This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1908 edition. Excerpt: ...c sec h + b tan h. (94) Since neither i nor y enters into this equation, the effect of these errors must be taken into account through b, the inclination of the horizontal axis. This is to be determined with a spirit-level, and each circle reading, R, must be corrected for the particular inclination of ...
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This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1908 edition. Excerpt: ...c sec h + b tan h. (94) Since neither i nor y enters into this equation, the effect of these errors must be taken into account through b, the inclination of the horizontal axis. This is to be determined with a spirit-level, and each circle reading, R, must be corrected for the particular inclination of the axis that corresponds to R. The factor tan h becomes zero for an object in the horizon, and for this special case the effect upon the azimuth readings of an error of level is zero. On the other hand, when the object to be observed is at a considerable elevation, e.g., the Pole Star in an azimuth determination, the factor, tan h, becomes large and the effect of level error is magnified. It is in fact one of the chief sources of error in such determinations. 50. Determination of Errors of Adjustment.--The error above represented by c is called the collimation, and its effect is usually to be eliminated through a reversal of the instrument. Since the angular distance of 5 from one end of the horizontal axis is go0 + c, its distance from the other end must be 900--c, and as in the reversal these ends change places the effect of c must have one sign Circle R., and the opposite sign Circle L., and will therefore be eliminated from the mean of observations taken in both positions. In precisely the same way it may be shown that the effect of i, error of adjustment of the axes, is eliminated from the mean of observations taken in the two positions, and wherever any considerable precision is required in azimuth observations or in the measurement of horizontal angles, the observer should not fail to make an equal number of pointings in each position of the instrument to secure this elimination of errors. In the triangle HVZ the angle HVZ = HZM is...
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