Surveying as Practised by Civil Engineers and Surveyors: Including the Setting-out of Works for Construction and Surveys Abroad, with Examples Taken from Actual Practice; Intended as a Handbook for Field and Office Use Also as a Text-book for Students
accuracy accurate adjustment altitude axis azimuth back sight barometer base bench marks bubble tube calculated centre line chain line Chapter circumpolar star clinometer collimation line compass contours correct cross hairs cross sections curve datum deflection angle difference equal Feet fence field book fixed fore sight given gradient graduated Greenwich mean ground horizontal instrument intersection latitude length longitude magnetic magnetic bearings mean measured meridian method metres miles millimetres minutes Nautical Almanac needle object glass observed angles offsets ordinary Ordnance Ordnance Survey parallel perpendicular plane plate plotted plumb line position radius railway ranging rod reduced level right angles right ascension scale screws sextant shaft shown in Fig side slope spherical spirit level stadia hairs staff reading star station surface survey surveyor tacheometer Tacheometry taken tangent point telescope temperature theodolite traverse triangle Troughton & Simms tunnel usually vernier vertical angle wire
Page 86 - 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 i - SURVEYING AS PRACTISED BY CIVIL ENGINEERS AND SURVEYORS. Including the Setting-Out of Works for Construction and Surveys Abroad, with many Examples taken from Actual Practice. A Handbook for use in the Field and the Office, intended also as a Text-book for Students. By JOHN WHITELAW, Jun., AMInst.CE, Author of
Page 197 - ... screws in such manner that the telescope may be turned around the horizon without the bubble of the level running a great number of divisions. The telescope is finally made horizontal by means of the elevating screw. The inclination at the moment of observing must not ordinarily exceed three divisions of the level and never five divisions. The instrument when in use ought always to be sheltered from the sun and •wind. It is carried from station to station without being dismounted, but the level...
Page 200 - The distance of bench-mark from instrument must be determined and recorded. Whenever work is stopped at least two temporary bench-marks should be established. These will consist of large nails or spikes driven their entire length vertically into the base of trees, or in the tops of sound stumps. When not in the vicinity of trees or stumps, wooden posts may be firmlyset in the ground with their tops flush with the surface and nails driven into them.
Page 194 - If the level bubble is well ground, equal displacements of the bubble, say of two divisions, will correspond to equal displacements on the rod. 3. Before using the level or determining its value, the fastening of the tube in its case should be examined. One end should be clamped down just tight enough to prevent the tube from moving easily, but not tight enough to strain the glass.
Page 200 - Now bisect the bench mark with the telescope normal and also inverted, noting the reading of the level. Read the rod on the plate with the telescope in both positions. It is necessary to eliminate collimation by inverting the telescope, since the collimation of the middle wire is not the same as that of the three wires.
Page 197 - In placing the foot-plates, great care should be taken that they be horizontal, on firm ground, and not liable to change. The surface of the ground, if not firm or level, should be removed. The errors of adjustment will be determined at beginning and end of each series of observations : that is to say, after having mounted the instrument and before dismounting it, and in all cases at least once each day. If the instrument has been deranged by a jar, the corrections must be determined anew.
Page 197 - To make the level and vertical axis of revolution perpendicular to each other, loosen the small clamp screw at one end of the horizontal bar fastened to the vertical axis, and by means of the elevating screw raise or lower that end of the upper horizontal bar until the telescope can be rotated 180° from any position, and have the level reading the same in both positions.
Page 474 - The extremity of each tape length will be marked on the zinc strips with a fine line and suitably numbered. The preservation of these strips furnishes a ready means of comparison of each tape length at any future time. The line should be measured two or more times, with a discrepancy when reduced of not more than I in 250,000.
Page 199 - If but one level can be used, the operation will be performed in the same order, but the time occupied in crossing must be as small as possible. With a single Kern level this process has given for a river 815 metres wide five results, the mean of which has a probable error of +0.5 millimetre.