GERSHOM BRADFORD 2d

Navigating Officer and Senior Instructor New York State Nautical Schoolship “Newport,” Late Nautical Expert, Hydrographic Office, U. S. N.

ILLUSTRATED

NEW YORK D. VAN NOSTRAND COMPANY 25 Park Place 1918

Copyright, 1918, by D. VAN NOSTRAND COMPANY

PRESS OF BRAUNWORTH & CO. BOOK MANUFACTURERS BROOKLYN, N. Y.

TO THE AMERICAN SUB-PATROL whose War Zone record of skill and daring has the author’s profound respect and admiration

PREFACE

When taking into consideration the number of excellent works now published on navigation there would seem to be a small chance of finding a different angle from which to discuss the subject. The purpose of the majority of such books is to give instruction to beginners. This book, however, is written particularly for the men who do their work mostly by rote and wish to know more of the reasons; or, perhaps, for schoolship graduates who may here find a chance to extend their horizons.

I have not considered it desirable to avoid repetition and in order to closely follow a line of thought have freely repeated many points already taken up. This has in a number of cases avoided the distraction of seeking a page of reference elsewhere.

I have had in mind that it serve as supplementary reading to the American Practical Navigator, Bowditch, that great bulwark of navigation which for over a hundred years has protected American ships through every deed of valor and every commercial adventure. It is placed beyond criticism by its venerable name and its remarkable record and, as a reference book for the navigator, it stands without a peer, but as a text book it founders the student.

If to such mariners as these a little insight is given to the “Whys and Wherefores” of their work, I shall be well repaid for the work of many watches below.

These discussions appeared several years ago, in a less extended form, in the Master, Mate and Pilot, the magazine formerly published by the American Association of Masters, Mates and Pilots.

I have freely consulted the following standard works: American Practical Navigator, Bowditch; Wrinkles in Practical Navigation, Lecky; The Theory and Practice of Navigation, Dunraven; General Astronomy, Young; Navigation and Compass Adjustment, Muir; Guide to the Marine Board’s Examinations, Reed.

I have received and am grateful for very valuable help and suggestions from Mr. George W. Littlehales, Hydrographic Engineer, U.S.N., Mr. Felix Riesenberg, C.E., Commander New York State Schoolship Newport, and George A. Collie (deceased), Nautical Expert, Hydrographic Office, U.S.N.

G. B.

New York, April 15, 1918.

CONTENTS

PAGE

CHAPTER I

Introductory Remarks 1

CHAPTER II

Nautical Astronomy 5

CHAPTER III

Declination and Right Ascension, including Precession 15

CHAPTER IV

Time 33

CHAPTER V

Corrections for Observed Altitudes 68

CHAPTER VI

Latitude 78

CHAPTER VII

Azimuths and Amplitudes 93

CHAPTER VIII

Longitude 101

CHAPTER IX

Sumner Method, including New Navigation 107

CHAPTER X

The Moon 139

CHAPTER XI

Charts 146

Index 161

THE WHYS AND WHEREFORES OF NAVIGATION