Just as the water of a river near its mouth, in its final form, is composed largely of many tributaries, so an idea, in its final form, is composed largely of later additions.

Maco Magazine Corporation. The Borders of Mathematics. Hachmeister & Thal.

Willy Ley (October 2 1906 - June 24 1969) was a German-American science writer spaceflight advocate and historian of science who helped popularize rocketry spaceflight and natural history in both Germany and the United States. The crater Ley on the far side of the Moon is named in his honor.