506
HISTORY OF PHYSICAL ASTRONOMY.
of the celestial bodies, liave resulted from the labours of Mr. Bond, the di-rector of the observatory, achieved by the use of this powerful instrument.
One of the inventions which do most honour to the Americans, consistsin the application of electro-magnetism to geographical aud astronomicalpurposes. As early as the year 1844, the instantaneous transmission oftime by the electric telegraph, was employed in determining the differenceof the longitudes of Washington and Baltimore . The same method hassince been practised for ascertaining the relative longitudes of variousother transatlantic cities. Recently, attempts' have been made, withcomplete success, to record transit observations of the celestial bodies, bymeans of the electro-magnetic principle. As soon as the star is seenbisected by the wire of the telescope, a slight pressure of the finger com-pletes or breaks the galvanic circuit, aud the effect is instantaneouslytransmitted, by the intervention of a magnet, upon a recording surface,to which a uniform motion is given by a peculiar mechanism. This in-genious contrivance for fixing the precise instant of a phenomenon, bycalling into exercise the sense of touch to aid that of vision, promises,at no distant period, to supplant the usual mode of recording by thecombined application of the eye and the ear*. We may remark, in con-cluding this chapter, that it ought to be borne in mind also, as anearnest of what may be expected from the future exertions of our trans-atlantic brethren, that to an American philosopher Practical Astronomy isindebted for the beautiful invention of the collimating telescope.
CHAPTER XIX.
Catalogues of the Fixed Stars.—Their importance as forming the Groundwork of Astro-nomical Science.—Earlier Catalogues Ptolemy.—Ulugh Beigh.—Tycho Brahe.—
Halley.—Hevelius.—Flamsteed.—Modern Catalogues.—Bradley.—Lacaille.—Mayer.—Maskelyne.— Publication of the Histoire Celeste of Lalande.— Piazzi.—Groom-bridge.—Zone Catalogues of Stars.—Bessel.—Argelander Santini.—Catalogue ofthe Astronomical Society.—Catalogues of Southern Stars.—Fallows.—Brisbane.—Johnson.—Henderson.—Standard Catalogues of Stars.—Catalogue of the British As-sociation.—Recent Standard Catalogues.
Catalogues of the fixed stars, considered as contributions to AstronomicalScience, possess an importance arising from tw’o distinct causes. In thefirst place, an accurate catalogue of such objects furnishes a series ofpoints of reference by means of which the positions of the various bodiescomposing the planetary system may be determined from observation, andthe laws of their motions investigated. Secondly, it constitutes thegroundwork of stellar astronomy. A comparison of catalogues constructedat different dates, enables the astronomer to ascertain the proper motions ofthe stars, and to arrive at conclusions respecting the changes which may betaking place in the physical constitution of the sidereal heavens. More-
* It would appear that several individuals in the United States are entitled to share inthe merit of this ingenious invention, among whom may be more especially mentionedMr. Bond, Mr. Sears Walker, Prof. Mitchell, and Dr. Locke. It has been stated iri thetext, that the instant of transit may be noted, either by completing the galvanic circuit,supposing that in the ordinary state of the apparatus the current of electricity is inter-rupted, or by making the electricity to flow in a continual current, and then suddenlybreaking the circuit. Both of these methods have been practised in America . At themeeting of the Astronomical Society held on the 9th of May, 1831, there was exhibited