whenever he can. This part of education is too often neglected; and grown men sometimes take any thing in print for gospel, and at other times are unreasonably sceptical. It would be well if readers required references throughout all popular works on science; but it would probably appear pedantic to fill this book with citations. Accordingly, it is only in the sixteenth chapter, which contains distinct statistical statements, that authorities are referred to. Care has been taken, however, throughout the book, to check, by means of original treatises, the statements derived from popular works; and it is hoped that few errors have escaped attention in the revision of the text. For the historical portion of the book, Delambre has consulted. been the chief authority The illustrative lithographs have been copied, with Professor Winlock's permission, from the series of "Astronomical Engravings from the Observatory of Harvard College." On consideration, it has been thought best not to attempt any representation of nebulæ or comets. Good representations would be so expensive as to add too much to the price of the work; while ordinary ones, such as usually appear in popular works on astronomy, are of little or no service to the reader. The thanks of the author are due to Professor Winlock for occasional assistance in settling doubtful points, and for many valuable suggestions. CONTENTS. The Sun. Its atmosphere. — Rotation. — Poles and equator. — Di- - - Bulk and mass of the Sun. — Its Star magnitudes. - Places of principal stars in the sky. - Clusters of stars. - Variable and temporary stars. - - General account of the planets. - Real and apparent movement. Laws of nature. The Earth's rotation. - Pendulum experiments. Sidereal time. - Local time. The ecliptic and the zodiac. — Ap- parent movements of the Moon and of the planets. - Transits, Solids, surfaces, lines, and points. - Rectilinear motion and rotation. - Distances, angles, and arcs. - Spheres and cones. - Triangles. The magnifying-glass. The astronomical refracting telescope. — Object-glasses and eye-pieces. — Power of telescopes. — Reflecting telescopes. - Spy-glasses and opera-glasses. Fixed lines in the The celestial sphere. — Apparent places. - Geocentric and heliocentric places. - Azimuth and altitude. — Terrestrial longitude and lati- tude. Right ascension and declination. - Celestial longitude and latitude. - Parallax. - Sidereal time. — Aberration. — Mean places. - cus, Tycho, Kepler. — Galileo, Huygens, Picard. — Newton and his |