324 TRIGONOMETRICAL SURVEYS. 



In the extent of this prolongation two new bases were 

 measured, — one at Putchapoliam, where the meridian inter- 

 sects the parallel of 11°, and another at Tinnevelly, near 

 the southern extremity of the arc. These bases were 

 nearly of the same length, but somewhat shorter than that 

 at Bangalore. In many places the country is high and 

 difficult to penetrate. There is a mountain here, the hill 

 of Permaul, in lat. 10° 18' ; its height is 7367 feet. On 

 this meridian, the distances of five stations, with the cor- 

 responding latitudes, were determined. The amplitude of 

 the whole arc, between Pmmae, the south extremity, and 

 Paughur, the northerimiost point, was 5° 56' 47.32", and 

 its length 359,595.4 fathoms. From this and the inter- 

 mediate points, the following degrees and their measures 

 were deduced : — 



Fathoms. Mid. lat. 



Punnae and Putchapoliam 60473 9° 34' 44" 



Punnae and Uodagoomah 6049ti 10 34 49 



Punnae and Bomosundrum ^ 60462 II 4 44 ) 



Punnae and Paughur ) 604S9 11 8 3S 



Mean of the two last 60465.5 11 6 23.5 



From a former measurement 60494 12 32 



In these degrees the same anomalies occur which have 

 been observed in France and England, and probably will 

 always occur when contiguous arcs are compared with one 

 another. We have already observed, that on the suppo- 

 sition that the earth is a figure generated by the revolution 

 of an elhpse about its lesser axis, the degrees should grad- 

 ually increase from the equator to the pole, according to a 

 determinate law. Here we see that the length of a degree, 

 of which the middle parallel is 1 1° 4' 44" is less than others 

 nearer the equator. A small part of this irregularity may 

 be owing to error of observation ; but the greater part must 

 be placed to account of the irregularities in the direction 

 of gravity arising from the inequalities at the surface, or 

 in the interior of the earth, the attraction of mountains, or 

 the local variation of density immediately under the surface. 

 This is an example of the difficulties which are to be ex- 

 pected in an extensive trigonometrical survey. In the 

 London Philosophical Transactions for 1818, Colonel 

 Lambton has given an abstract of the results of his meas- 

 urement of the meridian. He had then at different times 

 measured three complete sections of an arc of the meridian. 



