DIY History | Transcribe | Scholarship at Iowa | Theory of the astronomical transit instrument applied to the portable transit instrument Wuerdemann no.26: a compilation from various authorities, with original observations by Harry Edward Burton, 1903 | Theory of the astronomical transit instrument applied to the portable transit instrument Wuerdemann no. 26: a compilation from various authorities, with original observations by Harry Edward Burton, 1903, Page 41

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Theory of the astronomical transit instrument applied to the portable transit instrument Wuerdemann no.26: a compilation from various authorities, with original observations by Harry Edward Burton, 1903

Theory of the astronomical transit instrument applied to the portable transit instrument Wuerdemann no. 26: a compilation from various authorities, with original observations by Harry Edward Burton, 1903, Page 41

i.e. set one clock or chronometer nearly right. If the clock correction is known only approximately, say within one or two minutes, set the telescope for some bright star about to transit within ten degrees, say, of the zenith. Observe the clock time of transit of the star [inserted](a)[/inserted]. This star being nearly in the zenith, its time of transit will be but little affected by the aximuth errors of the instrument.
   (To avoid waiting for stars close to the zenith, the clock correction may also be estimated closely by comparing observations of two stars not very distant from the zenith, one north and one south, and then at the same time will give some idea of the amount and direction of the azimuth error.)
   The level and and collimation errors having previously been made small by adjustment, the right ascension of this star minus its clock time of transit will be a close approximation to the clock correction. We now have the time within a second or two.
(a) See "Methods of Observation" following.

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i.e. set one clock or chronometer nearly right. If the clock correction is known only approximately, say within one or two minutes, set the telescope for some bright star about to transit within ten degrees, say, of the zenith. Observe the clock time of transit of the star [inserted](a)[/inserted]. This star being nearly in the zenith, its time of transit will be but little affected by the aximuth errors of the instrument. (To avoid waiting for stars close to the zenith, the clock correction may also be estimated closely by comparing observations of two stars not very distant from the zenith, one north and one south, and then at the same time will give some idea of the amount and direction of the azimuth error.) The level and and collimation errors having previously been made small by adjustment, the right ascension of this star minus its clock time of transit will be a close approximation to the clock correction. We now have the time within a second or two. (a) See "Methods of Observation" following.