. The elements of railroad engineering . ticbearing as read from the needle and recorded in the columnheaded Mag. Bearing. Had the deflection angle been re-corded V instead of R, the deduced bearing would havebeen the difference between 75° 00 and 14° 30, which is60° 30, and would be recorded N 00° 30 E. The magneticbearing being N 89° 20 E would have at once revealed theerror. The confusion of the directions R and L is the com-monest source of error in recording deflections, thoughsometimes a mistake of ten degrees is made in reading thevernier. It is a wise precaution to read both angle andb
. The elements of railroad engineering . ticbearing as read from the needle and recorded in the columnheaded Mag. Bearing. Had the deflection angle been re-corded V instead of R, the deduced bearing would havebeen the difference between 75° 00 and 14° 30, which is60° 30, and would be recorded N 00° 30 E. The magneticbearing being N 89° 20 E would have at once revealed theerror. The confusion of the directions R and L is the com-monest source of error in recording deflections, thoughsometimes a mistake of ten degrees is made in reading thevernier. It is a wise precaution to read both angle andbearing after they are recorded and compare them with therecorded readings. B Simple Triangulation.—Triangulation is an application of the principles of trigonometry to the measurement of in-accessible lines angles. A commonoccasion for the useof trigonometry isillustrated in , where the lineof survey crosses astream too wide anddeep for actualmeasurement. Settwo points A andB on line, one on. Fig. 270. SURVEYING. G35 each side of the stream. Estimate roughly the distanceA B. Suppose the estimate is 425 feet. Set another pointC, making the distance A C equal to the estimated dis-tance A B — -425 feet. Set the transit at A and measurethe angle B A C = say 79° 00. Next set up at the pointC and measure the angle A C B — say 5(3° 20. Theangle A B C is then determined by subtracting the sumof the angles A and C from 180°; thus, 79° 00 + 50° 20 =135° 20. 180° 00-135° 20= 44° 40= the angle A B now have a side and three angles of a triangle given,to find the other two sides A B and C B. These sidesmay be easily found by the methods given for the solutionof triangles (see Arts. 759, etc.) by drawing a line fromthe vertex of one of the angles y^ or C so as to dividethe triangle ABC into two right-angled triangles. Asimpler and easier method, however, is the following: Inhigher works on trigonometry, it has been demonstratedth
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectrailroadengineering
