220 



NA TURE 



[April 22, 190Q 



dition, considered individually, leads to the same 

 conclusion. In general, the zone where the anti-trade 

 is most regular appears to be situated to the eastward 

 of the meridian passing through the centre of greatest 

 pressure. To the southward of the maximum, and 

 when it is very pronounced, northerly winds are 

 frequent up to so great a height as eleven kilometres, 

 which was the limit of observation here. 



From the beginning of the year 1906 we were able 

 to show by ascensions of pilot balloons, made over the 

 open ocean to the south-west of the Canaries, that the 

 winds with a southerly component, which we had 

 already observed in 1905, also occurred far away from 

 land, and even appeared to be more marked than near 

 the islands. 



During the months of May, June, Julv and August, 





strata, sometimes of great thickness, then winds with, 

 a northerly component mixed with interlaced currents 

 from the south-west, corresponding to the north-west 

 winds of the northern hemisphere (Fig. 3). This 

 region, however, has only been studied to about 

 latitude 8° S. 



At the limit of the two trades the winds are easterly 



1 of air in the region of the trade winds, showing a layer of N.W. wind and anti-trade: 



1906, the Otaria made another cruise which extended 

 to Ascension Island (latitude 7° 55' S.), and on this 

 expedition a number of ballous-soiides were launched. 

 These results, combined with those from kites flown 

 at the same time, enabled the types of vertical 

 temperature distribution to be de- 

 termined for the regions traversed. 



The lower stratum, having a 

 drift from north-east, shows a 

 rapid decrease of temperature (o°'9 

 to i°'8 C. per 100 metres) in the 

 first 500 or 600 metres, and an 

 especially rapid decrease north of 

 latitude 25°. Usually, above the 

 zone of rapid decrease there is an 

 inversion of temperature in which 

 the wind velocity diminishes. 

 Above the trade there is generally 

 a north-west current (Fig. 3); 

 then higher up, at about 2500 

 metres, near the Tropic of Cancer, 

 and at 3000 or 3500 metres north 

 of_ the tropic, there occurs a wind 

 with a southerly component, except 

 in the cases already mentioned. 

 The direction of these winds 

 possessing a southerly component, 

 however, changes with the lati- Fig. 3.— Moton of ai; 

 tude, as might be e.xpected from the 

 effect of terrestrial rotation. They 

 are south-east near 15° N. and west-south-west near 

 25" N., no doubt gradually changing from one to the 

 other of these directions after passing by the south. 



These same characteristics are found in the south- 

 east trade, above which there are in general calm 



NO. 2060, VOL. So] 



at all heights, up to at least 14 kilometres, with a 

 component which is sometimes north and sometimes 

 south, but in general very weak, depending upon 

 the exact spot where the rise of air takes place. 

 North of the Tropic of Cancer the distribution of 





nng S.E. trade w 

 atmosphe 



the winds becomes much more irregular, and it fre- 

 quently happens that there is no anti-trade (Fig. 4). 

 However, the regular regime of the trades appears to 

 persist to about latitude 35° N. for places situated to 

 the east of longitude 37° VV. Farther west, winds from 



