xxvi INTRODUCTION. 



show very nearly the same, both giving satisfactory evidence that as 

 the centre of the great Pacific is reached a depression occurs ; and I 

 take this opportunity of calling attention to it, that from whatever 

 direction this ocean is crossed, a like depression will be shown, as 

 will be clearly pointed out by an inspection of the diagrams exhibiting 

 the results of our observations. 



TAHITI TO THE SAMOA* oKoup After stopping a few days at 

 Eimeo, we passed to the northward and eastward of the Society 

 Group, and thence to the westward, on the parallel of 15 south lati- 

 tude. Even on this parallel the winds proved very light and variable 

 from the westward, and we did not obtain the winds from the south- 

 ward and eastward until we had reached the longitude of 160 west. 

 The length of our passage was fifteen days. The change in tempe- 

 rature was +3-53 in the air and +2-89 in the water; the radiation 

 of the sun, the thermometer similarly placed as in former experi- 

 ments, 98-1, 81-3, difference 16-8, the greatest and least differem < 

 being 29 - 5 and 6'5; the decrease of the mercurial column when at 

 sea was -133. The wind from the west, as we found it to the oast- 

 ward of the Paumotu Group, maintained a high column. The degree 

 of moisture '872. 



AH OAK GKOUP. We remained fifteen days in the harbour of Pago 

 Pago, situated on the south side of the Island of Tutuilla, during 

 which period we had an almost constant succession of strong winds from 

 the southward and east\\ ard. with light rain in slum crs. The harlxmr 

 of Pago Pago is surrounded by high hills, and the Peak of Matafoa 

 (the highest point of the island, 2,359 feet in altitude), which con- 

 densed the moisture. When the weather was clear, the vapour plain 

 was seen about 300 feet below the peak, extending on all sides over 

 tin- island. The difference of temperature on the top of Matafoa was 

 found, when compared with that on the level of the sea, to be 10 

 less, which gave 230 feet in altitude for every degree of the thermo- 

 meter : the observations \\ere made at 1 o'cloek I'. M. The mean 

 standing of the barometer at Tutuilla 30-033 inches; whole group 

 29'946, oscillation 40(). The mean temperature during our stay was 

 80 Kahr. ; the range of the thermometer was 17, from 74 to 91. 

 A register kept at this island gave the annual mean as 76. 



The trade winds, which come Inmi the southeast, blow al>out one- 

 hall 'of the year, from April to SeptemlT. In the months of January 

 and February they come from the northuard and westward. The 

 pro|M>rtion of clear weather to that which is cloudy and rainy, is alxiut 



