Part 1

TRANSCRIBER'S NOTE

Italic text is denoted by underscores.

Obvious typographical errors and punctuation errors have been corrected after careful comparison with other occurrences within the text and consultation of external sources.

More detail can be found at the end of the book.

PRACTICAL TALKS BY AN ASTRONOMER

Photographed by Loewy and Puiseux, February 13, 1894.]

PRACTICAL TALKS BY AN ASTRONOMER

BY HAROLD JACOBY

ADJUNCT PROFESSOR OF ASTRONOMY IN COLUMBIA UNIVERSITY

ILLUSTRATED

NEW YORK CHARLES SCRIBNER'S SONS 1902

COPYRIGHT, 1902, BY CHARLES SCRIBNER'S SONS

Published, April, 1902

TROW DIRECTORY PRINTING AND BOOKBINDING COMPANY NEW YORK

PREFACE

The present volume has not been designed as a systematic treatise on astronomy. There are many excellent books of that kind, suitable for serious students as well as the general reader; but they are necessarily somewhat dry and unattractive, because they must aim at completeness. Completeness means detail, and detail means dryness.

But the science of astronomy contains subjects that admit of detached treatment; and as many of these are precisely the ones of greatest general interest, it has seemed well to select several, and describe them in language free from technicalities. It is hoped that the book will thus prove useful to persons who do not wish to give the time required for a study of astronomy as a whole, but who may take pleasure in devoting a half-hour now and then to a detached essay on some special topic.

Preparation of the book in this form has made it suitable for prior publication in periodicals; and the several essays have in fact all been printed before. But the intention of collecting them into a book was kept in mind from the first; and while no attempt has been made at consecutiveness, it is hoped that nothing of merely ephemeral value has been included.

CONTENTS

PAGE

NAVIGATION AT SEA 1

THE PLEIADES 10

THE POLE-STAR 18

NEBULÆ 27

TEMPORARY STARS 37

GALILEO 47

THE PLANET OF 1898 58

HOW TO MAKE A SUN-DIAL 69