Maryland Geological Survey Volume 2 (Paperback)

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. 1898 Excerpt: ...and the meridian of the railroad time. A form of observation and record is appended. AZIMUTH OBSERVATIONS. Example of Record. Station: West base, near Little Rock, Ark. Fauth 8." theod. No. 300. December 27, 1888. 1 div. micr. = 2'. 1 div. level-3."l REDUCTION OF AZIMUTH OBSERVATIONS. The time of observation of a star is first to be corrected for the difference in longitude, assuming that railroad time has been used, and for the error of the watch. It is then reduced from mean to sidereal time. From the sidereal time of observation is to be subtracted the right ascension of Polaris, if that star is used, which is given in the Nautical Almanac, the result being the hour angle or the sidereal time which has elapsed since it passed the meridian of the place of observation, given in hours, minutes, and seconds. This result is to be converted into degrees, minutes, and seconds. Then tan A =--a sin 1-b cos t where a = sec f cot c, f = the latitude. b = tanJl = The declination of star, tan 3 t = hour angle. A = angle between north pole and the mark. This angle is to be corrected for level as follows: lever corr. =--'-j j ("' + "')--(- + 4) tank. d being the value of a division of the level. w + w', readings of west end of level bubble. e + e', readings of east end of level bubble. h, the angular elevation of pole star. An example of reduction is as follows: AZIMUTH OBSERVATIONS. Ezamph of Reduction. Station: West base; December 27,1888. Observer S. S. G. Latitude = 34 45 26.8. Longitude 92 13 31.5.l When observations for azimuth are to be made at elongation, it is necessary to know the mean time of elongation. This is computed by the following method: the hour angle at elongation is obtained from the following equation: cos te= tan c cot o...