HISTORY OF PHYSICAL ASTRONOMY.
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over, it is by sucli a comparison alone, that he can discover whether thereexist any real grounds for believing that the whole solar system is affectedwith a motion of translation in space.
The first individual who constructed a catalogue of the stars wasHipparchus , who may be considered as the true founder of AstronomicalScience. It is said by Pliny , that he was induced to enter upon thisundertaking, by the sudden apparition of a new star in his time. Be thisas it may, it is certain that he actually determined by observation, thelongitudes and latitudes of upwards of a thousand stars, and arranged theresults in a catalogue. The earliest production of this kind now extant,is the catalogue inserted by Ptolemy in the Syntaxis . It contains thelongitudes and latitudes of 1028 stars, arranged in 48 constellations.The epoch is the first year of the reign of the emperor Antoninus , whichcorresponds to the year 138 a.d. It has been suspected, on very probablegrounds, that this catalogue is nothing more nor less than the catalogue ofHipparchus , transported to the time of its reputed author, by applying tothe longitudes of all the stars a common additive quantity for the sup-posed effect of precession during the intermediate period.
The next catalogue of stars, in the order of time, is that of the Tartarprince, Ulugh Beigh . This individual, who was a grandson of the re-nowned Tamerlane, established an observatory at Samarcand, the capital of his father’s dominions, and devoted himself with great ardour to astro-nomical pursuits. Having found that the positions of the stars, asassigned by Ptolemy in his catalogue, were in many instances considerablyerroneous, he formed the resolution of constructing a new catalogue,founded exclusively upon his own observations. This design was actuallyrealised by him. The number of stars in the catalogue of this prince is1019, being only nine less than the number contained in Ptolemy ’scatalogue. The epoch is the year 1437 a.d. The mode of arrangementis the same as that employed by Ptolemy. Ulugh Beigh was treache-rously slain by his son in the year 1449, shortly after his accession to thethrone of his father.
The next catalogue recorded in the annals of astronomy, is that of theillustrious Tycho Brahe . It originally appeared in the work of thatastronomer, entitled Astronomies Instauratm Progymnasmata, which wasfirst published in the year 1602. The number of stars is 777. Theepoch is 1000 a.d. From the labour and skill employed by Tycho Brahe in its construction, this catalogue was vastly more accurate than any otherthat had been hitherto executed. Kepler subsequently enlarged it fromTycho Brahe 's observations to 1005 stars, and published it in the year1627, at the end of the Rudolphine Tables.
Halley’s Catalogue of Southern Stars was the next in succession after
a contrivance for recording transits by electro-magnetism, which had been used for sometime at the Cambridge Observatory, U. S. In this apparatus, the signal was made byinterrupting the galvanic circuit, the recording paper upon which the magnet acted beingapplied closely upon a cylinder, to which a uniform motion was given by a mechanismdevised at Cambridge, termed the spring governor. Mr. Airy proposes to introduce themode of recording transits by electro-magnetism at the Royal Observatory, where thenecessity of transmitting time from the meridian transit clock to the altitude and azimuthinstrument (the observations with which are made by noting the transit of the object overa system of horizontal and vertical wires) renders such a method peculiarly desirable. Itwould seem that the Astronomer Royal contemplates applying the principle so that theinstant of transit shall be indicated by completing the galvanic circuit, and that he purposesgiving a uniform motion to the recording cylindrical surface by means of a centrifugalpendulum.