OF THE CNITED STATES. .33a 



fiamps. it admits two ditferetit successions, dirt'eiiiio; ocily in 

 the ease ^vitll which the screws come to the hand in each 

 motion. 



The observation can evidently he made by one person 

 alone, as the level requires no particular attendance. It may 

 however be observed liom time to time, to be sure that the 

 instrument has not been disturbed. 



The following order will bring the screws so as to l)c al- 

 ways convenient to the hand of the observer. 



1. Place the vernier Z on 0° or any division, and read Z 

 and Y. These readings arc written in the third and fourth 

 columns of the Day-lJook. 



2. The clamp at X being loose, make the first observation 

 by the motion of the telescope alone, and point l)y means of 

 the tangent screw of the same vernier Z. When the object 

 observed is a celestial body, tlie time of this oI)scrvation is 

 observed, and written before the readings of Z and Y, in the 

 lirst column of tlie Day-Book. 



3. Then W and X arc read off, and written in the fifth 

 and sixth colunuis of the Day-Book, one line I'arther down 

 than the Zand Y have been written. 



4. Unclamp the circle at Z, turn tlie upper part of the in- 

 strument one half a circumference round hori/.ontally, and 

 the telescope together with the circle through the zenith 

 again to the object to be observed, upon which, the clamp at 

 Z being again fastened, the pointing is effected by the tan- 

 gent screw of the same Z. and the time observed is written 

 in the first column opposite to the foregoing readings. By 

 this, the fust angle of the series by Z will be obtained. 



5. Turning the instrument a semicircumference horizon- 

 tally, and after unclam|)ing the vernier X, also tlie telescope 

 alone without the circle through the zenith to the object to 

 be observed, the pointing is again performed by tlic tangent 

 screw of the same vernier X. wlierol)y the lirst angle of the 

 second series, or by W, X, is ol)taitied, and the time observed 

 is written again in the first column, 



n. The observer may proceed in this order, and in the 



