92 Proceedings of the Asiatic Society. [March, 



Blair itself, and consequently of the general group of the Andaman 

 Islands, was equally doubtful. 



It was therefore necessary to take steps to rectify the existing 

 Charts, either by determining astronomically the absolute longitude 

 of a station in each of the groups of Islands which lie between Cape 

 Negrais, the southernmost point of the Burmese Provinces, and 

 Acheen Head the northernmost point of the Island of Sumatra ; 

 or by the method of determining the latitudes and azimuths of 

 mutually visible points on the groups of Islands and thence computing 

 their differences in longitude. As the Islands trend in a nearly meri- 

 dional direction from Burmah to Sumatra, the second method might 

 if feasible be adopted, with the advantage of giving very much more 

 accurate results than observations for determining absolute longitudes. 

 Some of the groups of Islands are not ordinarily visible from each 

 other ; but, from a consideration of their distances and their heights 

 above the sea, I am of opinion that luminous signals erected on 

 lofty scaffoldings would be mutually visible at night ; and if so their 

 azimuths could be accurately measured, as the Pole Star never reaches 

 a high altitude in these latitudes. It would also be an easy matter 

 to execute at the same time an accurate triangulation, to fix the posi- 

 tions of certain of the surrounding Islands, some of which are known 

 to rise to heights exceeding 1,000 feet above the sea level ; thus an 

 accurate basis might have been prepared for the topography of the 

 Islands. 



In consequence, however, of the want of adequate means to enable 

 the Surveyors to pass from one Island to the other whenever con- 

 venient, it was necessary to abandon the method of combining Astro- 

 nomical with Trigonometrical observations, and to restrict the oper- 

 ations to the determination of absolute latitudes and longitudes by 

 Astronomical observations. At first it was intended that one or more 

 points should be fixed in each of the several groups of Islands, but an 

 intimation was subsequently received from the Secretary of State for 

 India, that a complete Maritime Survey of the Islands would be made 

 under instructions from the Admiralty, and that a battery of 15 

 chronometers would be employed for the determination of the differ- 

 ential longitudes. Consequently the operations were limited to fixing 

 the position of Port Blair as a point of origin for the Maritime Survey. 



