210 THE VOYAGE OF H.M.S. CHALLENGER. 



The surface temperature remained nearly uniform at 78°. 



The bottom temperatures varied with the depth, the coldest water being found at 

 the deepest sounding, a result quite different from that hitherto obtained in the North 

 Atlantic, where the temperature remained the same, or nearly the same, below 1800 

 fathoms no matter what the depth was. The lowest temperature registered in the 

 section was 3Z C '7, the depth being 2475 fathoms. 



The serial temperature soundings showed that the isotherms maintained a position as 

 nearly as possible parallel with the surface, the isotherm of 40° being at a depth of 400 

 fathoms, that of 50° at a depth of 150 fathoms, and that of 60° at a depth of 70 

 fathoms. 



On the 30th August, at Station 110, the velocity of the wind was 15 miles per hour 

 by the anemometer, the force registered being 2. On the 31st, at Station I'll, the 

 velocity was 1 1 miles per hour, the force registered being 2 to 3. During the night of 

 the 1st September, whilst at anchor at Fernando Noronha, the velocity was 9 miles per 

 hour, and during the day on the 2nd, 15 miles per hour. 



Between St. Paul's Rocks and Fernando Noronha there is a deep depression, the 

 greatest depth recorded being 2475 fathoms. At this depth there was 36 per cent, of 

 carbonate of lime in the deposit, while at the depths of 2275 and 2200 fathoms there 

 were respectively 72 and 81 per cent. This is a good instance illustrating the 

 diminution of carbonate of lime in the deposit with increasing depth, as here the surface 

 conditions were the same, and the character and size of the mineral particles alike in 

 all the soundings. The mineral particles did not exceed 0"05 mm. in diameter, and 

 consisted of felspars, hornblende, augite, magnetite, and vitreous particles. Eadiolarians, 

 Diatoms, and fragments of other siliceous organisms made up from 2 to 4 per cent, 

 of the deposits. 



On the 1st September, at 6 a.m., the island of Fernando Noronha was sighted, and 

 the day was devoted to obtaining a series of soundings to the shore (see Sheet 14). The 

 ship anchored in San Antonio Bay at 3 p.m. 



Fernando Noeonha. 



The intention was to have remained at this island for a week or ten days, to survey 

 and explore it thoroughly, but, no previous notice having been given to the Brazilian 

 Government, the Commandant would on no account take on himself the responsibility of 

 permitting collections to be made on shore or soundings to be taken adjacent to the 

 coast, although at first he appeared willing to allow this. Under the circumstances it 

 therefore became useless to remain in the neighbourhood, and the ship left on the 3rd 

 September for Bahia. 



On the 1st and 2nd a landing was effected on the main island, as well as on the 



