PREFACE.

IN launching this enlarged edition of my Epitome of Navigation before the Public, it will be unnecessary to enter into a detailed account of its contents. The slumbering spirit of research on this subject, which I awakened into activity, now nearly 20 years ago, has gone on adding improvement to improvement, and book to book, until the tide of information has swollen nearly to overwhelming my own little bark, which then was nearly alone on the wide ocean of mental darkness, which at that time overspread the Nautical world.

Suffice it then to say, that every care has been taken, that while nothing worthy of attention, or really important to the scientific or practical Navigator, has been omitted, all needless varieties of methods, and all extraneous matter, have been purposely avoided, that the attention of the Pupil may not wander from those essential points of his profession, the diligent study of which, will lead him on to the attainment of eminence in his profession.

The INTRODUCTION contains the requisite elementary information, at least, such as could alone be expected in a work of this kind. A description is given here of the Instruments used in navigating a ship at sea, with the method of finding the deviation of the compass in steam vessels, and correcting the courses for the errors found, a desideratum in this age of iron vessels, and Steam-boat Navigation

The SAILINGS Comprehend every variety, and are given in a clear and simple manner, applicable to the general purposes of navigation. To this edition, I have added the principles of Great Circle Sailing, so much used by our countrymen, now traversing continually, the wide expanse of the Southern Ocean. I have endeavoured to

shewing the spherical principles on which the tables now in use arc calculated. As it is contrary to custom, though perfectly correct in theory, I think it better to mention, that in referring to the points and quarter points of the compass, I have avoided backing the compass; thus, what is usually called S. W. S. I have named S.W. by S. W. this, besides being more correct, can cause no misunderstanding with the practical seaman, and would be better if generally adopted.

The science of ASTRONOMY, so beautiful in itself as a study, leading the mind of man into close contemplation of the mightiest works of his Creator, and which, in its practical application, is of such vital importance to the navigator, is treated at much greater length in this volume, than is usual in works of the same kind: and its application to the determination of the Latitude and Longitude at sea, and various other important Nautical Problems, is pointed out as clearly as possible, to enable the student, by making him acquainted with the principles upon which they are founded, fully to understand, and easily to retain the rules for performing those operations which follow in the work.

The Astronomical Definitions are considered at much length, it being imperatively necessary, that the technical terms of a science should be well understood, before the language, in which the science itself is treated, can be properly intelligible, and to those anxious for a true knowledge of Nautical Astronomy, these definitions will prove of great benefit.

For determining the LATITUDE by observations of the celestial bodies, the most recent and approved methods are introduced, every advantage being taken to facilitate the operations without endangering accuracy of result.

The extension of the well-known problem, of finding the Latitude by Double Altitudes, to the purpose of finding the Longitude, affords another opportunity of ascertaining the exact position of the ship, and I take this occasion of thanking Mr. Riddle, for his kindness in calling my attention to the subject.

The method of ascertaining the LONGITUDE by Lunar observa

brevity of its operations, which are such as to render the clearing the distance, a work of a few minutes, while the accuracy of the results has been successfully tested by the rigorous methods. These advantages, of the highest consideration at sea, have obtained for this method of solving one of the most important problems in Nautical science, the approval of our most skilful and intelligent Navigators, and the patronage of the first Nautical authorities of this as well as of several Foreign Countries.

In addition to the usual methods of finding the Longitude, is given concise and accurate rules for computing the Longitude from the rising and setting of the sun, and when the Navigator will pay attention to his barometrical indications, and calculate for the amount of refraction at the time of taking his observations, this method will be of great service to him, giving him an opportunity before night comes on, of ascertaining the situation of his vessel.

The theory of the rotatory storms is but briefly touched on, as it would be impossible in a work of this kind to enter fully into those interesting branches so necessary to be fully understood by the

seaman,

COL. REID has kindly afforded me an opportunity of illustrating the course of rotary storms, and the method of "heaving-to, and sailing from a gale's centre," by the introduction of diagrams from his work, "The Developement of the Law of Storms," and to such scientific and able works on the subject, I must refer the Navigator, my present object being to arouse attention to this important branch of nautical science: by which the hands of the Navigator may be strengthened, in prosecuting his way across seas traversed by the terrific Cyclones.

In the TABLES are little alterations, except that,

Table 36 now commences from 10° of Altitude, and that part of it up to 18° inclusive, has been re-calculated with great care and attention; the remainder will be arranged to every two degrees, and added from time to time, as the calculations are completed; in the mean time all the corrections above 18°, must be used as

Table 4a, attached to the first few pages of Table 36, will be continued in subsequent Editions, as the calculations are finished, it is added for a reduction of the Moon's variable horizontal parallax, and is to be applied according to the directions given with the Table.

Table 43, introduced from p. 562 in the Nautical Almanac, has been added for the purpose of converting mean solar time into sidereal time, the difference between which periods, is fully explained in p. 150; by using sidereal time mean noon instead of the sun's right ascension, much trouble is spared, and there is less liability of error in the reduction; and in finding the mean time by observation of the Moon, Planets, or Fixed Stars, the equation of time is not requisite; the use of this Table is fully explained in page 167.

Table 43a, the mean reduction of the moon's horizontal parallax for the spheroidal figure of the earth, is added in an abridged form as the correction for general nautical purposes may be disregarded, and when used, the present form is sufficiently correct.

The Table of Latitudes and Longitudes, or "Position of Places," has been revised and corrected with the utmost care, from the most recent surveys and observations, and the best sources of hydrographical information. The principal light-houses, with their respective heights above high water, with a description of the nature of the light exhibited, have likewise been added, and will be found of great use.

The general Tables, which are stereotyped, have been carefully revised, and in their extensive use the few errors at the commencement, have alone been discovered; and it is hoped that the great attention bestowed on the work, throughout all its various subjects, and the desire to increase, not only the knowledge of her countrymen, but the facilities of applying that knowledge, will secure a continuance of that extensive public patronage, which is now most gratefully acknowledged by

Nautical Academy,

THE AUTHORESS.