GREAT TRIGONOMETRICAL SURVEY OF INDIA. f>5 



telegraphic observations for the determination of differential longi- 

 tudes, at several of the stations of the principal triangulation. These 

 have already been completed to a considerable extent. Further 

 operations of this nature are in progress ; they are carried out by 

 the two small astronomical parties which are attached to the trigono- 

 metrical or geodetic branch of the Department, and by which all the 

 operations that are required to render the principal triangulation 

 fully subservient to geodetic science should be completed in the 

 course of time. An extensive series of pendulum observations for 

 investigations of variations of gravity and the figure of the earth, 

 taken chiefly at stations of the principal triangulation, has been 

 completed and connected with the groups of corresponding observa- 

 tions in other parts of the globe. Long lines of spirit-levels have 

 been carried on in connexion with the principal triangulation, from 

 the sea to the base-lines in the interior, and from sea to sea across 

 the peninsula ; they rest on determinations of the mean sea-level 

 which have been made at the tidal stations on the coasts.* 



On the conclusion of the measurement of the Mergui base-line, 

 Mr. J. McG-ill and Mr. C. D. Potter were deputed in 1882-3 to carry 

 a chain of secondary triangulation along the east coast, chiefly for 

 the purpose of setting up beacons for the use of the marine surveys. 

 These operations extended between Ichapur, in Ganjaru, to the town 

 of Pooree, the seat of the Jaganath temple. The country is generally 

 well populated and prosperous, including seaports and large towns, 

 but subject to unhealthy malarious influences. The Chilka lake 

 fell within the area of the work ; it is a vast sheet of salt water, 

 covering 350 square miles, with numerous islands, and fed by 

 freshets of the Mahanadi river and numerous small streams descending 

 from the Eastern Ghats ; it has one outlet into the sea by a small 

 breach in the said ridge, and a canal connects with the port of 

 Granjam. During 1883-84 the measurements were carried northward 

 along the coast of Orissa from Pooree to Balasor by Mr. A. D'Souza, 

 and the opportunity was taken to look up the old stations of Major 

 Saxton and Captain Depree's survey in 1858-59. In 1884-85 

 Mr. D'Souza worked southwards, and carried the old triangulation of 

 the Madras Coast Series, which had stopped at Coringa, to the mouth 

 of the Godavari. Some interesting notes on the principal coast 

 towns and rivers of the Ganjam, Vizagapatam, and Godavari 

 districts accompany his report on the operations. The following 



* From the Surveyor General's Report for 1881-82. 

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