Chicago, September 29, 1901

I have your letter of 25th. I send you herewith Huffaker's book. Please return it to me when you have done with it, and fill up such gaps as exist in his notes as you abstract it, as I have yet made no use of them.

There is a further paragraph in the Revue de l'Aéronautique which I had omitted; it is as follows:

With the same data, the horizontal component of the reaction is stated at 5.5 kilograms [12.1 lbs]. Admitting the same formula [P = 0.13V²] for the pressure, and the speed of 9 meters per second, this would be the reaction obtained by a plane of 0.5 square meters [5.38 sq. ft.] moving at right angles to the air. This normal plane would thus be the equivalent, as to resistance, of the surfaces in movement, aeronaut and machine. This amount, of (0.5)² meters, seems rather probable.

This seems to agree with your computations pretty well, but not quite. Please examine again the data about Bretonnière's stork. I think you will find the speed to be 44.7 miles an hour instead of 22, and the weight 1.08 lbs. per square foot instead of 0.71 lbs.

I am glad that you are about to make a test of the correctness of Lilienthal's coefficients. I have only one suggestion to make, i.e., to make exchanges in the places occupied in the quadrant by the respective surfaces, as Dines found discrepancies arising from the "aspects" of surfaces.

Did you at any time make a measurement of the pull of your machine with the man on?

I think I called your attention to the test of Aug. 8 (pull not measured) when the angle of the machine was 14 1/2° to the horizon & 24° to the relative wind, both of which give wild figures in a wind of 10.8 meters pr sec. — 24.1 miles an hour and pressure 2.9 lbs. per sq. foot. If the angle had been 8 1/2° with the relative wind we would have: