332 Progress of Indian Maritime Surveys. [Aug; 



In 1823, Captain Ross was appointed by the Court of Directors to 

 his present office of Marine Surveyor General. His operations were 

 necessarily interrupted during the Burmese war ; but the following 

 surveys have since been executed in succession under his superin- 

 tendence, and mostly by himself personally. 



1. The Rangoon river to its mouth. 



2. The straits, approaches, and harbour of Singapore. 



3. The Mergui archipelago, Tenasserim coast, and Martaban, with 

 the river at Amherst and Moulmein. The sheets of this Chart cover a 

 line of coast extending fromLat. 8°. 28'. N. to 16°. 32'. and include a vast 

 number of Islands never before laid down or even visited by Europeans, 



4. In the meantime, the coast of Ava from Negrais to Ramri, and 

 Sandowi, was surveyed by Captain Crawfurd, and Cheduba roads 

 and Ramri, by Captain Ross's assistant Lieut. Lloyd. 



5. The coast of Arracan, north of the point to which Captain Craw- 

 furd's Chart extended, was, in the past season, the object of Captain 

 Ross's personal survey ; and, in one or two seasons more, the entire 

 eastern shore of the Bay of Bengal will have been laid down by this 

 officer, or by those under his orders, with as much accuracy as can be 

 .claimed for the charts of the coasts of Europe and the Mediterranean. 



All Captain Ross's surveys, and those made under his orders by 

 junior officers of the department, are laid down from bases carefully 

 measured on shore, where this has been possible, and are strictly tri- 

 gonometrical ; and though necessarily wanting that minute correctness 

 aimed at in similar surveys on land, they possess, nevertheless, an accuracy 

 fully sufficient for the scale on which the Charts are delineated. The 

 base lines on shore are measured on the most favorable level spots that 

 can be found, by running a ten-foot rod along a cord, stretched tight 

 between the extreme points, and kept in position by stakes, of which 

 the direction is verified by a telescope at one end. Second and third 

 bases are measured for further assurance, and in correction of the first. 



If there be no means of measuring a base on shore, as when the 

 locality of rocks and sand-banks, out of sight of land, may have to be 

 ascertained, recourse is had to the measurement of a base by sound, 

 which in a long line of 5^ to 6 geometric miles is a process affording more 

 practical accuracy than would be supposed. The vessels being an- 

 chored at this distance, and a calm period chosen, the distance is taken 

 between the flash and report of a gun, and upon the assumption that 

 sound travels at the rate of 1140 feet per second, while with repeated 



Note. — The Andamau Islands were surveyed as far back as 1789, 90, and 1793, 

 by Captain Blair. 



