changes of distant worlds, and to enable us But when the re-examination of the stellar to interpret these results aright by the anal-heavens, on the plan adopted by his father, ogies of our own. The title-page of Sir John Herschel's book explains its nature and importance; it records "the completion of a telescopic survey of the whole surface of the visible heavens, commenced in 1825." The grave had not closed for three years over his illustrious father, when the son proceeded to carry out and complete, by rare sacrifices, the course of observation in which for half a century Sir William had no rival; and by extending the survey to the southern hemisphere, he rendered compact and comparable one of the most elaborate inquisitions of nature which two men ever attempted. was complete, it yet remained that that part of the sky invisible in Britain should be subjected to a similar critical examination, and the result handed down to posterity, so that changes may be recorded, and their causes investigated. The full value of the works of the Herschels will only become known when centuries shall have rolled on, and when all our present writings about terrestrial physics shall be consulted merely as historical curiosities long superseded by the advance of knowledge. To finish so great a monument to his own, but more especially to his father's fame, Sir John did not hesitate to quit in 1833 his home, endeared by many recollections, and undertake a voyage to another hemisphere, accompanied by his lady and a numerous family of young children, and embarrassed with unwieldy and fragile apparatus. But before a determination like his difficulties melted away. Having disembarked his instruments at Cape Town without accident, and placed them temporarily in one of the government storehouses, his next care was to look out for a residence in a locality suitable for their erection. This he was fortunate enough to find at the seat of a Dutch proprietor, Mr. Schonnberg, bearing the name of Feldhuysen, or Feldhausen, which he describes as Sir John Herschel's position and attainments fitted him admirably for so great a work, and justly entitle him to the unenvied position which he now holds amongst the cultivators of exact science. Bearing a name honored and revered by all, his career at Cambridge reflected upon it fresh lustre; the variety and extent of his acquirements gave him a reputation amongst his college contemporaries, afterwards fully confirmed by the not more impartial voice of mankind at large. Since that time he has been indefatigable as an author. First, in the systematizing of the higher mathematics, and in forwarding their study in his own university; afterwards by treatises contributed to the Encyclopædia Metropolitana, on Sound, Light, and Physical" about six miles from Cape Town, charmingly Astronomy, which still rank amongst the clearest, completest, and most philosophical in our own or in any other language. About the same time he wrote experimental essays on different branches of chemistry and optics in several Journals, and commenced his purely astronomical investigations, chiefly on nebulæ and double stars, partly in conjunction with Sir James South, of which the details are given in different volumes of the Astronomical and of the Royal Society's Transactions. These memoirs collectively include a complete revision of the objects of the same description catalogued and classified by Sir William Herschel. But amidst these serious and systematic employments he found time for writing two admirable elementary works in Dr. Lardner's Cyclopædia, one on Astronomy, the other on the Study of Natural Philosophy. They unite elegant and perspicuous language with logical order, great simplicity, and most apt illustrations, and have contributed in no small degree to the extended and popular reputation of their author. situated on the last gentle slope at the base of Table Mountain, on its eastern side, well sheltered from dust, and as far as possible from wind, by an exuberant growth of oak and fir timber; far enough removed from the mountain to be for the most part out of reach of the clouds which form so copiously over and around its summit, yet not so far as to lose the advantage of the reaction of its mural precipices against the southeast winds, which prevail with great violence during the finer and clearer months, but which seldom blow home to the rock on this side, being, as it were, gradually heaved up by a mass of comparatively quiescent air imprisoned at the root of the precipice, and so gliding up an inclined plane to the summit on the windward side, while they rush perpendicularly down on the leeward with tremendous violence like a cataract, sweeping the face of the cliffs towards Cape Town, which they fill with dust and uproar, especially during the night."— Introd. p. vii. During four entire years* (no inconsiderable portion of the best of man's life) Sir of the heavens (381 in number) commenced on the *The "sweeps" or nocturnal telescopic surveys 5th of March, 1834, and terminated 22d of January, 1838. John Herschel devoted his nights to obser- | vation, his days to calculation and manual labor, all directed to the fulfilment of his arduous enterprise. During this time, too, he managed to keep up an extensive correspondence with men of science at home, and to exert himself energetically for the moral and intellectual improvement of the colony with which he had been thus incidentally associated. Not the least remarkable part of this expedition was that it was defrayed out of his private fortune, notwithstanding liberal offers which he received of pecuniary aid from the late Duke of Northumberland, which he thought it inconsistent with the entire independence of his plans to accept; he even declined, as was understood, the use of a government vessel to convey him to his destination. Opinions will differ as to whether he might not, without any compromise of liberty of research, have availed himself of offers most creditable to those who made them; but the reason of his refusal, and afterwards availing himself of the generous proposal of the noblemen above named, to defray the expense of publishing the results, is best stated in his own words at a public dinner given to him after his return. He then said- "Much assistance was proffered to me from many quarters, both of instruments, and others of a more general nature--offers in the highest degree honorable to all parties, and I should be sorry to have it thought that, in declining them, I was the less grateful for them. I felt that if they were accepted, they would compel me to extend my plan of operations and make a larger campaign, and that in fact it would compel me to go in some degree aside from my original plan. But that campaign being ended, the harvest gathered in, and the mass of facts accumulated, I felt that the same objections did not apply to the publication of its results; and I therefore refer with pride and pleasure to the prospect of being enabled by the princely munificence of the Duke of Northumberland, to place those results before the public in a manner every way more satisfactory, and without becoming a burden, as they otherwise must have been a very severe one, on the funds of our scientific institutions."-Athenæum, 1838, p. 425. The generous offer thus accepted was peculiarly well-timed. The labor of extricating laws from masses of facts, great though it be, is a labor of love to the man of science; but the labor and anxiety of publication is not usually so; and is commonly attended with difficulties which, in the case of the abstruser sciences, would be insuperable to most private individuals, but for the exist ence of those societies alluded to by Sir J. Herschel, which with all their many faults of omission and commission must ever enjoy the credit of having brought to light, or assisted in doing so, the immortal labors of many a patient student, and even the Principia of Newton. But the common mode of publication by detached memoirs, buried in a mass of heterogeneous learning, accessible only by a research through piles of quartos, is after all but an imperfect publication. It is quite impossible to expect that any man's works, even the most celebrated, shall be fully appreciated when they can only be read or seen piecemeal, and by very many persons not at all. He who wishes to do a service to the reputation of an eminent man, living or dead, cannot do better than collect his writings in simple chronological sequence, and hand them down to posterity without note or comment. Such a specimen of fraternal piety has been shown by Dr. Davy in his collection of his brother's immortal writings: such Dr. Faraday has in part done for himself; such a high-spirited Peer has enabled Sir John Herschel to do, in the completest and fittest manner, in the publication before us; and such the scientific world hopes that Sir John himself will soon undertake with respect to the multifarious and important writings of his father, scattered over not less than thirty-seven volumes of the Philosphical Transactions, and consequently, though often talked of, in reality hardly known except by meagre and superficial abstracts. From the late noble Chancellor of Cambridge, therefore, Sir J. Herschel received a benefit which will contribute in no slight degree to the extension and perpetuation of his fame. The whole execution of the work is worthy of the subject, the author, and the patron. The eight years following Sir John Herschel's return to England were mainly spent in preparing the materials of this volume, nor will the time appear at all excessive when we consider, first, the vast mass of rough observations accumulated during four years of incessant work; secondly, that the reductions were all performed by the author's own hand; thirdly, that everything is worked out in the most complete and systematic manner, so as to afford in fact a model of this sort of analysis. To this may be added, that during the preparation of the work Sir John Herschel generously gave up much time to matters of general scientific interest, or for the sake of his friends. Amongst many which might be mentioned, the arrangements The 20 feet Newtonian, on Sir W. Herschel's construction, with specula of 18 inches clear aperture (of which three were provided,) was the sheet anchor of the campaign at the Cape. But along with it he carried a 7 feet achromatic by Tulley, with 5 inches aperture-a telescope which had served specially for the measurement of double stars in England, and of the performance of which Sir John gives in his papers in the Astronomical Memoirs a most flattering account, stating even that its performance appeared to improve with each fresh addition of power applied to it. of the Government Magnetic Observatories | very much more frequently required than in occupied much of his attention,* and within England; and it may be regarded as fortunate that I did not, as at first proposed, (relying on the a comparatively short time he wrote two most excellent and detailed biographies of possession of the three perfect metals.) leave the his astronomical friends, Baily and Bessel. sive that in a climate so much warmer, difficulties apparatus in question behind. Being apprehenWe may, and must, lament, indeed, that would arise in hitting the proper temper of the time so valuable to science should have been polishing material, slight imperfections of surface, largely spent upon the most mechanical induced by exposure, were for a while tolerated; arithmetical computations connected with but confidence in this respect once restored, and the reductions of places of double stars and practice continually improving, I soon became fastidious, and on the detection of the slightest nebulæ. The author no doubt laments it as dimness on any part of the surface, the metal was much as we do, and informs us (p. 5) that at once remanded to the polisher.”—Introd. p. x. he found himself at least unequal to the intended task of going through the whole of these reductions twice; but it appears that he has always found a difficulty, or felt a scruple, in employing an assistant for such operations; which we regret, because we have little doubt that a mere plodding arithmetician would have done the work with as few, if not fewer mistakes; and years might have been added to Sir John Herschel's term of vigorous exertion in the cause of science. The same objection does not, however, apply to the mechanical facility which he happily possesses (in common with his father) of fashioning his own tools and polishing the specula of his telescopes with his own hands. Such dexterity, and such mechanical habits, are of the highest value in themselves to the practical philosopher. They afford a seasonable variety of occupation conducive to mental and bodily health; as he is to employ the instruments, he can scrutinize their defects, and endeavor to remedy them in a way that a person not himself a mechanic might never think of. The very manipulation of such a kind as figuring reflectors will suggest to the ardent and anxious mind of the philosopher, who must devote many hours to it, improvements which might not theoretically occur to him, and which would never occur to an ordinary artisan. But the grand advantage of all is the absolute independence of external assistance and of skilled workmen which it gives: "The operation of repolishing was performed whenever needed, the whole of the requisite apparatus being brought for the purpose. It was * Amongst other efforts to engage public sympathy on behalf of the magnetic cause, Sir J. H. wrote a comprehensive article on the subject in the Quarterly Review, vol. lxvi., p. 271. In one of his former papers Sir John Herschel, speaking of numerical calculations, says, "for which I find in myself a great inaptitude." (Astr. Soc. Memoirs, vol. v. p. 221.) It is sad to think of the tear and wear of so accomplished a mind exerted in the mere arithmetic of the volume before us. VOL. XVIII. NO. L 6 We shall now give a short analysis of the contents of the volume before us, which is a handsome quarto of 452 well-filled pages, illustrated by 17 plates. The first chapter is on the NEBULE of the Southern Hemisphere. To enter into any detail on this subject would be to discuss a general question of astronomy which could receive no justice within our limits, and a great deal of which is as much connected with other writings of Sir John Herschel and with his father's as with the work before us. We have again the highly condensed, almost algebraical language, by which the characters and general effect of nebula have been so graphically described by the father and the son. Many, which are visible both at the Cape and in Europe, are here reobserved; the remainder are either new or "have been identified with more or less certainty with objects observed by Mr. Dunlop, and described in his Catalogue of Nebulæ." These are 206 in number. "The rest of the 629 objects comprised in that catalogue," adds Sir John, "have escaped my observation; and I am not conscious of any such negligence in the act of sweeping as could give rise to such a defalcation; but, on the contrary, by entering them on my working lists (at least until the general inutility of doing so, and loss of valuable time in fruitless search thereby caused, became apparent) took the usual precautions to ensure their dis- | classification of qualities in these respects (p. covery." Here is a sad tale and warning: for errors like Mr. Dunlop's not only deprive the more conscientious labors of their author of almost all their value, but they inflict a grave and positive injury upon the science which they pretend to promote. If men like Herschel are to spend the best years of their lives in recording for the benefit of a remote posterity the actual state of the heavens, in order that their changes may be examined and pronounced upon, what a galling discovery to find amongst their own contemporaries men who, without any wish to invent (we do not mean to charge Mr. Dunlop with that,) but merely from carelessness and culpable apathy hand down to posterity a mass of errors, bearing all the external semblance of truth; a quintessence of error so refined, that four hundred objects out of six hundred could not be identified in any manner, after only eight years, by the first observer of the day, and with a telescope seven times more powerful than that stated to have been used! We can add nothing to an exposure so humiliating. Sir John's chapter on Nebula contains several distinct sections. It would have added to convenience of reference as well as 140): The following is a specimen of the contracted description of a nebula : แ (No. 2422). v B; L; vm E; ps p mb M; has à * 10 m ; n f." Which, being translated, means— "Very bright; large; very much elongated; pretty suddenly pretty much brighter in the middle; has a star of the tenth magnitude, north following." Now this (which we select by chance) proves to be 139 of Sir John's Northern Catalogue. Turning it up, we find this description of the same object : "Very faint; round; a little brighter in the middle; 20" in diameter." The descriptions seem diametrically opposed. Such is the effect of difference of climate at Slough and Feldhausen. But if this be the case--if this be the effect of atmospheric influence (and such Sir John warns us, page 3, that it is) upon observations of the same object by the same telescope, and, within a few years, by the same eye, can we hope to perpetuate descriptions which shall enable posterity to decide upon real changes of physical constitution? given a more just idea of the variety and quantity of matter in the volume, had the Table of Contents of the volume been more full.* There is, in the first place, a catalogue of nebula and clusters of stars-1708 in number-chiefly in the southern hemisphere, which forms a sequel to the similar catalogue, by the same author, of 2307 objects of the same kind visible in England and Sir John gives more particular descriptions published in the Philosophical Transactions of some more remarkable objects. In genfor 1383. There is complete symmetry in eral we may observe that his figures show the mode of description and registration. less tendency to striking symmetry of form The descriptions (in abbreviated terms) have than some of those in his former catalogue; reference to Brightness, Size, Form; relation and it is now not denied that that symmetry to neighboring Stars; and more particularly was in some cases the involuntary deduction to the degree of Condensation of the seem- arising from a previous impression in favor of ing nebulous matter-a point of much deli- symmetric forms (as in the dumb-bell nebula cacy and difficulty of description, but of and the well-known No. 51 of Messier's catacapital importance with reference to Sir Wil-logue.) But the most interesting observaliam Herschel's theory of progressive condensation of rare into dense nebulæ, and finally into planetary nebulæ, nebulous stars, or even clusters of stars. Here is a pretty tions are upon the nebula in the sword-handle of Orion, the star Argûs, and the Magellanic clouds. Of the former, Sir John gives, which in all probability will be admitted by in Plate VIII., an exquisite representation, astronomers generally to be the most careful delineation of a celestial object ever transferred to copper. There are, perhaps, not ten persons alive in a position to judge of its minute accuracy; but this it will occur to no one to doubt who has read the present chapter and the paper on this nebula in the "Astronomical Memoirs" of 1824 by the same author. The total want of symmetry of the whole; the sometimes sudden, sometimes infinitely graduated shading off of the misty light, resembling slightly the exquisite shading of a snowy surface tossed into fantastic forms by eddies of wind, rising here and there into seeming ridges, elsewhere into gently swelling domes, or depressed into troughs and basins with cusped boundaries; sometimes apparently representing flats of extensive uniformity, or again mottled in an indescribable manner, as with the touch of the minature-painter's brush--these varieties are well brought out in this magnificent engraving. If we compare it with Sir J. Herschel's older one in the "Astronomical Memoirs," we find such a marked difference in the general character of the two that, though it is easy to see that they are representations of the same object, it appears to throw doubt (as we have already noticed) on the possibility of determining with sufficient exactness the features of such complex and ill-defined objects at one time, to give confidence to our belief of real changes at a future and distant one. Sir J. Herschel gives a hesitating expression of opinion that some of the diversities of the two drawings may be due to a nebular variation in thirteen years (p. 31); but such a conclusion would require strong evidence to support it. Of Argus, Sir J. Herschel observes: “There is, perhaps, no other sidereal object which unites more points of interest than this. Its situation is very remarkable, being in the midst of one of those rich and brilliant inasses, a succession of which, curiously contrasted with dark adjacent spaces, (called by the old navigators coal-sacks,) constitute the Milky-way in that portion of its course which lies between the Centaur and the main body of Argo. In all this region the stars of the Milky-way are well separated, and except within the limits of the nebula, on a perfectly dark ground, and, on an average, of larger magnitude than in most other regions. . In two hours, during which the area of the heavens swept over consisted of 47:03 degrees, the amazing number of 147,500 stars must have passed under review. In the midst of this vast stratum of stars occurs the bright star of Argûs, an object in itself of no ordinary interest, on account of the singular changes its lustre has undergone within the period of authentic astronomy." -p. 33. Sir John then goes on to state that by Halley (in 1677) Argûs was marked as of the fourth magnitude; in Lacaille's and later catalogues it is denoted by the second; and as observed by himself, from 1834 to 1837, was counted as a large star of the second, or small one of the first magnitude. It was on the 16th of December, 1837," he adds, "that my astonishment was excited by the appearance of a new candidate for distinction among the very brightest stars of the first magnitude." This was his old acquaintance Argûs. "Its light was, however, nearly tripled!" About the 2d of January, 1838, its light was judged to be a maximum, and all but equal to that of the very bright star a Centauri; but it had manifestly fallen below that on the 20th of the same month. At the conclusion of Sir John's personal observations, in April, 1838, it had "so far faded as to bear comparison with Aldebaran, though still somewhat brighter than that star. 'Beyond this date I am unable to speak of its further changes from personal observation. It appears, however, since that period to have made another and still greater step in advance, and to proached Sirius in lustre, the former of which have surpassed Canopus, and even to have apstars I estimate at double, the latter at more than quadruple of a Centauri, so that Jupiter and Venus may possibly have a rival amongst the fixed stars in Argo, as they have on recorded occasions had in Cassiopeia, Serpentarius, and Aquila.”—p. 34. The causes of fluctuations so great in the brightness of an object at so vast a distance, are amongst the most difficult even to guess be a matter of great interest to future astroat, and the watching of these changes must nomers, whilst it is yet a nearly untouched inquiry, but of which the basis is laid in the work before us. Of the nebula adjacent to Argûs we have not space to say much. Sir J. Herschel has given a large engraved representation of it, mapping the including stars- -a labor of no small amount: "To say that I have spent several months in the delineation of the nebula, the micrometrical measurement of the co-ordinates of the skeleton stars, the filling in, mapping down, and reading off of the skeletons when prepared, the subsequent reduction and digestion into a catalogue of the stars so determined, and the execution, final revision and correction of the drawing and engraving, would, I am sure, be no exaggeration." The tables of places of no less than 1216 stars belonging to the group of Argus testify to the truth of this statement; and the similar tables for the two nebuculæ, or Ma |
