Trigonometrical Surveying, Levelling, and Railway EngineeringW. Blackwood, 1842 - 181 pages |
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Trigonometrical Surveying, Levelling, and Railway Engineering William Galbraith No preview available - 2016 |
Common terms and phrases
accuracy accurately add the log adjustment angle apparent altitude Ascent astronomical circle axis azimuth barometer Bencampsie Bencleugh Benlomond bisect centre computed Constant log Constant logarithm convenient correction cosec cosine depression determine difference Edinburgh equal equator error feet log formula give given gradients Greenwich mean half height Hence horizontal hour angle Inchkeith inclined plane instrument Kellie Law Lamlash latitude 55 length limb log Log log secant log Table logarithm longitude mean solar measured meridian method microscope miles minutes Nautical Almanac nearly object Observatory parallax parallel perpendicular placed polar distance position radius railway reduction refraction right ascension screws seconds of arc sextant shewn shews sidereal sine slopes spherical spherical excess spheroid star star's subtracted sun's Table XIX taken telescope terrestrial theodolite thermometer tion transit triangle Trigonometrical Survey True altitude tude verniers versines zenith distance zenith-distance
Popular passages
Page 101 - ... triangle, or the number of links to be deducted from each chain's length, in measuring up or down an inclined plane, to reduce it to the horizontal measure. The level, which is shown under and parallel to the telescope, is attached to it at one end by a joint, and at the other by a...
Page 101 - The level, which is shown under and parallel to the telescope, is attached to it at one end by a joint, and at the other by a capstan-headed screw...
Page 101 - ... parallel to the optical axis of the telescope, or line of collimation ; the screw, g, at the opposite end, is to adjust it laterally, for true parallelism in this respect. The telescope has two collars, or rings, of bell metal, ground truly cylindrical, on which it rests in its supports...
Page 106 - Now release the upper plate, and move it round by hand till the telescope is directed to the second object, whose angular distance from the first is required...
Page 112 - ... with the load it carries, is prevented from pressing too heavily on its bearings, by two friction rollers on which it rests, one of which is shown at e. A spiral spring, fixed in the body of each pillar, presses the rollers upwards, with a force nearly a counterpoise to the superincumbent weight; the rollers on receiving the axis yield to the pressure, and allow the pivots to find their proper bearings in the Y's, relieving them, however, from a great portion of the weight. The telescope, K,...
Page 104 - ... of a distant object; then turn the telescope half round in its Y's till the level lies above it, and observe if the same point is again cut by the centre of the wire ; if not, move the wire...
Page 39 - I'), the sum will be the log. of an arc on the meridian in seconds, m", to be added to the latitude f, if approaching the pole, but subtracted from / if receding from it, the sum or difference will give x, the latitude of the foot of the perpendicular upon the given meridian from the point in that required. 3. To the log. of o add the log.
Page 125 - ... has five vertical and two horizontal wires. The centre vertical wire ought to be fixed in the optical axis of the telescope, and perpendicular to a line drawn through the pivots of the axis. It will be evident, upon consideration, that these wires are rendered visible, in the day-time, by the rays of light passing down the telescope to the eye ; but at night, except when a very luminous object (as the moon) is observed, they cannot be seen. Their illumination is therefore effected by piercing...
Page 115 - ... in its place, and must be removed as soon as the operation of levelling the horizontal axis is performed. The whole instrument stands upon three footscrews, placed at the extremities of the three branches which form the tripod, and brass cups are placed under the spherical ends of the foot-screws. A stone pedestal, set perfectly steady, is the best support for this as well as the portable transit instrument.
Page 105 - ... to the middle, the limb is horizontal in that direction; but if otherwise, half the difference must be corrected by the parallel plate-screws over which the telescope lies, and half, by elevating or depressing the telescope, by turning the tangent-screw...