| OCR Text |
Show 16 the distance between the line of collimation and the true meridian at the pole, by n'; and the distance between the line of collimation and the true meridian at the equator, by m'. The quantities represented by n' and m1 are used instead of errors of azimuth and level. By meaus of a collimating eye- piece, the error of collimation and level was determined by reversing the instrument over a basin of - mercury, and measuring with the right- ascension micrometer the distance between the central thread (<%) and its image reflected from the mercury. Denoting by- <?, 7i, and m the corrections obtained from the observed and computed errors (/, n', and m1; 2 J, the distance of the central thread west of its image, when the clamp- end of the axis is east; 2 J', the distance of the central thread west of its image when the clamp end of the axis is west; p1 the correction for the excess of the radius of the clamp- pi vot= 0". 0() 8; r, the equatorial distance of the middle thread from the mean of sets B, C, andD= 0M) 14; a, the correction for diurnal aberration = c0". 016; ft, the level- correction 5 a, the adopted place of the star; a7, the observed place of the star; d, the declination of the star; P, the latitude of the observing- station; CX, the approximate clock- correction ; and C, the clock- correction derived from the observation of each star- and we have the following formulas, which have been employed in reducing the observationa- for time: n was determined from the observations of circumpolar stars. The quantities J and J' are given in revolutions of the micrometer-head, each revolution = lfl. 586o. c = J( J - J') - p - r- a for clamp east. e= z-£( J- j') + |) + r - a for clamp west. &=-|( J+ J')- p for clamp east. &=- b( A+ 4')+ p for clamp west. ft= a-( af+ C'+ C Seed) sec d m = - n tan y> + b sec < p * C=? a-( a' + m + ntan £ + csecfl) In the column " Adopted right ascension" in the following table, the places of the clock- stars are those used at the observatory in 1871, some of the Nautical- Almanac places being slightly changed. |
