Mansfield Merriman

Elements of Precise Surveying and Geodesy Mansfield Merriman

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1899 Excerpt: ...a formula that takes barometer and thermometer into account, is applied. Thus the true zenith distance z is found, and from this and the given latitude of the place and declination of the star the hour-angle t is computed from the above formula, and converted into time measure. The true sidereal time then results by adding. the right ascension of the star, and this is converted into local mean solar time and then into Eastern standard time, from which finally the watch error is found to have been 37.25 seconds slow. The probable error of this determination is less than one-quarter of a second. The most favorable position of a star for this work is when it is on the prime vertical. For, if dz be an error in z, the corresponding error dt in /, obtained by differentiating the first equation of this Article, is svz.dz/zosj costf sin/, and since sins/costf sin/ = sinZ, this gives dt = dz/cosp snZ. Accordingly the azimuth Z should be 90 or 270 in order that dt may have its smallest value. In the same manner it is shown that errors in'the assumed latitude produce the least effect when the star is on the prime vertical. Prob. 47. Using the data of the above observation on Castor, find the error in the computed Eastern standard time which would be caused by an error of 01" in the altitude h; also the error whicb would be caused by an error of 01" in the latitude p. 48. Long1tude. When accurate standard time is at hand the comparison of it with the local mean time gives the longitude. Thus, if the local mean solar time of a place has been found by a star observation to be 14m084 faster than Central standard time, the place is 3 22' 04" east of the 90 meridian and hence its. longitude is 86 27' 56" west of Greenwich. This method is used at sea, whe...