“The principle by which birds overcome the action of gravity is commonly assumed by investigators to be the superiority of the resistance of the down stroke of the wingto that of the up. They assume that birds fly by thedifference of the resistances.

“I have already shown in a former Paper how flighttakes place by the proper resolution of the two resistances. I will now demonstrate the utter absurdity of the difference of resistance theories.

“We will observe the action of a bird just on the point of leaving the ground—and in the study of flight, this, with the period of a lighting, is the most important for observation, as it is during these two periods that the bird exercises most the principles by which it overcomes gravity.