April 22, 1909] 



NA TURE 



219 



GENERAL RESULTS OF THE METEOR- 

 OLOGICAL CRUISES OF THE " OTARIA " 

 ON THE ATLANTIC IN 1905, 1906, AND 1907. 



AirE have already reported preliminary results of 

 * •' the expedition which we organised in 1905 

 for the study of the trade-wind and the anti-trade by 

 means of free balloons the trajectories of which were 

 determined by triangulation (Nature, vol. Ixxiii., pp. 

 54-6, 449-50). 



-Since then two expeditions have been sent out 

 on the .Atlantic during the summers of igo6 

 and 1907, and Fig. i shows the regions which 

 have been studied. As may be seen by the dates 

 entered on the route of the Otaria (Fig. i), many of 

 the important points were visited in different j'ears and 



lished by M. Teisserenc de Bort twenty years ago, it 

 is seen that at about 4000 metres there e.xists a 

 barometric gradient extending from the Gulf of 

 Mexico towards the north-east, a gradient which 

 should in most cases, at these heights, produce 

 currents from the west or north-west. In his 

 communication to the Meteorological Conference 

 at St. Petersburg, Prof. Hergesell questioned the 

 existence of the ordinary south-west anti-trade, 

 believing that these north-west winds were themselves 

 a much deflected return branch of the equatorial 

 current. 



As we endeavoured to demonstrate by our first expe- 

 dition of 1906, the anti-trade exists generally above 

 the trade, and, as will be seen by the following results 

 of the two later e'xpeditions, the existence of the 



^iia- 7901, 



— £tei90i - W^7 \ \ 



Fig. I.— Map of the Cruise of the Otaria. 



at different times during the same year. This gives 

 a much greater value to our conclusions, because the 

 accidental phenomena are thereby, to a certain 

 extent, eliminated. 



In consequence of the investigations made by Prof. 

 Hergesell on board the Prince of Monaco's yacht 

 Princcssc Alice, in the region between the Canaries 

 and the .Azores, this distinguished meteorologist was 

 impressed by the existence of the north-west winds 

 which he observed at a variable height above the 

 surface winds, represented generally by the north- 

 east trade. These north-west winds, which had not 

 been observed before because the methods of aerial 

 soundings have only been employed for a few years, 

 do not themselves present marked peculiarities, since, 

 as Dr. Hann has remarked, if one turns to the chart 

 of isobars at different heights, which was pub- 



NO. 2060, VOL. So] 



north-west winds is not incompatible with the presence 

 of the anti-trade, and this fact should be emphasised. 

 Of course, since the meteorological phenomena do 

 not follow the regular zones that theory requires, but 

 group themselves around barometric maxima having 

 rhore or less ellipsoidal contours, it cannot be expected 

 that the normal superposition of winds above the same 

 place will be encountered every day. There are days, 

 for example, when the north-east winds, ordinarily 

 confined to a few hundred metres, extend up to five 

 or six kilometres, or even more; in other cases a 

 north-west current, superposed on the trade, en- 

 croaches more and more on the high atmosphere up 

 to such a height that the balloons do not show any 

 anti-trade. But the normal condition is easily 

 deduced from the documents gathered by our three 

 expeditions, and it occurs so frequently that each e.xpe- 



