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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 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 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 true bearing 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 472 - On these stakes strips of zinc will be fastened and remain until the whole measurement is completed. The temperature of the tape will be determined by three thermometers placed near the ends and in the middle of the tape. They will be attached to suitable supports and placed with their bulbs near the tape when measurements are being taken. Observers must be careful to keep sufficiently far away so as not to affect the thermometers. The tape will be suspended in hooks at intervals of 30 ft., and attached...
Page 443 - 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. (385) Observations 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.
Page 200 - If the bolt is horizontal in the wall of a building or other structure, it may be best connected in the following manner : Set up the instrument in such a position and at such an elevation that the small hole in the bolt may be bisected by the middle thread without displacing the level by more than five divisions, using the elevating screw for making this bisection. Since the instrument can be raised or...
Page 215 - 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 altered, the...
Page 383 - Longitude in time is then deduced from the difference between the local mean time and the Greenwich mean time of the observation and then converted into degrees.
Page 197 - The errors of adjustment will be determined at beginning and end of each series of obscrvations : 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. The error...
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 degrees from any position and have the level reading the same in both positions.
Page 332 - HI a microscope for reading the vernier, i is the index glass which is a small mirror attached to the index arm and perpendicular to the plane of the graduated arc. The horizon glass h is also perpendicular to the plane of the instrument, and is parallel to the index glass » when the index is at zero of the graduated arc. The lower half only of the horizon glass h is silvered. In Fig. 213 there is an opening in the upper part of the horizon glass. The horizon at sea or the reflection of the observed...