AstronomyDetermination of time, longitude, latitude, and azimuth . r, as with the alt-azimuth instrument for magneticpurposes, in which case the suns limbs are usually observed. In refined work in high latitudes,and for certain rare cases in low latitudes, the transit instrument is needed to furnish the chro-nometer correction. For primary azimuths, in latitudes not greater than those in the UnitedStates, the local time may be found with sufficient accuracy by means of an especially con-structed vertical circle, used in the Coast and Geodetic Survey, and shown in illustration For seconda
AstronomyDetermination of time, longitude, latitude, and azimuth . r, as with the alt-azimuth instrument for magneticpurposes, in which case the suns limbs are usually observed. In refined work in high latitudes,and for certain rare cases in low latitudes, the transit instrument is needed to furnish the chro-nometer correction. For primary azimuths, in latitudes not greater than those in the UnitedStates, the local time may be found with sufficient accuracy by means of an especially con-structed vertical circle, used in the Coast and Geodetic Survey, and shown in illustration For secondary azimuths, local time may be found by means of sextants or alt-azimuth instruments. PRIMARY AZIMUTH. The requirements for primary azimuth are that the astronomic azimuth observations and the necessary time observations should be made using such methods, instruments, and number of observations as to make it reasonably certain that the probable error of the astronomic azimuth does not exceed ± It is not desirable to spend much time or money in reducing 138. TWELVE-INCH DIRECTION THEODOLITE. No. 19.
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