f Capt 



315 





Wilkes 



mained, bat the notice attached had been removed. 



An aurora boreal is with colored streamers was observed beyond 

 the limits of the atmosphere. Several kinds of tea plants were 



seen in a garden on a mountain, cultivated with many other 



Chinese plants ; the flavor of the tea was excellent. 



October 31. — A coming storm compelled the ships, suddenly, 

 to depart ; November 4, They saw the Peak of TenerifFe— landed 

 their letters at Vera Cruz and bore away for the Cape de Verds, 

 and passed the tropic of Cancer on the 8th. 



The elevation of the plane of vapor was ascertained to be at 

 about 2,000 feet in these tropical regions. 



St. PauVs Rocks, lat. 0° 56' N., long. 29° 20' W.— These g 

 rocks are 500 miles from any continent, and are not in any part 

 more than seventy feet high. There is a crater, according to 

 Capt. Ross, who believes that they have been elevated by fire ; 

 but Mr. Darwin thinks them not to be of volcanic origin. They 

 hardly exceed half a mile in circumference. 



Soundings were obtained two-thirds of a mile from the rocks, 

 with 300 fathoms of line, but at twice the distance 500 fath- 

 oms of line were not sufficient, thus proving the great steepness 

 of the submarine mountain. J 



December 7th, the magnetic equator was crossed, in lat. S. 13° 

 45', long. W. 30° 41', with such precision that the magnetic dip- 

 ping needles were horizontal at the same instant in both ships, 

 being equally balanced between the northern and southern mag- 

 netic systems. 



Capt. Ross had some years before seen the needle standing ver- 

 tical over the northern magnetic pole, and now he looked forward 

 with hope to the time when he should find himself over the 

 south magnetic pole. The change of dip was very regular ; at 

 280 miles north of the magnetic equator the dip was 9° 36' ; at 

 292 miles south it was 9° 52', the former corresponding to 2 05 

 minutes, and the latter to 203 for every mile of latitude. This 

 large amount of change is confined to the vicinity of the equa- 

 tor ; near the poles it requires an approach of about two miles to 

 produce an alteration of a single minute of dip. 



Trinidad was seen December 17. The island is a mass of 

 volcanic material, in some parts 2000 feet high. The trap rocks 

 exhibit very extraordinary forms. The Nine Pm rock rises per- 



fect .., & 



proportion 



The trap rocks on shore influenced the magnetic needles so 

 touch as to render the observations useless, while those made on 

 s hip board were perfectly correct. 



Rain from a clear sky, in a cloudless night, fell for an hour ; dew 

 point by Daniel's hygrometer 72° — temperature of the air 74°. 





