SIR JOHN HERSCHEL

SIR JOHN FREDERICK WILLIAM HERSCHEL, BART., the illustrious astronomer, was the only son of Sir F. William Herschel. He was born at Slough, Buckinghamshire, England, in the year 1792. His scholastic education began at Eton, whence, at the age of seventeen, he was sent to St. John's College, Cambridge, where he attained to great eminence in mathematics. After leaving the University, he entered upon the study of astronomy, and in 1820, assisted by his father, completed a mirror of 18 inches diameter and 20 feet focal length for a reflecting telescope. This, as subsequently improved, became the instrument which enabled him to effect the astronomical observations that formed the basis of his fame. In 1821-23 he undertook the re-examination of his father's double stars. For this work he received in 1826 the gold medal of the Astronomical Society, and the Lalande Medal of the French Institute. From 1824 to 1827 he was Secretary of the Royal Society, and in 1827 was elected to the Chair of the Astronomical Society, which office he filled on two subsequent occasions. In 1831 the honor of knighthood was conferred on him by William IV., and he subsequently

was made a baronet. His exploration of the southern heavens constituted an epoch in astronomy, and secured for him the distinction of memberships in almost every important society in both hemispheres. His "Outlines of Astronomy," here reproduced, first appeared in 1849, and, notwithstanding the disadvantage arising from the practice of stereotyping text-books which relate to progressive sciences, there is no more instructive volume extant on the subject of which it treats. Sir John Herschel died in 1871; his remains are interred in Westminster Abbey, close to the grave of Sir Isaac Newton.

CONTENTS

PREFACE TO THE FIRST EDITION

PREFACE TO THE FIFTH EDITION

PREFACE TO THE TENTH EDITION

INTRODUCTION.

PART I

CHAPTER I

General Notions-Apparent and real Motions-Shape and Size of the Earth

-The Horizon and its Dip-The Atmosphere-Refraction-Twilight—

Appearances resulting from Diurnal Motion—From Change of Station

in General-Parallactic Motions-Terrestrial Parallax-That of the

Stars Insensible-First Step toward forming an Idea of the Distance

of the Stars-Copernican View of the Earth's Motion-Relative Mo-

tion-Motions partly Real, partly Apparent-Geocentric Astronomy,

or Ideal Reference of Phenomena to the Earth's Centre as a Common

Conventional Station.

CHAPTER II

Terminology and Elementary Geometrical Conceptions and Relations-Ter-

minology relating to the Globe of the Earth-To the Celestial Sphere

-Celestial Perspective

CHAPTER III

Of the Nature of Astronomical Instruments and Observations in General

-Of Sidereal and Solar Time-Of the Measurements of Time-

Clocks, Chronometers-Of Astronomical Measurements--Principle of

Telescopic Sights to Increase the Accuracy of Pointing-Simplest

Application of this Principle-The Transit Instrument-Of the Meas-

urement of Angular Intervals-Methods of Increasing the Accuracy of

Reading--The Vernier-The Microscope-Of the Mural Circle-The

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Meridian Circle-Fixation of Polar and Horizontal Points-The Level,

Plumb-line, Artificial Horizon-Principle of Collimation-Collimators

of Rittenhouse, Kater and Bohnenberger-Of Compound Instruments

with Co-ordinate Circles-The Equatorial, Altitude and Azimuth In-

strument-Theodolite-Of the Sextant and Reflecting Circle-Principle

of Repetition--Of Micrometers-Parallel Wire Micrometer-Principle

of the Duplication of Images--The Heliometer-Double Refracting

Eye-piece-Variable Prism Micrometer-Of the Position Micrometer

-Illumination of Wires-Solar Telescope and Eye-piece-Helioscopy

-Collimation of large Reflectors

CHAPTER IV

OF GEOGRAPHY

Of the Figure of the Earth-Its Exact Dimensions-Its Form that of Equi-

librium Modified by Centrifugal Force-Variation of Gravity on its

Surface-Statical and Dynamical Measures of Gravity-The Pendulum

-Gravity to a Spheroid-Other Effects of the Earth's Rotation-Trade

Winds-Veering of the Winds-Cyclones-Foucault's Pendulum—The

Gyroscope-Determination of Geographical Positions-Of Latitudes-

Of Longitudes-Conduct of a Trigonometrical Survey-Of Maps--Pro-

jections of the Sphere-Measurement of Heights by the Barometer

CHAPTER V

OF URANOGRAPHY

Construction of Celestial Maps and Globes by Observations of Right Ascen-

sion and Declination-Celestial Objects Distinguished into Fixed and

Erratic Of the Constellations-Natural Regions in the Heavens-The

Milky Way-The Zodiac-Of the Ecliptic-Celestial Latitudes and

Longitudes-Precession of the Equinoxes-Nutation-Aberration-

Refraction-Parallax-Summary View of the Uranographical Cor-

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CHAPTER VI

OF THE SUN'S MOTION AND PHYSICAL CONSTITUTION

Apparent Motion of the Sun not Uniform-Its Apparent Diameter also

Variable-Variation of its Distance Concluded-Its Apparent Orbit

an Ellipse about the Focus-Law of the Angular Velocity-Equable

Description of Areas-Parallax of the Sun-Its Distance and Magni-

tude-Copernican Explanation of the Sun's Apparent Motion—Parallel-

ism of the Earth's Axis-The Seasons-Heat Received from the Sun