A paper on “Flapping Flight of Aeroplanes ” by the present writer was communicated by the late Professor G. F. FitzGerald to the “ Proceedings ” of the Royal Society (Vol. 64, pp. 420-430) in 1899. At that date much that is now almost common knowledge concerning the mechanics of flight was little thought of, much less understood, practical aviation did not exist, and a limited supply of experimental results presented confusing specimens of discordant and unreliable data to the inquirer. The development, during the last eight years, of the practice and science of aviation, seems to justify a review of the paper1 of 1899 in the light of better information, and of a better understanding of the influence of head resistance and other things, ignored fifteen years ago.