on the Eddystone. 265 



meteorology^ and practically determines what is favourable 

 and what is unfavourable for the movements. From 

 observation^ I am convinced that the direction of the wind 

 is^ in itself, of no moment to the emigrants, for they flitted 

 across the Channel southwards with winds from all quarters *. 

 It is quite the reverse^ however, when its force or velocity 

 comes to be considered, and I found that none of the move- 

 ments, not even straggling flights during the daytime, were 

 performed when the velocity of the wind exceeded 28 miles 

 an hour (or force 5, fresh breeze, of tlie Beaufort scale). 

 With the velocity of the wind at 34 miles an hour (force 6), 

 odd Pipits and one or two young Swallows were seen in 

 distress, and endeavoured to seek shelter at the lighthouse. 

 The movement witnessed on the early morning of the 23rd 

 of September afforded an interesting instance of the effect of 

 the force of the wind on migration. On the wind falling 

 from a velocity of 40 miles an hour (force 7) to 23 miles an 

 hour (force 4), the other meteorological conditions (direction 

 of wind and heavy rain) remaining the same, a great emi- 

 gratory movement was initiated. 



The prevalence of rain is evidently a matter of indifference 

 to the birds. It is otherwise to the would-be observer, for the 

 beams from the lantern assume additional luminosity during 

 rain, and the birds, if migrating, are decoyed within the 

 range of observation. On clear nights one is entirely 

 dependent upon the intervention of a passing shower to 

 learn whether migration is in progress or not, but on such 

 occasions few birds actually strike the lantern, though many 

 fly around it. 



When fog prevailed no birds were observed, though the 

 luminosity of the rays of light then assumes the maximum 

 of its conspicuity, while not penetrating beyond the imme- 



* The direction of the wiud depends upon the distribution of atmo- 

 spheric pressure. Certain systems of pressure establish fine weather 

 conditions over the North Sea, and are tlius eminentlj^ favourable for 

 iiitermigration between the Continent and the British Isles. Conse- 

 quently the winds, which are also the result of these particular pressure- 

 systems, have erroneouj-ly come to be regarded as the miiiu factors 

 controlling these movements. 



