470 REPORT—1 896 
It is not until late in September, and during October and early 
November, that the movements into our Islands from the north-east are 
sufficiently pronounced to permit of their being associated with and 
attributable to the great weather changes of the autumn. In ordinary 
seasons the period named is characterised by a series of great immigratory 
movements simultaneously performed not only by many species, but also 
by a vast number of individuals. 
It has been ascertained that a// these great movements are due to 
the prevalence in north-western Europe of weather conditions favourable 
for emigration. These conditions are the result of the following type of 
pressure distribution—namely, the presence of a large and well-defined 
anticyclone over the Scandinavian Peninsula, with gentle gradients ex- 
tending in a south-westerly direction over the North Sea. On the other 
hand, cyclonic conditions prevail to the westward of the British area, 
with a low-pressure centre off the west coast of Ireland, or, though less 
frequently, over areas further to the south. Under these pressure con- 
ditions the weather is clear and cold, with light variable airs over Norway 
and Sweden ; while in Britain the sky is overcast, and moderate to strong 
easterly winds are experienced, with fog not unfrequently prevailing at 
many east coast stations. 
The formation of these Goikditions in the autumn usually follows the 
passing away from Scandinavia—the area in which the movement has its 
origin—of a spell of a more or less pronounced cyclonic nature, during 
the prevalence of which the ordinary course of the emigratory movements 
is either interrupted or rendered impossible. 
The effects of this sequence of meteorological conditions on bird 
migration are remarkable. 
During the cyclonic spell a weather barrier arrests the progress of, 
and dams back as it were, the ordinary seasonal migratory stream. 
These periods, too, are not unfrequently characterised by weather of 
great ungeniality, and this, no doubt, gives the summer birds warning 
that the time for seeking the south has arrived. Upon the duration and 
severity of these preliminary conditions depends, to some extent, the 
maguitude of the emigratory movement that follows. 
The formation of the anticyclone removes the cyclonic weather barrier, 
releases the flood, and provides conditions favourable for migration, 
adding also an incentive in the form of a decided fall in temperature. 
Thus it is not a matter for surprise that such a combination of meteoro- 
logical conditions in the north should produce a rush to the southwards of 
those vast numbers of migratory birds which appear during the hours of 
darkness on our eastern coasts at the fall of each year, and whose move- 
ments often extend over several successive nights. 
These great movements occur most frequently in October, but during 
that month in the year 1887 no such immigration was recorded for our 
coasts. On examining the Meteorological Record, it is found that this 
peculiar type of weather only prevailed for a few hours on the 9th, and 
that a marked immigratory movement immediately set in, only to be 
checked by the dispersal of the conditions necessary for a great emigration 
from North-Western Europe. This fact illustrates in a remarkable manner 
how very direct the bearing of these conditions is upon the great autumn 
migratory movements between Northern Europe and Eastern Great 
Britain. 
The movements just described take place when gentle pressure- 
