XXXviii INTRODUCTION. 



on the same plate a diagram of the Relief's track, the year before, and 

 refer to the Peacock's track and observations on Plate XXIIL, Ap- 

 pendix, the year after, which were nearly over the same course ; and, 

 the depression of their barometers being reduced to the same standard, 

 they very nearly correspond. The diagrams also point out the changes 

 that took place in the temperature of the air and water, and show that 

 they attain their maximum between 5 and 7 south latitude, in these 

 longitudes. It also will be seen that the thermometer indicates the 

 same temperature in the latitude of 21 north, that it has in 15 south 

 latitude. In passing through the belt of ocean comprised within the 

 10th degree of latitude on either side of the equator, we found the 

 mean degree of moisture to be -868, and the solar radiation 18. We 

 lost the southeast trades in 7 south latitude; they afterwards conti- 

 nued variable, lasting but a few hours from any one direction. When 

 in latitude 3 south, we had a heavy fall of rain, 5'2 inches, the tem- 

 perature of which was 02, air 70 ; the upper stratum of clouds, after 

 it ceased, was seen moving from the east-northeast. 



The variable winds accompanied us until we reached the latitude 

 of 8 north, when we met the northeast trades. During this passage 

 of 43 days, the maximum temperature was 88, minimum 73 ; the 

 greatest oscillation of the barometer -280 in. 



The other vessels of the squadron made the passage at the same 

 time, and all their observations tend to confirm those of the Vincennes. 



HAWAIIAN ISLANDS Our observations at these islands continued 

 through a space of six months, from September to April, 184041. 

 The first two months of this time they were made on the Island of 

 Oahu, and the last three on Hawaii, the former on the leeward and the 

 latter on the windward side. These will be found projected in the dia- 

 grams, on Plate XIV., page 440. The mean temperature in the first 

 period at Honolulu (Oahu), was 78'01, varying from 70 to 89, and 

 during the last at Hilo (Hawaii), 70'09, and varying from 57 to 82. 

 The oscillations of the barometer are greater than in south latitude, and 

 more fluctuating, being '540 in. The mean standing of the barometer 

 was 29-973 in. The column generally rises with the northwest winds, 

 and is depressed by the northeast. The tropical hours for 47 days 

 (hourly observations) correspond to 3 h. 36 m. A. M., 9 h. 36 m. A. M., 3 h. 

 12 m. P.M., 9 h. 30 m. p. M. The mean annual temperature, by the ob- 

 servations kept for several years at Honolulu, is 75'8, that of a sunken 

 thermometer, six and a half feet deep, gave 82'5.* The diurnal vari- 



* I am at a loss to account for this apparent discrepancy between what the buried 

 thermometer gives, and the moan annual temperature for several years ; the thermometer 



