## A treatise on navigation and nautical astronomy, including the theory of compass deviations |

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12 hours apparent noon applied approximate April astronomical azimuth Bowditch celestial chro chronometer circle coefficients column compass needle computed Corr correction corresponding cosec course and distance curve declination departure determined difference of latitude difference of longitude direction equal altitudes equation error force fore-and-aft formula given Greenwich mean heavenly body heeling horizon hour angle induced instant intersection interval line of position longitude magnetic bearing magnetic course mean noon mean sun Mercator chart meridian altitude method miles minutes minutes of arc moon moon's Nautical Almanac navigator observation obtained parallel parallel sailing plane polar pole prime vertical quadrantal deviation refraction result right ascension sailing sextant ship swings ship's head sidereal sight soft iron South star starboard sun's tangent tion transit triangle true altitude true course tude vernier versin zero

### Popular passages

Page 346 - The three days are the sidereal, apparent solar, ani mean solar days, each of which days is divided into 24 hours, each hour into 60 minutes, and each minute into 60 seconds ; the subdivisions of the sidereal day being sidereal time, of the apparent solar day apparent time, and of the mean solar day mean time. 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 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 two-tenths of a second, although a tenth more may he added by the relays in use on long telegraph lines.

Page 34 - NAVIGATION 29. Advantages and disadvantages of the different projections. — The polyconic chart has practically no distortion along the middle meridian, is well adapted to all latitudes, shows areas in their proper relation as to magnitudes, and permits the use of a single scale of distance anywhere. However, the meridians and parallels are curved, the rhumb line is curved, and there is distortion as the longitude departs from the middle meridian. The gnomonic chart is useful simply for finding...

Page 282 - By gnomonic charts. (2) By computation. (3) By graphic methods. — By gnomonic charts. — Draw lines from points of departure and destination tangent to the limiting parallel. In the case of the great circle sailing charts of the US Hydrographic Office, find the track from point of...

Page 490 - ... Observatory, near London, England, is almost universally used as the prime meridian. A small circle is a circle on the surface of the earth marking the intersection of the earth and a plane which does not pass through its center. Parallels of latitude are circles parallel to the plane of the equator. The latitude of a place is its angular distance north or south of the equator, from 0° to 90°.

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 47 - The air vessel has within it a hollow cone, open at its lower end, and provided with the pivot bearing or cap, containing a sapphire, which rests upon the pivot and thus supports the card; the cap is provided with adjusting screws for accurately centering the card. The pivot is fastened to the center of the bottom of the bowl by a flanged plate and screws. Through this plate and the bottom of the bowl are two small holes which communicate with the expansion chamber and admit of a circulation of the...

Page 308 - To prove this, let M and m be the two reflecting mirrors of a sextant whose planes are perpendicular to the plane of the sextant, in this case the plane of the paper (Fig.

Page 215 - AEB, set the sextant to this angle, and remembering that AB subtends the same angle at all points of the arc AEB, the ship will be outside the arc AEB, and clear the danger S', as long as AB does not subtend an angle greater than AEB, to which the sextant is set.

Page 364 - 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...