1 92 Mr. Ivory on Measurements on the Earth 1 s Surface 



The sum of the two results is the longitude of Dunkirk, 

 2° 22' 42"*88 : and as the meridian of Paris is 2' 22" west of 

 the meridian of Dunkirk *, we get the difference of longitude 

 of the two observations, equal to, 



In degrees. In time. 



2° 20' 20"*88 9 m 2P-39 



By experiment, P. T. 1826, 9 21-46 



Defect... 0-07 

 In order to confirm the result obtained at Beachy Head, 

 I shall add a similar instance taken from the New Survey. At 

 the station of Fairlightf, the angle between the meridian 

 and Blancnez, was found 85° 36' 36"*73 = m ; the latitude of 

 Blancnez is 50° 55' 29"*36 = A'. The arc on the earth's sur- 

 face between the two stations is 42117*6 fathoms; and hence 



= f£»& x 36 °0 7 = 41'.3l"-51. The formula (B) will now 

 give us the difference of longitude of the two stations equal to 

 1° 5' 33"*42. According to the Survey, the length of the per- 

 pendicular arc at Blancnez is 41998*66 fathoms; and the 

 amplitude of this arc, computed from the difference of longi- 

 tude, is 41' 19"*58; and hence, by proportion, the perpendi- 

 cular degree is 60976 fathoms. Now, at the latitude of Blanc- 

 nez, a perpendicular degree on the surface of the spheroid is 

 60974*5 fathoms. 



It appears lhat the perpendicular degrees at Beachy Head 

 and at Blancnez on the French coast, agree very exactly with 

 the elliptical spheroid deduced from the meridional arcs. The 

 coincidence of the curvature of the earth's surface with the 

 same spheroid in this region, may likewise be inferred from the 

 calculation of the difference of longitude between Greenwich 

 and Paris, which brings out a result so near the quantity ob- 

 tained by direct observation. Let us next inquire how the case 

 will stand at a very distant part of the globe. Colonel Lamb- 

 ton has made in India a measurement precisely similar to that 

 at Beachy Head and Dunnose in the British Survey. The 

 particulars of this measurement at the two stations are as fol- 

 lows :f : Curnatighur. Carangooly. 

 Azimuth, 92° 49' 15"*93 = w, Azimuth, 87° 0' 7"*54 

 Latitude, 12 34 38 -85, Latitude, 12 32 12 -27 = A' 



Feet. Fathoms. 



Rectilineal distance 291189*3=48531*5 



Perpendicular arc at Carangooly, 290841 = 48473*5 



* Conn, dcs Terns. t Phil. Trans, p. 186. 



% Asiatic Researches, vol. viii. 



As 



