## 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 |

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Page vii

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**reading**Microscopes . - Reduction of a Base measured on any elevated Plain to its Value at the Level of the Sea . - Prolonging and verifying a Measured Base by Triangulation . CHAPTER III . TRIANGULATION . Choice of Stations . - Method ... Page 25

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**readings**at which were , of course , always taken . Subsequently , the verniers at C and D were added , each of ...**reading**of the vernier A , and also in a smaller degree to B. The influence assigned to each vernier is , in fact ... Page 28

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**reading**the micrometer micro scope to the sector , and then completing the observation by the wire micrometer attached to the eye end of the telescope , noting also the level**readings**and the time . The instrument is then turned half ... Page 32

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**Reading**. Apparent Elevation or Depression . Remarks . The third column , headed " horizontal**reading**, " is the**reading**of the vertical arc when the telescope is levelled , and is in fact the index error , which is however best ... Page 33

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**reading**on the graduated limb when the telescope is pointed to the next forward station , is not the number of degrees contained between these two lines , but the angle that this second line forms D with the first meridian , or the line ...### 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 contour lines correction course curvature declination degree depression determined difference of longitude direction divisions earth equal feet field-book figure fixed formula Géodesie given Greenwich Greenwich mean ground height horizontal line hour angle inches index error instrument intersection interval laid latitude length lunar marked mean solar measured meridian method miles Nautical Almanac noon object observed angle obtained operation 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 104 - 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 106 - ACCOUNT OF THE MEASUREMENT OF AN ARC OF THE MERIDIAN, EXTENDING FROM DUNNOSE IN THE ISLE OF WIGHT, TO CLIFTON IN YORKSHIRE...

Page 51 - AS, 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 gAD, then * " Trigonometrical Survey,

Page 86 - 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 column.

Page 141 - Call the zenith distance north or south, according as the zenith is north or south of the object. If...

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.

Page 86 - SO'OO 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 85 - 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.

Page 84 - ... the thermometer fitted into the aperture in the lid of the sliding tube, by means of a collar of cork ; and the tin sliding tube pushed up or down to admit of the bulb of the thermometer being about two inches from the bottom of the pot. Before using a thermometer for this purpose, it is necessary to ascertain if the boiling point is correctly marked for the level of the sea by a number of careful observations, and the difference, if any, must be noted as an index error. It is always desirable...

Page 138 - Objects near the horizon appear more elevated by it above their true directions than those at a high altitude. 3dly. The rate of its increase is nearly in proportion to the tangent of the apparent angular distance of the object from the zenith. But this rule, which is not far from the truth, at moderate zenith distances, ceases to give correct results in the vicinity of the horizon, where the law becomes much more complicated in its expression. 4thly. The average amount of refraction, for an object...