The new transit, or meridian circle, erected lately at Greenwich, possesses considerable advantages for such purposes, and great hopes have been formed of the combined operations of these two instruments. In a letter to thc writer of this article, however, Dr. Brink ley expresses great confidence in his having determined, with accuracy, on principles which appear unexception able, the parallax of some of the fixed stars. He also thinks, that a circle with a vertical axis possesses several advantages over the mural circle, and that the method of referring each star to the zenith point, is preferable to that of comparing them with fundamental stars as practised at Greenwich.
At Armagh, the metropolitan city of Ireland, and for merly the seat of a large university, an observatory was erected and endowed, in 1793, by the Most Reverend Richard Lord Rokeby, then primate of Ireland. It is erected on the summit of a gently rising hill, about ninety feet above the general level of the town. In the tower adjoining the dwelling-house, there is a very fine equatorial by Troughton, fixed in a large pillar, which is raised to such a height that the instrument in the dome overlooks all the buildings. To thc east of the house there is a range of buildings, adapted for a transit room, and other astronomical purposes. The other principal instruments, besides the equatorial and transit, are, a ten feet sextant by Troughton ; a ten fect reflect ing telescope by Sir William Herschel ; a five feet triple object-glass achromatic telescope by Dollond ; and a fine night glass, on an equatorial stand. The clocks arc the workmanship of Earnshaw of London, and Cross thwaithe of Dublin.
In this establishment, a liberal income is allowed the principal astronomer, and a good salary to his assistant. It has been superintended, from its commencement, by the Rev. James Archibald Hamilton, D. D. Dean of the cathedral church of St. Coleman, Cloyne. The regis tered observations are those made with the transit in strumcnt and equatorial, accompanied with an account of the state of the barometer and thermometer. Of these, a series of about 18 years is preserved. The right ascension of the sun and moon, compared with the fixed stars, are regular and unbroken ; but their north polar distances have not been so regularly taken, as they are only observed by the principal astronomer, whose pas toral duties must occasionally interfere with his astrono mical labours.
French Observatories.
The Royal, or Imperial Observatory, as it is some times called, of Paris, was built in 1667. It is 160 feet in front, by 120 in breadth, and 90 feet in height. Its vaults are also 90 feet deep, so that it is 180 feet from top to bottom. A particular description of the building is given by Blonde], and the arrangement and disposi tion may be found in Bernoulli's Lettres ilatrononliques, in Lalande's Astronomic, and in Monnier's Histoire Celeste.
In addition to the original building, new rooms have been constructed, close by the side of the observatory, where a large transit and circle by Ramsden have been fitted up. In 1768, new vaults were made, and a small observatory formed on the top of the building, which commands an extensive view of the horizon. There Louis XVI. established three observers, in order to prevent, as much as possible, an interruption in the series of observations.
In 1792, Lalande gave the following account of other observatories, which may be noticcd here as interesting in the history ol practical astronomy.
The astronomers of thc academy had, besides the Royal Observatory, several private ones erected in dif ferent parts of Paris, as the former was not sufficient for the accommodation of all. That of Monnier has been, since the year 1742, in the garden of the Capuchins. That of the Marine, which Joseph de Lisle used in 1748, at the Hotel de Clugny, has been occupied by Messier. That of Lacaille is still in existence at the Mazarine College. That of the palace of Luxembourg is above the Port Royal, where Joseph de Lisle once observed, and which Lalande occupied also for some time. .M. Pingre's, at the Abbey of St. Genevieve, was built in 1756. Cagnoli's is in the Rue de Richlieu, which that able and active astronomer built, at his own expense, in 1785, when he resided at Paris.
The observatory of the military school was built for M. Jeaurat in 1768, and was afterwards occupied by M. d'Agelet. The late M. Bergcret, Receiver-General of Finances, had constructed, in 1774, a large mural quadrant, of eight English feet, the last and best instru ment made by the celebrated Bird. This instrument was obtained by the Military Academy, as well as an excellent transit instrument, and a parallactic telescope. M. d'Agelet made a great number of observations there, from 1778 to 1785, whcn he left it to make a voyage of discovery with La. Perouse. In 1788, the changes made in the Military School occasioned the demolition of this observatory ; but it has been re-built a little more to the west, with all necessary attention, so that it is now the most complete observatory at Paris. Lalande, having received the direction of it, began, in 1789, to make a series of observations. M. le Francois Lalande, his re lation and pupil, has also made a prodigious number of observations, and he observed, in 1791, more than ten thousand northern stars, with excellent instruments. An observatory was built in 1775, at the College Royal, for the use of the Professor of Astronomy in this celebrated school. M. Geoffroy d'Assy built, in 1788, an observa tory at his house, Rue de Paradis, which was used for some time by Delambre.