GREAT TRIGONOMETRICAL SURVEY OF INDIA. 57 



The actual measurements and comparisons of the compensation 

 bars with the standard of length occupied 24 days, and the 

 value of the length of the base-line, as determined by calculation 

 through the triangulation, which consists of a chain of polygonal 

 figures nearly 1.000 miles in length, proved to be only 34 inches, 

 or 1 inch per mile, in excess of the measured value. 



With a view to determine the height of the base-line above the 

 sea a line of spirit-levels was carried from one end down to the 

 coast — where arrangements were made for erecting a tidal 

 station. Astronomical observations for the determination of the 

 latitude and the azimuth were taken at four of the stations of 

 the principal triangulation in the vicinity of the base-line, and the 

 mean differences between these observations and the latitudes and 

 azimuths geodetically computed from Kalianpur — Colonel Everest's 

 station of astronomical origin — were 8-2" in latitude and 11 "2" in 

 azimuth ; but the theoretical probable errors generated in the 

 course of the triangulation between the origin at Kalianpur and the 

 terminus at Mergui are less than ±1" in latitude and ±3" in 

 azimuth ; thus the discrepancies between the observed astronomical 

 and the deduced geodetic results at Mergui are probably due mainly 

 to the influence of local attractions in deflecting the plumb-line at 

 the initial and terminal astronomical stations. 



Latitude observations were also made at Moulmein by Major 

 Rogers, and the same officer also inspected the working of the 

 tide-gauges at Moulmein, Amherst, Rangoon, Elephant point, and 

 Port Blair, and then proceeded to Poona to relieve Major Hill 

 of the charge of the tidal and levelling party. Thus the super- 

 vision of the calculations for the reduction of the principal 

 triangulation and the astronomical observations mainly devolved 

 on Colonel Bran fill, who, having brought ail the work to a satis- 

 factory completion and handed it over to Mr. Hennessey, at the 

 computing office of the great trigonometrical survey in Dehra Dun, 

 proceeded to Europe on furlough. The triangulation parties were 

 then broken up, most of the officers being transferred to topogra- 

 phical surveys, while the native establishments were reduced and 

 transferred to the new secondary triangulation party and the Nepal 

 Boundary survey. 



The chain of principal triangles known as the Eastern Frontier 

 Series had thus been brought down from Assam through Arakan 



