THE FLIGHT OF BIRDS. 
PIGEONS. 
Photographed at Palo Alto, 1879. 
The subjects of flight and soaring present so many intricate 
problems that the author is reluctantly compelled to 
relinquish his attempt to elucidate them. His investi¬ 
gation, however, brought to light some facts which, although 
they had been theorized upon, had never been proved. 
Phases 5, 6, 7, 16, 17, and 18 of the cockatoo, series 79, de¬ 
monstrate that the primary feathers of a bird’s wing, although 
interlocked in the downward stroke, are separated, and 
their thin edees turned in the direction of their movement 
during the recovery. This partial revolution of the primary 
