Abstract
REFERRING to Mr. Bryan's summary, on page 107 of the current volume of NATURE, of the observations on the resistance of the air, made by Le Dantec and by Canovetti, it is but fair to say that the conclusion “No. 3,” viz. that the resistance to a plane surface depends upon its contour, i.e. whether circular, square or triangular, is by no means new. Precisely this result was deduced by Prof. Hagen, of Berlin, in his most delicate experiments published by the Berlin Academy in 1874. His memoir is the first in Abbe's collection of translations, entitled “The Mechanics of the Earth's Atmosphere,” and a detailed discussion of his results is given at pp. 234–238 of his “Treatise on Meteorological Apparatus and Methods.” Hagen's results, when expressed in grams, decimetres and seconds, give the resistance per square decimetre as (0.00707 + 0.0001125 p) v2 where p is the contour of the plate and v the velocity. As his experiments were made with plates of only from 1 to 12 decimetres on a side, and as he showed that the size affects the coefficient quite as much as the shape, it would scarcely be proper to exterpolate from his small plates up to the large ones used by the French investigators. We should not expect any close agreement for a surface of one metre square between Hagen's figures and these newer ones, but the general law that the pressure per square unit depends upon both the size and the shape of the plate is due to Hagen. The explanation of this result is also largely due to him; it is not merely a question of gaseous viscosity or internal friction, but especially of that dissipation of energy that occurs in the ideal perfect fluid, and which has been called convective friction in the above-mentioned treatise and elsewhere. Le Dantec and Canovetti, by experimenting on a large scale, have necessarily encountered such irregularities and difficulties as must have limited the accuracy of their results quite as much as in the case of many other experiments since those of Sir Isaac Newton. In general, inasmuch as resistance per square unit varies with the size and shape of plane plates or other bodies, it can hardly be called an important physical constant of great scientific interest. It certainly has a practical interest to the aeronaut, the navigator, and the millwright, but the scientific interest of such experiments consist essentially in determining the lines of flow and the transformations of energy involved in the discontinuous motions.
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A., C. The Resistance of the Air . Nature 61, 248 (1900). https://doi.org/10.1038/061248a0
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DOI: https://doi.org/10.1038/061248a0
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