## Outline of the Method of Conducting a Trigonometrical Survey, for the Formation of Topographical Plans: And Instructions for Filling-in the Interior Detail, Both by Measurement and Sketching : Military Reconnaissance, Leveling, &c., &c., with the Explanation and Solution of Some of the Most Useful Problems in Geodesy and Practical Astronomy, to which are Added a Few Formulę and Tables of General Utility for Facilitating Their CalculationJohn Weale Architectural Library, 1840 - 200 pages |

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accuracy adjustment altitude angle of depression angles of elevation apparent ascertained Astronomy axis azimuth base calculated centre chain chronometer circle construction contents contour contour lines correction curvature degree determined diameter difference of latitude difference of longitude direction earth equal feet field-book figure fixed Geodesie Greenwich Greenwich mean ground height horizontal line inches index error instrument intersection interval laid latitude length longitude marked mean measured meridian method miles mountain barometer Nautical Almanac necessary object observed angles obtained Ordnance Survey parallax parallel perpendicular pickets plane plotting pole protractor purpose radius reciprocal angles refraction right angles right ascension rods scale screw semidiameter sextant sidereal sides sketch slopes spherical excess spirit-level staff star stations subtracted surface Survey of Ireland taken tangent telescope temperature theodolite thermometer tion topographical Townlands triangles trigonometrical points Trigonometrical Survey tube vane vernier vertical arc vertical distances zenith distance zero

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Page 109 - 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 111 - Wales," will be found all the details connected with the measurement of an arc of the meridian, extending from Dunnose in the Isle of Wight, to Clifton in Yorkshire. The calculations are resumed at page 354« of the third volume ; the length of one degree of the arc resulting from which, in latitude 52° 30...

Page 75 - AB, aBA, 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 g AD, then * " Trigonometrical Survey," TOl. ip 175. See also, on the subject of refraction, Woodhouse's...

Page 83 - ... 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 the levelling-staff is...

Page 76 - 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 refraction...

Page 145 - Z S") when to the north below the pole. Perhaps the rule given by Professor Young for the two first cases is more simply expressed thus : — Call the zenith distance north or south, according as the zenith is north or south of the object. If it is of the same name with the declination, their sum will be the latitude; if of different names, their difference; the latitude being of the same name as the greater. EXAMPLE I. On April 25, 1838, longitude 2m 30' east, the meridional double altitude of the...

Page 108 - 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 125 - 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 its representation, thus mapped on its base, is such as it would actually appear to an eye placed at an infinite distance from it.

Page 152 - ... 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.

Page 108 - When the thermometer has been boiled at the foot and at the summit of a mountain, nothing more is necessary than to deduct the number in the column of feet opposite the boiling point below, from the same of the boiling point above : this gives an approximate height, to be multiplied by the number opposite the mean temperature of the air in Table II., for the correct altitude.