THE IMPENETRABLE SEA 



world's wind movements we can at least appreciate the 

 skill and research involved in those meteorological 

 observations which produce our weather forecasts. 



The name ''trades" — short for "trade winds" — does 

 not come from their usefulness to commerce in sailing- 

 ship days, but from the nautical expression "to blow 

 trade", meaning to blow regularly. They are the steady, 

 faithful winds of the world, as opposed to the flirtatious 

 and fickle ones, and they occur in all open seas on both 

 sides of the equator, and to a distance of about thirty 

 degrees north and south of it. In the days of the old wind- 

 jammers they were certainly of the greatest value in 

 navigation. 



When a sailing-ship came into a trade wind belt it 

 could depend on making steady progress. The trade wind 

 might be moderate, or no more than a breeze, but if the 

 ship was sailing with the wind full advantage could be 

 taken of it, by rigging extra sails at the ends of the yards, 

 giving a broadened stretch of canvas which caught every 

 capful of moving air. 



Although seamen of a century or so ago had every 

 reason to appreciate the trade winds more than we do 

 today, the scientific explanations of the trades in those 

 days were often little short of ludicrous. One commonly 

 accepted hypothesis was that as the atmosphere was 

 carried round by the earth the lower layers managed to 

 keep pace with it, but the higher regions "dragged" or 

 were left behind altogether, so that disturbances near the 

 land and sea surfaces were caused by the "lag". Some 

 authorities, even as recently as a century ago, beHeved 

 that the "lag" caused a continual breeze from east to 

 west, along the equatorial belt. But such "explanations" 

 of the trades, erroneous as they are now known to be, are 

 practical and scientific indeed compared with one hypo- 

 thesis seriously put forward by a certain Dr. Lister, in the 

 Philosophical Transactions (Vol. 156) at the beginning of 

 the nineteenth century. 



62 



