This great catalogue contains the places of 47,390 stars, reduced to the beginning of the year 1800. Although the results are not distinguished by a high degree of accuracy, they have proved eminently useful as points of reference in extra-meridional observations, and have served to throw light upon several interesting points of astronomical science.

In 1803 Piazzi published, at Palermo, his first catalogue of 6748 stars. The fundamental points used in its construction were the thirty-six stars of Maskelyne's catalogue. As some doubt seemed to rest upon the accuracy of the right ascensions of these stars, the illustrious Italian resolved to establish his results solely upon his own observations, and, in accordance with this view, he formed a preliminary standard catalogue of 120 principal stars, which he published in 1807. These formed the basis of his more extensive catalogue of 7646 stars, which appeared in 1814*. This great work is justly considered to be one of the most important that has ever been executed by a single individual. Every star was observed several times, and a mean of all the results taken as the final place of the start. Moreover, the table of refractions employed by Piazzi in reducing the stars to their mean places, was deduced by him exclusively from his own observations. The epoch of the catalogue is the beginning of the year 1800. From the circumstance of its being at once so extensive, so accurate, and so independent in its construction, this catalogue has formed the groundwork of much valuable research to the theorist, while at the same time it has proved an inestimable boon to the practical

astronomer.

In 1806 De Zach published a catalogue containing the places of 1830 zodiacal stars, founded on observations made by him at the observatory of Seeberg in Saxe Gotha.

* "Præcipuarum Stellarum Inerrantium Positiones Media, ineunte seculo xix”. Quarto, Panormi, 1814. The observations employed in the formation of this catalogue were made by Piazzi, at the Observatory of Palermo, between the years 1792 and 1813, with the famous altitude and azimuth instrument constructed for him by Ramsden.

According to Captain Smyth, each star was observed from five or six to ten or twenty, or even occasionally to a greater number of times. The same author states that the whole number of observations amounted to nearly 150,000. (Cycle of Celestial Objects, vol. i., p. 433.)

Joseph Piazzi was born on the 16th of July, 1746, at Ponte in the Valteline, a district of Northern Italy, which then formed part of the Helvetic Confederation. In early life, he became a member of the monastic order of Theatines. As soon as he had qualified himself for holy orders, he was appointed to teach philosophy in a convent of Genoa, but having incurred the displeasure of the theological party by too free an expression of his opinions, he shortly afterwards resigned his situation. Having now devoted his attention more especially to the exact sciences, towards which he always evinced a strong inclination, he was appointed Professor of Mathematics at Malta, and subsequently at Rome. In 1780, he was appointed Professor of Mathematics in the Academy of Palermo. Shortly afterwards Ferdinand IV., King of Naples, having founded an observatory at that city, Piazzi was appointed director of the establishment. Having visited France and England, in order to extend his knowledge of practical astronomy, he returned to Palermo, bringing with him a collection of astronomical instruments from the latter country, and commenced his labours at the new observatory in 1792. He now proceeded to carry into effect his resolution of executing a great catalogue of stars, an undertaking which may be said to have formed the principal object of his life. Captain Smyth, who was a personal friend of the celebrated astronomer, referring to this great work, says of its author:-"I cannot forget his emphatic expression on putting a final correction to the last proof sheet in 1814. Now,' said he, my astronomical day is closed.' (Cycle of Celestial Objects, vol. i., p. 433.) Piazzi died on the 22nd of July, 1826. By his will he bequeathed his library and instruments to the Observatory of Palermo, and an annuity to be employed in educating young men who showed an inclination towards astronomical pursuits.

A remarkable instance of devotion to this department of astronomical science is exhibited in the case of Stephen Groombridge. In 1806, this individual commenced observations of all the stars, down to the eighth magnitude, situate within 50° of the North pole, and finally completed his task in the year 1816. These observations were made with a transit circle constructed by Troughton. During the period included between the years 1816 and 1827, he was engaged in reducing his observations, but, before he succeeded in bringing his labours to a close, he was compelled by the weak state of his health to desist from his undertaking. The task of completing the reductions was executed at the expense of the Government, under the superintendence of Mr. Airy, and a catalogue embodying the results was finally published in 1838. It exhibits the mean places of 4243 circumpolar stars reduced to the year 1810. This is universally admitted to be one of the most valuable contributions to practical astronomy made during the nineteenth century.

The astronomical career of the illustrious Bessel was distinguished by a remarkable series of sidereal observations. In 1821 he commenced observations of all the stars, down to the ninth magnitude, comprehended between the parallels of 15° south declination and 45° north declination. These observations were made in zones with a meridian circle by Reichenbach, the right ascension and declination of each star being determined at a single observation. This great undertaking was completed in 1833. The number of observations amounted to about 75,000. By means of subsidiary tables appended to them, it was easy to perform their reduction in any particular instance; but still it was desirable that they should be exhibited in a completely reduced form. This task was executed by Professor Weisse, of Cracow, for all the stars situate within the region extending 15° on each side of the equator, and a catalogue of the results was published in 1846, at the expense of the Academy of Sciences of St. Petersburg. The number of stars in this valuable catalogue is 31,895, reduced to the year 1825. The preface to it is written by M. Struve. Professor Weisse is at present engaged in completing the reduction of the remaining zones of Bessel's observations. Argelander has followed up Bessel's undertaking by a similar observation in zones of all the stars included between 45° and 80° of north declination. These observations were commenced in 1841, and were finished in 1844. The number of stars is about 22,000, arranged in 204 zones. Tables are appended to facilitate their reduction.

It ought to be mentioned that, previous to the publication of Weisse's catalogue, a similar catalogue of stars, although less extensive, had been published by Sig. Santini, of Padua, founded upon his own observations. The number of stars in this catalogue is 1677, comprehended between the equator and 10° of north declination. The observations were made during the years 1838-39-40. The epoch is January 1, 1840. The object of this catalogue was to establish a series of reference points which might be useful in extra-meridional observations of new planets or comets. For this purpose the catalogue was so planned that, on each parallel of declination, some well-determined star should be found at every eight or ten minutes of time. The catalogue is inserted in the twelfth volume of the "Memoirs of the Astronomical Society."

In 1827 the Astronomical Society of London rendered an important service to practical astronomy, by the publication of a general catalogue

of stars, founded upon the most celebrated catalogues that have been executed since the middle of the eighteenth century. This catalogue contains the places of 2881 stars, reduced upon a uniform system to the 1st of January, 1830. In addition to the mean place of each star, the constants for computing its apparent place, according to Bessel's method, are also inserted in the catalogue. The introductory explanation is by Francis Baily, to whom was assigned the important task of selecting the most trustworthy values of the uranographical corrections. The calculations were executed under the superintendence of Lieut. Stratford.

Hitherto the stars in the southern hemisphere had been almost entirely neglected by astronomers since the time of Lacaille. With the view of remedying this defect, the Government, in 1820, established an observatory at the Cape of Good Hope, appointing the Rev. F. Fallows to be its director. In the Philosophical Transactions for 1824 there is inserted a small catalogue by that astronomer, containing the mean places of nearly all the principal stars between the zenith of the Cape of Good Hope and the South Pole.

When Sir Thomas Brisbane was appointed Governor of New South Wales in 1821, he erected an observatory at Paramatta, which he furnished with excellent instruments. In the same noble spirit of disinterested liberality, he employed, at his own expense, two qualified assistants, Messrs. Rümker and Dunlop, to aid him in his astronomical labours. In 1832 M. Rümker published, at Hamburg, a small catalogue of stars observed in the southern hemisphere, designed as preliminary to one of greater extent. In 1835 Sir Thomas Brisbane published a catalogue of 7385 stars, chiefly in the southern hemisphere, founded also upon observations made at his establishment at Paramatta. M. Rümker is at present engaged in constructing from the same collection of observations a catalogue of 12,000 stars.

In 1830 an observatory was erected at St. Helena, and Lieut. Johnson, a talented officer who happened to be on duty on the island, was appointed its director. Two years only elapsed, when a stock of observations was amassed, which served for the formation of an admirable catalogue of 606 principal stars in the southern hemisphere. This catalogue was published in 1835, at the expense of the East India Com

pany.

In 1844 Taylor's catalogue of 11,015 stars, founded on observations made at Madras during the years 1822-43, was published at the expense of the East India Company. This catalogue includes upwards of three thousand stars situate in the southern hemisphere, observed with especial reference to the same stars in Sir Thomas Brisbane's catalogue.

In the tenth volume of the "Memoirs of the Astronomical Society," there are inserted the mean declinations of 172 principal stars in the southern hemisphere, reduced by the late Professor Henderson of Edinburgh, from his own observations at the Cape of Good Hope. In vol. xv. he has given the mean right ascensions of the same stars. While on the subject of the southern stars, it may be mentioned, that the observations made by Fallows at the Cape of Good Hope, during the years 1829-30-31, have been recently reduced under the superintendence of Mr. Airy, and that from the results, a catalogue has been constructed, containing the mean places of 425 stars, situate chiefly in the southern hemisphere.

The only catalogues of stars distinguished by a high degree of accuracy

which were accessible to astronomers in the year 1830, were those of Bradley and Piazzi. It was desirable, however, for purposes of research, as well as for facilitating the practice of observation, that a new catalogue of equal accuracy should be constructed from recent observations. In 1833, Pond, the Astronomer Royal, contributed towards supplying this desideratum by the publication of a catalogue containing the mean places of 1112 stars reduced to the beginning of the year 1830. In 1835, M. Argelander published a catalogue of 560 stars founded on observations made by him at Abo. The epoch is the same as that of Pond's catalogue. In the eleventh volume of the "Memoirs of the Astronomical Society," there is inserted a catalogue of 726 stars, formed by Mr. Airy from observations made by him at the Observatory of Cambridge during the interval included between the years 1828 and 1835. The epoch in this case also is January 1, 1830. In the Greenwich Observations for 1842, the same distinguished astronomer has published a catalogue of 1439 stars, founded on observations made at the Royal Observatory, between the years 1836 and 1841 inclusive. The epoch of reduction is January 1, 1840.

The publication of the catalogue of the Astronomical Society, in 1827, suggested the desirableness of re-observing the stars whose places were therein given, for the purpose of throwing light upon the question of their proper motions. In the tenth volume of the "Memoirs of the Astronomical Society" there is inserted a catalogue of the right ascensions of 1318 stars, determined by Mr. (now Lord) Wrottesley at a private observatory which he fitted up at Blackheath, the right ascension of each star being compared with the corresponding right ascension of the Astronomical Society's catalogue. A similar catalogue of the right ascensions of 1248 stars has been recently formed by Lieut. Gilliss, of the United States Navy. It may be mentioned, that one of the objects proposed by the American expedition to Chili, of which that excellent astronomer has been appointed the superintendent, is the formation of a catalogue of all the stars down to the eighth magnitude, situate within 60° of the South Pole.

The great utility of the catalogue published by the Astronomical Society, suggested to astronomers the expediency of forming a more extensive catalogue upon the same plan, but accompanied with some improvements in the details. At the meeting of the British Association which was held at Liverpool in 1837, it was agreed to defray the expense of constructing such a catalogue. The superintendence of the operation was undertaken by Mr. Baily; but that individual, whose unparalleled exertions in this department of astronomical science will not fail to excite the gratitude and admiration of all future astronomers, had not the satisfaction to witness its completion, having died on the 30th of August, 1844, only a few months before the catalogue was ready for publication. The British Association appointed a committee consisting of Dr. Robinson, Lieut. Stratford, and Prof. Challis, to superintend the remaining part of the operation, and the catalogue was finally published in 1845. The preface is by Mr. Baily. The materials of its construction are derived from all the trustworthy catalogues that have been executed since the time of Bradley. The number of stars is 8377. The epoch of reduction is January 1, 1850. This catalogue is distinguished from the catalogue

• Lord Wrottesley is at present engaged in prosecuting a series of observations with a view to the formation of a similar catalogue, which he purposes to compare with that of the British Association.

LL

of the Astronomical Society in two important particulars. In the first place, the secular variation of precession, both in right ascension and declination, is given for each star. Secondly, the proper motions of the stars are assigned with as great a degree of nearness to the truth, as the existing state of sidereal astronomy allowed. This catalogue has proved of vast service to astronomers in every part of the civilised world.

An important catalogue has recently issued from the Greenwich Observatory, founded on observations made during the twelve years commencing with 1836, and ending with 1847. On account of the increasing importance of the subject of the proper motions of the stars, it has been deemed expedient to employ two epochs in the formation of this catalogue. The observations made during the first six years, are reduced to the first of January, 1840; the epoch of the remaining observations is the commencement of 1845. The number of stars in the catalogue is 2156. One peculiarity of this catalogue consists in the constants of reduction being computed according to the modification of Bessel's method, which Mr. Airy had shortly before suggested.

Allusion has been made to Mr. Johnson's catalogue of southern stars. This distinguished astronomer, who was appointed Director of the Radcliffe Observatory, Oxford, upon the death of Prof. Rigaud in 1838, has been engaged for several years in re observing the circumpolar stars of Groombridge's catalogue. This great undertaking is now all but completed. The number of stars observed will exceed the number in Groombridge's catalogue by about 2000. The epoch of reduction is the beginning of 1845. A comparison of this catalogue with Groombridge's cannot fail to lead to results of great importance.

In addition to the catalogues of stars alluded to in the foregoing pages, accurate catalogues of a select number of stars have been formed at every observatory, both in this country and on the Continent, where meridional observations form the chief object of attention. Apart from the special utility of these catalogues in so far as the practice of observation is concerned, they have in many instances been employed in some of the most delicate researches of modern astronomy*.

CHAPTER XX.

Early Notions of the Telescope.-Invention of the Telescope in Holland.-Galileo constructs a Telescope.- Kepler proposes the Telescope composed of Two Convex Lenses. - This Instrument first applied to Astronomical Purposes by Gascoigne.— Telescopic Observations of Huyghens and Cassini.-Reflecting Telescope proposed by Gregory. Newton executes a Reflecting Telescope.-Efforts of his Successors to construct these Instruments. Invention of the Achromatic Telescope by Dollond.— Reflecting Telescopes executed by Herschel.- Modern Improvements in the Refracting Telescope.-Improvements in the Construction of Reflecting Telescopes.Lassell. Lord Rosse.

THE telescope is justly considered to be one of the which the annals of human ingenuity can boast of.

noblest inventions By its means the

It may be stated in illustration of this remark, that a small catalogue of stars which Bessel constructed from his own observations at Königsberg, was employed by him in combination with the observations of Bradley and Piazzi, in his celebrated investigation of the quantity and laws of Precession. Again, M. Otto Struve has availed himself of a small catalogue of stars founded on observations made at Dorpat, in his recent researches on the same subject, in connexion with the great problem of the Motion of the Solar System in space.