EFFECTS OF WEATHER 



difference in the way the air would be whirled round the 

 earth ; but we could take this point into consideration, 

 and should be able, if, as we have said, our earth were 

 quite uniform, to say always and at all times of the year 

 in what direction the prevailing wind should blow. 



Even with all the earth's irregularities we do know a 

 good deal with certainty about the earth's prevailing 

 winds : the trades ; the anti-trades ; the south-west 

 monsoon, which sets in so regularly in India that year by 

 year its advent hardly varies by more than a day ; and, 

 in the descending scale of regularity, the east winds 

 that usually sweep England in March, and the prevailing 

 south-westerly to westerly winds which bend most of the 

 young trees of the country a little to the north-east. 

 Besides these regularly or irregularly defined winds, 

 there are certain paths along the earth's surface where 

 the winds always move like a trout stream with eddies 

 in it. These eddies of the air we call cyclones, and they 

 are continually travelling in one direction. No doubt 

 they arise from the air in one place becoming hotter or 

 moister than in the surrounding regions. As the air 

 grows hotter it becomes lighter and ascends, while the 

 heavier air round it pours in. These eddies always travel 

 eastwards and incline in the northern hemisphere towards 

 the north. They usually originate somewhere on the 

 North American continent, and move across the Atlantic 

 about the pace of a slow railway train, winds whirling 

 round them all the time at a much greater pace. Usually 

 the centres of these eddies bear northward past the north 

 coast of Scotland to the north-west of Norway. Some- 



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