Thanks to all for the comments and suggested resources.
The reason I asked the question is that, after many years of teaching
Physics, that the idea of separating the concepts of weight and mass
seems to be decidedly non trivial especially to thinkers who are trapped
on the earth's surface. We seem to take it for granted today,
especially in the space age, that the distinction is obvious but my
question was simply to get at the mechanism for its development. What
was it that lead to the need for this concept?