60 GREAT TRIGONOMETRICAL SURVEY OF INDIA. 



found to- suffice for all geographical requirements, and more was not 

 wanted for geodetical requirements. An additional meridional chain 

 might have been constructed on the meridian of 84° within the 

 South-Bast Quadrilateral, and it doubtless would have been con- 

 structed but that before it could be commenced a network of 

 excellent topographical triangulation had been thrown over the entire 

 area which is included between the collateral principal chains, 

 and nothing more was wanted. Similarly in the Southern Trigon, 

 the execution of a chain of principal triangles along the west coast 

 from Cape Comorin to Mangalore was desirable for symmetry, 

 co-ordinately with the chain on the east coast from Cape Comorin 

 to Madras, but it was not wanted for geodesy. For geographical 

 purposes the Malabar coast seines of secondary triangles was amply 

 .sufficient. Tt had been mostly executed by Major Lambton, and it 

 stood connected with the modern operations. Major Lambton had 

 not, however, attempted to throw his triangulation over the broad 

 belt of plains on the east coast, which is covered with trees and 

 obstacles that he had no means of surmounting. Thus a chain 

 cf principal triangles has been extended of late years over these 

 plains, and has furnished a base from which a branch chain of 

 Iriangles has been carried across the Paumben straits to the 

 I. -land of Ceylon, in order to connect the surveys of India and 

 Ceylon. 



For geodetic purposes the amount of principal triangulation 

 which has been executed has been pronounced to be ample. The 

 first measurement of the sections of the Great Arc between Cape 

 Comorin and Sironj was accomplished with instruments far inferior 

 in accuracy to those with which the liberality of the Court of 

 Directors furnished Colonel Everest in subsequent years, and being 

 < ! emed of insufficient accuracy for geodetic requirements, its revi- 

 s'on was directed to be undertaken as soon as might be consistent 

 with the need of triangulation for geographical purposes in other 

 [) its iif India. The northern section, from Sironj down to Bidar, 

 was indeed revised under Colonel Everest's superintendence in 

 1 S38-39, but the revision of the southern sections — ■ Bidar, 

 Bangalore, Cape Comorin— was postponed for several years, and 

 was eventually accomplished during 1S69-74. 



The longitudinal series, from Sironj to Calcutta, was also revised, 

 as it was originally executed with very inferior instrumental 



