## 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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**taken**; if it is very irregular it may be divided into several parts . " " " The reduced length a b of the base AB is thus found , and if the length of the chord is required , a b B it is found by subtracting AB 24r2 . Beside the marks ... Page 11

... visible are most accurately observed with a large theodo- lite , which is then

... visible are most accurately observed with a large theodo- lite , which is then

**taken**to the other points on the line , as well as those selected on either side of it , where all MEASUREMENT OF A BASE LINE . 11 Dip of the Sea Horizon. Page 14

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**taken**. In using this " Heliostat " it is only necessary for the assistant , who is posted as near as possible to the station , to keep the enlightened object in the focus of the telescope , and the mirror is adjusted instrumentally so ... Page 18

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**taken**between objects situated in a plane oblique to the horizon to their horizontal values , which reduction , in any instrument measuring the exact angular distance between two objects having different zenith distances , is a matter ... Page 19

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**taken**correctly , be more than 180o . The lines containing the observed angles are in fact tangents to the sphere ( supposing the earth to be one ) , whereas to obtain the three points considered as vertices of a plane triangle , the ...### Other editions - View all

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 division earth equal feet field-book fixed formula 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 minute moon's Nautical Almanac noon object observed angles obtained Ordnance Survey parallax parallel pickets place of observation plane plotted polar distance pole portions position purpose radius reading reference refraction right ascension roads rods scale screw sections semidiameter sextant sidereal sides sketch slopes spherical spirit level star stations subtractive surface taken tangent telescope temperature theodolite thermometer tion traced transit triangles trigonometrical points Trigonometrical Survey tube vane vertical zenith distance

### Popular passages

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 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 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...