CONTENTS.
XIX
CHAPTER XVI.
PAGE
Importance of Facts in the Cultivation of Physics.—Astronomy a Science of Ob-servation.—Inequalities which affect the apparent Positions of the Celestial Bodies .
—Precession. —Its Discovery by Hipparchus. —Researches of Modern Astro-nomers on its Value.—Bessel.—Peters.—Otto Struve.—Refraction. — Its Effectupon the Place of a Celestial Body first remarked by Ptolemy.—Opinion ofTycho Brahe respecting its Nature. —The first Theory of Refraction due toCassini. —His Table of Refractions.—Newton.—His Correspondence with Flam-steed on the subject of Refraction.—Formula of Bradley.—French Tables ofRefraction.—Researches of Bessel.—Aberration.—Its Discovery by Bradley.—Modern Determinations of its Value.—Nutation discovered by Bradley.—Its mostapproved Value.—Researches on Parallax.—Methods for facilitating the Reductionof Observations.—Method of Bessel.—Physical Causes which more especiallyaffect the Aspect of the Celestial Bodies.—Diffraction.—Irradiation . . . 316
CHAPTER XVII.
Eclipses of the Sun and Moon.—Historical Statement of total Eclipses of the Sun .
—Annular Eclipses observed in modern Times.—Change of Colour which theSky undergoes during an Eclipse.—Its Explanation by M. Arago.—Corona ofLight observed around the Moon.—Allusions made to it by Ancient Authors.—Explanations of its physical Cause by different Individuals.—Protuberances onthe Moon ’s Limb.—Their most probable Nature.—Observations on the Surfaceof the Moon during Eclipses.—Undulations observed on the Occasion of theEclipse of 1842.—Similar Phenomena observed during the Eclipse of 1733.—Explanation of their Origin. — Optical Phenomena observed during Solar
Eclipses Threads, Beads, &c.—Explanation of their Origin.—Lunar Eclipses.
—Transits of Venus.—Physical Appearances observed during their Occurrence.—Transits of Mercury.—Spot observed on the Planet’s Disk.—Its Explanation byProfessor Powell.—Occultations of the Planets and Stars .... 358
CHAPTER XVIII.
Early Methods of observing the Celestial Bodies. —Instruments of the GreekAstronomers.—Accurate Principles of Observation first employed by the Astro-nomers of the Alexandrian School.—Improvements effected by Hipparchus. —Ptolemy substitutes the Quadrant for the Complete Circle.—Arabian Astronomers.
—The Method by which they indicated the Time of an Observation.—Revival ofPractical Astronomy in Europe.—Labours of Waltherus.—Tycho Brahe.—Land-grave of Hesse—Hevelius.— Close of the Tychonic School of Observation.—Observatory of Copenhagen established.—The Pendulum applied to Clocks byHuyghens. —The Royal Society of London , and the Academy of Sciences ofParis , established.—Invention of the Micrometer.—Application of the Telescopeto divided Instruments.— Observatories of Paris and Greenwich established.—Labours of Roemer.—Transit Instrument invented.—The use of Circular Instru-ments for taking Altitudes introduced.—Labours of Flamsteed and Halley.—Royal Observatory of Paris.—Commencement of the Era of accurate Observa-tion. — Bradley. — Lacaille Mayer.—Maskelyne. — Pond.—Airy.—Reduction
of Planetary and Lunar Observations.—Present state of Practical Astronomy . 434
CHAPTER XIX.
Catalogues of the Fixed Stars.—Their importance as forming the Groundwork ofAstronomical Science.—Earlier Catalogues.—Ptolemy.—Ulugh Beigh.—Tycho