AMERICAN PRACTICAL NAVIGATOR AN EPITOME OF NAVIGATION AND ORIGINALLY BY NATHANIEL BOWDITCH, LL. D. Published by the UNITED STATES HYDROGRAPHIC OFFICE under the Displacing 626 948 STATUTES OF AUTHORIZATION. There shall be a Hydrographic Office attached to the Bureau of Navigation in the Navy Department, for the improvement of the means for navigating safely the vessels of the Navy and of the mercantile marine, by providing, under the authority of the Secretary of the Navy, accurate and cheap nautical charts, sailing directions, navigators, and manuals of instructions for the use of all vessels of the United States, and for the benefit and use of navigators generally. (R. S. 431.) The Secretary of the Navy is authorized to cause to be prepared, at the Hydrographic Office attached to the Bureau of Navigation in the Navy Department, maps, charts, and nautical books relating to and required in navigation, and to publish and furnish them to navigators at the cost of printing and paper, and to purchase the plates and copyrights of such existing maps, charts, navigators, sailing directions, and instructions, as he may consider necessary, and when he may deem it expedient to do so, and under such regulations and instructions as he may prescribe. (R. S. 432.) 2 NAUTICAL ASTRONOMY. Besides the present epitome, entitled the American Practical Navigator, the Hydrographic Office issues related works to aid in the practice of navigation, which are titled and numbered as follows: 66 71 120 127 Arctic Azimuth Tables giving True Bearings of the Sun and the other celestial bodies within Azimuth Tables, giving the True Bearings of the Sun at Intervals of Ten Minutes between The Azimuths of Celestial Bodies whose Declinations range from 24° to 70°, for parallels Star Identification Tables, giving simultaneous values of declination and hour angle for values of latitude, altitude, and azimuth ranging from 0° to 80° in latitude and altitude and 0° to 180° in azimuth. 200 Altitude, Azimuth, and Line of Position. Presents all the navigational and mathematical tables, except those of the Nautical Almanac, that are essential for the working of a sight for line of position by the cosine-haversine formula, Marcq Saint Hilaire method. The second part is Aquino's Altitude and Azimuth Tables, with Examples. Simultaneous Altitudes and Azimuths of Celestial Bodies. Gives true bearings and altitude of sun, moon, planets, and the fixed stars of declinations up to 24°, at 10-minute intervals for latitudes up to 60° N. and S. While its prime object is to furnish the Altitudes and Azimuths required in finding the Sumner Line by the Method of Marcq Saint Hilaire it can also give Course and Distance in Great Circle Sailing and can enable navigators to identify stars employed in navigation. 201 202 203 204 Noon Interval Tables. [NOTE.-The rate of change of longitude of the sun's geographical position in its diurnal path from east to west is 15° or 900 per hour, and if to this be added the hourly change in longitude of the observer when his change of place is to the eastward, or if from it be subtracted his hourly change in longitude when his change of place is to the westward, the result will be the rate of approach per hour of the meridian of the sun toward the meridian of the observer, expressed in minutes of arc of longitude. And this rate of approach being divided into the number of minutes of arc expressing the difference of longitude which separates the meridians of the sun and the observer at the instant of the morning time sight, will give the interval to noon expressed in hours and fractions of an hour, provided the course and speed of the vessel remain uniform or, at least, the rate of change of longitude continues the same throughout. Side by side in each double column of the tables the interval to noon is stated in hours and decimals of an hour to the fourth decimal place, and also in hours, minutes, and seconds, reckoned from the local apparent time stated at the head of the column, and corresponding to values of the hourly change of longitude of the observer ranging from 1' to 40, both to the eastward and to the westward. The local apparent times for which the intervals to noon are tabulated extend from 7 a. m. to 10 a. m. every 30 seconds.] The Sumner Line of Position furnished ready to lay down upon the Chart by means of Tables of Simultaneous Hour Angle and Azimuth of Celestial Bodies. Contains the values of the hour angle and the azimuth, side by side in tabular form, of celestial bodies ranging in declination from 27° north to 27° south of the Celestial Equator at successive altitudes, 1° or less apart, from 5° to culmination above the horizon of an observer situated on successive parallels of latitude, 1° apart, from 60° north to 60° south of the Equator, together with an explanation and illustrations of the ready use of the tables in finding the Sumner line. The Sumner Line of Position furnished ready to lay down upon the Chart by means of Tables of Simultaneous Hour Angle and Azimuth of the Navigator's Stars. Extends the tables of H. O. 203 to embrace declinations from 27° to 63° from the Celestial Equator. 208 Navigation Tables for Mariners and Aviators. Within the compass of 82 pages, this book of tables affords the means of determining (a) the Sumner line, (b) the compass error, (c) the meridian altitude, (d) the great circle course and distance, and (e) the identification of stars. In the present edition this epitome has been brought into conformity with the American Ephemeris and Nautical Almanac, in which, in the tabulation of the ephemerides of the celestial bodies, the hours of the day are counted from midnight to midnight of the civil day instead of from noon to noon of the astronomical day as was done in the volumes before 1925, and the time is designated Civil Time instead of Mean Time. The chapters containing materials appertaining to the branches of knowledge of which cognizance is taken by other institutions of the Federal Government have been submitted to them for remark, and acknowledgments are accordingly made to the Coast Guard of the Treasury Department, to the Weather Bureau of the Department of Agriculture, to the Coast and Geodetic Survey of the Department of Commerce, and to each of the several branches of the Navy Department represented in the Bureau of Navigation, the Bureau of Engineering, the Bureau of Aeronautics, and the Naval Observatory. which have reference to examples for that year given in this work....- II. A collection of Forms for working Dead Reckoning and various Astronomical Sights, with notes explaining their application under all circumstances___ III. Explanation of certain Rules and Principles of Mathematics of use in the |