1. * Since the submission of this paper a comment on the same subject by Muttray has appeared in the "Jahrbuch 1937 der Deutschen Luftfahrtforschung," pp.1-66. He states that the measured profile drags were found too high by about 12 percent at the trailing edge, by about 8 percent at a distance x/c = .10 behind the trailing edge (compared to measurements a great distance behind the wing). I n every case of a wing with finite thickness the Betz formula gave a variation of the profile drag with distance from the wing. Only in t h e case of a flat surface consisting of thin pieces of sandpaper glued back to back was the profile drag found to be independent of distance behind the wing.Theseresults confirm the above conclusions very closely.
2. Über das ebene Windschattenproblem