## A Treatise on Navigation and Nautical Astronomy: Including the Theory of Compass Deviations, Prepared for Use as a Text-book at the U. S. Naval Academy |

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### Contents

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### Common terms and phrases

apparent noon approximate April astronomical azimuth Bowditch chronometer circle coefficients column compass course compass heading compass needle component computed Corr correction corresponding course and distance curve declination departure determined deviation due difference of latitude difference of longitude dygogram earth and ship East or West easterly equation fore-and-aft formula given Greenwich mean heavenly body heeling error horizontal force hour angle inducing force instant interval limb line of position magnetic bearing magnetic course mean noon Mercator chart meridian altitude method middle latitude miles minutes of arc Nautical Almanac navigator North end North point observation obtained parallel parallel sailing plane plane sailing polar pole prime vertical quadrantal deviation represented rhumbs right ascension sextant ship swings ship's head sidereal sight star starboard sun's tion transit triangle true altitude true course tude versin westerly zenith zero

### Popular passages

Page 434 - Cyclic permutation gives cos a = cos 6 cos c + sin b sin c cos A...

Page 672 - This daily inequality is due to the inclination of the plane of the moon's orbit to that of the equator, and to the rotation of the earth on its axis. FIG. 148. In Fig. 148, let PP...

Page 345 - Mean Solar Day is the interval between two successive transits of the mean sun over the same meridian ; it begins when the mean sun is on the meridian.

Page 348 - If the astronomical time is less than twelve hours, simply write PM after it. If greater than twelve hours, subtract twelve hours from it, mark the result A.

Page 179 - The first step in compensation of the compass is to correct approximately the quadrantal deviation and the heeling error, in the order named. This is necessary because a material factor in the deviation may be caused by the induction in quadrantal spheres set up by the magnet correctors, and it is essential that the semicircular correction, which is the largest and most important one, should be made when the magnetic conditions approximate as nearly as possible to those when the compensation is complete.

Page 177 - ... of suspension may be measured by a scale on the glass cover. There is a small glass window in each end provided with an index line to mark the horizontal plane. Without the small weight, the needle before being magnetized was exactly balanced, so the weight is intended to balance the vertical magnetic force ashore or on board. If a...

Page 306 - Fig. 1002, let the sextant be held vertically and let a be the index glass after the index arm ad has been turned so that the index glass is parallel to the horizon glass b and the index d coincides with the zero of the limb. A ray of light...

Page 557 - The transmitting clock that sends out the signals is corrected very accurately, shortly before noon, from the mean of three standard clocks that are rated by star sights with a meridian transit instrument. The noon signal is seldom in error to an amount greater than one or two tenths of a second, although a tenth more may be added by the relays in use on long telegraph lines. Electric transmission over a continuous wire is practically instantaneous.

Page 605 - , crosses the second Sumner line will be the position of the ship at the time of the second observation, and a, her position at the first observation.

Page 344 - A sidereal day has already been denned as the interval of time between two successive transits of the vernal equinox, or the first point of Aries, over the upper branch of the same meridian.