350 THE STRUCTURE AND LIFE OF BIRDS cHap. 
The occasional occurrence of a rather wild theory 
does not much detract from the merit of the book. 
‘In 1880 the British Association appointed a com- 
mittee to investigate the migration of birds, and with 
the help of the keepers of lighthouses, against which 
the migrants often dash themselves, the committee 
have accumulated a vast body of facts, some of which 
have already been published. But the work of 
analysing the facts has not yet been completed. 
When it is, our knowledge of the subject will, probably, 
be much advanced. Even then it must be very defec- 
tive, if only for this reason, that nearly all the 
observations are made in the northern hemisphere. 
Observers are wanted in North and South Africa, and 
owing to the absence, or the great paucity, of them, it 
is probable that there will long be a great blank in our 
knowledge of migration. 
Ordinary people, who have no special opportunities, 
who do not live in Heligoland, or. Malta, or the Ber- 
mudas, or keep a lighthouse, and who cannot travel to 
particularly favoured spots, can yet see a good deal of 
migrant birds. They can watch for the coming of the 
Swallow, the Nightingale, the Cuckoo, the Chiffchaff, 
and a host of others in spring. When the woods 
have long been almost silent save for the song of the 
Thrush and the Robin, there comes a chorus of voices 
resounding on all sides and most of the singers are 
migratory birds. It is difficult to see their coming, 
for it is usually at night. You get up in the morning 
and you find the Swallow comfortably catching the 
flies of his northern home and the Blackcap pro- 
claiming his arrival in his favourite covert. In autumn 
