ON

ASTRONOMY.

L

BY

SIR JOHN F. W. HERSCHEL, KNT. GUELP.

F.R.S.L. & E. M.R.I.A. F.R.A.S. F.G.S. M.G.U.P.S.

CORRESPONDent of the ROYAL ACADEMY OF SCIENCES OF PARIS, AND OTHER
FOREIGN SCIENTIFIC INSTITUTIONS.

A NEW EDITION,

WITH A PREFACE,

AND A SERIES OF QUESTIONS FOR THE EXAMINATION
OF STUDENTS,

BY S. C. WALKER.

PHILADELPHIA:

LEA & BLANCHARD.

"Et quoniam eadem natura cupiditatem ingenuit hominibus veri inveniendi, quod facillimi apparet, cum vacui curis, etiam quid in cœlo fiat, scire avemus: his initiis inducti omnia vera diligimus; id est, fidelia, simplicia, constantia; tum vana, falsa, fàllendia odimus." Cicero, de Fin. Bon. et Mal. ii. 14.

And forasmuch as nature itself has implanted in man a craving after the discovery of truth (which appears most clearly from this, that, when unoppressed by cares, we delight to know even what is going on in the heavens),-led by this instinct, we learn to love all truth for its own sake; that is to say, whatever is faithful, simple, and consistent; while we hold in abhorrence whatever is empty, deceptive, or untrue.

ENTERED according to the act of Congress, in the year 1836, by CAREY, LEA, & BLANCHARD, in the clerk's office of the district court for the eastern district of Pennsylvania.

T. K. & г. G. COLLINS. PRINTERS. PHILA

Seriosted 7-14-373 m

INTRODUCTION

Page 7

CHAPTER I.

General Notions-For and Magnitude of the Earth-Horizon and

its Dip-The Atmosphere-Refraction-Twilight-Appearances

resulting from diurnal Motion-Parallax-First Step towards form-

ing an Idea of the Distance of the Stars-Definitions

CHAPTER II.

Of the Nature of astronomical Instruments and Observations in gene-

ral-Of sidereal and solar Time-Of the Measurement of Time-

Clocks, Chronometers, the Transit Instrument-Of the Measure-

ment of angular Intervals-Application of the Telescope to Instru-

ments destined to that Purpose-Of the Mural Circle-Determina-

tion of polar and horizontal Points-The Level-Plumb Line-

Artifici Horizon-Collimator-Of compound Instruments with

co-ordinate Circles, the Equatorial-Altitude and Azimuth Instru-

ment of the Sextant and Reflecting Circle-Principle of Repeti-

tion

14

66

CHAPTER III.

OF GEOGRAPHY

Of the Figure of the Earth-Its exact Dimensions-Its Form that of

Equilibrium 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 Earth's Rota-

tion-Trade-winds-Determination of geographical Positions-Of

Latitudes-Of Longitudes-Conduct of a trignometrical Survey-

Of Maps-Projections of the Sphere-Measurement of Heights by

the Barometer

- 105

CHAPTER IV.

OF URANOGRAPHY.

Construction of celestial Maps and Globes by Observations of right

Ascension 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-Celes-

tial Latitudes and Longitudes-Precession of the Equinoxes-Nu-

tation-Aberration-Uranographical Problems

3

151