C. Morton, whose excellent set of lives published by the S.P.C.K.
saved me much trouble in the early part of the course.

As we approach recent times the subject grows more complex, and the men
more nearly contemporaries; hence the biographical aspect diminishes and
the scientific treatment becomes fuller, but in no case has it been
allowed to become technical and generally unreadable.

To the friends (C.C.C., F.W.H.M., E.F.R.) who with great kindness have
revised the proofs, and have indicated places where the facts could be
made more readily intelligible by a clearer statement, I express my
genuine gratitude.

UNIVERSITY COLLEGE, LIVERPOOL,
_November, 1892_.

CONTENTS

_PART I_

LECTURE I

PAGE

COPERNICUS AND THE MOTION OF THE EARTH 2

LECTURE II

TYCHO BRAHE AND THE EARLIEST OBSERVATORY 32

LECTURE III

KEPLER AND THE LAWS OF PLANETARY MOTION 56

LECTURE IV

GALILEO AND THE INVENTION OF THE TELESCOPE 80

LECTURE V

GALILEO AND THE INQUISITION 108

LECTURE VI

DESCARTES AND HIS THEORY OF VORTICES 136

LECTURE VII

SIR ISAAC NEWTON 159

LECTURE VIII

NEWTON AND THE LAW OF GRAVITATION 180

LECTURE IX

NEWTON'S "PRINCIPIA" 203

_PART II_

LECTURE X

ROEMER AND BRADLEY AND THE VELOCITY OF LIGHT 232

LECTURE XI

LAGRANGE AND LAPLACE--THE STABILITY OF THE SOLAR SYSTEM,
AND THE NEBULAR HYPOTHESIS 254

LECTURE XII

HERSCHEL AND THE MOTION OF THE FIXED STARS 273

LECTURE XIII

THE DISCOVERY OF THE ASTEROIDS 294

LECTURE XIV

BESSEL--THE DISTANCES OF THE STARS, AND THE DISCOVERY OF
STELLAR PLANETS 304

LECTURE XV

THE DISCOVERY OF NEPTUNE 317

LECTURE XVI

COMETS AND METEORS 331

LECTURE XVII

THE TIDES 353

LECTURE XVIII

THE TIDES, AND PLANETARY EVOLUTION 379

ILLUSTRATIONS

FIG. PAGE

1. ARCHIMEDES 8

2. L