452 The Surveys of India. [Oct.. 



miles, between the stations at Carangooly and Carnatighnr, nearly 

 due east and west of one another. Very accurate measures of the 

 angles which that line made with the meridian at its extremities, 

 were here required ; and these were obtained by observations of the 

 Polar star when at its greatest distance from the meridian. For 

 this purpose a lamp was lighted, or blue lights were fired at a given 

 station, the azimuth of which was found by the Polar star observa- 

 tions, and afterwards its bearing was taken in respect of the line in 

 question. Thus the angle which the meridian of Carangooly makes 

 at the pole with that of Carnatighnr, or the difference of longitude 

 of these two places, was computed. It was then easy to calculate 

 the amplitude of the arch between them; and thence the degree 

 perpendicular to the meridian at Carangooly was found to be 

 61061 fathoms. Upon comparing this degree of the perpendicular 

 with the degree of the meridian, the compression at the poles would 

 appear to be equal to yto- A writer in the ' Philosophical Trans- 

 actions ' for 1812, p. 342, contended that, on account of an error 

 in calculation which escaped Colonel Lambton, the foregoing mea- 

 surement should be diminished by 200 fathoms, thus reducing the 

 length of the degree of the perpendicular to 60861 fathoms, which 

 would give ^hj for the compression. These measurements were 

 made in 1803. 



In May, 1804, a base of verification of 39793 -7 feet (7-536 

 miles, reduced to mean sea-level) was measured by Lieutenant 

 Warren, Colonel Lambton's assistant, near Bangalore ; and though 

 the distance was nearly 160 miles, the computed and measured 

 lengths of this base differed only 3 ■ 7 inches, or about half an inch 

 in the mile ; a proof of the great care and accuracy with which the 

 work was conducted. This base was adopted for the origin of the 

 great Indian arc series, to which we shall presently refer more 

 particularly. From it a series of triangles was carried across the 

 peninsula to the Malabar coast, which they intersected at banga- 

 lore on the north and Tellicherry on the south. The heights of 

 the stations were all determined from the distances and observed 

 angles of elevation. The most considerable heights were at Soobra- 

 manee and Taddiandamole, in the western ghauts, not very far from 

 the coast, the former being 5583 feet, and the latter 5682 feet 

 above the level of the sea; but notwithstanding having to cross 

 such elevations, after carrying the survey over a distance of 360 

 miles, it was found that the sum of all the ascents, and of all the 

 descents, reckoned from the level of the sea, differed from one an- 

 other only by 8£ feet. From the triangles thus carried across the 

 peninsula, a correct measurement of its breadth was obtained, and 

 one considerably different from what was before supposed. The 

 distance from Madras to the opposite coast, in the same parallel, 

 was ascertained to be very nearly 360 miles ; whereas, until then, 



