Determining the Absolute Parameters of the Meridian Circle by Observing the Prime Vertical——III. The Overall Effects of Several Errors and Corrected Values on the Determination of Azimuth Equations

The observation made with an instrument which is turned over at the angle of 180 degrees is called the rotation (horizontal) axis observation.When the rotation axis observation is carried out in the prime direction, the instrument has much greater azimuth equations, for the observations before and after the rotation axis are all those made in the deviation from the prime vertical.Besides, there are the changes in the inclination when a star is observed from the east to the west.Therefore, the collimation error can not be completely eliminated, and the corrected values of some quadratic items must be added to the determined values of the azimuth equations.The quadratic item, corrections are evaluated numerically by using the given azimuth equations and changes in the inclination.The result of the corrected values relative to the zenith distance of a star observed in the prime direction is that the shorter the zenith distance of a star,the greater the corrected values, and the corrected values may be neglected when the zenith distance is greater than 40°.The effect of the diurnal abberation and the atmospheric refraction during the observation.made in the prime direction is also estimated.It is seen from the result (hat the effect may be neglected on the whole.