Trigonometrical Survey. 629 



same conclusion is derived ; for, the bearing of Black Down 

 west of Dunnose being 84° 54' 52", 5, we get the distance of 

 that station from the meridian of the latter = 313072 feet, 

 and from the perpendicular, 27861 feet ; which, converted into 

 parts of an arch, according to the lengths of their respective 

 degrees, gives 50 41' 14" for the latitude, and i° 20' 46",4 for 

 the longitude west of Dunnose. According to the troublesome 

 yet ingenious method recommended by M. Sejour, in his 

 Traite Analytique des Mouvemens apparens des Corps Celestes, the 

 latitude of Black Down comes out 50 41' 13",9, and the longi- 

 tude i° 20' 45", 75. We may, therefore, admitting the supposi- 

 tion of Dunnose being situated in 50 37' 7",g, safely take 50 

 41' i3 // ,8 for the latitude, and 2 32' 22",4 for the longitude, of 

 Black Down; that of Dunnose being i° n' 36" west of the 

 meridian of Greenwich. 



Art. xviii. Calculation of the Distance between the Stations on 

 Black Down, in Dorsetshire, and Rippin Tor, in Devonshire. 



For the calculation of this distance, we must have recourse 

 to the XLViith, xLvmth, XLixth, and Lth triangles. (See Phi- 

 losophical Transactions for 1797, and Plate XXX, Fig. 1 of this 

 Volume. ) In the two first, we have the whole angle at Pilsden, be- 

 tween Dumpdon and Black DoWn = 152 37' zf'&fj, which, re- 

 duced to the angle formed by the chords, becomes 1 52 37' 24",25. 

 The sides forming this angle, are Dumpdon and Pilsden, Pilsden 

 and Black Down : the distance between the two first stations 

 being 78459,3 feet, and between the two last 79110,7 feet. 

 From these data, the distance between Dumpdon and Black 

 Down is found to be 153095,7 feet, the triangle for computa- 

 tion being, 



mdccc. 4 M 



