xviii Phi/sical and Gcopiostic Suggestions^ 



As I do not exactly know what course it is intended 

 the Novara shall follow in navigating the Atlantic, nor iu 

 what meridian it is proposed to cross the Equator, (in con- 

 formity with the sound and useful directions of my friend 

 Lieut. Maury, of Washington), on her voyage to Rio de 

 Janeiro, nor how near she shall keep to Cape San Roque 

 and Fernando de Noronha, I must content myself with 

 inviting the attention of the voyagers in a general way to 

 the temperature of the sea, as also to the variations and 

 aberrations of the magnetic curves, and their currents. 



A lower degree of temperature is usually observed W. of 

 the Canaries, and Cape Verde Islands, commencing with the 

 Salvages, the thermometer indicating as low as 72° 7' Fahr. 

 This has been already ascertained by Mr. Charles Deville, in 

 his chart of temperature on the voyage " aux Antilles, a 

 Teneriffe et a Fogo." I consider this diminution of tempe- 

 rature results from the North Guinea current, bringing 

 with it cold water from the north southwards as far as the 

 Bight of Biafra and the River Gaboon, at which point it 

 is encountered by an opposite current flowing northwards 

 along the south-western coast of Africa from Loando and 

 Congo. 



In 1825, Captain Duperrey had accurately laid down the 

 point of intersection of the magnetic, with the terrestrial 

 equator. In 1837, we learned from Sabine's investigations 

 of magnetic inclination near the Island of St. Thomas (on the 

 Equator, adjoining the above portion of the coast of Africa), 



