44 GREAT TRIGONOMETRICAL SURVEY OF INDIA. 



to VIII. of the Account of the Operations of the Great Trigono- 

 metrical Survey. Of these volumes, nine in all — of which No. I. is 

 on the Base-lines, No. V. on the Pendulum Operations, and No. IX. 

 on the Longitude Operations — were published under Colonel Walker. 



The principal triangulation of the Indian Survey was designed, 

 from its commencement, to furnish data for employment in the 

 determination of the figure of the Earth. The central chain, executed 

 by Colonels Lambton and Everest, which extends from Cape Comorin 

 to the Himalayas, has several stations at which astronomical observa- 

 tions of the latitude were taken to convert it into a geodetic arc, 

 and it is a most valuable arc, and has been employed in all the latest 

 and best investigations of the Earth's figure. But east and west of 

 this central chain there were several other meridional chains when 

 the triangulation was completed, some of them of an accuracy at 

 least equal to and perhaps greater than that of the Great Arc, and 

 these only required to have the latitudes of certain of their stations 

 determined astronomically to become valuable meridional arcs for 

 geodetic purposes. Moreover, a further contribution to geodesy 

 became practicable as soon as a sufficient number of telegraph lines 

 had been run over the country, by connecting certain of the 

 trigonometrical stations with those lines, and then determining the 

 differences in longitude between the stations telegraphically. 

 Colonel "Walker obtained a supply of new instruments for these 

 observations, and a large number of astronomical latitudes and 

 differential longitudes were observed under his directions, and 

 employed by Colonel Clarke. R.E., C.B., of the Ordnance Survey, in 

 his latest investigations of the earth's figure, published in his work 

 on Geodesy. Much of this work, however, still remained for 

 completion on Colonel Walker's retirement, but the principal 

 triangulation of all India proper was completed, and the greater 

 portion of it had been finally reduced. 



Colonel Walker also initiated the pendulum operations, which 

 were completed under his superintendence, and the tidal and 

 levelling operations, which are still in progress. 



In 1S64 he went to Russia to make the acquaintance of the 

 officers at the head of the Russian Topographical Department, and 

 for several years he was indebted to them for copies of their latest 

 maps of regions in Central Asia, which he employed in the com- 

 pilation of the successive editions of his well-known map of 

 Turkestan. He also did much to advance the operations of the 



