done on board H.M.S. ' Challenger/ 601 



superficial nature of the variation ; the water at 10 fathoms from the 

 surface had a specific gravity of 1*02580. Although there was here no 

 drift-wood to be seen, I have little doubt that we had to do with warm 

 water, although the nearest point of New Gruinea was at least 80 miles 

 distant ; and indeed Capt. Scoresby, who sailed along this coast much 

 closer in shore, observed in this part large quantities of drift-wood, and 

 inferred the existence of a large river in the neighbourhood. 



North of Admiralty Island the specific gravity is somewhat higher ; 

 between the equator and 3° north latitude the mean is 1*02648 ; thence 

 all the way north to Japan it remains very uniform, the mean being about 

 1*02600. 



Leaving Japan in the month of June, the course lay entirely between 

 the parallels of 34° and 40° N. as far as the meridian of 155° W. The 

 specific gravity was slightly greater on the western side of the ocean than 

 on the eastern. The following mean specific gravities were observed for 

 every ten degrees of longitude : — 



140 to 150 E 1-02586. 



150 to 160 102574. 



160 to 170 1-02585. 



170 to 180 1-02568. 



180 to 170 W 1*02569. 



170 to 160 1-02544. 



160 to 155 1-02532. 



Arrived at 155° W. longitude, a southerly course was pursued by way of 

 the Sandwich Islands and Tahiti, when the following mean specific 

 gravities were observed : — 



35 to 25 N 1-02618. 



25 to 15 1-02593.. 



15 to 5 1-02574. 



5N.to 5S 1-02649. 



5 8. to 15 1-02658. 



15 to 25 1-02699. 



25 to 35 1-02620. 



Whence it will be seen that the minimum value is reached between 15° 

 and 5°N. latitude, the lowest value actually observed having been 

 1*02488 in latitude 7° 26' N". The maximum to the south between 15° 

 and 25° is very much more pronounced than that to the north of it ; in 

 fact round about Tahiti is the only spot in the Pacific where I have 

 observed the specific gravity reaching 1*02700 ; the actually highest 

 observed value was 1*02728 on the 3rd October, when the ship was 

 being swung a few miles off Papeete Harbour. 



The easterly course to Valparaiso was made principally between the 

 parallels of 35° and 40° S. latitude. Prom 125° W. longitude to Valpa- 

 raiso the mean specific gravity was 1*02534, the maximum being 1*02552 

 and the minimum 1*02513. 



