Dayton, March 2, 1905
We are sorry that you have had so severe a siege of the grippe. The various members of our family have all had the same malady this winter but escaped with rather mild attacks.
Since my last letter I have secured and measured a crow and find the results as follows: Weight 14 oz. Spread 35 inches. Width of wing 7 1/2 inches. Surface about 1 1/2 sq. ft. Diameter of body 3 inches. Thickness of wing at front edge about 1/4 inch. In regular flight it flaps its wings about 3 1/3 times a second. I have no measurement of its regular speed but think it probably about twenty four or twenty five miles an hour. After considering its structure and its flight, I am far from believing that it expends less power, in proportion to weight and speed, than is readily attainable in a dynamic flying machine of large size.
If the buzzard be taken as the bird which flies with the least expenditure of power, and its rate of gliding descent be taken as 1 in 10, then man has already reached a point within 20 percent of the maximum, for other conditions being similar, the power expended will vary directly as the ratio of descent.
We have had so little energy since recovering from the grippe that we have done little work. However we have added oiling and feeding devices to the engine which will make it safe to run it for several hours at a time if desired.
Hoping that your strength may be fully and quickly restored, [&c.]