108 THE FLIGHT OF BIRDS 



apart ; they run at right angles to the usual stream 

 of autumn migration, which flows from NN.E. to 

 SS.W. He takes up his position at a point in one 

 of these lines ; at the corresponding point in the 

 other line his assistant is stationed. With a stop- 

 watch he marks the moment at which a bird passes 

 his post of observation : at the moment it passes the 

 other post, the assistant telephones the fact to Dr. 

 Thienemann, who records it on his stop-watch. The 

 direction of the wind is taken and the exact angle 

 it makes with the bird's line of flight ; its pace is 

 measured by means of an anemometer. With these 

 data, whatever the angle may be, it is not difficult 

 to calculate the distance travelled by the wind with 

 the bird or in the opposite direction, while he is 

 covering the measured half kilometre. After finding 

 the rate at which the bird travels per second, per 

 minute, per hour, Dr. Thienemann subtracts or adds 

 the distance travelled by the wind, with or against, 

 during the same time. Thus the disturbing wind- 

 factor is eliminated and he arrives at the bird's own 

 velocity. All this is wonderfully ingenious and 

 wonderfully thorough ; the results have great value 

 because they are undoubtedly dependable. We can 

 only regret that the species of birds observed do not 

 include any of those observed by Commander Lynes. 

 Moreover it seems probable that they were not flying 

 at full speed. Migration, as a rule, goes on at a great 

 height ; these birds had descended to a low level, 

 and with land beneath them were flying probably 

 in leisurely style. The much greater velocity of 

 Commander Lynes's Quails is accounted for, I believe, 

 if we bear two facts in mind ; they are, presumably, 



