Navigation and Nautical Astronomy

NAVIGATION.

AND

NAUTICAL ASTRONOMY.

PART I.

CONTAINING

RULES FOR FINDING THE LATITUDE AND LONGITUDE, AND THE
VARIATION OF THE COMPASS.

With numerous Examples.

By H. W. JEANS, F.R.A.S.

ROYAL NAVAL COLLEGE, PORTSMOUTH;

Author of a Work on "Plane and Spherical Trigonometry;" "Handbook of the Stars;"
"Problems in Astronomy, Navigation, &c. with Solutions:" formerly Mathematical
Master in the Royal Military Academy, Woolwich; and an Examiner of Officers in the
Merchant-Service in Nautical Astronomy, &c.

LONDON:

LONGMAN, BROWN, GREEN, AND LONGMANS.
1861.

PREFACE.

PART I., containing practical rules and examples, is designed for beginners, and for those who have had no opportunity of acquiring sufficient elementary instruction in mathematics to enable them to comprehend the investigation or reason of the rules and problems in Nautical Astronomy. These investigations will be found in the theoretical treatise on Navigation and Nautical Astronomy forming Part II.* In order, however, to simplify the subject as much as possible, Part II. is made to consist only of such investigations (with one or two exceptions) as require in the student nothing beyond a knowledge of Trigonometry. It is for this reason that the demonstrations of the rules for finding the longitude by solar eclipses, transits of the moon, &c., as well as the explanation of refraction, of precession, interpolation, &c., and of certain methods for determining the latitude and longitude, which, from the peculiar elegance of the artifices used, are instructive and deserve the consideration of the advanced student, are in Part II. omitted. The author may possibly hereafter collect and form them into a separate volume as Part III.

To the present volume is added, in the Appendix, a rule

* The mathematical student will probably read Part II. before Part I., using the latter volume simply as a book of examples for practice.

for finding the time of high water,* and also one for finding the latitude by the altitude of the pole-star: these rules have been introduced chiefly for students who use Inman's Nautical Tables. In the Appendix also will be found a few simple rules for the construction of a Mercator's Chart, and for the adjustment and use of the Sextant: these, as well as the book itself, are necessarily of a brief character, and must be considered as introductory to larger works on the same subjects.

Another important and very necessary addition will be found in the page of corrections. To obtain this the examples have been recalculated, and the author trusts the principal errata have been discovered: still, in a work like the present, in which so many thousand figures must be used to obtain the answers, it is difficult to avoid mistakes; and it is only after several revisions that a near approach to correctness can be made.

* This rule is now become of little practical use: the time of high water being known by means of tables computed for all the principal ports and stations.

ROYAL NAVAL COLLEGE.

April 27, 1861.

CONTENTS.

NAVIGATION.

Fage

Definitions