## A Treatise on Surveying, Volume 1 |

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accuracy accurate adjustment altitude arrow axis of rotation back-sights beam compass bearing bisected bubble centre chain circle clamp clinometer compass computed contour convenient correction curvature deducting departure determined diaphragm difference of latitude difference of level direction equal eye-piece feet fence field-book fixed focal length focus foot-screws fore-sights glass graduated ground Height of instrument horizontal distance inch index of refraction intersection latitude lens lenses line of collimation log sines mark means meridian meridional distance method needle object-glass observed angle obtained offset optical axis ordinary paper parallel parallel ruler perpendicular placed plane plane-table plate plotted plumb-bob polygon position protractor rays reduced level refraction right angles scale screen screws sextant sheet side sight-rule square staff station subtended surface surveyor tape telescope theodolite traverse triangles trigono true north vernier vertical angles vertical axis vide fig wires zero

### Popular passages

Page 100 - All the interior angles of any rectilineal figure, together with four right angles, are equal to twice as many right angles as the figure has sides.

Page 43 - Whatever the obliquity of the incident ray, the ratio which the sine of the angle of incidence bears to the sine of the angle of refraction is always constant for the same two media, but varies with different media.

Page 75 - Fig. 166. — Adjustment of Level. the staff reading at B should be. If now the actual staff reading at B does not agree with this, raise or depress the whole instrument by means of the levelling screws s, s, Fig. 104, until the reading at B is correct. Now bring the bubble to the centre of its run by means of the adjusting capstan screws at e connecting the level with the telescope. See now if the reading of the staff at A is altered, and if not, the adjustment is correct. If the reading at A is...

Page 280 - ... to the season of the year. The inclination or dip also varies, from hour to hour, in a similar manner to the declination. The declination and dip are also subject to secular variations, the duration of which is not accurately known. Accidental perturbations, due to magnetic storms, affect the needles. These variations in the position of the magnets occur with great suddenness, deflecting the needle right and left with great rapidity, almost like ordinary telegraphic signalling, and are generally...

Page 151 - ... departure, each correction being so applied as to diminish the whole error in departure. Proceed in same way for the correction in latitude.

Page 27 - Purposes feel that it is impossible to lay down a hard and fast rule as to the initiation of a candidate not perfect in his body, as required in article 4 of the Ancient Charges.

Page 99 - Example 1, the sum of the northings is equal to the sum of the southings, being 11.56 in each case ; and the sum of the eastings is equal to the sum of the westings, being 9.40 in each case. Hence, the work balances. In actual practice the work seldom balances. When it does not balance, corrections are generally applied to the latitudes and departures, by the following rules...

Page 33 - Find the product of the half sum and the three remainders. The square root of the product will be the area of the triangle.

Page 151 - As the sum of all the distances is to each particular distance, so is the whole error in latitude (or departure) to the correction of the corresponding latitude (or departure)* each correction being so applied as to diminish the whole error in each case.

Page 69 - ... these galls give rise to the females which live in the galls over winter and come out before the leaves appear in the spring. The galls just described are usually preceded -in the spring by a crop which affects the leaves only, and causes an enormous development of the midvein, often to the extent of an inch in diam.eter and an inch and a half in length. These latter galls are smooth and green but irregular in shape, succulent and a little harder than an unripe grape.