9th Magnitude

Ascension.
I.

9th Magnitude. Ascension.

1516

XIII.

1533

II.

1609

XIV.

1766

III.

1547

XV.

1896

IV.

2146

XVI.

1661

determined by Argelander. He gives an Hours of R. Stars from 1st to Hours of R. Stars from 1st to account of the researches of Bessel, on the proper motions of Sirius and Procyon, from which that distinguished astronomer inferred the existence of large opaque bodies round which these motions are performed, and he mentions, without giving it any countenance, the bold speculation of M. Mædler of Dorpat, that the Pleiades forms the central group of the system of the Milky Way, and that Alcyone, the brightest star of the Pleiades, may be regarded as the central sun of the Milky Way, round which all the stars move with the same mean angular velocity, whatever be the inclination of their orbit, and their lineal distance from the central body.

Passing over his notice of the labors of the Russian astronomers, of Sir John Herschel, and Mr. Dunlop, on the subject of nebulæ and double stars, he treats of the structure of the Milky Way, as deduced from the catalogues of Weisse, Argelander, Piazzi, and Bessel. With this view he inquires into the arrangement of the stars in the equatorial zone or belt, 30° wide, extending to 15° N. and 15° S. of the equator. In the catalogue of Weisse, there are in that belt 31,085 stars, which are divided as follows:

XII.

Hence, dividing the whole zone into six regions, of four hours each, two of these are rich in stars, and four poor, the two rich regions being from V. to VIII. and from XVII. to XX.; and hence, M. Struve concludes, from a closer inspection of the table, that there is a gradual condensation of the stars towards a principal line, which is a diameter of the equatorial zone situated between the points VI 40m and XVIII 40' of the disc. The line of least condensation is situated between the points 1 30' and XIII 30', making an angle of 78° with the line of greatest condensation. If we divide the disc or zone into six circles parallel to the principal diameter, the density in successive bands diminishes on both sides with the distance. The line of greatest condensation does not pass through the sun. The distance of the sun from the principal diameter is about 0 15 a,* which is nearly equal to the radius of the sphere which separates the stars of the first from those of the second magnitude. The line of greatest condensation is not quite a straight line, but presents extraordinary lacunæ, as in Serpentarius, and accumulations, as in Orion. Hence the angle density is explained by these anomalies, for of 78° between the lines of greatest and least

it would otherwise have been 90".

the stars in the equatorial zone which encirComparing this description of the state of cles the sun, with the phenomena of the Milky Way, M. Struve arrives at the conclusion, "that the phenomenon of the condensation of the stars toward a principal line of the equatorial zone is closely connected with the nature of the Milky Way, or rather that this condensation and the aspect of the Milky Way are identical phenomena.

The letter a denotes the radius of a sphere including all the stars seen by the naked eye.

3. The extreme stars descried by Sir W. spheres containing the first six classes of Herschel in his sweeps with his 20-feet stars, or those between the first and the sixth telescope, are 227.8 unities, or two hundred magnitude, M. Struve takes as the basis of and twenty-eight times the distance of the his calculation the stars in our northern he-stars of the first magnitude, or 25.672 times misphere, as given by Argelander in his stars of the first magnitude, or 25.672 times Uranometrie. Thus :

Magnitudes, 1 2 3 4 5 6 No. of Stars, 9 34 96 214 550 2342 and from these numbers he obtained the

following results, the unity in the second column being the radius in a sphere containing all the stars visible to the naked

-of suns, each of which, like our own, feet is 61.18, 31.83-74.89 times the shone with its own light and on this suppo- distance of the stars 6. A, or 74.83+8.876 sition, he demonstrated that the whole 663.96 times the mean distance of stars visible heavens should shine with the lustre of the first magnitude. But instead of equal to that of our own sun. But as such 74.83, the gauges of Herschel give us a condition of the firmament does not exist, 25.672 for the radius of the stars 6 A. It he infers that there must be such an absorp- follows therefore that the range of Herschel's tion of this sidereal light as to reduce it to telescope, as determined by astronomical obwhat we now see in the heavens. In pro-servations, exceeds by scarcely one-third ducing such an effect, he proves that an the range which corresponds to its optical absorption of 1-800th part of the light of each star in its passage through a distance equal to that of Sirius from the sun, would be sufficient. In favor of such a hypothesis, no facts have been produced, but M. Struve conceives that a proof of the actual extinction of light may be found in the enumeration of stars of different orders of brightness, and that even the rate of extinction may, within certain limits, be determined.

force. How are we to explain this fact, asks M. Struve? I can see no other explanation, he adds, than that of admitting "that the intensity of light decreases in a greater proportion than the inverse ratio of the squares of the distances, or what is the same thing, that there exists a loss of light, an extinction, in the passage of light through celestial space." In computing the amount of the extinction, M. Struve finds that it is one per cent. for stars of the first magnitude (1 A), eight per cent. for stars of the sixth magnitude (6 A), thirty per cent. for those of the ninth magnitude (9 B), and eightyeight per cent. for the Herschelian stars, H.

The penetrating power of Sir W. Herschel's 20-feet telescope, he found to be 61.18, that is, by the help of this instrument, we can see stars 61.18 times more distant, than the last stars (sixth magni- These views, which appear to us well tude), which can be seen by the naked eye. founded, have been challenged by an eminent This number 61.18, supposes the opening writer in the Edinburgh Review,* who, of the pupil, to be exactly 0.2 of an English while he admits the absolute infinity in the inch, but as long-sighted and short-sighted number of the stars, maintains that the persons have different powers of sight, foundation of the reasoning of Olbers and the force of the eye is not a proper Struve may be "struck away," by certain unity, in measuring the force of a telescope." modes of systematic arrangement of the M. Struve therefore substitutes for the eye stars in space," which, "it is easy to imaa small achromatic telescope of 0.211 aper-gine," these modes being "entirely in conture, and magnifying three times, which sonance with what we see around us of subwill introduce into the eye exactly the same ordinate grouping actually followed out." quantity of light that passes directly through It would have been desirable that the rethe pupil when its aperture is 0.2, while it viewer had stated one of these modes in gives a precise image, independent of the justification of this bold challenge. We character of the eye. With this modulus, confess ourselves unable to conceive such a representing the eye as unity, he could mode of arrangement, although we cannot almost double the number of the stars con- agree either with Olbers or Struve in their tained in the maps of Argelander, or to conclusion, that the extinction of light, if it speak more exactly, he counted 183 when does exist, proves that sidereal space is only 100 were in the same space in the filled with some fluid such as ether, which is map. In taking, therefore, for unity the capable of intercepting a portion of the light distance of the last stars of the sixth mag- which it transmits. To fill infinite space nitude (6 A), which Argelander has seen, with matter, in order to explain a phenomethe visual radius or penetrating power of non, seems to us the very last resource of a the Herschelian modulus will be 31.83 sound philosophy. The sun has an atmo=1.2231, or equal to 1.2231+8.8726= sphere widely extended in the apprehension 10.582 times the mean distance of a star of of every astronomer. The planets have atthe first magnitude, but Herschel has deter-mospheres too: our solar system boasts of mined photometrically that this radius is equal to twelve times the distance of stars of the first magnitude, a remarkable coincidence which could scarcely be expected. Hence the range of the telescope of twenty

of about 700 recorded comets; and M. Arago is of opinion that if the perihelia of comets are distributed throughout the system

* Edinburgh Review, January 1848. No. 175.

1

Probable

Error.

Absolute
Parallaxes.

+0.349 0.080

+0.103 0.053

+0.067 0.012 (1830,) +0.226 0.141

Pole Star,
Groombridge
Capella,
Ursa Majoris,
Arcturus,
a Cygni,

+0.046 0.200

+0.133 0.106

+0.127 0.073

+0.082 0.043

as between the sun and the orbit of Mercury, minutes, and by means of four micrometer there would be three and a half millions of microscopes, its indications can be read off comets within the sphere of Uranus. Within to the tenth of a second. The telescope has the sphere of Neptune, of course, there an aperture of six inches diameter, and a must be many more; and Capt. Smith, in magnifying power of 215. The following mentioning the opinion of Arago, adds, are the results which he obtained :— that there are many considerations which, on the same hypothesis, would greatly increase that number. If we consider, also, 61 Cygni,* the enormous extent of the tails of these a Lyræ,t bodies, some of them millions of miles long, and the increase in the dimensions of comets as they recede from the sun, we shall have no difficulty in concluding that, within the limits of our own system, there is an immense mass of atmosphere or nebulosity capable of extinguishing a portion of the In attempting to determine the parallax light which falls upon it. Let us, then, fill of stars of the first and second magnitude, the infinite universe with similar systems-M. Peters founds his researches on all the with similar obstructions to light, and we parallaxes which have been determined with shall not require an ethereal medium to ac- sufficient precision. He finds that there are count for the want of luminosity in the thirty-five stars, whose parallaxes, whether starry firmament. The reviewer whom we absolute or relative, are determined with a have quoted, not satisfied with an instanta- degree of precision sufficient for his purpose; neous demolition of the speculation of Olbers but he excludes 61 Cygni and Groombridge and Struve, again slays the slain. "Light, 1830, as having a great proper motion. The it is true," he says, "is easily disposed of. general result at which he arrives is, "that Once absorbed, it is extinct for ever, and the mean parallax of stars of the second will trouble us no more. But with radiant magnitude is+ 0".116 and that the probable heat the case is otherwise. This, though error of this determination is only Ō".014." absorbed, remains still effective in heating By combining this value with the table of the absorbing medium, which must either relative distances in page 527, he obtains increase in temperature, the process continu- the results in the following table given by ing, ad infinitum, or, in its turn, becoming M. Struve :radiant, give out from every point, at every instant, as much heat as it receives." We do not think that we are in a condition to draw this conclusion. The law of the transmission of heat through the celestial spaces is a problem unsolved; and till we can explain how the luminous and chemical rays of the Sun reflected from the Moon, are transmitted to the earth, while those of heat cannot be exhibited, even when concentrated by the most powerful burning instruments, we are not entitled to urge the objection of the reviewer.

M. Struve concludes his interesting report by giving us an abstract of the unpublished but highly interesting researches of M. C. A. F. Peters, of the Central Observatory of Pulkova, on the Parallaxes and Distances of the fixed Stars. After a historical notice of the labors of preceding astronomers on the subject, M. Peters determines the actual parallaxes of the stars from observations made with the great vertical circle of Ertel. This noble instrument, forty-three inches in diameter, is divided into every two

Distances

No. of Julian expressed in years in which radii of the light traverses

Apparent magnitudes.

Parallaxes.

Earth's orbit. these distances.

1 A

0.209

986000

15.5

The velocity of the
Solar System
do.

Do.
Do.

Do.

do.

do. Do. do.

}

English Miles. 154,185,000 in the year.

422,424 in a day. 17,601 in an hour. 293 in a minute. 57 in a second.

This table exhibits to us grand truths, That is, taking 95 millions of English which, we may venture to say, neither New-miles as the mean radius of the Earth's orton nor La Place ever contemplated as bit, we have 95 x 1·623 = = 154 185 milwithin the range of human intellect. But lions of miles, and, consequently, even these are surpassed in interest by the determination of the actual velocity with which our own solar system, our sidereal home, is wheeling its ethereal round, guided by some great central body, whose light, if it has any, we may, perhaps, not have seen, and whose position we have not determined. To the solution of this great problem, M. Peters applies the numbers in the preceding table. M. Otto Struve, by combining the results of his calculations with those of M. Argelander, has determined that the point to which our solar system is advancing is situated at the epoch of 1840 in

Right Ascension, 259° 35'.1, with a probable error of 2° 57'.5; and north Declination, 34° 33.6, with a probable error of 2° 24'.5.

M. O. Struve has also determined the angular value of the annual motion of the sun as seen at a right angle to its path, and at the mean distance of the stars of the first magnitude.

By Right Ascension of stars, 0.32122, with a probable error of 0.03684; by Declination of do. 0.35719, with a probable error of 0.03562; or by combining these 0.3392, with probable error of 0.0252.

But as the parallax of stars of the first magnitude is 0".209, we can change the angular motion of the sun into linear motion in space; and hence, taking the radius of the earth's orbit as unity, we have 1-623, with a probable error of 0.229, for the annual motion of the sun in space.

0-3393

0-309

we

"Here, then," says M. F. W. G. Struve, " have the splendid result of the united studies of MM. Argelander, O. Struve, and Peters, grounded on observations made at the three (Russian) observatories of Dorpat, Abo, and Pulkova, and which is expressed in the following thesis:

μ

The sun and all his planets, primary and secondary, are therefore now in rapid motion round an invisible focus. To that now dark and mysterious centre, from which no ray, however feeble, shines, we may in another age point our telescopes-detecting, perchance, the great luminary which controls our system, and bounds its paths-into that vast orbit which man during the whole cycle of his race may never be allowed to round. If the buried relics of primeval life have taught us how brief has been our tenure of this terrestrial paradise compared with its occupancy by the brutes that perish, the sidereal truths which we have been expounding impress upon us the no less humbling lesson, that from the birth of man to the extinction of his race, the system to which he belongs will have described but an infinitesimal arc of that immeasurable circle in which it is destined to revolve. It is as if the traveller or naturalist, equipped for the survey of nature's beauties and wonders had been limited only to a Sabbath's journey. Some mountain tops might rise to his view as he creeps along, and some peaks might disappear beyond the horizon which he leaves behind; but had the first man surveyed the constellation Hercules, to which our system is advancing, it would have seemed to him as remote as it will appear to the last of our race.

In the contemplation of the infinite in number and in magnitude, the mind ever fails us. We stand appalled before the mighty spectre of boundless space, and fal

The motion of the solar system in space is directed to a point of the celestial vault situated on the right line which joins the two stars T and Herculis, at a quarter of the apparent dis-tering reason sinks under the load of its tance of these stars, reckoning from Herculis. bursting conceptions. But placed, as we The velocity of this motion is such that the sun, are, on the great locomotive of our system, with all the bodies which depend upon it, ad- destined surely to complete at least one vances annually in the above direction 1.623 round of its ethereal course, and learning times the radius of the earth's orbit, or 33,550,- that we can make no apparent advance on 000 geographical miles. The possible error our sidereal journey, we pant with new arof this last number amounts to 1,733,000 dor for that distant bourne which we congeographical miles, or to a seventh of the whole value. We may then wager 400,000 stantly approach without the possibility of to 1 that the sun has a proper progressive mo- reaching it. In feeling this disappointment, tion, and 1 to 1 that it is comprised between the and patiently bearing it, let us endeavor to limits of thirty-eight and thirty-nine millions realize the great truth from which it flows. of geographical miles.'"-p. 108. It cannot occupy our mind without exalting