  From Newton's point of view, then, the basic problem — assuming that three independent mechanisms contribute to the total resistance forces, only one of which is proportional to the fluid density ρf — was to find an experimental phenomenon that would allow him to determine (1) the three exponents in the following schema, and (2) laws defining the three coefficients — or, more minimally, at least the variation of the coefficient of the last term for the specific case of spheres: