IV. 



ON THE 



FORMULA FOR CALCULATING 

 AZIMUTH 

 IN TRIGONOMETRICAL OPERATIONS. 



By Captain G. EVEREST, f.r.s. m.a.s., &c. 



Surveyor General and Superintendent of the Great Trigonometrical Survey of India. 



In offering to the notice of the Society the accompanying paper, I beg 

 to explain that my object is to put on record certain formulfe, connected 

 with the method generally employed in the Trigonometrical Surveys of 

 England and of India, for determining Azimuths. 



Those of my readers, who are familiar with this subject, will remem- 

 ber that the method in question consists in observing the difference of 

 Azimuth between a fixed lamp of reference and some circumpolar star, 

 generally a ursse minoris, at the time of its greatest distance on the east 

 or west side of the meridian. 



But to accomplish this, the actual time of the phenomenon, and 

 frequently the altitude, require to be known, and as it is advisable to 

 have these elements prepared for the occasion at leisure, the latitude of 

 the place is sometimes drawn from data to which the Cinal corrections 

 have not been applied, and the polar distance is perhaps taken from a 

 catalogue which succeeding observations have shoNvn to be imperfect. 



The second part of this paper is intended thcroft)ie to furnish foniiula\ 

 whereby the observer may introduce the rc(jiiiicd corrections without 



