wat AQVOLOGIST 
No. 858.—December 15th. 1912. 
A CONTRIBUTION TOWARDS A SOLUTION OF THE 
PROBLEM OF MIGRATION. 
By F. J. Srusss. 
In the following paper an attempt has been made to group 
together a number of well-ascertained facts with a view to the 
solution of the ancient problem of migration; but the present 
essay is merely a preliminary one, for the subject is too vast to 
be treated adequately here and now. Although the question is 
very simple, the necessity of explaining a number of separate 
details gives it a superficial aspect of complexity; yet I think 
the majority of readers will be able to see the drift of my 
reasoning before they have covered many paragraphs. 
Thanks to the pertinacious labours of an army of workers 
we are to-day in possession of a mass of accurate observations 
more than sufficient for the present purpose. The result, to 
my mind, becomes more than a theory, and this array of facts 
appears to be governed by a law which, provisionally, may be 
given briefly as follows :—The present balance of life on the earth 
is made possible by the existence of a mobile mass of animal life 
flowing twice yearly from hemisphere to hemisphere ; and I hope 
to show that migration, instead of being merely a question for 
ornithologists, is really a tremendous cosmical function of the 
utmost importance. 
The present discussion confines itself to facts that are the 
commonplaces of science. There is no necessity to turn for 
support to matter that is not accepted without question by all 
Zool, 4th ser. vol. XVI., December, 1912. 2M 
