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



CHAPTER VI. 



Cape Verde Islands to St. Paul's Rocks and Fernando Noronha — Balanoglossus — The Eohinoidea — Description of 

 St Paul's Rocks and Fernando Noronha — Coast of Brazil — Bathypterois — Surface Fauna of Guinea and 

 Equatorial Currents — The Radiolaria — Bahia. 



Cape Verde Islands to St. Paul's Rocks. 



The Expedition left Porto Praya at 8 p.m. on the 9th August, and a course was shaped 

 for St. Paul's Rocks. Owing to the season of the year in which the passage was made, 

 the course was necessarily somewhat erratic ; the ship proceeding to the southeastward 

 along the African coast until the S.E. trade was reached in lat. 3° 8' N., long. 14° 49' W., 

 and then standing over to the westward for St. Paul's Rocks. The soundings and tem- 

 peratures obtained must, therefore, be divided into two sections. — 1st, the southeasterly 

 section towards the equator ; and 2nd, the equatorial section. 



From Porto Praya to the parallel of 7° N. the wind varied from W. by N. to S. by 

 W. with cloudy, squally, rainy weather ; from thence to the position where the S.E. trade 

 was met with, viz., in lat. 3° 8' N., long. 14° 49' W., the wind was from S.S.W. to S., 

 with fine weather, and from that position the S.E. trade was retained to St. Paul's Rocks. 



On the section to the southeastward from Porto Praya to a position in lat. 3° 8' N. 

 long. 14° 49' W. six soundings, eight serial temperature soundings, and one dredging and 

 one trawling were obtained (see Sheet 12). 



The surface temperature varied from 77°'7 to 79°"5. 



The bottom temperature when the depth exceeded 1800 fathoms still continued 

 remarkably uniform, the mean being 36°"5 and the extremes 36°"6 and 36°'4. 



Serial temperature soundings showed that the isotherm of 40°, which was at a depth 

 of 800 fathoms at St. Iago, rose gradually to the southward to 500 fathoms in the 

 parallel of 3° N. The isotherm of 50° maintained an average depth of 180 fathoms, 

 varying from 150 to 200 fathoms; but the isotherm of 55° approached at Station 96 

 to within 40 fathoms of the surface, although the surface temperature was 79° ; thus 

 showing a decrease of 24° in 40 fathoms. 



On the 16th, at Station 100, the dingey was anchored by the sounding line, and 

 the surface current was found running N. 70° E. half a mile per hour. The current drag 

 at 50 fathoms indicated a set of 0*45 mile per hour, N. 17° E.; at 100 fathoms, 

 N. 15° E. 0'3 mile per hour; and at 200 fathoms, N. 17° E. 0*2 mile per hour. On the 

 19th, at Station 101, the cutter was anchored by the trawl, and the surface current 



