## 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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12 hours apparent noon approximate April astronomical azimuth Bowditch celestial chronometer circle coefficients column compass heading compass needle component Corr correction corresponding course and distance curve declination departure deviation due difference of latitude difference of longitude direction dygogram earth and ship easterly equal equation equinoctial fore-and-aft formula given glass Greenwich mean heavenly body horizon horizontal force hour angle inducing force instant interval limb longitude magnetic bearing magnetic course mean sun Mercator chart meridian middle latitude miles minutes minutes of arc moon moon's Nautical Almanac navigator North point observations parallax parallel parallel sailing perpendicular plane polar pole position prime vertical quadrantal deviation radius refraction represented right ascension sailing sextant ship swings ship's head sidereal sin2 South star starboard sun's Table tangent tion transit triangle true course tude upper vernal equinox vernier versin zenith zero

### Popular passages

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 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 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 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...

Page 362 - Moon's Semidiameter and Equatorial Horizontal Parallax for each mean noon and midnight at Greenwich. Columns adjoining those of the horizontal parallax give the change of that quantity in one hour, by means of which it can be reduced to any other Greenwich mean time, in the same way as the Sun's declination and the equation of time in the preceding examples. The...

Page 47 - ... used, though not indicated on the card. A system of numbering the degrees from 0° to 360°, always increasing toward...

Page 488 - These are modifications of the fundamental formula: sin h = sin L sin d + cos L cos d cos t, which is itself often preferred for the computation of the altitude from the latitude, declination, and hour angle.

Page 293 - ... force depends on this inclination, the amount of precession due to the action of the moon has a period equal to one revolution of the moon's node, or 18-6 years. These inequalities in the motion of precession are termed nutation. Changes in the Right Ascensions and Declinations of the Stars. — Since the declination of a heavenly body is its angular distance from the celestial equator, it is evident that any change in the position of the equator must change the declinations of the fixed stars....

Page 290 - Latin meridies, mid-day), is a great circle of the celestial sphere, passing through the poles of the earth and the zenith and nadir, crossing the equator at right angles, and dividing the sphere into an eastern and western hemisphere.