three Degrees of the Meridian. m 



and in round numbers. With these elements, and with 

 the data to be found in the work of M. Svanberg, we have 

 by the western series of triangles .')S4o",19fi and 5SAO'\\3B 

 by the eastern. So that the mean calculated arc is 1** 37' 

 eo",l67, while the arc observed was 1° 3/' 19",566. The 

 difference then is o",6 for the total arc, and 0",37 for the 

 mean degree, or 3,86 toises excess in the linear extent. 

 One can never depend upon (juanlities so small as this; 

 50 that the agreement between the results of computation 

 and actual observation, proves not only the skill of the ob- 

 servers and the accuracy of which their instruments admit, 

 but also that the elliptic elements employed in the calcula- 

 tion are a sufficiently near approximation to the truth to 

 be deserving of confidence. 



In the yiiith volume of the Asiatic Researches, published 

 by the Society at Calcutta, are contained the details of an- 

 other measurement performed in 1802, bv Major William 

 Lambton in Bengal, on the Coromandel coast. In this 

 undertaking, which was executed with great skill and at- 

 tention. Major Lambton employed Bengal lights as signals, 

 chains for the linear measures, and a theodolite, and a, 

 zeniih-sector made by Ramsden. The base measured was 

 6667,740 fathoms reduced to the level of the sea, and to 

 the temperature of 62^ Fahrenheit ; and the stations were 

 so chosen, that four of the sides of the triangles were al- 

 most in the same line, and nearly parallel to the meridian 

 at the southern extremity of the arc, so that their sum but 

 little exceeds its whole extent. The lengths of these arcs 

 in fathoms reduced to the meridian are thus given in the 

 memoir of Major Lambton. 



AB 207 38,13 north latitude of A li°44'32",59 

 BC 17481,245 



CD 22237,04 north latitude of E 13° I9'49",0ia 

 DE 3.5246,43 

 From these data Major Lambton deduces the degree of 

 the meridian to be 60435 fathoms, or 56762,3 toises. By 

 applying to this the same elements as we did to the mea- 

 surement by Svanberg, we have the entire arc measured 

 equal to \° 34' 35",896; so that the difference between the 

 results of calculation and of the observation.*, is only o",532 

 for the whole arc, or o",337 for the mean degree. The 

 elliptic hypothesis and observation agree more correctly in 

 this instance, for the difference is rather less than xu that 

 of Lapland, although the two arcs arc verv nearly of the 

 same extent. Thus the degree on the meridian measured 

 in Bengal, iu the latitude of 12° 32' 2l" north, cannot be 



supposed 



