  During the past 25 years there has been a controversy regarding the adequacy
of Newton's proof of Prop. 1 in Book 1 of the {\it Principia}. This proposition
is of central importance because its proof of Kepler's area law allowed Newton
to introduce a geometric measure for time to solve problems in orbital dynamics
in the {\it Principia}. It is shown here that the critics of Prop. 1 have
misunderstood Newton's fundamental limit argument by neglecting to consider the
justification for this limit which he gave in Lemma 3. We clarify the proof of
Prop. 1 by filling in some details left out by Newton which show that his proof
of this proposition was adequate and well grounded.
