210 GEODETIC OBSERVATIONS. 



Consequently as the Indian geodetic operations have come to be 

 extended over the whole peninsula, along the Burmese coast and 

 across the mountains into Siam, and as far east as Bangkok, 

 it has become more and more important to determine the amount of 

 error in the further stations. 



The data for such investigations are furnished by — 



(1.) Comparison of observed latitudes with geodetic latitudes; 



(2.) Comparison of observed longitudes with geodetic longitudes ; 

 and 



(3.) Comparison of observed azimuths with azimuths deduced 

 through the triangulation from the station of origin. 



The astronomical observations are of great importance in various 

 ways, among which may be mentioned that they contribute largely 

 toward the investigation of local attraction, and also towards the 

 accurate determination of the position of India with respect to its 

 distance from Greenwich, and lastly they furnish data for improving 

 existing star tables in the case of about 900 stars. 



But before the application of the electric telegraph to the 

 determining of longitudes the comparison (2) could not be made, 

 because the longitudes determined by the old methods were not 

 sufficiently accurate for such a purpose, a case in point being 

 that of Madras which, though the result of many years careful 

 observations and taken with all the refinements of a well-equipped 

 observatory, was discovered through these electro-telegraphic 

 operations to be erroneous by about 2\ minutes of arc, which had 

 the effect of placing India nearly 3 miles too far from Greenwich, 

 ami of ascribing an error of 10 seconds to the chronometers of all 

 ships arriving at Indian ports from Europe or America.* Thus the 

 introduction of electro-telegraphic longitude operations into Indiawas 

 a most valuable addition to the geodetic operations of the Survey. 



The Government of India have always taken a very liberal view 

 of the more purely scientific ends of the Great Trigonometrical Survey, 

 and almost from its commencement the operations of the Survey have 

 furnished data for investigating the figure of the earth. Its earliest 

 contributions to the science of geodesy were determinations of 

 the lengths and amplitudes of meridional arcs, as described in 

 Colonel Everest's accounts of the measurement of sections of the 

 meridional arcs of India published in 1830 and 1847. Then came 

 the series of Pendulum observations for the purpose of determining 

 * See infra, p. 213. 



