American Practical Navigator

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U.S. Government Printing Office, 1939 - Nautical astronomy

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Page 324 - All circles are supposed to have their circumferences divided into 360 equal parts, called degrees ; each degree is divided into 60 equal parts, called minutes ; and each minute into 60 equal parts, called seconds; an
Page 96 - value when the height of the tide within is changing most rapidly, ie, at a time about midway between high and low water. The water in the basin keeps at approximately the same level as the water outside. The flood stream corresponds with the rising and the ebb with the falling of the tide.
Page 57 - (Fr.-Cu.). 9. Cumulo-nimbus (Cu.-Nb.) ? the thunder-cloud; shower-cloud.—Heavy masses of cloud rising in the form of mountains, turrets, or anvils, generally surmounted by a sheet or screen of fibrous appearance (false Cirrus) and having at its base a mass of cloud similar to nimbus. From the base local showers of
Page 324 - A plane surface is one in which, any two points being taken, the straight line between them lies wholly within that surface. Parallel lines are such as are in the same plane
Page 44 - THE BAROMETER The barometer is an instrument for measuring the pressure of the atmosphere, and is of great service to the mariner in affording a knowledge of existing meteorological conditions and of the probable changes therein. There are two classes of barometer—mercurial and aneroid.
Page 56 - thin, whitish sheet of clouds sometimes covering the sky completely and giving it only a milky appearance (it is then called Cirro^nebula), at other times presenting, more or less distinctly, a formation like a tangled web. This sheet often produces halos around the sun and moon.
Page 96 - Tide rips are made by a rapid current setting over an irregular bottom, as at the edges of banks where the change of depth is considerable. Current arrows on the chart must not be regarded as indicating absolutely the conditions that are to be encountered. They represent the mean of the direction and force observed, but the
Page 96 - A swift current often occurs in the narrow passage connecting two large bodies of water, owing to their considerable difference of level at the same instant. The several passages between Vineyard Sound and Buzzards Bay are cases in point. In the Woods Hole Passage the maximum strength of the tidal streams
Page 97 - will be found most useful when it is desired to enter port or pass through inclosed waters during fog by means of the buoys ; here safety demands that the buoys be made successively, to do which requires, if the fog be dense, very accurate courses and careful attention to the times,
Page 98 - in passing between dangers where there are no suitable leading marks, as, for instance, between two islands or an island and the main shore, with dangers extending from both, a midchannel course may be steered by the eye alone with great accuracy, as the eye is able to estimate very closely the

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