INSTRUCTIONS. 61 



Transit telescope and turn microscopes 180°. 



Pointing on 1? and readings of both microscopes. 



Pointing on A and readings of both microscopes. 



180° 

 Shift circle by ' and proceed as before until n such sets of measures 

 n 



have been obtained. 



Then measure the angles B to C, C to D, etc., including the angle 

 necessary to close the horizon, in the same manner. 



A form lor record and computation of the results is given below. 



When repeating instruments are used, the same programme will be fol- 

 low ed except that there should be five pointings instead of one on each of 

 A and B, the circle being read for the first pointing on A and the fifth on 

 B, and again for the sixth pointing on B and the tenth on A. 



The importance of having the measures of a set follow in quick succes- 

 sion must be constantly borne in mind. Under ordinarily favorable condi- 

 tions an observer can make a pointing and read the microscopes once a 

 minute, and a set of five repetitions should be made in five minutes or less. 



When several stations or signals are visible and a nonrepeating instru- 

 ment is used, time may be saved without material loss of precision in the 

 angles, by observing on all the signals successively according to the follow- 

 ing programme, the signals being supposed in the order A, B, C, etc., as above. 



Pointing on A with microscope readings. 



Pointing on B with microscope readings. 



Pointing on C with microscope readings. 



Pointing on A with microscope readings. 

 Transit telescope and turn microscopes 180°. 

 Pointing on A with microscope readings. 

 Pointing on B with microscope readings. 

 Pointing on C with microscope readings. 



Pointing on A with microscope readings. 



Shift circle by — and proceed as before until n such sets have been 

 J n L 



obtained. 



