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T. 646, T. 1277. [Advisory Committee for Aeronautics, T. 1296, 1919.]
IN response to the request for comments on this work, I may say that I have read these papers with interest.
The experiments recorded relate directly to the air pressures at various distances in the close neighbourhood of the surface of a long board parallel to the current of air in a wind channel. Three series of such pressures, and deduced air velocities/were obtained at different distances (A, B, G) from the leading edge. Major Taylor suggests that these experiments • should be repeated and extended at the National Physical Laboratory, and in this recommendation I fully concur, as it is of importance to improve our imperfect comprehension of the character of " skin-friction."
From the air pressure measurements the author deduces by calculation the actual force exercised upon the board, and in the second paper corrects, as far as possible, some deficiencies in the first. These calculations are a little difficult to follow as approximations are introduced whose validity is difficult to estimate, at any rate, without the instinct which familiarity with the subject matter may bring with it. For example, at some points, the problem is treated as if it were two-dimensional, which the actual dimensions of the board do not seem to justify.
Without-undervaluing the interest of connecting the forces experienced by the various parts of the board with the air pressures in its neighbourhood, I am inclined to prefer—or at any rate to recommend as alternative—direct measurements of the forces on the board, more as in Zahm's experiments.
The objection made in T. 646, p. 7, that in Zahrn's shorter boards the influence of the end pieces is too important, could, I think, be met by suspending the end pieces separately from the rest of the board, on the principle of the " guard ring " in electrometers. In the case of short boards the two end pieces could be rigidly connected together by rods passing freely through