54 Voyage of the Novara. 



The wind, hitherto easterly, chopped round to the North- 

 east, which, according to Maury's excellent directions and 

 charts, may be considered as a tra.de wind, and in this 

 season might be called so. In fact, the trade winds are pro- 

 duced by a current of air, which is directed towards the 

 Equator, and only in consequence of the earth's motion round 

 its axis acquires a north-easterly direction to the north of the 

 equator, and a south-easterly to the south of it. But the 

 trade winds become perceptible at a certain distance from 

 the equator, or rather from the hottest zone of the earth's 

 surface ; and it is clear, that when the zone assumes a 

 greater breadth, the boundary of the trade winds is ex- 

 tended further towards the poles, as the position of this 

 zone and its heat obtained from the sun are the causes 

 of these phenomena. 



This is exactly the case in these waters ; Africa, with 

 its sandy deserts, presents a broader zone of the greatest heat 

 than is possible on the sea, and the trade winds, accordingly, 

 reach further towards the north. Its direction, however, can- 

 not always be north-easterly, and depends necessarily on the 

 direction of the northern boundaries of this zone of greatest 

 heat. Accordingly, we at first had a more northerly wind, 

 which in our progress towards Madeira became much more 

 easterly. The weather continued on the whole beautiful, 

 the sea was calm, and only the increased length of the 

 waves showed the greater expanse of water we were now 

 navigating. 



