## 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 |

### From inside the book

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Page vii

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**Longitude**are known - Convergence of Meridians - Variation of Compass - Projections of the Sphere ........ 109 CHAPTER X. PRACTICAL ASTRONOMY . Sextant and Repeating Circle - Definitions . PROBLEMS . I. To convert Sidereal Time into ... Page viii

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**Longitude**on the surface of the Earth ... 196 16. Corrections for Curvature and Refraction ...... .. 197 17. Reduction upon each Chain's Length for different Vertical Angles .. 198 18. Inclination of Slopes for different Vertical Angles ... Page 2

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**longitude**of a number of the principal and most con- spicuous stations are determined by astronomical observations , and the distances between them calculated to enable their positions to be laid down as correctly as they can be ... Page 11

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**longitudes**between two meridians , such as those of the observatories at Greenwich and Paris , and the measurement of an arc of the meridian to obtain the length of a degree in different latitudes , from whence to deduce the figure and ... Page 13

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**longitudes**by signals , which will be explained hereafter . * It has been already stated , that the sides of. * It is also eminently calculated for those light - houses where powerful illumina- * This instrument was raised on a scaffold ...### Other editions - View all

### Common terms and phrases

accuracy adjustment angles of elevation Apparent altitude ascertained Astronomy axis azimuth barometer base calculated centre chain chronometer co-latitude contour contour lines correction curvature declination degree determined diameter difference of latitude difference of longitude direction earth equal equator feet field-book figure fixed Geodesie given Greenwich Greenwich mean ground height horizontal line hour angle inches index error instrument intersection interval laid latitude length lunar distance marked measured meridian method mountain barometer Nautical Almanac necessary object observed angle obtained Ordnance Survey parallax parallel perpendicular pickets place of observation plane plotting polar distance pole purpose radius reading reciprocal angles refraction right angles right ascension scale screw Semidiameter sextant sidereal sidereal day sides sketching slopes spherical excess spherical triangle staff star stations subtracted surface taken tangent telescope temperature theodolite thermometer tion topographical trigonometrical points Trigonometrical Survey tube vane vernier zenith distance zero

### Popular passages

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.