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HISTORY OF PHYSICAL ASTRONOMY.

This great catalogue contains the places of 47,390 stars, reduced to thebeginning of the year 1800. Although the results are not distinguishedby a high degree of accuracy, they have proved eminently useful as pointsof reference in extra-meridional observations, and have served to throwlight 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 ofMaskelyne’s catalogue. As some doubt seemed to rest upon the accuracyof the right ascensions of these stars, the illustrious Italian resolved toestablish his results solely upon his own observations, and, in accordancewith this view, he formed a preliminary standard catalogue of 120 prin-cipal stars, which he published in 1807. These formed the basis of hismore extensive catalogue of 7646 stars, which appeared in 1814 *. Thisgreat work is justly considered to be one of the most important that hasever been executed by a single individual. Every star was observedseveral times, and a mean of all the results taken as the final place ofthe star f. Moreover, the table of refractions employed by Piazzi in re-ducing the stars to their mean places, was deduced by him exclusivelyfrom his own observations. The epoch of the catalogue is the beginningof the year 1800. From the circumstance of its being at once so ex-tensive, so accurate, and so independent in its construction, this cataloguehas formed the groundwork of much valuable research to the theorist,while at the same time it has proved an inestimable boon to the practicalastronomer J.

In 1806 I)e Zacli published a catalogue containing the places of 1830zodiacal stars, founded on observations made by him at the observatory ofSeeberg in Saxe Gotha.

* “ Prtecipuarum Stellarum Inerrantium Positiones Mediae, ineunte seculo xix”.Quarto, Panormi, 1814. The observations employed in the formation of this cataloguewere 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.

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

$ Joseph Piazzi was born on the 16th of July, 1746, at Ponte in the Valteline, a dis-trict of Northern Italy, which then formed part of the Helvetic Confederation . In earlylife, he became a member of the monastic order of Theatines . As soon as he hadqualified himself for holy orders, he was appointed to teach philosophy in a convent ofGenoa, but having incurred the displeasure of the theological party by too free anexpression of his opinions, he shortly afterwards resigned his situation. Having now de-voted his attention more especially to the exact sciences, towards which he always evinceda strong inclination, he was appointed Professor of Mathematics at Malta , and subse-quently at Rome . In 1780, he was appointed Professor of Mathematics in the Academyof Palermo. Shortly afterwards Ferdinand IV., King of Naples, having founded anobservatory at that city, Piazzi was appointed director of the establishment. Havingvisited France and England, in order to extend his knowledge of practical astronomy, hereturned to Palermo, bringing with him a collection of astronomical instruments from thelatter country, and commenced his labours at the new observatory in 1792. He nowproceeded to carry into effect his resolution of executing a great catalogue of stars, anundertaking which may be said to have formed the principal object of his life. CaptainSmyth, who was a personal friend of the celebrated astronomer, referring to this greatwork, says of its author : —“ I cannot forget his emphatic expression on putting a finalcorrection 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 ofJuly, 1826. By his will he bequeathed his library and instruments to the Observatory ofPalermo, and an annuity to be employed in educating young men who showed an incli-nation towards astronomical pursuits.