HISTOEY OF PHYSICAL ASTEONOMY.

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A remarkable instance of devotion to this department of astronomicalscience is exhibited in the case of Stephen Groombridge . In 1806, thisindividual commenced observations of all the stars, down to the eighthmagnitude, situate within 50° of the North pole , and finally completedhis task in the year 1816. These observations were made with a transitcircle constructed by Troughton. During the period included betweenthe years 1816 and 1827, he was engaged in reducing his observations,but, before he succeeded in bringing his labours to a close, he was com-pelled by the weak state of his health to desist from his undertaking. Thetask of completing the reductions was executed at the expense of the Govern-ment, under the superintendence of Mr. Airy, and a catalogue embodyingthe results was finally published in 1838. It exhibits the mean placesof 4243 circumpolar stars reduced to the year 1810. This is universallyadmitted to be one of the most valuable contributions to practical astro-nomy made during the nineteenth century.

The astronomical career of the illustrious Bessel was distinguished bya remarkable series of sidereal observations. In 1821 he commencedobservations of all the stars, down to the ninth magnitude, comprehendedbetween the parallels of 15° south declination and 45° north declination.These observations were made in zones with a meridian circle by Ileichen-bach, the right ascension and declination of each star being determinedat a single observation. This great undertaking was completed in 1833.The number of observations amounted to about 75,000. By means ofsubsidiary tables appended to them, it was easy to perform their reductionin any particular instance; but still it was desirable that they should beexhibited in a completely reduced form. This task was executed byProfessor Weisse, of Cracow , for all the stars situate within the'regionextending 15° on each side of the equator, and a catalogue of the resultswas 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 ofthe remaining zones of Bessel's observations. Argelander has followedup Bessel’s undertaking by a similar observation in zones of all the starsincluded between 45° and 80° of north declination. These observationswere commenced in 1841, and were finished in 1844. The number ofstars is about 22,000, arranged in 204 zones. Tables are appended tofacilitate their reduction.

It ought to be mentioned that, previous to the publication of Weissescatalogue, a similar catalogue of stars, although less extensive, had beenpublished by Sig. Santini, of Padua , founded upon his own observations.The number of stars in this catalogue is 1677, comprehended between theequator and 10° of north declination. The observations were made duringthe years 1838-39-40. The epoch is January 1, 1840. The object ofthis catalogue was to establish a series of reference points which mightbe useful in extra-meridional observations of new planets or comets. Forthis purpose the catalogue wbs so planned that, on each parallel of decli-nation, some well-determined star should be found at every eight or tenminutes 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 importantservice to practical astronomy, by the publication of a general catalogue