Kepler's Move From Orbs to Orbits - free online essay
Kepler's Move From Orbs to Orbits: Documenting a Revolutionary Scientific Concept
Bernard R. Goldstein and Giora Hon
http://mitpress.mit.edu/item.asp?ttype=6&tid=18561&mlid=424
Kepler's Move From Orbs to Orbits: Documenting a Revolutionary Scientific Concept
Bernard R. Goldstein and Giora Hon
http://mitpress.mit.edu/item.asp?ttype=6&tid=18561&mlid=424