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 the Beaufort scale). 
With the velocity of the wind at 34 miles an hour (force 6), 
odd Pipits and one or two young Swallows w^ere 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 migratiug, 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 
ot its conspicuity, while not penetrating beyond the imme- 
* The direction of the wind depends upon the distribution of atmo- 
spheric pressure. Certain systems of pressure estabhsh fine weather 
conditions over the North Sea, and are thus eminently favourable for 
intermigration between the Continent and the British Isles. Conse- 
quently the winds, which are also the result of these particular pressure- 
systems, have erroneously come to be regarded as the main factors 
controlling these movements. 
