Diagram wing angle 38' dive boom position I waved my hat again and the bird dove exactly as before but turned the wing down at the turn and the booming sound was produced. This turning of the wing must cause the boom as the bird repeated the stunt close to me many times. The wings seem to be pull that stretched on the plunge the only turned down and braised for the boom. Evidently the bird can readily check the dive with the tail and not boom. The boom apparently does not check the flight greatly as the bird seems to prove or only at at an even rate of speed. The boom is then surely made by the wing and simply for the effect; also it easily be avoided. The greater the speed of the bird the louder