117 



servations for determining the longitude of the 

 mole of Santa Cruz, and the dip of the needle. 

 Berthoud's chronometer gave, for the first 18° 

 33 / 10". This differs three or four minutes from 

 the result of former observations by Fleurieu, 

 Pingr6, Borda, Vancouver, and La Peyrouse. 

 Mr. Quenot nevertheless obtained 18° 33' 36", 

 and the unfortunate Captain Bligh 18° 34 A 20". 

 The precision of my result was confirmed three 

 years after, on the voyage of the chevalier Kru- 

 senstern, who found Santa Cruz 16° 12' 45" west 

 of Greenwich, and consequently 18° 33' 0" west 

 of Paris." The data prove, that the longitudes 

 Captain Cook assigned to Teneriffe and the 

 Cape of Good Hope are much too far west*. 

 The same navigator had found the magnetic dip, 

 in 1 799, 61° 52'. Mr. Bonpland and myself ob- 

 served it at 62° 24', a result conformable to that 

 which was obtained in 1791 bv Mr. de Rossel in 

 the voyage of D'EntrecasteauX-}-. The variation 

 of the needle differs several degrees, according 

 to the place where the observation is made, at 

 the Mole, or at several points to the north, along 

 the shore. We must not be surprised at these 

 variations in a place surrounded by volcanic 

 rocks. I remarked with Mr. Gay-Lussac, that 



* Galeano. Viage ad Magellanes, p. 8. Kru sen stern, Reise 

 urn die Welt, th. i. s. 78 : and my Obs. Astron. t. i, p. xxxvii, 

 11, and 33. 



f Voyage a la Recherche de la Peyrouse, t. ii, p. 291, 



