178 MEASUREMENT OF AN ARC ON THE 



the length of a degree has been computed for every 

 ten degrees from the meridian to its perpendicular 

 on an Ellipsoid, whose diameters were in the ratio 

 of one to 1,0067, which is derived from taking the 

 degree on the meridian, in latitude 50** 41' to be 

 60851, and the degree perpendicular thereto 61 182, 

 in the same latitude. These data would give the 

 meridional degree, in latitude 13°, to be 6019I, 

 <ind the degree perpendicular equal 60957, which, 

 however, is not the case; but no sensible error will 

 arrive in making those corrections from taking the 

 arcs a few seconds more or less than the truth. 



SECTION VI. 



^Reduction of the distances to the 7iieridian of Tvivan- 

 deporum, /or determ'ming the length qf the ter- 

 restrial arc. 



The sides of the great triangles, from which the 

 arc is derived, falling very nearly in the same me- 

 ridian, and not more than 16363,3 feet west from 

 the meridian of Trivandeporum, the south extre- 

 mity of the arc, there required no reference to any 

 hypothesis of the earth's figure for getting the exact 

 distance between the parallels, so that the latitude 

 of a point where a great circle falling from the sta- 

 tion of observation near Paudreey will cut the me- 

 ridian of Trivandeporum at right angles, may be de- 

 termined with sufficient accuracy by computing 

 spherically, and the distances, when reduced to the 

 meridian, (the distance from Trixiandeporum to 

 Coonimi hill excepted,) may be considered as the 

 chords of arcs on the meridian, and therefore the 

 arcs themselves may be had, by allowing 60494 

 fathoms to the degree, as had been obtained from 

 the sum of those reduced distances, the sum there- 

 fore of all these arcs will make the whole meri- 

 dional arc, which is a nearer approximation to the 

 truth. 



