898 Report of the Great Trigonometrical Survey. [No. 4 



difficult for me to exercise that degree of supervision over the oper- 

 ations, which their delicate and difficult nature required. 



By the end of 1862, Mr. Mcolson reported that he had taken a 

 sufficient number of observations to fix the position of Port Blair- he 

 therefore, applied for a vessel to be placed at his disposal to enable him 

 to proceed to fix the positions of the Great Coco, and other islands. 

 Owing to postal and other delays, it was not until the end of February 

 1863, on my return from Vizagapatam, that I learnt from the Marine 

 Department that no vessel was available, nor could one be got ready- 

 before the fine weather season would have terminated. 



From the same communication I also learnt that the Secretary of 

 State for India had ordered a complete Maritime Survey of the 

 Andaman Islands to be executed. Being then in Calcutta, I went to 

 Captain Rennie, the Secretary to Government of India, Marine Depart- 

 ment, and was informed that, under instructions from the Admiralty 

 Hydrographer, it had been determined to find the differences of 

 Longitude between the various groups of islands, chronometrically, 

 by a battery of thirteen or fourteen chronometers. 



The circumstances under which it was originally proposed to fix a 

 series of positions by astronomical observations had thus entirely 

 altered. The complete Maritime Survey, which has been ordered by 

 the Right Hon. the Secretary of State for India, renders further 

 astronomical observations unnecessary. The determinations of differ- 

 ences of Longitude, which are the only really difficult portion of the 

 work, can be done chronometrically by the Marine Surveyors, with 

 much greater rapidity and economy, and, probably, even with greater 

 accuracy, than by the best astronomical observations for absolute 

 Longitude. 



Consequently, in March last I desired Mr. Nicolson to restrict his 

 operations to taking as many more observations for the determination 

 of the Longitude of Port Blair as could be obtained before the setting 

 in of the monsoon, and then to return to Calcutta. He reached the 

 Presidency in June, and has ever since been employed in reducing his 

 observations. They consist of 32 lunar culminations, 136 lunar zenith 

 distances, 130 transits of clock stars, and 162 meridional zenith 

 distances of stars for Latitude, observed up to the 12th March, when 

 the astronomical clock met with an accident, and Mr. Nicolson was 

 afterwards obliged to employ a chronometer. His subsequent observ- 



