Acquaintance with the asteroidal family began as the 19thGiuseppe Piazzi.Max Wolf.century opened. On the 1st of January 1801 Giuseppe Piazzi (1746-1826) discovered Ceres, at Palermo, while engaged in collecting materials for his star-catalogues. A prolonged succession of similar events followed. But in the mode of detecting these swarming bodies, a typical change was made on the 22nd of December 1891, when Dr Max Wolf of Heidelberg photographically captured No. 323. Repetitions of the feat are now counted by the score.
Practical astronomy was only secondarily concerned withLassell.the addition of Neptune, on the 23rd of September 1846, to the company of known planets; but William Lassell’s discovery of its satellite, on the 10th of October following, was a consequence of the perfect figure and high polish of his 2-ft. speculum. With the same instrument, he further detected, on the 19th of September 1848, Hyperion, the seventh of Saturn’s attendants, and, on the 24th of October 1851, Ariel and Umbriel, the interior moons of Uranus. Simultaneously with Lassell, on the opposite shore of theBond.Atlantic, W.C. Bond identified Hyperion; and he perceived, on the 15th of November 1850, Saturn’s dusky ring, independently observed, a fortnight later, by W.R. Dawes, at Wateringbury in Kent. With the Washington 26-in. refractor, on the 11th of August 1877,Hall.Barnard.Professor Asaph Hall descried the moons of Mars, Deimos and Phobos; and a minute light-speck, noticed by Professor E.E. Barnard in the close neighbourhood of Jupiter on the 9th of September 1892, proved representative of a small inner satellite, invisible with less perfect and powerful instruments than the Lick 36-in. achromatic. The Jovian system has been reinforced by three remote and extremely faint members, twoPerrine.W.H. Pickering.photographed by Professor C.D. Perrine with the Crossley reflector in 1904-1905, and the third at Greenwich in1908; and a pair of Saturnian moons, designated Phoebe and Themis, were tracked out by Professor W.H. Pickering, in 1898 and 1905 respectively, amid the thicket of stars imprinted on negatives taken at Arequipa with the Bruce 24-in. doublet lens. This raises to 26 the number of discovered satellites in the solar system.
Cometary science has ramified in unexpected ways during the last hundred years. The establishment of a class of “short-period” comets by the computations of J.F. Encke in 1819, and of Wilhelm von Biela in 1826, led to theComets.theory of their “capture” by the great planets, for which a solid mathematical basis was provided by H. Newton, F. Tisserand and O. Callandreau. An argument for the aboriginal connexion of comets with the solar system, founded by R.C. Carrington in 1860 upon their participation in its translatory movement, was more fully developed by L. Fabry in 1893; and the close orbital relationships of cometary groups, accentuated by the pursuit of each other along nearly the same track by the comets of 1843, 1880 and 1882, singularly illustrated the probable vicissitudes of their careers. The most remarkable event, however, in the recent history of cometary astronomy was itsMeteors.assimilation to that of meteors, which took unquestionable cosmical rank as a consequence of the Leonid tempest of November 1833. The affinity of the two classes of objects became known in 1866 through G.V. Schiaparelli’s announcement that the orbit of the bright comet of 1862 agreed strictly with the elliptic ring formed by the circulating Perseid meteors; and three other cases of close coincidence were soon afterwards brought to light. Tebbutt’s comet in 1881 was the first to be satisfactorily photographed. The study of such objects is now carried on mainly through the agency of the sensitive plate. The photographic registration of meteor-trails, too, has been lately attempted with partial success. The full realization of the method will doubtless provide adequate data for the detailed investigation of meteoric paths.
The progress of science during the 19th century had no more distinctive feature than the rapid growth of sidereal astronomySidereal astronomy.(seeStar). Its scope, wide as the universe, can be compassed no otherwise than by statistical means, and the collection of materials for this purpose involves most arduous preliminary labour. The multitudinous enrolment of stars was the first requisite. Only one “catalogue of precision”—Nevil Maskelyne’s of 36 fundamental stars—was available in 1800. J.J. Lalande, however, published in 1801, in hisHistoire céleste, the approximate places of 47,390 from a re-observationStar catalogues.of which the great Paris catalogue (1887-1892) has been compiled. A valuable catalogue of about 7600 stars was issued by Giuseppe Piazzi in 1814; Stephen Groombridge determined 4239 at Blackheath in 1806-1816; while through the joint and successive work of F.W. Bessel and W.A. Argelander, exact acquaintance was made with 90,000, a more general acquaintance with the 324,000 stars recorded in theBonn Durchmusterung(1859-1862). The southern hemisphere was subsequently reviewed on a similar duplicate plan by E. Schönfeld (1828-1891) at Bonn, by B.A. Gould and J.M. Thome at Córdoba. Moreover, the imposing catalogue set on foot in 1865 at thirteen observatories by the German astronomical society has recently been completed; and adjuncts to it have, from time to time, been provided in the publications of the royal observatories at Greenwich and the Cape of Good Hope, and of national, imperial and private establishments in the United States and on the continent of Europe. But in the execution of these protracted undertakings, the human eye has been, to a large and increasing extent, superseded by the camera. Photographic star-charting was begun by Sir David Gill in 1885, and the third and concluding volume of theCape Photographic Durchmusterungappeared in 1900. It gives the co-ordinates of above 450,000 stars, measured by Professor J.C. Kapteyn at Groningen on plates taken by C. Ray Woods at the Cape observatory. And this comprehensive work was merely preparatory to the International Catalogue and Chart, the production of which was initiated by the resolutions of the Paris Photographic Congress of 1887. Eighteen observatories scattered north and south of the equator divided the sky among them; and the outcome of their combined operations aimed at the production of a catalogue of at least 2,000,000 strictly determined stars, together with a colossal map in 22,000 sheets, showing stars to the fourteenth magnitude, in numbers difficult to estimate. (SeaPhotography,Celestial.)
The arrangement of the stars in space can be usefully discussed only in connexion with their apparent light-power, or “magnitude.” Photometric catalogues, accordingly, form an indispensable part of stellar statistics; andPhotometric catalogues.their construction has been zealously prosecuted. TheHarvard Photometryof 4260 lucid stars was issued by Professor E.C. Pickering in 1884, theUranometria Nova Oxoniensis, giving the relative lustre of 2784 stars, by C. Pritchard in 1885. The instrument used at Harvard was a “meridian photometer,” constructed on the principle of polarization; while the “method of extinctions,” by means of a wedge of neutral-tinted glass, served for the Oxford determinations. At Potsdam, some 17,000 stars have been measured by C.H.G. Müller and P.F.F. Kempf with a polarizing photometer; but by far the most comprehensive work of the kind is the HarvardPhotometric Durchmusterung(1901-1903), embracing all stars to 7.5 magnitude, and extended to the southern pole by measurements executed at Arequipa. The embarrassing subject of photographic photometry has also been attacked by Professor Pickering. The need is urgent of fixing a scale, and defining standards of actinic brightness; but it has not yet been successfully met.
The investigation of double stars was carried on from 1819 to 1850 with singular persistence and ability at Dorpat and Pulkowa by F.G.W. Struve, and by his son and successor, O.W. Struve. The high excellence of theDouble stars.data collected by them was a combined result of their skill, and of the vast improvement in refracting telescopes due to the genius of Joseph Fraunhofer (1787-1826). Among the inheritors of his renown were Alvan Clark and Alvan G. Clark of Cambridgeport, Massachusetts; and the superb definition of their great achromatics rendered practicable the division of what might have been deemed impossibly close star-pairs. These facilities were remarkably illustrated by Professor S.W. Burnham’s record of discovery, which roused fresh enthusiasm for this line of inquiry by compelling recognition of the extraordinary profusion throughout the heavens of compound objects. Discoveries with the spectroscope have ratified and extended this conclusion.
Only spurious star-parallaxes had claimed the attention of astronomers until F.W. Bessel announced, in December 1838, the perspective yearly shifting of 61 Cygni in an ellipse with a mean radius of about one-third of a second.Stellar parallax.Thomas Henderson (1798-1844) had indeed measured the larger displacements of α Centauri at the Cape in 1832-1833, but delayed until 1839 to publish his result. Out of several hundred stars since then examined, seventy or eighty have yielded fairly accurate, though very small parallaxes. But this amount of knowledge, however valuable in itself, is utterly inadequate to the needs of sidereal research; and various attempts have accordingly been made, chiefly by Professors J.C. Kapteyn and Simon Newcomb, to estimate, through the analysis of their proper motions, the “mean parallax” of stars assorted by magnitude. And the data thus arrived at are reassuringly self-consistent. A wide photographic survey, by which parallaxes might be secured wholesale, has further been recommended by Kapteyn; but is unlikely to be undertaken in the immediate future.
The exhaustive ascertainment of stellar parallaxes, combined with the visible facts of stellar distribution, would enable us to build a perfect plan of the universe in three dimensions. Its perfection would, nevertheless, be underminedProper motions.by the mobility of all its constituent parts. Their configuration at a given instant supplies no information as to their configuration hereafter unless the mode and laws of their movements have been determined. Hence, one of the leadinginducements to the construction of exact and comprehensive catalogues has been to elicit, by comparisons of those for widely separated epochs, the proper motions of the stars enumerated in them. Little was known on the subject at the beginning of the 19th century. William Herschel founded his determination in 1783 of the sun’s route in space upon the movements of thirteen stars; and he took into account those of only six in his second solution of the problem in 1805. But in 1837 Argelander employed 390 proper motions as materials for the treatment of the same subject; and L. Struve had at his disposal, in 1887, no less than 2800. From the re-observation of Lalande’s stars, after the lapse of not far from a century, J. Bossert was enabled to deduce 2675 proper motions, published at Paris in four successive memoirs, 1887-1902; and the sum-total of those ascertained probably now exceeds 6000. Yet this number, although it represents a portentous expenditure of labour, is insignificant compared with the multitude of the stellar throng; nor had any general tendency been discerned to regulate what seemed casual flittings until Professor Kapteyn, in 1904, adverted to the prevalence among all the brighter stars of opposite stream-flows towards two “vertices” situated in the Milky Way (seeStar). The assured general fact as regards the direction of stellar movements was that they included a common parallactic element due to the sun’s translation. And it is by the consideration of this partial accordance in motion that the advance through space of the solar system has been ascertained.
The apex of the sun’s way was fixed by Professor Newcomb in 1898 at a point about 4° S. of the brilliant star Vega; but was shifted nearly 7° to the S.W. by J.C. Kapteyn’s inquiry in 1901; so that the range of uncertainty as to its position continues unsatisfactorily wide. The speed with which our system progresses is, on the other hand, fairly well known. It cannot differ much from 12½ m. a second, the rate assigned to it by Professor W.W. Campbell in 1902. He employed in his discussion the radial velocities of 280 stars, spectroscopicallyAstrophysics.determined; and the upshot signally exemplified the community of interests between the rising science of astrophysics and the ancient science of astrometry. Their characteristic purposes are, nevertheless, entirely different. The positions of the heavenly bodies in space, and the changes of those positions with time, constitute the primary subject of investigation by the elder school; while the newSpectrum analysis.astronomy concerns itself chiefly with the individual peculiarities of suns and planets, with their chemistry, physical habitudes and modes of luminosity. Its distinctive method is spectrum analysis, the invention and development of which in the 19th century have fundamentally altered the purpose and prospects of celestial inquiries.
A beam of sunlight admitted into a darkened room through a narrow aperture, and there dispersed into a vario-tinted band by the interposition of a prism, is not absolutelyWollaston.Fraunhofer.continuous. Dr W.H. Wollaston made the experiment in 1802, and perceived the spaces of colour to be interrupted by seven obscure gaps, which took the shape of lines owing to his use of rectangular slit. He thus caught a preliminary glimpse of the “Fraunhofer lines,” so called because Joseph Fraunhofer brought them into prominent notice by the diligence and insight of his labours upon them in 1814-1815. He mapped 324, chose out nine, which he designated by the letters of the alphabet, to be standards of measurement for the rest, and ascertained the coincidence in position between the double yellow ray derived from the flame of burning sodium and the pair of dark lines named by him “D” in the solar spectrum. There ensued forty-five years of groping for a law which should clear up the enigma of the solar reversals. Partial anticipations abounded. The vital heart of the matter was barely missed by W.A. Miller in 1845, by L. Foucault in 1849, by A.J. Ångström in 1853, by Balfour Stewart in 1858; while Sir George Stokes held the solution of the problem in theKirchhoff.hollow of his hand from 1852 onward. But it was the synthetic genius of Gustav Kirchhoff which first gave unity to the scattered phenomena, and finally reconciled what was elicited in the laboratory with what was observed in the sun. On the 15th of December 1859 he communicated to the Berlin Academy of Sciences the principle which bears his name. Its purport is that glowing vapours similarly circumstanced absorb the identical radiations which they emit. That is to say, they stop out just those sections of white light transmitted through them which form their own special luminous badges. Moreover, if the white light come from a source at a higher temperature than theirs, the sections, or lines, absorbed by them show dark against a continuous background. And this is precisely the case with the sun. Kirchhoff’s principle, accordingly, not only afforded a simple explanation of the Fraunhofer lines, but availed to found a far-reaching science of celestial chemistry.Chemistry of the sun.Thousands of the dark lines in the solar spectrum agree absolutely in wave-length with the bright rays artificially obtained from known substances, and appertaining to them individually. These substances must then exist near the sun. They are in fact suspended in a state of vapour between our eyes and the photosphere, the dazzling prismatic radiance of which they, to a minute extent, intercept, thus writing their signatures on the coloured scroll of dispersed sunshine. By persistent research, powerfully aided by the photographic camera and by the concave gratings invented by H.A. Rowland (1848-1901) in 1882, about forty terrestrial elements have been identified in the sun. Among them, iron, sodium, magnesium, calcium and hydrogen are conspicuous; but it would be rash to assert that any of the seventy forms of matter provisionally enumerated in text-books are wholly absent from his composition.
Solar physics has profited enormously by the abolition of glare during total eclipses. That of the 8th of July 1842 was the first to be efficiently observed; and the luminous appendages to the sun disclosed by it were such asSolar eclipses.to excite startled attention. Their investigation has since been diligently prosecuted. The corona was photographed at Königsberg during the totality of the 28th of July 1851; similar records of the red prominences, successively obtained by Father Angelo Secchi and Warren de la Rue, as the shadow-track crossed Spain on the 18th of July 1860, finally demonstrated their solar status. The Indian eclipse of the 18th of August 1868 supplied knowledge of their spectrum, found to include the yellow ray of an exotic gas named by Sir Norman Lockyer “helium.” It further suggested, to Lockyer and P. Janssen separately, the spectroscopic method of observing these objects in daylight. Under cover of an eclipse visible in North America on the 7th of August 1869, the bright green line of the corona was discerned; and Professor C.A. Young caught the “flash spectrum” of the reversing layer, at the moment of second contact, at Xerez de la Frontera in Spain, on the 22nd of December 1870. This significant but evanescent phenomenon, which represents the direct emissions of a low-lying solar envelope, was photographed by William Shackleton on the occasion of an eclipse in Novaya Zemlya on the 9th of August 1896; and it has since been abundantly registered by exposures made during the obscurations of 1898, 1900, 1901 and 1905. A singular and unlooked-for result of eclipse-work has been to include the corona within the scope of solar periodicity. Heinrich Schwabe established, in 1851, the cyclical variation, in eleven years, of spot-frequency; terrestrial magnetic disturbances manifestly obeyed the same law; and the peculiar winged aspect of the corona disclosed by the eclipse of the 29th of July 1878, at an epoch of minimum sun-spots, intimated to A.C. Ranyard a theory of coronal types, changing concurrently with the fluctuations of spot-activity. This was amply verified at subsequent eclipses.
The photography of prominences was, after some preliminary trials by C.A. Young and others, fully realized in 1891 by Professor George E. Hale at Chicago, and independently by Henri Deslandres at Paris. The pictures wereProminence photography.taken, in both cases, with only one quality of light; the violet ray of calcium, the remaining superfluous beams being eliminated by the agency of a double slit. Thelast-named expedient had been described by Janssen in 1867. Hale devised on the same principle the “spectroheliograph,” an instrument by which the sun’s disk can be photographed in calcium-light by imparting a rapid movement to its image relatively to the sensitive plate; and the method has proved in many ways fruitful.
The likeness of the sun to the stars has been shown by the spectroscope to be profound and inherent. Yet the general agreement of solar and stellar chemistry does not exclude important diversities of detail. FraunhoferStellar spectroscopy.was the pioneer in this branch. He observed, in 1823, dark lines in stellar spectra which Kirchhoff’s discovery supplied the means of interpreting. The task, attempted by G.B. Donati in 1860, was effectively taken in hand, two years later, by Angelo Secchi, William Huggins and Lewis M. Rutherfurd. There ensued a general classification of the stars by Secchi into four leading types, distinguished by diversities of spectral pattern; and the recognition by Huggins of a considerable number of terrestrial elements as present in stellar atmospheres. Nebular chemistry was initiated by the same investigator when, on the 29th of August 1864, he observed the bright-line spectrum of a planetary nebula in Draco. About seventy analogous objects, including that in the Sword of Orion, were found by him to give light of the same quality; and thus after seventy-three years, verification was brought to William Herschel’s hypothesis of a “shining fluid” diffused through space, the possible raw material of stars. In 1874, Dr H.C. Vogel published a modification of Secchi’s scheme of stellar diversities, and gave it organic meaning by connecting spectral differences with advance in “age.” And in 1895, he set apart, as in the earliest stage of growth, a new class of “helium stars,” supposed to develop successively into Sirian, solar, Antarian, or alternatively into carbon stars.
On the 5th of August 1864, G.B. Donati analysed the light of a small comet into three bright bands. Sir William Huggins repeated the experiment on Winnecke’s comet in 1868, obtained the same bands, and traced them to theirSpectra of comets.origin from glowing carbon-vapour. A photograph of the spectrum of Tebbutt’s comet, taken by him on the 24th of June 1881, showed radiations of shorter wave-lengths but identical source, and in addition, a percentage of reflected solar light marked as such by the presence of some well-known Fraunhofer lines. Further experience has generalized these earlier results. The rule that comets yield carbon-spectra has scarcely any exceptions. The usual bands were, however, temporarily effaced in the two brilliant apparitions of 1882 by vivid rays of sodium and iron, emitted during the excitement of perihelion-passage.
The adoption, by Sir William Huggins in 1876, of gelatine or dry plates in celestial photography was a change of decisive import. For it made long exposures possible; and only with long exposures could autographic impressionsProgress in spectrography.be secured of such faint objects as nebulae, telescopic comets, and the immense majority of stars, or of the dim ranges of stellar and nebular spectra. The first conspicuous triumph of the new “spectrographic” art thus established was the record by Huggins in 1879 of the dispersed light of several “white” or Sirian stars, in which the chief traits of absorption were the rhythmical series of hydrogen-lines, then memorably discovered. Again by Sir William Huggins, the spectrum of the Orion nebula was photographed on the 7th of March 1882; and the method has gradually become nearly exclusive in the study of nebular emanations. The “Draper Catalogue” of 10,351 stellar spectra was published by Professor E.C. Pickering in 1890. The materials for it were rapidly accumulated by the use of an objective prism, that is, of a prism placed in front of, instead of behind the object-lens, by which means the spectra of all the stars in the field, to the number often of many score, imprinted themselves simultaneously on the sensitive plate. The progress of this survey was marked by a number of important discoveries of “new” and variable stars and of spectroscopic binaries, mainly through the acumen of Mrs Williamina Paton Fleming of Harvard College in scrutinizing the negatives forming the data for the great catalogue.
The principle that the refrangibility of light is altered by end-on motion was enunciated by Christian Doppler of Prague in 1842. The pitch of a steam-whistle quite obviously rises and falls as the engine to which it is attached approachesDoppler’s principle.and recedes from a stationary auditor; and light-pulses are modified like sound-waves by velocity in the line of sight. They are crowded together and therefore rendered shorter and more frequent by the advance of their source, but drawn apart and lengthened by its recession. These effects vary with the rate of motion, which they consequently serve to measure; and they are produced indifferently by movements of the spectator or of the light-source. But Doppler’s idea that they might be detected by colour-change was entirely illusory. It would apply only if the spectrum had no infra-red and ultraviolet extensions. These, however, since they share the general lengthening or shortening of wave-length through motion, are thereby shifted, to a certain definite extent, into visibility, and so produce accurate chromatic compensation. Integrated light, accordingly, tells nothing about velocity; but analysed light does, when it includes bright or dark rays the normal positions of which are known. The distinction was pointed out by Hippolyte Fizeau in 1848. By comparison with their analogues in the laboratory it can be determined whether, in which direction, and how much, lines of recognized origin are displaced in the spectra of the heavenly bodies. This subtle mode of research was made available by Sir William Huggins in 1868. He employed it, with an outcome of striking promise, to measure the radial speed of some of the brighter stars. In the following year, Sir Norman Lockyer was enabled to prove, by its means, the extraordinary vehemence of chromospheric disturbances, the bright prominence-rays in his spectroscope betraying, through their opposite shiftings, movements and counter-movements up to 120 m. a second; while its validity and refinement were, in 1871, vouched for by H.C. Vogel’s observations on the 9th of June 1871, of differences due to the sun’s rotation in the refrangibility of Fraunhofer lines derived respectively from the east and west limbs. Stellar line-of-sight work, however, made no satisfactory progress until, in 1888, Vogel changed thevenuefrom the eye to the camera. A high degree of precision in measurement thus became attainable, and has since been fully attained. Not only the grosser facts concerning radial velocity, but variations in it so small as a mile, or less, per second, have been recorded and interpreted in terms of deep meaning. For the investigation of the general scheme of sidereal structure, the multiplication of results of the kind is indispensable. But as yet, the recessional or approaching movements of only a few hundred stars have been registered; and this store of information is scanty indeed compared with the needs of research. How the stars really move in space, and how the sun travels among them, can be ascertained only with the aid of materials collected by the spectrograph, which has now fortunately been brought to comply with the arduous conditions of exactitude requisite for collaboration with the transit instrument and its allies, the clock and chronograph. And here, to their great mutual advantage, the old and the new astronomies meet and join forces.
Authorities.—R. Grant,History of Physical Astronomy(1852); Sir G. Cornewall Lewis,An Historical Survey of the Astronomy of the Ancients(1862); J.B.J. Delambre,Hist. de l’astr. ancienne;Hist. de l’astr. au moyen âge;Hist. de l’astr. moderne;Hist, de l’astr. au XVIIIesiècle; J.S. Bailly,Histoire de l’astronomie(5 vols., 1775-1787); J.F. Weidler,Historia Astronomiae(1741); J.H. Mädler,Geschichte der Himmelskunde(1873); R. Wolf,Geschichte der Astronomie(1876);Handbuch der Astronomie(1890-1892); W. Whewell,Hist. of the Inductive Sciences; A.M. Clerke,Hist. of Astronomy during the 19th Century(4th ed., 1903); A. Berry,Hist. of Astronomy(1898); J.K. Schaubach,Geschichte der griechischen Astronomie bis auf Eratosthenes(1802); Th. H. Martin, “Mémoire sur l’histoire des hypotheses astronomiques,”Mémoires de l’lnstitut, t. xxx. (Paris, 1881); P. Tannery,Recherches sur l’histoire de l’astronomie ancienne(1893); O. Gruppe,Die kosmischen Systeme der Griechen(1851); G.V. Schiaparelli,I Precursori del Copernico(1873);Le Sfere Omocentriche di Eudosso(1875); P. Jensen,Kosmologie der Babylonier(1890);F.X. Kugler,Die babylonische Mondrechnung(1900); J. Epping and J.N. Strassmeier,Astronomisches aus Babylon(1889); F.K. Ginzel,Die astronomischen Kenntnisse der Babylonier(1901); C.L. Ideler,Historische Untersuchungen über die astronomischen Beobachtungen der Alten(1806);Handbuch der math. Chronologie(2 vols., 1825-1826);Untersuchungen über den Ursprung der Sternnamen(1809); G. Costard,History of Astronomy(1767); J. Narrien,An Historical Account of the Origin and Progress of Astronomy(1833); J.L.E. Dreyer,Hist. of the Planetary Systems(1906); G.W. Hill, “Progress of Celestial Mechanics,”The Observatory, vol. xix. (1896).
Authorities.—R. Grant,History of Physical Astronomy(1852); Sir G. Cornewall Lewis,An Historical Survey of the Astronomy of the Ancients(1862); J.B.J. Delambre,Hist. de l’astr. ancienne;Hist. de l’astr. au moyen âge;Hist. de l’astr. moderne;Hist, de l’astr. au XVIIIesiècle; J.S. Bailly,Histoire de l’astronomie(5 vols., 1775-1787); J.F. Weidler,Historia Astronomiae(1741); J.H. Mädler,Geschichte der Himmelskunde(1873); R. Wolf,Geschichte der Astronomie(1876);Handbuch der Astronomie(1890-1892); W. Whewell,Hist. of the Inductive Sciences; A.M. Clerke,Hist. of Astronomy during the 19th Century(4th ed., 1903); A. Berry,Hist. of Astronomy(1898); J.K. Schaubach,Geschichte der griechischen Astronomie bis auf Eratosthenes(1802); Th. H. Martin, “Mémoire sur l’histoire des hypotheses astronomiques,”Mémoires de l’lnstitut, t. xxx. (Paris, 1881); P. Tannery,Recherches sur l’histoire de l’astronomie ancienne(1893); O. Gruppe,Die kosmischen Systeme der Griechen(1851); G.V. Schiaparelli,I Precursori del Copernico(1873);Le Sfere Omocentriche di Eudosso(1875); P. Jensen,Kosmologie der Babylonier(1890);F.X. Kugler,Die babylonische Mondrechnung(1900); J. Epping and J.N. Strassmeier,Astronomisches aus Babylon(1889); F.K. Ginzel,Die astronomischen Kenntnisse der Babylonier(1901); C.L. Ideler,Historische Untersuchungen über die astronomischen Beobachtungen der Alten(1806);Handbuch der math. Chronologie(2 vols., 1825-1826);Untersuchungen über den Ursprung der Sternnamen(1809); G. Costard,History of Astronomy(1767); J. Narrien,An Historical Account of the Origin and Progress of Astronomy(1833); J.L.E. Dreyer,Hist. of the Planetary Systems(1906); G.W. Hill, “Progress of Celestial Mechanics,”The Observatory, vol. xix. (1896).
(A. M. C.)
1The Observatory, Nos. 231-234, 1895.2Observations of Comets, translated from the ChineseAnnalsby John Williams, F.S.A. (1871).3J.L.E. Dreyer,Proc. Roy. Irish Acad.vol. iii. No. 7 (December 1881).4F.K. Ginzel, “Die astronomischen Kenntnisse der Babylonier,” C.F. Lehmann,Beiträge zur alten Geschichte, Heft i. p. 6 (1901).5Knowledge and Scientific News, vol. i. pp. 2, 228.6Astronomisches aus Babylon(Freiburg im Breisgau, 1889).7Ginzel, loc. cit. Heft ii. p. 204.8Die babylonische Mondrechnung, p. 50 (1900).9S. Newcomb,Astr. Nach.No. 3682; P.H. Cowell,Month. Notices Roy. Astr. Soc.lxv. 867.10G.V. Schiaparelli,I Precursori del Copernico, pp. 23-28, Pubbl. del R. Osservatorio di Brera, No. iii. (1873).11G.V. Schiaparelli,I Precursori del Copernico, pp. 23-28, Pubbl. del R. Osservatorio di Brera, No. ix.12Marie.Hist. des sciences, t. i. p. 79; P. Tannery,Hist. de l’astronomie ancienne, ch. v. p. 115.13Published by H.C. Schjellerup in a French translation (St Petersburg, 1874).14Newcomb,Researches on the Motion of the Moon, Washington Observations for 1875, Appendix ii. p. 20.15F. Baily,Memoirs Roy. Astr. Society, vol. xiii. p. 19.16J.L.E. Dreyer,Life of Tycho Brahe, p. 321.
1The Observatory, Nos. 231-234, 1895.
2Observations of Comets, translated from the ChineseAnnalsby John Williams, F.S.A. (1871).
3J.L.E. Dreyer,Proc. Roy. Irish Acad.vol. iii. No. 7 (December 1881).
4F.K. Ginzel, “Die astronomischen Kenntnisse der Babylonier,” C.F. Lehmann,Beiträge zur alten Geschichte, Heft i. p. 6 (1901).
5Knowledge and Scientific News, vol. i. pp. 2, 228.
6Astronomisches aus Babylon(Freiburg im Breisgau, 1889).
7Ginzel, loc. cit. Heft ii. p. 204.
8Die babylonische Mondrechnung, p. 50 (1900).
9S. Newcomb,Astr. Nach.No. 3682; P.H. Cowell,Month. Notices Roy. Astr. Soc.lxv. 867.
10G.V. Schiaparelli,I Precursori del Copernico, pp. 23-28, Pubbl. del R. Osservatorio di Brera, No. iii. (1873).
11G.V. Schiaparelli,I Precursori del Copernico, pp. 23-28, Pubbl. del R. Osservatorio di Brera, No. ix.
12Marie.Hist. des sciences, t. i. p. 79; P. Tannery,Hist. de l’astronomie ancienne, ch. v. p. 115.
13Published by H.C. Schjellerup in a French translation (St Petersburg, 1874).
14Newcomb,Researches on the Motion of the Moon, Washington Observations for 1875, Appendix ii. p. 20.
15F. Baily,Memoirs Roy. Astr. Society, vol. xiii. p. 19.
16J.L.E. Dreyer,Life of Tycho Brahe, p. 321.
ASTROPALIA(classicalAstypalaea), an island, with good harbours, in the south part of the Aegean, situated in 36.5° N. and immediately west of 26.5° E. It was colonized by Megara, and its constitution and buildings are known from numerous inscriptions. The Roman emperors recognized it as a free state, and in the middle ages it was calledStampalia, and belonged to the noble Venetian family of Quirini. It was taken by the Turks in the 16th century, and is now noted for its sponges. The customs and dress of the people, who speak a patois of romaic origin, are interesting.
ASTROPHYSICS,the branch of astronomical science which treats of the physical constitution of the heavenly bodies. So long as these bodies could be known to men only as points or disks of light in the sky, no such science was possible. Even later, when the telescope was the only instrument of research, knowledge on this subject was confined to the appearances presented by the planets, supplemented by more or less probable inferences as to the nature of their surfaces. When, in the third quarter of the 19th century, spectrum analysis was applied to the light coming to us from the heavenly bodies, a new era in astronomical science was opened up of such importance that the body of knowledge revealed by this method has sometimes been termed the “new astronomy.” The development of the method has been greatly assisted by photography, while the application of photometric measurements has been a powerful auxiliary in the work. It has thus come about that astrophysics owes its recent development, and its recognition as a distinct branch of astronomical science, to the combination of the processes involved in the three arts of spectroscopy, photography and photometry. The most general conclusions reached by this combination may be summed up as follows:—
1. The heavenly bodies are composed of like matter with that which we find to make up our globe. The sun and stars are found to contain the more important elements with which chemistry has made us acquainted. Iron, calcium and hydrogen may be especially mentioned as three familiar chemical elements which enter largely into the constitution of all the matter of the heavens. It would be going too far to say that all the elements known to us exist in the sun or the stars; nor is the question whether the rarer ones can or cannot be found there of prime importance. The general fact of identity in the main constituents is the one of most fundamental importance. It would be going too far in the other direction to claim that all the elements which compose the heavenly bodies are found on the earth. There are many lines in the spectra of the stars, as well as of the nebulae, which are not certainly identified with those belonging to any elements known to our chemistry. The recent discoveries growing out of the investigation of newly discovered forms of radiation lead to the conclusion that the question of the forms of matter in the stars has far wider range than the simple question whether any given element is or is not found outside our earth. The question is rather that of the infinity of forms that matter may assume, including that most attenuated form found in the nebulae, which seem to be composed of matter more refined than even the atoms supposed to make up the matter around us.
2. The second conclusion is that, as a general rule, the incandescent heavenly bodies are not masses of solid or liquid matter as formerly assumed, but mainly masses either of gas, or of substances gaseous in their nature, so compressed by the gravitation of their superincumbent parts toward a common centre that their properties combine those of the three forms of matter known to us. We have strong reason to believe that even the sun, though much denser than the general average of the stars, may possibly be characterized as gaseous rather than solid. Probabilities also seem to favour the view that this may, to a certain extent, be true of the four great planets of our system. The case of bodies like our earth and Mars, which are solid either superficially or throughout, is probably confined to the smaller bodies of the universe.
3. A third characteristic which seems to belong to the great bodies of the universe is the very high temperature of their interior. With a modification to be mentioned presently, we may regard them as intensely hot bodies, probably at a temperature higher than any we can produce by artificial means, of which the superficial portions have cooled off by radiation into space. A modification in this proposition which may hereafter be accepted involves an extension of our ideas of temperature, and leads us to regard the interior heat of the heavenly bodies as due to a form of molecular activity similar to that of which radium affords so remarkable an instance. This modification certainly avoids many difficulties connected with the question of the interior heat of the earth, sun, Jupiter and probably all the larger heavenly bodies.
A limit is placed on our knowledge of astrophysics which, up to the present time, we have found no means of overstepping. This is imposed upon us by the fact that it is only when matter is in a gaseous form that the spectroscope can give us certain knowledge as to its physical condition. So long as bodies are in the solid state the light which they emit, though different in different substances, has no characteristic so precisely marked that detailed conclusions can be drawn as to the nature of the substance emitting it. Even in a liquid form, the spectrum of any kind of matter is less characteristic than that of gas. Moreover, a gaseous body of uniform temperature, and so dense as to be non-transparent, does not radiate the characteristic spectrum of the gas of which it is composed. Precise conclusions are possible only when a gaseous body is transparent through and through, so that the gas emits its characteristic rays—or when the rays from an incandescent body of any kind pass through a gaseous envelope at a temperature lower than that of the body itself. In this case the revelations of the spectroscope relate only to the constitution of the gaseous envelope, and not to the body below the envelope, from which the light emanates. The outcome of this drawback is that our knowledge of the chemical constitution of the stars and planets is still confined to their atmospheres, and that conclusions as to the constitution of the interior masses which form them must be drawn by other methods than the spectroscopic one.
When the spectroscope was first applied in astronomy, it was hoped that the light reflected from living matter might be found to possess some property different from that found in light reflected from non-living matter, and that we might thus detect the presence of life on the surface of a planet by a study of its spectrum; but no hope of this kind has so far been realized.
We have, in this brief view of the subject, referred mainly to the results of spectrum analysis. Growing out of, but beyond this method is the beginning of a great branch of research which may ultimately explain many heretofore enigmatical phenomena of nature. The discovery of radio-activity may, by explaining the interior heat of the great bodies of the universe, solve a difficulty which since the middle of the 19th century has been discussed by physicists and geologists—that of reconciling the long duration which geologists claim for the crust of the earth with the period during which physicists have deemed it possible that the sun should have radiated heat. Evidence is also accumulating to show that the sun and stars are radio-active bodies, and that emanations proceeding from the sun, and reaching the earth, have important relations to the phenomena of Terrestrial Magnetism and the Aurora.
The subject of Astrophysics does not admit of so definite a subdivision as that of Astrometry. The conclusions which researches relating to it have so far reached are treated in the articlesStar;Sun;Comet;Nebula;Aurora Polaris, &c.
(S. N.)
ASTRUC, JEAN(1684-1766), French physician and Biblical critic, was born on the 19th of March 1684 at Sauve, in Languedoc.He graduated in medicine at Montpellier in 1703, and in 1710 he was appointed to the chair of anatomy at Toulouse, which he retained till 1717, when he became professor of medicine at Montpellier. Subsequently he was appointed successively superintendent of the mineral waters of Languedoc (1721), first physician to the king of Poland (1729), and regius professor of medicine at Paris (1731). He died on the 5th of May 1766 at Paris. Of his numerous works, that on which his fame principally rests is the treatise entitledDe Morbis Venereis libri sex, 1736. In addition to other medical works he published anonymouslyConjectures sur les mémoires originaux dont il parait que Moyse s’est servi pour composer le livre de la Genèse, (1753), in which he pointed out that two main sources can be traced in the book of Genesis; and two dissertations on the immateriality and immortality of the soul, 1755.
See Hauck,Realencyk. f. prot. Theol., 1897, vol. ii. pp. 162-170.
See Hauck,Realencyk. f. prot. Theol., 1897, vol. ii. pp. 162-170.
ASTURA,formerly an island, now a peninsula, on the coast of Latium, Italy, 7 m. S.E. of Antium, at the S.E. extremity of the Bay of Antium. The name also belongs to the river which flowed into the sea immediately to the S.E., at the mouth of which there was, according to Strabo, an anchorage. The medieval castle of the Frangipani, in which Conradin of Swabia vainly sought refuge after the battle of Tagliacozza in 1268, is built upon the foundations of a very large villa, ofopus reticulatumwith later additions in brickwork, and with a small harbour attached to it on the south-east. Remains of buildings also exist behind the sand dunes, which possibly mark the line of the channel which separated the island from the mainland, and these may have belonged to the post-station on the Via Severiana. As far as can be seen at present, there are remains of only one villa on the island itself;1but along the coast a mile to the north-west a line of villas begins, which continues as far as Antium. To the south-east, on the other hand, remains are almost entirely absent, and this portion of the coast seems to have been as sparsely populated in Roman times as it is now. The island seems to have existed as such in the time of Pope Honorius III. Astura was the site of a favourite villa of Cicero, whither he retired on the death of his daughter Tullia in 453B.C.It appears to have been unhealthy even in Roman times; according to Suetonius, both Augustus and Tiberius contracted here the illnesses which proved fatal to them.
See T. Ashby, inMélanges de l’École Française de Rome(1905), p. 207.
(T. As.)
1Servius, in speaking of it asoppidum, must be referring to the post-station.
1Servius, in speaking of it asoppidum, must be referring to the post-station.
ASTURIAS,an ancient province and principality of northern Spain, bounded on the N. by the Bay of Biscay, E. by Old Castile, S. by Leon and W. by Galicia. Pop. (1900) 627,069; area, 4205 sq. m. By the division of Spain in 1833, the province took the name of Oviedo, though not to the exclusion, in ordinary usage, of the older designation. A full description of its modern condition is therefore given under the headingOviedo; the present article being confined to an account of its physical features, its history, and the resultant character of its inhabitants. Asturias consists of a portion of the northern slope of the Cantabrian Mountains, and is covered in all directions with offshoots from the main chain, by which it is almost completely shut in on the south. The higher summits, which often reach a height of 7000-8000 ft., are usually covered with snow until July or August, and the whole region is one of the wildest and most picturesque parts of Spain. Until the first railway was opened, in the middle of the 19th century, few of the passes across the mountains were practicable for carriages, and most of them are difficult even for horses. A narrow strip of level moorland, covered with furze and rich in deposits of peat, coal and amber, stretches inland, from the edge of the sheer cliffs which line the coast, to the foot of the mountains. The province is watered by numerous streams and rivers, which have hollowed out deep valleys; but owing to the narrowness of the level tract, their courses are short, rapid and subject to floods. The most important is the Nalon or Pravia, which receives the waters of the Caudal, the Trubia and the Narcea, and has a course of 62 m.; after it rank the Navia and the Sella. The estuaries of these rivers are rarely navigable, and along the entire littoral, a distance of 130 m., the only important harbours are at Gijón and Avilés.
A country so rugged, and so isolated by land and sea, naturally served as the last refuge of the older races of Spain when hard pressed by successive invaders. Before the Roman conquest, the Iberian tribe of Astures had been able to maintain itself independent of the Carthaginians, and to extend its territory as far south as the Douro. It was famous for its wealth in horses and gold. About 25B.C., the Romans subjugated the district south of the Cantabrians, to which they gave the name of Augustana. Their capital was Asturica Augusta, the modern Astorga, in Leon. The warlike mountaineers of the northern districts, known as Transmontana, never altogether abandoned their hostility to the Romans, whose rule was ended by the Visigothic conquest, late in the 5th century. In 713, two years after the defeat and death of Roderick, the last Visigothic king, all Spain, except Galicia and Asturias, fell into the hands of the Moors. One of the surviving Christian leaders, Pelayo the Goth, took refuge with three hundred followers in the celebrated cave of Covadonga, or Cobadonga, near Cangas de Onís, and from this hiding-place undertook the Christian reconquest of Spain. The Asturians chose him as their king in 718, and although Galicia was lost in 734, the Moors proved unable to penetrate into the remoter fastnesses held by the levies of Pelayo. After his death in 737, the Asturians continued to offer the same heroic resistance, and ultimately enabled the people of Galicia, Leon and Castile to recover their liberty. The title of prince of Asturias, conferred on the heir-apparent to the crown of Spain, dates from 1388, when it was first bestowed on a Castilian prince. The title of count of Covadonga is assumed by the kings of Spain. In modern times Asturias formed a captaincy-general, divided into Asturias d’Oviedo, which corresponds with the limits of the ancient principality, and Asturias de Santillana, which now constitutes the western half of Santander.
Owing to their almost entire immunity from any alien domination except that of the Romans and Goths, the Asturians may perhaps be regarded as the purest representatives of the Iberian race; while their dialect (linguaje bable) is sometimes held to be closely akin to the parent speech from which modern Castilian is derived. It is free from Moorish idioms, and, like Galician and Portuguese it often retains the original Latinfwhich Castilian changes intoh. In physique, the Asturians are like the Galicians, a people of hardy mountaineers and fishermen, finely built, but rarely handsome, and with none of the grace of the Castilian or Andalusian. Unlike the Galicians, however, they are remarkable for their keen spirit of independence, which has been fostered by centuries of isolation. Despite the harsh land-laws and grinding taxation which prevent them, with all their industry and thrift, from securing the freehold of the patch of ground cultivated by each peasant family, the Asturians regard themselves as the aristocracy of Spain. This pride in their land, race and history they preserve even when, as often happens, they emigrate to other parts of the country or to South America, and earn their living as servants, water-carriers, or, in the case of the women, as nurses. They make admirable soldiers and sailors, but lack the enterprise and commercial aptitude of the Basques and Catalans; while they are differentiated from the inhabitants of central and southern Spain by their superior industry, and perhaps their lower standard of culture. It is, on the whole, true that by the exclusion of the Moors they lost their opportunity of playing any conspicuous part in the literary and artistic development of Spain. One class of the Asturians deserving special mention is that of the nomad cattle-drovers known as Baqueros or Vaqueros, who tend their herds on the mountains of Leitariegos in summer, and along the coast in winter; forming a separate caste, with distinctive customs, and rarely or never intermarrying with their neighbours.