MIGRATION AND WEATHER 95 



I have endeavoured to show that often the force 

 \of wind is greater at a high than a low altitude, and 

 there is ample evidence to prove that birds fly 

 at a great height when conditions are favourable. 

 Birds usually leave Scandinavia when there are 

 descending currents flowing outwards from the 

 centre of high pressure ; is it wild speculation to 

 suggest that it is the southward flowing currents, 

 which are also deflected westwards, upon which 

 the birds intend to travel ? Thus the bulk of the 

 Scandinavian birds might not touch Britain at all, 

 but those* which started upon light to moderate 

 north-east to easterly winds from the western 

 shores of Norway would be helped to Britain. 

 Mr Clarke mentions that when he was at Fair 

 Island, north-west to westerly winds did not stop 

 migration from the north, but is it certain that 

 the birds did travel in or against these westerly 

 winds ? May they not actually have travelled on the 

 " good side " of the cyclonic system, with these very 

 winds carrying them towards Fair Island ? their 

 actual visible approach from the north does not prove 

 that they had travelled all the way in this line. 



On September 22nd, he says " The favourable 

 meteorological conditions of yesterday fine weather 

 and moderate south-east breezes, has had a marked 

 effect, for to-day goldcrests are swarming every- 

 where/' But what does he mean ? Favourable 



