I think I've found the original paper from Pearson on correlation coefficients (equation on p 279, also cited here), but I'm not sure it's the right one. Pearson mentions normality multiple times in the paper, but I'm not sure it actually applies to the correlation equation.
Two questions -- is this (the first paper, rsta) the right paper (as in the original paper for Pearson's correlation coefficient), and what are the original assumptions in the formulation of the correlation coefficient? I've seen things ranging from "normality and homoscedasticity" to only "variables are interval".