Robert H. Goddard
Aerodynamics and motion

Goddard's interest in aerodynamics led him to study some of Samuel Langley 's scientific papers in the periodical Smithsonian. In these papers, Langley wrote that birds flap their wings with different force on each side to turn in the air. Inspired by these articles, the teenage Goddard watched swallows and chimney swifts from the porch of his home, noting how subtly the birds moved their wings to control their flight. He noted how remarkably the birds controlled their flight with their tail feathers, which he called the birds' equivalent of ailerons. He took exception to some of Langley's conclusions and in 1901 wrote a letter to St. Nicholas magazine with his own ideas. The editor of St. Nicholas declined to publish Goddard's letter, remarking that birds fly with a certain amount of intelligence and that "machines will not act with such intelligence." Goddard disagreed, believing that a man could control a flying machine with his own intelligence.

Around this time, Goddard read Newton's Principia Mathematica, and found that Newton's Third Law of Motion applied to motion in space. He wrote later about his own tests of the Law:

I began to realize that there might be something after all to Newton's Laws. The Third Law was accordingly tested, both with devices suspended by rubber bands and by devices on floats, in the little brook back of the barn, and the said law was verified conclusively. It made me realize that if a way to navigate space were to be discovered, or invented, it would be the result of a knowledge of physics and mathematics.
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