  The manuscripts that presumably contained Newton's early development of the
fundamental concepts that led to his Principia have been lost. A plausible
reconstruction of this development is presened based on Newton's exchange of
letters with Robert Hooke in 1679, with Edmund Halley in 1686, and on some
clues in the diagram associated with Proposition1 in Book1 of the Principia
that have been ignored in the past. The graphical method associated with this
proposition leads to a rapidly convergent method to obtain orbital curves for
central forces, and elucidates how Newton may have have been led to formulate
some of his other propositions in the Principia.
