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SOME ACCOUNT OF THE 



folid pillar, of 

 any height at 

 pleafure ; on 

 B build a 

 wall, equal in 

 height to the 

 pillar at A ; 

 and on C a 

 wall of dou- 

 ble that height. 

 From the 

 north, fouth, 

 eafl, and well 

 points, on the 

 top of the 

 wall C flretch 

 the threads N.S. W.E. interfering each other in the 

 point D, directly above the centre of the pillar A. To 

 the centre of that pillar fallen a thread, which is to 

 be laid over the top of the wall C, and to be ilretched 

 bv a weight fufpended to the other end of it. 



The ufe of this inftrument is for obferving the azi- 

 muth (dig-anfa) of the heavenly bodies ; and the ob- 

 fervations with it are made in the following manner: 

 The obferver Handing at the circumference of the 

 circle B 5 while an afliltant manages the thread move- 

 able round the circle C, places his eye fo that the ob- 

 rcc to be cbierved, and the intcrfeclion of the threads 

 N.S. W.E. may be in one vertical plane, while he 

 directs the afliltant to carry the moveable thread into 

 the fame plane. Then the degrees en the circle C 

 cut off by the moveable thread, give the azimuth re- 

 quired. In order to make this obfervation with ac- 

 curacy, it feems neceflary that the point D, and the 

 centre of the pillar A, mould be connected by a 



thread 



