Manchester Memoirs, Vol. Hii. (1909), No. 15. 7 



been led towards this point of view, and it is unfortunate 

 that so excellent an observer has not thought fit to go 

 deeper into the subject. As it is, his remarks are apparently 

 merely tentative. I give the passage in full. " Except by 

 aid derived from the operation of physical laws, the 

 nature and extent of which are unknown to me, and by 

 taking advantage of ' Trade wind ' circulations in the 

 upper air, I believe that migration is impossible for short- 

 winged forms of sedentary habit .... But that aid, 

 and those advantages, may facilitate, and perhaps vastly 

 accelerate, a process which is otherwise impossible." 



I suggest that the bird takes up its position in the 

 nearest part of the rim of the cyclone to its point of 

 departure, and flies in the same direction as the wind 

 until that portion of the aerial medium that supports and 

 carries it arrives over that part of the world, or the nearest 

 point, which the bird desires to reach. I will not run the 

 risk of obscuring my point by dealing with anti-cyclones ; 

 the general process would be much the same. The 

 ascending currents of cyclones must be mentioned, for a 

 bird supported in one would soon be carried to a great 

 height, from which it might start a long "glide" on 

 open wings, supported by the upward current in the 

 manner of a Gull flying above a cliff. 



Mr. Clarke's actual observations support my theory 

 {t.c. p. 470). He points out that favourable conditions for 

 autumnal migration are " the presence of a large anti- 

 cyclone over Scandinavia, and cyclonic conditions to the 

 westward of the British area, with a low pressure centre off 

 the west coast of Ireland." There is a strong outward and 

 downward current from above the core of an anti-cyclone, 

 and this would be most useful to birds crossing the North 

 Sea in autumn. This was the state of affairs on September 

 23rd, 1908, when a large migration was noticed on the 



