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tion is made on the east or on the west side of the meridian. 
Then, counting the beats of the chronometer, we watch until the 
line joining the two become horizontal, and thus obtain the instant 
at which the star had the elevation shown on the altitude circle. 
It is better, when making this observation for time alone, to let 
the image pass at a little distance — say two or three minutes — from 
the star, than to attempt to make them coincide, because the eye 
can very readily judge of the horizontality of the line joining the 
two luminous points. But the altitude azimuth and time can all 
be obtained at once in the following way : — 
Having brought about the coincidence, we watch for one or two 
minutes, and estimate carefully the direction of the separation, then, 
by help of the tangent-screws, we cause the image and the star to 
exchange places, as it were, keeping the same inclination, and leaving 
the instrument untouched, we count the beats of the chronometer 
until the coincidence take place. In this way we obtain the time 
and the simultaneous readings on the altitude and azimuth circles ; 
from these the longitude and the direction of the meridian can be 
computed. 
The direction of the meridian is very readily obtained from the 
greatest easting or westing of a star which passes between the pole 
and the zenith, particularly in low latitudes. The manner of pro- 
ceeding with the crystal pointer is to make the coincidence, to wait 
a little and observe the direction of separation ; when this direction 
is vertical the star is at its greatest azimuth. 
Lastly, the latitude of the place may be corrected by observing 
the two transits of a star over the prime vertical near to the zenith ; 
the operation is exactly analogous to those already described. 
When the horizontal axis is made perpendicular to the meridian 
the instrument can be used as a transit. The instant of the sun’s 
passage can be found by observing the contact of the first limb, then 
the entire coincidence, and lastly, the contact of the second limb. 
The average of these three may, in general, be depended upon to 
within two seconds of time ; while, by observing the moon’s meridian 
passage, and comparing it with those of two stars, the Greenwich 
time may be obtained to within one minute from a single set of 
observations. 
The lightness and portability of the instrument, and its adaptation 
to near or distant objects, promise to bring the practice of geode- 
