## Outline of the Method of Conducting a Trigonometrical Survey, for the Formation of Geographical and Topographical Maps and Plans: Military Reconnaissance, Levelling, EtcWeale, 1850 - 253 pages |

### From inside the book

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**computed**from D and C ; and the length of EF is afterwards obtained in the two triangles DEF and FEC . In like manner the relative positions of the points H , G , K , & c . , are obtained , and this system should be pursued till the ... Page 19

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**computed**for the purpose of facilitating this calculation for every minute of H and h , and for every ten minutes of A. When the altitudes differ more than 2 ° or 3 ° from zero , the following formula is to be used in preference : - Sin ... Page 21

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**computed**by all three methods . On the Ordnance Survey they were formerly mostly calculated by the second , and checked by the third , but at present the last of these modes , that by Legendre's formula , is the only one used . This ... Page 31

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**computed**from the " Register , " made out directly from the field - book , the calculation from the plot being afterwards made simply as a check upon the other . All trigonometrical points and levelling marks should , if practicable ... Page 34

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**computed**, though the hedges and other inclosures are shown on the plot . The contents of inclosures can be very quickly ascertained from the plan , by drawing lines in pencil about one or two chains distant , across the paper , both ...### Contents

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Outline of the Method of Conducting a Trigonometrical Survey, for the ... Edward Charles Frome No preview available - 2016 |

### Common terms and phrases

accuracy accurate acres adjustment angles of elevation Apparent altitude ascertained astronomical axis azimuth barometer base boundaries calculated centre chain chronometer circle computed contour lines correction course curvature declination degree depression determined difference of longitude direction divisions earth equal feet field-book fixed Géodesie 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 traced triangles trigonometrical points Trigonometrical Survey tube vane vertical zenith distance

### Popular passages

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 - 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,

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 112 - ... diameter. B, a sliding tube of tin, moving up and down in the pot ; the head of the tube is closed, but has a slit in it, C, to admit of the thermometer passing through a collar of cork, which shuts up the slit where the thermometer is placed. D, thermometer, with so much of the scale left out as may be desirable. E, holes for the escape of steam. The pot is filled four or five inches with pure water ; the thermometer fitted into the aperture in the lid of the sliding tube, by means of a collar...

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...

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 14 - heliotrope," which is a piece of looking-glass, so adjusted as to reflect the sun directly to any desired point, is the most perfect arrangement. For night signals, an Argand lamp is used ; or, best of all, Drummond's light, produced by a stream of oxygen gas directed through a flame of alcohol upon a ball of lime. Its distinctness is exceedingly increased by a parabolic reflector behind it, or a lens in front of it. Such a light was brilliantly visible at 66 miles distance. (385) Observations of...