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

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### Common terms and phrases

approximate astronomical azimuth Bowditch celestial 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 earth's East or West easterly equal equation fore-and-aft formula given Greenwich mean heavenly body horizontal force hour angle inducing force instant intersection interval latitude and longitude limb line of position longitude magnetic bearing magnetic course mean noon Mercator chart meridian altitude method middle latitude miles minutes of arc Nautical Almanac navigator North point observation obtained parallel parallel sailing plane polar pole prime vertical quadrantal deviation represented rhumbs right ascension set and drift sextant ship swings ship's head sidereal star starboard sun's tangent tion transit triangle true altitude true course tude zenith zero

### Popular passages

Page 452 - A cos 6 = cos a cos c + sin a sin c cos B cos c = cos a cos 6 + sin a sin 6 cos C Law of Cosines for Angles cos A = — cos B...

Page 362 - Sun, and other fundamental astronomical data for equi-distant intervals of Greenwich mean time. Part II, Ephemeris for the Meridian of Washington, gives the ephemerides of the fixed stars, sun, moon, and major planets for transit over the meridian of the old Naval Observatory, Washington.

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 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 518 - From the law of cosines derive the formula sin h = sin L sin d + cos L cos d cos t.

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 344 - A sidereal day has already been defined 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.

Page 70 - ... distance must depend on the range the ship takes when swinging ; if she be at anchor, in a tide-way, from 6 to 8 miles is not too much ; brought up by the middle (in a dock) 2 miles will suffice. 239. The next step is to determine the correct magnetic bearing of the selected object from the ship ; or in other words, the compass bearing it would have from on board if it were not disturbed by the attraction of the iron in the ship. This is effected by taking the compass to some place on...

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 559 - 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...