INTRODUCTION. xxv 



render the climate sultry and hot at that season. The climate may 

 be divided into wet and dry periods : the former includes the summer 

 months, the latter the winter. Although there is but little respite 

 from the heat, the difference of the mean being only 6, yet the setting 

 in of the southeast trade winds brings fine weather, dissipates the 

 vapours, and clears the atmosphere, and for a time produces an exhila- 

 rating effect, both during the day and at night, from the prevalence of 

 a land-breeze which sets in soon after sunset, and causes the night to 

 be cool and pleasant. No one who has not experienced it can estimate 

 the pleasant sensation this wind produces, scented as it is with all the 

 perfumes of this " queen of the ocean." The variations of the thermo- 

 meter during our stay were only 7 for the air, and 2 for the water; 

 the mean of the barometer 30'083 inches, higher than it stood in the 

 Paumotu Group or at sea. The amount of rain which fell was 4 '2 

 inches : I was not able to procure any data for the annual quantity, 

 the missionaries who have laboured so long in this field never having 

 attended to any of these interesting results in meteorology. The heat 

 on the western side of the island is much more oppressive during the 

 day than on the east, but less so at night, from a longer continuance 

 and more certainty in the land-breeze coming down from the high 

 mountains. The southeast side has almost constant showers through- 

 out the year, particularly during the season of the trade winds. The 

 degree of moisture obtained from our observations on the north side 

 was '800 ; the result on the southeast side would probably have been 

 greater. Many plants succeed better on the southeast side of the 

 islands ; but from the habits of the natives, the north side being more 

 thickly settled, we might infer that the latter is the most agreeable 

 and salubrious. The vapour plain generally exists at two thousand 

 feet, and it is seldom that the mountains are clear of clouds above this 

 height. The solar radiation was 94'9 sun, 804 shade, difference 

 14'5 ; mean of 27 observations. 



While we were making the transit from Callao to Tahiti, the Relief, 

 one of the squadron, was on her passage to the Hawaiian Islands from 

 the same port : a view of the oscillations made by her instruments 

 can be seen by comparing the diagram, Plate XXIV., Appendix, 

 with that of the Vincennes, on Plate VIII. The track of the Relief 

 was not parallel to that of the Vincennes, until she reached the same 

 latitude north of the equator, where it appears that both barometers 

 suffered a depression that of the Relief the greatest; but although 

 the times were somewhat different, yet about the same meridians they 



7 



