Thanks for pointing on this! 
Wind + dust outside makes them change over time.
The fall is unphysical: without some balancing at the moment of cut he'd fall straight down; and the fall speed would increase during the fall. Balancing (from his movements) and bobbing (from rope elasticity) would look better anyway. Nice rebound.
Why do the sun beams change?
+1 to longer rope, even in case it was cut, thanks!
Lovecraft, his work is priceless. Now I have desire to read "the thing on the doorstep" once more)
The text makes it seem as though the men lowering him down drop the rope. If this is the case, then I think having a longer rope would work better. At the moment, it feels more like a snap.
On a rather odd tangent, I was reminded of this passage from the H.P. Lovecraft story 'Under the Pyramids', which you might enjoy:
"I have said that the falling rope was piling up about and upon me. Now I saw that it was continuing to pile, as no rope of normal length could possibly do. It gained in momentum and became an avalanche of hemp, accumulating mountainously on the floor, and half burying me beneath its swiftly multiplying coils."
Wow. Just amazing!