A Treatise on Levelling, Topography, and Higher Surveying |
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Other editions - View all
TREATISE ON LEVELLING TOPOGRAP William Mitchell 1816-1868 Gillespie,Cady 1840 Staley No preview available - 2016 |
Common terms and phrases
adjustment admirable United angle of elevation angular artificial horizon back-sight barometer bisected bottom centre CHAPTER circle clamp column compass contour-lines coördinates correction cross-hairs curvature desired height desired point determined difference of heights direction equal feet fore-sight formula gamboge greatest slope ground half-way hill horizon-glass horizontal inch Indian-ink intermediate latitude length level line line of collimation line of sight lines of greatest measured mercury method miles millimetres mirror note the reading object object-glass oblique observed angle parallel perpendicular placed plane of reference plumb-line precisely reflected represented right angles scale screws set the instrument sextant shade shaft side spherical angles spherical excess stakes starting-point station subtract surface survey taken target temperature thalwegs theodolite tint tion Topographical transit triangle tripod tube turn the telescope underground upper usually vernier vernier-plate vertical angles vertical plane zenith distance
Popular passages
Page 144 - All buoys along the coast, or in bays, harbors, sounds, or channels, shall be colored and numbered, so that passing up the coast or sound, or entering the bay, harbor, or channel, red buoys with even numbers shall be passed on the starboard hand, black buoys with uneven numbers on the port hand, and buoys with red and black stripes on either hand. Buoys in channel-ways shall be colored with alternate white and black perpendicular stripes.
Page 89 - ... lines of greatest slope when looking along them from below upwards. They can be readily determined by the slope level. On these lines are found the projecting or protruding bends of the contour lines. Valley lines are the reverse of ridge lines. They are indicated by the water courses which follow or occupy them. They are the lines of greatest slope when looked at from above and of least slope when looked at from below. On these lines are found all the receding or reentering points of the contour...
Page 171 - In terms of the coordinates of rectangular axes referred to one of the points of the triangulation, the latitude and longitude of which are known, — y being the ordinate in the direction of the meridian, and x the ordinate perpendicular to it...
Page 30 - The rodman holds the rod on the starting-point, which may be a peg. a door-sill, or other "bench-mark." He stands square behind his rod, and holds it as nearly vertical as possible. 2. The leveler sets up the instrument, somewhere in the direction in which he is going, But not necessarily, or usually, in the precise line. He then levels the instrument by the parallel platescrews, sights to the rod, and notes the reading, whether of target or speaking-rod, as a
Page 43 - VII. DIFFICULTIES. • (67.) Steep Slopes. In descending or ascending a hill, the instrument and the rod should be so placed that the sight should strike as near as possible to the bottom of the rod on the up-hill side, and the top of the rod on the down-hill side. Try this by levelling over two screws, setting the instrument so that one pair of opposite plate-screws shall point iti the direction of the line, but do not be too particular ; it is a waste of time.
Page 159 - ... Captain Kater. By means of this a station 48 miles distant was observed. The most powerful night signal is, however, Drummond's light. This was invented by Lieutenant Drummond, and consists of a ball of lime about \ in. diameter placed in the focus of a parabolic reflector and raised to an intense heat by a stream of oxygen gas directed through a flame of alcohol. This produces a light eighty times the intensity of an Argand burner. In boisterous and hazy weather this light was brilliantly visible...
Page 154 - ... reports, and to which the personal knowledge of the members of the committee could not be presumed to extend. MEASUREMENTS OF BASES. — There have been measured in all, up to the date of the present report, nine principal baselines, two of which are now connected by a primary triangulation. These two are the Fire Island base, on the south side of Long Island, and the Kent Island base, in Chesapeake bay. Both of these, and also a third one in Massachusetts, were measured with the apparatus designed...
Page 170 - K = distance in yards between two stations, the latitude and longitude of one of which is known, and u" this same distance converted to seconds of arc. L = latitude of 1st station. M = longitude of 1st station, -(- if west. Z = azimuth of 2d station at 1st, counted from the south round by the west, from 0° to 360°. The algebraic signs of the sine and cosine of this angle must be carefully...
Page 119 - The line of collimation of the telescope is an imaginary line, passing through the optical centre of the object-lens, and a point midway between the two parallel wires. These wires are made parallel to the plane of the sextant by revolving the tube in which they are placed. To see whether the line of collimation of the telescope is in adjustment, bring the images of two objects, such as the sun and moon, into contact at the wire nearest the instrument, and then, by moving the instrument, bring them...
Page 89 - ... of valleys. The former are lines which divide the water falling upon them, and from which it passes off on contrary sides. They are the lines of least slope when looking along them from above downward, and they are the lines of greatest slope when looking from below upward. They can therefore be readily determined by the slope level, etc. They are the lines of least zenith distances when viewed from either direction. On these lines are found all the projecting or protruding bends of the contour...