THE VELOCITIES OF MIGRATORY BIRDS. 245 



ciation (Liverpool, 1896, pp. 451-477), but expresses a belief that 

 winds have little or no influence on migration (i. p. 178). Possibly 

 some day we shall have an account of the observations and 

 the deductions on which this remarkable opinion is based, but 

 in the absence of these details, I am inclined to urge that every 

 single mile in the velocity of the wind has its influence on the 

 speed and the routes of the migrants that happen to be on the 

 wing at that time. It is perhaps my own obtuseness, but I con- 

 fess I do not quite follow Mr. Clarke's "matured opinions." I 

 was greatly disappointed to find this important matter of winds 

 almost entirely overlooked in the book, and the question left 

 much as it was twenty years ago, with the exception of an 

 opinion— that winds have no influence — which is unfortunately 

 in direct disagreement with the results of the experiments now 

 to be described. I may be pardoned for pointing out that these 

 results support the conclusions given in my paper, which was 

 published in the spring of 1909, before the genesis of the 

 successful aeroplane. 



It was my good fortune to be present in the House of Commons 

 on March 19th last, when the Secretary of State for War de- 

 livered his notable speech on Aviation in the Army. This speech 

 was widely published, but no part of it reached the ornithological 

 literature of the day, although certainly it came within the pro- 

 vince of the student of birds. Two items worth notice are 

 accounts of experiments that can be made most useful in the 

 present discussion. One day, when the wind was blowing at 

 57 miles per hour, an officer rose in his aeroplane in the teeth 

 of the wind, and after 16 minutes' flying had covered a distance 

 of no more than 400 yards, at a net velocity in relation to the 

 earth of less than a mile an hour. On another occasion, with 

 " a wind of great violence," a second officer flew to and from a 

 point 21 miles away. " Head to wind," the journey occupied 

 1\ hours, at a velocity of 17 miles per hour ; and " tail to wind," 

 the distance was covered in 3 minutes 56 seconds, a velocity of 

 115 miles per hour. Is any supporter of the " Head Wind " 

 theory ready to claim one law for the bird and another for the 

 machine ? If not, the "Head Wind" theory must be abandoned. 



In my "Wind and Migratory Birds " paper, I discuss the 

 influence of cyclones on migration. It occurred to me that this 



