Manual of topographic methods

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Govt. Print. Off., 1906 - 88 Seiten
 

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Seite 49 - On deck protected" the cylinders shall be protected from the direct rays of the sun by means of structural erections or awnings. Tarpaulins covering cylinders and in contact therewith are not considered adequate protection. Protection by use of wood dunnage Is permitted. [CQFR 53-54, 18 FR 8239. Dec. 16, 1953] § 146.24-35 "Under deck" stowage. (a) Cylinders stowed "Under deck...
Seite 17 - ... accurately at the first attempt, the instrument is placed nearly in the meridian and is ready for work, but it commonly happens that more than one trial is required before the meridian is reached. In any case, the result should be verified by a second star, before proceeding with the observations. OBSERVATIONS FOR LATITUDE. As preliminary to this work it is necessary to prepare a list of pairs of stars, the two stars of each pair having such zenith distances that they will culminate at nearly...
Seite 52 - The precision of centering an instrument or signal over the reference or geodetic point increases in importance inversely as the length of the triangulation lines. Thus, if it is desired to exclude errors from this source as small as a second, one must know the position of the instrument within one-third of an inch for lines a mile long or within 6 inches for lines 20 miles long. The following easily remembered relations will serve as a guide to the required precision in any case: 1 second is equivalent...
Seite 41 - ... measurement is made along the railway tangent, nailed down to the railway ties. These boards are designed to support the devices for maintaining the tension, and the contacts are marked upon the strips of zinc. Mr. Baldwin's apparatus consists essentially of a wheel worked by a lever and held by ratchets in any desired position. This wheel is attached to the spring balance in such a way that by turning it the strain is put upon the spring balance, which is held at the desired tension by the ratchets....
Seite 60 - Each triangle, therefore, furnishes an equation of condition, which is known as an angle equation. The number of angle equations in any figure is equal to the number of closed triangles into which it can be resolved. But since certain of these are a consequence of the others, the number of angle conditions which it is desirable to introduce is less than the number of triangles. The number of angle equations in any figure is equal to the number of closed lines in the figure plus one, minus the number...
Seite 90 - Goode. 1900. 67 pp., 14 pis. 171. Boundaries of United States and of the several States and Territories, with outline of history of all important changes of territory (second edition), by Henry Gannett. 1900.
Seite 12 - Commission, whether by astronomic work or by triangulation, may be utilized for the above purposes. DEFINITIONS. Sidereal time is the time indicated by the stars, a sidereal day being the time which elapses between two passages of the vernal equinox across the meridian. Solar or apparent time is the time U.
Seite 61 - ... log. sin 0, 1, 3. The number of side equations which can be formed in any figure is equal to the number of lines in the figure, plus 3, minus twice the number of stations in it or I + 3 — 2n.
Seite 32 - ... which break is recorded on the chronograph sheets at both stations. The breaks are repeated at every two seconds for at least one full minute. The operation is then reversed by the observer at the second station making the breaks which are recorded at both stations as before. The differences of time between the chronometers at the two stations are read from the chronograph sheets at each station and corrected for error of the chronometers. The results from the two chronograph sheets will differ...
Seite 60 - The measured angles of each triangle should equal 180° plus the spherical excess. Each triangle, therefore, furnishes an equation of condition, which is known as an angle equation. The number of angle equations in any figure is equal to the number of closed triangles into which it can be resolved. But since certain of these are a consequence of the others, the number of angle conditions which it is desirable to introduce is less than the number of triangles. The...

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