Doesn't he? Do you want anything, dear? asked the obliging Violet with officious alacrity. Do you know, I think that my lady is at the bottom of it. 鈥楢ccording to Smeaton鈥檚 table of atmospheric resistances, to produce a force of one pound on a square foot, the wind must move against the plane (or which is the same thing, the plane against the wind), at the rate of twenty-two feet per second, or 1,320 feet per minute, equal to fifteen miles per hour. The resistance of the air will now balance the weight on the descending surface, and, consequently, it cannot exceed that speed. Now, twenty-two feet per second is the velocity acquired at the end of a fall of eight feet鈥攁 height from which a well-knit man or animal may leap down without much risk of injury. Therefore, if a man with parachute weigh together 143 lbs., spreading the same number of square feet of surface contained in a circle fourteen and a half feet in diameter, he will descend at perhaps an unpleasant velocity, but with safety to life and limb. 欧美Av色爱综合网欧美Av— "Who wrote that letter?" "Martin came up I went down." It would scarcely be fitting that this Volume should go forth to the Public without a few words of Preface from one of A. L. O. E.鈥檚 own family. Yes, Mr. Powell, she is his wife; and more's the pity, if all tales be true! An important result of this experimental work was that it in many cases enabled designers to produce aeroplane parts from less costly material than had previously been considered necessary, without impairing the strength. It may be mentioned that it was found undesirable to use welded joints on aircraft in any part where the material is subject to a tensile or bending load, owing to the danger resulting from bad workmanship causing the material to become brittle鈥攁n effect which cannot be discovered except by cutting through the weld, which, of course, involves a test to destruction. Written, as it has been, in August, 1920, it is impossible in this chapter to give any conception of how the developments of War will be applied to commercial aeroplanes, as few truly commercial machines have yet been designed, and even those still show distinct traces of the survival of war mentality. When, however, the inevitable recasting of ideas arrives, it will become evident, whatever the apparent modification in the relative importance of different aspects of design, that enormous advances were made under the impetus of War which have left an indelible mark on progress.