FOREIGN LITERATURE, AUGUST, 1850. From the Edinburgh Review. NATIONAL OBSERVATORIES. Astronomical Observations made at the Royal Observatory, Greenwich, in the Year 1847. Under the Direction of GEORGE BIDDELL AIRY, Esq., M.A., Astronomer Royal. an unenclosed waste until the reign of Henry VI., when a charter conveying 200 acres of it was given to Humphry, Duke of Gloster, the king's uncle, and to Eleanor his wife. No one has ever sailed down or up the Thames, and surveyed the stately domes and colonnades of Greenwich Hospital, without admiring the background which the wooded heights of Greenwich Park give to the land- This curious charter (of which a copy is scape, and the contrasting architecture of the now before us) is dated 26th of March, brick towers and minarets of the Royal Ob- 1437.* Perhaps the foundations of Duke servatory, placed on a commanding height in Humphrey's tower still exist; at all events, the prolongation of the middle area of the it is certain that the Observatory is built on Hospital, and thus terminating the vista. the same site, being a position of no inconBut few of these voyagers, we suspect, take siderable strength. It is a kind of peninsula time to consider that the British Navy owes jutting out toward the Thames from the an important part of its efficiency not less to general level of Blackheath and the southern the Observatory than to the Hospital,-that district of the Park, with which it is connectHumanity is interested in the former as welled by a tolerably narrow isthmus, whilst the as in the latter,-that the sovereign who foresaw the ultimate consequence to certain and safe Navigation of a good system of Astronomical observations, was in this instance as wise and patriotic as he who provided a magnificent asylum for the helpless old age of those who had already often owed the preservation of life to the patient vigils of the astronomer. The fortunes of Greenwich Park have been as varied as those of most places the property of the crown in the vicinity of a capital. The manor of East Greenwich was *Deptford was West Greenwich. VOL. XX. NO. IV. *Rot. Patent, 15 Hen. 6., M. 7. As a specimen of the quaint latinity, we quote the following permission:-" Muris petra et calce includere et turrellare, ac quandam Turrim infra Parcum præfirmare, et muros illos kernellare, battellare, et dictum similiter petra et calce de novo construere, edificare, et tam turrim illam sic de novo constructam et edificatam quam dictum manerium sive mansionem ut præmittitur inclusum, firmatum, kernellatum, imbattelatum, et turrellatum, tenere possint sibi et hæredibus suis prædictis in perpetuum," &c. Copied from the original in the Tower. 1 Kernellare, from creneaux, (Fr.) to make battlements for defence. 2 Hence it appears that there must have been some still older structure. 28 ground slopes rapidly in every other direc- | tion from the little table-land occupied by the Observatory. The natural strength of the situation has evidently been increased by lofty retaining walls on the north, south, and west sides-sustaining both the building and a part of the pleasure ground. This gives to the place an air of great seclusion and privacy, as well as apparent strength, not less suitable to its present than to its original destination-freedom from interruption and indiscreet curiosity being an inestimable advantage in an institution dedicated to such purposes in the midst of one of the most public resorts in the neighborhood of the metropolis. Mr. Francis Baily states, on the authority of some MS. notes in a copy of Maskelyne's Observations," that the tower was repaired or rebuilt by Henry VIII. in 1526; "that it was sometimes the habitation of the younger branches of the royal family, sometimes the residence of a favorite mistress, sometimes a prison, and sometimes a place of defence. Mary, fifth daughter of Edward IV., (betrothed to the King of Denmark) died at the Tower in Greenwich Park, in 1482. Henry VIII. visited "a fayre lady whom he loved here. In Queen Elizabeth's time it was called Mirefleur. In 1642, being then called Greenwich Castle, it was thought of so much consequence as a place of strength, that immediate steps were ordered to be taken for securing it. After the Restoration, Charles II., in 1675, pulled down the old tower, and founded on its site the present "Royal Observatory." It should be noticed, that there was a distinct royal residence on the same manor, between Duke Humphrey's Tower and the river, called The Pleasaunce, which was frequented by Queen Elizabeth and other sovereigns. Astronomy is a subject so palpable in its results, and conversant with facts so astounding, yet so plain, that there is scarcely any age or period of the world in which most men have not, at some time or other of their lives, been drawn to it with a strong feeling of interest and awe. Perhaps some readers may be able to sympathize with our juvenile recollections of a time when the towers and walls of Greenwich Observatory seemed to us to enclose a profound yet tempting mystery, which we hardly dared * An accurate map of the grounds and buildings has been constructed and engraved by the present Astronomer Royal. Life of Flamsteed, p. 39, note. hope ever to explore; or when we traversed the weary diameter of Paris to gaze on the Observatory built by Cassini, and directed by Arago, or trod with respect the very stones of the Rue du Bac, at that time inhabited by Laplace. Considering that the practical details of observatories are witnessed by comparatively few persons, and that of those so privileged still fewer can pick up anything like an intelligent idea of what is going on, and how the astronomical paraphernalia they behold are made to yield a knowledge of the facts which they read of in books at home, we have thought that an attempt might be made to make this branch of knowledge accessible to all who have any acquaintance with its elements, and to reveal some of the mysteries of the art and practice of an astronomical observer, to many who may never think of becoming either profound astronomers or practiced observers themselves. We propose, therefore, in the present article, to consider, first, what it is which the practical astronomer professes to determine; secondly, to notice the instruments which he uses in order to make these determinations; and, thirdly, to attempt a sketch of the economy and management of an Observatory, its personnel, as well as its matériel,—which we shall illustrate by a more especial reference to the National Observatory of Greenwich. The two first heads we will make as brief as may serve to a due understanding of our third and principal topic. I. Practical astronomy has two great branches. That to which the telescope may be said to have given birth; and that which is comparatively independent of it. Before the invention of the telescope, Copernicus had announced the true system of the world, namely, that the sun is the centre of a planetary system, of which the earth is one member, with the moon circulating round it; and that the fixed stars are altogether independent, and placed at a vastly greater distance. The periods and comparative distances of all the principal planets were known; as well as the deviation of the orbits of some of them from a circle; and a certain approximation was made to the singularly irregular form of the lunar path; eclipses could be calculated with tolerable accuracy; latitudes and longitudes roughly ascertained; and even such delicate phenoheavenly bodies by refraction, and mena as the apparent displacement of the the general excessively slow motion of the fixed stars relatively to a point altogether imagin ary, termed the equinoctial point, had been | face of the earth, or latitude and longitude. clearly discovered and imperfectly measured. Though the terrestrial and celestial globes But when the telescope gave to man are not only different in their delineations almost a new sense, and enabled him to ex- (as a certain lady of fashion is said to have amine objects at a distance, with the advan-discovered, when she returned her globes to tage of a vast magnifying power, a new de- the maker because they were not a pair), partment of practical astronomy arose. As- but also in their idea or principle, the appatronomers had hitherto only seen the rude rent place of a star on the celestial sphere outline of our own system, and the still ruder may be defined by two angles, called declilandmarks of the starry firmament. The nation and right ascension, corresponding telescope not only revealed thousands, nay accurately to those of latitude and longimillions of bodies, hitherto unseen because tude, which determine the spot on the surinvisible, but it displayed complications of face of the earth occupied (for example) by arrangement and feature, which gave as it New York or Mont Blanc. Whirl a globe were a coloring to the broad natural outlines round its axis, and a pencil approached to with which hitherto the astronomer had to the surface will touch all places having the content himself. The moons of Jupiter and same latitude-all stars having the same Saturn, the rings of the latter, and the vary- declination. Stretch a thread tightly from ing phases of Venus and Mercury were, of pole to pole, and it will meet the position of course, among the first points of telescopic all places on the surface having a common vision—and a glorious insight they gave into longitude, and (on the celestial globe) of all the arrangements of our system. Then the stars having the same right ascension. The actual physiognomy of the moon, the sun, pencil mark will meet the thread but in one and some of the nearer planets, after which point; thus the place is fixed completely by the unaided eye could only vainly strain it-two angles, measured each from the centre self, and desire for more help, opened fresh of the globe along those circles; the zero fields of inquiry. More lately, the indefati-point of reference for right ascension being gable study of the fixed stars and nebulawith the aid of powerful instruments, and especially by the two Herschels-has enlarged so prodigiously the boundaries of our knowledge and of rational and interesting speculation, that it is impossible to overrate the charms of this branch of practical astronomy. It has, however, been so fully considered in a recent article on Sir John Herschel's "Observations of the Cape of Good Hope," that we gladly abstain from further notice of it at present; desiring to concentrate the reader's attention on the department of practical astronomy cultivated alike by the ancients and moderns before and since the invention of the telescope, and which consists in the measurement of space with reference to the places of the heavenly bodies, and the comparison of those places with theory. Whoever would record the positions of the heavenly bodies at any moment, and compare them (as regards their apparent movements relatively to one another) at some future time, must do so by referring them to certain lines or directions, which may be regarded as fixed and known. The easiest reference is found by a comparison with that which is familiarly used to determine the position of places on the sur * Ed. Rev. vol, lxxxviii, determined by a particular point called the Vernal Equinox, or the first point of Aries: Whilst on the terrestrial globe the longitudes are measured from the meridian of Greenwich. If we imagine the eye placed in the centre of a celestial globe, and the fictitious stars to be each pierced with holes through its surface, that eye would, if the globe were properly turned, see each star in the heavens through its appropriate hole. Such, in fact, is all the information which a celestial globe is intended to convey-the idea of direction, or apparent place-not at all that of distance. The moving lights of heavensun and moon, planets and comets-change, from day to day and from hour to hour, their seeming place. To be able to define accurately their apparent place at a given instant, is the first aim of the practical astronomer. This is done by ascertaining their declinations and right ascensions—the former being the apparent angular distance of a star from the celestial equator; the latter, the angle formed by the meridian (or line traced by the thread stretched from pole to pole and touching its place) with some other meridian, drawn arbitrarily or otherwise among the stars; just as in geography we, in Britain, refer the longitude of places to that of Greenwich. The astronomer, having traced the motions of an erratic star or planet 436 NATIONAL OBSERVATORIES. on the apparent surface of the sphere, pos- | tation. lax. The greatest amount of parallax which the moon could possibly have, would be, if we imagine a spectator placed at either pole The displacement to each, of the earth. compared to the moon's position as seen from the earth's centre, would be about a degree, or the whole angle under which the earth's diameter (8000 miles) is seen at the moon, is two degrees. But though our voluntary peregrinations be confined to narrow limits-although our globe is but a speck in space, and although a voyage from pole to pole would be, by the shortest route, but some paltry 12,000 miles, In the same manner the parallax of the planet Mars and the planet Venus, when nearest the earth-and even the distance of the sun-may be ascertained by observations made, under favorable circumstances, at different parts of the earth's surface; and But the power of tracing with accuracy since we are personally confined, by a phythe places of the heavenly bodies on the ap- sical necessity, to the surface of our globe, we can only make the best of the limits of parent vault of the sky, and therefore with reference to one another, carries us a step voluntary excursion which Nature and Profurther, even to the measurement of the im-vidence have assigned to us. passable and seemingly illimitable spaces We cannot, inwhich divide them from us. deed, apply a rod or chain to measure the moon's distance, but we may do as those surveyors did who measured the height of Mont Blanc ere it had been ascended. Our fortunately for astronomy, we make an anearth, to be sure, is very small, compared nual tour in the course of our orbital revolution round the sun, which carries us to two with the spaces which separate from us even the nearest of the heavenly bodies, and a points of space nearly 200 millions of English miles apart. Seated on this comfortable mere mathematical point as compared to the It is, however, railway carriage called the globe, we are distances of the fixed stars. so large that the moon, for instance, is very actually tearing through space at the rate of visibly displaced as we regard her from one nineteen miles per second, or 67,000 miles The direction an hour; and the distance and position of part of the earth or another. of the earth's axis is a perfectly well-ascer- the sun being known at any time by obsertained line. If we look in its direction from vation, the actual distance between the points any part of the earth's surface, the whole of space occupied by us, the traveling specfirmament appears to revolve round it by the tators, on any two days, is accurately known. diurnal movement; in this direction, then, For instance, on the longest and on the a telescope may be accurately pointed. Let shortest day, our positions are, as we have said, nearly 200,000,000 miles apart. Of this telescope next be turned on the moon: course this annual trip makes a vast change the angle which the telescope describes may be called the moon's north (or south) polar in the celestial scenery of the bodies nearest distance. If this experiment were perform to us. The other planets, if they did not move themselves, would appear to do so by ed simultaneously at Greenwich and at the Cape of Good Hope, the moon would appear our own relative motion ;-as it is, they have further north from the latter than from the apparent movements, resulting from their former station; for the same reason that if own, as well as from our earth's orbital moBut the most extraordinary fact is we go from the lower to the upper window tions. of a house, the neighboring chimney, which this: that, notwithstanding the vast space the scenery of year, in the former case seemed to touch the dis- which separates the position of our earth at tant weathercock, now falls far beneath it. opposite seasons of the Thus also the moon, when she passes centri- the fixed stars is noways sensibly distorted cally over a fixed star, as viewed by a spec- by our change of place. The vast distance from the earth to the sun is seen from the tator near the equator, will leave it unenearest fixed star under an angle probably clipsed to an astronomer in the Arctic or Antarctic Seas, passing to the south of it in not exceeding one second-which is about one two-thousandth of that which the sun's or the one case, and to the north in the other. This seeming displacement is called paral-moon's disc subtends! This is called the |