Outline of the method of conducting a trigonometrical survey, for the formation of geographical and topographical maps and plans: military reconnaissance, levelling, etc.; with the most useful problems in geodesy and practical astronomy, and formul: and tables for facilitating their calculation
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accuracy accurate acres adjusted angles of elevation Apparent altitude ascertained astronomical axis azimuth barometer base boundaries calculated centre chain chronometer circle contour lines correction course curvature declination degree depression determined difference of longitude direction divisions earth equal feet field-book fixed formula Geodesie given Greenwich Greenwich mean ground height horizontal line hour angle inches index error instrument intersection interval laid latitude length lunar distance marked mean solar measured meridian method miles Nautical Almanac necessary noon object observed angles obtained Ordnance Survey parallax parallel pickets place of observation plane plotted pole portions position purpose radius reading reference refraction right ascension roads rods scale screw sections semidiameter sextant sidereal sides sketch slopes spherical spherical excess spirit level star stations subtractive surface taken tangent telescope temperature theodolite thermometer tion tracing triangles trigonometrical points Trigonometrical Survey tube vane vertical zenith distance
Page 138 - Ocean, the first thing which strikes us is, that, the north-east and south-east monsoons, which are found the one on the north and the other on the south side of the...
Page 140 - An Account of the Measurement of an Arc of the Meridian, extending from Dunnose, in the Isle of Wight, Latitude 50° 37
Page 73 - BA, the sum of the two refractions ; hence, supposing half that sum to be the true refraction, we have the following rule when the objects are reciprocally depressed. Subtract the sum of the two depressions from the contained arc, and half the remainder is the mean refraction : — If one of the points B, instead of being depressed be elevated, suppose to the point g, the angle of elevation being gA.D, then * " Trigonometrical Survey,
Page 81 - ... indigo), till it nearly reaches to the necks of the bottles, which are then corked for the convenience of carriage. On setting the stand tolerably level by the eye, these corks are both withdrawn, which must be done carefully, and when the tube is nearly level, or the water will be ejected with violence ; and the surface of the water in the bottles, being necessarily on the same level, gives a horizontal line in whatever direction the tube is turned, by which the vane of a levelling staff is...
Page 181 - Call the zenith distance north or south, according as the zenith is north or south of the object.
Page 114 - Assuming 30'00 inches as the average height of the barometer at the level of the sea (which is however too much), the altitude of the upper station is at once obtained by inspection of Table I, correcting for temperature of the stratum of air traversed by table II.
Page 74 - BP£ ; that is, subtract the depression from the sum of the contained arc and elevation, and half the remainder is the mean refraction. Perhaps it may be necessary to remark, that previous to the observations the error of the instrument must be accounted for (163).
Page 158 - In the orthographic projection, every point of the hemisphere is referred to its diametral plane or base, by a perpendicular let fall on it, so that the representation of the hemisphere thus mapped on its base, is such as it would actually appear to an eye placed at an infinite distance from it. It is obvious, from the annexed figure, that in this projection only the central portions are represented of their true forms, while all the exterior is more and more distorted and crowded together as we...
Page 190 - ... correction, with its proper sign. If the sign be +, the correction must be added to the reduced altitude; but if it be — , it must be subtracted : in either case the result will give an Approximate Latitude. With the Altitude and Sidereal Time of observation, take out the second correction, and with the day of the month and the same Sidereal time, take out the third correction.