vitae 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 that of Sirius, a Lyrse, 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, I 
 measured with great care, convinced me of its perfect immo- 
 bility. Already, in December, 1572, its brilliancy began to
 
 NiJW STARS. 153 
 
 diminish, and the star gradually resettled Jupiter ; but by 
 January, 1573, it had become less bright than that planet. 
 Successive photometric estimates gave the following results : 
 for February and March, equality with stars of the first mag- 
 nitude (stellarum affixarum primi honoris for Tycho Brahe 
 seems to have disliked using Manilius's expression of stellse 
 fixae) ; for April and May, with stars of the second magni- 
 tude ; for July and August, with those of the third ; for Oc- 
 tober and November, 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 
 shone seventeen months, was no longer discernible to the 
 naked eye." (The telescope was not invented until thirty 
 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 77 Argus, though indeed that is not to be 
 called a new star) interrupted 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 velocity of colored rays 
 in 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, and especially in May, its white color re- 
 turned (albedinem quandam sublividam induebat, qualis Sa- 
 turni stellse subesse videtur). So it remained in January, 
 1574 ; 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 
 scintillation in proportion to its faintness. 
 
 The circumstantial minuteness of these statements* is of 
 
 * De admiranda Nova Stella, anno 1572, exorta in, Tychonis Brahe 
 AttronomicE instauratce Progymnatmata, 1603, p. 298-304, and 578. In 
 the text I have closely followed the account which Tycho Brahe him- 
 self gives. The very doubtful statement (which is, however, repeated 
 in several astronomical treatises) that his attention was first called to
 
 154 COSMOS. 
 
 itself a proof of the interest which this natural phenomenon, 
 could not fail to awaken, by calling forth many important 
 questions, in an epoch so brilliant in the history of astronomy. 
 For (notwithstanding the general rarity of the appearance of 
 new stars) similar phenomena, accidentally crowded togeth- 
 er within the short space of thirty-two years, were thrice re- 
 peated within the observation of European astronomers, and 
 consequently served to heighten the excitement. The im- 
 portance of star catalogues, for ascertaining the date of the 
 sudden appearance of any star, was more and more recog- 
 nized ; the periodicity* (their reappearance after many cen- 
 turies) was discussed ; and Tycho Brahe himself boldly ad- 
 vanced a theory of the process by which stars might be 
 formed and molded out of cosmical vapor, which presents 
 many points of resemblance to that of the great William 
 Herschel. He was of opinion that the vapory celestial mat- 
 ter, which becomes luminous as it condenses, conglomerates 
 into fixed stars : " Coeli materiam tenuissimam, ubique nostro 
 visui et planetarum circuitibus perviam, in unum globum con- 
 densatam, stellam effingere." This celestial matter, which 
 is universally dispersed through space, has already attained 
 to a certain degree of condensation in the Milky Way, which 
 glimmers with a soft silvery brightness. Accordingly, the 
 place of the new star, as well as of those which became sud- 
 denly visible in 945 and 1264, was on the very edge of the 
 Milky Way (quo factum est quod nova stella in ipso galaxise 
 margine constiterit). Indeed, some went so far as to believe 
 that they could discern the very spot (the opening or hiatus) 
 whence the nebulous celestial matter had been drawn from 
 the Milky Way.f All this reminds one of the theories of 
 
 the phenomenon of the new star by a concourse of country people, 
 need not, therefore, be here noticed. 
 
 * Cardanus, in his controversy with Tycho Brahe, went back to the 
 star of the Magi, which, as he pretended, was identical with the star 
 of 1572. Ideler, arguing from his own calculations of the conjunctions 
 of Saturn with Jupiter, and from similar conjectures advanced by Kep- 
 ler on the appearance of the new star in Ophiucus in 1604, supposes 
 that the star of the Magi, through a confusion of atnrjp with uarpnv, 
 which is so frequent, was not a single great star, but a remarkable con- 
 junction of stars the close approximation of two brightly-shining plan- 
 ets at a distance of less than a diameter of the moon. Tychonis Pro- 
 gymnasmata, p. 324-330; contrast with Ideler, Handbuch der Malhe- 
 matischen nnd Technischen Chronologic, 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 the
 
 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, owing 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 they 
 respectively appeared. 
 
 (a) 134 B.C. 
 
 in Scorpio. 
 
 (b) 123 A.D. 
 
 .... in Ophiuchus. 
 
 (c) 173 " 
 
 .... in Centaurus 
 
 (d) 369 " 
 
 7 
 
 (e) 386 " 
 
 .... in Sagittarius. 
 
 [f) 389 " 
 
 . in Aquila. 
 
 (s\ 393 " 
 
 in Scorpio. 
 
 \O / 
 
 ft) 827 " 
 
 in Scorpio. 
 
 (i) 945 
 
 .... between Cepheus and Cassiopeia. 
 
 A) 1012 " 
 
 in Aries. 
 
 Z) 1203 
 
 ' 
 
 in Scorpio. 
 
 m) 1230 
 
 
 
 in Ophiuchus. 
 
 n) 1264 
 
 
 
 between Cepheus and Cassiopeia. 
 
 (o) 1572 
 
 1 
 
 in Cassiopeia. 
 
 (p) 1578 
 
 
 
 
 (o) 1584 
 
 ' 
 
 in Scorpio. 
 
 r) 1600 
 
 ' 
 
 in Cygnus. 
 
 s) 1604 
 t) 1609 
 
 ' 
 
 in Ophiuchus. 
 
 u) 1670 
 
 
 
 in Vulpes. 
 
 v) 1848 ' 
 
 in Ophiuchus. 
 
 EXPLANATORY REMARKS. 
 
 (<z) 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 
 ( Connaistance des Temps pour Van 1846, p. 6 1). Its place was between 
 P and p of Scorpio. Among the extraordinary foreign-looking stars of 
 these records, called also guest-stars (etoiles hdtes, " 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- 
 tainly sometimes mixed up. But in the record of their motion (Ke-sing 
 
 tails of comets (the vapory radiation from their nuclei) with the galaxy 
 to which I have already alluded. (Cotmos, vol. i., p. 103.)
 
 156 COSMOS. 
 
 of 1092, 1181, and 1458), and in the absence of any si ch record, as also 
 in the occasional addition, " the Ke-sing dissolved" (disappeared), there 
 is contained, if not an infallible, yet a very important criterion. Besides, 
 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 Hipparchus, 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." (Hist, 
 de VAstr. Anc., torn, i., p. 290; and Hist, de VAstr. Mod., torn, i., p. 186.) 
 Since, according to the express statement of Ptolemy (Almag., vii., p. 2, 
 13, Halmd), 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 irreconcilable 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 motn addubitationem adcluctus" 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 Herculis and a Ophiuchi. Ed. Biot, from Ma-tuan-lin. (It 
 is also asserted that a new star appeared in the reign of Hadrian, about 
 A.D. 130.) 
 
 (r) A singular and very large star. This also is taken from Ma-tuan- 
 lin, as well as the three following ones. 
 
 Jt appeared on the 10th of December, 173, between a and /? Centauri 
 and at the end of eight months disappeared, after exhibiting the five 
 colors one after another. " Successivement" is the term employed by 
 Ed. Biot in his translation. Such an expression would almost tend to 
 suggest a series of colors similar to those in the above-described star 
 of Tycho Brahe ; but Sir John Herschel more correctly takes it to mean 
 a colored scintillation (Ozttlines, 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 <j> Sagittarii. In the Chinese Record it is expressly 
 observed, " where the star remained (i. e., without movement) from 
 April to July, 386. 
 
 (/) A new star, close to a Aquilso. 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 Cuspinianus, 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, Element d'Astronomie, 1740 (Etottes Nouvelles), p. 59.
 
 TEMPORARY STARS. 157 
 
 (g) March, 393. This star was also in Scorpio, in the tail of that 
 coustellation. From the Records of Ma-tuan-lin. 
 
 (h) The precise year (827) is doubtful. It may with more certainty 
 be assigned to the first half of the ninth century, 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 
 atar disappeared after a period of four months. 
 
 (t) The appearance of this star (which is said to have shone forth in 
 the year 945, under Otho the Great), like that of 1264, is vouched for 
 solely by the testimony of the Bohemian astronomer Cyprianus 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 1264) 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., p. 331 and 709) defends the credibility of Cyprianus Leovi- 
 tius against the attacks of Pontanus and Camerarius, who conjectured 
 that the statements arose from a confusion of new stars with long-tailed 
 comets. 
 
 (&) 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 brilliancy 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 insolitae magnitudinis, 
 aspectu fulgurans et oculos verberans non sine terrore. Qua? mirum in 
 modum aliquando contractior, aliquando diffusior, etiam extinguebatur 
 interdum. Visa est autem per tres menses in intimis finibus Austri, ul- 
 tra omnia signa qute videntur in ccelo." (See Hepidanni, Annales bre- 
 ves, in Duchesne, Histories Francorum Scriptores, t. iii., 1641, p. 477. 
 Compare also Schnurrer, 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 majores, in Pertz, Afonumenta Germanise historica Scriptorum, 
 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 the conflagration and 
 extinction of a fixed star. Hind (Notices of the Asfron. 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 <p of Sagittarius. But in that 
 case there 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. 
 
 (A 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.) 
 
 (TO) Another Chinese observation, from Ma-tuan-lin, whose astronom- 
 ical records, containing an accurate account of the positions f comet*
 
 158 COSMOS. 
 
 and fixed stars, go back to the year 613 B.C., to the times of Thalea 
 and the expedition of Golaeus of Samoa. 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, Gypri- 
 anus Leovitius (and referred to under the ninth star, in the year 945). 
 About the same time (July, 1264), a great comet appeared, 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 Gas- 
 siopeia. 
 
 (o) This is Tycho Brahe's star of the llth 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 ia 
 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 !" 
 
 (?) 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, was the first, as an inscription on his celes- 
 tial globe testifies, to draw 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 years 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 mense Maio, anni 1602, primum litteris 
 monerer de novo Cygni phffinomeno." (Kepler, De Stella Nova tertii 
 
 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' ; Decl. 36 52' (therefore for 1800 : R. A. 302 36' ; Decl. -f 37 27'). 
 The star decreased in brilliancy, especially after the year 1619, and van- 
 ished in 1621. Dominique Cassini (see Jacques Cassini, Ellmens d'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 in Cassiopeia, the most famous of the new 
 stars is that of 1604 in Ophiuchus (R. A. 259 42' ; and S. Decl. 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 1 Oth 
 of October, 1604, not by Kepler himself, but by his pupil, the Bohemian 
 astronomer, John Bronowski. It was larger than all stars of the first 
 order, greater than Jupiter and Saturn, but smaller than Venus. Her- 
 licias asserts that he had previously seen it on the 27th of September. 
 Its brilliancy was less than that of the new star discovered by Tycho 
 Brahe in 1572. Moreover, unlike the latter, it was not discernible in 
 the daytime. But its scintillation was considerably greater, and espe-
 
 TEMPORARY STARS. 159 
 
 cially excited the astonishment of all who saw it. As scintillation is 
 always accompanied with dispersion of color, much has been said of 
 its colored and continually-changing light. Arago (Annuaire pour 1834, 
 p. 209-301, and Ann. pour 1842, p. 345-347) has already called atten- 
 tion to the fact that the star of Kepler did not by any means, like that 
 of Tycho Brahe, assume, at certain long intervals, different colors, such 
 as yellow, red, and then again white. Kepler says expressly that his 
 star, as soon as it rose above the exhalations of the earth, was white. 
 When he speaks of the colors of the rainbow, it is to convey a clear 
 idea of its colored scintillation. His words are: " Exemplo adamantis 
 multanguli, qui solis radios inter convertendum ad spectantium oculos 
 variabili fulgore revibraret, colores Iridis (stella nova in Ophiucho) sue- 
 sessive vibratu continue reciprocabat." (De Nova Stella Serpent., p. 5 
 and 125.) In the beginning of January, 1605, this star was even brighter 
 than Antares, but less luminous than Arcturus. By the end of March in 
 the same year it was described as being of the third magnitude. Its 
 proximity to the sun prevented all observation for four months. Be- 
 tween February and March, 1606, it totally disappeared. The inaccu- 
 rate statements as to the great variations in the position of the new star, 
 advanced by Scipio Claramontius and the geographer Blaew, are scarcely 
 (as Jacques Cassini, Elemens d'Astr., p. 65, long since observed) deserv- 
 ing of notice, since they have been refuted by Kepler's more trustworthy 
 treatise. The Chinese Record of Ma-tuan-lin mentions a phenomenon 
 which exhibits some points of resemblance, as to time and position, with 
 this sudden appearance of a new star in Ophiuchus. On the 30th of 
 September, 1604, there was seen in China a reddish-yellow (" ball- 
 like?") star, not far from TT of Scorpio. It shone in the southwest till 
 November of the same year, when it became invisible. It reappeared 
 on the 14th of January, 16t)5, in the southeast; but its light became 
 slightly duller by March, 1606. (Connaissance des Temps pour 1846, 
 p. 59.) The locality, TT of the Scorpion, might easily be confounded 
 with the foot of Ophiuchus ; but the expressions southwest and south- 
 east, its reappearance, and the circumstance that its ultimate total dis 
 appearance is not mentioned, leave some doubts as to its identity. 
 
 () This also is a new star of considerable magnitude, and seen in the 
 southwest. It is mentioned in Ma-tuau-lin. No further particulars are 
 recorded. 
 
 (M) This is the new star discovered by the Carthusian monk Anthel- 
 mus on the 20th of June, 1670, in the head of Vulpes (R. A. 294 27'; 
 Decl. 26 47'), and not far from /? Cygni. At its first appearance it was 
 not of the first, but merely of the third magnitude, and on the 10th of 
 August it diminished to the fifth. It disappeared after three months, 
 but showed itself again on the 17th of March, 1671, when it was of the 
 fourth magnitude. Dominique Cassini observed it very closely in April, 
 1671, and found its brightness very variable. The new star is reported 
 to have regained its original splendor after ten months, but in Februa- 
 ry, 1672, it was looked for in vain. It did not reappear until the 29th 
 of March in the same year, and then only as a star of the sixth magni- 
 tude ; since that time it has never been observed. (Jacques Cassini, 
 Element d'Astr., p. 6971.) These phenomena induced Dominique 
 Cassini to search for stars never before seen (by him !). He main 
 tained that he had discovered fourteen such stars of the fourth, fifth, 
 and sixth magnitudes (eight in Cassiopeia, two ir Eridanus, and four 
 near the North Pole). From the absence of any precise data as to their 
 respective positions, and especially since, like those said to have been
 
 160 COSMOS. 
 
 discovered by Maraldi between 1694 and 1709, their existence is more 
 than questionable, they can not be introduced in our present list. 
 (Jacques Cassini, Elimens tfAstron., p. 73-77 ; Delambre, Hist, de 
 VAstr. Mod., t. ii., p. 780.) 
 
 (t?) One hundred and seventy-eight years elapsed after the appear- 
 ance of the new star in Vulpes without a similar phenomenon having 
 occurred, although in this long interval the heavens were most care- 
 fully explored, and its stars counted, by the aid of a more diligent use 
 of telescopes and by comparison with more correct catalogues of the 
 stars. On the 28. h of April, 1848, at Mr. Bishop's private observatory 
 (South Villa, Regent's Park), Hind made the important discovery of a 
 new reddish-yellow star of the fifth magnitude in Ophiuchus (R. A. 16 
 50' 59" ; S. Decl. 12 39' 16", for 1848). In the case of no other new 
 star have the novelty of the phenomenon and the invariability of its po- 
 sition been demonstrated with greater precision. At the present time 
 (1850) it is scarcely of the eleventh magnitude, and, according to Lich 
 tenberger's accurate observations, it will most likely soon disappear. 
 (Notices of the Astr.Soc.,vo\. viii., p. 146 and 155-158.) 
 
 The above list of new stars, which, within the last two 
 thousand years, have suddenly appeared and again disap- 
 peared, is probably more complete than any before given, and 
 may justify a few general remarks. We may distinguish three 
 classes : new stars which suddenly shine forth, and then, after 
 a longer or shorter time, disappear ; stars whose brightness is 
 subject to a periodical variability, which has been already 
 determined ; and stars, like 77 Argus* which suddenly exhib- 
 it an unusual increase of brilliancy, the variations of which 
 are still undetermined. All these phenomena are, most prob- 
 ably, intrinsically related to each other. The new star in 
 Cygnus (1600), which, after its total disappearance (at least 
 to the naked eye), again appeared and continued as a star of 
 the sixth magnitude, leads us to infer the affinity of the two 
 first kinds of celestial phenomena. The celebrated star dis- 
 covered by Tycho Brahe in Cassiopeia in 1572 was consid- 
 ered, even while it was still shining, to be identical with the 
 new star of 945 and 1264. The period of 300 years which 
 Goodricke conjectured, has been reduced by Keill and Pigott 
 to 150 years. The partial intervals of the actual phenom- 
 ena, which perhaps are not very numerically accurate, amount 
 to 319 and 308 years. Arago* has pointed out the great 
 improbability that Tycho Brahe's star of 1572 belongs to 
 those which are periodically variable. Nothing, as yet, 
 seems to justify us in regarding all new stars as variable in 
 long periods, which from their very length have remained 
 unknown to us. If, for instance, the self-luminosity of all 
 the suns of the firmament is the result of an electro-mag- 
 
 * Arago, Annuaire pour 1842, p. 332.
 
 NEW STARS 161 
 
 netic process in their photospheres, we may consider this 
 process of light as variable in many ways, without assuming 
 any local or temporary condensations of the celestial ether, 
 or any intervention of the so-called cosmical clouds. It may 
 either occur only once or recur periodically, and either regu- 
 larly or irregularly. The electrical processes of light on our 
 earth, which manifest themselves either as thunder-storms 
 in the regions of the air, or as polar effluxes, together with 
 much apparently irregular variation, exhibit nevertheless a 
 certain periodicity dependent both on the seasons of the year 
 and the hours of the day ; and this fact is, indeed, frequent- 
 ly observed in the formation for several consecutive days, 
 during perfectly clear weather, of a small mass of clouds in 
 particular regions of the sky, as is proved by the frequent 
 failures in attempts to observe the culmination of stars. 
 
 The circumstance that almost all these new stars burst 
 forth at once with extreme brilliancy as stars of the first mag- 
 nitude, and even with still stronger scintillation, and that 
 they do not appear, at least to the naked eye, to increase 
 gradually in brightness, is, in my opinion, a singular pecul- 
 iarity, and one well deserving of consideration. Kepler* at- 
 tached such weight to this criterion, that he refuted the idle 
 pretension of Antonius Laurentinus Politianus to having seen 
 tiio star in Ophiuchus (1604) before Bronowski simply by 
 the circumstance that Laurentinus had said, " Apparuit nova 
 Stella parva et postea de die in diem crescendo apparuit lu- 
 mine non multo inferior Venere, superior Jove." There are 
 only three stars, which may be looked upon in the light of 
 exceptions, that did not shine forth at once as of the first 
 magnitude ; viz., the star which appeared in Cygnus in 
 1600, and that in Vulpes in 1670, which were both of the 
 third, and Hind's ne tar in Ophiuchus in 1848, which is 
 of the fifth magnitude. 
 
 It is much to be regretted, as we have already observed, 
 that after the invention of the telescope in the long period 
 of 178 years, only two new stars have been seen, whereas 
 these phenomena have sometimes occurred in such rapid suc- 
 cession, that at the end of the fourth century four were ob- 
 served in twenty-four years ; in the thirteenth century, three 
 in sixty-one years ; and during the era of Tycho Brahe and 
 Kepler, at the end of the sixteenth and beginning of the sev- 
 enteenth centuries, no less than six were observed within a 
 
 * Kepler, De Stella Nova in pede Serp., p. 3.
 
 162 COSMOS. 
 
 period of thirty-seven years. Throughout this examination I 
 have kept in view the Chinese observations of extraordinary 
 stars, most of which, according to the opinion of the most 
 eminent astronomers, are deserving of our confidence. Why 
 it is that of the new stars seen in Europe, that of Kepler in 
 Ophiuchus (1604) is in all probability recorded in the rec- 
 ords of Ma-tuan-lin, while that of Tycho in Cassiopeia (1572) 
 is not noticed, I, for my part, am as little able to explain as 
 I am to account for the fact that no mention was made in 
 the sixteenth century, among European astronomers, of the 
 great luminous phenomenon which was observed in China 
 in February, 1578. The difference of longitude (1 14) could 
 only, HI a few instances, account for their not being visible. 
 Whoever has been engaged in such investigations, must be 
 well aware that the want of record either of political events 
 or natural phenomena, either upon the earth or in the heav- 
 ens, is not invariably a proof of their never having taken 
 place ; and on comparing together the three different cata- 
 logues which are given in Ma-tuan-lin, we actually find com- 
 ets (those, for instance, of 1385 and 1495) mentioned in one 
 but omitted in the others. 
 
 Even the earlier astronomers (Tycho Brahe and Kepler), 
 as well as the more modern (Sir John Herschel and Hind), 
 have called attention to the fact that the great majority (four 
 fifths, I make it) of all the new stars described both in Eu- 
 rope and China have appeared in the neighborhood of or 
 within the Milky Way. If that which gives so mild and 
 nebulous a light to the annular starry strata of the Milky 
 Way is, as is more than probable, a mere aggregation of 
 small telescopic stars, Tycho Brahe's hypothesis, which wo 
 have already mentioned, of the formation of new, suddenly- 
 shining fixed stars, by the globular condensation of celestial 
 vapor, falls at once to the ground. What the influence of 
 gravitation may be among the crowded strata and clusters 
 of stars, supposing them to revolve round certain central nu- 
 clei, is a question not to be here determined, and belongs to 
 the mythical part of Astrognosy. Of the twenty-one new 
 stars enumerated in the above list, five (those of 134, 393, 
 827, 1203, and 158 1) appeared in Scorpio, three in Cassi- 
 opeia and Cepheus (945, 1264, 1572), and four in Ophiu- 
 chus (123, 1230, 1604, 1848). Once, however (1012), one 
 was seen in Aries at a great distance from the Milky Way 
 (ths star seen by the monk of St. Gall). Kepler himself 
 who, however, considers as a new star that described by Fa
 
 VANISHED STARS. 163 
 
 bricius as suddenly shining in the neck of Cetus in the year 
 1596, and as disappearing in October of the same year, like- 
 wise advances this position as a proof to the contrary. (Kep- 
 ler, De Stella Nova Serp., p. 112.) Is it allowable to in- 
 fer, from the frequent lighting up of such stars in the same 
 constellations, that in certain regions of space those, name- 
 ly, where Cassiopeia and Scorpio are to be seen the condi- 
 tions of their illuminations are favored by certain local re- 
 lations ? Do such stars as are peculiarly fitted for the ex- 
 plosive temporary processes of light especially lie in those 
 directions ? 
 
 The stars whose luminosity was of the shortest duration 
 were those of 389, 827, and 1012. In the first of the above- 
 named years, the luminosity continued only for three weeks ; 
 in the second, four months ; in the third, three. On the 
 other hand, Tycho Brahe's star in Cassiopeia continued to 
 shine for seventeen months ; while Kepler's star in Cygnus 
 (1600) was visible fully twenty-one years before it totally 
 disappeared. It was again seen in 1655, and still of the 
 third magnitude, as at its first appearance, and afterward 
 dwindled down to the sixth magnitude, without, however 
 (according to Argelander's observations), being entitled to 
 rank among periodically variable stars. 
 
 STARS THAT HAVE DISAPPEARED. The observation and 
 enumeration of stars that have disappeared is of importance 
 for discovering the great number of small planets which prob- 
 ably belong to our solar system. Notwithstanding, however, 
 the great accuracy of the catalogued positions of telescopic 
 fixed stars and of modern star-maps, the certainty of convic- 
 tion that a star in the heavens has actually disappeared since 
 a certain epoch can only be arrived at with great caution. 
 Errors of actual observation, of reduction, and of the press,* 
 
 * On instances of stars which have not disappeared, see Argelander, 
 in Schumacher's Astronom. Nachr., No. 624, e. 371. To adduce an ex- 
 ample from antiquity, I may point to the fact that the carelessness with 
 which Aratus compiled his poetical catalogue of the stars has led to the 
 often-renewed question whether Vega Lyrze is a new star, or one which 
 varies in long periods. For instance, Aratus asserts that the constella- 
 tion of Lyra consists wholly of small stars. It is singular that Hippar- 
 chus, in his Commentary, does not notice this mistake, especially as he 
 censures Aratus for his statements as to the relative intensity of light in 
 the stars of Cassiopeia and Ophiuchus. All this, however, is only ac- 
 cidental and not demonstrative ; for when Aratus also ascribes to Cyg- 
 nus none but stars " of moderate brilliancy," Hipparchus expressly re- 
 futes this error, and adds the remark that the bright star in the Swan
 
 164 COSMOS. 
 
 often disfigure the very best catalogues. The disappearance 
 of a heavenly body from the place in which it had before 
 been distinctly seen, may be the result of its own nution as 
 much as of any such diminution of its photometric process 
 (whether on its surface or in its photosphere), as would ren- 
 der the waves of light too weak to excite our organs of sight. 
 What we no longer see is not necessarily annihilated. The 
 idea of destruction or combustion, as applied to disappearing 
 stars, belongs to the age of Tycho Brahe. Even Pliny, in 
 the fine passage where he is speaking of Hipparchus, makes 
 i a question : Stellae an obirent nascerenturve ? The ap- 
 parent eternal cosmical alternation of existence and destruc- 
 tion is not annihilation ; it is merely the transition of matter 
 into new forms, into combinations which are subject to new 
 processes. Dark cosmical bodies may by a renewed process 
 of light again become luminous. 
 
 PERIODICALLY VARIABLE STARS. Since all is in motion in 
 the vault of heaven, and every thing is variable both in space 
 and time, we are led by analogy to infer that as the fixed 
 stars universally have not merely an apparent, but also a 
 proper motion of their own, so their surfaces or luminous at- 
 mospheres are generally subject to those changes which re- 
 cur, in the great majority, in extremely long, and, therefore, 
 unmeasured and probably undeterminable periods, or which, 
 in a few, occur without being periodical, as it were, by a 
 sudden revolution, either for a shorter or for a longer time. 
 The latter class of phenomena (of which a remarkable in- 
 stance is furnished in our own days by a large star in Argo) 
 will not be here discussed, as our proper subject is those fixed 
 stars whose periods have already been investigated and as- 
 certained. It is of importance here to make a distinction 
 between three great sidereal phenomena, whose connection 
 has not as yet been demonstrated ; namely, variable stars of 
 known periodicity ; the instantaneous lighting up in the heav- 
 ens of so-called new stars ; and sudden changes in the lu- 
 minosity of long-known fixed stars, which previously shone 
 
 (Deneb) is little inferior in brilliancy to Lyra (Vega Lyra;). Ptolemy 
 classes Vega among stars of the first magnitude, and in the Cataster 
 isms of Eratosthenes (cap. 25), Vega is caEed Tievnov KOI TiOfnrpnv. Con 
 sidering the many inaccuracies of a poet, who never himself observed 
 the stars, one is not much disposed to give credit to the assertion that it 
 was only between the years 272 and 127 B.C., i. e., between the times 
 of Aratus and Hipparchus, that the star Vega Lyrae (Fidicula of Pliny, 
 xviii., 25) became a star of the first magnitude.
 
 PERIODICAL STARS. 165 
 
 with uniform intensity. We shall first of all dwell exclu- 
 sively on the first kind of variability ; of this, the earliest in- 
 stance accurately observed is furnished (1638) by Mira, a 
 star in the neck of Cetus. The East-Friesland pastor, David 
 Fabricius (the father of the discoverer of the spots on the 
 sun), had certainly already observed this star on the 13th of 
 August, 1596, as of the third magnitude, and in October of 
 the same year he saw it disappear. But it was not until for- 
 ty-two years afterward that the alternating, recurring vari- 
 ability of its light, and its periodic changes, were discovered 
 by the Professor Johann Phocylides Holwarda, Professor of 
 Franeker. This discovery was further followed in the same 
 century by that of two other variable stars, ft Persei (1669), 
 described by Montanari, and % Cygni (1687), by Kirch. 
 
 The irregularities which have been noticed in the periods, 
 together with the additional number of stars of this class 
 which have been discovered, have, since the beginning of the 
 nineteenth century, awakened the most lively interest in this 
 complicated group of phenomena. From the difficulty of the 
 subject, and from my own wish to be able to set down in the 
 present work the numerical elements of this variability (as 
 being the most important result of all observations), so far as 
 in the present state of the science they have been ascertain- 
 ed, I have availed myself of the friendly aid of that astrono- 
 mer who of all our cotemporaries has devoted himself with 
 the greatest diligence, and with the most brilliant success, 
 to the study of the periodically varying stars. The doubts 
 and questions called forth by my own labors I confidently 
 laid before my worthy friend Argelander, the director of the 
 Observatory at Bonn, and it is to his manuscript communi 
 cations that I am solely indebted for all that follows, which 
 for the most part has never before been published. 
 
 The greater number of the variable stars, although not all, 
 are of a red or reddish color. Thus, for instance, besides /3 
 Persei (Algol in the head of Medusa), /3 Lyrae and e Aurigse 
 have also a white light. The star 77 Aquilae is rather yellow- 
 ish ; so also, in a still less degree, is Geminorum. The old 
 assertion that some variable stars (and especially Mira Ceti) 
 are redder when their brilliancy is on the wane than on the 
 increase, seems to be groundless. Whether, in the double 
 star a Herculis (in which, according to Sir John Herschel, 
 the greater star is red, but according to Struve yellow, while 
 its companion is said to be dark blue), the small companion, 
 estimated at between the fifth to the seventh magnitude, ia
 
 166 COSMOS. 
 
 itself also variable, appears very problematical. Struve* 
 himself merely says, Suspicor minorem esse variabilem, 
 Variability is by no means a necessary concomitant of red- 
 ness. There are many red stars : some of them very red 
 as Arcturus and Aldebaran in which, however, no variabil- 
 ity has as yet been discovered. And it is also more than 
 doubtful in the case of a star of Cepheus (No. 7582 of the 
 catalogue of the British Association), which, on account of 
 its extreme redness, has been called by William Herschel 
 the Garnet Star (1782). 
 
 It would be difficult to indicate the number of periodically 
 variable stars for the reason that the periods already determ- 
 ined are all irregular and uncertain, even if there were no 
 other reasons. The two variable stars of Pegasus, as well 
 as a Hydra, s Aurigse, and a Cassiopeise, have not the cer- 
 tainty that belongs to Mira Ceti, Algol, and 6 Cephei. In 
 inserting them, therefore, in a table, much will depend on 
 the degree of certainty we are disposed to be content with. 
 Argelander, as will be seen from the table at the close of 
 this investigation, reckons the number of satisfactorily de- 
 termined periods at only twenty-four.t 
 
 The phenomenon of variability is found not only both in 
 red and in some white stars, but also in stars of the most di- 
 versified magnitude ; as, for example, in a star of the first 
 magnitude, a Orionis ; by Mira Ceti, a Hydra, a Cassiopeiae, 
 and (3 Pegasi, of the second magnitude ; ft Persei, of the 2'3d 
 magnitude ; and in 77 Aquilse, and (3 Lyrse, of the 3'4th mag- 
 nitude. There are also variable stars, and, indeed, in far 
 greater numbers, of the sixth to the ninth magnitude, such 
 as the variabiles Coronae, Virginis, Cancri, et Aquarii. The 
 star % Cygni likewise presents very great fluctuations at its 
 maximum. 
 
 * Compare Madler, Astr., s. 438, note 12, with Struve, Stellarum, 
 compos. Mensurce Microm., p. 97 and 98, star 2140. "I believe," says 
 Argelander, "it is extremely difficult with a telescope having a great 
 power of illumination to estimate rightly the brightness of two such 
 different stars as the two components of a Herculis. My experience 
 is strongly against the variability of the companion; or, during my 
 many observations in the daytime with the telescopes of the meridian 
 circles of Abo, Helsingfors, and Bonn, I have never seen a Herculis 
 single, which would assuredly have been the case if the companion at 
 its minimum were of the seventh magnitude. I believe the latter to 
 be constant, and of the fifth or 5-6th magnitude." 
 
 t Madler's Table (Astron., s. 435) contains eighteen stars, with widely 
 differing numerical elements. Sir John Herschel enumerates more than 
 forty-five, including those mentioned in the notes. Outlines, 819-826.
 
 VARIABLE STARS. 167 
 
 That the periods of the variable stars are very irregular 
 has. been, long known ; but that this variability, with all its 
 apparent irregularity, is subject to certain definite laws, was 
 first established by Argelander. This he hopes to be able 
 to demonstrate in a longer and independent treatise of his 
 own. In the case of % Cygni, he considers that two perturb- 
 ations in the period the one of 100, the other of 8^ are 
 more probable than a single period of 108. Whether such 
 disturbances arise from changes in the process of light which 
 is going on in the atmosphere of the star itself, or from the 
 periodic times of some planet which revolves round the fixed 
 star or sun % Cygni, and by attraction influences the form of 
 its photosphere, is still a doubtful question. The greatest 
 irregularity in change of intensity has unquestionably been 
 exhibited by the variabilis Scuti (Sobieski's shield) ; for this 
 star diminishes from the 5 - 4th down to the ninth magnitude ; 
 and, moreover, according to Pigott, it once totally disappeared 
 at the end of the last century. At other times the fluctua- 
 tions in its brightness have been only from the 6 - 5th to the 
 sixth magnitude. The maximum of the variations of% Cygni 
 have been between the 6'7th and fourth magnitude ; of Mira, 
 from the fourth to the 2- 1st magnitude. On the other hand, 
 in the duration of its periods 6 Cephei shows an extraordi- 
 nary, and, indeed, of all variable stars, the greatest regularity, 
 as is proved by the 87 minima observed between the 10th 
 of October, 1840, and 8th of January, 1848, and even later. 
 In the case of e Aurigse, the variation of its brilliancy, dis- 
 covered by that indefatigable observer, Heis, of Aix-la-Cha 
 pelle,* extends only from the 3'4th to the 4'5th magnitude. 
 
 A great difference in the maximum of brightness is exhib- 
 ited by Mira Ceti. In the year 1779, for instance (on the 
 6th of November), Mira was only a little dimmer than Alde- 
 baran, and, indeed, not unfrequently brighter than stars of 
 the second magnitude ; whereas at other times this variable 
 star scarcely attained to the intensity of the light of 6 Ceti, 
 which is of the fourth magnitude. Its mean brightness is 
 equal to that of y Ceti (third magnitude). If we designate 
 by the brightness of the faintest star visible to the naked 
 eye, and that of Aldebaran by 50, then Mira has varied in 
 its maximum from 20 to 47. Its probable brightness may be 
 expressed by 30 : it is oftener below than above this limit. 
 The measure of its excess, however, when it does occur, ia 
 
 * Argelander, in Schumacher's Aslron. Nachr., bd. xxvi. (1848), No, 
 624, s. 369.
 
 168 COSMOS. 
 
 in proportion more considerable. No certain period of these 
 oscillations has as yet been discovered. There are, however, 
 indications of a period of 40 years, and another of 160. 
 
 The periods of va nation in different stars vary as 1:250. 
 The shortest period is unquestionably that exhibited by (3 
 Persei, being 68 hours and 49 minutes ; so long, at least, as 
 that of the polar star is not established at less than two days. 
 Next to ft Persei come 6 Cephei (5d. 8h. 49m.), 77 Aquilaa 
 (7d. 4h. 14m.), and $ Geminorum (lOd. 3h. 35m.). The 
 longest periods are those of 30 Hydrae Hevelii, 495 days ; 
 X Cygni, 406 days ; Variabilis Aquarii, 388 days ; Serpentis 
 S., 367 days ; and Mira Ceti, 332 days. In several of the 
 variable stars it is well established that they increase in brill- 
 iancy more rapidly than they diminish. This phenomenon 
 is the most remarkable in 6 Cephei. Others, as, for instance, 
 ft Lyrse, have an equal period of augmentation and diminu- 
 tion of light. Occasionally, indeed, a difference is observed 
 in this respect in the same stars, though at different epochs 
 in their process of light. Generally Mira Ceti (as also 6 Ce- 
 phei) is more rapid in its augmentation than in its diminu 
 tion ; but in the former the contrary has also been observed 
 
 Periods within periods have been distinctly observed in 
 the case of Algol, of Mira Ceti, of ft Lyrao, and with great 
 probability also in % Cygni. The decrease of the period of 
 Algol is now unquestioned. Goodricke was unable to per- 
 ceive it, but Argelander has since done so ; in the year 1842 
 he was enabled to compare more than 100 trustworthy ob- 
 servations (comprising 7600 periods), of which the extremes 
 differed from each other more than 58 years. (Schumacher's 
 Astron. Nachr., Nos. 472 and 624.) The decrease in the 
 period is becoming more and more observable.* For the 
 
 * " If," says Argelander, " I take for the epoch the minimum bright- 
 ness of Algol, in 1800, on the 1st of January, at 18h. 1m. mean Paris 
 time, I obtain the duration of the periods for 
 
 1987, 2d. 20h. 48m., or 59s.-416iOs.-316 
 1406, " 58s.-737iOs.-094 
 
 58s.-393JtOs.-175 
 58s.-154-tOs.-039 
 58s.-193-tOs.-096 
 57s.-971iOs.-045 
 558.-182-j-Os.-348 
 " In this table the numbers have the following signification : if we 
 designate the minimum epoch of the 1st of Jan., 1800, by 0, that im- 
 mediately preceding by 1, and that immediately following by -^-1, and 
 BO on, then the duration between 1987 and 1986 would be exactly 
 2d. 20h. 48m. 59s -416. but *Jie duration between -f-5441 and +5442
 
 VARIABLE STARS. 169 
 
 periods of the maximum of Mira (including the maximum of 
 brightness observed by Fabricius in 1596), a formula* has 
 been established by Argelander, from which all the maxima 
 can be so deduced that the probable error in a long period of 
 variability, extending to 33 Id. 8h., does not in the mean ex- 
 ceed 7 days, while, on the hypothesis of a uniform period, it 
 would be 15 days. 
 
 The double maximum and minimum of (3 Lyrae, in each 
 of its periods of nearly 13 days, was from the first correctly 
 ascertained by its discoverer, Goodricke (1784) ; but it has 
 been placed still more beyond doubtf by very recent observ- 
 ations. It is remarkable that this star attains to the same 
 brightness in both its maxima, but in its principal minimum 
 it is about half a magnitude fainter than in the other. Since 
 the discovery of the variability of (3 Lyrae, the period in a 
 period has probably been on the increase. At first the vari- 
 ability was more rapid, then it became gradually slower ; and 
 this decrease in the length of time reached its limit between 
 the years 1840 and 1844. During that time its period was 
 nearly invariable ; at present it is again decidedly on the de- 
 crease. Something similar to the double maximum of (3 Lyrse 
 occurs in 6 Cephei. There is a tendency to a second maxi- 
 
 would be 2d. 20h. 48m. 55s. -182 ; the former applies to the year 1784, 
 the latter to the year 1842. 
 
 "The numbers which follow the signs ^ are the probable errors. 
 That the diminution becomes more and more rapid is shown as well by 
 the last number as by all my observations since 1847." 
 
 * Argelander's formula for representing all observations of the maxima 
 of Mira Ceti is, as communicated by himself, as follows : 
 
 1751, Sep., 9-76 -f331d.-3363 E. 
 
 +10d.-5, sin. ( 3 T 6 T E. +86 23') +18d.-2, sin. (ff E. +231 42') 
 +33d.-9, sin. (ff E. +170 19') -f 65d.-3, sin. (fp E. -j-6 37') 
 where E. represents the number of maxima which have occurred since 
 Sept. 9, 1751, and the co-efficients are given in days. Therefore, for 
 the current year (E. being =109), the following is the maximum: 
 1751, Sep., 9-76+36115d.-G5-|-8d.-44 12d.-24. 
 
 4-18d.-59+27d.-34=1850, Sep., 8d.-54. 
 
 " The strongest evidence in favor of this formula is, that it represents 
 even the maximum of 1596 {Cosmos, vol. ii., p. 330), which, on the 
 supposition of a uniform period, would deviate more than 100 days. 
 However, the laws of the variation of the light of this star appear so 
 complicated, that in particular cases e. g., for the accurately observed 
 maximum of 1840 the formula was wrong by many days (nearly twen- 
 ty-five)." 
 
 t Compare Argelander's essay, written on the occasion of the cen- 
 tenary jubilee of the KOnigsberg University, and entitled De Stella 
 8 Lyra; Variabili, 1844. 
 
 VOL. III. H
 
 170 COSMOS. 
 
 uaum, in so far as its diminution of light does not \ &/ 
 uniformly ; but, after having been for some time tolerably 
 rapid, it comes to a stand, or at least exhibits a very Incon- 
 siderable diminution, which suddenly becomes rapicj again. 
 In some stars it would almost appear as though th,j light 
 were prevented from fully attaining a second maximum. In 
 % Cygni it is very probable that two periods of variability 
 prevail a longer one of 100 years, and a shorter on; of 8. 
 The question whether, on the whole, there is greater reg- 
 ularity in variable stars of very short than in those of very 
 long periods, is difficult to answer. The variations from a 
 uniform period can only be taken relatively ; i. e., in parts 
 of the period itself. To commence with long periods, ^ Cygni, 
 Mira Ceti, and 30 Hydrse must first of all be consideied. In 
 X Cygni, on the supposition of a uniform variability, the devi- 
 ations from a period of 406-0634 days (which is the most 
 probable period) amount to 39-4 days. Even though a por- 
 tion of these deviations may be owing to errors of observa- 
 tion, still at least 29 or 30 days remain beyond doubt ; i. e., 
 one fourteenth of the whole period. In the case of Mira 
 Ceti,* in a period of 331 '340 days, the deviations amount to 
 55'5 days, even if we do not reckon the observations of David 
 Fabricius. If, allowing for errors of observation, we limit 
 the estimate to 40 days, we still obtain one eighth ; conse- 
 quently, as compared with % Cygni, nearly twice as great a 
 deviation. In the case of 30 Hydrse, which has a period of 
 495 days, it is still greater, probably one fifth. It is only 
 during the last few years (since 1840, and still later) that the 
 variable stars with very short periods have been observed 
 steadily and with sufficient accuracy, so that the problem in 
 question, when applied to them, is still more difficult of solu- 
 tion. From the observations, however, which have as yet 
 been taken, less considerable deviations seem to occur. In 
 the case of 77 Aquilse (with a period of 7d. 4h.) they only 
 amount to one sixteenth or one seventeenth of the whole pe- 
 riod ; in that of ft Lyrse (period 12d. 21h.) to one twenty- 
 seventh or one thirtieth ; but the inquiry is still exposed to 
 much uncertainty as regards the comparison of long and short 
 periods. Of j3 Lyra between 1700 and 1800 periods have 
 been observed ; of Mira Ceti, 279 ; of % Cygni, only 145. 
 The question that has been mooted, whether stars which 
 
 * The work of Jacques Cassini (Eltmens Astronomic, 1740, p. 66- 
 69) belongs to the earliest systematic attempts to investigate tb? mean 
 duration of the period of the variation of Mira Ceti.
 
 VARIABLE STARS. 171 
 
 have long appeared to be variable in regular periods ever 
 cease to be so, must apparently be answered in the nega- 
 tive. As among the constantly variable stars there are 
 some which at one time exhibit a very great, and at anoth- 
 er a very small degree of variability (as, for instance, vari- 
 abilis Scuti), so, it seems, there are also others whose vari- 
 ability is at certain times so very slight, that, with our lim- 
 ited means, we are unable to detect it. To such belongs 
 variabilis Coronae bor. (No. 5236 in the Catalogue of the 
 British Association), recognized as variable by Pigott, who 
 observed it for a considerable time. In the winter of 1795-6 
 this star became totally invisible ; subsequently it again 
 appeared, and the variations of its light were observed by 
 Koch. In 1 8 1 7 , Harding and Westphal found that its bright- 
 ness was nearly constant, while in 1824 Olbers was again 
 enabled to perceive a variation in its luminosity. Its con- 
 stancy now again returned, and from August, 1843, to Sep- 
 tember, 1845, was established by Argelander. At the end 
 of September, a fresh diminution of its light commenced. 
 By October, the star was no longer visible in the comet-seek- 
 er ; but it appeared again in February, 1846, and by the be- 
 ginning of June had reached its usual magnitude (the sixth). 
 Since then it has maintained this magnitude, if we overlook 
 some small fluctuations whose very existence has not been 
 established with certainty. To this enigmatical class of stars 
 belong also variabilis Aquarii, and probably Janson and Kep- 
 ler's star in Cygnus of 1600, which we have already men- 
 tioned among the new stars.
 
 172 
 
 TABLE OP THE VARIABLE STARS, BY F. ARGELANDEE. 
 
 No.! Name of tli* Star. 
 
 Length of 
 Period. 
 
 Brigbtnes 
 
 s in the 
 Minimum. 
 
 NameofniscoTeraraod 
 Date of DiKjorery. 
 
 1 o Ceti 
 
 J). H. M. 
 
 331 20 
 
 Magnit. 
 4to2-l 
 23 
 6-7 to 4 
 5 to 4 
 5 
 34 
 3-4 
 43 
 3 
 6 
 6 5 to 5-4 
 7to6'7 
 9 to 6 7 
 67 
 8 to 7-8 
 7 
 2 
 1 
 2 
 34 
 4-3 
 2 
 8 
 7-8 
 
 Magnit. 
 
 4 
 
 
 
 5-4 
 45 
 5-4 
 34 
 
 9 to 6 
 
 
 
 
 
 3-2 
 1-2 
 23 
 4-5 
 5-4 
 2*3 
 
 Holwarda, 1639. 
 Montanari, 1669. 
 Gottfr. Kirch, 1687. 
 Maraldi, 1704. 
 Koch, 1782. 
 E. Pigott, 1784. 
 Goodricke, 1784. 
 Ditto, 1784. 
 Wm. Herschel 1795. 
 E. Pigott, 1795. 
 Ditto, 1795. 
 Harding, 1809. 
 Ditto, 1810. 
 Ditto, 1826. 
 Ditto, 1828. 
 Schwerd, 1829. 
 Birt, 1831. 
 John Herschel, 1836. 
 Ditto, 1837. 
 Heis, 1846. 
 Schmidt, 1847. 
 Ditto, 1848. 
 Hind, 1848. 
 Ditto, 1848. 
 
 210 Perse i 
 
 22049 
 406 1 30 
 495 
 31218 
 7-414 
 122145 
 5 849 
 66 8 
 323 
 71 17 
 145 21 
 388 13 
 359 
 367 5 
 380 
 79 3 
 196 
 55 
 i 
 
 10 335 
 4023 
 350 
 
 i 
 
 3 \ x Cygni 
 
 430 Hydra He v. . 
 5LeonisR.,420M. 
 
 6 17 A(| u il;i- 
 
 7/3 Lyra 
 
 8 6 Cephei . 
 
 9 a Herculis 
 10 Coronje R. 
 
 11 Scuti R. 
 
 12 Virginia R 
 13Aquarii R 
 
 14Serpentis R 
 ISSerpentis S 
 l6Cancri R 
 
 17 a Cassiopeiae ... 
 18 a Orionis 
 
 19 o Hydra 
 
 20eAurigae 
 
 21 f Geminorum ... 
 22 {3 Pegasi 
 
 23PegasiR 
 24CancriS 
 
 EXPLANATORY REMARKS. 
 
 The in the column of the minima indicates that the star is then 
 fainter than the tenth magnitude. For the purpose of clearly and con- 
 veniently designating the smaller variable stars, which for the most part 
 have neither names nor other designations, I have allowed myself to ap- 
 
 C,d to them capitals, since the letters of the Greek and the smaller 
 in alphabet have, for the most part, been already employed by 
 Bayer. 
 
 Besides the stars adduced in the preceding table, there are almost as 
 many more which are supposed to be variable, since their magnitudes 
 are set down differently by different observers. But as these estimates 
 were merely occasional, and have not been conducted with much pre- 
 cision, and as different astronomers have different principles in estima- 
 ting magnitudes, it seems the safer course not to notice any euch cases 
 until the same observer shall have found a decided variation in them at 
 different times. With all those adduced in the table, this is the case ; 
 and the fact of their periodical change of light is quite established, even 
 where the period itself has not been ascertained. The periods given in 
 the table are founded, for the most part, on my own examination of all 
 the earlier observations that have been published, and on my own ob- 
 servations within the last ten years, which have not as yet been pub- 
 lished. Exceptions will be mentioned in the following notices of the 
 several stars. 
 
 In these notices the positions are those for 1850, and are expressed in
 
 VARIABLE STARS. 173 
 
 right ascension and declination. The frequently-repeated term grada- 
 tion indicates a difference of brightness, which may be distinctly recog- 
 nized even by the naked eye, or, in the case of those stars which are 
 invisible to the unaided sight, by a Frauenhofer's comet-seeker of twen- 
 ty-five and a half inches focal length. For the brighter stars above the 
 sixth magnitude, a gradation indicates about the tenth part of the dif- 
 ference by which the successive orders of magnitude differ from one an- 
 other ; for the smaller stars the usual classifications of magnitude are 
 considerably closer. 
 
 (l)o Ceti, R. A. 32 57', Decl. 3 40' ; also called Mira, on account 
 of the wonderful change of light which was first observed in this star. 
 As early as the latter half of the seventeenth century, the periodicity of 
 this star was recognized, and Bouillaud fixed the duration of its period 
 at 333 days ; it was found, however, at the same time, that this dura- 
 tion was sometimes longer and sometimes shorter, and that the star, at 
 its greatest brilliancy, appeared sometimes brighter and sometimes faint- 
 er. This has been subsequently fully confirmed. Whether the star ever 
 becomes perfectly invisible is as yet undecided; at one time, at the 
 epoch of its minimum, it has been observed of the eleventh or twelfth 
 magnitude ; at another, it could not be seen even with the aid of a three 
 or a four-feet telescope. This much is certain, that for a long period it 
 is fainter than stars of the tenth magnitude. But few observations of 
 the star at this stage have as yet been taken, most having commenced 
 when it had begun to be visible to the naked eye as a star of the sixth 
 magnitude. From this period the star increases in brightness at first 
 with great rapidity, afterward more slowly, and at last with a scarcely 
 perceptible augmentation ; then, again, it diminishes at first slowly, aft- 
 erward rapidly. On a mean, the period of augmentation of light from 
 the sixth magnitude extends to fifty days ; that of its decrease down to 
 the same degree of brightness takes sixty-nine days ; so that the star is 
 visible to the naked eye for about four months. However, this is only 
 the mean duration of its visibility ; occasionally it has lasted as long as 
 five months, whereas at other times it has not been visible for more than 
 three. In the same way, also, the duration both of the augmentation 
 and of the diminution of its light is subject to great fluctuations, and the 
 former is at all times slower than the latter ; as, for instance, in the year 
 1840, when the star took sixty-two days to arrive at its greatest bright- 
 ness, and then in forty-nine days became visible to the naked eye. The 
 shortest period of increase that has as yet been observed took place in 
 1679, and lasted only thirty days; the longest (of sixty-seven days) oc- 
 curred in 1709. The decrease of light lasted the longest in 1839, being 
 then ninety-one days ; the shortest in the year 1660, when it was com- 
 pleted in nearly fifty-two days. Occasionally, the star, at the period of 
 its greatest brightness, exhibits for a whole month together scarcely any 
 perceptible variation; at others, a difference may be observed within a 
 very fe w days. On some occasions, after the star had decreased in bright- 
 ness for several weeks, there was a period of perfect cessation, or, at 
 least, a scarcely perceptible diminution of light during several days ; this 
 was the case in 1678 and in 1847. 
 
 The maximum brightness, as already remarked, is by no means al- 
 ways the same. If we indicate the brightness of the faintest star that 
 is visible to the naked eye by 0, and that of Aldebaran (a Tauri), a star 
 of the first magnitude, by fifty, then the maximum of light of Mira fluc- 
 tuates between 20 and 47, i. e., between the brightness of a star of the 
 fourth, and of the first or second magnitude : the mean brightness is 28
 
 174 COSMOS. 
 
 or that of the star y Ceti. But the duration of its periods is still more 
 irregular: its mean is 33 Id. 20h., while its fluctuations have extended 
 to a month ; for the shortest time that ever elapsed from one maximum 
 to the next was only 306 days, the longest, on the other hand, 367 days. 
 These irregularities become the more remarkable when we compare the 
 several occurrences of greatest brightness with those which would take 
 place if we were to calculate these maxima on the hypothesis of a uni- 
 form period. The difference between calculation and observation then 
 amounts to 50 days, and it appears that, for several years in succession, 
 those differences are nearly the same, and in the same direction. This 
 evidently indicates that the disturbance in the phenomena of light is one 
 of a very long period. More accurate calculations, however, have prov- 
 ed that the supposition of one disturbance is not sufficient, and that sev- 
 eral must be assumed, which may, however, all arise from the same 
 cause ; one of these recurs after 1 1 single periods ; a second after 88 ; 
 a third after 176 ; and a fourth after 264. From hence arises the form- 
 ula of sines (given at p. 169, note *), with which, indeed, the several 
 maxima very nearly accord, although deviations still exist which can 
 not be explained by errors of observation. 
 
 (2) (3 Persei, Algol ; R. A. 44 36', Decl. 4-40 22'. Although Gemi- 
 niano Montanari observed the variability or this star in 1667, and Ma- 
 raldi likewise noticed it, it was Goodricke that first, in 1782, discovered 
 the regularity of the variability. The cause of this is probably that this 
 star does not, like most other variable ones, gradually increase and di- 
 minish in brightness, but for 2d. 13h. shines uniformly as a star of the 
 2-3d magnitude, and only appears less bright for seven or eight hours, 
 when it sinks to the fourth magnitude. The augmentation and dimi- 
 nution of its brightness are not quite regular; but when near to the 
 minimum, they proceed with greater rapidity; whence the time of 
 least brightness may be accurately calculated to within ten to fifteen 
 minutes. It is moreover remarkable that this star, after having increased 
 in light for about an hour, remains for nearly the same period at the 
 same brightness, and then begins once more perceptibly to increase 
 Till very recently the duration of the period was held to be perfectly- 
 uniform, and Wurm was able to present all observations pretty closely 
 by assuming it to be 2d. 21h. 48m. 58is. However, a more ai curate cal- 
 culation, in which was comprehended a space of time nearly- twice as 
 long as that at Wurm's command, has shown that the period becomes 
 gradually shorter. In the year 1784 it was 2d. 20h. 48m. 59-4s., and in 
 the year 1842 only 2d. 20h. 48m. 55-2s. Moreover, from the most re- 
 cent observations, it becomes very probable that this diminution of the 
 period is at present proceeding more rapidly than before, so that for this 
 star also a formula of sines for the disturbance of its period will in time 
 be obtained. Besides, this diminution will be accounted for if we as- 
 sume that Algol comes nearer to us by about 2000 miles every year, or 
 recedes from us thus far less each succeeding year ; for in that case his 
 light would reach us as much sooner every year as the decrease of the 
 period requires; *. e., about the twelve thousandth of a second. If this 
 be the true cause, a formula of sines must eventually be deduced. 
 
 (3) X Cygni, R. A. 296 12', Decl. +32 32'. This star also exhibits 
 nearly the same irregularities as Mira. The deviations of the observed 
 maxima from those calculated for a uniform period amount to forty days, 
 but are considerably diminished by the introduction of a disturbance 
 of 8J^ single periods, and of another of 100 such periods. In its maxi- 
 mum this star reaches the mean brightness of a faint fifth magnitude, or
 
 VARIABLE STARS. 175 
 
 one gradat/on brighter than the star 17 Cygni. The fluctuations, how 
 ever, are in this case also very considerable, and have been observed 
 from thirteen gradations below the mean to ten above it. At this low- 
 est maximum the star would be perfectly invisible to the naked eye, 
 whereas, on the contrary, in the year 1847, it could be seen without 
 the aid of a telescope for fully ninety-seven days ; its mean visibility 
 extends to fifty-two days, of which, on the mean, it is twenty days on 
 the increase, and thirty-two on the decrease. 
 
 (4) 30 Hydras Hevetii, E. A. 200 23', Decl. 22 30'. Of this star, 
 which, from its position in the heavens, is only visible for a short time 
 during every year, all that can be said is, that both its period and its 
 maximum brightness are subject to very great irregularities. 
 
 (5) Leonis R. =420 Mayeri; R. A. 144 52', Decl. -f 12 7'. This 
 star is often confounded with 18 and 19 Leonis, which are close to it, 
 and, in consequence, has been very little observed ; sufficiently, how- 
 ever, to show that the period is somewhat irregular. Its brightness at 
 the maximum seems also to fluctuate through some gradations. 
 
 (6) n Aquilss, called also y Antinoi ; R. A. 296 12', Decl. +0 37'. 
 The period of this star is tolerably uniform, 7d. 4h. 13m. 53s. ; observa- 
 tions, however, prove that at long intervals of time trifling fluctuations 
 occur in it, not amounting to more than 20 seconds. The variation of 
 light proceeds so regularly, that up to the present time no deviations 
 have been discovered which could not be accounted for by errors of ob- 
 servation. In its minimum, this star is one gradation fainter than i 
 Aquilis ; at first it increases slowly, then more rapidly, and afterward 
 again more slowly ; and in 2d. 9h. from its minimum, attains to its great- 
 est brightness, in which it is nearly three gradations brighter than /?, 
 but two fainter than 6 Aquilse. From the maximum its brightness does 
 not diminish quite so regularly; for when the star has reached the bright- 
 ness of (3 (*. e., in Id. lOh. after the maximum), it changes more slowly 
 than either before or afterward. 
 
 (7) /3 Lyra;, R. A. 281 8', Decl. -f-33 11'; a star remarkable from 
 the fact of its having two maxima and two minima. When it has been 
 at its faintest light, one third of a gradation fainter than f Lyrse, it rises 
 in 3d. 5h. to its first maximum, in which it remains three fourths of a 
 gradation fainter than y Lyrse. It then sinks in 3d. 3h. to its second 
 minimum, in which its light is about five gradations greater than that of 
 f. After 3d. 2h. more, it again reaches, in its second maximum, to the 
 brightness of the first ; and afterward, in 3d. 12h., declines once more 
 to its greatest faintness; so that in 12d. 21h. 46m. 40s. it runs through 
 all its variations of light. This duration of the period, however, only 
 applies to the years 1840 to 1844; previously it had been shorter in 
 the year 1784, by about 2^h ; in 1817 and 1818, by more than an hour ; 
 and at present, a shortening of it is again clearly perceptible. There 
 is, therefore, no doubt that in the case of this star the disturbance of its 
 period may be expressed by a formula of sines. 
 
 (8) 6 Cephei, R. A. 335 54', Decl. +57 39'. Of all the known va- 
 riable stars, this exhibits in every respect the greatest regularity. The 
 period of 5d. 8h. 47m. 39is. is given by all the observations from 1784 
 to the present day, allowing for errors of observation, which will ac- 
 count for all the slight differences exhibited in the course of the altern 
 ations of light. This star is in its minimum three quarters of a gradation 
 brighter than e ; in its maximum it resembles i of the same constellation 
 (Cepheus). It takes Id. 15h. to pass from the former to the latter ; but, 
 on the other hand, more than double that time, viz., 3d. 18h., to change
 
 176 COSMOS. 
 
 again to its minimum during eight hours of the latter period, however 
 it scarcely changes at all, and very inconsiderably for a whole day. 
 
 (9) a Herculis, R. A. 256 57', Decl. +14 34'; an extremely red 
 double star, the variation of whose light is in every respect very irreg- 
 ular. Frequently, its light scarcely changes for months together; at 
 other times, in the maximum, it is nearly five gradations brighter than 
 in the minimum ; consequently, the period also is still very uncertain. 
 The discoverer of the star's variation had assumed it to be sixty-three 
 days. I at first set it down at ninety-five, until a careful reduction of all 
 iny observations, made during seven years, at length gave me the peri- 
 od assigned in the text. Heis believes that he can represent all the ob- 
 servations by assuming a period of 184-9 days, with two maxima and 
 
 (10) Corona; R., R. A. 235 36', Decl. +28 37'. This star is varia- 
 ble only at times ; the period set down has been calculated by Koch 
 from his own observations, which unfortunately have been lost. 
 
 (11) Scuti R., R. A. 279 52', Decl. 5 51'. The variations of bright- 
 ness of this star are at times confined within a very few gradations, 
 whereas at others it diminishes from the fifth to the ninth magnitude. It 
 has been too little observed to determine when any fixed rule prevails 
 in these deviations. The duration of the period is also subject to con- 
 siderable fluctuations. 
 
 (12) Virginis R., R. A. 187 43', Decl. +7 49'. It maintains its pe- 
 riod and its maximum brightness with tolerable regularity ; some devi- 
 ations, however, do occur, which appear to me too considerable to be 
 ascribed merely to errors of observation. 
 
 (13) Aquarii R., R. A. 354 11', Decl. 16 6'. 
 
 (14) Serpentis R., R. A. 235 57', Decl. -f 15 3.T. 
 
 (15) Serpentis S., R. A. 228 40', Decl. -f 14 o^'. 
 
 (16) Cancri R., R. A. 122 6', Decl. 4-12 9'. 
 
 Of these four stars, which have been but very slightly observed, little 
 more can be said than what is given in the table. 
 
 (17) a Cassiopeia, R. A. 8 0', Decl. +55 43'. This star is very diffi- 
 cult to observe. The difference between its maximum and minimum 
 only amounts to a few gradations, and is, moreover, as variable as the 
 duration of the period. This circumstance explains the varying state- 
 ments on this head. That which I have given, which satisfactorily rep- 
 resents the observations from 1782 to 1849, appears to me the most prob- 
 able one. 
 
 (18) a Orionis, R. A. 86 46', Decl. +7 22'. The variation in the 
 light of this star likewise amounts to only four gradations from the min- 
 imum to the maximum. For 91^ days it increases in brightness, while 
 its diminution extends over 104-fc, and is imperceptible from the twen- 
 tieth to the seventieth day after the maximum. Occasionally its varia 
 bility is scarcely noticeable. It is a very red star. 
 
 (19) a Hydras, R. A. 140 3', Decl. 8 1'. Of all the variable stars, 
 this is the most difficult to observe, and its period is still altogether un- 
 certain. Sir John Herschel sets it down at from twenty-nine to thirty 
 
 1) e Aurigae, R. A. 72 48', Decl. -f 43 36'. The alternation of 
 in this star is either extremely irregular, or else, in a period of sev- 
 eral years, there are several maxima and minima a question which can 
 not be decided for many years. 
 
 (21) f Geminorum, R. A. 103 48', Decl. +20 47'. This star has 
 hitherto exhibited a perfectly regular course in the variations of its ligbt
 
 VARIABLE STARS. 177 
 
 Ita brightness at its minimum keeps the mean between v and v of the 
 same constellation ; in the maximum it does not quite reach that of A. 
 It takes 4d. 21h. to attain its full brightness, and 5d. 6h. for its diminu- 
 tion. 
 
 (22) Pegasi, R. A. 344 7', Decl. -j-27 16'. Its period is pretty 
 well ascertained, but as to the course of its variation of light nothing can 
 as yet be asserted. 
 
 (23) Pegasi R., R. A. 344 47'. Decl. +9 43'. 
 
 (24) Cancri 8., R. A. 128 50', Decl. +19 34'. 
 Of these two stars nothing at present can be said. 
 
 FK. ARGELANDBR. 
 
 Bonn, August, 1850. 
 
 VARIATION OF LIGHT IN STARS WHOSE PERIODICITY is 
 UNASCERTAINED. In the scientific investigation of important 
 natural phenomena, either in the terrestrial or in the sidereal 
 sphere of the Cosmos, it is imprudent to connect together, 
 without due consideration, subjects which, as regards their 
 proximate causes, are still involved in obscurity. On this 
 account we are careful to distinguish stars which have ap- 
 pe^red and again totally disappeared (as in the star in Cas- 
 siopeia, 1572) ; stars which have newly appeared and not 
 again disappeared (as that in Cygnus, 1600) ; variable stars 
 with ascertained periods (Mira Ceti, Algol) ; and stars whose 
 intensity of light varies, of whose variation, however, the pe- 
 riodicity is as yet unascertained (as i\ Argus). It is by no 
 means improbable, but still does not necessarily follow, that 
 these four kinds of phenomena* have perfectly similar causes 
 in the photospheres of those remote suns, or in the nature of 
 their surfaces. 
 
 As we commenced our account of new stars with the most 
 remarkable of this class of celestial phenomena the sudden 
 appearance of Tycho Brahe's star so, influenced by similar 
 considerations, we shall begin our statements concerning the 
 variable stars whose periods have not yet been ascertained, 
 with the unperiodical fluctuations in the light of 77 Argus, 
 which to the present day are still observable. This star is 
 situated in the great and magnificent constellation of the 
 
 * Newton (Philos. Nat. Principia Mathem., ed. Le Seur et Jacquier, 
 1760, torn, iii., p. 671) distinguishes only two kinds of these sidereal 
 phenomena. " Stella? fixse quae per vices apparent et evanescunt, quae- 
 quo paulatim crescunt, videntur revolvendo partem lucidam et partem 
 obscuram per vices ostendere." The fixed stars, which alternately ap. 
 pear and vanish, and which gradually increase, appear by turns to show 
 an illuminated and a dark side. This explanation of the variation of 
 light had been still earlier advanced by Riccioli. With respect to the 
 caution necessary in predicating periodicity, see the valuable remarks 
 of Sir John Herschel, in his Observations at the Cape, $ 261. 
 
 K2
 
 178 COSMOS. 
 
 Ship, " the glory of the southern skies." Halley, as long 
 ago as 1677, on his return from his voyage to St. Helena, 
 expressed strong doubts concerning the alternation of light 
 in the stars of Argo, especially on the shield of the prow and 
 on the deck (damdiaKT] and KardoTpufid), whose relative or- 
 ders of magnitude had been given by Ptolemy.* However, 
 in consequence of the little reliance that can be placed on 
 the positions of the stars as set down by the ancients, of the 
 various readings in the several MSS. of the Almagest, and 
 of the vague estimates of intensity of light, these doubts failed 
 to lead to any result. According to Halley's observation in 
 1677, r) Argus was of the fourth magnitude ; and by 1751 
 it was already of the second, as observed by Lacaille. The 
 star must have afterward returned to its fainter light, for 
 Burchell, during his residence in Southern Africa, from 1811 
 to 1815, found it of the fourth magnitude ; from 1822 to 1826 
 it was of the second, as seen by Fallows and Brisbane ; in 
 February, 1827, Burchell, who happened at that time to be 
 at San Paolo, in Brazil, found it of the first magnitude, per- 
 fectly equal to a Crucis. After a year the star returned to 
 the second magnitude. It was of this magnitude when Bur- 
 chell saw it on the 29th of February, 1828, in the Brazilian 
 town of Goyaz ; and it is thus set down by- Johnson and Tay- 
 lor, in their catalogues for the period between 1829 and 1833. 
 Sir John Herschel also, at the Cape of Good Hope, estimated 
 it as being between the second and first magnitude, from 
 1834 to 1837. 
 
 When, on the 16th of December, 1837, this famous astron- 
 omer was preparing to take the photometric measurements 
 of the innumerable telescopic stars, between the eleventh 
 and sixteenth magnitudes, which compose the splendid neb- 
 ula around 77 Argus, he was astonished to find this star, which 
 had so often before been observed, increase to such intensity 
 of light that it almost equaled the brightness of a Centauri, 
 and exceeded that of all other stars of the first magnitude, 
 except Canopus and Sirius. By the 2d of January, 1838, it 
 had for that time reached the maximum of its brightness. 
 It soon became fainter than Arcturus ; but in the middle of 
 April, 1838, it still surpassed Aldebaran. Up to March, 
 1843, it continued to diminish, but was even then a star of 
 the first magnitude ; after that time, and especially in April, 
 1843, it began to increase so much in light, that, according 
 
 * Delambre, Hist, de VAstron. Ancicnne, torn, ii., p. 280, arid Hist, de 
 I'Attron. au IScme Siecle, p. 119.
 
 VARIABLE STARS. 179 
 
 to the observations of Mackay at Calcutta, and Maclear at 
 the Cape, 77 Argus became more brilliant than Canopus, and 
 almost equal to Sirius.* This intensity of light was contin- 
 ued almost up to the beginning of the present year (1850). 
 A distinguished observer, Lieutenant Gilliss, who commands 
 the astronomical expedition sent by the government of the 
 United States to the coast of Chili, writes from Santiago, 
 in February, 1850 : " rj Argus, with its yellowish-red light, 
 which is darker than that of Mars, is at present next in brill- 
 iancy to Canopus, and is brighter than the united light of 
 a Centauri."t Since the appearance of the new stars in 
 Ophiuchus in 1604, no fixed star has attained to such an in- 
 tensity of light, and for so long a period now nearly seven 
 years. In the 173 years (from 1677 to 1850) during which 
 we have reports of the magnitude of this beautiful star in 
 Argo, it has undergone from eight to nine oscillations in the 
 augmentation and diminution of its light. As an incitement 
 to astronomers to continue their observations on the phenom- 
 enon of a great but unperiodical variability in rj Argus, it was 
 fortunate that its appearance was coincident with the famous 
 five years' expedition of Sir John Herschel to the Cape. 
 
 In the case of several other stars, both isolated and double, 
 observed by Struve (Stellarum compos. Mensurce Microm., 
 p. Ixxi.-lxxiii.), similar variations of light have been no- 
 ticed, which have not as yet been ascertained to be period- 
 ical. The instances which we shall content ourselves with 
 adducing are founded on actual photometrical estimations 
 and calculations made by the same astronomer at different 
 times, and not on the alphabetical series of Bayer's Uranom- 
 etry. In his treatise De fide Uranometricz Bayeriante, 
 1842 (p. 15), Argelander has satisfactorily shown that Bayer 
 did not by any means follow the plan of designating the 
 brightest stars by the first letters of the alphabet ; but that, 
 on the contrary, he arranged the letters by which he desig- 
 nated stars of equal magnitude according to the positions of 
 
 * Compare Sir John Herschel's Observations at the Cape, $ 71-78; 
 and Outlines of Astron., $ 830 (Cosmos, vol. i., p. 153). 
 
 t Letter of Lieutenant Gilliss, astronomer of the Observatory at Wash- 
 ington, to Dr. Fid gel, consul of the United States of North America at 
 Leipsic (in manuscript). The cloudless purity and transparency of the 
 atmosphere, which last for eight months, at Santiago, in Chili, are so 
 great, that Lieutenant Gilliss (with the first great telescope ever con- 
 structed in America, having a diameter ol seven inches, constructed by 
 Henry Fitz, of New York, and William Young, of Philadelphia) wa 
 able clearly to recognize the sixth star in the trapezium of Orion.
 
 180 COSMOS. 
 
 the stars in a constellation, beginning usually at the head, 
 and proceeding, in regular order, down to the feet. The or- 
 der of letters in Bayer's Uranometria has long led to a be- 
 lief that a change of light has taken place in a Aquilae, in 
 Castor Geminorum, and in Alphard of Hydra. 
 
 Struve, in 1838, and Sir John Hersohel, observed Capella 
 increase in light. The latter now finds Capella much bright- 
 er than Vega, though he had always before considered it 
 fainter.* Galle and Heis come to the same conclusion, from 
 their present comparison of Capella and Vega. The latter 
 finds Vega between five and six gradations, consequently 
 more than half a magnitude, the fainter of the two. 
 
 The variations in the light of some stars in the constella- 
 tions of the Greater and of the Lesser Bear are deserving of 
 especial notice. " The star 77 Ursae majoris," says Sir John 
 Herschel, "is at present certainly the most brilliant of the 
 seven bright stars in the Great Bear, although, in 1837, e 
 unquestionably held the first place among them." This re- 
 mark induced me to consult Heis, who so zealously and care- 
 fully occupies himself with the variability of stellar light. 
 " The following," he writes, " is the order of magnitude which 
 results from my observations, carried on at Aix-la-Chapelle 
 between 1842 and 1850 : 1. Ursse majoris, or Alioth ; 2. 
 a, or Dubhe ; 3. r\, or Benetnasch ; 4. 6, or Mizar ; 5. /3 ; 6. 
 ; 7. 6. The three stars, e, a, and rj, of this group, are near- 
 y equal in brightness, so that the slightest want of clearness 
 in the atmosphere might render their order doubtful ; is de- 
 cidedly fainter than the three before mentioned. The two 
 stars ft and y (both of which are decidedly duller than ) are 
 nearly equal to each other ; lastly, 6, which in ancient maps is 
 usually set down as of the same magnitude with ft and y, is 
 by more than a magnitude fainter than these ; e is decided- 
 ly variable. Although in general this star is brighter, I have 
 nevertheless, in three years, observed it on five occasions to 
 be undoubtedly fainter than a. I also consider ft Ursre ma- 
 joris to be variable, though I am unable to give any fixed 
 periods. In the years 1840 and 1841, Sir John Herschel 
 found ft UrszB minoris much brighter than the Polar star ; 
 whereas still earlier, in May, 1846, the contrary was ob- 
 
 * Sir John Herschel ( Observations at the Cape, p. 334, 350, note 1, and 
 440). For older observations of Capella and Vega, see William Her- 
 schel, in the Philos. Transact., 1797, p. 307, 1799, p. 121 ; and Bode's 
 Jahrbuchfur 1810, B. 148. Argelander, on the other hand, advances 
 many doubts as to the variation of Capella and of the stars of the Bear. 
 
 r,
 
 VARIABLE STARS. 181 
 
 served by him. He also conjectures (3 to be variable.* Since 
 1843, I have, as a rule, found Polaris fainter than ft Urssa 
 minoris ; but from October, 1843, to July, 1849, Polaris was, 
 according to my registers, fourteen times brighter than (3. I 
 have had frequent opportunities of convincing myself that the 
 color of the last-named star is not always equally red ; it is 
 at times more or less yellow, at others most decidedly red."f 
 All the pains and labor spent in determining the relative 
 brightness of the stars will never attain any certain result 
 until the arrangement of their magnitudes from mere esti- 
 mation shall have given place to methods of measurement 
 founded on the progress of modern optical science.J The 
 possibility of attaining such an object need not be despaired 
 of by astronomers and physicists. 
 
 The probably great physical similarity in the process of 
 light in all self-luminous stars (in the central body of our own 
 planetary system, and in the distant suns or fixed stars) has 
 long and justly directed attention to the importance and 
 significance which attach to the periodical or non-periodical 
 variation in the light of the stars in reference to climatology 
 generally ; to the history of the atmosphere, or the varying 
 temperature which our planet has derived in the course of 
 thousands of years from the radiation of the sun ; with the 
 condition of organic life, and its forms of development in dif- 
 ferent degrees of latitude. The variable star in the neck of 
 the Whale (Mira Ceti) changes from the second magnitude 
 to the eleventh, and sometimes vanishes altogether ; we have 
 seen that t\ Argus has increased from the fourth to the first 
 magnitude, and among the stars of this class has attained to 
 the brilliancy of Canopus, and almost to that of Sirius. Sup- 
 posing that our own sun has passed through only a very few 
 of these variations in intensity of light and heat, either in an 
 increasing or decreasing ratio (and why should it differ from 
 other suns ?), such a change, such a weakening or augment- 
 
 * Observations at the Cape, $ 259, note 260. 
 
 t Heis, in his Manuscript Notices of May, 1 850 ; also Observations at 
 the Cape, p. 325 ; and P. von Boguslawski, Uranus for 1848, p. 186. 
 The asserted variation of n, a, and 6 Ursse majoris is also confirmed in 
 Outlines, p. 559. See Madler, Astr., p. 432. On the succession of the 
 stars which, from their proximity, will in time mark the north pole, 
 until, after the lapse of 12,000 years, Vega, the brightest of all possible 
 polar stars, will take their place. ; Vide supra, p. 96 
 
 $ William Herschel, On the Changes that happen to the Fixed Stars, 
 in the Philos. Transact, for 1796, p. 186. Sir John Herschel, in the 
 Observations at the Cape, p. 350-352 ; as also in Mrs. Somerviue's ex- 
 cellent work, Connection of the Physical Sciences, 1846, p. 407.
 
 182 COSMOS. 
 
 ation of its light-process, may account for far greater and 
 more fearful results for our own planet than any required for 
 the explanation of all geognostic relations and ancient telluric 
 revolutions. William Herschel and Laplace were the first 
 to agitate these views. If I have dwelt upon them some- 
 what at length, it is not because I would seek exclusively in 
 these the solution of the great problem of the changes of 
 temperature in our earth. The primitive high temperature 
 of this planet at its formation, and the solidification of con- 
 glomerating matter ; the radiation of heat from the deeper 
 strata of the earth through open fissures and through unfilled 
 veins ; the greater power of electric currents ; a very differ- 
 ent distribution of sea and land, may also, in the earliest 
 epochs of the earth's existence, have rendered the diffusion 
 of heat independent of latitude ; that is to say, of position 
 relatively to a central body. Cosmical considerations must 
 not be limited merely to astrognostic relations. 
 
 V. 
 
 PROPER MOTION OF THE FIXED STARS. PROBLEMATICAL EXIST- 
 ENCE OF DARK COSMICAL BODIES. PARALLAX MEASURED DIS- 
 TANCES OF SOME OF THE FIXED STARS. DOUBTS AS TO THE AS- 
 SUMPTION OF A CENTRAL BODY FOR THE WHOLE SIDEREAL HEAV- 
 ENS. 
 
 THE heaven of the fixed stars, in contradiction to its very 
 name, exhibits not only changes in the intensity of light, but 
 also further variation from the perpetual motion of the indi- 
 vidual stars. Allusion has already been made to the fact 
 that, without disturbing the equilibrium of the star-systems, 
 no fixed point is to be found in the whole heavens, and that 
 of all the bright stars observed by the earliest of the Greek 
 astronomers, not one has kept its place unchanged. In the 
 case of Arcturus, of/z Cassiopeise, and of a double star in Cyg- 
 nus, this change of position has, by the accumulation of their 
 annual proper motion during 2000 years, amounted respect- 
 ively to 2|, 3i, and 6 moon's diameters. In the course of 
 3000 years about twenty fixed stars will have changed their 
 places by 1 and upward.* Since the proper motions of the 
 fixed stars rise from $th of a second to 7 - 7 seconds (and 
 
 * Encke, Betrachtungen fiber die Anordnung des Stern-systems, B. 12. 
 Vidctupra, p. 27. Madler, Astr., s. 445.
 
 PROPER MOTION OF THE STARS. 183 
 
 consequently differ, at the least, in the ratio of 1 : 154), the 
 relative distances also of the fixed stars from each other, and 
 the configuration of the constellations themselves, can not in 
 long periods remain the same. The Southern Cross will not 
 always shine in the heavens exactly in its present form, for 
 the four stars of which it consists move with unequal veloc- 
 ity in different paths. How many thousand years will elapse 
 before its total dissolution can not be calculated. In the re- 
 lations of space and the duration of time, no absolute idea 
 can be attached to the terms great and small. 
 
 In order to comprehend under one general point of view 
 the changes that take place in the heavens, and all the mod- 
 ifications which in the course of centuries occur in the phys- 
 iognomic character of the vault of heaven, or in the aspect 
 of the firmament from any particular spot, we must reckon 
 as the active causes of this change: (1), the precession of 
 the equinoxes and the mutation of the earth's axis, by the 
 combined operation of which new stars appear above the 
 horizon, and others become invisible ; (2), the periodical and 
 non-periodical variations in the brightness of many of the 
 fixed stars ; (3), the sudden appearance of new stars, of 
 which a few have continued to shine in the heavens ; (4), 
 the revolution of telescopic double stars round a common 
 center of gravity. Among these so-called fixed stars, which 
 change slowly and unequally both in the intensity of their 
 light and in their position, twenty principal planets move in 
 a more rapid course, five of them being accompanied by 
 twenty satellites. Besides the innumerable, but undoubt- 
 edly rotatory fixed stars, forty moving planetary bodies have 
 up to this time (October, 1850) been discovered. In the 
 time of Copernicus and of Tycho Brahe, the great improver 
 of the science of observation, only seven were known. Near- 
 ly two hundred comets, five of which have short periods of 
 revolution and are interior, or, in other words, are inclosed 
 within those of the principal planets, still remain to be men- 
 tioned in our list of planetary bodies. Next to the actual 
 planets and the new cosmical bodies which shine forth sud- 
 denly as stars of the first magnitude, the comets, when, dur- 
 ing their usually brief appearance they are visible to the na 
 ked eye, contribute the most vivid animation to the rich^'c- 
 ture I had almost said the impressive landscape of the 
 starry heavens. 
 
 The knowledge of the proper motion of the fixed stars is 
 closely connected historically with the progress of the sci-
 
 184 COSMOS. 
 
 ence of observation through the improvement of instruments 
 and methods. The discovery of this motion was first ren- 
 dered practicable when the telescope was combined with 
 graduated instruments ; when, from the accuracy of within 
 a minute of an arc (which after much pains Tycho Brahe 
 first succeeded in giving to his observations on the island of 
 Hven), astronomers gradually advanced to the accuracy of 
 a second and the parts of a second ; and when it became 
 possible to compare with one another results separated by a 
 long series of years. Such a comparison was made by Hal- 
 ley with respect to the positions of Sirius, Arcturus, and Al- 
 debaran, as determined by Ptolemy in his Hipparchian cat- 
 alogue, 1844 years before. By this comparison he consid- 
 ered himself justified (1717) in announcing the fact of a 
 proper motion in the three above-named fixed stars.* The 
 high and well-merited attention which, long subsequent even 
 to the observations of Flamstead and Bradley, was paid to 
 the table of right ascensions contained in the Triduum of 
 Romer, stimulated Tobias Mayer (1756), Maskelyne (1770), 
 and P;azzi (1800) to compare Homer's observations with 
 more recent ones.f The proper motion of the stars was in 
 some degree recognized as a general fact, even in the mid 
 die of the last century ; but for the more precise and numer- 
 ical determination of this class of phenomena we are in- 
 debted to the great work of William Herschel in 1783, found- 
 ed on the observations of Flamstead, $ and still more to Bes- 
 sel and Argelander's successful comparison of Bradley's "Po- 
 sitions of the Stars for 1755" with recent catalogues. 
 
 The discovery of the proper motion of the fixed stars has 
 proved of so much the greater importance to physical astron- 
 omy, as it has led to a knowledge of the motion of our own 
 solar system through the star-filled realms of space, and, in- 
 deed, to an accurate knowledge of the direction of this mo- 
 tion. We should never have become acquainted with this 
 fact if the proper progressive motion of the fixed stars were 
 so small as to elude all our measurements. The zealous at- 
 tempts to investigate this motion, both in its quantity and 
 its direction, to determine the parallax of the fixed stars, and 
 
 * Halley, in the Philos. Transact, for 1717-1719, vol. xxx.. p. 736. 
 The essay, however, referred solely to variations in latitude. Jacques 
 Cassini was the first to add variations in longitude. (Arago, ii the An- 
 Huairepour 1842, p. 387.) 
 
 t Delambre, Hist, de V Aslron. Moderne, t. ii., p. 658. Als , f& 
 de VAstron. au IMme Slide, p. 448. 
 
 t Philos. Transact., vol. Ixxiii., p. 138.
 
 PROPER MOTION OP THE STARS. 185 
 
 their distances, have, by leading to the improvement and 
 perfection of arc-graduation and optical instruments in con- 
 nection with micrometric appliances, contributed more than 
 any thing else to raise the science of observation to the 
 height which, by the ingenious employment of great merid- 
 ian-circles, refractors, and heliometers, it has attained, espe- 
 cially since the year 1830. 
 
 The quantity of the measured proper motions of the stars 
 varies, as we intimated at the commencement of the present 
 section, from the twentieth part of a second almost to eight 
 seconds. The more luminous stars have in general a slower 
 motion than stars from the fifth to the sixth and seventh mag- 
 nitudes.* Seven stars have revealed an unusually great 
 motion, namely : Arcturus, first magnitude (2"- 25) ; a Cen- 
 tauri, first magnitude (3 //- 58) ;t ft Cassiopeia?, sixth magni- 
 tude (3"-74) ; the double star, 6 Eridani, 5'4 magnitude 
 (4"-08) ; the double star 61 Cygni, 5'6 magnitude (5"'123), 
 discovered by Bessel in 1812, by means of a comparison with 
 Bradley 's observations ; a star in the confines of the Canes 
 Venatici,J and the Great Bear, No. 1830 of the catalogue of 
 the circumpolar stars by Groombridge, seventh magnitude 
 (according to Argelander, 6"-974) ; e Indi (7"'74, according 
 to D'Ariest) ; 2151 Puppis, sixth magnitude (7"-&7l). The 
 uilihrn-oiicalll mean of the several proper motions of the fixed 
 stars in all the zones into which the sidereal sphere has been 
 divided by Madler would scarcely exceed 0"'102. 
 
 An important inquiry into the " Variability of the proper 
 motions of Procyon and Sirius," in the year 1844, a short 
 
 * Bessel, in the Jahrbuch wn Schumacher fur 1839, s. 38. Arago 
 Annuaire pour 1842, p. 389. 
 
 t a Centauri, see Henderson and Maclear, in the Memoirs of the 
 Astron. Soc., vol. xi., p. 61 ; and Piazzi Smyth, in the Edinburgh 
 Transact., vol. xvi., p. 447. The proper motion of Arcturus, 2"-25 
 (Daily, in the same Memoirs, vol. v., p. 165), considered as that of a 
 very bright star, may be called very large in comparison with Aldeba 
 ran, 0"-185 (Madler, CentraUonne, a. 11), and o Lyra, 0"-400. Among 
 the stars of the first magnitude, a Centauri, with its great proper motion 
 of 3"-58, firms a very remarkable exception. The proper motion of 
 the binary system of Cygnus amounts, according to Bessel (Schum 
 Astr. Nochr., bd. xvi., s. 93), to 5"-123. 
 
 { Schumacher's Astr. Nochr., No. 455. 
 
 $ Op. cit., No. 618, s. 276. D'Arest founds this result on comparisons 
 of LacaiDe (1750) with Brisbane (1825), and of Brisbane with Taylor 
 (1835). The star 2151, Puppis, has a proper motion of 7"-871, and ia 
 of the sixth magnitude. (Maclear, in Madler's Unlert. uber die Fix- 
 ttern-Sytteme, th. ii., s. 5.) 
 
 || Schum., Aslr Nochr., No. 661, s. 201
 
 186 COSMOS. 
 
 time, therefore, before the beginning of his last and painful 
 illness, led Bessel, the greatest astronomer of our time, to the 
 conviction " that stars whose variable motion becomes appar- 
 ent by means of the most perfect instruments, are parts of 
 systems confined to very limited spaces in proportion to their 
 great distances from one another." This belief in the exist- 
 ence of double stars, one of which is devoid of light, was so 
 firmly fixed in Bessel's mind, as my long correspondence with 
 him testifies, that it excited the most universal attention, 
 partly on his account, and partly from the great interest 
 which independently attaches itself to every enlargement of 
 our knowledge of the physical constitution of the sidereal 
 heavens. " The attracting body," this celebrated observer 
 remarked, " must be very near either to the fixed star which 
 reveals the observed change of position, or to the sun. As, 
 however, the presence of no attracting body of considerable 
 mass at a very small distance from the sun has yet been per- 
 ceived in the motions of our own planetary system, we are 
 brought back to the supposition of its very small distance 
 from a star, as the only tenable explanation of that change 
 in the proper motion which, in the course of a century, be- 
 comes appreciable."* In a letter (dated July, 1844) in an- 
 swer to one in which I had jocularly expressed my anxiety 
 regarding the spectral world of dark stars, he writes : "At 
 all events, I continue in the belief that Procyon and Sirius 
 are true double stars, consisting of a visible and an invisible 
 star. No reason exists for considering luminosity an essen- 
 tial property of these bodies. The fact that numberless stars 
 are visible is evidently no proof against the existence of an 
 equally incalculable number of invisible ones. The physical 
 difficulty of a change in the proper motion is satisfactorily 
 set aside by the hypothesis of dark stars. No blame attaches 
 to the simple supposition that the change of velocity only 
 takes place in consequence of the action of a force, and that 
 forces act in obedience to the Newtonian laws." 
 
 A year after Bessel's death, Fuss, at Struve's suggestion, 
 renewed the investigation of the anomalies of Procyon and 
 Sirius, partly with new observations with Ertel's meridian- 
 telescope at Pulkowa, and partly with reductions of, and com- 
 parisons with, earlier observations. The result, in the opin- 
 ion of Struve and Fuss,t proved adverse to Bessel's assertion. 
 
 * Schuin., Attr. Nachr., Nos. 514-516. 
 
 t Struve, Etudes cCAstr. Stellaire, Texte, p. 47, Notes, p. 26, and 51- 
 57 ; Sir John Herschel, Outl., $ 859 and 860.
 
 PROPER MOTION OP THE STARS. 187 
 
 A. laborious investigation which Peters has now completed 
 at Konigsberg, on the other hand, justifies it ; as does also a 
 similar one advanced by Schubert, the calculator for the 
 North American Nautical Almanac. 
 
 The belief in the existence of non-luminous stars was dif- 
 fused even among the ancient Greeks, and especially in the 
 earliest ages of Christianity. It was assumed that among 
 the fiery stars which are nourished by the celestial vapcrs, 
 there revolve certain other earth-like bodies, which, however, 
 remain invisible to us."* The total extinction of new stars, 
 especially of those so carefully observed by Tycho Brahe and 
 Kepler in Cassiopeia and Ophiuchus, appears to corroborate 
 this opinion. Since it was at the time conjectured that the 
 first of these stars had already twice appeared, and that, too, 
 at intervals of nearly 300 years, the idea of annihilation 
 and total extinction naturally gained little or no credit. The 
 immortal author of the Mecanique Celeste bases his convic- 
 tion of the existence of non-luminous masses in the universe 
 on these same phenomena of 1572 and 1604 : " These stars, 
 that have become invisible after having surpassed the brill- 
 iancy of Jupiter, have not changed their place during the 
 time of their being visible." (The luminous process in them 
 has simply ceased.) " There exist, therefore, in celestial 
 space dark bodies of equal magnitudes, and probably in as 
 great numbers as the stars, "t So also Madler, in his Un- 
 tersuchungen uber die Fixstern-Systeme, says :J "A dark 
 body might be a central body ; it might, like our own sun, 
 be surrounded in its immediate neighborhood only by dark 
 bodies like our planets. The motions of Sirius and Procyon, 
 pointed out by Bessel, force us to the assumption that there 
 are cases where luminous bodies form the satellites of dark 
 masses. " It has been already remarked that the advocates 
 of the emanation theory consider these masses as both invis- 
 ible, and also as radiating light : invisible, since they are of 
 such huge dimensions that the rays of light emitted by them 
 (the molecules of light), being impeded by the force of at- 
 traction, are unable to pass beyond a certain limit. H If, as 
 
 * Origen, in Gronov. Thesaur., t. x., p. 271. 
 
 t Laplace, Expos, du Syst. du Monde, 1824, p. 395. Lambert, in his 
 Kosmologische Brief e, shows remarkable tendency to adopt the hypoth- 
 esis of large dark bodies. 
 
 \ Madler, Untersitch. tober die Fixstern-Systeme, th. ii. (1848), s. 3; 
 and his Astronomy, B. 416. $ Vide note t, p. 186 
 
 II Vide supra, p. 88, and note ; Laplace, in Zach's Alia. Geogr 
 Epkcm., bd. iv., B. 1 ; Madler, Astr., B. 393.
 
 188 COSMOS. 
 
 may well be assumed, there exist, in the 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 of the motion of 
 the fixed stars (both of the true motion proper to them, and 
 also of their apparent motion, produced by the change in 
 the place of observation, as the earth moves in its orbit), the 
 determination of the distances of the fixed stars from the 
 sun by ascertaining their parallax, and the conjecture as to 
 the part in universal space toward which our planetary 
 system is moving, are three problems in astronomy which, 
 through the means of observation 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 pres 
 ent knowledge of isolated fixed stars. 
 
 As early as the beginning of the seventeenth century, 
 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), " che 
 tutte le stella siano sparse in una sferica superficie egual- 
 tnente distanti da un centra; ma stimo, che le loro lonta- 
 nanze da noi siano talmente varie, che alcune ve ne possano 
 esser 2 e 3 volte piu remote di alcune altre ; talche quando 
 si trovasse col telescopic qualche picciolissima Stella vici- 
 
 * Opere di Galileo Galilei, vol. xii., Milano, 1811, p. 206. This re- 
 markable passage, which expresses the possibility and the project of 
 a measurement, was pointed out by Arago ; see his Annuaire pour 1842 
 p. 382.
 
 DISTANCES OF THE STARS. 189 
 
 nissima ad alcuna delle maggiori, e che pero quella fussc al- 
 tissima, potrebbe accadere che qualche sensibil mutazione 
 succedes&e tra di loro." " \\Ther6fore I do not believe." says 
 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 be 
 two or three times as remote as others, so that when some 
 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 himself, 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 (165 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 -very 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 3438 
 times the earth's mean distance from the sun, or semi-di- 
 ameter of its orbit.* This lower limit of distances rose to 
 206,265 semi-diameters when certainty to a second was 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 , Rob- 
 ert Hooke (1669), did not lead to the desired end. Picard, 
 Horrebow (who worked out Romer's rescued observations) 
 
 * Bessel, in Schumacher's Jahrb. fur 1839, s. 511.
 
 190 COSMOS 
 
 and Flamstead believed that they had discovered parallaxes 
 of 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. 234-264) 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-diffused 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, 
 with little success, selected for observation by Calandrelli 
 and the meritorious Piazzi (1805). These observations must 
 be classed with Jhose 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 (1846), estimates the number of parallaxes 
 hitherto 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 Kbnigsberg 
 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 of 
 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.f So late as 1815 and 1816, Bessel, to use his own 
 
 * Struve, Astr. Slell., p. 104. 
 
 t Arago, in the Connaissance des Temps pour 1834, p. 281 : " Nous 
 observames avec beaucoap de soin, M. Mathieu et moi, pendant le 
 mois d'Aout, 1812. et pendant le mois de Novembre suivant, In hauteur 
 angulaire de l'4toile audessus de 1'horizon de Paris. Cette hauteur, & 
 la seconde <poque, ne surpasse la hauteur angulaire a la premiere quo 
 de 0"-66. Une parallaxe absolue d'une seule seconde aurait n&sessairo- 
 raent amend entre ces deux hauteurs une difference de l"-2. Nos ob- 
 servations u'indiqueut douc pas quo le rayon de 1'orbite terreste, que
 
 DISTANCES OF THE STARS. 191 
 
 words, " had arrived at no available result."* The observa- 
 tions taken from August, 1837, to October, 1838, by means 
 of the great heliometer erected in 1829, first led him to the 
 parallax of 0"-3483, which corresponds with a distance of 
 592,200 mean distances of the earth, and a period of 9| 
 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. 1 
 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 vus de la 61" du Cygne sous un angle de 
 plus d'une demi-seconde. Mais une base vue perpendiculairement sou- 
 tend un angle d'une demi-seconde quand on est eloigne de 412 mille 
 fois sa longueur. Done la 61 e du Cygne est au moins a une distance 
 de la terre egale a 412 mille fois 39 millions de lieues." " During the 
 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 seeu 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 Cygni 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 and 
 final result was 0"-3483. (Astr. Nachr., No. 402, in bd. xvii., s. 274.) 
 Peters obtained by his own observations 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, in 
 fact, partially fulfilled in the first volume of his Astronomische 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 the 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 in 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 gradually nearer to us 
 in light passages amounting respectively to 10, 9\, and 8 T 7 ff yeara
 
 192 COSMOS. 
 
 1832, and by those of Maclear in 1839.* According to this 
 statement, it is the nearest of all the fixed stars that have 
 yet been measured, being three times nearer than 61 Cygni. 
 
 The parallax of a Lyrse has long been the object of 
 Struve's observations. The earlier observations (1836) 
 gavet 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. t 
 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 by 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, Capella, is still less, being, 
 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, 1"-08, and therefore greater than the 
 parallax of a Centauri. || 
 
 * Sir John Herschel, Outlines, p. 545 and 551. Madler (Astr., s. 425) 
 gives in the case of a Centauri the parallax 0"-9213 instead of 0"-9128. 
 
 t Struve Stell. compos. Mens. Microm., p. clxix.-clxxii. Airy makes 
 the parallax of a Lyrse, which Peters had previously reduced to 0"-1, 
 still lower; indeed, too small to be measurable by our present instru- 
 ments. (Mem. of the Royal Astr. Soc., vol. x., p. 270.) 
 
 J Struve, On the Micrometrical Admeasurements by the Great Refract" 
 or at Dorpat (Oct., 1839), in Schum., Astr. Nachr., No. 396, s. 178. 
 
 $ Peters, in Struve, Aitr. Stell., p. 100. II Id., p. 101.
 
 DISTANCES OF THE STARS. 
 
 19 j 
 
 Filed Star. 
 
 Parallax. 
 
 ProtabEi 
 
 Error. 
 
 Name of Observer. 
 
 a Centauri 
 
 0"- 913 
 
 0"-070 
 
 Henderson and Maclear. 
 
 61 Cygni 
 
 0"3744 
 
 0"-020 
 
 Bessel. 
 
 Sirius . ....... 
 
 0"- 230 
 
 
 Henderson 
 
 1830, Groombridge. 
 i Ursse Maj. 
 
 0"- 226 
 0"- 133 
 
 0"-141 
 0"-106 
 
 Peters. 
 Peters. 
 
 Arcturus 
 
 0"- 127 
 
 0"073 
 
 Peters. 
 
 a Lyras 
 
 0"- 207 
 
 0"-038 
 
 Peters. 
 
 Polaris 
 
 0"- 106 
 
 0"-012 
 
 Peters. 
 
 Capella 
 
 0"- 046 
 
 0"-200 
 
 Peters. 
 
 It does not in general follow from the results hitherto ob- 
 tained that the brightest stars are likewise the nearest to us. 
 Although the parallax of a Centauri is the greatest of all at 
 present known, on the other hand, Vega Lyrte, 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 
 star (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, mass, 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 
 brilliancy 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 which 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 of 
 
 * On the proportion of the amount of proper motion to the proximity 
 of the brighter stars, see Struve, Stell, compot. Mensuree Aficrom., p 
 clxi?. 
 
 VOL. Ill -I
 
 194 COSMOS. 
 
 the whole structural configuration of the universe, lends a pe- 
 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 turned 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 tlio half revolution 
 through its more remote side will prove to be longer than the 
 time in the side turned toward the observer. The sum of 
 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 
 geographical miles in twenty-four hours), to arrive at the 
 absolute magnitude of a semi-diameter of the earth's orbit , 
 and the distance of the central body and its parallax may be 
 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 parallaxes 
 instructs us as to the distances of a small number of the fixed 
 stars, 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, in the Connaissance des Temps pour 1830, p. 56-69, and 
 p. 163-171; and Struve, ibid., D. clxiv.
 
 PROPER MOTION OF THE STARS. 195 
 
 light on two mutually dependent problems ; namely, the mo- 
 tion of the solar system,* and the position of 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- 
 lander'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, t 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 
 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 translation in space of the whole sola? 
 system, and that also which is the result of the actual propel 
 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 
 desirable methods of observing it.J " 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 
 
 Cosmot, vol. i., p. 146. t Madler, Astronomic, B. 414. 
 
 t Arago, in his Annuaire pour 1842, p. 383, was the first to call at- 
 tention to this remarkable passage of Bradley's. See, in the same An- 
 nuaire, the section on the translation of the entire solar system, p. 389- 
 399.
 
 i96 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 laws 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 writings 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 R. A. 
 260 44', and N. Decl. 26 16' (reduced to the year 1800). 
 Argelander, by a comparison of 3 1 9 stars, and with a refer- 
 ence to Lundahl's investigations, found it for 1800: R.A. 
 257 54'-l, 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 : R. 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' ; R. A. 258 42', Decl. 
 +30 57'; R.A. 259 13', Decl. +31 9'; R.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 result! 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 Sebum., Astr. Nachr., No. 622, 
 6. 348. 
 
 t Galloway, on the Motion of the Solar System, in the Phdot. Trant- 
 act. for 1847, p. 98.
 
 MOTION OF THE STARS. 197 
 
 question naturally arises, Is the world of the fixed stars com- 
 oosed merely of a number of neighboring partial systems di- 
 vided into groups, or must we assume the existence of a uni- 
 versal relation, a rotation of all self-luminous celestial bodies 
 (suns) around one common center of gravity which is either 
 filed u-ith matter or void ? We here, however, enter the 
 domain of mere conjecture, to which, indeed, it is not im- 
 possible to give a scientific form, but which, owing to the 
 incompleteness of the materials of observation and analogy 
 which are at present before us, can by no means lead to the 
 degree of evidence attained by the other parts of astronomy 
 The fact that we are ignorant of the proper motion of an in- 
 finite number of very small stars from the tenth to the four- 
 teenth magnitude, which appear to be scattered among the 
 brighter ones, especially in the important part of the starry 
 stratum to which we belong, the annuli of the Milky Way, 
 is extremely prejudicial to the profound mathematical treat- 
 ment of problems so difficult of solution. The contempla- 
 tion of our own planetary sphere, whence we ascend, from 
 the small partial systems of the moons of Jupiter, Saturn, 
 and Uranus, to the higher and general solar system, has 
 naturally led to the belief that the fixed stars might in a 
 similar manner be divided into several individual groups, 
 and separated by immense intervals of space, which again 
 (in a higher relation of these systems one to another) may 
 be subject to the overwhelming attractive force of a great 
 central body (one sole sun of the whole universe).* The in- 
 ference here advanced, and founded on the analogy of our 
 own solar system, is, however, refuted by the facts hitherto 
 observed. In the multiple stars, two or more self-luminous 
 stars (suns) revolve, not round one another, but round an 
 external and distant center of gravity. No doubt something 
 similar takes place in our own planetary system, inasmuch 
 as the planets do not properly move round the center of the 
 solar body, but around the common center of gravity of all 
 the masses in the system. But this common center of grav- 
 ity falls, according to the relative positions of the great plan- 
 ets Jupiter and Saturn, sometimes within the circumference 
 of the sun's body, but oftener out of it.f The center of 
 gravity, which in the case of the double stars is a void is 
 
 * Toe value or worthlessness of such views has been discussed by 
 Argelanderin his essay, " Ueber die eigene Bewegung des Sonnensysteott 
 kergelettet avs der eigenen Bewegwng der Sterne, 1837, s. 39. 
 
 t See Cosmot, vol. i., p. 145. (Madler, Attr., p. 400.)
 
 accordingly, in the solar system, at one time void, at another 
 occupied by matter. All that has been advanced with re- 
 gard to the existence of a dark central body in the center 
 of gravity of double stars, or at least of one originally dark, 
 but faintly illuminated by the borrowed light of the planets 
 which revolve round it, belongs to the ever-enlarging realm 
 of mythical hypotheses. 
 
 It is a more important consideration, and one more de- 
 serving of thorough investigation, that, on the supposition of 
 a revolving movement, not only of the whole of our planet- 
 ary system which changes its place, but also for the proper 
 motion of the fixed ^stars at their various distances, the cen- 
 ter of this revolving motion must be 90 distant* from the 
 point toward which our solar system is moving. In this con- 
 nection of ideas, the position of stars possessing a great or 
 very small proper motion becomes of considerable moment. 
 Argelander has examined, with his usual caution and acute- 
 ness, the degree of probability with which we may seek for 
 a general center of attraction for our starry stratum in the 
 constellation of Perseus. t Madler, rejecting the hypothesis 
 of the existence of a central body preponderating in mass, 
 as the universal center of gravity, seeks the center of grav- 
 ity in the Pleiades, in the very center of this group, in or 
 nearf to the bright star TJ Tauri (Alcyone). The present is 
 
 * Argelander, ibid., p. 42 ; Madler, CentraJsonne, s. 9, and Astr., s. 
 403. 
 
 t Argelauder, ibid., p. 43 ; and in Sebum., Astr. Nachr., No. 566. 
 Guided by no numerical investigations, but following the suggestions of 
 fancy, Kant long ago fixed upon Sirius, and Lambert upon the nebula 
 in the belt of Orion, as the central body of our starry stratum. (Struve, 
 Astr. Stell., p. 17, No. 19.) 
 
 t Madler, Astr., s. 380, 400, 407, and 414 ; in his Centraltonne, 1846, 
 p. 44-47 ; in Untersiickungen uber die Fixstern-Systeme, th. ii., s. 183- 
 185. Alcyone is in R. A. 54 30', Decl. 23 36', for the year 1840. If 
 Alcyone's parallax were really 0"-0065, its distance would be equal to 
 3H million semi-diameters of the earth's orbit, and thus it would be 
 fifty times further distant from us than the distance of the double star 
 61 Cygni, according to Bessel's earliest calculation. The light which 
 comes to the earth from the sun in 8' 18"-2, would in that case take 500 
 years to pass from Alcyone to the earth. The fancy of the Greeks de- 
 lighted itself in wild visions of the height of falls. In Hesiod's Theo- 
 gonia, v. 722-725, it is said, speaking of the fall of the Titans into Tar- 
 tarus: " If a brazen anvil were to fall from heaven nine days and nine 
 nights long, it would reach the earth on the tenth." This descent of 
 the anvil in 777,600 seconds of time gives an equivalent in distance of 
 309,424 geographical miles (allowance being made, according to Galle's 
 calculation, for the considerable diminution in the force of attraction at 
 planetary distances), therefore 1 i times the distance of the moon from
 
 DOUBLE STARS. 199 
 
 not the place to discuss the probability or improbability* of 
 such an hypothesis. Praise is, however, due to the eminent- 
 ly active director of the Observatory at Dorpat for having, 
 by his diligent labors, determined the positions and proper 
 motions of more than 800 stars, and at the same time ex- 
 cited investigations which, if they do not lead to the satis- 
 factory solution of the great problem itself, are nevertheless 
 calculated to throw light on kindred questions of physical 
 astronomy. 
 
 VI. 
 
 MULTIPLE OR DOUBLE STARS. THEIR NUMBERS AND RECIPROCAL 
 DISTANCES. PERIOD OF REVOLUTION OF TWO SUNS ROUND A COM- 
 MON CENTER OF GRAVITY. 
 
 WHEN, in contemplating the systems of the fixed stars, we 
 descend from hypothetical, higher, and more general consid- 
 erations to those of a special and restricted nature, we enter 
 a domain more clearly determined, and better calculated for 
 direct observation. Among the multiple stars, to which be- 
 long the binary or double stars, several self-luminous cosmic- 
 al bodies (suns) are connected by mutual attraction, which 
 necessarily gives rise to motions in closed curved lines. Be- 
 fore actual observation had established the fact of the revo- 
 lution of the double stars.t such movements in closed curves 
 were only known to exist in our own planetary solar system. 
 On this apparent analogy inferences were hastily drawn, 
 which for a long time gave rise to many errors. As the 
 term " double stars" was indiscriminately applied to every 
 
 the earth. But, according to the Iliad, i., v. 592, Hephaestus fell down 
 to Lemnos in one day, "when but a little breath was still in him." 
 The length of the chain hanging down from Olympus to the earth, by 
 which all the gods were challenged to try and pull down Jupiter (Il- 
 iad, viii., v. 18), is not given. The image is not intended to convey an 
 idea of the height of heaven, but of Jupiter's strength and omnipo- 
 tence. 
 
 * Compare the doubts of Peters, in Schum., Astr. Nachr., 1849, s. 
 661, and Sir John Herschel, in the Outl. of Astr., p. 589 : " In the pres- 
 ent defective state of our knowledge respecting the proper motion of 
 the smaller stars, we can not but regard all attempts of the kind as to 
 a certain extent premature, though by no means to be discouraged as 
 forerunners of something more decisive." 
 
 t Compare Cosmos, vol. i., p. 146-149. (Struve, Ueber Dopplesternc 
 *ach Dorpater Micnmeter-Messungen von 1824 bis 1837, s. 11.)
 
 200 COSMOS. 
 
 pair of stars, the close proximity of which precluded their 
 separation by the naked eye (as in the case of Castor, a 
 Lyrse, (3 Orionis, and a Centauri), this designation naturally 
 comprised two classes of multiple stars : firstly, those which, 
 from their incidental position in reference to the observer, 
 appear in close proximity, though in reality widely distant 
 and belonging to totally different strata ; and, secondly, those 
 which, from their actual proximity, are mutually dependent 
 upon each other in mutual attraction and reciprocal action, 
 and thus constitute a particular, isolated, sidereal system. 
 The former have long been called optically, the latter phys- 
 ically, double stars. By reason of their great distance, and 
 the slowness of their elliptical motion, many of the latter are 
 frequently confounded with the former. As an illustration 
 of this fact, Alcor (a star which had engaged the attention of 
 many of the Arabian astronomers, because, when the air is 
 very clear, and the organs of vision peculiarly sharp, this small 
 star is visible to the naked eye together with in the tail of 
 Ursa Major) forms, in the fullest sense of the term, one of 
 these optical combinations, without any closer physical con- 
 nection.* In sections II. and III. I have already treated of 
 the difficulty of separating by the naked eye adjacent stars, 
 with the very unequal intensity of light, of the influence of 
 the higher brilliancy and the star's tails, as well as of the 
 organic defects which produce indistinct vision. 
 
 Galileo, without making the double stars an especial ob- 
 ject of his telescopic observations (to which his low magni- 
 fying powers would have proved a serious obstacle), men- 
 tions (in a famous passage of the Giornata terza of his Dis- 
 courses, which has already been pointed out by Arago) the 
 use which astronomers might make of optically double stars 
 (quando si trovasse nel telescopic qualche picciolissima stella 
 vicinissima ad alcuna delle maggiori) for determining the 
 parallax of the fixed stars, t As late as the middle of the 
 last century, scarcely twenty double stars were set down in 
 the stellar catalogues, if we exclude all those at a greater 
 
 * Vide tupra. As a remarkable instance of acuteness of vision, we 
 may further mention that MSstlin, Kepler's teacher, discovered with the 
 naked eye fourteen, and some of the ancients nine, of the stars in the 
 Pleiades. (Madler, Untersuch. fiber die Fixslern-Systeme, th. ii., s. 36.) 
 
 t Vide supra. Dr. Gregory, of Edinburgh, also, in 1675 (consequent- 
 ly thirty-three years after Galileo's decease), recommended the samo 
 parallactic method. See Thomas Birch, Hist, of the Royal Soe., vol. 
 iii., 1757, p. 225. Bradley (1748) alludes to this method at the conclu- 
 sion of his celebrated treatise on Nutation.
 
 DOUBLE STARS. 201 
 
 distance from each other than 32" ; at present, a hundred 
 yeais later (thanks chiefly to the great labors of Sir Will- 
 iam Herschel, Sir John Herschel, and Struve), about 60UO 
 have been discovered in the two hemispheres. To the ear- 
 liest described double stars* belong Ursae maj. (7th Sep- 
 tember, 1700, by Gottfried Kirch), a Centauri (1709, by Feu- 
 illee), y Virginis (1718), a Geminorum (1719), 61 Cygni 
 (1753) (which, with the two preceding, was observed by 
 Bradley, both in relation to distance and angle of direction), 
 p Ophiuclii and Cancri. The number of the double stars 
 recorded has gradually increased from the time of Flamstead, 
 who employed a micrometer, down to the star-catalogue of 
 Tobias Mayer, which appeared in 1756. Two acutely spec- 
 ulative thinkers, endowed with great powers of combination, 
 Lambert (Photometria, 1760 ; Kosmologische Briefe uber 
 die Einrichtung des Weltbaues, 1761) and John Michell, 
 1767, though they did not themselves observe double stars, 
 were the first to diffuse correct views upon the relations of 
 their attraction in partial binary systems. Lambert, like 
 Kepler, hazarded the conjecture that the remote suns (fixed 
 stars) are, like our own sun, surrounded with dark bodies, 
 planets, and comets ; but of the fixed stars proximate to each 
 other,! he believed, however much, on the other hand, he 
 may appear inclined to admit the existence of dark central 
 bodies, " that within a not very long period they completed a 
 revolution round their common center of gravity." Michell,$ 
 who was not acquainted with the ideas of Kant and Lam- 
 bert, was the first who applied the calculus of probabilities 
 to small groups of stars, which he did with great ingenuity, 
 especially to multiple stars, both binary and quaternary. He 
 showed that it was 500,000 chances to 1 that the colloca- 
 tion of the six principal stars in the Pleiades did not result 
 from accident, but that, on the contrary, they owed their 
 grouping to some internal and reciprocal relation. He was 
 so thoroughly convinced of the existence of luminous stars 
 revolving round each other, that he ingeniously proposed to 
 employ these partial star-systems to the solution of certain 
 astronomical problems. $ 
 
 * Miicller, Astr., s. 477. t Arago, in the Annuairepour 1842, p. 400. 
 
 t An Inquiry into the probable parallax and magnitude of the fixed 
 stars, from the quantity of light which they afford us, and the particu- 
 lar circumstances of their situation, by the Rev. John Michell; in the 
 Pkilos. Transact., vol. Ivii., p. 234-261. 
 
 $ John Michell, ibid., p. 238. " If it should hereafter be found that 
 any of the stars have others revolving about them (for 110 satellites bv
 
 202 COSMOS. 
 
 Christian Mayer, the Manheim astronomer, has the great 
 merit of having first (1778) made the fixed stars a special 
 object of research, by the sure method of actual observations. 
 The unfortunate choice of the term satellites of the fixed 
 stars, and the relations which he supposed to exist among 
 the stars between 2 30' and 2 55' distant from Arcturus, 
 exposed him to bitter attacks from his cotemporaries, and 
 among these to the censure of the eminent mathematician, 
 Nicolaus Fuss. That dark planetary bodies should become 
 visible by reflected light, at such an immense distance, was 
 certainly improbable. No value was set upon the results of 
 his carefully-conducted observations, because his theory of 
 the phenomena was rejected ; and yet Christian Mayer, in 
 his rejoinder to the attack of Father Maximilian Hell, Di- 
 rector of the Imperial Observatory at Vienna, expressly as- 
 serts " that the smaller stars, which are so near the larger, 
 are either illuminated, naturally dark planets, or that both 
 of these cosmical bodies the principal star and its compan- 
 ion are self-luminous suns revolving round each other." 
 
 a borrowed light could possibly be visible"), we should then have the 
 means of discovering " Throughout the whole discussion he de- 
 nies that one of the two revolving stars can be a dark planet shining 
 with a reflected light, because both of them, notwithstanding their dis- 
 tance, are visible to us. Calling the larger of the two the " central 
 star," he compares the density of both with the density of our sun, and 
 merely uses the word " satellite" relatively to the idea of revolution or 
 of reciprocal motion ; he speaks of the " greatest apparent elongation 
 of those stars that revolve about others as satellites." He further says, 
 at p. 243 and 249 : " We may conclude with the highest probability 
 (the odds against the contrary opinion being many million millions to 
 one) that stars form a kind of system by mutual gravitation. It is high- 
 ly probable in particular, and next to a certainty in general, that such 
 double stars as appear to consist of two or more stars placed near to- 
 gether are under the influence of some general law, such, perhaps, as 
 
 gravity " (Consult also Arago, in the Annuaire pour 1834, p. 308, 
 
 and Ann. 1842, p. 400.) No great reliance can be placed on the indi- 
 vidual numerical results of the calculus of probabilities given by Michell, 
 as the hypotheses that there are 230 stars ir the heavens which, in in- 
 tensity of light, are equal to (3 Capricorn!, KJid 1500 equal to the six 
 greater stars of the Pleiades, are manifestly incorrect. The ingenious 
 cosmological treatise of John Michell ends with a very bold attempt to 
 explain the scintillation of the fixed stars by a kind of " pulsation in 
 material effluxes of light" an elucidation not more happy than that 
 which Simon Marius, one of the discoverers of Jupiter's satellites (see 
 Cosmos, vol. ii., p. 320) has given at the end of his Mundus Jovialis 
 (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 
 of the fixed stars a change of color." ( Vide supra.)
 
 DOUBLE STARS. 203 
 
 The importance of Christian Mayer's labors has, long after 
 his death, been thankfully and publicly acknowledged by 
 Struve and Madler. In his two treatises, Vertheidigung 
 neuer Beobachtungen von Fixstern-trabanten (1778), and 
 Dissertatio de novis in Ccdo 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 Gluadrant ; " many even now constitute very 
 difficult objects of observation, which none but very power- 
 ful instruments are capable of representing, such as p and 
 71 Herculis, 5 Lyrse, and GJ 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 omitted 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 although Herschel's first catalogue 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 we at present know of the manifold 
 formation of the double stars has its origin in Sir William 
 Herschel's work. In the catalogues of 1782, 1783, and 
 1804, he has not only set down 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 Recueil des Actes de la Stance publique de VAcad. 
 Imp. des Sciences de St. Petersbourg, le 29 Dec., 1832, p. 48-50. Mad- 
 ler, A*tr., s. 478. 
 
 t Philos. Transact, for the Year 1782, p. 40-126; for 1783, p. 112- 
 124 ; for 1804, p. 87. Regarding the observations on which Sir Will- 
 iam Herschel founded his views respecting the 846 double stars, see 
 Madler, in Schumacher's Jahrbuchfur 1839, s. 59, and his Untertuchun- 
 gen itler die Fixstern-Systeme, th. i., 18 17. s. 7.
 
 204 COSMOS. 
 
 of their mutual distances. Full of imagination, yet alwayg 
 proceeding with great caution, it was not till the year 1794, 
 while distinguishing between optically and physically double 
 Btars, that he threw out his preliminary suggestions as to the 
 nature of the relation of the larger star to its smaller com- 
 panion. Nine years afterward, he first explained his views 
 of the whole system of these phenomena, in the 93d volume 
 of the Philosophical Transactions. The idea of partial 
 star-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, 
 which, with a parallax of 0"-3744, is distant from the sun 
 18,240 semi-diameters of Neptune's orbit (i. 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 catalogues, 
 were confined to epochs too near together to admit of perfect 
 certainty in determining the several numerical relations of 
 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 Madler),* 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). 
 
 After 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, ibid., th. i., s. 255. For Castor we have two old observa- 
 tions of Bradley, 1719 and 1759 (the former taken in conjunction with 
 Pond, the latter with Maskelyne), and two of the elder Herschel, taken 
 in the years 1779 and 1803. For the period of revolution of y Virginia, 
 ee Madler, Fixslern-Syst., th. ii., s. 234-40, 1848.
 
 DOUBLE STARS 205 
 
 dation of this important branch of astronomy. In 1820, 
 Struve published his first Dorpat Table of double 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 were examined by means of the great Fraun- 
 hofer refractor. Struve's third table of multiple stars ap- 
 peared in the year 1837, and forms the important work Stel- 
 larum compositarum Mensurcs Micrometrices.* 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,t 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.^. 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. 
 
 We trace in this historical sketch the gradual advance 
 made by the science of astronomy toward a thorough knowl- 
 edge of partial, 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 G-alle at Berlin 
 
 * Struve, Mensuree Microm., p. 40 and 234-248. On the whole, 
 26414-146, . e., 2787 double stars have been observed. (Madler, in 
 Sebum., Jakrb., 1839, s. 64.) 
 
 t Sir John Herschel, Attron. Observ. at the Cape of Good Hope, p. 
 16.5-303. t 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. 
 Stellarum fixarum positionet media, ineunte anno 1830, ex observ. Aboa 
 habitit (Heltingfortia, 1825)." Madler (Astr., a. 625) estimates the
 
 206 COSMOS. 
 
 (1836 and 1839), by Preuss and Otto Struve in Pulkowa 
 (since the catalogue of 1837), by Madler 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, 
 how many are so-called physical (revolving} 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, like 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. Madler 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 with 
 certainty, and 105 in which it might be regarded as more 
 or less probable ; 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 table 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 the northern hemisphere, discovered at 
 Pulkowa 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 has 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 stars are be- 
 tween 0" and 1", 2" and 8 , or 16" and 32", are given by Struve, in his 
 Mens. Microm., p. xciv. Distances less than 0"-8 have been taken, and
 
 DOUBLE STARS. 207 
 
 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. 
 
 Very little has as yet been numerically determined re 
 garding the relative distribution of the binary star-systems 
 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 Herschel 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, 
 with 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 published in 1837, gave the following re- 
 sults 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 with green (as in the ternary star y 
 Andromedae),t 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- 
 experiments with very complicated systems have confirmed the astron- 
 omer in the hope that these estimates are mostly correct within 0"'l 
 (Strnve, iiber Doppelsterne nach Dorpater Beob., B. 29.) 
 
 * Sir John Herschel, Observations al tht Cape, p. 166. 
 
 t Struve, Mensurte Microm., p. Ixxvii. to Ixxxiv. 
 
 t Sir John Herschel, Outlines of Aslr., p. 579.
 
 208 COSMOS. 
 
 ors the subjective colors, which, when united, form white.* 
 It is a well known optical phenomenon that a faint white 
 light appears green when a strong red light is brought near 
 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. t 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 friend 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. " Lorsqu'une lumiere forte ue 
 trouve aupres d'une lumiere faible, la derniere prend la teinte comple- 
 mentaire de la premiere. C'est la le contrast*; mais comme le rouge 
 n'est presque jamais pur, on peut tout aussi bien dire que le rouge est 
 complementaire du bleu. Les couleurs voisines du spectre solaire so 
 substitueut." " When a strong light is brought into contact with a 
 feeble one, the latter assumes the complementary color of the former. 
 This is the effect of contrast ; but as red is scarcely ever pure, it may 
 as correctly be said that red is the complementary of blue : the colors 
 nearest to the solar spectrum reciprocally change." (Arago, MS. of 
 1847.) 
 
 t Arago, in the Connaisance des Temps pour Van 1 828, p. 299-300 ; 
 and in the Annuaire pour 1834, p. 246-250; pour 1842, p. 347-350: 
 " Les exceptions que je cite, prouvent que j'avais bien raison en 1825 
 de n'introduire la notion physique du contraste dans la question des etoi- 
 les doubles qu'avec la plus grande reserve. Le bleu est la couleur re- 
 elle de certaines etoiles. II resulte des observations recueillies jusqu'ici 
 que le firmament est non seulement parseme de soleils rouges etjaunes, 
 comme le savaient les auciens, ma isencore de soleils Ileus et verts. 
 C'est au terns et a des observations futures & nous apprendre si les etoi- 
 les vertes et bleues ne sont pas des soleils deja en voie de decroissance ; 
 si les differentes nuances de ces astres n'indiquent pas que la combustion 
 s'y ope re 4 differens degres ; si la teinte, avec exces de rayons les plus 
 refrangibles, que presente souvent la petite etoile, ne tiendrait pas a la 
 force absorbante d'une atmosphere que developperait Faction de *' etoile, 
 ordinairement beaucoup plus brillante, qu'elle accompagne." " The 
 exceptions I have named proved that in 1825 I was quite right in the 
 cautious reservations with which I introduced the physical notion of 
 contrast in connection with double stars. Blue is the real color of cer 
 tain stars. The result of the observations hitherto made proves that 
 the firmament is studded not only with red and yellow suns (as was 
 known long ago to the ancients), but also with blue and green suns. 
 Time and future observations must determine whether red and blue 
 stars are not suns, the brightness of which is already on the wane; 
 whether the varied appearances of these orbs do not indicate the de- 
 gree of combustion at work within them ; whether the color and the 
 excess of the most refrangible rays often presented by the smaller of 
 two stars be not owing to the absorbing force of an atmosphere devel
 
 DOUBLE STARS. 209 
 
 stances in which a brilliant white star (1527 Leonis, 1768 
 Can. ven.) is accompanied by a small blue star ; others, where 
 in a double star (8 Serp.) both the principal and its companion 
 are blue.* In order to determine whether the contrast of 
 colors is merely subjective, he proposes (when the distance 
 allows) to cover the principal star in the telescope by a thread 
 or diaphragm. Commonly it is only the smaller star that 
 is blue : this, however, is not the case in the double star 23 
 Orionis (696 in Struve's Catalogue, p. Ixxx.), where the prin- 
 cipal star is bluish, and the companion pure white. If, in 
 the multiple stars, the differently colored suns are frequently 
 surrounded by planets invisible to us, the latter, being differ- 
 ently illuminated, must have their white, blue, red, and green 
 days.f 
 
 As the periodical variability^, of the stars is, as we have 
 already pointed out, by no means necessarily connected with 
 their red or reddish color, so also coloring in general, or a 
 contrasting difference of the tones of color between the prin- 
 cipal star and its companion, is far from being peculiar to 
 the multiple stars. Circumstances which we find to be fre- 
 quent are not, on that account, necessary conditions of the 
 phenomena, whether relating to a periodical change of light, 
 or to the revolution in partial systems round a common cen- 
 ter of gravity. A careful examination of the bright double 
 stars (and color can be determined even in those of the ninth 
 magnitude) teaches that, besides white, all the colors of the 
 solar spectrum are to be found in the double stars, but that 
 the principal star, whenever it is not white, approximates in 
 general to the red extreme (that of the least refrangible rays), 
 but the companion to the violet extreme (the limit of the 
 most refrangible rays). The reddish stars are twice as fre- 
 quent as the blue and bluish ; the white are about 21 times 
 as numerous as the red and reddish. It is moreover remark- 
 able that a great difference of color is usually associated with 
 
 oped by the action of the accompanying star, -which is generally much 
 the more brilliant of the two." (Arago, in the Annuairepour 1834, p. 
 295-301.) 
 
 * Struve, Ueber Doppdtterne nach Dorpater Beobachtungen, 1837, a. 
 33-36, and Mensurce Microm., p. Ixxxiii., enumerates sixty-three double 
 Btarsin which both the principal and companion are blue or bluish, and 
 in which, therefore, the colcrs can not be the effect of contrast. When 
 \ve 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 
 some observers as blue, and by others as green. 
 
 t Arago, Annuain pour 1834, p. 302. t Vide tupra, p. 130-136.
 
 210 COSMOS. 
 
 a corresponding difference in brightness. In two cases in 
 Bootis and y Leonis which, 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 hemisphere, 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 t several times made mention 
 of the somewhat irregular variability of luster in the 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.J 
 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, 
 and, if refractors have not been employed, the frequently red- 
 dening influence of the metallic speculum. 
 
 Among the multiple systems we may cite as ternaries, 
 Librae, Cancri, 12 Lyncis, 11 Monoc. ; as quaternaries, 
 102 and 2681 of Struve's Catalogue, a Andromedae, e Lyrae : 
 in 6 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 orange color, though that of the 
 smaller is of a somewhat more somber and brownish cast." (Sir John 
 Herschel, Observations at the Cape of Good Hope, p. 300.) And, ac- 
 cording to the important observations taken by Captain Jacob, of the 
 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 tht Royal Soc. of Edinb., vol. X'vn 
 1849, p. 451.) 
 
 t Videtupra, p. 165, 166, and note. 
 
 t Struve, Ueber Doppeltt. nach Dorp Beob., s. 33. $ Ibid., s. 36
 
 DOUBLE STARS. 211 
 
 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.; ll'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 ternary 
 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 more 
 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. t 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 
 Savary ( Ursae Maj.), Encke (70 Ophiuchi), and Sir John 
 Herschel. These have been subsequently followed by Bes- 
 sel, Struve, Madler, Hind, Smyth, and Captain Jacob. Sa- 
 vary's and Encke'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 Verrier's Neptune. The eccentricity 
 of the elliptical orbits of the double stars, according to the 
 investigations hitherto made, is extremely considerable, re- 
 sembling that of comets, increasing from 0'62 (a Coronae) 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 Midler's and Hind's calculations, i\ Coronas 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 
 
 * Madler, Astr., s. 517. Sir John Herschel, Ovtl., p. 568. 
 
 t Compare Madler, Untertuch. uber die Fixstcm-Systeme, th. i., s. 
 225-273 ; th. ii., s. 235-240 ; and his Astr., a. 541 Sir John HerscheL 
 Outl., p. 573.
 
 212 COSMOS. 
 
 two of the smaller principal planets in our solar system, the 
 eccentricity of the orhit 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 of 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 subordinate to more general movements animating th 
 regions of space.
 
 DOUBLE STARS. 
 ELEMENTS OF THE ORBITS OF DOUBLE STARS. 
 
 213 
 
 _t 
 
 Semi-Major 
 Axis. 
 
 Eccentricity. 
 
 Period of 
 Revolution 
 in yean. 
 
 Calculator. 
 
 (1) f UrsseMaj.... 
 
 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) pOphiuchi 
 
 4"-328 
 
 04300 
 
 73-862 
 
 Encke, 1832. 
 
 (3) fHerculis 
 (4) Castor 
 
 1"-208 
 8"-086 
 
 04320 
 0-7582 
 
 3022 
 252-66 
 
 Madler, 1847 
 John Herschel 
 
 
 5"-692 
 
 0-2194 
 
 519-77 
 
 Tables of 1849. 
 Madler, 1847. 
 
 
 6"-300 
 
 0-2405 
 
 632-27 
 
 Hind, 1849. 
 
 (5) y Virginia 
 
 3"-580 
 3"-863 
 
 0-8795 
 0-8806 
 
 182-12 
 169-44 
 
 John Herschel. 
 Tables of 1849. 
 Madler, 1847. 
 
 (6) oCentauri 
 
 15"-500 
 
 09500 
 
 7700 
 
 Captain Jacob, 
 1848.
 
 INDEX TO VOL. III. 
 
 ACHROMATIC 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. 
 
 Anaxagoras of Clazomense, 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 effect of telescopes on 
 the visibility of the stars, 69 ; on the 
 velocity of light, 80, 84 ; on photometry, 
 92, 90 ; his cyanometer, 97. 
 
 Aratus, a fragment of the work of Hip- 
 parchas preserved in, 109. 
 
 Archimedes, his " Arenarius," 30. 
 
 Avcturus, true diameter of, 89. 
 
 Argulander, his view of the number of 
 the fixed stars, 105, 106 ; his additions 
 to Bessel's Catalogue, 115 ; on period- 
 ically variable stars, 166. 
 
 ij 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 
 the spheres, 124. 
 
 aosy, the domain of the fixed stars, 
 
 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 ; effects 
 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. 
 
 Baily , Francis, his revision of De Lalande's 
 Catalogue, 115. 
 
 Bayer's lettering of the stars of any con- 
 stellation not an evidence of their rel- 
 ative brightness, 98. 
 
 Berard, Captain, on the change of color 
 of the star y Crucis, 135. 
 
 Berlin Academy, star maps of the, 11B. 
 
 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 double 
 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 of 
 light 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 
 
 Catasterisma 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, 140 ; 
 list of the principal, 141-143. 
 
 Coal-sacks, a portion of the Milky Way in 
 the southern hemisphere so called, 137. 
 
 Colored rings afford 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. 
 
 Contrasted colors of double stars, 207. 
 
 Cosmical contemplation, extension of, la 
 the Middle Ages, 16.
 
 Cosmical vapor, question as to condensa- 
 tion of, 37 ; Tycho Brahe's and Sir Will- 
 iam Herschel's theories, 154. 
 
 " Cosmos," a pseudo-Aristotelian work, 
 16. 
 
 Crystal vault of heaven, date of the desig- 
 nation, 133 ; its signification according 
 to Empedocles, 123 ; the idea favored 
 by the Fathers of the Church, 125. 
 
 Cyanometer, Arago's, 97. 
 
 Dark cosmical bodies, question of, 164, 
 187. 
 
 Dolambrc on the velocity of light, 82. 
 
 Descartes, his cosmical views, 19, 20 ; sup- 
 presses his work from deference to the 
 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 which 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 their orbits, 
 211 ; table of the elements, 213. 
 
 Earth-animal, Kepler and Fludd's fancies 
 
 regarding the, 19. 
 Edda-Songs, allusion to, 8. 
 Egypt, zodiacal constellations 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 of, through the 
 
 Elements, Indian origin of the hypothesis 
 of four or five, 11. 
 
 Emanations from 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 Berlin Academy, 
 116 ; an early calculator of the orbits 
 of double stars, 2C \ ; his theory of their 
 motion, 212. 
 
 Encke's comet, considerations 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. 
 
 Ether (Ak so, in Sanscrit), one of the In- 
 dian five elements, 31. 
 
 Ether, the, fiery, 35. 
 
 Euler's comparative estimate of the light 
 f the sun and moon, 95. 
 
 Fixed stars, the term erroneous, 27, 122 ; 
 scintillation of the, 73 ; variations in its 
 intensity, 76 ; our sun one of the fainter 
 fixed stars, 95; photometric arrange- 
 ment of, 99 ; their number, 105 ; num- 
 ber visible 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 those 
 in which change of position has been 
 observed, 206, 207. 
 
 Fizeau, M., his experiments on the veloc- 
 
 ity of light, 80, 83. 
 Formula for 
 
 computing variation of light 
 of a star, by Argelander, : 
 
 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 Hcrschel, 1G6. 
 
 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 ij Argus, 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 Sinus and 
 other fixed stars, 26, 27. 
 
 Hassenfratz, his description of the rays 
 of stars as caustics on the crystalline 
 lens, 52, 127. 
 
 Heat, radiating, 35. 
 
 Hepidannus, monk of Saint Gall, a new 
 star recorded by, 157, 162. 
 
 Herschel, Sir William, on the vivifying 
 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'g 
 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 stars 
 seen in daylight^ 57; on photometry.
 
 217 
 
 93 ; photometric arrangement of the 
 fixed stars, 99 ; on the number of stars 
 
 Lassell's telescope, discoveries made by 
 means of, 65. 
 
 actually registered. 106 ; on the cause 
 of the red color of Sirius, 131, 132 ; on 
 
 Lepsius, on the Egyptian name (Sothis) 
 of Sinus, 134. 
 
 fhe Milky Way, 145; on the sun's place, 
 150; on the determined periods of vari- 
 
 Leslie's photometer, defects of, 96. 
 Libra, the constellation, date of its intro- 
 
 able stars, 166; number of double stars 
 
 duction into the Greek sphere, 120. 
 
 the elements of whose orbits have been 
 
 Light, always refracted, 44 ; prismatic 
 
 determined, 211. 
 
 spectra differ in number of dark lines 
 
 Hieroglyphical signification of a star, ac- 
 cording to Horapollo, 128. 
 
 according to their source, 44, 45 ; polar- 
 ization of, 45 ; velocity of, 79 ; ratio of 
 
 Hind's discovery of a new reddish-yellow 
 
 solar, lunar, and stellar, 95 ; variation 
 
 star of the fifth magnitude, in Ophiu- 
 
 of, in stars of ascertained and unascer- 
 
 magnitude, 160 ; calculation of the or- 
 
 tained periodicity, 168, 177. 
 Light of the sun and moon, Euler's and 
 
 bits of double stars by, 211. 
 Hipparchus. on the number of the Plei- 
 
 Michelo's estimates of the comparative, 
 95. 
 
 ades, 48 ; his catalogue contains the 
 
 Limited transparency of the celestial re- 
 
 earliest determination of the classes of 
 
 gions. 38. 
 
 magnitude of the stars, 90 ; a fragment 
 of his work preserved to us in Aratus, 
 
 IftO 
 
 Macrobius, " Sphsera aplanes" of, 27. 
 Madler, on Jupiter's satellites. 52 ; on the 
 
 ioy. 
 
 Holtzmann, on the Indian zodiacs, 121. 
 Homer, not an authority on the state of 
 Greek astronomy in his day, 119, 123. 
 Humboldt, Alexander von, works of, 
 quoted in various notes: 
 Ansichten der Natur, 79. 
 Asie Centrale, 111, 112. 
 Essai sur la Geogr. des Plantes, 58. 
 Examen Critique de 1'Histoire de la 
 
 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. 
 Mafus, his discoveries regarding light, 45. 
 ' Mappa ccelestis" of Schwinck, 140. 
 Ma-tuan-lin, a Chinese astronomical rec- 
 ord of 109 
 
 G6ographie, 49, 112, 137. 
 Lettre a M. Schumacher, 93. 
 Recueil 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 1'Amer- 
 
 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, 
 201 ; little reliance to be placed in its 
 individual numerical result?, 202. 
 Michelo's comparative estimate of the 
 
 ique, 121, 136. 
 Humboldt, Wiihelm von, quoted, 25. 
 Huygens, Christian, his ambitious but un- 
 satisfactory Cosmotheoros, 20; exam- 
 ined the Milky Way, 144. 
 
 light of the sun and moon, 95. 
 Milky Way, average number of stars in, 
 and beyond the, according to Struve, 
 139 ; intensity of its light in the vicinity 
 of the Southern Cross, 147 ; its course 
 
 Huygens, Constantin, his improvements 
 
 and direction, 147; most of the new 
 
 in the telescope, 02. 
 Hvergelmir, the caldron-spring of the Ed- 
 
 stars have appeared in its neighbor- 
 hood, 162. 
 
 da-Songs, 8. 
 
 Morin proposes the application of the tel- 
 
 Indian fiction regarding the stars of the 
 Southern hemisphere, 138. 
 
 escope to the discovery of the stars in 
 daylight, 41, 66. 
 
 Indian theory of the five elements (Pant- 
 
 Motion, proper, of the fixed stars, 182; 
 
 echota*), 31. 
 
 variability of, 185, 186. 
 
 Indian zodiacs, their high antiquity doubt- 
 ful, 121. 
 
 Multiple stars, 130, 199 ; variable bright- 
 ness of, difference of opinion regarding, 
 210. 
 
 Jacob, Capt, on the intensity of light in 
 the Milky Way. 146; calculation of the 
 
 Nebulas, probably closely crowded stellar 
 
 orbits of double stars, by, 211. 
 Joannes Philoponus, on gravitation, 18. 
 Jupiter's satellites, estimate of the magni- 
 tudes of, 50; case in which they were 
 visible by the naked eye, 52 ; occulta- 
 tious of, observed by daylight, 62. 
 
 swarms, 37. 
 Neptune, the planet, its orbit used as a 
 measure of distance of 61 Cygni, 204. 
 New stars, 151 ; their small number, 151 ; 
 Tycho Brahe's description of one, 152 ; 
 its disappearance, 153 ; speculations as 
 to their origin, 161 : most have appear- 
 
 Kepler, his approach to the mathematical 
 application of the theory of gravitation. 
 18; rejects the idea of solid orbs, 126. 
 
 ed near the Milky Way, 162. 
 Newton, embraces by his theory of gravi- 
 tation the whole uranological portion 
 
 
 of the Cosmos, 21. 
 
 Lalande, his Catalogue, revised by Baily, 
 115. 
 
 Non-luminous stars, problematical exist- 
 ence of, 187. 
 
 VOL III. K
 
 218 INI 
 
 Numerical results exceeding the grasp 
 of the comprehension, furnished alike 
 by the minutest organisms and the so- 
 called fixed stars, 30 ; encouraging views 
 on the subject, 31. 
 
 Optical and physical double stars, 200; 
 often confounded, 200. 
 
 Orbits of double stars, calculation of the, 
 211 ; their great eccentricity, 211 ; hy- 
 pothesis, that the brighter of the two 
 stars is at rest, and its companion re- 
 volves about it, probably correct, and a 
 great epoch in cosmical knowledge, 212. 
 
 Orion, the six stars of the trapezium of 
 the nebula of, probably subject to pe- 
 culiar physical attraction, 210, 211. 
 
 Pantschata or Pantschatra, the Indian the- 
 
 ory of the five elements, 31. 
 Parallax, means of discovering the, point- 
 
 ed out by Galileo, 183 ; number of par- 
 
 allaxes hitherto discovered, 190 ; detail 
 
 of nine of the best ascertained, 190. 
 Penetrating power of the telescope, 145, 
 
 146. 
 
 Periodically changeable stars, 164. 
 Periods within periods of variable stars, 
 
 168 ; Argelander on, 168. 
 Peru, climate of, unfavorable to astronom- 
 
 ical observations, 103. 
 Peters on parallax, 192. 
 Photometric relations of self-luminous 
 
 bodies, 89 ; scale, 99. 
 Photometry yet in its infancy, 94 ; first 
 
 numerical scale of, 94 ; Arago's meth- 
 
 od, 96. 
 
 Plato on ultimate principles, 12, 13. 
 Pleiades, one of the, invisible to the naked 
 
 eye of ordinary visual power, 48 ; de- 
 
 scribed, 141. 
 Pliny estimates the number of stars vis- 
 
 ible in Italy at only 1600, 108. 
 Poisson, his view of the consolidation of 
 
 the earth's strata, 36, 37. 
 Polarization of light, 45, 47. 
 Poles of greatest cold, 36. 
 Pouillet's estimate of the temperature of 
 
 space, 36. 
 Prismatic spectra, 44 ; difference of the 
 
 dark lines of, 45. 
 Ptolemy, his classification of the stars, 
 
 90 ; southern constellations known to, 
 
 137. 
 Pulkowa, number of multiple stars dis- 
 
 covered at, 205, 206. 
 Pythagoreans, mathematical symbolism 
 
 of tno, 12. 
 
 Quaternary systems of stars, 210. 
 
 Radiating heat, 35. 
 
 Ratio of various colors among the mul- 
 
 tiple and double stars, 209. 
 Rays of ftars, 52, 126-128 ; number of, in- 
 
 dicate distances, 128; disappear when 
 
 the star is viewed through a very sma 
 
 aperture, 138, 129. 
 Red stars, 131 ; varia 
 
 j Reflecting sextants applied to the determ- 
 I ination of the intensity of stellar light. 
 
 1. 
 variable stars mostly red, 
 
 Reflecting and refracting telescopes, 63. 
 i Regal stars of the ancients, 136. 
 j Resisting medium, proved by observa- 
 tions on Kncke's and other comets, 39. 
 Right ascension, distribution of stars ac- 
 cording to, by Schwinck, 140. 
 Rings, colored, measurement of the in- 
 tensity of light by, 96. 
 Rings, concentric, of stars, the hypothesis 
 of, favored by the most recent observa- 
 ! tions, 149. 
 i Rosse's, Lord, his great telescope, 65 ; it* 
 
 services to astronomy, 66. 
 I Ruby-colored stars, 135. 
 
 Saint Gall, the monk of, observed a new 
 j star distant from the Milky Way, 162. 
 
 Saussure asserts that stars may be seen 
 in daylight on the Alps, 57 ; the asser- 
 tion not supported by other travelers' 
 j 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 Indian 
 zodiacs, 121 
 
 Schwinck, distribution of the fixed stars 
 in his " Mappa coslestis," 140. 
 
 Scintillation of the stars, 73 ; variations 
 in its intensity, 76 ; mentioned in the 
 Chinese records, 77 ; little 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 first 
 magnitude, 93. 
 
 Self-luminous cosmical bodies, or suns, 
 199. 
 
 Seneca, on discovering new planets, 28. 
 
 Simplicius, the Eclectic, contrasts the cen- 
 tripetal and centrifugal forces, 12 ; his 
 vague view of gravitation, 18. 
 
 Sirius, its absolute intensity of light, 95 ; 
 historically proved to have changed its 
 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 the 
 orbits of double stars by, 211. 
 
 Smyth, Piazzi, on the Milky Way, 146, 
 147 ; on a Centauri, 185. 
 
 Sothis, the Egyptian name of Sirius, 133, 
 
 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.
 
 219 
 
 Space, conjectures regarding, 29 ; com- | its influence 
 pared to the mythic period of history, I 37. 
 29; fallacy of attempts at measurement , Temporary stars, 
 
 the climate of the earth, 
 
 t of, 155 ; notoe to, 
 
 of, 30 ; po'rtions between cosmical bod- I 155-160." 
 jes not void, 31 ; its probable low tem- Ternary stars, 210. 
 
 perature, 35. 
 
 Spectra, the prismatic, 44 ; difference of 
 the dark lines of, according to their 
 sources, 45. 
 
 " Sphtera aplanes" of Macrobiue, 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- 
 
 Timur Ulugh Beg, improvements in prac- 
 tical astronomy in the time of, 91. 
 
 Translation in space of the whole solar 
 system, 195; first hinted by Bradley, 
 195 ; verified by actual observation by 
 William Herschel, 196; Argelander. 
 Strove, and Gauss's views, 196. 
 
 Trapezium in the great nebula of Orion, 
 investigated by Sir Wm. Herschel, 203. 
 
 Tycho Brahe, his vivid description of the 
 appearance of a new star, 152 ; his the- 
 ory of the formation of such, 154. 
 
 Ultimate mechanical cause" of all mo- 
 tion, unknown, 24, 25. 
 
 bility of the, 48 ; seen through shafts I Undulation of the stars, 58, 59. 
 
 of chimneys, 57 ; undulation of the, 58, ' Undulations of rays of light, various 
 
 59 ; observation of, by daylight, 66 ; ! lengths of, 84. 
 
 scintillation of the, 73 ; variations in its Unity of nature distinctly taught by Aris- 
 
 intensity, 76 ; the brightest the earliest totle, 13-15. 
 
 named, 89; rays of, 52, 127, 128 ; color Uranological and telluric domain of the 
 Cosmos, 26. 
 
 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 electricity, 87 ; 
 his photometer, 93. 
 
 Stellar clusters or swarms, 140. 
 
 Struve on the velocity of light, 82 ; his 
 estimate of the number of tine fixed 
 stars, 1 17 ; on the Milky Way, 139 ; his 
 Dorpat Tables, 205 ; 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 fixed stars, 95 ; its place prob- 
 ably in a comparatively desert region 
 of the starry stratum, and eccentric, 150. 
 
 Suns, self-luminous cosmical bodies, 199. 
 
 Uranus observed as a star by Flamstead 
 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 ; methods of determ- 
 ining, 80 ; applied to the 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- 
 mirrors,45; velocity of electrical 
 
 ing IT 
 
 light determined by, 86." 
 Table of photometric arrangement of 190 White Ox, name given to the nebula now 
 fixed stars, 100 ; of 17 stars of first mag- known as one of the Magellanic clouds, 
 
 nitude, 102; of the variable stars, by 
 
 91. 
 
 Argelander, 172, and explanatory re- Wollaston's photometric researches, 95. 
 
 marks, 172-177; of ascertained paral- Wright, of Durham, his view of the origin 
 
 laxes, 193 : of the elements of the or- of the form of the Milky Way, 149. 
 bits of double stars, 213. 
 
 Telescope, the principle of, known to the Yggdrasil, the World-tree of the Edda- 
 
 Arabs, and probably to the Greeks and Songs, 8. 
 Romans, 42, 43 ; di 
 
 :overies by its 
 
 means, 61 ; successive improvements ' 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 cataa- 
 toriems, 120; great antiquity of the In- 
 
 of the, 62; enormous focal lensrth of 
 som.', 63; Lord Rosse's, 65; Bacon's 
 comparison of, to discovery ships, 130; 
 penetrating power of the, 145, 146. 
 Telesio, Bernardino, of Cosenza, his v: 
 
 of the 
 
 iews 
 phenomena of inert matter, 16. 
 
 Temperature, low, of cclcstiiil 
 uncertainty of results "el obta 
 
 space, 35; 
 ained, 36 ; 
 
 dian ver 
 
 130; great 
 y doubtful, 
 
 -ID. 
 THE END. 
 
 Zodiacal light, Sir John Herschel on the,
 
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