OBSERVATIONS WITH THE ZENITH TELESCOPE. 



89 



The Latitude Observations, 



The details of the latitude determination arc found in the pages following. The 

 expression for the latitude is — 



,/. .', (<S [ .5') [ iR {M— 3T) I id [(ft— »') — («'— «)] | (m. | m') \- \ (r—r 1 ) 



-Mand M' are the corrected readings of the micrometer. 



n, s, n', s', the readings of the north and south end of the level for the two stars. 



m, rib' , corrections lor curvature. 



r, r' , corrections for refraction. 



The contents of most of the columns will be sufficiently explained by the headings. 



Column P gives the position of the instrument. 



I), direct, the telescope east when pointing south of the zenith. 



R, reverse, the telescope west when pointing south of the zenith. 



Column C gives the correction for progressive errors of the screw. 



Levels A and B, the value of (n— n') — (s'—s) for each level. 



Column 8 gives the correction required on account of AiE, found on page 83. In 

 case of those pairs observed with threads U and /Fthis is combined with the correction 

 for the amount by which the distance between those threads differs from twenty revo- 

 lutions of the screw. 



