## 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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**approximation**to their horizontal angular distance is obtained by observing each of them with reference to some distant mark considerably to the right or left , and taking the difference of these angles for the one required . The index ... Page 65

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**approximate**distance ; but even without this scale , if the pencil b be held up to the eye at any distance a , and the height or diameter of any object h of h * About 1100 feet in one second . A light breeze will increase or diminish ... Page 105

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**approximate**height is then obtained by inspection , taking the difference between the numbers corre- * As a proof , however , that the results given by the barometer are not always to be de- pended upon when extended to very great ... Page 106

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**approximate**7075 altitude 110 ft . 30.281 5660 6.3675 In Table 2nd opposite 30-281 is opposite 30-409 611 501**Approximate**diff . of alt . 110 · · Add correction table 6.3 True difference of altitude 116.3 or Dr. Hutton's rule for the ... Page 107

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**approximate**height in fathoms . 3rd . Correct the number last found for the atmospheric tempe- rature , shown by the detached thermometers , as follows : -For every degree that the mean of the two differs from 31 ° , take so many 35 ...### 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 Additives adjustment altitude angle apparent applied approximate ascertained axis azimuth barometer base boundaries calculated centre chapter chronometer circle contained contents contours correction course declination depression described detail determined difference direction distance divisions drawn earth elevation equal error evidently feet figure fixed given gives ground half height horizontal hour inches instrument intersection interval known laid land latitude latter laying length longitude marked mean measured meridian method miles minute nature nearly necessary noon object observed obtained operation parallax parallel plane plotted pole portions position practical proportion quantity reading reference refraction represented right ascension roads scale screw sidereal sides sketch spherical star stations supposed surface survey taken taking telescope temperature theodolite thermometer tion traced transit triangles trigonometrical true 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...