SHORT ARTICLES.-Thom, the Sculptor; The Bishop's Leddy, 411.-Rest, 413.-Safety Valve of Church; Grass on Railroads; Wire Lath, 424.-Spiritual Intoxication, 427.-Remonstrance with Emerson; A Dutch Byron; Wonders of Steam, 430.-New Books, 431.

Or all the Periodical Journals devoted to literature and science which abound in Europe and in this country, this has appeared to me the most useful. It contains indeed the exposition only of the current literature of the English language, but this, by its immense extent and comprehension, includes a portraiture of the human mind in the utmost expansion of the present age. J. Q. ADAMS

LITTELL'S LIVING AGE.-No. 316.-8 JUNE, 1850.

5. Description de l'Observatoire Central de Poulkova. Par F. G. W. STRUVE. St. Petersbourg, 1845. Fol.

6. A Cycle of Celestial Objects observed, reduced, and discussed. By Captain WM. HENRY SMYTH, R. N., &c. 2 vols. 8vo.

1844.

From the Edinburgh Review. before us) is dated 26th March, 1437.* Perhaps 1. Astronomical Observations made at the Royal Ob- the foundations of Duke Humphry's tower still servatory, Greenwich, in the Year 1847. Under exist; at all events, it is certain that the observatory the Direction of GEORGE BIDDELL AIRY, Esq., is built on the same site, being a position of no M. A., Astronomer Royal. 2. Magnetical and Meteorological Observations made inconsiderable strength. It is a kind of peninsula at the Royal Observatory, Greenwich, in the jutting out towards the Thames from the general Year 1847. Under the Direction of GEORGE level of Blackheath and the southern district of the BIDDELL AIRY, Esq., M. A., Astronomer park, with which it is connected by a tolerably Royal. narrow isthmus, whilst the ground slopes rapidly 3. Reduction of Observations of the Planets made at in every other direction from the little table-land the Royal Observatory, Greenwich, from 1750 to 1830. Computed by Order of the Lords occupied by the observatory. The natural strength Commissioners of the Treasury, under the of the situation has evidently been increased by Superintendence of GEORGE BIDDELL AIRY, lofty retaining walls on the north, south, and west Esq., M. A., Astronomer Royal. 4to. 1845. sides-sustaining both the building and a part of 4. Reduction of Observations of the Moon, from 1750 the pleasure ground. This gives to the place an to 1830. By G. B. AIRY, Esq. 2 vols. 4to. air of great seclusion and privacy, as well as ap1848. parent 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 No one has ever sailed down or up the Thames, the habitation of the younger branches of the royal and surveyed the stately domes and colonnades of family, sometimes the residence of a favorite misGreenwich Hospital, without admiring the back-tress, sometimes a prison, and sometimes a place ground which the wooded heights of Greenwich of defence. Mary, fifth daughter of Edward IV., Park give to the landscape, and the contrasting architecture of the brick towers and minarets of the Royal Observatory, placed on a commanding height in the prolongation of the middle area of the hospital, and thus terminating the vista. But few of these voyagers, we suspect, take time to consider that the British navy owes an important part of its efficiency not less to the observatory than to the hospital—that humanity is interested in the former as well 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.

7. Six Lectures on Astronomy, delivered at Meetings of the Friends of the Ipswich Museum. By GEORGE BIDDELL AIRY, Esq., M. A., tronomer Royal. 8vo. 1849.

As

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 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.

(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

quaint latinity, we quote the following permission:

*Rot. Patent., 15 Hen. 6. M. 7. As a specimen of the

Muris petra et calce includere et firmare, et muros illos kernellare, batellare, et turrellare, ac quandam Turrim infra Parcum prædictum similiter petra et calce de novo2 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.

been constructed and engraved by the present Astronomer + An accurate map of the grounds and buildings has Royal.

Life of Flamsteed, p. 39, note.

1 Kernellare, from créneaux (Fr.) to make battlements for 2 Hence it appears that there had been some still older struGture.

This curious charter (of which a copy is now defence.
*Deptford was West Greenwich.
VOL. XXV. 28

CCCXVI. LIVING AGE.

Duke Humphry's tower and the river, called The fixed stars relatively to a point altogether imaginPleasaunce, which was frequented by Queen Eliz-ary, termed the equinoctial point, had been clearly abeth and other sovereigns. discovered and imperfectly measured.

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 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 practised 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.

But when the telescope gave to man almost a new sense, and enabled him to examine objects at a distance, with the advantage of a vast magnifying power, a new department of practical astronomy arose. Astronomers had hitherto only seen the rude outline of our own system, and the still ruder landmarks of the starry firmament. The telescope not only revealed thousands, nay millions of bodies, hitherto unseen because invisible, but it displayed complications of arrangement and feature, which gave, as it were, a coloring to the broad natural outlines with which hitherto the astronomer had to content himself. The moons of Jupiter and Saturn, the rings of the latter, and the varying phases of Venus and Mercury were, of course, among the first points of telescopic vision—and a glorious insight they gave into the arrangements of our system. Then the actual physiognomy of the moon, the sun, and some of the nearer planets, after which the unaided eye could only vainly strain itself, and desire for more help, opened fresh fields of inquiry. More lately, the indefatigable study of the fixed stars and nebula-with 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 at 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.

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 The easiest reference is found by a comparison of the world-namely, that the sun is the centre with that which is familiarly used to determine of a planetary system, of which the earth is one the position of places on the surface of the earth, member, with the moon circulating round it; and or latitude and longitude. Though the terresthat the fixed stars are altogether independent and trial and celestial globes are not only different in placed at a vastly greater distance. The periods their delineations (as a certain lady of fashion is and comparative distances of all the principal said to have discovered, when she returned her planets were known; as well as the deviation of globes to the maker because they were not a pair,) the orbits of some of them from a circle; and but also in their idea or principle, the apparent a certain approximation was made to the singu- place of a star on the celestial sphere may be delarly irregular form of the lunar path; eclipses fined by two angles, called declination and right could be calculated with tolerable accuracy; lati- ascension, corresponding accurately to those of tudes and longitudes roughly ascertained; and latitude and longitude, which determine the spot on even such delicate phenomena as the apparent dis- the surface of the earth occupied (for example) by placement of the heavenly bodies by refraction, and the general excessively slow motion of the

* Ed. Rev., vol. lxxxviii., p. 104.

New York or Mount Blanc. Whirl a globe round sure, is very small, compared with the spaces its axis, and a pencil approached to the surface which separate from us even the nearest of the will touch all places having the same latitude-all heavenly bodies, and a mere mathematical point as stars having the same declination. Stretch a compared to the distances of the fixed stars. It is,

however, so large that the moon, for instance, is very visibly displaced as we regard her from one part of the earth or another. The direction of the earth's axis is a perfectly well ascertained

thread tightly from pole to pole, and it will meet the position of all places on the surface having a common longitude, and (on the celestial globe) of all stars having the same right ascension. The pencil mark will meet the thread but in one point; line. If we look in its direction from any part of thus the place is fixed completely by two angles, the earth's surface, the whole firmament appears measured each from the centre of the globe along to revolve round it by the diurnal movement; in those circles; the zero point of reference for this direction, then, a telescope may be accurately right ascension being determined by a particular pointed. Let this telescope next be turned on the point called the vernal equinox, or the first point moon -the angle which the telescope describes of Aries: whilst on the terrestrial globe the longi-may be called the moon's north or south polar tudes are measured from the meridian of Green- distance. If this experiment were performed simulwich.

taneously at Greenwich and at the Cape of Good If we imagine the eye placed in the centre of a Hope, the moon would appear further north from celestial globe, and the fictitious stars to be each the latter than from the former station; for the pierced with holes through its surface, that eye same reason that if we go from the lower to the upwould, if the globe were properly turned, see each per window of a house, the neighboring chimney, star in the heavens through its appropriate hole. which in the former case seemed to touch the disSuch, in fact, is all the information which a celes- tant weathercock, now falls far beneath it. Thus, tial globe is intended to convey-the idea of direc- also, the moon, when she passes centrically over a tion, or apparent place-not at all that of distance. fixed star, as viewed by a spectator near the equaThe moving lights of heaven-sun and moon, tor, will leave it uneclipsed to an astronomer in planets and comets-change, from day to day and the Artic or Antartic seas, passing to the south of from hour to hour, their seeming place. To be it in the one case, and to the north in the other. able to define accurately their apparent place at a This seeming displacement is called parallax. The given instant, is the first aim of the practical | greatest amount of parallax which the moon could astronomer. This is done by ascertaining their possibly have, would be, if we imagine a spectator declinations and right ascensions-the former be- placed at either pole of the earth. The displaceing the apparent angular distance of a star from ment to each, compared to the moon's position as the celestial equator; the latter, the angle formed by seen from the earth's centre, would be about a the meridian (or line traced by the thread stretched degree, or the whole angle under which the from pole to pole and touching its place) with earth's diameter (8000 miles) is seen at the moon, some other meridian, drawn arbitrarily or other-is two degrees.

tained by observations made, under favorable circumstances, at different parts of the earth's surface; and since we are personally confined, by a physical necessity, to the surface of our globe, we can only make the best of the limits of voluntary excursion which Nature and Providence have assigned to us.

wise among the stars; just as in geography we, In the same manner the parallax of the planet in Britain, refer the longitude of places to that of Mars and the planet Venus, when nearest to the earth Greenwich. The astronomer, having traced the-and even the distance of the sun-may be ascermotions of an erratic star or planet on the apparent surface of the sphere, possesses the data for testing the truth of astronomical theories, whether of merely formal theories like those of epicycles and deferents, (as they were called,) or of physical theories like those of vortices and of gravitation. The apparent complication of these movements is in nature exceedingly great; consequently, the coincidence of observed with predicted places is the best test of theories; and thus the perfection of our observations becomes essential for the establishment of theories, especially of that greatest of physical laws hitherto detected by man-the law of gravitation.

But the power of tracing with accuracy the places of the heavenly bodies on the apparent vault of the sky, and therefore with reference to one another, carries us a step further, even to the measurement of the impassable and seemingly illimitable spaces which divide them from us. We cannot indeed 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 earth, to be

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-fortunately for astronomy, we make an annual tour in the course of our orbital revolution round the sun, which carries us to two points of space nearly 200 millions of English miles apart. Seated on this comfortable railway carriage called the globe, we are actually tearing through space at the rate of nineteen miles per second, or 67,000 miles an hour; and the distance and position of the sun being known at any time by observation, the actual distance between the points of space occupied by us, the travelling spectators, on any two days, is accurately known. For instance, on the longest and on the shortest day, our positions are, as we have said, nearly 200,000,000

miles apart. Of course this annual trip makes a vast change in the celestial scenery of the bodies nearest to us. The other planets, if they did not move themselves, would appear to do so by our own relative motion ;- -as it is, they have apparent movements, resulting from their own, as well as from our earth's orbital motions. But the most extraordinary fact is this; that, notwithstanding the vast space which separates the position of our earth at opposite seasons of the year, the scenery of the fixed stars is noways sensibly distorted by our change of place. The vast distance from the earth to the sun is seen from the nearest fixed star under an angle probably not exceeding one second -which is about one two-thousandth of that which the sun's or the moon's disc subtends! This is called the annual parallar; and, admitting it to exist, the nearest fixed star must be 206,000 times more distant from the sun than our earth is; or 5,000,000,000 diameters of our globe, or about twenty billions of English miles!

Now on these processes we have two remarks to make. First, that the operations of practical astronomy, as far as they regard the fixation of the distances and positions of the heavenly bodies, depend upon one single fundamental measurement of space, just as in surveying land with a Theodolite ;-that measurement being the single measured side of the network of triangles which (rigorously speaking) is all that is required to measure an arc of the meridian, and consequently the axial diameter of our globe. Any error in that single fundamental linear measure is proportionally transmitted through all the succeeding calculations. The rod used in measuring a base line is commonly somewhere about ten feet long; and the astronomer may be said truly to apply that very rod to mete the distance of the stars! An error in placing a fine dot which fixes the length of the rod, amounting to one five-thousandth of an inch, (the thickness of a single silken fibre,) will amount to an error of 70 feet on the earth's Thus our knowledge of the distance of the fixed diameter, of 316 miles on the sun's distance, and stars (the greatest to which the art of mensuration to 65,200,000 miles on that of the nearest fixed has yet extended) depends upon the diameter of star! The second point to which we would adthe earth's orbit; which, again, is deduced from a vert is, that as the astronomer in his observatory triangle having the earth's diameter for one of its has nothing further to do with ascertaining lengths sides. But how is this last quantity determined? as distances, (except by calculation,) his whole The measurement of the earth was one of the skill and artifice are exhausted in the measuremost justly celebrated problems of antiquity. The ment of angles; for it is by these alone that spaces science of geometry owes its name to this single inaccessible can be comparéd. Happily, a ray of application. We must refer to previous papers in light is straight; were it not so, (in celestial this Journal for its history and solution. But spaces at least,) there were an end of our astronomy. we may observe that the fertile principle of trian- If we may be permitted a pleasantry on such a gulation is here, again, the basis of operation. subject, it is our beam compass, and it is inflexiAt first, extensive though rude measurements of ble as adamant-which our instruments for ascerconsiderable spaces of the earth's surface were taining its position unfortunately are not. Now attempted. Norwood, about 1635, guessed, rather an angle of a second (3600 to a degree) is a subtle than ascertained, the distance from London to York, thing. It is an apparent breadth utterly invisible by measuring with a chain along the highway, to the unassisted eye, unless accompanied with so allowing for its bends and obliquities, and some- intense a splendor (as in the case of the fixed times merely by pacing. But the ingenious Snell stars) as actually to raise by its effect on the nerve made a better determination, by ascertaining a of sight a spurious image having a sensible breadth. comparatively short distance by means of exact A silk-worm's fibre, such as we have mentioned measurement, and extending that measure, by a above, subtends an angle of a second, at 33 feet series of connected triangles, to a comparatively distance; a cricket ball 2 inches diameter must large portion of the meridian--a process improved, be removed, in order to subtend a second, to 43,000 in later times, by measuring a second base line feet, or about 8 miles-where it would be utterly near the close of the operation, and comparing it invisible to the sharpest sight, aided even by a with the result of calculation carried forwards telescope of some power. Yet it is on the measthrough the whole intermediate network of tri-ure of one single second that the ascertainment angles. A coincidence of the calculated and observed results gives the very highest probability to the accuracy of the whole operation. From such an extended arc of the meridian the dimension of the whole globe is inferred, by reasoning which we cannot stop here to explain, but which in the simple case of the earth, being supposed truly spherical, is exceedingly easy and direct.

of a sensible parallax in any fixed star depends; and an error of Too of that amount (a quantity still unmeasurable by the most perfect of our instruments) would place the star too far or too near by 200,000,000,000 miles-a space which light requires 118 days to travel.

The practical astronomer is not, however, constantly or principally employed in directly measuring the distances of the heavenly bodies, or the The earth's diameter is dimensions of the earth. now known with very great exactness, and the distance of the sun cannot become much better known, at least until the recurrence of the rare phenomenon called the transit of Venus. But