INTRODUCTION. 



of the Gulf Stream. It will be seen we passed without the Gulf 

 Stream, in longitude about 60 west, yet we continued to be carried 

 onward by an easterly current, until we reached the longitude of 

 45 west. The temperature of the water during this passage between 

 the latitudes of 32 and 42 N. was generally higher than that of the 

 air; the difference in temperature of the ocean on the two sides was 

 nearly 7, although we had decreased our latitude 4, and this gra- 

 dually from the United States to Madeira. The mean temperature of 

 the water was 76'8, and that of the air 75'1, which will express the 

 standing of the thermometer in the Atlantic within these parallels 

 for the months of August and September. 



The mean height of the barometer was 30-215, which is higher than 

 it ranged at any other time during the voyage. Easterly winds were 

 found to have a tendency to elevate the column, while those from 

 the western quarter depressed it. The mean degree of moisture on 

 this passage was '666. 



MADEIRA. Whilst at Madeira, the mean standing of the barometer 

 was 30-176 in.; mean temp, of the air 74-9; water 73'6. We found 

 the height of the vapour plain to be about 4,000 feet above the level 

 of the sea, which, according to our measurements, corresponds with 

 that of the height of the Roche d'Empeiia, observed to be the highest 

 point of cultivation. There is little doubt that the vapour plain must 

 have considerable influence upon the climate of Madeira as well as 

 its productions. In determining the altitudes of this island, an oppor- 

 tunity was afforded us of ascertaining the decrease of temperature as to 

 elevation : the result of simultaneous observations gave for the altitude 

 of Pico Ruivo (6,180 feet), 254-1 feet for each degree of temperature, 

 that of Roche d'Empena (4,100 feet), 384-2 feet, and that of Camancha 

 (2,000 feet), 333 feet. The observations were made between meri- 

 dian and 6 P. M. 



The degree of moisture at Madeira was '599. 



MADEIRA TO RIO JANEIRO. This passage occupied a period of 

 fifty-nine days, including two days' delay at Porto Praya. Between 

 Madeira and Porto Praya (18 of latitude), the water and air increased 

 in temperature 9, the former being generally two degrees warmer. 

 The trade winds were met with in the latitude of 27 north; previous 

 to which we experienced a strong breeze, whose limit included some 

 of the vessels of the squadron, carrying them rapidly onward, while 

 the others were left for several hours becalmed. These winds are 

 of most frequent occurrence at the outer verge of the trade winds, 

 and particularly on the eastern side of the Atlantic : though no doubt 



