192 Use of the Zenith Telescope in Determining Latitudes. 
ing the star with the horizontal wire, and moving the instrument 
in azimuth, if it appears necessary, as the time of culmination 
approaches, to bring the star in the middle of the field. When 
within ten seconds, the recorder calls each second, and the instant 
of the previously computed culmination, when, the wire being 
upon the star, the first part of the observation iscomplete. The 
level and micrometer are read and recorded. 'The same process 
is repeated after the instrument has been turned 180° to observe 
the opposite star of the pair, on the other side of the zenith. A 
single observation on the meridian has, in our experience, been 
found preferable to several circum-meridian observations. 
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ord is not essentially different from that used by 
by subsequent observers. By recording the 
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