. Report of the Boundary commission upon the survey and re-marking of the boundary between the United States and Mexico west of the Rio Grande, 1891-1896 ... meridian of Monument No. 15 of commencing the erection of monuments this tangent was retraced, for direction only, witha probable back-azimuth error of 1. In locating monuments offsets between Monuments Nos. IIG UNITED STATES AND MEXICAN BOUNDARY. 3 and -11 were referred to the original tangent and corrected to conforui to the new Monuments Nos. U and l> ol^sets were referred to tangent No. 13, and the ori
. Report of the Boundary commission upon the survey and re-marking of the boundary between the United States and Mexico west of the Rio Grande, 1891-1896 ... meridian of Monument No. 15 of commencing the erection of monuments this tangent was retraced, for direction only, witha probable back-azimuth error of 1. In locating monuments offsets between Monuments Nos. IIG UNITED STATES AND MEXICAN BOUNDARY. 3 and -11 were referred to the original tangent and corrected to conforui to the new Monuments Nos. U and l> ol^sets were referred to tangent No. 13, and the originaltaugeut was uot used. 3. OhsenHitions at the end of the tdmjent to determine its i>ack-azimuth error.—The azimuthobservations at the end of the tangent were identical with those at its initial point and servedboth to determine the back-azimuth of this taugeut and to give the initial direction to the newone. The ditterence between the observed and theoretical value of the back-azimuth is designatedas the back-azimuth error. and indicates the degree of accuracy with which the tangent wastraced. Back-azimuth error of tangenU on parallel Sl^ 4. Computing the offsets.—From Appendix 7, Eeport for 1884 of the United States Coast audGeodetic Survey, we have the following general formula for computing difference of latitude:-(/ L=K ;?.B+K3 Sin- + (dL)- D-7( K^ sin^ , in which K = distance in meters; L =latitude; Z = azimuth of line; R = radius of curvature; N = normal to the polar axis at the Station; B=^, ^ ^-; G= ^-^^^^-^,,R arc 1 2 arc 1 When Z = 90° the above fornmla becomes —d L=K- 0, in wliich —d L is expressed in secondsof arc. To obtain the offset in meters this must be multiplied l>y the value of 1 of :irc in meters forthe latitude used. For parallel 31° 47, 1 of arc = .. meters, and the ;- formula for this parallel log d L=2 log The offset obtained from this formula is from a theoretically accurately traced t
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