A Text Book on Surveying, Projections, and Portable Instruments.1876 |
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Common terms and phrases
accurately adjustment altitude angular distance astronomical bearing axis of collimation axis of rotation azimuth plates base line boat bubble centre chart circle clamp clock collimation error computed cos² cross-wires determined difference direction equal equatorial intervals equatorial star feet fixed formula harbor height high water horizontal angle hour angle HYDROGRAPHICAL SURVEYING inches instrument intersection latitude and longitude length line of sight lower plate Lunitidal Interval mark mean thread measured method micrometer micrometer thread middle meridian miles moon move Navigation necessary noted object observed parallel perpendicular plane plane of reference plotted points polyconic position principal stations projection reading reduced reference right angles right ascension sextant ship sin² soundings spherical excess spheroid star tangent screw tape telescope theodolite tide wave tion transit triangle tripod tube turn upper plate velocity vernier versin vertical wire zenith distances zenith telescope zero
Popular passages
Page 40 - Definition. The excess of the sum of the angles of a spherical triangle over two right angles is called the spherical excess.
Page 32 - The following examples will serve to illustrate the use of the preceding table : I. Elevation of Instrument required to overcome Curvature and Refraction. — Let us suppose that a line, A to B, was 18 miles in length over a plain, and that the instrument could be elevated at either station, by means of a portable tripod, to a height of 20 or 30 or 50 feet. If we determine upon 36.7 feet at A, the tangent would strike the curve at the distance represented by that height in the table, viz., 8 miles,...
Page 21 - ... Fahrenheit. The velocity of sound through the air is independent of the barometric pressure, and experiments show it to be sensibly unaffected by its hygrometrical state of moisture and dryness; by the nature of the sound itself, whether produced by a blow, gunshot, the voice, or a musical instrument; by the original direction of the sound, whether, for instance, the muzzle of a gun is turned one way or the other ; or by the nature and position of the ground over which the sound is conveyed....
Page 89 - ... components) the amplitudes and phases of the long-period components are corrected by the process of elimination heretofore referred to. MEAN VALUES AND EPOCHS OF COMPONENTS 102. Mean values. — The amplitude of each component of the actual tide increases and decreases with the changing inclination of the moon's orbit to the plane of the earth's Equator, and the amplitudes computed from a particular set of observations must therefore be corrected before they may be used at another period. The...
Page 32 - Refraction.—Let us suppose that a line, A to B, was 18 miles in length over a plain, and that the instrument could be elevated at either station, by means of a portable tripod, to a height of 20 or 30 or 50 feet. If we determine upon 36.7 feet at A, the tangent would strike the curve at the distance represented by that height in the table, viz., 8 miles, leaving the curvature (decreased by the ordinary refraction) of 10 miles to be overcome. Opposite to 10 miles we find 57.4 feet, and a signal...
Page 16 - But as e is generally a small angle and need not be known with extreme precision, it is better to compute the excess of B above b, and supposing 0 to be given in minutes. 8 sin2!
Page 41 - ... determined, the previous determination of the spherical excess is not necessary for the calculation of the sides, though it will be required for estimating the relative value of the observations.