is now no longer a dim misty speck, but a sharp | desecrate with their sorceries those hallowed rebrilliant point. I cannot, however, raise a well-gions on which the wizard and the conjuror have defined disc on it." "It is like a planetary neb- long ceased to tread.* ula, a little hazy at the edges, 2" or 21′′, in The elements and perturbations of the sixth diameter." "I now see a sharp, all but plane-satellite of Saturn having been elaborately investitary disc, diameter fully 1", quite distinct from the haze about it. It is like one of Jupiter's satellites in a thick fog of hazy light." "I can hardly doubt," Sir John adds, "that the comet was fairly evaporated in perihelio by the sun's heat, and resolved into transparent vapor, and is now in process of rapid condensation and re-precipitation on the nucleus." The comet resumed its former size on the 29th, and afterwards gradually disappeared as it receded from the sun. Sir John notices the following points as especially remarkable : gated by Bessel, and very little being known respecting the rest, Sir John Herschel availed himself of his advantageous position at the Cape, to make a series of observations on these interesting bodies. Our readers are no doubt aware that after the fourth satellite had been discovered by Huygens in 1655, Cassini discovered the fifth in 1671, and the first, second, and third, in 1684. Sir W. Herschel discovered, in 1780, the sixth and seventh nearer the planet than the rest, the seventh being the nearest. As this nomenclature was very unsatisfactory, many astronomers named them by 1st. The astonishingly rapid dilatation of its giving numbers corresponding to their distances visible dimensions. 2d. The preservation of the same geometrical form of the dilated and dilating envelope. 3d. The rapid disappearance of the coma; and, 4th. The increase in the density and relative brightness of the nucleus. Our limits will not permit us to discuss the speculative views which these phenomena have suggested to our author. He rejects the hypothesis of Valz, that the volume of the comet is directly proportional to its distance from the sun. He maintains that the laws of gravitation are insufficient to account for such a form of equilibrium as that of the comet, which was paraboloidal, and that such a form, as one of equilibrium, is inconceivable without the admission of repulsive as well as of attractive forces. "But if we admit," he adds, "the matter of the tail to be at once repelled from the sun and attracted by the nucleus, it no longer presents any difficulty." In order to obtain the repulsive power, Sir John hazards a theory which supposes the sun to be permanently charged with electricity. The cometic matters vaporized by the sun's heat, in perihelio, the two electricities separated by vaporization, the nucleus becoming negative and the tail positive, and the electricity of the sun directing the tail, in the same manner as a positively electrified body would an elongated non-conducting body, having one end positively, and the other negatively excited. The separation of Bielas' comet into two, travelling side by side, like the Siamese twins, presents a new difficulty which it would not be easy to explain. But here we are beyond our depth; and rather than admit electricity as an agent residing in every sun and acting upon every system, we remain content with the humbler supposition that the rays of the sun may, in the exercise of their chemical and physical influences, find some ingredients in the tails of comets, upon which, by their joint action, they may generate forces capable of producing the phenomena which we have been considering. If we once admit magnetism and electricity as agents in our sidereal systems, the mesmerists and phrenologists will form an alliance with the astrologer, and again from the planet; and Sir John Herschel has proposed to distinguish them by a series of heathen names, as in the following table : Although it would be difficult to banish from our solar system the names of the heathen gods by which the primary planets are distinguished, yet we must enter our protest against the admission of a brood of demigods. The nomenclature in the first column of the preceding table is doubtless the proper one, and the adoption of it can be attended with no more inconvenience than we are accustomed to in analogous matters. If the houses of a street are numbered before it is completed, the numbers must be changed whenever a new house is placed on a vacant area. If it is proper or necessary to give names to the secondary planets, our mythological knowledge must be more extensively put in requisition, for we cannot allow the planet Saturn to have a monopoly of the gods We must find names for the four satellites of Jupiter, and Uranus; and Neptune will make a similar and a heavy demand upon Lemprière. Sir John Herschel concludes his work with a Seventh chapter, containing Observations on the Solar Spots, and conjectures respecting their cause. The figures of the spots, of which he has given us thirteen in a very interesting plate, were delineated that M. Leverrier has found that the periodical comets * Our astronomical readers will be gratified to learn of 1770 and 1844 are two different bodies; that two of the comets of Faye, Vico, and Lexell, passed close to tached to our system, have come into it and been detained Jupiter; and that all these comets, now permanently atby the action of Jupiter and other bodies. M. Leverrier proves that the comets of Faye and Lexell have been in of times near the earth without being observed. The our system for at least a century, and have come a dozen comet of 1844 he proves to be the same as that of 1678, which has travelled into our system from the depths of infinite space, and been fixed among us centuries ago. It will revisit us in 1849. nothing but small tornadoes) appears to retreat observed during the obliteration of the solar spots, upwards. Now, this agrees perfectly with what is which appear as if filled in by the collapse of their sides, the penumbra closing in upon the spot, and disappearing after it." from magnified images formed on a screen by action, which lies in a higher region, so that their means of a seven-feet achromatic refractor. One centre (as seen in our water-spouts, which are of these spots, seen on the 29th March, 1837, occupied an area of nearly five square minutes, equal to 3,780,000,000 square miles. "The black centre of the spot of May 25, 1837, (not the tenth part of the preceding one,) would have allowed the globe of our earth to drop through it, leaving We have been much disappointed at finding that a thousand miles clear of contact on all sides of Sir John Herschel either has not observed or has that tremendous gulf." For such an amount of not described the extraordinary structure of the fully disturbance on the sun's atmosphere, what reason luminous disc of the sun, as we and others have can be assigned? Sir John Herschel justly ob-repeatedly seen it through Sir James South's serves, that the heating power of the sun is the great Achromatic;-a structure which should cause of the great disturbances in our own atmos- have been more distinctly seen at the Cape than phere; but as there is no such source of heat to act upon the sun, we must seek for the cause within the sun itself. Now, the spots are clearly in our climate. This structure of which, if we recollect rightly, we have seen a beautiful drawing made by Mr. Gwilt, resembles compressed curd, or white Almond soap, or a mass of asbestos fibres lying in a quaquaversus direction, and compressed into a solid mass. There can be no illusion in this phenomenon :-It is seen by every person with good vision, and on every part of the sun's luminous surface or envelope; and we think affords an ocular demonstration that that surface or envelope is not a flame, but a soft solid, or thick fluid maintained in an incandescent state by subjacent heat, and capable of being disturbed by differences of temperature, and broken up as we see it when the sun is covered with spots or openings in the luminous matter. Such is a brief and very imperfect analysis of a work which exhibits in a high degree the patience and the genius of its author-a work which had he done nothing else would have given immortality to his name. connected with the sun's rotation; and it has been long known that they do not appear in the sun's polar regions, but are confined to two zones, extending, according to our author, to about 35 degrees of N. and S. latitude, and separated by an equatorial belt, on which spots are very seldom found. Hence he considers the phenomenon of the spots as due to circulatory movements, to and from the sun's poles, in the fluids which cover its surface, modified by its rotation about its axis; and he tries to find a probable cause for these movements. Having observed a striking deficiency of light in the borders of the sun's visible disc, extending to some distance within it, he justly infers from this deficiency the existence of an atmosphere; and he adduces "the extraordinary phenomenon of the rose-colored solar clouds witnessed during the total eclipse of July 8th, 1842, as definitively settling this question pendent production, or as the completion of the in the affirmative." Assuming, then, the extent labors of his distinguished parent, it is a work of such an atmosphere "to be considerable--not truly national, to which, however, the nation has merely in absolute measure-but as an aliquot contributed nothing. To the liberality and devopart of the sun's radius," its form, in virtue of the tion to science of one individual we owe the laws of fluid equilibrium, must be oblately sphe- valuable results which it records, and to the munifroidal, and consequently its equatorial thickness icence of another its publication in a separate form, greater than its polar thickness. Hence, the and its gratuitous presentation to the universities, escape of heat must be greater from the polar than the societies, and the principal philosophers in from the equatorial zone, and the latter must pos- Europe and America. Wealth may well be coveted sess a higher temperature. In this respect, the when we find it thus judiciously employed when sun resembles our own earth; and on this sup-in the possession of genius, and thus liberally exposition our author thus reasons respecting the causes of the spots : Whether we view it as an inde pended when belonging to rank and station. It is then that "the fruit of wisdom is better than gold, and her revenue than choice silver," and that they "who love wisdom shall inherit substance, and have their treasures filled." Since the work of Sir John Herschel was drawn "The spots in this view of the subject would come to be assimilated to those regions on the earth's surface in which, for the moment, hurricanes and tornadoes prevail-the upper stratum being temporarily carried downwards, displacing by its impetus the two strata of luminous matter beneath, "P, Astronomy has been making rapid advances (which may be conceived as forming an habitually in Europe; and as an opportunity may not soon tranquil limit between the opposite upper and under occur of resuming the consideration of the subject, currents,) the upper, of course, to a greater extent we shall now give a brief notice of some of the than the lower-thus wholly or partially denuding most remarkable results which have been obtained, the opaque surface of the sun below. Such pro- and which have very recently been published by cesses cannot be unaccompanied with vorticose M. Struve of Pulcova, in his Etudes d'Astronomie motions, which, left to themselves, die away by Stellaire. This interesting work, to which we have degrees, and dissipate; with this peculiarity, that their lower portions come to rest more speedily than already had occasion to refer, is, we believe, in the their upper, by reason of the greater resistance possession only of M. Struve's private friends. below, as well as the remoteness from the point of It is drawn up as a report, addressed to his ex cellency M. Le Comte Ouvaroff, minister of public instruction, and president of the Imperial Academy of Sciences at St. Petersburg, and has the subsidiary title of Sur la Voie Lactée, et Sur les Distances des Etoiles Fixes. an ingenious calculation, that there are 52,199 existing in the equatorial zone. M. Struve had shown in 1827, that if we divide the celestial vault visible in Europe by circles parallel to the equator, the stars are almost uniformly After some historical notices of the speculations distributed in the zones thus formed, if we include of Galileo, Kepler, Huygens, Kant, Lambert, and at once all the 24 hours of R. Ascension; but Michel, M. Struve gives a general view of the that a very variable condensation takes place in discoveries of Sir W. Herschel on the construc- each zone in the successive hours of R. Ascention of the heavens, and of his peculiar views sion. This will appear from the following table, respecting the Milky Way. He compares his showing the number of stars existing in the equaopinion on this subject, as maintained in 1785, torial belt from the 1st to the 9th magnitude for with that to which he was subsequently led, and each hour of R. Ascension:arrives at the conclusion, which we have already had occasion to mention, that, according to Sir W. Herschel himself, the visible extent of the Milky Way increases with the penetrating power of the telescopes employed; that it is impossible to discover by his instruments the termination of the Milky Way (as an independent cluster of stars;) and that even his gigantic telescope of forty feet focal length, does not enable him to extend our knowledge of the Milky Way, which is incapable of being sounded. Hours of R. Ascension. I. Stars from 1st to 9th Hours of R. Stars from 1st to 9th Magnitude. 1516 XIII. 1533 II. 1609 XIV. 1766 III. 1547 In his next section, on the "Progress of Stellar Astronomy since the time of Herschel," he Hence, dividing the whole zone into six regions, gives an account of the labors of M. Argelander, of four hours each, two of these are rich in stars, in establishing beyond a doubt the translation of and four poor, the two rich regions being from V. our sun, with its planets in absolute space, and to VIII. and from XVII. to XX.; and hence, M. those of his own son, M. O. Struve, in ascertain- Struve concludes, from a closer inspection of the ing the angular velocity of its motion, and in veri- table, that there is a gradual condensation of the fying the direction in which it moves, as deter-stars towards a principal line, which is a diameter mined by Argelander. He gives an account of of the equatorial zone situated between the points the researches of Bessel, on the proper motions of VI 40m and XVIII 40′ of the disc. The line Sirius and Procyon, from which that distinguished of least condensation is situated between the points astronomer inferred the existence of large opaque I 30' and XIII 30', making an angle of 78° with bodies round which these motions are performed, the line of greatest condensation. If we divide the and he mentions, without giving it any counte- disc or zone into six circles parallel to the principal nance, the bold speculation of M. Maedler of diameter, the density in successive bands diminDorpat, that the Pleiades forms the central group ishes on both sides with the distance. The line of the system of the Milky Way, and that Alcyone, of greatest condensation does not pass through the brightest star of the Pleiades, may be regarded the sun. The distance of the sun from the prinas the central sun of the Milky Way, round which cipal diameter is about 0 15 a,* which is nearly all the stars move with the same mean angular equal to the radius of the sphere which separates velocity, whatever be the inclination of their orbit, the stars of the first from those of the second magand their lineal distance from the central body. nitude. 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 of 78° between the lines of greatest and least density is explained by these anomalies, for it would otherwise have been 90°. 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: Bright stars, from 1st to 6th magnitude, Comparing this description of the state of the stars in the equatorial zone which encircles the sun, with the phenomena of the Milky Way, M. Struve arrives at the conclusion, "that the phenomenon of the condensation of the stars towards 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. In extending this inquiry to the six million *The letter a denotes the radius of a sphere including all the stars seen by the naked eye. nearly (5,819,100) of stars visible in the twenty-tending this law to stars of other magnitudes, and feet telescope of Sir W. Herschel, M. Struve finds adopting for a new unity the mean distance of stars that the greatest and least densities fall very nearly of the first magnitude, he obtains the following taon the same points of the periphery of the disc, as ble of the relative distances of all classes of stars, in the case of stars of the 9th magnitude; and he | A denoting the magnitudes in Argelander's catagives the following distribution of these stars in logue, B those in Bessel's zones, and H those seen every four hours of R. Ascension:in the 20-feet telescope : towards a principal plane. After ascertaining that That is, the number of stars in the whole celestial sphere, 1. The last stars visible to the naked eye, acas seen by Sir W. Herschel's twenty-feet tele-cording to Argelander, are at the distance of 8scope, amount to (20,374,034) upwards of twenty .8726 times unity, or nearly nine times the distance millions, he obtains the following values of the of the stars of the first magnitude. density of the stars, and of the mean distance between two neighboring ones, at different distances from the principal plane of the Milky Way :Mean distance between Distance from the principal plane. Density in two neighboring stars. 1.458 In order to determine the radii of the spheres containing the first six classes of stars, or those between the first and the sixth magnitude, M. Struve takes as the basis of his calculation the stars in our northern hemisphere, as given by Argelander in his Uranométrie. Thus Magnitudes, 1 2 3 4 5 6 No. of Stars, 9 34 96 214 550 2342 and from these numbers he obtains the following results, the unity in the second column being the radius of a sphere containing all the stars visible to the naked eye : Apparent magnitudes according to Argelander. Radius of the Sphere. Progression calculated. 1.000 1.000 2. The last stars of the ninth magnitude, which Bessel has descried in his zones, are at the distance of 37.73 unities, or nearly thirty-eight times the distance of stars of the first magnitude; and, 3. The extreme stars descried by Sir W. Herschel in his sweeps with his 20-feet telescope, are 227.8 unities, or two hundred and twenty-eight times the distance of the stars of the first magnitude, or 25.672 times more remote than the stars of the sixth magnitude, or the furthest seen by the naked eye. But M. Struve next directs our attention to a new and very singular speculation, respecting "the extinction of the light of the fixed stars in its passage Dr. Olbers, in a memoir On the transparency of through celestial space." So long ago as 1823, the celestial spaces, assumed that in the infinity of space there existed an infinity of created worldsof suns, each of which, like our own, shone with its own light; and on this supposition, he demonstrated that the whole visible heavens should shine with a lustre equal to that of our own sun. as such a condition of the firmament does not exist, he infers that there must be such an absorption of this sidereal light as to reduce it to what we now see in the heavens. In producing such an effect, he proves that an 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 an 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. 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 magnitude,) which can be seen by the naked eye. escope. This number 61.18, supposes the opening | bold challenge. We confess ourselves unable to of the pupil, to be exactly 0.2 of an English inch, conceive such a mode of arrangement, although but as long-sighted and short-sighted persons have we cannot agree either with Olbers or Struve in different powers of sight, the force of the eye is their conclusion, that the extinction of light, if it not a proper unity, in measuring the force of a tel- does exist, proves that sidereal space is filled with M. Struve therefore substitutes for the some fluid such as ether, which is capable of intereye a small achromatic telescope of 0.211 aperture, cepting a portion of the light which it transmits. and magnifying three times, which will introduce To fill infinite space with matter, in order to exinto the eye exactly the same quantity of light that plain a phenomenon, seems to us the very last passes directly through the pupil when its aperture resource of a sound philosophy. The sun has an is 0.2, while it gives a precise image, independent atmosphere, widely extended in the apprehension of the character of the eye. With this modulus, of every astronomer. The planets have atmosrepresenting the eye as unity, he could almost pheres too: our solar system boasts of about 700 double the number of the stars contained in the recorded comets; and M. Arago is of opinion that maps of Argelander, or to speak more exactly, if the perihelia of comets are distributed throughout he counted 183 when only 100 were in the same the system as between the sun and the orbit of space in the map. In taking, therefore, for unity Mercury, there would be three and a half millions the distance of the last stars of the sixth magni- of comets within the sphere of Uranus. Within tude, (6 A,) which Argelander has seen, the the sphere of Neptune, of course, there must be visual radius or penetrating power of the Herschel- many more; and Capt. Smith, in mentioning the ian modulus will be 1.83 = 1.2231, or equal opinion of Arago, adds, that there are many conto 1.22318.8726 = 10.582 times the mean siderations which, on the same hypothesis, would If we consider, distance of a star of the first magnitude. But greatly increase that number. Herschel has determined photometrically that this also, the enormous extent of the tails of these radius is equal to twelve times the distance of stars bodies, some of them millions of miles long, and of the first magnitude, a remarkable coincidence the increase in the dimensions of comets as they which could scarcely be expected. Hence the recede from the sun, we shall have no difficulty in range of the telescope of twenty-feet is 61.18, concluding that, within the limits of our own sys1.83 74.89 times the distance of the stars 6 A, tem, there is an immense mass of atmosphere or or 74.838.876663.96 times the mean dis- nebulosity capable of extinguishing a portion of the Let us, then, fill the tance of stars of the first magnitude. But instead light which falls upon it. of 74.83, the gauges of Herschel give us 25.672 infinite universe with similar systems—with similar for the radius of the stars 6 A. It follows there- obstructions to light, and we shall not require an fore that the range of Herschel's telescope, as de- ethereal medium to account for the want of lumitermined by astronomical observations, exceeds by nosity in the starry firmament. scarcely one third the range which corresponds to whom we have quoted, not satisfied with an instanits optical force. How are we to explain this fact, taneous demolition of the speculation of Olbers and asks M. Struve? I can see no other explanation, Struve, again slays the slain. "Light, it is true,” "is easily disposed of. Once absorbed, he adds, than that of admitting "that the intensity of light decreases in a greater proportion than the it is extinct forever, and will trouble us no more. inverse ratio of the squares of the distances, or, But with radiant heat the case is otherwise. This, what is the same thing, that there exists a loss of though absorbed, remains still effective in heating light, an extinction, in the passage of light through the absorbing medium, which must either increase celestial space." In computing the amount of the in temperature, the process continuing, ad infiniextinction, M. Struve finds that it is one per cent. tum, or, in its turn, becoming radiant, give out for stars of the first magnitude, (1 A,) eight per from every point, at every instant, as much heat as cent. for stars of the sixth magnitude, (6 A,) thirty it receives." We do not think that we are in a per cent. for those of the ninth magnitude, (9 B,) condition to draw this conclusion. The law of the and eighty-eight per cent. for the Herschelian transmission of heat through the celestial spaces is a problem unsolved; and till we can explain how stars, H. 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. * These views, which appear to us well founded, have been challenged by an eminent writer in the Edinburgh Review, who, while he admits the absolute infinity in the number of the stars, maintains that the foundation of the reasoning of Olbers and Struve may be "struck away," by certain "modes of systematic arrangement of the stars in space," which, it is easy to imagine," these modes being "entirely in consonance with what we see around us of subordinate grouping actually followed out." It would have been desirable that the reviewer had stated one of these modes in justification of this 66 * Edinburgh Review, January, 1848. No. 175. he says, 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 paralAfter a laxes and distances of the fixed stars. historical notice of the labors of preceding astronomers on the subject, M. Peters determines the actual parallaxes of the stars from observations |
