pasteboard tubes. He might have advanc-[ were the subjects of his constant study; ed a step farther in these interesting occupa- and he at last succeeded in obtaining contions, but he would soon have found him-siderable pieces of uniform transparency self in the same course in which Huygens and refractive power, sometimes twelve, and and Campani had reached the goal. An in one case eighteen inches in diameter! achromatic telescope of English manufac- He at last acquired the art of soldering two ture had come into the possession of his or more pieces of good glass, and though master, Jacquet Droz. He was permitted the line of junction was often marked with to examine it—to separate its lenses-and globules of air or particles of sand, yet by to measure its curves;-and after studying grinding out these imperfections on an its properties, he was seized with the desire emeried wheel, and by replacing the mass of imitating the wondrous combination. in a furnace, so that the vitreous matter Flint Glass was to be had only in England, might expand and fill up the excavations, and he and his friend M. Reordon, who he succeeded in effacing every trace of went to England to take out a patent for junction, and was consequently able to prohis self-winding watches, purchased as duce with certainty the finest discs of flint much of it for him as enabled him to make glass." several achromatic telescopes. The glass, After the Achromatic telescope had been however, was bad; and the bold peasant, banished from England as it were by Act seeing no way of getting it of a better qual- of Parliament, it found a hospitable recepity, resolved upon making good flint glass tion in the optical establishment of Frauenfor his own use. "We are confident, as hofer, at Benedict Baiern, near Munich. we have elsewhere had occasion to remark, This illustrious individual, who united the that no chemist in England or in France highest scientific attainments with great would have ventured on such a task;-mechanical and practical knowledge, havbut ignorance was in this case power, and ing heard of Guinand's success in the manuglass, fortunately for science, was not an facture of flint glass, repaired to Brenetz in exciseable commodity in the village of 1804, and induced the village optician to Brenetz. Studying the chemistry of fusion, settle at Munich, where, from 1805 to 1814, he made daily experiments in his blast fur- he practised his art, and taught it to his nace, between 1784 and 1790, with melt- employers. Frauenhofer was an apt and ings of three or four pounds each, and willing scholar, and possessing a thorough carefully noted down the circumstances, knowledge of chemistry and physics, he and the results of each experiment. Marked success invigorated his ever-failing efforts, and the intelligence that learned academicians had offered prizes for the object at which he strained, animated him with fresh and glowing excitements. Having abandoned his profession for the more lucrative one of making bells for repeaters, his means became more ample, and his leisure hours more numerous. He purchased a piece of ground on the banks of the Doubs, where he constructed a furnace capable of fusing two hundred weight of glass. The failure of his crucibles, the bursting of his furnaces, and a thousand untoward accidents, which would have disconcerted less ardent minds, served only to invigorate his. The disappointments of one day were the pedestal on which the resolutions of the preceding one reached a higher level; and in the renewed energy of his spirit, and the increasing brightness of his hopes, the unlettered peasant seems to have been assured that fate had destined him to triumph. The threads, and specks, and globules which destroyed the homogeneity of his glass, speedily learned the processes of his teacher, and discovered the theory of manipulation, of which Guinand knew only the results. Experience added daily to his knowledge. He detected imperfections even in the crown glass, which had hitherto been considered faultless, and reconstructing his furnaces, and directing his whole mind to the work, he succeeded in bringing the manufacture of flint and crown glass to the highest perfection. Thus supplied with the finest materials of his art, he studied their refractive and dispersive powers, and by his grand discovery of the fixed lines in the spectrum, he arrived at methods of constructing achromatic telescopes which no other artist had possessed. In these laborious researches he was patronized by Maximilian Joseph, king of Bavaria, and had not an insidious disease, aggravated in its amount, and accelerated in its course, by corpóreal and mental labor, carried him off in the prime of life, he would long before this have astonished Europe with the production of Achromatic object glasses of eighteen inches in diameter. The practical results of these discover-erally sold at prime cost for £950. The ies and improvements we shall now briefly other telescope, 18 feet in focal length, was detail. In 1820, several years after Gui- made for the King of Bavaria, at the price nand had returned to his native village, he of £2720. Messrs. Merz and Mahler, of was honored with a visit from M. Lere- Munich, have more recently executed, for bours, a celebrated Parisian optician, who the Russian Observatory of Pulkova, an had heard of the success of his processes. Achromatic Telescope, whose object glass Lerebours purchased all his glass, and left has 15 inches of effective aperture, and a orders for more, and M. Cauchoix, another focal length of 22 feet. Frauenhofer was skilful Parisian artist, procured from him willing to undertake an achromatic telelarge discs of glass. With the glass ob- scope, with an object-glass 18 inches in ditained from Guinand, M. Cauchoix exe-ameter, and which, according to his own cuted two object glasses, one nearly twelve estimate, would have cost about £9200; inches in diameter, with a focal length of but no wealthy amateur of science, and no twenty feet, and the other thirteen and a sovereign, desirous of immortalizing his third inches in diameter, with a focal length of twenty-five feet three inches. The first of these object glasses was mounted at the Royal Observatory in Paris; but though the French government had prepared a stand for it at the expense of £500, they grudged the sum that was necessary to acquire the object glass. Sir James South, who happened to be in Paris, and whose liberality and scientific acquirements are well known to our readers, saw the value of this object glass, and purchased it for his observatory at Kensington. The other object glass, thirteen and a third inches in diameter, was purchased by a young Irish gentleman, then in Paris, Mr. Edward Cooper, M. P., and the telescope to which it belongs has been erected at Marckrea Castle, in the county of Sligo, with an equatorial mounting by Mr. Grubb of Dublin. This splendid instrument has been recently removed to Nice, where, we regret to say, Mr. Cooper has been obliged to reside for the benefit of his health. The telescopes executed by Frauenhofer, and by his successors at Munich, have been especially distinguished not only by their excellence as optical instruments for the purposes of general observation, but for the ingenuity and value of the micrometers and other appendages, which are indispensable in astronomical investigations. Before his death, Frauenhofer executed two fine instruments, one with an achromatic object glass nearly 10 inches (9,2,) in diameter, and another 12 inches in diameter. The first of these was ordered by the Emperor of Russia, for the observatory at Dorpat in Livonia, and is the instrument with which M. Struve has made his fine observations on double stars. Its focal length is 13 feet. It has four eye-glasses, with magnifying powers, varying form 175 to 700, and its price was £1300, though it was lib own name, and extending this branch of knowledge, has been induced to give an order for such an instrument. If the Achromatic Telescope, therefore, has reached its climax, it is because the power of art has outstripped the liberality of wealth, and because the intellectual desires of our species have ceased to be commensurate with their intellectual capacity. If astronomy, then, is to be advanced by means of this class of instruments, some new mode must be devised of constructing them in a cheaper and more effective form. Regarding it therefore as impracticable to construct an achromatic object glass more than 15 inches in diameter, for such a sum as we can reasonably expect to command, may we not effect this object by composing the lens of different portions of glass made out of the same pot, and therefore having the same refractive and dispersive powers. This idea, which we suggested many years ago, may be effected in two ways, either by grinding or polishing the different portions of the lens separately, and fixing them in their proper place by mechanical means, or by uniting them together with a cement of the same expansibility by heat as the glass itself. Or we may unite into one telescope two or more object glasses, either of the same or of different focal lengths;-the superposition of the images being effected by reflectors, and in the case of object glasses of unequal focal lengths, the equality in the images being produced by a second and smaller object glass, convex or concave as the case requires.* * Since this article was written, we have learned that M. Bontemps of Paris has acquired M. Guinand's art of making large discs of flint glass, and that he has actually offered to produce perand Co. of Birmingham have taken out a patent for M. Bontemps' process, and are prepared to fect discs three feet in diameter! Messrs. Chance But whether the Achromatic Telescope | his residence from Dorpat to Pulkova; and be destined or not to attain greater magni- the catalogue, containing upwards of 3000 tude and perfection, it has, in its present double stars, is now about to be published state, done vast service to astronomical by the Imperial Academy of Sciences at science. To two achromatic telescopes, St. Petersburg.* mounted equatorially, the one five feet long, As we have no knowledge of the relawith an object glass 33 inches in diameter, tive distances of the fixed stars, our readers executed by Dollond, and the other seven will doubtless wish to know on what grounds feet long, with an object glass five inches astronomers assume that two stars which in diameter, and executed by Tully, we may be only accidentally in the same line, owe the splendid series of observations or near each other, form a binary system, made in 1821, 22, 23, by Sir John Hers- physically and not merely optically, conchel and Sir James South, on the apparent distances and positions of 380 double and triple stars; and it was by the same instruments that Sir James South, in 1823, 24, 25, determined the distances and positions of no fewer than 458 double and triple stars, a task of herculean magnitude, which, had he done nothing else for science, would have immortalized him. His observations were made in a foreign country, at Passy, near Paris, and include about 160 double and triple stars previously undiscovered. nected. Double stars are found in every part of the heavens; but in general, they are less numerous in those places where there are fewer stars, diminishing about the Great Bear, the Dragon, and under the Canes Venatica, and increasing proportionally as we approach the Milky Way. They are very numerous about Lyra, in the Goose, the Fox, and the Arrow, in Perseus, and in Aries. In Struve's Catalogue of 3063 double stars, the double stars in the different classes, or with different degrees of closeness, are as follows: 1st Class, 4th Class, 32 distant, 736 2d Class, 8 distant, 675 3d Class, 16" distant, 659 Total in all 3063 While the astronomy of Binary and Ternary systems were thus rapidly advancing in England, the liberality of the Emperor of Russia was providing for his observatory of Dorpat the magnificent achromatic telescope of Frauenhofer, which we have already mentioned. This fine instrument was, in 1824, placed in the hands of M. Struve, who has pre-eminently distinguish- Now, if these stars were only optically ed himself in this branch of astronomical double, those of the 4th class ought to be inquiry; and in 1837, the Academy of the most numerous. For as the surfaces of Sciences at Petersburg publishedt his micrometrical measures of all the double and multiple stars which he had observed during thirteen years, from 1823 to 1e37, with the great telescope of Frauenhofer. In order to give these results their full value, Struve undertook the determination of the absolute mean places of these stars, that is, of the principal star of each group, by fixed meridional instruments and repeated observations. This great work was begun in 1822, when the great meridian circle of Reichenbach arrived at Dorpat, and was continued till 1838, when Struve changed manufacture discs of all sizes, either of crown or flint glass up to three feet. *Sir John Herschel had, previous to 1829, publi shed, in the Memoirs of the Astronomical Society, three series of observations on double and multiple stars, completing the first thousand of these objects detected with the twenty-feet reflecting telescope. Stellarum duplicium et multiplicium mensuræ micrometricæ, auctore F. GW. STRUVE. 1837. Fol. spheres, as Struve justly reasons, whose radii are 4, 8, 16, 32 seconds (the distances of the stars in the different classes) are as the squares of 1, 2, 4, 8, or as 1, 4, 16, 64, the doctrine of probabilities teaches us that the number of optically double stars of various classes will be as the differences, 1, 3, 12, 48, between the last numbers, and therefore it follows, that out of SIXTY-FOUR stars optically double, there should be only ONE of the 1st class, whereas there are 987! Again, assuming that the 736 double stars of the fourth class are optically double, it will follow, from the preceding ratios, that * Under the title of "Stellarum inerrantium, imprimis compositarum, quæ in Catalogis Dorpatensibus annorum 1820 et 1827 continentur, positiones media ex 22 annorum et 1822 ad 1843 observationibus, in specula Dorpatensi institutis deducate." Astronomische Nachrichten, Altona, 1844, Juli 6. The number of stars which passed in review through Struve's telescope was estimated at 120,000, though his survey extended only to 105° from the pole, or to stars whose meridian altitude exceeded 16010. the different classes should contain the following numbers of optically double stars, viz. 1st Class, 16 2d Class, 3d Class, In all these three Classes, 247 Whereas they contain of double stars, 1st Class, 987 2d Class, 3d Class, sun. square of the distance, is extended to the sesidereal systems. M. Savary has gone still farther, and has pointed out a singularly ingenious method of obtaining an approximate determination of the distances of some of the double stars from our earth or This method, which we cannot pretend to explain without diagrams, consists in determining the difference between the duration of the two halves of the revolution of the lesser star, in an orbit much inclined to the visual ray drawn from the earth to the star, arising from the velocity of light. The semi-revolution performed by the star Hence we may conclude with our author, in describing the half of its orbit, in which that almost all the stars of the first class it advances towards us, must, owing to the are physically double, and likewise those of velocity of light, appear to be performed in the second class, and a very great part of less time than it is in reality, while the duthe third class. M. Struve goes farther, and ration of its semi-revolution in the other maintains that the stars even of the fourth half, while moving from us, must appear class ought to be considered as physically to be augmented. In applying this method, double, and he establishes or rather con- we must of course assume, that the orbit firms this opinion in the following man ner: In all these three Classes, of the star is symmetrical in relation to its major axis, and that there are two points "In the celestial maps of Harding, which in the orbit equidistant from the greater may be considered as perfect, as far as regards star, at which the lesser star moves with the stars of the seventh magnitude, we reckon 10,- same velocity. When the inclination of 229 stars of the first to the seventh magnitude, the orbit, therefore, and its angular extent even to the distance of 15° south of the equa- have been otherwise previously determined, tor. If we apply to this number the doctrine the difference of time between the two of probabilities, we shall obtain the very remarkable result that we ought to find in this semi-revolutions, will afford a basis for apspace but one pair of stars 32 seconds distant proximating to the linear dimensions of from each other. If, then, it be possible that the orbit, and the star's true distance from some one of the double bright stars of the third the earth. and fourth classes are in a manner optically double, all the double stars of the first class, and a great part of those of the fourth ought to be considered physically double, or as forming a particular system of two stars joined together." "-Struve's Report on Double Stars, addressed to Prince Lieven. Such, we were about to say, is all the knowledge of the binary sidereal systems which we have to communicate; but a notice has just appeared of an important discovery by that distinguished astronomer, Professor Bessel of Königsberg, which promises to us the development of new Notwithstanding the number and accura- mysteries, the exhibition of sidereal bodies, cy of the observations which have been which, though invisible to the eye of man, made on these double stars, which really stands revealed to his reason-just as the form binary systems, it is very difficult to concealed loadstone is detected by its at deduce from them any general results in tractions when the magician happens to which the mind can rest with satisfaction. have a philosopher among his audience. Sir John Herschel, and Savary, and Encke, Hitherto it had appeared that the proper have attempted to determine the laws which motions of the fixed stars were uniform, regulate the revolution of the lesser star, arising, as was supposed, from the advanceand to obtain some information respecting ment of the solar system to the constella the distance of these bodies from the earth. tion Hercules; but more accurate observaBy employing only the position of the line tions were still required to give plausibility joining the two stars, Sir John Herschel to this bold hypothesis. The fine observahas arrived at the conclusion that the small- tions now made in our observatories with er star describes an ellipse round the great-fixed meridional instruments, have enabled er star, supposed to be at rest in one of the Professor Bessel to investigate the nature foci of that ellipse, and therefore that the law of gravity, varying inversely as the * Athenæum, August 31st, 1844. and the principal discoveries which they have enabled astronomers to make, our readers will be the better able to appreciate of these motions with an accuracy previously unattainable; and, with this view, he has discussed by a laborious process, his own observations and those of different astrono- the genius, the talent, the patience, and mers since 1753, the epoch of Bradley's the liberality with which an Irish nobleobservations. In this inquiry, he has man has constructed telescopes far transfound that the proper motion of Sirius in cending in magnitude and power all previ right ascension, and that of Procyon in ous instruments, whether they were the declination, deviate very sensibly from uni- result of private wealth, or of royal or naformity. Hence it follows, that these stars tional munificence. That nobleman is must describe orbits in space under the in- Lord Oxmantown, now the Earl of Rosse, fluence of central forces; and following out one of a distinguished group of Irish phithese principles, he has arrived at the con-losophers, who, educated in the same acaclusion, that the apparent motions of these demical institution, now adorn it with their two stars are such as might be produced by genius, and sustain it by their labors. In their revolution about non-luminous centri- the records of modern science there are cal bodies not very remote from the star few brighter names than those of Robinson, itself. Hence they will prove binary sys- Hamilton, Lloyd, and Maccullagh, and in tems, like those of double stars, and differ- the persons of the Earl of Rosse and Lord ing from them only in this, that they have Enniskillen, the aristocracy of Ireland have dark in place of bright partners, to which contributed their contingent to her intelthey perform the functions of revolving lectual chivalry. But to us in a sister land, suns. Sirius and Procyon are, therefore, the land of sober judgment and of serious double stars; and we may indulge the hope faith, genius, however bright, is shorn of that this remarkable fact, deduced only its purest rays, when it seeks and finds but from their motions, may yet be rendered the bubble reputation among the wonders visible by their being more or less eclipsed which it unfolds; and when in search of by the dark planet which controls them. In this case the visible partners will exhibit the phenomena of variable stars, and the law of their variation may enable us to form some conclusion respecting the form and position of their orbits. The phenomena of variable stars have been hitherto ascribed to the rotation of the star about its axis, which may bring into view portions of its disc more or less luminous; but may we not now suppose that stars are rendered variable by the interposition of their non-luminous partners? In like manner we may ascribe the appearance of new stars to their emerging from behind their dark partners, and the disappearance of others to their undergoing a lengthened eclipse from the same non-luminous bodies. There is an obvious difficulty, however, to which the existence of non-luminous bodies is exposed. The revolution of Sirius or Procyon, as suns, round their dark companions, must have the effect of illuminating them, and though their light may not be sufficiently great to become visible with our present telescopes, yet we may hope that the huge instruments which will yet be directed to the heavens may render them visible, and thus add to our knowledge of these remarkable sidereal systems. the richest gems, it has missed the pearl of the greatest price. It is, therefore, a matter of no ordinary satisfaction, that the intellectual energy of Ireland is concentrated in men of like faith with ourselves, who will be found girt for the same contest when the wisdom of this world shall be arrayed against the faith once delivered to the saints. If, in an eloquent address to the British Association at Cork, Dr. Robinson has given expression to his delight, "that so high a problem as the construction of a six feet speculum should have been mastered by one of his countrymen-by one whose attainments are an honor to his rank--an example to his equals—and an instance of the perfect compatibility of the highest intellectual pursuits with the most perfect discharge of the duties of domestic and social life;"-we also may indulge in the pleasing recollection that Lord Oxmantown's earliest plans for improving the reflecting telescope were first given to the world in three communications which were published in a Scottish Journal of Science, and that some of us were the first to recognize their value, and to see looming in the distance that mighty instrument with which we are about to make our readers acquainted. After these preliminary details respect- As the surfaces of all lense and specula ing the construction of gigantic telescopes, are necessarily of a spherical form, they |