The flight of birds; the flapping cycle of the pigeon.

For many years there has been discussion on the details of the wing movements of birds in flight, and many attempts have been made to produce clear cinematograph records of the flapping cycle. Until recently no photographic system has combined a sufficiently short exposure with a rapid repetition rate and a reasonably large field of view. The development of the Arditron discharge tube has provided a light source which is of very high intensity, and has a flash duration of about 1 /xsec. This lamp, though designed for single-flash operation, has been found very suitable for highspeed cinematography. The purpose of this paper is to describe the cinematographic technique which has been developed, and to give a preliminary account of some of the information which has been obtained on the slow flight of the pigeon.