Popular Science Monthly/Volume 6/March 1875/The English Observatories
|THE ENGLISH OBSERVATORIES.|
TRANSLATED FROM THE FRENCH, BY EMMA M. CONVERSE.
THE English Astronomer Royal has in his possession a very curious collection of papers, including letters that have been addressed to him by persons of every condition, in which they ask his price for casting a horoscope. In spite of such simplicity, England is one of the countries where the taste for practical astronomy is very widely diffused, and also the one where the greatest number of public and private observatories is found. Establishments of the last category abound in the United Kingdom, and attest by their number and importance the popularity of the most sublime of the sciences. There are at the present time forty observatories in the British Isles, and fifteen in the English colonies; this is a quarter of the total number that is found in the whole globe, for there are in Europe something like a hundred and twenty establishments meriting this name, and about two hundred in the entire world.
The Royal Observatory of Greenwich takes the lead, for its past labors as well as for its present position, over the other establishments of the same kind possessed by the English. It was founded in 1675, three years after the Observatory of Paris. Charles II. chose a locality for the edifice on a hill commanding the Thames and the passage of vessels, so that his astronomers would be able, by the study of the movements of the heavens, to direct the distant courses of ships over the surface of the sea. The interest of the marine was in reality the controlling motive that determined the foundation of this establishment. The ordinance of 1673 decrees that "the astronomer royal shall devote his time to rectifying the tables of celestial bodies and the positions of the fixed stars in order to obtain the means of finding the longitude at sea." To indicate in a precise manner the position of the stars, to predict with certainty the course of the moon in relation to these fixed data, is the great work reserved for sedentary astronomy in the progressive improvement of the art of navigation. The heavens constitute, as it were, a revolving dial-plate, on which the moon, making her way from star to star, marks for the navigator the absolute time, the time at Greenwich, while the height of the sun above the horizon furnishes the time of the place where he chances to be, and it is by comparison that he finds out his longitude, that is, the meridian under which he is passing. The regular and long-continued observation of the fixed stars, sun and moon, was then traditional in this illustrious establishment of Greenwich, which has had for directors such astronomers as Flamsteed, Halley, Bradley, Maskelyne, Pond, and George-Biddell Airy, who has been director since 1835. It is there that the first foundation of modern astronomy has been laid, that is to say, the astronomy of precision. Far from seeking an easily-obtained glory in the discoveries, more brilliant than really important, that strike the mind of the crowd, the Greenwich astronomers have invariably applied themselves to the laborious investigation of those minutiæ upon which the edifice of science reposes, and where often the trace of great unknown laws is revealed.
Flamsteed, the first director, made all his observations by the aid of a sextant and a mural arc, which were his own private property; the first reports were printed without his consent, and were so imperfect that he burned all of the first edition that had not been distributed, in order to have a new one made under his own inspection, and at his own expense. His successor, Halley, found the building stripped of all the apparatus; the heirs of Flamsteed had carried away every thing. This was perhaps a piece of good fortune for science, as Halley was obliged to procure new instruments, and in 1721 he caused a transit instrument to be constructed. This became the prime mover in astronomical researches, and the observations that Bradley made with its aid are the points of departure for our catalogues of the stars, for they permit us to appreciate with certainty the changes that have been brought about by time in the relative situation of the fixed stars, and consequently to reduce the observations of each day to a given epoch.
When Bradley was called, in 1742, to the direction of the Greenwich Observatory, he was already celebrated by discoveries of the first order, and known as an accomplished observer. It has always been thus; the scientific men who have been successively placed at the head of this establishment were, at the time of their nomination, perfectly familiar with the routine of their profession. They have all in like manner devoted themselves with special zeal to the improvement of instruments, and to the perfection of methods; the result has been that happy stability in principles, that continuity in labors, which is the first condition for the success of researches destined to reveal to us the slow variations that are going on in the system of the world.
Greenwich is so much the more free to concentrate all its efforts upon the astronomy of precision, as numerous observatories around it, erected by opulent universities, or due to the enlightened initiative of some rich proprietors and the great merchants of the city, share the labors that the central establishment leaves out of its programme. Oxford possesses an important observatory, founded in 1771, by the aid of a legacy of Dr. Radcliffe, now under the direction of the Rev. Robert Main, and the university has decided to found a second one. Cambridge has the Trinity Observatory, that Mr. Airy directed from 1827 to 1835, and which is now intrusted to Mr. Adams; the University of Durham possesses also a very well-organized observatory, founded by the city thirty years since.
The observatory of Liverpool was created specially for the study of marine chronometers. There, the numerous ships that enter the port of the Mersey can have their timepieces regulated. The "chronometrical chamber" is a vast sweating-room, warmed by steam; each of the hundred marine-watches that the observatory can study at the same time is inclosed in a glass case, in which the air is still heated by a gas-burner, supplied with a regulator, in order to be able to carry the temperature successively from 10° to 18° and to 27° Centigrade. After having tried in this chamber the chronometers that have been intrusted to him by the marine, the observer returns them with the table of their movements.
The Edinburgh Observatory was built in 1818, on Calton Hill, situated northeast of the city, where there has been in existence since the last century an old tower destined for observations of all kinds. The foundation of this establishment was due in the beginning to an astronomical society, organized for this purpose in the ancient capital of Scotland; but, not being able to pay for the instruments Ordered, nor to appoint astronomers, it was decided in 1834 to yield the observatory to the Government. The first "astronomer royal for Scotland," charged with the direction of the Edinburgh Observatory, was Henderson, who returned there from the Cape of Good Hope. His successor, Mr. Piazzi Smyth, has established on Calton Hill a time-gun, a cannon of twenty pounds, which, fired by means of an electric current at one o'clock in the afternoon, signals the time to the mariners, and gives them the means of regulating their chronometers. For some years, the signal was given by a time-ball, as at Greenwich, Glasgow, and elsewhere; this is a great ball suspended from an elevated standard, and made to fall at a precise moment by means of electrical mechanism. Unfortunately, the Edinburgh Observatory is a victim to the centralizing tendencies that rule now in England; its budget is very much reduced, and it is hardly permitted to vegetate. The Royal Observatory of Dublin, founded in 1774, and now under the direction of Mr. Brunnow, Astronomer Royal for Ireland, is not in much better condition. On the contrary, the observatory of the University of Glasgow, and the Ecclesiastical Observatory of Armagh, founded by the Irish primate, are well operated, and render real service.
The celebrated establishment of Kew, which depends at the same time upon the British Association for the Advancement of Science, and upon the Royal Society of London, is the central meteorological observatory of England; new apparatus and new methods are studied there; besides, astronomy, so called, increases its resources by the application of photography to the study of celestial phenomena. Mr. Warren de La Rue has here inaugurated his process of solar observation by the aid of photoheliography, the first decisive step in the eminently fruitful path, the earliest idea of which is due to two French scientists, MM. Fizeau and Léon Foucault.
Mr. Warren de La Rue, who very recently presided over the Astronomical Society of London, is the largest paper-manufacturer in England, and a noteworthy improvement in photographic paper is due to him. He had since 1852 a small observatory at his house in Canonbury, at London, where he undertook his first essays in celestial photography. Five years later, he transported it to the village of Cranford, at the west of London, and since then he has divided his leisure time between this residence, where he studied the moon, and Kew, where solar investigations were carried on under his direction. At the same time, he has given his attention to the improvement of optical instruments. He made himself the mirror of a telescope that he used in most of his observations. But these labors injured his eyesight, and, despairing of being able any longer to make observations himself, he has presented his magnificent collection of instruments to the University of Oxford.
Rich merchants and opulent manufacturers have done themselves honor in founding a series of small observatories, that by their useful labors have assisted the progress of science. That of Mr. Bishop, for instance, erected at first near Regent's Park, then transported to Twickenham, where Messrs. Hind and Pogson discovered so many asteroids; that of Mr. Barclay, the brewer, at Leyton, near London; that of Mr. Lassell, near Liverpool. Like the elder Herschel and Lord Rosse, Mr. Lassell made with his own hands the mirrors of his telescopes, by whose aid he discovered the satellites of Neptune, Saturn, and Uranus. The last telescope of his construction had four feet of aperture, and was thirty-seven feet long. The impure atmosphere of a manufacturing centre like Liverpool prevented the utilization of the whole power of an instrument of such dimensions. Mr. Lassell resolved to transport it to Malta, where he had already installed, ten years before, a telescope of twenty feet. From 1862 to 1865 the new telescope was constantly turned toward the sky, and employed in scrutinizing its depths. Mr. Lassell discovered more than 600 new nebulæ, whose feeble light, under the humid sky of the North, had escaped the investigations of William Herschel and Lord Rosse. Mr. Lassell is now occupied in the publication of the numerous materials gathered during his two sojourns at Malta.
What an example and what instruction may be found in the long career of William Herschel, who passed half a century in sounding the mysterious depths of the universe! The son of a poor musician—burdened with a numerous family—he embraced the paternal profession, and went, when twenty years old, to try his fortune in England. He barely earned a living by giving music-lessons and directing concerts or oratorios, when he was appointed organist at Halifax, then soon after filled the same office in Bath. He passed his leisure time in studying works on astronomy. As he was not rich enough to purchase a telescope, he went to work, and, after a thousand attempts, succeeded in making, in 1774, a five-foot reflector, with which he observed Saturn's ring. Encouraged by this first success, the organist of Bath entered upon the construction of mirrors of seven feet, then ten, and twenty feet of focus. He made more than 200 before attaining the desired perfection, and the total number of mirrors that he worked upon in succession exceeded 400. In 1781 he had the good fortune to discover the planet Uranus, which extended the boundary of the solar system. He was then forty-three years old. This discovery drew upon him the attention of Europe; George III. granted him a pension and a dwelling at Slough, near Windsor Castle. He then commenced that methodical review of the heavens, by means of which he discovered more than 2,000 nebulæ, and suggested so many new views of the universe. The greatest part of his labor was executed with instruments of moderate dimensions; he rarely used the great telescope of forty feet, the mirror of which was easily tarnished by the action of the moisture of the night; he used it, however, in the discovery of the sixth satellite of Saturn. William Herschel died in 1822; the year before his death, at the age of eighty-three, he communicated his last paper to the Astronomical Society of London, which, since its foundation, had chosen him for president. In all his researches he was assisted by his sister Caroline, who had lived with him ever since she was twenty-two years old, and who aided him in his observations as well as in his calculations. In this way he was able to astonish the scientific world by the rapidity with which his publications succeeded each other. Caroline Herschel died at Hanover, her native city, in 1849, at the age of ninety-eight. Sir John Herschel, the only son of the great astronomer, worthily continued these illustrious traditions. He resumed and completed the exploration of the heavens commenced by his father, at first at Slough, then at the Cape of Good Hope, where he transported a telescope of twenty feet. He died in 1871, after having contributed, by labors of the highest order, to the progress of science. One of his sons, Alexander Herschel, is equally devoted to astronomical pursuits.
The gigantic telescope of Lord Rosse, which was finished in 1845, the same year when the noble lord was elected representative peer of Ireland, is fifty-five feet in length, and has six feet of aperture. The mirror weighs over four tons, the tube seven tons, and the total weight exceeds eleven tons. The Leviathan, as this giant telescope is called, is suspended between two stone walls at Birr Castle, the hereditary residence of Lord Rosse, in King's County, Ireland. When, in 1826, the young Lord Oxmantown—the title that he then bore—turned his attention toward practical astronomy, there was no constructor capable of furnishing instruments such as he desired. William Herschel had kept the secret of the alloy he used for his mirrors, and the process by which he constructed them. James Short, the greatest constructor of the eighteenth century, so skillful in casting and polishing mirrors, had burned and destroyed before his death his whole stock of tools, in order to remain without a rival. Every thing was then to be discovered anew, and it took Lord Rosse twenty years before he attained the construction of a mirror by means of which he could sound the depths of space and resolve into a mass of stars the most of the nebulae toward which he directed his gigantic instrument. All the nebulæ, however, are not resolvable; some of them are decidedly agglomerations of cosmical matter not yet condensed. Lord Rosse was the first to demonstrate that the great nebula of Orion, one of the finest in the heavens that belongs to the last category, has within a few years changed its appearance in consequence of the concentration of the matter of which it is formed. This celebrated observer died in 1867; his son worthily continues the labors commenced by the father with such brilliant success.
Lord Rosse preferred mirrors to objectives, on account of the difficulty that attends the manufacture of objectives of large dimensions. But great improvements have since been made; Mr. Clark, an American, constructed in 1862 a powerful instrument, with an object-glass of eighteen and a half inches of aperture. Messrs. Cooke & Son, celebrated constructors of York, finished in 1868 an equatorial of twenty-five inches of aperture, and twenty-nine feet of focal length. The telescope of this gigantic apparatus is mounted on an iron column 350 feet high, and weighs nearly ten tons. This equatorial was constructed for Mr. Newall, proprietor of the submarine cable-works at Gateshead, near Newcastle; it is destined for the island of Madeira, where it will be installed at the same time with a meridian circle of very large dimensions. Under a sky of exceptional transparency these fine instruments will serve for important researches in the hands of an experienced astronomer, Mr. Marth, the former assistant of Mr. Lassell.
The question of the constitution of nebulæ entered upon a new phase by the appearance of spectrum analysis among the methods applicable to the study of celestial bodies. Since 1869, Messrs. Huggins and Miller have concentrated all their efforts upon this department of research. They have discovered that the unresolvable nebulæ are masses of incandescent gas—they are suns in process of formation; while the resolvable nebulæ are masses of solid matter, hosts of suns already formed. It has also been established by the aid of the spectroscope that comets have a light of their own independent of that which comes from the sun, and is reflected by these wandering stars. These discoveries will give to the little observatory of Upper Tulse Hill an honorable mention in the history of astronomy.
On his side, Mr. Norman Lockyer, at Hampstead, devotes himself to the spectroscopic study of the sun. He sought for a long time to discover a process for observing in a regular manner the rosy protuberances on the solar border, which had thus far been seen only during total eclipses. Hoping that the spectroscope would betray the presence of the red flames on the contour of the star at ordinary times, Mr. Lockyer constructed an apparatus of several prisms, and in October, 1868, succeeded in discovering the traces of a protuberance in the spectrum of the solar border. Two months previous, M. Janssen, a French astronomer, who went to India to observe the total eclipse of the 19th of August, was in possession of an analogous method for the study of protuberances, but the announcement of his discovery reached Europe on the very day when Mr. Lockyer announced his own to the scientific world. By enlarging the slit of the spectroscope, the red flames can be seen directly, and the rapid changes followed. Astronomers now draw them at any time. Two years since, Mr. Lockyer succeeded in producing artificial eclipses of the sun by the interposition of a copper disk, which plays the rôle of the moon in eclipses, and he thus obtained several drawings of the solar atmosphere with all its minute details.
Mr. Carrington, at Redhill, has chosen another specialty; he has devoted eight years to a long series of observations of solar spots, which have led to remarkable conclusions relative to the constitution of the sun: the unequal velocity of rotation of the different regions of the solar globe would prove the existence of immense currents in the atmosphere of this star. The observatory of Mr. Isaac Fletcher, at Tarn-Bank, Cumberland, was created for the systematic study of double stars, a study which had also for many years occupied the attention of Admiral Smyth, at the observatory of Hartwell, where he was installed by his friend Dr. Lee. During the last year, one of the rich proprietors of Scotland, Lord Lindsay, founded a splendid observatory at Dun-Echt, for the study of Jupiter's satellites, which Mr. Airy had recommended as the best means for obtaining a knowledge of the mass of that planet. At the same time that he installed his instruments, Lord Lindsay organized at great expense—estimated at $80,000—an expedition to observe at Mauritius the transit of Venus, which took place on the 8th of December, 1874.
This division of labor into numerous specialties is very important for the progress of general science. "Then only," said Bacon, "men will begin to know their strength—when no more all will wish to do the same thing, but the one this, and the other that." The application of photography and spectroscopy to the study of celestial bodies by independent astronomers opens to physical astronomy an entirely new horizon, and promises to this branch a most rapid development. At the same time, it is clear that private establishments cannot be relied upon for the extended researches that demand the continuous labor of many generations of observers. The creation of a public observatory, assured of a permanent existence, and exclusively devoted to researches in physical astronomy, appeared then desirable and expedient. This chasm has just been filled by the foundation of the Oxford Observatory, for the construction of which the senate of that powerful university voted last year considerable funds, and to which Mr. Warren de La Rue presented all his instruments, and especially his famous reflector and his machine for working and polishing mirrors.
The British Association for the Advancement of Science, and the Royal Astronomical Society have exerted a happy influence upon the development of the observatories as well as other English scientific institutions, by creating a tie between learned men led by the same aspirations, in provoking a generous emulation, and in stimulating private enterprise by great examples. By its monthly bulletin, the Monthly Notices, the Astronomical Society assures to the useful efforts of amateurs that publicity which is the most powerful incentive to a disinterested devotion.
The numerous and vast colonies that compose the British Empire have not remained, in this respect, behind the mother-country. British India possesses several observatories, of which the first was founded in 1819, at Madras, by the East India Company. In 1841, the King of Oude, still independent at that epoch, erected a rival establishment at Lucknow, and installed there the astronomer Wilcox, with three native assistants. Eight years after, Wilcox having died, the observatory was suppressed, the registers of observation were eaten by the white ants, and the instruments were destroyed during the war that ended by the annexation of Oude. The Rajah of Travancore founded, on the Malabar coast, the observatory of Trevandérem, which has furnished specially good meteorological and magnetic observations. Finally, there exists at Madras a private observatory, belonging to Mr. Burton Powell.
The Cape of Good Hope was an astronomical station long before a permanent observatory was thought of. From 1751 to 1753 the celebrated Abbé do LaCaille prepared his catalogue of the stars of the southern heavens, at the same time that he measured a meridional arc, and that he determined with Lalande, who had been sent to Berlin, the parallax of the moon, by means of a series of simultaneous observations. The immense labors accomplished by La Caille, in his short abode at the Cape, are so much the more worthy of praise as he had to struggle against a climate unfavorable for observation, for in this latitude there are only two months when the days are calm and serene; during the rest of the year the weather is variable, or a violent south wind fills the air with dust, and deprives it of its transparency. In spite of these inconveniences, the Cape is from its geographical situation one of the best stations for the study of the southern heavens, without taking into the account that the necessities of navigation demand the maintenance of an observatory in these regions. But it was not till 1820 that the English Admiralty decided upon the foundation of an observatory at the Cape, which should be constructed upon the model of that of Greenwich. The first director was the Rev. Fearon Fallows, who began regular observations in 1829; but, soon left alone by the departure of his assistant, he was obliged to avail himself of the assistance of his wife, who observed with the mural circle, while he made use of the transit instrument. Fallows died in 1831, and was succeeded by Henderson, to whom Sir Thomas Maclear succeeded in 1834. Better provided with instruments and personnel than his predecessor, Mr. Maclear resumed the geodesic operations of La Caille, and measured anew, with the superior means at his command, a meridian arc more extended than the former. Among the other works of the establishment, noteworthy mention must be made of numerous cometic observations. Mr. Maclear resigned his office in 1870, and was replaced by a Greenwich astronomer, Mr. Stone. It should be mentioned here that, outside of the Royal Observatory, Sir John Herschel prepared, from 1833 to 1838, at the Cape of Good Hope, his celebrated catalogue of the nebulae and double stars of the southern heavens, by the aid of a telescope and an equatorial which he had brought with him.
Since the abode of La Caille at the Cape, no serious attempt had been made to add to our knowledge of the southern half of the heavens, when, in 1821, Sir Thomas Brisbane, then governor of the colony of New South Wales, resolved to supply the want at his own expense. He founded three observatories, one at Makerstown, where Mr. Allen Brown, who has since become the astronomer of the Rajah of Travancore, began a series of meteorological and magnetic observations, the two others at Brisbane and at Paramatta near Sydney. Of the last two, only that of Paramatta was utilized; the astronomers Rumker and Dunlop prepared there precious catalogues of stars mostly invisible in our hemisphere. Abandoned after the death of Dunlop, this establishment was suppressed in 1855, and replaced by the observatory of Sydney, that the government of New South Wales caused to be constructed at its own expense to satisfy the complaints of the mariners, who found in these regions no means for regulating their chronometers. Already, two years before, the rapid increase of navigation between Europe and Australia in consequence of the discovery of the gold-mines had led the government of the colony of Victoria to found an observatory at Melbourne, which, under the intelligent direction of Mr. Ellery, quickly took rank among the most active establishments. Melbourne has possessed since 1870 a telescope of colossal dimensions. The tube and the mirror, which is four feet in diameter, weigh together nearly nine tons, and the clockwork movement that regulates this immense machine is of such precision that the wire of the micrometer follows a fixed star for more than an hour. As a precautionary measure, two four-feet mirrors were sent from London instead of one; unfortunately, they were both injured in the passage, it was necessary to repolish them, and, in spite of the impatience and bad humor of the inhabitants of Melbourne, all the results promised from this great telescope have not yet been attained. Instruments of this kind are so much the more delicate as their dimensions are increased, and they demand long practice before being used with success. At present the greater part of the work of the Melbourne establishment is carried on with the ordinary implements of observatories. Mr. Ellery arranged with the astronomers at Sydney and at the Cape for undertaking a grand review of the southern heavens, which were divided into zones, and the three stations shared the systematic exploration. A large portion of these observations has been already published.
The rapid picture we have sketched will give an idea of the extraordinary flight practical astronomy has taken not only on the soil of the British Isles, but upon every point of the globe where the Anglo-Saxon race has planted its colonies. The necessities of navigation have been the prominent motive for the creation of some of the most important English observatories; but the volunteers in science have also done no inconsiderable portion of the common work. The landed aristocracy, the higher branches of trade, the arts and manufactures, hold the honor of being united with the professional men of science, or at least of coöperating in their labors, by an enlightened munificence. Can a better use be made of fortune or leisure? It has been said concerning the organization of the Greenwich Observatory that the essentially practical and utilitarian spirit of the English is manifested also in science, since all the labor in Greenwich is directed toward a special purpose, the incessant improvement of that portion of astronomy that renders so great service to navigation. However, in seeing that varied activity displayed in the numerous observatories of Great Britain, and including in its sphere every branch of celestial science, must it not be granted that something else is developed besides a tendency to the positive or the research of applications immediately useful?
It is worthy of note that the efforts of amateurs are particularly directed toward the realization of instruments of unusual dimensions, destined to sound the depths of the firmament. But the construction of mirrors or object-glasses of very great diameter is of fundamental interest for the progress of physical astronomy. Not only is the brightness of images proportioned to the aperture, that is, to the diameter of the instrument, but the optical power, or the faculty of separating two luminous points closely united, increases also in a direct ratio with the aperture. According to Léon Foucault, an aperture of at least thirty-nine inches is required to distinguish two points from each other whose apparent distance is equal to the tenth of a second of an arc. The two Herschels, Lord Rosse, Mr. Lassell, finally the commission that had charge of the construction of the Melbourne telescope, gave the preference to telescopes with a metallic mirror; is this preference justifiable? The question admits of doubt. The mirrors of silvered glass in which Léon Foucault attained so great perfection reflect a larger portion of light than metal mirrors; according to the experience of Mr. Wolf, a telescope with a silvered mirror reflects 80 per cent, of the incident light, while with metallic mirrors only 40 per cent, can be utilized. Besides, glass mirrors are lighter, and it is easy to silver them anew when the surface is tarnished. Metal mirrors need to be frequently repolished, which is no inconsiderable work; the experience at Melbourne affords an illustration of this fact. It is then with good reason that telescopes of the Foucault system are preferred in France. Finally, to sum up every thing, the future is perhaps not for great mirrors, but for great object-glasses. Indeed, with an equal aperture, a refracting telescope furnished with a good object-glass far surpasses a reflecting telescope; the great refractors of Dorpat and Pultowa rival reflectors of a double or triple diameter. We have already seen that a refractor of twenty-five inches aperture has been completed by Messrs. Cooke. The Observatory of Paris has possessed since 1855 a disk of flint-glass and one of crown-glass whose dimensions are sufficient to make an object-glass of nearly thirty inches in diameter, and in 1868 the Government voted $80,000 for the construction of a refractor which should be furnished with this object-glass and for that of a reflector with nearly four feet aperture. The mirror of the reflector, the work of which was intrusted to Mr. Martin, is almost finished; the cutting of the object-glass will be immediately commenced. This will be the most powerful glass that has yet been undertaken, and this time it is France that will take the precedence of other nations. It is hoped that this will not be the only effort attempted for the purpose of making practical astronomy flourish among us with a splendor worthy of a glorious past.