Outline of the Method of Conducting a Trigonometrical Survey, for the Formation of Geographical and Topographical Maps and Plans: Military Reconnaissance, Levelling, Etc
Weale, 1850 - 253 pages
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accuracy accurate Additives adjustment altitude angle apparent applied ascertained axis azimuth barometer base boundaries calculated centre chapter chronometer circle compared contained contents contours correction course declination depression described detail determined difference direction distance divisions drawn earth elevation equal error evidently example feet figure fixed given gives ground half height horizontal hour inches instrument interval known laid land latitude latter laying length longitude marked mean measured meridian method miles minute nature nearly necessary noon object observed obtained operation parallax parallel plane plotted pole portions position practical proportion reading reference refraction represented right ascension roads scale screw sidereal sides sketch spherical star stations supposed surface survey taken taking telescope temperature theodolite thermometer tion tracing transit triangles trigonometrical true vertical zenith distance
Page 169 - A Solar Day is the interval of time between two successive transits of the sun over the same meridian; and the hour-angle of the sun is called Solar Time.
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 114 - When the boiling point at the upper station alone is observed, and for the lower the level of the sea, or the register of a distinct barometer is taken, then the barometric reading had better be converted into feet, by the usual method of subtracting its logarithm from 1-47712 (log. of 30 inches) and multiplying by '0006, as the differences in the column of " barometer " vary more rapidly than those in the ''''feet
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 74 - BA, the sum of the two refractions ; the rule for the mean refraction then in this case is, subtract the depression from the sum of the contained arc and the elevation, and half the remainder is the mean refraction -. The...
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 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...