How and by Whom Was It First Determined That the Rings

How and by whom was it first determined that the rings of Saturn must be made up of a myriad of small particles, all separately orbiting Saturn in a wide, flat plane?

A) Astronomers at JPL and NASA found from photographs by the Voyager 1 spacecraft that the rings were composed of thousands of tiny ringlets, with particles orbiting even in the Cassini division.
B) Sir George Airy observed that wave-like brightenings propagated through the rings in the direction of rotation, as could be true only if the rings were composed of interacting particles.
C) James Keeler observed that the Doppler shift in reflected sunlight increased inward across the rings, whereas if the rings rotated as a solid body the Doppler shift should increase outward.
D) James Clerk Maxwell calculated that no material could be strong enough to withstand the differential gravitational forces of Saturn on the rings if they were solid.