Cosmos: A Sketch of the Physical Description of the Universe Part 13

The amount or quant.i.ty of these alterations in the fixed stars (that is to say, the changes in the relative position of self-luminous stars toward each other), can be determined with a greater degree of certainty than we are able to attach to the genetic explanation of the phenomenon. After taking into consideration what is due to the precession of the equinoxes, and the nutation of the earth's axis produced by the action of the Sun and Moon on the spheroidal figure of our globe, and what may be ascribed to the transmission of light, that is to say, to its aberration, and to the parallax formed by the diametrically opposite position of the Earth in its course round the Sun, we still find that there is a residual portion p 146 of the annual motion of the fixed stars due to the translation of the whole solar system in universal s.p.a.ce, and to the true proper motion of the stars.

The difficult problem of numerically separating these two elements, the true and the apparent motion, has been effected by the careful study of the direction of the motion of certain individual stars, and by the consideration of the fact that, if all the stars were in a state of absolute rest, they would appear perspectively to recede from the point in s.p.a.ce toward which the Sun was directing its course. But the ultimate result of this investigation, confirmed by the calculus of probabilities, is, that our solar system and the stars both change their places in s.p.a.ce. According to the admirable researches of d'Argelander at Abo, who has extended and more perfectly developed the work begun by William Herschel and Prevost, the Sun moves in the direction of the constellation Hercules, and probably, from the combination of the observations made of 537 stars, toward a point lying (at the equinox of 1792.5) at 257degrees 49.'7 R.A., and 28degrees 49.'7 N.D. It is extremely difficult, in investigations of this nature, to separate the absolute from the relative motion, and to determine what is aloone owing to the solar system.*

[footnote] *Regarding the motion of the solar system, according to Bradley, Tobias Mayer, Lambert, Lalande, and William Herschel, see Arago in the 'Annuaire', 1842, p. 388-399' Argelander, in Schum., 'Astron. Nachr ., No. 363, 364, 398, and in the treatise 'Von der eigenen Bewegung des Sonnensystems' (On the proper Motion of the Solar System), 1837, s. 43, respecting Perseus as the central body of the whole stellar stratum, likewise Otho Struve, in the 'Bull. de l'Acad. de St. P?tersb.', 1842, t.

x., No. 9, p. 137-139. The last-named astronomer has found, by a mo4re recent combination, 261degrees 23' R.A.+37degrees 36' Decl. for the direction of the Sun's motion; and, taking the mean of his own results with that of Argelander, we have, by a combination of 797 stars, the formula 259degrees 9' R.A.+34degrees 36' Decl.

If we consider the proper, and not the perspective motions of the stars, we shall find many that appear to be distributed in groups, having an opposite direction; and facts. .h.i.therto observed do not, at any rate, render it a necessary a.s.sumption that all parts of our starry stratum, or the whole of the stellar islands filling s.p.a.ce, should move round one large unknown luminous or non-luminous central body. The tendency of the human mind to investigate ultimate and highest causes certainly inclines the intellectual activity, no less than the imagination of mankind, to adopt such an hypothesis. Even the Stagirite proclaimed that "every thing which is moved must be referable to a motor, and that there would be no end to p 147 the concatenation of causes if there were not one primordial immovable morot."*

[footnote] *Aristot., 'de Clo', iii., 2, p. 301, Bekker: 'Phys.', viii., t, p. 256.

This material taken from pages 147-203

COSMOS: A Sketch of the Physical Description of the Universe, Vol. 1 by Alexander von Humboldt

Translated by E C Otte

from the 1858 Harper & Brothers edition of Cosmos, volume 1 --------------------------------------------------

The manifold translatory changes of the stars, not those produced by the parallaxes at which they are seen from the changing position of the spectator, but the true changes constantly going on in the regions of s.p.a.ce, afford us incontrovertible evidence of the 'dominion of the laws of attraction' in the remotest regions of s.p.a.ce, beyond the limits of our solar system. The existence of these laws is revealed to us by many phenomena, as, for instance, by the motion of double stars, and by the amount of r.e.t.a.r.ded or accelerated motion in different parts of their elliptic orbits.

Human inquiry need no longer pursue this subject in the domain of vague conjecture, or amid the undefined a.n.a.logies of the ideal world; for even here the progress made in the method of astronomical observations and calculations has enabled astronomy to take up its position on a firm basis.

It is not only the discovery of the astounding numbers of double and multiple stars revolving round a center of gravity lying 'without' their system (2800 such systems having been discovered up to 1837), but rather the extension of our knowledge regarding the fundamental forces of the whole material world, and the proofs we have obtained of the universal empire of the laws of attraction, that must be ranked among the most brilliant discoveries of the age. The periods of revolution of colored stars present the greatest differences; thus, in some instances, the period extends to 43 years, as in pi of Corona, and in others to several thousands,, as in 66 of Cetus, 38 of Gemini, and 100 of Pisces. Since Herschel's measurements in 1782, the satellite of the nearest star in the triple system of [Greek letter] of Cancer has completed more than one entire revolution. By a skillful combination of the altered distances and angles of position,* the elements of these orbits may be found, conclusions drawn regarding the absolute distance of the double stars from the Earth, and comparisons made between their ma.s.s and that of the Sun.

[footnote] *Savary, in the 'Connaissance des Tems', 1830, p. 56 and 163.

Encke, 'Berl. Jahrb.', 1832, s. 253, etc. Arago, in the 'Annuaire' 1834, p.

260, 295. John Herschel, in the 'Memoirs of the Astronom. Soc.', vol. v., p. 171.

Whether, however, here and in our solar system, quant.i.ty of matter is the only standard of the amount of attractive force, or whether 'specific'

forces of attraction proportionate to the ma.s.s may not at the same time come into operation, as Bessel was the first to conjecture, are questions p 148 whose practical solution must be left to future ages.*

[footnote] * Bessel, 'Untersuchung. des Theils der planetarischen Storungen, welche aus der Bewegung der Sonne entstchen' (An Investigation of the portion of the Planetary Disturbances depending on the motion of the Sun) in 'Abh. der Berl. Akad. der Wissensch.', 1824 (Mathem. Cla.s.se), s.

2-6. The question has been raised by John Tobias Mayer, in 'Comment. Soc.

Reg. Gotting.', 1804-1808, vol. xvi., p. 31-68.

When we compare our Sun with the other fixed stars, that is, with other self-luminous Suns in the lenticular starry stratum of which our system forms a part, we find, at least in the case of some, that channels are opened to us, which may lead, at all events, to an 'approximate' and limited knowledge of their relative distances, volumes, and ma.s.ses, and of the velocities of their translatory motion. If we a.s.sume the distance of Ura.n.u.s from the Sun to be nineteen times that of the Earth, that is to say, nineteen times as great as that of the Sun from the Earth, the central body of our planetary system will be 11,900 times the distance of Ura.n.u.s from the star 'a' in the constellation Centaur, almost 31,300 from 61 Cygni, and 41,600 from Vega in the constellation Lyra. The comparison of the volume of the Sun with that of the fixed stars of the first magnitude is dependent upon the apparent diameter of the latter bodies -- an extremely undertain optical element. If even we a.s.sume, with Herschel, that the apparent diameter of Arcturus is only a tenth part of a second, it still follows that the true diameter of this star is eleven times greater than that of the Sun.*

[footnote] *'Philos. Trans.' for 1803, p. 225. Arago, in the 'Annuaire', 1842, p. 375. In order to obtain a clearer idea of the distances ascribed in a rather earlier part of the text to the fixed stars, let us a.s.sume that the Earth is a distance of one foot from the Sun; Ura.n.u.s is then 19 feet, and Vega Lyrae is 158 geographical miles from it.

The distance of the star 61 Cygni, made known by Bessel, has led approximately to a knowledge of the quant.i.ty of matter contained in this body as a double star. Notwithstanding that, since Bradley's observations, the portion of the apparent orbit traversed by this star is not sufficiently great to admit of our arriving with perfect exactness at the true orbit nd the major axis of this star, it has been conjectured with much probability by the great Konigsberg astronomer,* "that the ma.s.s of this double star can not be very considerably larger or smaller than half of the ma.s.s of the Sun."

[footnote] *Bessel, in Schum., 'Jahrb.', 1839, s. 53.

This result is from actual measurement. The a.n.a.logies deduced from the relatively larger ma.s.s of those planets in our solar system that are attended by satellites, and from the fact that Struve has discovered six times more double stars among p 194 the brighter than among the telescopic fixed stars, have led other astronomers to conjecture that the average ma.s.s of the larger number of the binary stars exceeds the ma.s.s of the Sun.*

[footnote] *M?dler, 'Astron.', s. 476; also in Schum, 'Jahrb.', 1839, s.

95.

We are, however, far from having arrived at general results regarding this subject. Our Sun, according to Argenlander, belongs, with reference to proper motion in s.p.a.ce, to the cla.s.s of rapidly-moving fixed stars.

The aspect of the starry heavens, the relative position of stars and nebullae, the distribution of their luminous ma.s.ses, the picturesque beauty, if I may so express myself, of the whole firmament, depend in the course of ages conjointly upon the proper motion of the stars and nebulae, the translation of our solar system in s.p.a.ce, the appearance of new stars, and the disappearance or sudden diminution in the intensity of the light of others, and lastly and specially, on the changes which the Earth's axis experiences from the attraction of the Sun and Moon. The beautiful stars in the constellation of the Centaur and the Southern Cross will at some future time be visible in our northern lat.i.tudes, while other stars, as Sirius and the stars in the Belt of Orion, will in their turn disappear below the horizon. The places of the North Pole will successively be indicated by the stars -- beta and a alpha Cephei, and -- delta Cygni, until after a period of 12,000 years, Vega in Lyra will s.h.i.+ne forth as the brightest of all possible pole stars. These data give us some idea of the extent of the motions which, divided into infinitely small portions of time, proceed without intermission in the great chronometer of the universe. If for a moment we could yield to the power of fancy, and imagine the acuteness of our visual organs to be made equal with the extremest bounds of telescopic vision, and bring together that which is now divided by long periods of time, the apparent rest that reigns in s.p.a.ce would suddenly disappear. We should see the countless host of fixed stars moving in thronged groups in different directions; nebulae wandering through s.p.a.ce, and becoming condensed and dissolved like cosmical clouds; the vail of the Milky Way separated and broken up in many parts, and 'motion' ruling supreme in every portion of the vault of heave, even as on the Earth's surface, where we see it unfolded in the germ, the leaf, and the blossom, the organisms of the vegetable world. The celebrated Spanish botanist Cavanilles was the first who entertained the idea of "seeing gra.s.s grow," and he directed the horizontal micrometer threads of a powerfully magnifying gla.s.s at one time to p 150 the apex of the shoot of a bambusa, and at another on the rapidly-growing stem of an American aloe ('Agave Americana', precisely as the astronomer places his cross of net-work against a culminating star. In the collective life of physical nature, in the organic as in the sidereal world, all things that have been, that are, and will be, are alike dependent on motion.

The breaking up of the Milky Way, of which I have just spoken, requires special notice. William Herschel, our safe and admirable guide to this portion of the regions of s.p.a.ce, has discovered by his star-guagings that the telescopic breadth of the Milky Way extends from six to seven degrees beyond what is indicated by our astronomical maps and by the extent of the sidereal radiance visible to the naked eye.*

[footnote] *Sir William Herschel, in the 'Philos. Transact.' for 1817, Part ii p. 438.

The two brilliant nodes in which the branches of the zone unite, in the region of Cepheus and Ca.s.siopeia, and in the vicinity of Scorpio and Sagittarius, appear to exercise a powerful attraction on the contiguous stars; in the most brilliant part, however between beta and [Greek symbol]

Cygni, one half of the 330,000 stars that have been discovered in a breadth of 5 degrees are directed toward one side, and the remainder to the other.

It is in this part that Herschel supposes the layer to be broken up.*

[footnote] *Arago, in the 'Annuaire', 1842, p. 569

The number of telescopic stars in the Milky Way uninterrupted by any nebulae is estimated at 18 millions. In order, I will not say, to realize the greatness of this number, but, at any rate, to compare it with something a.n.a.logous, I will call attention to the fact that there are not in the whole heavens more than about 8000 stars between the first and the sixth magnitudes, visible to the naked eye. The barren astonishment excited by numbers and dimensions in s.p.a.ce, when not considered with reference to applications engaging the mental and perceptive powers of man, is awakened in both extremes of the universe, in the celestial bodies as in the minutest animalcules.*

[footnote] *Sir John Herschel, in a letter from Feldhuysen, dated Jan.

13th, 1836. Nicholl, 'Architecture of the Heavens', 1838, p. 22. (See, also, some separate notices by Sir William Herschel on the starless s.p.a.ce which separates us by a great distance from the Milky Way, in the 'Philos.

Transact.' for 1817, Part ii., p. 328.)

A cubic inch of the polis.h.i.+ng slate of Bilin contains, according to Ehrenberg, 40,000 millions of the silicious sh.e.l.ls of Galionellae.

The stellar Milky Way, in the region of which, according to Argelander's admirable observations, the brightest stars of the firmament appear to be congregated, is almost at right angles p 151 with another Milky Way, composed of nebulae. The former const.i.tutes, according to Sir John Herschel's views, an annulus, that is to say, an independent zone, somewhat remote from our lenticular-shaped starry stratum, and similar to Saturn's ring. Our planetary system lies in an eccentric direction, nearer to the region of the Cross than to the diametrically opposite point, Ca.s.siopeia.*

[footnote] *Sir John Herschel, 'Astronom.', 624; likewise in his 'Observations on Nebulae and Cl.u.s.ters of Stars' ('Phil. Transact.', 1833, Part ii., p. 479, fig. 25): "We have here a brother system, bearing a real physical resemblance and strong a.n.a.logy of structure to our own."

An imperfectly seen nebulous spot, discovered by Messier in 1774, appeared to present a remarkable similarity to the form of our starry stratum and the divided ring of our Milky Way.*

[footnote] *Sir William Herschel, in the 'Phil. Trans.' for 1785, Part i., p. 257. Sir John Herschel, 'Astron.', 616. ("The 'nebulous' region of the heavens forms 'a nebulous Milky Way', composed of distinct nebulae, as the other of stars." The same observation was made in a letter he addressed to me in March, 1829.)